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I. INTRODUCTION

Fig.1 Solar panels board Fig.2 Grid supply to Energy meter

As the price of oil continues to be unpredictable, and as the cost of energy

continues to increase, people around the world are looking for efficiency, and an

alternative means to reduce their cost of living. Renewable energy is the answer for

which everyone is searching [1]. Solar energy is a safe alternative to fossil fuels, and

provides electrical power free of cost, aside from maintenance, and the initial capital

costs. However, this initial capital investment is a major disadvantage to the

utilization of solar energy and although new technologies are beginning to make

Photovoltaic (PV) arrays competitive, there is still a strong need to optimize the size

of PV arrays according to their intended usage [2].

The i-v characteristic of solar modules makes them suitable voltage sources.

However, a major technical challenge of PV modules comes when the current

supplied by the PV module passes the knee point of the i-v curve. This issue has been

addressed in a number of investigations for Maximum Power Point Tracking (MPPT)

such as in [3]-[4].

The principles that define the need for MPPT are the same reasons that the

PV arrays are typically oversized to supply stand-alone motor-drives. This is due to

several factors. One of the primary reasons is that if there is a rapid power reduction

due to a change in isolation, then there is a possibility for voltage collapse at the input

terminals.


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On Power-Sharing of Solar-Based Hybrid Motor-Dri e Systems

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Once the voltage collapses, the DC-bus voltage of the drive will collapse

resulting in motor shutdown. This lack of reliability can be overcome by using either

an energy storage device or Ac Grid as a supplementary source.

(A) MAXIMUM POWE POINTT ACKING (MPPT)

Fi .3 Sol panel Fi .4 MMPT Module

Maximum Power Point Tracking, frequently referred to as MPPT, is an electronic

system that operates the Photovoltaic (PV) modules in a manner that allows the

modules to produce all the power they are capable of. MPPT is not a mechanical

tracking system that physically moves the modules to make them point more

directly atthe sun.

MPPT is a fully electronic system that varies the electrical operating point ofthe

modules so thatthe modules are able to deliver maximum available power. Additional

power harvested from the modules is then made available as increased battery charge

current. MPPT can be used in conjunction with a mechanicaltracking system, butthe

two systems are completely different.

To understand how MPPT works, lets first consider the operation of a

conventional (non-MPPT) charge controller. When a conventional controller is

charging a discharged battery, it simply connects the modules directly to the

battery.


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On Power-Sharing of Solar-Based Hybrid Motor-Drive Systems

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This forces the modules to operate at battery voltage, typically not the ideal

operating voltage at which the modules are able to produce their maximum available

power.

The PV Module Power/Voltage/Current graph shows the traditional

Current/Voltage curve for a typical 75W module at standard test conditions of 25 C

celltemperatures and 1000W/m2 ofisolation.

This graph also shows PV module power delivered vs. module voltage. Forthe

example shown, the conventional controller simply connects the module to the battery

and therefore forces the module to operate at 12V. By forcing the 75W module to

operate at 12V the conventional controller artificially limits power production to

53W.Rather than simply connecting the module to the battery; the patented MPPT

system in a Solar Boost charge controller calculates the voltage at which the

module is able to produce maximum power. In this example the maximum power

voltage ofthe module (VMP) is 17V.

The MPPT system then operates the modules at 17V to extract the full 75W,

regardless of present battery voltage. A high efficiency DC-to-DC power converter

converts the 17V module voltage at the controller input to battery voltage at the

output. If the whole system wiring and all was 100% efficient, battery charge current

in this example would be VMODULE VBATTERY x IMODULE, or 17V 12V x

4.45A = 6.30A. A charge current increase of 1.85A or 42% would be achieved by

harvesting module power that would have been left behind by a conventional

controller and turning it into useable charge current. But, nothing is 100% efficient

and actual charge current increase will be Typical 75W PV Module

Power/Voltage/Current At Standard Test Conditions somewhat lower as some power

is lost in wiring, fuses, circuit breakers, and in the Solar Boost charge controller.

Actual charge currentincrease varies with operating conditions. As shown above, the

greaterthe difference between PV module maximum power voltage VMP and battery

voltage, the greater the charge current increase will be. Cooler PV module cell

temperatures tend to produce higher VMP and therefore greater charge current

increase.


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This is because VMP and available power increase as module cell temperature

Decreases as shown in the PV Module Temperature Performance graph. Modules

with a 25 C VMP rating higher than 17V will also tend to produce more charge

currentincrease because the difference between actual VMP and battery voltage will

be greater.

A highly discharged battery will also increase charge current since battery voltage

is lower, and output to the battery during MPPT could be thought of as being

constant power.

What most people see in cool comfortable temperatures with typical battery

conditions is a charge currentincrease of between 10 25%. Coolertemperatures and

highly discharged batteries can produce increases in excess of 30%. Customers in

cold climates have reported charge current increases in excess of 40%. What this

means is that current increase tends to be greatest when it is needed most; in cooler

conditions when days are short, sun is low on the hori on, and batteries may be more

highly discharged. In conditions where extra power is not available (highly charged

battery and hot PV modules) a Solar Boost charge controller will perform as a

conventional PWM

Fi .5 PV characteristic and Eq. (d) intersection indicates the operating point

of the hybrid motor-drive system.


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II. LITE ATURE SURVEYThe National Resources Defense Council (NRDC) estimates that there are as

many as 4.5 million residential swimming pools nationally, which roughly spend

between $1.1 and $1.6 billion dollars yearly which is a cost of between $250 and

$360 dollars per household yearly. The NRDC, and the Department of Energy have

released recommendations regarding common practices involving pool pump energy

consumption, and ways to increase the efficiency of energy usage when one owns a

pool.

Among the recommendations delineated by the NRDC is to replace existing singlespeed pool pumps with higher efficiency two speed pumps, or variable speed pumps.

Since variable speed pumps utili e inverters to drive their motors, they present the

opportunity to power the AC motor-pumps from renewable energies. In this paper,

some technical concerns of PV-based hybrid motor-drive systems are elaborated on

through a developed hybrid adjustable-speed water pump.

The remainder ofthis paper is organi ed into seven sections. In Section II, the case

study hybrid motor drive system is briefly described. In Section III, the output power

ofthe PV-DC-DC module is formulated based on the DCDC module input/output and

switching parameters. In Section IV, the DC-bus overvoltage due to the motor

deceleration is briefly discussed. In Section V, a reliability issue with respectto high-

frequency voltage spikes due to the resonance between stray inductance and the DC-

bus capacitors is described. In Section VI, the power sharing between the grid and PV

is illustrated via experimentally obtained data. Discussions ofthe results are given in

Section VII, and Section VIII concludes the paper.


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(A) H BRID MOTOR DRIVE S STEMS

Fig.6 Hybrid model ofinputs

In hybrid motor-drive systems, the contribution made by the AC-grid serves to

stabilize the DC-bus voltage of the variable speed drive. Fluctuations in incident solar

radiation make solar power unpredictable, so by utilizing power grid to stabilize the

C-bus voltage, solar-based hybrid systems can use solar energy as it becomesavailable.

By using solar energy in a supplementary configuration, the benefits of

renewable energy are combined with the reliability and stability of the power grid and

thereby increase the reliability of the system while using solar power as it becomes

available. Through proper switching of the DC-DC module, power can be injected

into the pump from the solar array instead of the grid. This allows the AC power to

operate as a supplementary source. The pump can run solely on the available solar

power unless there are very rapid changes in the load (i.e. stating transient), or in theincident solar radiation when the pump will draw power from the grid to compensate.

Pump

motor


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III. SYSTEM DESCRIPTIONThe functional block diagram ofthe case study hybrid solar-based adjustable-

speed pump is depicted in Fig.6. The system consists of a 4kW DC power supply, a

DC-DC module, a 2.5 hp 3150 rpm brushless permanent magnet motor, an adjustable

speed drive and a water pump, see Fig. 7 and Fig. 8. Moreover, a dSPACE CLP 1104

controller board and Simulinkis used to controlthe DC-DC module duty cycle ratio.

The DC power supply is a high-power switching power supply rated for

125Vdc and 32A. For this particular application, the supply is programmed to be

between 0 and 100Vdc with a maximum of 21A, and it is also programmed to

behave like a solar array by adjusting the outputto match an i

curve thatis typical

to solar modules.

The relationship between motor output and motor speed is given by pump

motorlosses, i.e. the motor draws between 200W and 250W at 1500 rpm. The drive

inputterminals are rated for a single phase 230Vac and the DC-bus typically operates

in the range of 290-340V, which also varies with motor speed (load). However, the

DC-bus voltage can be stabili ed using the DC-DC module where it becomes

independent ofthe motor speed.


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BLOCK DIAGRAM

Fig.7.Block diagram of the laboratory test setup.

Fig.8.the solar-based hybrid variable speed pump test setup lab


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The PV array emulator is connected to the input terminals of the DC-DC

module, and the outputterminals of the module are connected directly to the DC-bus

ofthe variable Frequency drive, see Fig.7 and Fig.8. Notice that the combination ofthe module and DC-bus capacitors constitutes a DC-DC boost converter. The

converter utili es the voltage sensor that is present at the output of the module as a

feedback reference to regulate the duty cycle ratio of the boost converter. Accurate

control of IGBTs duty cycle ratio becomes an importantissue in this system, because

there can be a tendency forthe DC-bus voltage of the drive to increase to destructive

levels if the duty cycle ratio exceeds the level that is necessary for the proper

operation ofthe pump. This is most obvious during deceleration ofthe pump motor.

The DC-DC module topology is not a specific subject of investigation in this

paper, and design and construction considerations were consistent with those

described in many Power electronics books, such as in [5]. However, one difference is

that the DC-DC module, shown in Fig.8 and Fig.9, does not contain any capacitor,

instead the DC-bus capacitors of the adjustable-speed motor drive is shared by the

DC-DC module to form a boost DC-DC converter.

IV. PV-DC-DC MODULE DEVELOPED POWER

Fig.9. Prototype of the DC-DC module (the physicalsize of the module; 8L-6W-

2.1Hinches).


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In hybrid motor-drives, the main objective is to minimize the number of PV

panels in order to maintain the capital cost of installations as low as possible. Thus,

the DC-DC boost converter is required to operate in discontinuous conduction mode.

This is due to the fact that a higher output-input voltage ratio can be achieved at lower

duty cycle ratios in discontinuous conduction mode than in continuous mode.Meanwhile, this discontinuous conduction mode of operation has a better stability

feature than the continuous conduction mode of operation [5]. The current and voltage

waveforms of the DC-DC module inductor are the fact that for an

inductor, the following equations can be written:

Where, inductor current mean and inductor current peak and are respectively the

average and the peak current of the DC-DC module inductor. Using (1) through (3)

and neglecting the system losses, the average output power of the PV-DC-DC module

can be obtained as follows:

Where, DC-DC module switching period, is the switching duty cycle ratio, is

the PV Array voltage, and is the DC-bus voltage. Notice that capacitance is not a

factor in this equation. In this hybrid system, the grid voltage inherently regulates the

minimum level of output voltage, given that the grid contributes to the potential

energy at the DC-bus. Thus, is obtained from in which is the grid rms line to-line

voltage, and is equal to 32 for a three-phase Bridge- rectifier operating under

steady-state conditions. The capability of PV array and the peak current of the DCDC

module inductor are the major restriction factors of the Output power, which is

illustrated in (4). Furthermore, the intersection point of the PV characteristic and the

PV-DCDC module output power, see (4), indicates the hybrid system Operating point.


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In other words, the initial value ofthe switching duty cycle, for any maximum

power point tracking (MPPT) algorithm can be obtained from (4), for solar-based

hybrid motor-drives, see Fig. 5.

V. HYBRID-DRIVE STEADY-STATE CONDITIONSIn this section, the steady-state behaviors ofthe hybrid motor-drive system are

studied through experimentally obtained data. The measurements in this experiment

were performed using a LeCroy Wave runner 64XI oscilloscope with one CP031

current probe, one CP030 current probe, and one ADP305 differential voltage probe.

The bandwidth ofthe oscilloscope is 600MHz, while the bandwidths of the CP031,

CP030, and the ADP305 are 100MHz, 50MHz, and 100MHz, respectively. In Fig 11,

the input current ofthe DCDC module is displayed in contrastto the modules outputcurrent. As can be seen from the figure, the input current ofthe module conforms to

the expected current waveform in Fig.10. Current and voltage waveforms of the DC

inductor in the DC-DC module. Fig.11. PV characteristic and Eq. (4) intersection

indicates the operating point ofthe hybrid motor-drive system. Fig. 4 and the output

current decreases from the peak input current over the time period. The motor was

running at 1500rpm, and the input voltage to the DC-DC module was 33.5V, while it

was operating at 5 kHz, with a constant 30% duty cycle ratio. The motor and DC-DC

module were operating under these same characteristics in Fig. 13, where the AC

input currentto the drive is shown overthe motor current out ofthe drive. In this case,

motor was operating at 230W. The power injected to the DC bus from the DC-DC

module was approximately 45W, and the power from the grid was around 195W. As

can be seen from the figures, the Injected power from the DC-DC module does not

cause any disruptions in the motor current waveform, while relieving some of the

demand on the grid.


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Fig.10. Current and voltage waveforms of the DC inductor in the DC-DC

Fig.11. PV characteristic and Eq. (4) intersection indicates the operating point of

the hybrid motor-drive system.

Fig.12. DC-DC input and output current while the motor was at 1500rpm, the

module at 33.5V PV input voltage, 30% duty cycle, and fs = 5 kHz.


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Fig.13. Motor current and AC input current while the motor was at 1500rpm,

with the module at 33.5V PV input voltage, 30% duty cycle, and fs = 5 kHz.

Fig.14. Line loss (AC-grid voltage loss) test, while motor was running at 1500

rpm.

The first step is to demonstrate the degree of system robustness in the presence

of line-loss, which can also give us an idea about the capability of the system

islanding phenomenon. In Fig. 14, the DC-bus and the AC-grid voltage waveforms

are shown while the AC-grid was disconnected for about 200 msec. As can be seen,

the DC bus voltage maintains its steady-state value during the line-loss test. This Test

was performed while the motor was running at 1500 rpm and the DC-DC module duty

cycle ratio was 30% at 5 kHz switching frequency. Of course, at a higher motor speed

the Duty cycle ratio should be automatically tuned into an appropriate value in order

to keep the DC-bus voltage stable. In the case ofthis test, the input voltage to the DC-

DC module was a= 66.5V, and the output power was about 300W.


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VI. DC-BUS OVERVOLTAGE DUE MOTORDECELERATION

Regardless of the type of AC motors, the regenerative energy during the

deceleration time interval will be a common concern in hybrid motor-drives. When

the motor speed increases during the acceleration period, it draws a pulsed power

from the drive, which results in voltage drop at the DC-bus. When motor speed

reduces during the deceleration period, the kinetic energy of the mechanical system,

which contains load and rotor inertia, converts back to electrical power. This

regenerative power will cause a voltage swell at the DC-bus. This overvoltage can

cause the drives DC-bus capacitors and/or IGBT modules to fail.

In Order to prevent the occurrence of this type of failure, a resistor cascaded

with an IGBT chopper, so-called dynamic (resistive) brake, is connected in parallel

with the DC-bus Capacitor bank. While a fraction of the regenerative energy is

dissipated in the motor and its feeder cable, most ofit transfers back to the DC-bus

through the anti-parallel diodes of IGBT modules.

Another technique is to regulate the DC bus voltage by increasing the drive

output frequency. However, the overvoltage can be managed in hybrid motor drives

by increasing the speed reduction time. Let us investigate it through mathematical

formulations.

For an Incremental change in the motor speed, one can write the following

equation forthe motor kinetic energy.

Where,J

is the motor-load moment of inertia, and Wm

is the speed of motor.Similarly, the energy change in the DC-bus capacitor bank due to the motor speed

change is given by:


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Where the total capacitance is value atthe DC-bus, and is the average DC-bus

voltage. In this system, as can be seen in Fig. 7, both energy sources, i.e. grid and PV

array, can merely transfer energy in one direction into the DC-bus. However, their

behaviors are different. The PV-DC-DC module behaves like a current source, while

the Grid- Rectifier behaves like a voltage source as long as the average DC-busvoltage stays below the peaks ofthe grid voltage absolute value.

Assuming thatthe DC-bus voltage exceeds the grid peak voltage and consequently the

rectifier diodes become reverse biased and the DC-DC module controller turns the

module off during the motor deceleration period, one can write It should be noted,

thatifthe rate of acceleration, or deceleration is not of criticalimportance, such as in

this case, that of a water pump, the rate of change in the pump speed can be adjusted

so as to minimize the increase in bus voltage by adjusting the speed ofthe motor over

a longer period of time. In the case of servo drives, this is not an option due to the

criticaltiming Restrictions

VII. DC-BUS HIGH-FREQUENCY VOLTAGE SPIKESIn some hybrid energy conversion systems, which consist of one or several

sustainable (renewable) energy sources, such as PV arrays and fuel cells, PWM DC-

to-DC converters, are required to boost the DC voltage to an acceptable level which

can then be converted to an AC voltage with a fixed frequency and a fixed voltagemagnitude.

The DC-DC converter typically contains high-speed power electronic switching

devices, which provide higher efficiency as well as higher controllability (higher

bandwidth) of integrated power systems. However, these may have drawbacks, such

as transient over-voltage oscillations due to reflected-wave phenomenon, common-

mode/differential-mode resonance phenomena, and electromagnetic interference

(EMI). In Fig.15, it is shown that the PV-DC-DC module is connected throughparasitic (stray) inductances to the DC bus capacitors of the adjustable speed drive.

This L-C combination can resonate due the steep rise-time and falltime ofthe IGBT

(e.g. 50-100 nsec) in the DC-DC module.


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Fig.15 Stray (parasitic) inductances can cause voltage spikes at the DC-busCapacitors of hybrid motor drives.

Fig.16. Voltage spikes due to a resonance phenomena between DC-buscapacitors and the stray inductorsin Fig.7.

This creates voltage spikes at the DC-bus as demonstrated in Fig. 16. These

voltage spikes can reduce the capacitors lifetime and they will generate

electromagnetic interference.


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In orderto avoid these spikes, the lead wires, and/ortrace lengths between the

external DC-DC-module and the DC-bus should be as short as possible. The result of

reducing these lengths will serve to minimize the required high- frequency filter in

this system.

VIII. POWER SHARINGThe instantaneous powers of the AC-grid and PV (DC-DC input) are shown in

Fig. 17. As can be seen, the DC-DC module is designed to operate in discontinuous

conduction mode. The experimental results illustrate that PV power sharing is not a

function of motor speed in hybrid solar-based motor-drives, as long as the average

power contribution ofthe AC-grid stays above zero, see Figs. 17 and 18.

In these figures, the average output power of the DC-DC module, and the

average input power to the motor drive is plotted versus the motor speed under

various duty cycles. In Fig. 17,the input voltage to the DC-DC module is maintained

at 52.4V, the switching frequency fs is maintained at 5 kHz, and the experiment is

performed forthree duty cycles. The same testis performed in Fig 18, butthe

Switching frequency has been changed to 5 kHz, and the input voltage hasbeen increased to 75V. In both figures, the dotted blackline displays the power drawn

by the motor drive when there is zero contribution to the DC bus other than that

provided from the AC-DC rectifier. Itis importantto take notice ofthe differences not

of just the duty cycles in each individual experiment, but also of the differences

between the two experiments in their entirety. For example, itis easily noticed thatthe

power supplied to the drive from the DC-DC module is significantly higher at 10 kHz

if the duty cycle ratio is 40% instead of 20%, but there is also a distinguishable

difference between the magnitudes of the power contributed at the 40% duty cyclefrom 10 kHz to 5 kHz. The power injected into the DC bus at 10 kHz is on average

280W, while the power injected into the DC bus at 5 kHz averages 300W. This is

consistent with Eq. (4) in


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Fig.17.Experimentally obtained instantaneous powers of PV (top) and

Single-phase 230V AC-grid (bottom) vs. time over 5 msec, for 10 kHz.

Moreover, itis importantto mention again the factthatthe input voltage to the

DC-DC module is significantly lower at 5 kHz, where instead of an input voltage of

75V, the module was able to operate at 52.4V. The efficiency ofthe module averaged

83.8% at 5 kHz, and 73.6% at 10 kHz. These figures also show that the power

injected by the DC-DC module is nearly constant, regardless ofthe changes in motor

Speed, and that depending on the speed ofthe motor, the DCDC module and the AC-

grid can either contribute equally to the motorinput power, orthe DC-DC module can

act as the sole power source.

Reductions in solar insolation due to inclement weather, orthe collection of

debris on solar module surfaces resultin reductions in voltage at solar module output

terminals [6]-[7]. To account for these variations, a demonstration of power sharing

during variations in the inputterminal voltage ofthe DC-DC module is visible in Fig.

19. In this figure, the average input powerto the motor drive, and the power injected

by the DC-DC module is plotted versus the input voltage at two different switching

frequencies (fs = 10 kHz, and fs = 5 kHz) when the speed ofthe motoris maintained

at a constant 1500rpm. It can be seen in this figure, thatthe point at which the power

injected to the motor becomes equalto the power drawn from the AC grid is the same

Magnitude for both switching frequencies, but is reached at a lower input voltage

when the frequency is 5 kHz.


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This demonstrates the relationship between output power and input voltage to

the DC-DC module shown in Eq. (4), in Section III. It can be seen thatthere exists a

non-linear relationship between the output power of the module and the supply

voltage when the load and duty cycle are constant, and that as the output power ofthe

DC-DC module declines, the average AC-grid power increases to compensate, andthe operation of the motor is unaffected. This change in source without interruption

makes the pump more robust, as was shown in Fig. 8, in Section IV with the AC line

loss test. In Fig. 15, the average AC input power to the motor drive and the DC-DC

injected poweris plotted versus the input voltage at various duty cycles. In this case,

the switching frequency was maintained at fs = 5 kHz.

Fig.17.Experimentally obtained average power of the grid, PV (horizontal

Lines), and motor in wattsvs. motor speed in rpm for the duty cycles of D =

20%, D = 30%, and D = 40% at the switching frequency of5 kHz for the


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IX. DC-DC MODULE

Fig.19.Experimentally obtained average power of the grid, PV (horizontal

lines), and motor in wattsvs. motor speed in rpm for the duty cycles of D =

20%, D = 30%, and D = 40% at the switching frequency of10 kHz for the

DC-DC module.

Fig. 20Experimentally obtained average power-sharing in wattsvs. PV(DC power supply) voltage in volts, while the pump is running at a constant

speed (1500 rpm), the duty cycle of D = 30% with the switching frequencies 10 kHz (gray) and 5 kHz (black).


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Fig. 21.Experimentally obtained average power-sharing in wattsvs. PV

(DC power supply) voltage in volts, while the pump is running at a constant

speed (1500 rpm), the switching frequency of5kHz and the duty cycle of D

= 20% (black), D = 30% (dark-gray), and D = 40% (light-gray).

Notice the way thatthe point at which the AC and DC average power intersect

decreases as the duty cycle ratio increases. This is due the non-linear relationship that

exists between the DC-DC output power and the DC-DC duty cycle ratio, in additionto the impact ofthe input voltage. Therefore, this point of intersection will decrease

nonlinearly as the duty cycle ratio increases.


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X. DISCUSSIONThe topics presented is this discussion are in regard to several phenomena

observed during the testing process ofthe solar-based hybrid motor drive, as well as a

brief consideration ofthe power sharing equation described in this work. Specifically,

this discussion will conclude with the implications of this power sharing technique,

but will begin with some reflection into the lifetime reducing phenomena which could

create problems in similar applications, namely rapid increases in DC bus voltage, and

high frequency voltages spikes.

Although this paperis focused on power sharing, two Interesting phenomena were

encountered during testing which warrant further review. The first of these is thetendency ofthe DC bus voltage to rise to damaging levels during deceleration when

the injected power exceeds the power required by the motor.

During the deceleration process, the motor converts mechanical powerinto

electrical power, and thereby becomes regenerative. The regenerative energy supplied

by motor, in conjunction with the electrical energy supplied by the DC-DC module,

results in a rapid increase in DC bus voltage.

This overvoltage can lead to the destruction of the drive, and requires a fast

response from the duty cycle ratio in systems that have high acceleration or

deceleration rates, such as in servo drive systems. However, these systems typically

utilize a dynamic brake to compensate for DC bus overvoltage conditions. The second

phenomenon which is ofinterest is the high frequency voltage spikes on the DC bus

which were caused by parasitic inductances.

As can be seen from Fig. 16, 0.073sec is equivalent to approximately 13 MHzThe electromagnetic interference (EMI) generated by these voltages spikes from the

DC-DC module can be considered to be high frequency, and are close to being

radiated. With the movement toward micro-inverters, micro-DC-DC converters, and

integrated PV panel/DC-DC converters, voltage spikes, and EMI may be a major

technical problem.


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When one considers the lengths of the connections in these systems, they are

likely to have connection lengths that far exceed the lengths that were used in this

investigation. In these cases, the lengths may cause the reflected wave phenomena,

which can theoretically raise the voltage atthe terminals to twice the bus voltage.

Additionally, in integrated PV/DC-DC converters, the devices may each prove to

each be an individual source of EMI, and although there were not any issues with

serious interference during the experiments, the proximity to homes and personal

electronic equipment is likely to cause equipment malfunctions, and possibly some

equipment failures. Utilization of micro inverters in these cases may be more ideal,

Instead of micro-DC-DC converters, especially when the connections lengths are

significantly long. In conclusion, the power sharing principles explained in this

investigation pose some interesting possibilities.

For instance, if one considers the power sharing equation and takes note of the

factthatthe capacitance ofthe bus is not a factorin the equation, then presumably the

same converter can be used for multiple drives without any changes as long as there is

atleast a minimum contribution from the grid.

Although there is a minimum capacitance that must be met forthe DC module to

work properly, a motor drive always contains DC link capacitors that readily provide

forthis prerequisite.


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XI. CONCLUSIONIn this paper, an application for power-sharing between a solar array, and the

AC-grid has been demonstrated through the construction of a hybrid solar-based

adjustable-speed pump where a DC-DC module was designed, constructed, and

connected to the DC link capacitors of a 2.5 HP variable speed motor-drive.

From the figures, it can be seen that the concept of power-sharing between a

PV source, and a variable speed motor drive is not a function of motor speed, as long

as there is a minimum contribution from the grid.

Additionally, it can be seen that the dynamic behavior of the motor is

decoupled from the grid as long as there is as the PV-DC-DC module can sufficiently

cover the load. This is a simple, but effective method of reducing the amount ofenergy used from the AC grid.


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