PERFORMANCE ANALYSIS AND COMPARISON OF MPPT METHOD FOR A SOLAR PV SYSTEM

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

62

 R I

PERFORMANCE ANALYSIS AND COMPARISON OF MPPT METHOD FOR A SOLAR PV SYSTEM

BASED INDUCTION MOTOR DRIVE

MD. Ayaan Siddiqui

¹

, D.V.Avasthi

²

, Durgesh Kumar

³

Department of Electrical and Electronics Engineering SUBHARTI INSTITUTE OT TECHNOLOGY AND ENGINEERING, MEERUT

ABSTRACT: This work aims to simulate extraction of maximum power from the PV array source feeding ac supply to inverter for induction Motor drive for a commercial, industrial, agricultural or household application. The Perturb and Observe (P&O) MPPT technique is applied to extract maximum power from the PV module for DC-DC boost converter which inputs supply to the inverter for induction motor application. The simulation results of the overall system are found to match with the theoretical calculation within the limits of experimental error.

Perturb & Observe (P&O) based MPPT technique is considered due to its popularity and fair degree of accuracy it provides in the simulation.

Keywords-- Renewable Energy, PV System, MPPT Techniques (CVC, P&O, IC), DC-DC Boost Converter.

I.INTRODUCTION:

Multiplying electricity demand everywhere, high pollution levels emanating from the fossil fuels causing carbon monoxide and GHG emissions and progressive depletion of fuel reserves in the earth’s crest are motivating researches to explore possible deployment of renewable energy resources for producing electricity at an economic cost on a commercial scale. Fortunately, the sun is an abundant source of energy which is clean, pollution free, affordable and inexhaustible and hence the most preferred renewable energy resource in the Indian situation. India’s geographic location near to the equator makes it a rich resource of insolation energy and

curve where maximum output power is derived from the PV module. MPPT techniques as elaborated in this Paper must be applied to maintain the PV array to derive maximum power output from the solar PV module.

This study, after giving a passing reference to the mathematical treatment for the analysis of energy conversion process in PV module, explains the concept underlying MPPT. Three popular approaches for MPPT simulation and analysis namely, the Constant voltage controlled (CVC) Method, Perturb & Observe (P&O) Method and the Incremental Conductance (IC) Method are briefly explained.

These methods are applied to track maximum power points on the output characteristic curves of the PV module. Finally, the suitability of the PV module for a three phase induction motor load after power conditioning of the output to ac as the drive for a water pump is evaluated through simulation.

II. SOLAR PV SYSTEM:

Equivalent circuit and operational characteristics: A PV system directly converts solar energy into electricity. The PV array consists of a series-parallel grouping of PV modules supplying load. The equivalent circuit and electrical behavior of the PV cell can be understood by referring to the figures (1) in which insolation energy and temperatures are considered as parameters in the characteristic curve [20].

RS

given the right application of appropriate technologies to convert this energy into electricity on a mass scale the energy crisis in the country can imminently disappear bringing India in the category of energy rich nations of the world.

PV modules which essentially convert solar energy into

Ipv

Id I

R^Sh Vc

electricity. Solar PV systems are capable of providing upto 28% energy efficiency. The electric energy output of solar PV

Fig (1): Equivalent circuit of solar PV system array undergoes instantaneous change due to variations in AkT I I I 

temperature and environmental conditions. Generally V _C  ^C ln  ^{ph o c}  ^{s c} (1) speaking, there exists a unique point on the I-V and P-V

characteristic of PV module corresponding to the maximum output power popularly known as the maximum power point (MPP). It is precisely this operating point on the characteristic

e  I_o 

VC: output voltage of PV system.

A: curve fitting factor.

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

63

k : Boltzmann constant (J/K).

IC: Output cell current.

Io: Reverse Saturation Current.

Ipv: PV current.

Id: Diode current.

Rs: Series resistance Rsh: Shunt resistance.

The expression for voltage in Eq.(1) gives the output voltage of single solar cell, which should be multiplied by the number

III. MAXIMUM POWER POINT:

The PV system has non-linear P-V and I-V characteristics.

The conversion output power depends upon environmental conditions such as solar irradiation and temperature etc. The output power of the PV system is maximum at the knee point of the P-V characteristic, also known as MPP. As MPP keeps on changing in accordance with the varying irradiation levels, suitable MPPT mechanisms are designed to track instantaneous MPP of the system for deriving maximum power from it at each instant corresponding to these points.

of solar cells in series in order to determine the rated PV cell

voltage. _I ^ISC

I-V Curve

P_MAX

The temperature change (∆T^c) occurs during solar irradiation process. It can be obtained by using Eq. (2) [20] as,

MPP

P-V Curve

T

_c

 

_s

 ^S

x

S

_c

 ^

⁽²⁾ Voltage (V) V_MPP V_OC

SX= New Solar Irradiation.

Sc= Benchmark Reference.

αs =0.2 (Constant).

The modified values of PV array voltage (VCX) and 0PV current (IPHX) are obtained from the Eq (3) & (4) [20] given by,

(3) (4)

VC: benchmark reference PV cell output voltage.

Iph: benchmark reference PV cell current.

β: Open circuit voltage coefficient (0.004).

γT: Short circuit current coefficient (0.06).

Ta: Ambient Temperature (

C

_).

TX: Actual temperature (

C

_).

SX: New solar irradiation level.

SC: Benchmark Reference solar irradiation level.

Fig (2): Typical P-V and I-V characteristics of a PV cell IV. Maximum Power Point Tracking – An Overview:

A typical solar panel converts only upto 28 percent of the incident solar irradiation into electrical energy. MPPT is applied to improve efficiency of the solar panel by matching source impedance with the load impedance. On the source side in this research, a boost convertor is connected to the solar panel to enhance output voltage suitable for the applications like motor load. By changing duty cycle of the boost converter appropriately we can match the source impedance with that of the load impedance. Popular algorithms available to track the maximum power point include, Perturb and Observe method, Incremental Conductance method, Cons(t4a)nt Voltage Control method, Neural networks Method and Fuzzy logic method etc. The choice of the MPPT algorithm for a particular application depends on the time the algorithm takes to track the MPP, implementation cost and the ease of implementation. The schematic of representative MPPT is shown in Fig (3).

The MPPT methods applied in this work are as below;

.

Where,

Power (W)

Current (A)

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

64

VL 500

400

300

200

100

0 0.5 1 1.5 2 2.5 3

Time (sec)

Fig (3): Schematic Diagram showing MPPT Application 1. Constant voltage controlled (CVC) method: In this method, the voltage across the PV terminals is held at a fixed value and the power output measured to ensure that the maximum power transfer is obtained by the connected load. The method requires a single voltage sensor and it is introduced by simple implementation of the MPP. The block diagram of the CVC method is depicted in Fig (4).

Fig (6):CVC Based MPPT O/P Voltage (V) based MPPT technique

2. Perturb & Observe (P&O): In this method only one sensor, namely the voltage sensor is used to sense the PV array voltage so that this algorithm can be implemented at an economic cost. It has very less time complexity compared to other MPPT methods. However, it keeps on perturbing in both directions even after voltage approaching close to the MPP which requires an appropriate error limit to be set in the algorithm. A limitation of this method is that it does not account for rapid changes in the irradiation level and considers it as a change in MPP due to perturbation and ends up introducing error in the MPP calculation. This problem is taken care of in the incremental conductance method. The stepwise flow chart for the method is depicted in Fig (7). The signal of the PV system.

Fig (4): Block diagram of CVC MPPT method

The algorithm corresponding to CVC uses proportional- integral control in which duty cycle D is changed for tracking MPPT by taking e(t) as the error voltage, Kp and Ki as the proportional and integral gains. The system equation can be written in the form:

D K_pe(t) K_i



^e(t)dt _(a)

The MATLAB / Simulink diagram corresponding to this simulation is given in Fig (5). Simulation results for this method are shown in Fig (6)

Fig (5):MATLAB/Simulink model of CVC

Fig (7):Flowchart of P&O MPPT method

The stepwise flowchart for the P&O MPPT can be explained as follows. The voltage of the PV system is considered as a reference signal. The target of this method is to force the reference voltage of the PV system to Vmpp, which causes the instantaneous PV voltage to track Vmpp. This is done by applying small and constant perturbation to the PV voltage a

Boost Convereter

DC/DC

Sensed

Parameters P&O MPPT

PV System I_PV IL

G

V_PV R

T

Conventional MPPT methods D

V I PWM

Pulse S

CVC MPPT

Generator IC MPPT

DC/DC Boost converter of

V_{ref +} ^Kp

e(t) V_PV

-

PI Controller





D

K_i

V_PV



^e(t)

Increase module V

Decrease module V Start

Measure V(n) and I(n)

Calculate P(n)= V(n)*I(n) dP= P(n)-P(n-1)

Y dP=0

N

N Y

dP>0

V(n)-V(n-1)<0 V(n)-V(n-1)>0

Y N Y N

Decrease module V

Increase module V

Return

CVC based MPPT o/p Voltage (V)

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

65

 

step-by-step. After each perturbation the variation in output power (dP) is measured. A positive dP indicates that output power will approach MPP. Therefore, a perturbation of

positive sign is applied to the PV voltage in the next stage. On



_{dP 0 }

 I

at MPP



I

left

of MPP

(1) the other hand, if dP is negative, a negative sign perturbation

is applied. These steps are repeatedly performed until the MPP of the system is reached where dP is equal to zero.

The representative Matlab/Simulink diagram illustrating P &



^dV



_{dP 0}



dV

 ^V

^V

 I



I

 ^V

V

right of MPP

O method is depicted in Fig.8. The results corresponding to

the method are shown in Fig (9).

The maximum output power as,

P_MPP

V

_MPP I_MPP (2)

Fig (8): MATLAB/Simulink model of P&O based MPPT technique

Fig (10): Incremental Conductance MPPT

440

420

400 0 0.5 1 1.5 2 2.5 3

Time (sec)

Fig (9): P&O based MPPT O/P Voltage (V)

3. Incremental Conductance (IC) method: This MPPT method is based on the principle that the slope of the power curve of the PV system at the MPP is zero, positive when the output power is less than MPP and negative when the output power is greater than the MPP.

Three derivative conditions are expressed as;

Fig (11): Flowchart of IC MPPT method

Start

Measure V(n) and I(n)

Calculate dV= V(n)-V(n-1)

dI= I(n)-I(n-1)

N Y

dV=0

Y Y

dI/dV = -I/V dI = 0

N N

Y Y

dI/dV > -I/V dI > 0

N Increase Decrease module V module V

N

Decrease Increase module V module V

V(n-1) = V(n) I(n-1) = I(n)

Return

P&O based MPPT o/p Voltage (V)



^dP

 ^I

^I



_dV

^0

  _V ^ _

 ^

^V

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

66

1000 900 800 700 600 500 400 300 200 100

S =1000 W/m2

x

S =800 W/m2

x

S =600 W/m2

x

S =400 W/m2

x

Fig (12): MATLAB/Simulink model of IC based MPPT technique

In this method the MPP tracking speed can be increased by adjusting the increment or decrement size of Vstep but it will cause the system to oscillate around the MPP.

1000

0 0 50 100 150 200 250 300

Voltage (Volt)

Fig (15)

Temp=55 °C Temp=30 °C

500 480 460 440 420 400

380 0 0.5 1 1.5 2 2.5 3

Time (sec)

800

Temp=45 °C Temp=15 °C 600

400

200

0 0 50 100 150 200 250 300

Voltage(V)

Fig (13): IC based MPPT output voltage (V) V: SIMULATION CIRCUIT:

Fig (14): MATLAB/Simulink model of P&O based MPPT Source Induction Motor Drive

VI: SIMULATION RESULTS:

 Performance of PV system under different operating conditions: The I-V and P-V characteristic curves of the PV system can be seen in Fig (15)-(18).

Fig (16)

7 S =400 W/m2

x

6 S =600 W/m2

x S =800 W/m2

5^x S =1000 W/m2 _x

4 3 2 1 0

0 50 100 150 200 250 300

Voltage (Volt)

Fig (17)

7

Temp= 15 °C

6 Temp= 30 °C

Temp= 45 °C

5 Temp= 55 °C

4 3 2 1

0 50 100 150 200 250 300

Voltage (Volt)

Fig (18)

IC based MPPT o/p voltage (V) Current (Amp)Current (Amp) Power(W) Power (Watt)

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

67

EM Torque (Nm)

 Transient analysis of P&O, CVC and IC based MPPT

techniques: the comparative study of all three MPPT 40 techniques is done, it is observed that the P&O based

MPPT techniques has less transient and settling time 20 in compare to other used MPPT techniques shown in

Fig (19) as, 0

600

400

200

P&O CVC IC

-20 0 1 2 3 4

Time (Sec)

Fig (21): EM torque (Nm)

0 0.5 1 1.5 2 2.5 3

Time (sec)

Fig (19): Transient analysis of P&O, CVC and IC based MPPT techniques

 The rotor speed of induction motor is found 1740 rpm at fixed torque load (11 Nm) and EM torque also found 12.5Nm, which are shown in Fig (20) and (21) respectively as,

2000

1600

1200

60 40 20 0 -20 -40

-60 0 1 2 3 4

Time (Sec)

Fig (22): Stator current Iabc (A)

VII: CONCLUSION 800

400

0 0.4 0.8 1 1.4 1.8

Time (Sec)

Fig (20): Rotor Speed (rpm)

A comparative study of MPPT methods such as P&O, IC and CVC has been conducted in this work. It is found that the performance of P&O MPPT method is superior as tracking by this method reduces transients in the PV module output.

Accordingly, therefore, the P&O based MPPT method is applied for PV system under study to achieve smooth electrical output. The performance of PV system has been

 The stator current of inductance motor is 8.5A at fixed torque load (11 Nm) after variation in applied torque load upto 30 Nm then the stator current Iabc is 23.5 A it is shown in Fig (22) as,

studied using I-V and P-V characteristics at different temperature and irradiation levels. The analysis of PV system has been done and performance of complete system is found to be satisfactory for induction motor pump load which thereby validating the system model

.

This research can be extended by using other MPPT methods for diverse loads in order to improve efficiency of the systems. Replication of this work shall possibly help in the improvements of the efficiency of electrical system

.

Output Voltage (V) Rotor Speed (RPM) Stator Current I (A) abc

International Journal of Advanced Engineering Science and Technological Research (IJAESTR) ISSN: 2321-1202, www.aestjournal.org @2015 All rights reserved

68

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