SUPER CAPACITORS AND BATTERY POWER MANAGEMENT FOR HYBRID

VEHICLE APPLICATIONS USING MULTI BOOST AND FULL BRIDGE

CONVERTERS

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ABSTRACT

In the last few years the pollution problems and the increase of the cost of fossil energy

(oil, gas) have become planetary problems. The car manufacturers started to react to the urban

pollution problems in nineties by commercializing the electric vehicle. But the battery weight

and cost problems were not solved. The batteries must provide energy and peaks power during

the transient states. These conditions are severe for the batteries. To decrease these severe

conditions, the super capacitors and batteries associate with a good power management present a

promising solution. Hybridization using batteries and super capacitors for transport applications

is needed when energy and power management are requested during the transient sates and

steady states. The multi boost and multi full bridge converters will be investigated because of the

high power

This paper presents super capacitors and battery association methodology for ECCE

Hybrid vehicle. ECCE is an experimental Hybrid Vehicle developed at L2ES Laboratory in

collaboration with the Research Center in Electrical Engineering and Electronics in Belfort

(CREEBEL) and other French partners. This test bench has currently lead-acid batteries with a

rated voltage of 540 V, two motors each one coupled with one alternator. The alternators are

feeding a DC-bus by rectifiers. The main objective of this paper is to study the management of

the energy provides by two super capacitor packs. Super capacitors are storage devices which

enable to supply the peaks of power to hybrid vehicle during the transient states. Each super

capacitors module is made of 108 cells with a maximum voltage of 270V. The multi boost and

multi full bridge converter topologies are studied to define the best topology for the embarked

power management. This method achieved a good power management strategy by using the

multi boost and the multi full bridge converter topologies.

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CONTENTS

1. INTRODUCTION

2. SUPER CAPACITORS

3. BOOST CONVERTER

4. ELECTRIC VEHICLE

5. ADVANTAGES OF HEV

6. FULL BRIDGE CONVERTER

7. POWER MANAGEMENT

8. DC/DC CONVERTERS TOPOLOGIES AND MODELING

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1. INTRODUCTION

In the last few years the pollution problems and the increase of the cost of fossil energy (oil,

gas) have become planetary problems. The car manufacturers started to react to the urban

pollution problems in nineties by commercializing the electric vehicle. But the battery weight

and cost problems were not solved. The batteries must provide energy and peaks power during

the transient states. These conditions are severe for the batteries. To decrease these severe

conditions, the super capacitors and batteries associate with a good power management present a

promising solution.

Super capacitors are storage devices which enable to supply the peaks of power to hybrid

vehicle during the transient states. During the steady states, batteries will provide the energy

requested. This methodology enables to decrease the weight and increases the lifespan of the

batteries. Hybridization using batteries and super capacitors for transport applications is needed

when energy and power management are requested during the transient sates and steady states.

The multi boost and multi full bridge converters will be investigated because of the high power.

For range problems, traction batteries used until now cannot satisfy the energy needed for future

vehicles. To ensure a good power management in hybrid vehicle, the multi boost and multi full

bridge converters topologies and their control are developed. Two topologies proposed for the

power management in ECCE Hybrid Vehicle are presented in Figure.

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2. SUPER CAPACITORS

Capacitors store electric charge. Because the charge is stored physically, with no

chemical or phase changes taking place, the process is highly reversible and the discharge-charge

cycle can be repeated over and over again, virtually without limit. Electrochemical capacitors

(ECs), variously referred to by manufacturers in promotional literature as Super capacitors also

called ultra capacitors and electric double layer capacitors (EDLC) are capacitors with

capacitance values greater than any other capacitor type available today. Capacitance values

reaching up to 400 Farads in a single standard case size are available. Supercapacitors have the

highest capacitive density available today with densities so high that these capacitors can be used

to applications normally reserved for batteries. Supercapacitors are not as volumetrically

efficient and are more expensive than batteries but they do have other advantages over batteries

making the preferred choice in applications requiring a large amount of energy storage to be

stored and delivered in bursts repeatedly.

The most significant advantage supercapacitors have over batteries is their ability to be

charged and discharged continuously without degrading like batteries do. This is why batteries

and supercapacitors are used in conjunction with each other. The supercapacitors will supply

power to the system when there are surges or energy bursts since supercapacitors can be charged

and discharged quickly while the batteries can supply the bulk energy since they can store and

deliver larger amount energy over a longer slower period of time.

Super capacitor construction

What makes’ supercapacitors different from other capacitors types are the electrodes used in

these capacitors. Supercapacitors are based on a carbon (nano tube) technology. The carbon

technology used in these capacitors creates a very large surface area with an extremely small

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separation distance. Capacitors consist of 2 metal electrodes separated by a dielectric material.

The dielectric not only separates the electrodes but also has electrical properties that affect the

performance of a capacitor. Supercapacitors do not have a traditional dielectric material like

ceramic, polymer films or aluminum oxide to separate the electrodes but instead have a physical

barrier made from activated carbon that when an electrical charge is applied to the material a

double electric field is generated which acts like a dielectric. The thickness of the electric double

layer is as thin as a molecule. The surface area of the activated carbon layer is extremely large

yielding several thousands of square meters per gram. This large surface area allows for the

absorption of a large amount of ions.

The charging/discharging occurs in an ion absorption layer formed on the electrodes of activated

carbon.

The activated carbon fiber electrodes are impregnated with an electrolyte where positive and

negative charges are formed between the electrodes and the impregnant. The electric double

layer formed becomes an insulator until a large enough voltage is applied and current begins to

flow. The magnitude of voltage where charges begin to flow is where the electrolyte begins to

break down. This is called the decomposition voltage.

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The double layers formed on the activated carbon surfaces can be illustrated as a series of

parallel RC circuits.

As shown below the capacitor is made up of a series of RC circuits where R1, R2 …Rn are the

internal resistances and C1, C2..., Cn are the electrostatic capacitances of the activated carbons.

When voltage is applied current flows through each of the RC circuits. The amount of time

required to charge the capacitor is dependent on the CxR values of each RC circuit.

Obviously the larger the CxR the longer it will take to charge the capacitor. The amount

of current needed to charge the capacitor is determined by the following equation:

In= (V/Rn) exp (-t/ (Cn*Rn))

Supercapacitor is a double layer capacitor; the energy is stored by charge transfer at the

boundary between electrode and electrolyte. The amount of stored energy is function of the

available electrode and electrolyte surface, the size of the ions, and the level of the electrolyte

decomposition voltage. Supercapacitors are constituted of two electrodes, a separator and an

electrolyte. The two electrodes, made of activated carbon provide a high surface area part,

defining so energy density of the component. On the electrodes, current collectors with a high

conducting part assure the interface between the electrodes and the connections of the

supercapacitor. The two electrodes are separated by a membrane, which allows the mobility of

charged ions and forbids no electronic contact. The electrolyte supplies and conducts the ions

from one electrode to the other.

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Usually supercapacitors are divided into two types: double-layer capacitors and

electrochemical capacitors. The former depends on the mechanism of double layers, which is

result of the separation of charges at interface between the electrode surface of active carbon or

carbon fiber and electrolytic solution. Its capacitance is proportional to the specific surface areas

of electrode material. The latter depends on fast faraday redox reaction. The electrochemical

capacitors include metal oxide supercapacitors and conductive polymer supercapacitors. They all

make use of the high reversible redox reaction occurring on electrodes surface or inside them to

produce the capacitance concerning with electrode potential. Capacitance of them depends

mainly on the utilization of active material of electrode. The working voltage of electrochemical

capacitor is usually lower than 3 V. Based on high working voltage of electrolytic capacitor, the

hybrid super-capacitor combines the anode of electrolytic capacitor with the cathode of

electrochemical capacitor, so it has the best features with the high specific capacitance and high

energy density of electrochemical capacitor. The capacitors can work at high voltage without

connecting many cells in series. The most important parameters of a super capacitor include the

capacitance(C), ESR and EPR (which is also called leakage resistance).

Equivalent circuit

Supercapacitors can be illustrated similarly to conventional film, ceramic or aluminum

electrolytic capacitors

This equivalent circuit is only a simplified or first order model of a supercapacitor. In actuality

supercapacitors exhibit a non ideal behavior due to the porous materials used to make the

electrodes. This causes supercapacitors to exhibit behavior more closely to transmission lines

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than capacitors. Below is a more accurate illustration of the equivalent circuit for a

supercapacitor.

How to measure the capacitance

There are a couple of ways used to measure the capacitance of supercapacitors.

1. Charge method

2. Charging and discharging method.

Charge method

Measurement is performed using a charge method using the following formula.

C=t/R

t= .632Vo where Vo is the applied voltage.

This method is similar to the charging method except the capacitance is calculated during the

discharge cycle instead of the charging cycle.

Discharge time for constant current discharge

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t= Cx (V0-V1)/I

Discharge time for constant resistance discharge

t= CRln (V1/V0)

Where t= discharge time, V0= initial voltage, V1= ending voltage, I= current.

Capacitance

Supercapacitors have such large capacitance values that standard measuring equipment cannot be

used to measure the capacity of these capacitors.

Capacitance is measured per the following method:

1. Charge capacitor for 30 minutes at rated voltage.

2. Discharge capacitor through a constant current load.

3. Discharge rate to be 1mA/F.

4. Measure voltage drop between V1 to V2.

5. Measure time for capacitor to discharge from V1 to V2.

6. Calculate the capacitance using the following equation:

C= I*(T2-T1)

V1-V2

Where V1=0.7Vr, V2=0.3Vr (Vr= rated voltage of capacitor)

ESR

AC ESR - Measure using a 4 probe impedance analyzer at 1 kHz.

DC ESR - measured using the following procedure

1. Charge capacitor using a constant current.

2. After reaching rated voltage hold voltage for at least 1 minute.

3. Discharge capacitor at a rate of 1mA/F.

4. Measure the time it takes to have the voltage drop from V1 to V2.

5. Calculate ESR using the following formula:

ESR (DC) = VI

Life expectancy

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The life expectancy of supercapacitors is identical to aluminum electrolytic capacitors. The life

of supercapacitors will double for every 10°C decrease in the ambient temperature the capacitors

are operated in. Supercapacitors operated at room temperature can have life expectancies of

several years compared to operating the capacitors at their maximum rated temperature.

L2=L1*2X X=Tm-Ta/2

L1= Load life rating of the super capacitor.

L2= expected life at operating condition.

Tm= Maximum temperature rating of the supercapacitor.

Ta= Ambient temperature the supercapacitor is going to be exposed to in the application.

Importance of Proper Design of SCES and Future Scope of Work

The utmost requirement of proper design and implementation of SCES is maintaining the

reliability of the power distribution system in the grid connected mode, the switching transient

mode, the island mode. This is also important in various analyses such as sustained interruptions,

voltage flicker, voltage sags, harmonics, voltage regulation, voltage stability. There are other

different aspects related to power distribution system where the storage study is essential, some

are listed as follows.

1. Calculation of load schedule,

2. Optimal use of non-conventional energy sources,

3. Dispatch ability of Power,

4. Ride trough capability of Supply

5. Reduced insulation,

6. Transformer connections and ground faults,

7. Design of system elements: transformer, feeders.

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Applications Of Supercapacitors

Supercapacitors have found uses include:

• Computer systems

• UPS systems

• Power conditioners

• Welders

• Inverters

• Automobile regenerative braking systems

• Power supplies

• Cameras

• Power generators

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3. BOOST CONVERTER

A boost converter (step-up converter) is a power converter with an output DC voltage

greater than its input DC voltage. It is a class of switching-mode power supply

(SMPS) containing at least two semiconductor switches (a diode and a transistor) and at least

one energy storage element. Filters made of capacitors (sometimes in combination

with inductors) are normally added to the output of the converter to reduce output voltage ripple.

Power can also come from DC sources such as batteries, solar panels, rectifiers and DC

generators. A process that changes one DC voltage to a different DC voltage is called DC to DC

conversion. A boost converter is a DC to DC converter with an output voltage greater than the

source voltage. A boost converter is sometimes called a step-up converter since it “steps up” the

source voltage. Since power (P = VI or P = UI in Europe) must be conserved, the output current

is lower than the source current.

A boost converter may also be referred to as a 'Joule thief'. This term is usually used only

with very low power battery applications, and is aimed at the ability of a boost converter to 'steal'

the remaining energy in a battery. This energy would otherwise be wasted since a normal load

wouldn't be able to handle the battery's low voltage.*

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This energy would otherwise remain untapped because in most low-frequency

applications, currents will not flow through a load without a significant difference of

potential between the two poles of the source (voltage.)

Block Diagram

The basic building blocks of a boost converter circuit are shown in Fig.

Fig. Block diagram

The voltage source provides the input DC voltage to the switch control, and to the magnetic field

storage element. The switch control directs the action of the switching element, while the output

rectifier and filter deliver an acceptable DC voltage to the output.

Operating principle

The key principle that drives the boost converter is the tendency of an inductor to resist

changes in current. When being charged it acts as a load and absorbs energy (somewhat like a

resistor), when being discharged, it acts as an energy source (somewhat like a battery). The

voltage it produces during the discharge phase is related to the rate of change of current, and not

to the original charging voltage, thus allowing different input and output voltages.

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Voltage

Source

Magnetic

Switch Control

SwitchingElement

Output

Rectifier and

Fig: Boost converter schematic

Fig. The two configurations of a boost converter, depending on the state of the switch S.

The basic principle of a Boost converter consists of 2 distinct states (see figure ):

in the On-state, the switch S (see figure) is closed, resulting in an increase in the inductor

current;

In the Off-state, the switch is open and the only path offered to inductor current is

through the flyback diode D, the capacitor C and the load R. This result in transferring the

energy accumulated during the On-state into the capacitor.

The input current is the same as the inductor current as can be seen in figure. So it is not

discontinuous as in the buck converter and the requirements on the input filter are relaxed

compared to a buck converter.

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Continuous mode

When a boost converter operates in continuous mode, the current through the inductor (IL) never

falls to zero. Figure shows the typical waveforms of currents and voltages in a converter

operating in this mode. The output voltage can be calculated as follows, in the case of an ideal

converter (i.e. using components with an ideal behavior) operating in steady conditions:

Fig: Waveforms of current and voltage in a boost converter operating in continuous mode.

During the On-state, the switch S is closed, which makes the input voltage (Vi) appear across the

inductor, which causes a change in current (IL) flowing through the inductor during a time period

(t) by the formula:

At the end of the On-state, the increase of IL is therefore:

D is the duty cycle. It represents the fraction of the commutation period T during which the

switch is on. Therefore D ranges between 0 (S is never on) and 1 (S is always on).

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During the Off-state, the switch S is open, so the inductor current flows through the load. If we

consider zero voltage drop in the diode, and a capacitor large enough for its voltage to remain

constant, the evolution of IL is:

Therefore, the variation of IL during the Off-period is:

As we consider that the converter operates in steady-state conditions, the amount of energy

stored in each of its components has to be the same at the beginning and at the end of a

commutation cycle. In particular, the energy stored in the inductor is given by:

So, the inductor current has to be the same at the start and end of the commutation cycle. This

means the overall change in the current (the sum of the changes) is zero:

Substituting   and   by their expressions yields:

This can be written as:

Which in turns reveals the duty cycle to be?

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From the above expression it can be seen that the output voltage is always higher than the input

voltage (as the duty cycle goes from 0 to 1), and that it increases with D, theoretically to infinity

as D approaches 1. This is why this converter is sometimes referred to as a step-up converter.

Discontinuous mode

In some cases, the amount of energy required by the load is small enough to be transferred in a

time smaller than the whole commutation period. In this case, the current through the inductor

falls to zero during part of the period. The only difference in the principle described above is that

the inductor is completely discharged at the end of the commutation cycle (see waveforms in

figure ). Although slight, the difference has a strong effect on the output voltage equation. It can

be calculated as follows:

Fig: Waveforms of current and voltage in a boost converter operating in discontinuous mode.

As the inductor current at the beginning of the cycle is zero, its maximum value   (at

t = DT) is

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During the off-period, IL falls to zero after δT:

Using the two previous equations, δ is:

The load current Io is equal to the average diode current (ID). As can be seen on figure 4, the

diode current is equal to the inductor current during the off-state. Therefore the output current

can be written as:

Replacing ILmax and δ by their respective expressions yields:

Therefore, the output voltage gain can be written as flow:

Compared to the expression of the output voltage for the continuous mode, this expression is

much more complicated. Furthermore, in discontinuous operation, the output voltage gain not

only depends on the duty cycle, but also on the inductor value, the input voltage, the switching

frequency, and the output current.

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APPLICATIONS

Battery powered systems often stack cells in series to achieve higher voltage. However,

sufficient stacking of cells is not possible in many high voltage applications due to lack of space.

Boost converters can increase the voltage and reduce the number of cells. Two battery-powered

applications that use boost converters are hybrid electric vehicles (HEV) and lighting systems.

The NHW20 model Toyota Prius HEV uses a 500 V motor. Without a boost converter, the Prius

would need nearly 417 cells to power the motor. However, a Prius actually uses only 168 cells

and boosts the battery voltage from 202 V to 500 V. Boost converters also power devices at

smaller scale applications, such as portable lighting systems. A white LED typically requires 3.3

V to emit light, and a boost converter can step up the voltage from a single 1.5 V alkaline cell to

power the lamp. Boost converters can also produce higher voltages to operate cold

cathode fluorescent tubes (CCFL) in devices such as LCD backlights and some flashlights.

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4.ELECTRIC VEHICLE

An electric vehicle (EV), also referred to as an electric drive vehicle, uses one or

more electric motors for propulsion. Electric vehicles include electric cars, electric trains, electric

lorries, electric aero-planes, electric boats, electric motorcycles and scooters and electric

spacecraft.[1]

Electric vehicles first came into existence in the mid-19th century, when electricity was

among the preferred methods for motor vehicle propulsion, providing a level of comfort and ease

of operation that could not be achieved by the gasoline cars of the time. The internal combustion

engine (ICE) is the dominant propulsion method for motor vehicles but electric power has

remained commonplace in other vehicle types, such as trains and smaller vehicles of all types.

During the last few decades, increased concern over the environmental impact of the

petroleum-based transportation infrastructure, along with the spectre of peak oil, has led to

renewed interest in an electric transportation infrastructure. Electric vehicles differ from fossil

fuel-powered vehicles in that the electricity they consume can be generated from a wide range of

sources, including fossil fuels, nuclear power, and renewable sources such as tidal power, solar

power, and wind power or any combination of those. However it is generated, this energy is then

transmitted to the vehicle through use of overhead lines, wireless energy transfer such

as inductive charging, or a direct connection through an electrical cable. The electricity may then

be stored onboard the vehicle using a battery, flywheel, or super capacitors. Vehicles making use

of engines working on the principle of combustion can usually only derive their energy from a

single or a few sources, usually non-renewable fossil fuels. A key advantage of electric or hybrid

electric vehicles is regenerative braking and suspension; their ability to recover energy normally

lost during braking as electricity to be restored to the on-board battery.

In 2003, the first mass-produced hybrid gasoline-electric car, the Toyota Prius, was

introduced worldwide, and the first battery electric car produced by a major auto company,

the Nissan Leaf will debut in December 2010. Other major auto companies have electric cars in 21

development, and the USA and other nations are building pilot networks of charging stations to

recharge them.

Vehicle types

Hybrid electric vehicle

A hybrid electric vehicle combines a conventional (usually fossil fuel-powered) power train with

some form of electric propulsion. Common examples include hybrid electric cars such as

the Toyota Prius.

On- and off-road electric vehicles

Electric vehicles are on the road in many functions, including electric cars, electric

trolleybuses, electric bicycles, electric motorcycles and scooters, neighborhood electric

vehicles, golf carts, milk floats, and forklifts. Off-road vehicles include electrified all-terrain

vehicles and tractors.

Rail borne electric vehicles

A streetcar (or Tram) drawing current from a single overhead wire through a pantograph

The fixed nature of a rail line makes it relatively easy to power electric vehicles through

permanent overhead lines or electrified third rails, eliminating the need for heavy onboard

batteries. Electric locomotives, electric trams/streetcars/trolleys, electric light rail systems, and

electric rapid transit are all in common use today, especially in Europe and Asia.

Since electric trains do not need to carry a heavy internal combustion engine or large batteries,

they can have very good power-to-weight ratios. This allows high speed trains such as France's

double-deck TGVs to operate at speeds of 320 km/h (200 mph) or higher, and electric

locomotives to have a much higher power output than diesel locomotives. In addition they have

higher short-term surge power for fast acceleration, and using regenerative braking can put

braking power back into the electrical grid rather than wasting it.

Maglev trains are also nearly always electric vehicles.

Airborne electric vehicles

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Since the beginning of the era of aviation, electric power for aircraft has received a great deal of

experimentation. Currently flying electric aircraft include manned and unmanned aerial vehicles.

Seaborne electric vehicles

Electric boats were popular around the turn of the 20th century. Interest in quiet and potentially

renewable marine transportation has steadily increased since the late 20th century, as solar

cells have given motorboats the infinite range of sailboats. Submarines use batteries (charged

by diesel or gasoline engines at the surface), nuclear power, or fuel cells run electric motor

driven propellers.

Space borne electric vehicles

Electric power has a long history of use in spacecraft. The power sources used for spacecraft are

batteries, solar panels and nuclear power. Current methods of propelling a spacecraft with

electricity include the arc jet rocket, the electrostatic, the Hall Effect thruster, and Field Emission

Electric Propulsion. A number of other methods have been proposed, with varying levels of

feasibility.

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5. ADVANTAGES OF ELECTRIC VEHICLES:

Environmental

Due to efficiency of electric engines as compared to combustion engines, even when the

electricity used to charge electric vehicles comes a CO2 emitting source, such as a coal or gas

fired powered plant, the net CO2 production from an electric car is typically one half to one third

of that from a comparable combustion vehicle.

Electric vehicles release almost no air pollutants at the place where they are operated. In

addition, it is generally easier to build pollution control systems into centralized power stations

than retrofit enormous numbers of cars.

Electric vehicles typically have less noise pollution than an internal combustion engine vehicle,

whether it is at rest or in motion. Electric vehicles emit no tailpipe CO2 or pollutants such

as NOx, NMHC, CO and PM at the point of use.

Electric motors don't require oxygen, unlike internal combustion engines; this is useful

for submarines.

Mechanical

Electric motors are mechanically very simple.

Electric motors often achieve 90% energy conversion efficiency over the full range of speeds and

power output and can be precisely controlled. They can also be combined with regenerative

braking systems that have the ability to convert movement energy back into stored electricity.

This can be used to reduce the wear on brake systems (and consequent brake pad dust) and

reduce the total energy requirement of a trip. Regenerative braking is especially effective for

start-and-stop city use.

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They can be finely controlled and provide high torque from rest, unlike internal combustion

engines, and do not need multiple gears to match power curves. This removes the need

for gearboxes and torque converters.

Electric vehicles provide quiet and smooth operation and consequently have less noise

and vibration than internal combustion engines. While this is a desirable attribute, it has also

evoked concern that the absence of the usual sounds of an approaching vehicle poses a danger to

blind, elderly and very young pedestrians. To mitigate this situation, automakers and individual

companies are developing systems that produce warning sounds when electric vehicles are

moving slowly, up to a speed when normal motion and rotation (road, suspension, electric motor,

etc.) noises become audible.

Energy resilience

Electricity is a form of energy that remains within the country or region where it was produced

and can be multi-sourced. As a result it gives the greatest degree of energy resilience.

Energy efficiency

Electric vehicle 'tank-to-wheels' efficiency is about a factor of 3 higher than internal combustion

engine vehicles. It does not consume energy when it is not moving, unlike internal combustion

engines where they continue running even during idling. However, looking at the well-to-

wheel efficiency of electric vehicles, their emissions are comparable to an efficient gasoline or

diesel in most countries because electricity generation relies on fossil fuels.

Cost of recharge

The GM Volt will cost "less than purchasing a cup of your favorite coffee" to recharge. The Volt

should cost less than 2 cents per mile to drive on electricity, compared with 12 cents a mile on

gasoline at a price of $3.60 a gallon. This means a trip from Los Angeles to New York would

cost $56 on electricity, and $336 with gasoline. This would be the equivalent to paying 60 cents

a gallon of gas.

Stabilization of the grid

Since electric vehicles can be plugged into the electric grid when not in use, there is a potential

for battery powered vehicles to even out the demand for electricity by feeding electricity into the 25

grid from their batteries during peak use periods (such as mid afternoon air conditioning use)

while doing most of their charging at night, when there is unused generating capacity.

This Vehicle to Grid (V2G) connection has the potential to reduce the need for new power

plants.

Furthermore, our current electricity infrastructure may need to cope with increasing shares of

variable-output power sources such as windmills and PV solar panels. This variability could be

addressed by adjusting the speed at which EV batteries are charged, or possibly even discharged.

Some concepts see battery exchanges and battery charging stations, much like gas/petrol stations

today. Clearly these will require enormous storage and charging potentials, which could be

manipulated to vary the rate of charging, and to output power during shortage periods, much as

diesel generators are used for short periods to stabilize some national grids.

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6.FULL BRIDGE CONVERTER

A bridge is an arrangement of four (or more) diodes in a bridge configuration that

provides the same polarity of output for either polarity of input. When used in its most common

application, for conversion of an alternating current (AC) input into direct current a (DC) output,

it is known as a bridge rectifier. A bridge rectifier provides full-wave rectification from a two-

wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input

from a transformer with a center-tapped secondary winding.

A rectifier is an electrical device that converts alternating current (AC), which

periodically reverses direction, to direct current (DC), current that flows in only one direction, a

process known as rectification. Rectifiers have many uses including as components of power

supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum

tube diodes, mercury arc valves, and other components.

A device which performs the opposite function (converting DC to AC) is known as

an inverter.

When only one diode is used to rectify AC (by blocking the negative or positive portion of

the waveform), the difference between the term diode and the term rectifier is merely one of

usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost all

rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting

AC to DC than is possible with only one diode. Before the development of silicon semiconductor

rectifiers, vacuum tube diodes and copper(I) oxide or selenium rectifier stacks were used.

HALF-WAVE RECTIFIER:

In half wave rectification, either the positive or negative half of the AC wave is passed,

while the other half is blocked. Because only one half of the input waveform reaches the output,

it is very inefficient if used for power transfer. Half-wave rectification can be achieved with a

single diode in a one-phase supply, or with three diodes in a three-phase supply.

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The output DC voltage of a half wave rectifier can be calculated with the following two ideal

equations:

FULL-WAVE RECTIFIER:

A full-wave rectifier converts the whole of the input waveform to one of constant polarity

(positive or negative) at its output. Full-wave rectification converts both polarities of the input

waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center

tapped transformer, four diodes are required instead of the one needed for half-wave

rectification. Four diodes arranged this way are called a diode bridge or bridge rectifier:

For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back

(i.e. anodes-to-anode or cathode-to-cathode) can form a full-wave rectifier. Twice as many

windings are required on the transformer secondary to obtain the same output voltage compared

to the bridge rectifier above.

28

A very common vacuum tube rectifier configuration contained one cathode and

twin anodes inside a single envelope; in this way, the two diodes required only one vacuum tube.

The 5U4 and 5Y3 were popular examples of this configuration.

Fig. A three-phase bridge rectifier.

Fig. 3-phase AC input, half & full wave rectified DC output waveforms

29

For three-phase AC, six diodes are used. Typically there are three pairs of diodes, each

pair, though, is not the same kind of double diode that would be used for a full wave single-phase

rectifier. Instead the pairs are in series (anode to cathode). Typically, commercially available

double diodes have four terminals so the user can configure them as single-phase split supply

use, for half a bridge, or for three-phase u

Most devices that generate alternating current (such devices are called alternators)

generate three-phase AC. For example, an automobile alternator has six diodes inside it to

function as a full-wave rectifier for battery charging applications.

The average and root-mean-square output voltages of an ideal single phase full wave

rectifier can be calculated as:

Where:

Vdc,Vav - the average or DC output voltage,

Vp - the peak value of half wave,

Vrms - the root-mean-square value of output voltage.

π = ~ 3.14159

PEAK LOSS:

An aspect of most rectification is a loss from the peak input voltage to the peak output

voltage, caused by the built-in voltage drop across the diodes (around 0.7 V for ordinary silicon

p-n-junction diodes and 0.3 V for Schottky diodes). Half-wave rectification and full-wave

rectification using two separate secondaries will have a peak voltage loss of one diode drop.

Bridge rectification will have a loss of two diode drops. This may represent significant power

loss in very low voltage supplies. In addition, the diodes will not conduct below this voltage, so

the circuit is only passing current through for a portion of each half-cycle, causing short

segments of zero voltage to appear between each "hump".

30

RECTIFIER OUTPUT SMOOTHING:

While half-wave and full-wave rectification suffice to deliver a form of DC output,

neither produces constant-voltage DC. In order to produce steady DC from a rectified AC

supply, a smoothing circuit or filter is required.[1] In its simplest form this can be just a reservoir

capacitor or smoothing capacitor, placed at the DC output of the rectifier. There will still remain

an amount of AC ripple voltage where the voltage is not completely smoothed.

RC-Filter Rectifier: This circuit was designed and simulated using Multisim 8 software.

Sizing of the capacitor represents a tradeoff. For a given load, a larger capacitor will

reduce ripple but will cost more and will create higher peak currents in the transformer

secondary and in the supply feeding it. In extreme cases where many rectifiers are loaded onto a

power distribution circuit, it may prove difficult for the power distribution authority to maintain

a correctly shaped sinusoidal voltage curve.

For a given tolerable ripple the required capacitor size is proportional to the load current

and inversely proportional to the supply frequency and the number of output peaks of the

rectifier per input cycle. The load current and the supply frequency are generally outside the

control of the designer of the rectifier system but the number of peaks per input cycle can be

affected by the choice of rectifier design.

31

A half-wave rectifier will only give one peak per cycle and for this and other reasons is

only used in very small power supplies. A full wave rectifier achieves two peaks per cycle and

this is the best that can be done with single-phase input. For three-phase inputs a three-phase

bridge will give six peaks per cycle and even higher numbers of peaks can be achieved by using

transformer networks placed before the rectifier to convert to a higher phase order.

To further reduce this ripple, a capacitor-input filter can be used. This complements the

reservoir capacitor with a choke (inductor) and a second filter capacitor, so that a steadier DC

output can be obtained across the terminals of the filter capacitor. The choke presents a high

impedance to the ripple current.

A more usual alternative to a filter, and essential if the DC load is very demanding of a

smooth supply voltage, is to follow the reservoir capacitor with a voltage regulator. The reservoir

capacitor needs to be large enough to prevent the troughs of the ripple getting below the voltage

the DC is being regulated to. The regulator serves both to remove the last of the ripple and to

deal with variations in supply and load characteristics. It would be possible to use a smaller

reservoir capacitor (these can be large on high-current power supplies) and then apply some

filtering as well as the regulator, but this is not a common strategy. The extreme of this approach

is to dispense with the reservoir capacitor altogether and put the rectified waveform straight into

a choke-input filter. The advantage of this circuit is that the current waveform is smoother and

consequently the rectifier no longer has to deal with the current as a large current pulse, but

instead the current delivery is spread over the entire cycle. The downside is that the voltage

output is much lower – approximately the average of an AC half-cycle rather than the peak.

VOLTAGE DOUBLING RECTIFIERS:

The simple half wave rectifier can be built in two versions with the diode pointing in

opposite directions, one version connects the negative terminal of the output direct to the AC

supply and the other connects the positive terminal of the output direct to the AC supply. By

combining both of these with separate output smoothing it is possible to get an output voltage of

32

nearly double the peak AC input voltage. This also provides a tap in the middle, which allows

use of such a circuit as a split rail supply.

A variant of this is to use two capacitors in series for the output smoothing on a bridge

rectifier then place a switch between the midpoint of those capacitors and one of the AC input

terminals. With the switch open this circuit will act like a normal bridge rectifier with it closed it

will act like a voltage doubling rectifier. In other words this makes it easy to derive a voltage of

roughly 320V (+/- around 15%) DC from any mains supply in the world, this can then be fed

into a relatively simple switched mode power supply.

Fig. Cockcroft Walton Voltage multiplier

Cascaded stages of diodes and capacitors can be added to make a voltage multiplier

(Cockroft-Walton circuit). These circuits can provide a potential several times that of the peak

value of the input AC, although limited in current output and regulation. Voltage multipliers are

used to provide the high voltage for a CRT in a television receiver, or for powering high-voltage

tubes such as image intensifiers or photo multipliers.

The essential feature of a diode bridge is that the polarity of the output is the same

regardless of the polarity at the input. The diode bridge circuit is also known as the Graetz

circuit after its inventor, physicist Leo Graetz.

Basic operation:

According to the conventional model of current flow originally established by Benjamin

Franklin and still followed by most engineers today, current is assumed to flow through electrical

conductors from the positive to the negative pole. In actuality, free electrons in a conductor

nearly always flow from the negative to the positive pole. In the vast majority of applications,

however, the actual direction of current flow is irrelevant. Therefore, in the discussion below the

conventional model is retained.

33

In the diagrams below, when the input connected to the left corner of the diamond is positive,

and the input connected to the right corner is negative, current flows from the upper supply

terminal to the right along the red (positive) path to the output, and returns to the lower supply

terminal via the blue (negative) path.

When the input connected to the left corner is negative, and the input connected to

the right corner is positive, current flows from the lower supply terminal to the right along

the red (positive) path to the output, and returns to the upper supply terminal via

the blue (negative) path.

34

Fig. AC, half-wave and full wave rectified signals.

In each case, the upper right output remains positive and lower right output negative. Since this

is true whether the input is AC or DC, this circuit not only produces a DC output from an AC

input, it can also provide what is sometimes called "reverse polarity protection". That is, it

permits normal functioning of DC-powered equipment when batteries have been installed

backwards, or when the leads (wires) from a DC power source have been reversed, and protects

the equipment from potential damage caused by reverse polarity.

Prior to the availability of integrated circuits, a bridge rectifier was constructed from "discrete

components", i.e., separate diodes. Since about 1950, a single four-terminal component

containing the four diodes connected in a bridge configuration became a standard commercial

component and is now available with various voltage and current ratings.

Output smoothing:

For many applications, especially with single phase AC where the full-wave bridge serves to

convert an AC input into a DC output, the addition of a capacitor may be desired because the

bridge alone supplies an output of fixed polarity but continuously varying or "pulsating"

magnitude, an attribute commonly referred to as "ripple" (see diagram to right).

35

The function of this capacitor, known as a reservoir capacitor (or smoothing capacitor) is to

lessen the variation in (or 'smooth') the rectified AC output voltage waveform from the bridge.

One explanation of 'smoothing' is that the capacitor provides a low impedance path to the AC

component of the output, reducing the AC voltage across, and AC current through, the resistive

load. In less technical terms, any drop in the output voltage and current of the bridge tends to be

canceled by loss of charge in the capacitor. This charge flows out as additional current through

the load. Thus the change of load current and voltage is reduced relative to what would occur

without the capacitor. Increases of voltage correspondingly store excess charge in the capacitor,

thus moderating the change in output voltage / current.

The simplified circuit shown has a well-deserved reputation for being dangerous, because, in

some applications, the capacitor can retain a lethal charge after the AC power source is removed.

If supplying a dangerous voltage, a practical circuit should include a reliable way to discharge

the capacitor safely. If the normal load cannot be guaranteed to perform this function, perhaps

because it can be disconnected, the circuit should include a bleeder resistor connected as close as

practical across the capacitor. This resistor should consume a current large enough to discharge

the capacitor in a reasonable time, but small enough to minimize unnecessary power waste.

The capacitor and the load resistance have a typical time constant τ = RC where C and R are the

capacitance and load resistance respectively. As long as the load resistor is large enough so that

this time constant is much longer than the time of one ripple cycle, the above configuration will

produce a smoothed DC voltage across the load.

36

In some designs, a series resistor at the load side of the capacitor is added. The smoothing can

then be improved by adding additional stages of capacitor–resistor pairs, often done only for sub-

supplies to critical high-gain circuits that tend to be sensitive to supply voltage noise.

The idealized waveforms shown above are seen for both voltage and current when the load on

the bridge is resistive. When the load includes a smoothing capacitor, both the voltage and the

current waveforms will be greatly changed. While the voltage is smoothed, as described above,

current will flow through the bridge only during the time when the input voltage is greater than

the capacitor voltage. For example, if the load draws an average current of n Amps, and the

diodes conduct for 10% of the time, the average diode current during conduction must be 10n

Amps. This non-sinusoidal current leads to harmonic distortion and a poor power factor in the

AC supply.

In a practical circuit, when a capacitor is directly connected to the output of a bridge, the bridge

diodes must be sized to withstand the current surge that occurs when the power is turned on at

the peak of the AC voltage and the capacitor is fully discharged. Sometimes a small series

resistor is included before the capacitor to limit this current, though in most applications the

power supply transformer's resistance is already sufficient.

Output can also be smoothed using a choke and second capacitor. The choke tends to keep the

current (rather than the voltage) more constant. This design is not generally used in modern

equipment due to the high cost of an effective choke compared to a resistor and capacitor.

Some early console radios created the speaker's constant field with the current from the high

voltage ("B +") power supply, which was then routed to the consuming circuits, (permanent

magnets were then too weak for good performance) to create the speaker's constant magnetic

field. The speaker field coil thus performed 2 jobs in one: it acted as a choke, filtering the power

supply, and it produced the magnetic field to operate the speaker.

Poly-phase Bridge

The diode bridge can be generalized to rectify poly-phase AC inputs. For example, for a three-

phase AC input, a half-wave rectifier consists of three diodes, but a full-wave bridge rectifier

consists of six diodes.

37

Fig: Three phase bridge rectifier.

Fig. 3-phase AC input waveform, half-wave rectified waveform, and full-wave rectified

waveform.

38

RECTIFICATION TECHNOLOGY:

Electromechanical

Early power conversion systems were purely electro-mechanical in design, since electronic

devices were not available to handle significant power. Mechanical rectification systems usually

rely on some form of rotation or resonant vibration in order to move quickly enough to match the

frequency of the input power source, and cannot operate beyond several thousand cycles per

second.

Due to the complexity of mechanical systems, they have traditionally needed a high level of

maintenance to keep operating correctly. Moving parts will have friction, which requires

lubrication and replacement due to wear. Opening mechanical contacts under load results in

electrical arcs and sparks that heat and erode the contacts.

Synchronous rectifier

To convert AC currents into DC current in electric locomotives, a synchronous rectifier may be

used. It consists of a synchronous motor driving a set of heavy-duty electrical contacts. The

motor spins in time with the AC frequency and periodically reverses the connections to the load

just when the sinusoidal current goes through a zero-crossing. The contacts do not have

to switch a large current, but they need to be able to carry a large current to supply the

locomotive's DC traction motors.

Vibrator

In the past, the vibrators used in battery-to-high-voltage-DC power supplies often contained a

second set of contacts that performed synchronous mechanical rectification of the stepped-up

voltage.

Motor-generator set

A motor-generator set or the similar rotary converter, is not a rectifier in the sense that it doesn't

actually rectify current, but rather generates DC from an AC source. In an "M-G set", the shaft of

an AC motor is mechanically coupled to that of a DC generator. The DC generator produces

multiphase alternating currents in its armature windings, and a commutator on the armature shaft

39

converts these alternating currents into a direct current output; or a homopolar

generator produces a direct current without the need for a commutator. M-G sets are useful for

producing DC for railway traction motors, industrial motors and other high-current applications,

and were common in many high power D.C. uses (for example, carbon-arc lamp projectors for

outdoor theaters) before high-power semiconductors became widely available.

Electrolytic

The electrolytic rectifier was an early device from the 1900s that is no longer used. When two

different metals are suspended in an electrolyte solution, it can be found that direct current

flowing one way through the metals has less resistance than the other direction. These most

commonly used an aluminum anode, and a lead or steel cathode, suspended in a solution of tri-

ammonium ortho-phosphate.

The rectification action is due to a thin coating of aluminum hydroxide on the aluminum

electrode, formed by first applying a strong current to the cell to build up the coating. The

rectification process is temperature sensitive, and for best efficiency should not operate above 86

°F (30 °C). There is also a breakdown voltage where the coating is penetrated and the cell is

short-circuited. Electrochemical methods are often more fragile than mechanical methods, and

can be sensitive to usage variations which can drastically change or completely disrupt the

rectification processes.

Similar electrolytic devices were used as lightning arresters around the same era by suspending

many aluminum cones in a tank of tri-ammonium ortho-phosphate solution. Unlike the rectifier,

above, only aluminum electrodes were used, and used on A.C., there was no polarization and

thus no rectifier action, but the chemistry was similar.

The modern electrolytic capacitor, an essential component of most rectifier circuit configurations

was also developed from the electrolytic rectifier.

Mercury arc

A rectifier used in high-voltage direct current power transmission systems and industrial

processing between about 1909 to 1975 is a mercury arc rectifier or mercury arc valve. The

device is enclosed in a bulbous glass vessel or large metal tub. One electrode, the cathode, is

submerged in a pool of liquid mercury at the bottom of the vessel and one or more high purity 40

graphite electrodes, called anodes, are suspended above the pool. There may be several auxiliary

electrodes to aid in starting and maintaining the arc. When an electric arc is established between

the cathode pool and suspended anodes, a stream of electrons flows from the cathode to the

anodes through the ionized mercury, but not the other way. [In principle, this is a higher-power

counterpart to flame rectification, which uses the same one-way current transmission properties

of the plasma naturally present in a flame].

These devices can be used at power levels of hundreds of kilowatts, and may be built to handle

one to six phases of AC current. Mercury arc rectifiers have been replaced by silicon

semiconductor rectifiers and high power thyristor circuits, from the mid 1970s onward. The most

powerful mercury arc rectifiers ever built were installed in the Manitoba Hydro Nelson River Bi-

pole HVDC project, with a combined rating of more than one million kilowatts and 450,000

volts.

Argon gas electron tube

The General Electric Tungar rectifier was an argon gas-filled electron tube device with a

tungsten filament cathode and a carbon button anode. It was useful for battery chargers and

similar applications from the 1920s until low-cost solid-state rectifiers (the metal rectifiers at

first) supplanted it. These were made up to a few hundred volts and a few amperes rating, and in

some sizes strongly resembled anincandescent lamp with an additional electrode.

The 0Z4 was a gas-filled rectifier tube commonly used in vacuum tube car radios in the 1940s

and 1950s. It was a conventional full wave rectifier tube with two anodes and one cathode, but

was unique in that it had no filament (thus the "0" in its type number). The electrodes were

shaped such that the reverse breakdown voltage was much higher than the forward breakdown

voltage. Once the breakdown voltage was exceeded, the 0Z4 switched to a low-resistance state

with a forward voltage drop of about 24 volts.

Vacuum tube (valve)

Since the discovery of the Edison effect or thermionic emission, various vacuum tube devices

have been developed to rectify alternating currents. Low-power devices are used as signal

detectors, first used in radio by Fleming in 1904. Many vacuum-tube devices also used vacuum

rectifiers in their power supplies, for example the All American Five radio receiver. Vacuum

41

rectifiers were made for very high voltages, such as the high voltage power supply for

the cathode ray tube of television receivers, and the kenotron used for power supply in X-

ray equipment. However, vacuum rectifiers generally had low current capacity owing to the

maximum current density that could be obtained by electrodes heated to temperatures compatible

with long life. Another limitation of the vacuum tube rectifier was that the heater power supply

often required special arrangements to insulate it from the high voltages of the rectifier circuit.

Crystal detector

The cat's-whisker detector, using a crystal such as galena, was the earliest type of solid state

diode.

Selenium and copper oxide rectifiers

Once common until replaced by more compact and less costly silicon solid-state rectifiers, these

units used stacks of metal plates and took advantage of the semiconductor properties

of selenium or copper oxide. While selenium rectifiers were lighter in weight and used less

power than comparable vacuum tube rectifiers, they had the disadvantage of finite life

expectancy, increasing resistance with age, and were only suitable to use at low frequencies.

Both selenium and copper oxide rectifiers have somewhat better tolerance of momentary voltage

transients than silicon rectifiers.

Typically these rectifiers were made up of stacks of metal plates or washers, held together by a

central bolt, with the number of stacks determined by voltage; each cell was rated for about 20

volts. An automotive battery charger rectifier might have only one cell: the high-voltage power

supply for a vacuum tube might have dozens of stacked plates. Current density in an air-cooled

selenium stack was about 600 mA per square inch of active area (about 90 mA per square

centimeter).

Silicon and germanium diodes

In the modern world, silicon diodes are the most widely used rectifiers and have largely replaced

earlier germanium diodes.

42

7.POWER MANAGEMENT

Power management is a feature of some electrical appliances,

especially copiers, computers and computer peripherals such as monitors and printers, that

turns off the power or switches the system to a low-power state when inactive. In computing this

is known as PC power management and is built around a standard called ACPI. This

supersedes APM. All recent (consumer) computers have ACPI support.

Motivation:

PC power management for computer systems is desired for many reasons, particularly:

Reduce overall energy consumption

Prolong battery life for portable and embedded systems

Reduce cooling requirements

Reduce noise .

Reduce operating costs for energy and cooling.

Lower power consumption also means lower heat dissipation, which increases system stability,

and less energy use, which saves money and reduces the impact on the environment.

Processor level techniques:

The power management for microprocessors can be done over the whole processor, or in specific

areas.

With dynamic voltage scaling and dynamic frequency scaling, the CPU core voltage, clock rate,

or both, can be altered to decrease power consumption at the price of potentially lower

performance. This is sometimes done in real time to optimize the power-performance tradeoff.

43

Examples:

AMD Cool'n'Quiet

AMD PowerNow! [1]

IBM EnergyScale [2]

Intel SpeedStep

Transmeta LongRun and LongRun2

VIA LongHaul (PowerSaver)

Additionally, processors can selectively power off internal circuitry (power gating). For

example:

Newer Intel Core processors support ultra-fine power control over the functional units

within the processors.

AMD CoolCore technology get more efficient performance by dynamically activating or

turning off parts of the processor.[3]

Intel VRT technology split the chip into a 3.3V I/O section and a 2.9V core section. The lower

core voltage reduces power consumption.

Power Management System helps to:

Avoid Black-outs

In case of a lack of power, Load Shedding secures the electrical power to critical loads by

switching off non-critical loads according to dynamic priority tables.

Reduce Energy Costs / Peak Shaving

When all on-site power generation is maximized and the power demand still tends to exceed the

contracted maximum electricity import, the system will automatically shed some of the low

priority loads.

Enhanced Operator Support

44

At sites where electricity is produced by several generators, the demands with respect to control

activities by operators are much higher. Advanced functions such as intelligent alarm filtering,

consistency analysis, operator guidance, and a well organized single-window interface support

the operator and prevent incorrect interventions.

Achieve Stable Operation

The Power Control function shares the active and reactive power between the different

generators and tie-lines in such a way that the working points of the machines are as far as

possible away from the border of the individual PQ-capability diagrams so that the plant can

withstand bigger disturbances.

Optimize Network Design

Because the set points for the generators, turbines and transformers are calculated in such a way

that no component will be overloaded and the electrical network can be used up to its limits,

over-dimensioning of the network is no longer needed.

Minimize Cabling and Engineering

All the signals and information which are available in protection/control relays,

governor/excitation controllers and other microprocessor based equipment can be easily

transmitted to the Industrial PMS via serial communication links. This avoids marshalling

cubicles, interposing relays, cable ducts, spaghetti wiring, cabling engineering and provides extra

functionality such as parameter setting/reading, stored events, disturbance data analysis and a

single window to all electrical related data.

45

8. DC/DC CONVERTERS TOPOLOGIES AND MODELING

8.1. Multi boost and Multi full bridge converters modeling

• Figure (a) shows the multi boost converter topology.

The general model for this topology is given by equation; where (α1) and (n) define respectively

the duty cycle and parallel input converter number.

46

The voltage drops in the Ln and λ inductances are given by equation.

The converter average model has a nonlinear behavior because of crosses between α1 control

variable and Vbus1 parameter. The Vbus1, Vsc1, Vsc2, Vscn , Ich and Vbat variables can to

disturb the control, they must be measured and used in the estimate of the control law to ensure a

dynamics of control [3]. The multi boost converter [4] topology control law which results from

the boost converter modeling is presented by α1 duty cycle; where Np = max(n) is the maximum

number of parallel converters.

The multi boost converter control strategy is presented in Fig (a).

It ensures the super capacitor modules discharge with variable current. The super capacitors

reference current (Iscref) is obtained starting from the power management between batteries and

hybrid vehicle DC-link. This control strategy includes the super capacitors and batteries current

control loops. PWM1 signal ensures the multi boost converters control during super capacitor

modules discharge. These modules being identical, the energy management between the modules

and the hybrid vehicle DC-link enables to write the super capacitors current references.

47

To simplify the super capacitors current references estimation, the multi boost converter

efficiency (η) was fixed at 85%.

• The multi full bridge converter [5] control strategy proposed in this paper consists to establish

the full bridge converters standardized voltage [6]. The control law which result from the multi

full bridge converter modeling is presented by equation, where (m) defines the transformer turns

ratio.

This standardized voltage is compared with two triangular carrier waves of amplitude Vmax =

1V with a switching frequency of 20 kHz. The inverter control strategy is presented in Fig.(b);

where Q1, Q2, Q3 and Q4 are the control signals applied to K1, K2, K3 and K4 switches. The

simulations and experimental parameters are presented in table below.

8.2 Full bridge converter simulation results for Np = 2

The simulation has been made for Np = 2 [7]. The maximum and minimum voltages of the super

capacitor modules are respectively fixed at 270V and 135V. The hybrid vehicle requested current

(Ich) is respectively fixed at 100A from 0 to 0.5s, 400A from 0.5s to 18s and 100A from 18s to

20s. Battery reference current (Ibatref) is fixed at 100A independently of the hybrid vehicle

power request.

48

Fig (a): Super capacitor modules voltages, (b): Super capacitor modules currents

Super capacitor modules voltages (Vsc1, Vsc2) presented in Fig.(a) are identical. The

currents amplitudes (Isc1, Isc2) presented in Fig.(b) are also identical. Control enables to

maintain the battery current (Ibat) at 100A; but around 0.5s and 18s the battery current control

loop has not enough time to react Fig (a). The important power of the transient states is ensured

by the super capacitors modules (IL) Fig (b). Simulation parameters are presented in TABLE.

TABLE: FULL BRIDGE TOPOLOGIE SIMULATIONS PARAMETERS

8.3. Design and Experimental results

Wiring in power electronic design is a general problem for electrical energy system and

the voltage inverters do not escape to this problem. The switch action of semiconductors causes

instantaneous fluctuations of the current and any stray inductance in the commutation cell will

produce high voltage variations. Semiconductors, when switching off, leads to high voltage

transitions which is necessary to control within tolerable limits. The energy stored in parasitic

inductances, during switching on, is generally dissipated by this semiconductor.

49

In the case of the single-phase inverter, each cell includes two switches and a decoupling

capacitor placed at the cell boundaries, which presents a double role. It enables to create an

instantaneous voltage source very close to the inverter. The (C) capacitor associated to an

inductor enables to filter the harmonic components of the currents which are generated by the

inverter. Parasitic inductances staying in the mesh include the capacitor inductance, the internal

inductance of semiconductors and the electric connection inductances.

A good choice of the components with an optimal wiring enables to minimize parasitic

inductances. Using the semiconductors modules solves the connection problems between

components. All these efforts can become insufficient, if residual inductances remain too high or

if the inverter type is the low voltages and strong currents for which the voltage variations are

much important. In both cases, the use of the chopping devices is necessary. These devices must

be placed very close to the component to avoid any previous problem. The parameters used for

experimental tests are presented in TABLE and the principle of such circuits [8] is given in Fig.

TABLE: FULL BRIDGE EXPERIMENTAL PARAMETERS

50

Figure. Full bridge converter with chopping devices

During switching off of the semiconductors, the corresponding current stored in wiring

inductances circulates in the following meshes C1, D1 ; C2 , D2; C3, D3 and C4 , D4 which

limits the voltages applied to the switches. When electrical energy is fully transferred in C1, C2,

C3 and C4 capacitors, the current becomes null and the meshes become closed. The C1, C2, C3

and C4 capacitors are used only for transient energy tank and it is necessary to recycle this

switching energy while controlling the voltage at the semiconductors boundary. This function is

ensured by R1, R2, R3 and R4 resistances. R1, R2, R3 and R4 resistances are identical and C1,

C2, C3 and C4 capacitors are also identical.

8.4 Experimental setup at reduced scale

For reasons of cost components and safety, the experimental test benches were carried out at a

reduced scale (1/10).

• The boost converter test bench Fig (a) is made of: a battery module of 4 cells in series, two

super capacitors modules of 10 cells (Maxwell BOOSTCAP2600) in series for each one, an

active load which is used to define power request, two boost converters in parallel which ensure

power management in hybrid vehicle.

Figure. Boost and full bridge converters experimental setup

• For the full bridge converter [9] test bench Fig (b), a batteries module, a super capacitors

module, two high frequency planar transformer, the DC/AC and AC/DC converters have been

designed. The super capacitors modules voltages must be between 27 V and 13.5 V. The

batteries module which imposes the DC-bus voltage presents a rated voltage of 48 V and the DC-

51

link voltage level must be between 43 V and 60 V. The converters are controlled by a

PIC18F4431 microcontroller with 10 kHz control frequencies for boost converters and 20 kHz

for the full bridge converter.

8.5. Boost converters simulation and experimental results

The boost converters experimental test is carried out in the following conditions: During

the super capacitors discharge, the batteries current reference (Ibatref) is fixed at 13A so that, the

super capacitors modules provide hybrid vehicle power request during the transient states. For

these tests, the hybrid vehicle request (Ich) was fixed at 53A. The experimental and simulations

results of the modules voltage are compared in Fig (a) and Fig (b). The (Isc1) and (Isc2)

experimental currents are not identical

Figure. Super capacitor modules experimental and simulation voltage results

Fig (a), Fig (b) because the super capacitors dispersion and the power electronic circuits (boost

converters) inequality.

Figure. Super capacitor modules experimental and simulation current results

The first boost converter ensures 50% and the second ensures also 50% of the DC-link current

(IL). In other words the two super capacitors modules ensure a (IL) current of 40A to hybrid52

vehicle as presented in Fig (a), and 13A only is provided by the batteries Fig (b).

Figure. DC-link voltage and current experimental validation

53

CONCLUSION

In this paper, multi boost and multi full bridge converter topologies and their control

strategies for batteries and super capacitors coupling in the hybrid vehicle applications were

proposed. The system control is ensured by PIC18F4431 microcontroller type which includes 9

analog inputs and 8 PWM outputs. For reasons of simplicity and cost, the multi boost converter

is the most interesting topology regarding the multi full bridge converter topology. It enables a

good power management in hybrid vehicle. Full bridge experimental tests conditions were

different from that of boost converter topology, so at this time it is not easy to make a good

comparison between the two topologies. However, multi full bridge converter topology is well

suitable to adapt the level of available voltage to the DC-link. For low voltage and high current

applications such as super capacitors, the full bridge converter seems to be less interesting

because of its higher cost ( many silicon and passive components), and a lower efficiency.

54

REFERENCES

[1] J.M Timmermans, P. Zadora, J. Cheng, Y. Van Mierlo, and Ph. Lataire. Modelling and

design of super capacitors as peak power unit for hybrid electric vehicles. Vehicle Power and

Propulsion, IEEE Conference, 7-9 September, page 8pp, 2005.

[2] Huang jen Chiu, Hsiu Ming Li-Wei Lin, and Ming-Hsiang Tseng. A multiple- input dc/dc

converter for renewable energy systems. ICIT2005, IEEE, 14-17 December, pages 1304–1308,

2005.

[3] M.B. Camara, H. Gualous, F. Gustin, and A. Berthon. Control strategy of hybrid sources for

transport applications using supercapacitors and batteries. IPEMC2006, 13-16 August, Shanghai,

P.R.CHINA, 1:1–5, 2006.

[4] L. Solero, A. Lidozzi, and J.A. Pomilo. Design of multiple-input power converter for hybrid

vehicles. IEEE transactions on power electronics, 20, Issue 5, 2005.

[5] Xin KONG and A. KHA. Analysis and implementation of a high efficiency, interleaved

current-fed full bridge converter for fuel cell system. IEEE, 28-01 Nov, 1:474–479, 2005.

[6] M.B. Camara, F. Gustin, H. Gualous and A. Berthon. Studies and realization of the buck-

boost and full bridge converters with multi sources system for the hybrid vehicle applications.

Second European Symposium on Super capacitors and Applications, ESSCAP2006, Lausanne,

Switzerland,2-3 November, 2006.

[7] Huang-Jen Chiu, Hsiu-Ming, Li-Wei Lin, Ming-Hsiang Tseng. A Multiple-Input DC/DC

Converter for Renewable Energy Systems, Industrial Technology, ICIT2005, IEEE international

Conference, 14-17 December 2005, Pages:1304-1308

[8] LOUNIS Zohra. APPOTS DES TECHNIQUES DE CABLAGES LAMINAIRES DANS UN

ONDULEUR A IGBT DE MOYENNE PUISSANCE. PhD thesis, Institut National

Polytechnique de Lorraine, 2000.

[9] Seong-Jeub Jeon, Gyu-Hyeong Cho. A Zero-Voltage and Zero-Current Switching Full

Bridge DC-DC Converter With Transformer Isolation, IEEE Transactions on power Electronics,

Vol.16, No.5, September 2001, Pages:573-580

[10] Yungtaek Jabg, Milan M.Jovanovic, Yu-Ming Chang. A New ZVS-PWM Full-Bridge

Converter, IEEE Transactions on power Electronics, Vol.18, No.5, September 2003, Pages:1122-

1129 Authorized

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