Analysis and Implementation of Single Stage Bridgeless Boost Rectifier for Piezo Electric

Energy Harvesting Applications

1P.Muthu thiru vengadam,

2A.Allwyn Clarance Asis,

3S.Edward Rajan

1PG Scholar, 2Assistant Professor,3Professor, Department of Electrical and Electronics Engineering

MepcoSchlenk Engineering College, Sivakasi, India 1muthuthiruvengadam.10@gmail.com, 2iamallwyn@rediffmail.com,3sedward@mepcoeng.ac.in

Abstract-This paper projects a proficient single stage AC-

DC boost power electronic converter to efficaciously

scavenge the energy from low voltage piezoelectric source.

Normally the traditional ac-dc converter for energy

scavenging system with diode bridge rectifier incurs a

considerable drop across the diodes results in an increase

in losses and also in the complexity of the circuit. In order

to overcome the issues of the diode rectifiers a bridgeless

converter topology was developed which has an exclusive

combination of both boost and buck – boost operation

with a single inductor to control the positive and negative

half cycle of the ac voltage as a input from piezo source.

The rectifier also engaged with finely controlled soft

switching (ZCS) scheme and minimum number of passive

energy storage components to achieve the efficacy as much

as possible. The preferred converter avoids the use of

bridge rectifiers, and the ac input is rectified and boosted

which could be used to power wireless sensors, electronic

devices, and biomedical implants (or) to store the energy

in battery with control mechanism for future use to attain

high reliability in the system. In order to validate the

design of the preferred converter and comparative studies

on conventional two stage converter, a software simulation

was carried out with a help of MATLAB/SIMULINK.

Keywords-AC/DC boost converter,bridgeless, boost,buck-boost, ZCS, energyharvesting,low-voltagepiezo source.

I INTRODUCTION

Scavenging energy from ambient source plays

a crucial role in recent years.Energy capturing, (or) energy collecting is a task by which energy is obtained

from unconsumed energy as a by-product of some

innate process or industrial process and it is regarded as

free-energy.The unused energies were liberated to the

surroundings as wasted potential energy and that can be

effectively exploited to meet the enormous

applications.Now the researchers turn towards micro

energy harvesting that can scavenge milliwatts from

thermal, biological and vibrational sourcesetc.This

micro energy harvesting technologies offers some

advantages like providing inexhaustible source,no

adverse environmental impact, and also renders a clean source of energy.There are numerousmethods are

available to acquire the energy from the above sources.

One of the eminent ways to harvest energy from

vibrations is by using piezo electric materials. Piezo

electric energy scavenging is wise because of its simple

mechanism and can be implemented in ample varieties

of applications.

With an ever increasing in the demand for

electrical energy tempted the researchers to mainly

focus on harvesting the low voltage energy since three

decades. Traditionally the researchers concentrated on

kinetic energy harvesters that convert mechanical

energy into electrical energy [1] this conversion is

accomplished with a help of piezo electric,

electromagnetic (or) electro static mechanism. The energy consumed by the compact electronic devices and

other low voltage applications shows greater renewed

interests to scavenging energy from immediate

surroundings, which is considered to be the best

alternative sources of energies. Energy harvesting using

piezo electric material is an innovative approach used

chiefly to power the wireless sensor network [2].

There are several inexpensive (or) renewable

(or) clean energy sources are available in order to meet

the power demand [3].In present scenario, in order to

supply the clean and sustainable energy to meet the

demand is fulfilled by capturing the low voltage from the surroundings [4].Due to the emergence of VLSI

design and embedded technologies open up the gate for

powering the wireless sensor nodes from the low

voltage vibrational energy harvested from the

immediate surroundings[5].Energy scavenging process

became easier due to the advent of power electronic

interfaces. Power electronic interface (PEI) plays a

crucial role in both energy harvesting and utilization

phase. This PEI encompasses with input/output static

power electronic converter, which is able to interface

sources, storage and loads. The efficiency, functionality and the size of the integrated system is assured by the

both electrical and physical characteristics of the power

conditioning circuit[6].

II ENERGY HARVESTING SYSTEM

The most promising approach to supply the

sustainable energy for the wireless sensor nodes is to

harnessing the energy from ambient sources. There are

abundant ambient sources are available like light,

thermal, vibrations, radio frequency waves [7].Among

them, vibrations are frequently occurring in household

and industrial places near the machinery. The vibrations from these sources are generally produce power density

in the ranges of micro or few hundreds of milliwatts.

Piezo electric materials are used to harness the energy

effectively from these vibrational sources. The generic

low voltage energy scavenging system is shown Fig.1.

Fig.1. Energy harvesting system

Piezo electric materials play a crucial role in energy

capturing process because of its simple operating

principle and the power requirement for harvesting is

also low. Piezo crystals are ideal for energy scavenging

process and these materials have a unique property of

piezo electric effect. They generate electric potential

whenever it is subjected to any pressure or vibration, i.e

it uses kinetic energy from the environment into electrical energy for future use. Future applications of

such system include charging of mobile phones, radio

communication equipment, remote area data

transmission etc [8].After that energy harvesters

involves various types of converter depends on

feasibilities and then stored energy is utilized for

applications such as mentioned above (or) stored in

battery for future use.

A.Piezo electric source

Piezo electric materials have an exclusive

attributes to create electric potential proportional to the applied stress and also this power development is

mainly relies on the deformation in the piezo materials.

There are copious natural piezo crystals are viable like

quartz, sugar etc.. In recent years plentiful piezo crystals

are manufactured and they are recognized as the

synthetic group of materials. Among those

materialsPZT (Lead Zirconate Titanate) materials are

resilient, chemically inert and highly resistant to

temperature and pressure [9]. All these aspects offer

more advantages over other piezo electric materials and

also attract the researchers to focus on these PZT materials. Even the miniaturized deformations on such

ceramic crystals are responsible for charge

accumulation. Thus, the power generated from these

materials is large enough to power the Wireless Sensor

Network (WSN).The energy obtained can also be stored

in battery.

B.Piezo electric device modeling

There are distinct methods feasible for

modeling piezo source like FEM (Finite Element

Method), Spring model, Thermal analogy and passive

equivalent circuit method [10]. Of which equivalent circuit method is recognized as uncomplicated when

compared to other methods and also renders less

complexities. The frequent method of electrical

modeling of piezo electric devices is regarded as a

passive method comprises of constant current source

(or) charge source in shunt with capacitance Cs and

internal resistance Rs [11]-[13](or) voltage source in

Series with capacitance and resistance. This modeling is

shown in Fig.2.

Fig.2. (a) Charge model (b) Voltage model (c)Schematic symbol

The generated charge in the device is mainly relies on

piezo electric constant and area, width and dielectric

constant of the materialrequired to derive the capacitance of the crystal.Rprepresents leakage

resistance of the crystal,Cp denotes capacitance of the

crystal.and qp stands for charge created.Rp betoken as

static charge dissipation. The output voltage created

from piezo materials is normally in the ranges of

millivolts to few volts that depend on applied stress (or)

pressure. In order to obtain the reliable output to meet

the demand the piezo electric device is modeled using

some data reference, parameters and equations

[14],[15].

III PREFERRED CONVERTER FOR PIEZO ANALYSIS

Customarily, the two stage energy conversion

technique incurs excessive power loss and it is not

suitable for low voltage energy scavenging

system[16].In this method of conversion the diode

bridge acts as first stage and dc-dc boost converter as

second stage, to regulate and boosted the rectified

voltage from the first stage. The bridge rectifier

converts low voltage ac into pulsating dc and this

pulsating dc voltage is again boosted to a certain level

in order to meet the requirement of the load. This traditional method holds good for some high voltage

applications however it is not applicable for low voltage

applications because the energy captured from low

vibrational source using piezo electric materials is in the

order of some millivolts or few hundred micro volts. To

overcome these drawbacks, the conventional p-n

junction diodes were replaced with low voltage drop

CMOS diodes and that possess some threshold

cancellation techniqueand these methods were

considered to be the obsoletefor low voltage energy

conversion[17].By the use of MOSFET controlled by

extrinsic comparators make the design more complex and renders more losses in the circuit [18].The

alternative approach is to design the converter to

enhance the conversion proficiency, the bidirectional

switches with different split capacitor topologies were

also investigated[19].In these configurations, usage of

more energy storage components provokes much

energy losses and also increases the design

complexities.Boost converters are predominantly used

as a power conditioning interface due to

itsuncomplicated structure. Moreover it renders voltage

step up capabilities and greater efficiency. Buck-boost

converter hasa potential to step up the voltage in reverse

polarity. Consequently it is auspicious to condition the

negative half cycle of the AC input voltage. In addition

to this, these topologies share minimum passive storage components to attain the small size and other design

requirements.To make the design attractive, a novel

single stage bridgeless topology to harvest piezo source

is preferred which is shown in Fig.3.

Fig.3.Circuit of bridgeless boost converter

This preferred converterhas an exclusive attributes like

the integration of both boost and buck boost operation

using single inductor and capacitor to condition the

positive and negative half cycle of the input voltage

obtained from the piezo electric source. When the input

voltage is positive the switch S1 turned on and diode D1 is in the reverse bias condition and circuit operated in

boost mode. Once the input becomes negative the

switch S2 turned on and D2 is in reverse bias and circuit

operated as buck boost mode. The switches with

bidirectional conduction capability to condition the both

positive and negative half cycle of the AC input

voltage. This topology is widely used for piezo electric

energy scavenging applications because of its circuit

functionality. The modes of operation of the proposed

converter are understood undoubtedly with a help of the

diagram sown in Fig.4.

Fig.4. Modes of operation of the preferred converter

A. Modes of operation:

There are six modes of operations are feasible

for the preferred converter.

Mode 1

During positive half cycle, at time t=t0 the

switch S2 gets turned ON and the current in the inductor

is zero at that time so the switch is turned on at zero

current which reduces stresses over the switches. The

inductor L is energized by the input from the piezo

source and both switches S1 and S2 is conducting. Both

diodes are in reverse bias condition. The load is

powered by the output capacitor.

Mode 2

Switch is turned OFF at time t=t1, the energy stored during mode 1 is delivered to the load via the

diode D2, hence the inductor current decreases linearly,

and some losses occurs due to turn on of the diode

D2.The converter behaves like boost mode.

Mode 3

Diode D2 is turned OFF as soon as the inductor

current became zero at t2.This avoids the reverse

recovery losses of the diode. At that time the load is

powered by the energy stored in the output capacitor.

The converter returned to mode 1 and S2 is still ON

until the input voltage becomes negative.

Mode 4 During the negative half cycle, the mode 4

starts and switch S1 is turned ON at t =t0. Zero current

switching (ZCS) condition is attained and the energy is

transferred to the inductor again, while the output filter

capacitor C feeds the load.

Mode 5

At time t=t1, switch S1 turned OFF and the

energy stored in the inductor is delivered to the load via

diode D1and it follows buck boost operation. The

inductor current decreases gradually. During this mode

the losses incurs due to the turn ON of diode D1. Mode 6

When the inductor current became zero the

diode D1 gets turned OFF and the load is continuously

powered by the stored energy in the capacitor. Now the

converter returned to mode 4 and the switch S1 is still

on until the next cycle commences.

B. Analysis of the converter

The preferred converter is analyzed in dis

continuous mode and two switches in the converter

share the same duty cycle and for this analysis so many

factors are taken into an account like 1. The output side capacitor must be sufficient to fed the

load during the turn on condition of the switch

2. The switching frequency of the switches must be

higher in order to reduce the size of the inductor during

hardware realization.

The converter is scrutinized with a help of large signal

analysis and also extract the relevant design equations

for the converter to attain the expected results. From

this investigations the optimal duty cycle, value for the

inductor, capacitor and chosen load values are estimated

to get the better results and improved efficacy. The duty cycle equation for the proposed converter for

both boost/buck boost mode

D = d1 = d′ = 2V0

Vm

√Lfs

R

Cout=q*ΔV;

∆iL =Vin t DTs

L

Where,𝑉0

𝑉𝑚-boost ratio, L-inductance in mH, fs-

switching frequency in kHz

Vin-input voltage in mV,R-resistance in Ω,q-charge in

C,Ts-switching time in ms,

ΔiL-ripple current in mA,ΔV -Ripple voltage (0-10% of

output voltage)

C. Variable frequency concept:

All energy capturing process involves various stages and it is obvious to consider the source of energy

and power electronics interfaces as well as power

conditioners to achieve the reliable output to meet the

demand.The piezo electric ceramics are exposed to

ambient vibrations with a precise magnitude and

frequency. These materials convert the vibrating

mechanical movements into the electric potential due to

its internal mechanism called piezo electric effect. In

this passive technique for piezo device modeling the

materials undergoes vibrations of changing frequency

and magnitude that must be damped and controlled in such a way that to maximizes the power distributed to

the load [20]. Performance and the power density rely

on frequency because the piezo electric sourcedevelops

maximum power at its resonant frequency.This

frequency swings must be balanced and controlled in

order to coordinate the impedances of piezo electric

source and the converter stage as well as load to assure

the maximum power transfer to the load .If the

frequency stabilization is not taken into an account

thenit will reflects in the output.The proposed

converter’s control mechanism has an exclusive aspect

that precludes output of the converter while it is subjected to the fluctuating frequency.

IV ENERGY STORAGE

In earlier days many researchers concentrated

on the development of novel approach to provide a

sustainable energy captured from the immediate

surroundings to power the WSN (Wireless Sensor

Networks).Even though they argued that this

sustainable energy supply hinders the complexities with

the battery powered system, but this paper relies on the

reliable power supply to the load even in the absence of the piezo electric source that makes an wise choice for

hardware implementation. The energy is stored in

batteries with control mechanisms. There are numerous

rechargeable batteries feasible for this storage purposes

but in this paper nickel metal hydride battery is used

with its control. Also charging of battery is a

troublesome task because of the low input power and

milli ampere rating of battery needs several hours to

charge a battery. There are countless methods viable for

charging a battery like constant current charging,

constant voltage charging [21] and pulse charging etc

[22].This paper concentrated on pulse charging method. Here the charging current from the piezo source is fed

to the battery in the form of pulses. The pulse width

decides the charging rate of the battery.so it renders

many benefits like useless chemical reactions, prohibits

the formation of gases, growth of crystals and

passivation. The pulse charging method also

incorporates many schemes to charging the battery

efficaciously and improves the performance of charging

methods as well as the battery. In this following

process, the battery is charged using constant current

charging method until the battery reaches its nominal voltage after that once the nominal voltage is attained

then constant voltage charging method is carried out to

maintain the voltage to that required level.

V SIMULATION RESULTS

A. Simulation results of conventional two stage

converter

Simulations of the conventional two stage

converter for low voltage energy harvesting and the

proposed bridgeless converter are validated with a help

of MATLAB Simulink software. Simulation model for two stage converter with piezo model is shown in Fig.5.

Fig.5.Matlab simulation of two stage converter with piezo model

Fig.6.Simulation Response of Input Voltage, Output voltage,

Voltage across Diode Bridge Stage

Fig.7.Simulation output of gate pulse, input current and

Output current

B. Simulation of proposed bridgeless converter

Fig.8.Matlab simulation of proposed bridgeless converter

Fig.9.Gate pulse waveform of the proposed converter

Fig.10. Input voltage and input current waveform

Fig.11.Output voltage and output current waveform

C. Simulation of proposed converter for variable

frequency stabilization

Fig.12.Matlab Simulation of Proposed Converter for Variable

Frequency Stabilization

Fig .13.Gate pulse waveform for varying frequency condition

Fig.14.Input voltage and input current waveform

Fig.15. Output voltage and output current waveform

D. Simulation of battery connected proposed converter

Fig.16 Matlab simulation of battery connected proposed converter

Fig.17 SOC, Nominal Voltage, charging current and current

waveform of battery

V COMPARISON RESULTS

Performance comparison between the

conventional two stage boost rectifier, proposed

bridgeless converter and along with variable frequency

stability testing of proposed converter was compared

effectively. The validations are carried out for the input

voltage for the definite values for all the three cases. The closed-loop voltagecontrolstabilizes at 0.72 duty

cycle in steady sate. The comparison results are shown

in Table 1.

Table.1. comparison results

VI CONCLUSION

This paper work projects the analysis of

piezoelectric material along with a single stage

bridgeless boost rectifier with battery storage. This

work presents a passive technique for a rapid and

reliable identification of model parameters of piezoelectric transducers, with a special focus on energy

harvesting applications. The purpose was to give power

circuit designers a methodology for early, quick and

reliable estimation of the response of transducers to

arbitrary input vibrations and with generic electronic

circuits. Also, a finely controlled zero-current-switching

(ZCS) scheme of the rectifier using only two active

switches is proposed. The converter also has only two

passive energy storage components results in less

complexity and losses in the circuit. The topology of the

converter incorporates itself a soft switching also

reduces the body diode reverse recovery problem; hence converter operates in discontinuous conduction mode.

Standard components are used to justify that the

preferred converter is working with an acceptable

performance compared with conventional converters.

This work also presents that the proposed converter

possess higher stability for varying frequencies

occurring from the input piezo source and the overall

system can be used for low voltage energy harvesting

with higher efficacy than the traditional two stage

harvesting methods along with battery storage and its

control mechanism also presented for high reliability and accuracy.

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