performance analysis of novel dc-dc converter employing ... · observe (p&o) and particle swarm...

International Conference on Computing Technologies (ICONCT’17)

Organized by Department of Computer Science and Engineering & Information Technology 65

Performance Analysis of Novel DC-DC

Converter Employing PSO based MPPT

Technique for Thermoelectric Energy

Harvesting Systems

G. Meribba Jeyaselvi1,T. Rakesh

2 and Dr.S.Edward Rajan

3

1 PG scholar,

2 Assistant Professor (Sr. Grade),

3 Professor,

Department of Electrical and Electronics Engineering,

Mepco Schlenk Engineering College (Autonomous), Sivakasi, TamilNadu, India.

Email: [email protected]; [email protected]; [email protected]

Abstract- This paper presents two input high gain DC-DC

converter with maximum power point tracking (MPPT)

technique for thermoelectric (TE) energy harvesting systems.The

features of two input DC-DC converter are flexibility to connect

independent sources and power sharing. The proposed system

uses numerous diode-capacitor stages in a converter which are

combined together to boost up the voltage. The converter

renders some advantages like large voltage conversion ratio, low

voltage stress in a MOSFET switch and small input current

ripple. In order to harvest the maximum power from

thermoelectric generator (TEG) modules, the perturb and

observe (P&O) and particle swarm optimization (PSO) MPPT

technique have been used independently in each source. Finally,

the simulation results of the proposed system with a conventional

P&O techniqueare compared with PSO technique.

Keywords-Thermoelectric generator (TEG), two input high gain

DC-DC boost converter, diode-capacitor stages, perturb and

observe (P&O), particle swarm optimization (PSO).

I. INTRODUCTION

In recent years, energy harvesting has become

popular in industrial and academic world, so current areas of

research interest mainly focused on waste heat recovery

(WHR) and ambient energy harvesting. Among all research

direction waste heat recovery is most concerned due to

widespread existence and high accessibility of suitable

resources. The benefits of WHR include reduction in the

consumption costs, reduction in pollution and equipment sizes

and also reduction in auxiliary energy consumption. Even

though many WHR systems are available,TEGis widely

utilized in most of the automotive applications.Recently, TEG

is often mentioned as a promising energy harvesting device in

the near future. Alternative energy source is one of the

important players in the world’s energy sources and it gives

one of the biggest contributions to electricity generation even

though it generates low voltage output.TEG is a solid state

device that converts thermal energy (temperature variation’s)

into electrical energy, by using the principle of Seebeck effect

[1].Therefore, connecting a high gain DC–DC converter to

TEG module is considered as a better solution.In order to

achieve high gain, the classical boost converter operates at

large switch duty ratios. This results in voltage stress in boost

switch,efficiency is gradually reduced and the life time of the

switch is decreased.

The ripples on input current and output voltage affect

the performance of the boost converter [2]. Typically

converter with coupled inductors can provide high gain

without large duty ratio and hence reduce the switch

voltagestress. The coupled inductor design is complicated. To

obtain a high conversion ratio, thecoupled inductor leakage

inductance is increased owing to the high winding turns. This

result in voltage spike across the switches and voltage

clamping technique is needed to limit voltage stresses on the

switches [3].

Fig.1. The block diagram of proposedthermoelectric energy harvesting

systems.

The DC-DC converter is integrated with voltage

multiplier stages, and the voltage multiplier is composed of

diode and capacitors. Replacing the step up transformer by

voltage multiplier stages with the boost structure, it provides a

high voltage conversion ratio [4]-[12].The preferred converter

uses numerous diode-capacitor stages which are combined

together to boost up the voltage and also it limits the stresses

on the switches, diodes and capacitors.TEGs as a source

require a suitable control technique to achieve Maximum

Power Point (MPP), in order to enhance the utilization and

performance. Generally, maximum power point tracker is

engaged in between the DC-DC converter and TEG source.



The aim of MPPT is to assure that the system can always

yield the maximum power from the TEG modules. There are

numerous methods available in order to track the maximum

power. Amongwhich the most prominent technique is Perturb

and Observe method. In later days, the researchers

concentrated on advanced evolutionary techniques to address

the drawbacks of the traditional methods. Even though P&O

method renders more advantages it encounters with

oscillations around its MPP [13]-[17]. The small perturbation

leads to better accuracy, but it requires more time for its

convergence. PSO is a meta heuristic technique that provides

an enhanced output power for the TEG module which is

discussed in this paper. Finally, the comparison is done

between both conventional P&O and PSO MPPT techniques.

II. TWO INPUT HIGH GAIN DC-DC POWER CONVERTER

The two input high gain DC-DCpower converter

having four voltage multiplier stages, whose voltage gain

relies on number of voltage multiplier stages and duty ratio of

boost stages which is shown in Fig. 2.

Fig.2. Circuit diagram of high gain DC-DC power converter.

For normal operation of the converter, there should

be some overlapping time when both switches are ON and

also one of the switches should be ON at any given time.

Therefore, the converter has threemodes of operation. The

converter can operate when the switch duty ratios are small

and there is no overlap time between the conduction of the

switches.

A.Mode-1

During mode-1, both switches S1 and S2 are turned

ON. Both the inductors in the boost stage are charged through

the input sources TEG1 and TEG2. The current in both the

inductors increased gradually. The diodes in various VM

stages are in reverse biased so they do not conduct .And also

the output diode 𝐷𝑜𝑢𝑡 is in reverse bias condition. Moreover,

the VM capacitor’s voltage also still unchanged, which is

shown in Fig.3.

Fig.3. Equivalent Circuit for Mode-1 Operation.

At this time the load is fed by the capacitor 𝐶𝑜𝑢𝑡 .If the number of stages is odd, then the output diodegets reverse

bias and at that instant the load is fed by the charge stored in

the output capacitor. However, if the stage is even, then the

output diode is to forward bias thereby charging the output

capacitor and also power the load.

B.Mode- 2

During mode 2, switch S1 is in OFF condition and S2

in ON state which is shown in Fig. 4. All the odd numbered

diodes are conducting and the inductor current flows through

the VM capacitors and thereby charging all odd numbered

capacitors(C1,C3...)and the even numbered capacitors(C2,C4..)

gets discharged.

Fig.4. Equivalent circuit of mode-2 operation.

C.Mode-3

During this mode-3,switch S1 is ON and switch S2 is

OFF which is shown in Fig.5. In this mode all the even

numbered diodes are in conducting state and the inductor

current flows though the VM capacitors and thereby charging

the all even numbered capacitors(C2,C4...)and the odd

numbered capacitors (C1,C3...)gets discharged.



Fig.5. Equivalent Circuit for Mode-3 Operation.

If the number of stagesis odd, then the output diode gets ON

and charging the output capacitor and supplies the load.

However, if the stage is even, then theoutput diode gets OFF

and the load is powered by the charge stored in the output

capacitor.

D. Voltage Gain Expression

The capacitor voltages for the converter with four VM

stages can be expressed as

𝑉𝑐1 =𝑉𝑖𝑛1

(1 − 𝑑1) (1)

𝑉𝑐2 =𝑉𝑖𝑛1

1 − 𝑑1 +

𝑉𝑖𝑛2

1 − 𝑑2 (2)

𝑉𝑐3 =2𝑉𝑖𝑛1

1 − 𝑑1 +

𝑉𝑖𝑛2

1 − 𝑑2 (3)

𝑉𝑐4 =2𝑉𝑖𝑛1

1 − 𝑑1 +

2𝑉𝑖𝑛2

1 − 𝑑2 (4)

whered1 and d2 are the duty cycle of S1and S2

respectively.𝑉𝑖𝑛1and𝑉𝑖𝑛2is the voltage across TEG1 and TEG2

respectively. The output voltage is given as,

𝑉𝑜𝑢𝑡 = 𝑉𝑐4 +𝑉𝑖𝑛1

1 − 𝑑1

=3𝑉𝑖𝑛1

1 − 𝑑1 +

2𝑉𝑖𝑛2

1 − 𝑑2 (5)

The voltage gain of the converter can be approximated as,

𝑉𝑜𝑢𝑡

𝑉𝑖𝑛

= 𝑁 + 1

1 − 𝐷 (6)

whereN is the number of voltage multiplier stages.If the

converter operates then the diodes D1 andD2 are chosen to be

identical and both the boost stages will have symmetrical

inductor.

III. MAXIMUM POWER POINT TRACKING

MPPT technique is based on the principle of the

maximum power transfer theorem. The output power is

maximized only when the source impedance is equal to the

load impedance. Countless methods are available to track the

maximum power, such as Perturb and Observe, Incremental

conductance, Modified Incremental conductance, Fractional

short circuit current method, Fractional open circuit voltage

method etc.MPPT techniqueis mandatory for TEG

applications because the MPP of a TEG module varies with

the temperature. It regulates the duty cycle of the proposed

converter and allows the TEG module to operate at MPP for

all temperature difference.

A. P&O Based MPPT Technique

The Fig.6shows the flow chart of P&O MPPT

technique. A slight perturbation exists in this algorithm. This

perturbation causes the maximum power of the TEG module

to change continuously. If the power increases due to the

perturbation, then the changes proceeded in the same path. At

the next instant the perturbation process converses only after

the peak power was attained at the time of decrease in power.

Thistechnique oscillates around the peak point.The step size is

kept very small in order to keep the power variation small.

Fig.6.Flow chart for P&O based MPPT technique.

It is seen that there are a low power loss owing to the

perturbation and it fails to track the maximum power under

rapid varying atmospheric conditions. This algorithm is used

because of its less complicated nature.

B. PSO Based MPPTTechnique

PSO based MPPT technique is a one of the

population based intelligent optimization technique. PSO is

inspired by behavioral patterns of birds flocking or fish

schooling. In this technique, several similar behaviors of birds

is used and each bird is referred as a particle. Each particle

flying in the search space has its particular fitness value which

is mapped by the objective function and velocity to decide the

direction and the distance of their movement.



Fig.7. Movement of the particle.

Each particle exchanges information that is achieved

in its respective search direction. The movement of particles

in this optimization technique is shown in Fig. 7.PSO is

initialized with a group of random particles and then searches

for attaining the optimum point is done by updating the

generations. On every iteration particle updating relieson two

best values. The first one is the best solution, it has attained so

far which is represented as Pbest.The best valueobtained by

any particle in the neighborhood particle still now is

recognized asgbest. The basic PSO can be defined by using

following velocity and position update equation:

𝑣𝑖 𝑘 + 1 = 𝜔𝑣𝑖 𝑘 + 𝑐1𝑟1 𝑝𝑏𝑒𝑠𝑡 − 𝑥𝑖 𝑘 +

𝑐2𝑟2 𝑔𝑏𝑒𝑠𝑡 − 𝑥𝑖 𝑘 (7)

𝑋𝑖 𝐾 + 1 = 𝑋𝑖 𝐾 + 𝑉𝑖 𝐾1 (8)

𝑖 =1, 2…, N

𝜔 =𝜔𝑚𝑎𝑥 − 𝜔𝑚𝑎𝑥 − 𝜔𝑚𝑖𝑛 ∗ 𝑖𝑡𝑒𝑟

𝑚𝑎𝑥𝑖𝑡𝑒𝑟

(9)

where,𝑋𝑖 is the position of particle 𝑖;𝑣𝑖 is the velocity of

particle 𝑖; 𝐾is the iteration number; 𝜔 is the inertia weight;

𝑟1,𝑟2are random variables uniformly distributed within [0,1];

𝑐1,𝑐2are the cognitive and social coefficient, respectively.

𝑝𝑏𝑒𝑠𝑡 is used to store the best position that the 𝑖 particle so far;

and𝑔𝑏𝑒𝑠𝑡 is used to store the best position of all

particles;𝜔𝑚𝑎𝑥 is the initial weight; 𝑖𝑡𝑒𝑟 is the current iteration

number;𝜔𝑚𝑖𝑛 is the final weight; 𝑚𝑎𝑥𝑖𝑡𝑒𝑟 is the maximum

iteration number. Fig.8. Flow chart for PSO based MPPT technique.

The flowchart of a PSO technique is shown in Fig. 8. From

the figure, the operating principles of a PSO based MPPT

technique can be explained as follows:

1) PSO initialization:Particles are generally initialized

randomly following a uniform distribution over the search

space are initialized. The initial velocity is taken randomly.

2) Fitness evaluation: MPPT algorithm is to maximize the

generated power 𝑃𝑡𝑒𝑔 .TEG voltage 𝑉𝑡𝑒𝑔and current𝐼𝑡𝑒𝑔 can be

measured. These values can then be used to calculate the

fitness value 𝑃𝑡𝑒𝑔 of particle i.

3) Update Individual and Global Best Data: If the fitness

value of particle is better than the best fitness value in the

history𝑝𝑏𝑒𝑠𝑡 ,𝑖 set current value as the new𝑝𝑏𝑒𝑠𝑡 ,𝑖 . Choose the

particle along the best fitnessvalue of the entire particles as

the𝑔𝑏𝑒𝑠𝑡 .

4)Update Velocity and Position of Each Particle: After all the

particles are calculated, the velocity and position ofeach

particle in the swarm should be updated with equations (7),

(8) and (9).

5)Convergence criteria: Check the convergence criterion.

When the termination condition is met the process gets

stopped, unless the iteration number will increase by 1 and go

to algorithm step 2.

Here, in order to track the maximum power which is

a function of voltage and current and the particle position is

defined as the duty cycle d of the DC–DC converter. Then the

fitness value evaluation function is chosen as the generated

power PTEG.

IV. RESULTS& ANALYSIS

A.Analysis of the proposed system without MPPT

TheMatlab-Simulinkmodelof high gain DC-

DCconverter with TEG module as a source is shown in Fig.9.

Fig.9. Matlab-Simulink model of high gain DC-DC converter with TEG.

The Fig.10and Fig.11 show the results of voltage across and

current flowing through the TEG1 and TEG2, respectively.



Fig. 10. Voltage acrossTEG1 and TEG2.

Fig. 11. Currentthrough TEG1 and TEG2.

The Voltage across the diodes for the converter with four

voltage multiplier stages is shown inFig.12.The odd number

of diodes conducts duringmode-2 operation. The even number

of diodes conducts during the mode-3 operation. The odd

numbers of diodes are in blocking mode in the mode-3

operation, when S1 is ON and S2 is OFF. The response of

current through switch1, switch2 is shown in Fig.13. The

spike is observed in current through switch2, when the

number of voltage multiplier stage is even. The spike in the

switch current is due to the voltage imbalance between VM

stage capacitors. The spike in current through S2 appears

during mode-2 operation of the converter.

Fig.12. Voltage across the diodes.

Fig.13. Current through switch1 and switch2.

Fig.14.Output voltage and current of converter.

Theoutput voltage and output current of the converter are

shown in Fig.14. The output voltage and output current of the

converter is settled at 111.7V and 0.2822A, respectively.

B. Analysis of the proposed system with P&O based MPPT

technique

The Fig.15shows the simulation circuit of high gain

DC-DC converter with TEG moduleand P&O MPPT

technique for a temperature difference of 195°C. The Fig. 16

shows the obtained power of TEGmodules with DC-DC boost

converter using P&O based MPPT for a temperature

difference of 195°C. The output voltage and output current of

the TEG module is sensed and applied as an input to the

MPPT controller. The output of the MPPT controller is the

duty cycle that corresponds to MPP which is given to the

converter to extract maximum power. The output voltage

obtained from the converter is 114.8V corresponding to the

duty cycle of 0.8.

Fig.15.The Simulink model of TEG module with the converter and P&O

MPPT technique.



Fig.16.Input power responses of TEG1 and TEG2 using P&Otechnique.

Fig.17.Output power response of converterwith P&OMPPT.

The output power obtained from the converter is

32.93Wcorresponding to the temperature difference of 195°C

TEG modules using P&O technique shown in Fig.17.

C. Analysis of the proposed system with PSO MPPT

technique

The Fig.18.shows the simulation circuit of high gain

DC-DC converter with TEG module and PSO MPPT

technique for a temperature difference of 195°C.Fig. 19.

shows the obtained power of TEG modules with DC-DC

boost converter using PSO based MPPT for temperature

difference of 195°C. PSO MPPT technique tracks the

maximum power from the TEG module at a duty ratio of

0.814. Also, it tracked a higher power when compared to

P&O technique.The output power obtained from the converter

is 38.67W corresponding to the temperature difference of

195°C with PSO MPPT technique is shown in Fig. 20.

Fig.18.The Simulink model of TEG module with the converter and PSO MPPT technique.

The performance comparison of both P&O and PSO

techniques for various temperature difference of TEG are

performed and are shown in Table 1.

From the Table 1, it is observed that the PSO MPPT

technique has better performance when compared to the

traditional P&O method.

Fig.19. output power of TEG1 and TEG2 using PSO technique.

Fig.20.output power response of converter using PSO MPPT.

Table1. Comparison of open loop, P&O and PSO based MPPT technique for various temperature differences (∆T).

∆T 195°C 125°C 40°C

Testing

Methods

Open

Loop

MPPT technique

Open

Loop

MPPT technique Open

Loop

MPPT technique

P&O

PSO

P&O

PSO

P&O

PSO

Vout(V) 111.7 114.8 131.9 67.86 69.18 79.61 30.51 31.15 34.86

Iout(A) 0.2822 0.2869 0.2932 0.1696 0.1729 0.1767 0.0761 0.0763 0.07748

Pin(W) 44.76 46.10 52.80 16.572 17.05 19.50 3.412 3.475 3.946



Pout(W) 31.521 32.93 38.67 11.509 11.96 14.04 2.321 2.376 2.70

ɳ (%) 70.42 71.43 73.23 69.44 70.13 72.04 68.02 68.374 68.423

V.CONCULSION

A two input DC-DC converter with MPPT for TEG

has been proposed. The preferred converter is incorporated

with diodes and capacitors as multipliers to enhance the

voltage gain along with some flexible features to modify the

stages of arrangements based on the requirement of the gain.

The efficiency obtained is 70% for the converter using TEG

in open loop for a temperature difference of 195°C.

Moreover, a P&O and PSO based MPPT techniquesare

proposed and they obtained an efficiency of 71% and 73%,

respectively for a temperature difference of 195°C. The

versatility of the converter is to operate under the maximum

power resulted in the increased efficiency when compared to

the conventional schemes.

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performance analysis of novel dc-dc converter employing ... · observe (p&o) and particle swarm...

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