Performance Analysis of Novel DC-DC Converter Employing ... · observe (P&O) and particle swarm...
Transcript of 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.
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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.
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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.
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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.
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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.
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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
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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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