The new combined maximum power point tracking algorithm using fractional estimation in photovoltaic systems

The New Combined Maximum Power Point Tracking Algorithm Using Fractional Estimation in Photovoltaic Systems Dzung Phan Quoc, Quang Nguyen Nhat, Phuong Le Minh, Khoa Le Dinh, Vu Nguyen

The New Combined Maximum Power Point

Tracking Algorithm Using Fractional Estimation in

Photovoltaic Systems

Dzung Phan Quoc, Quang Nguyen Nhat, Phuong Le Minh, Khoa Le Dinh, Vu Nguyen Truong Dan and Anh Nguyen Bao Faculty of Electrical & Electronic Engineering, HCMC University of Technology, Ho Chi Minh City, Vietnam

pqdung@hcmut.edu.vn ; nguyennhatquang29@gmail.com

Hong Hee Lee School of Electrical Engineering, University of Ulsan, Ulsan, Korea

hhlee@mail.ulsan.ac.kr

Abstract - This paper presents an improved algorithm of quick

and accurate Maximum Power Point Tracking (MPPT)

algorithm which is based on Incremental conductance

algorithm, Fractional Open Circuit Voltage and Short Circuit

Current The proposed algorithm estimates the short circuit

current or open circuit voltage, following by using Fractional

Short Circuit Current or Fractional Open Circuit Voltage

algorithm to quickly determine point close to MPP MPP will be

accurately determined due to Incremental conductance

algorithm The proposed algorithm can identify quickly and

correctly MPP when the environmental temperature and solar

radiation change The results of proposed algorithm are made

by simulating with MATLAB/Simulink program and

experimenting with kit DSpace DS 1104

Keyword: Maximum power point tracking (MPPT), Incremental

Conductance (Inc-cond), Fractional Open Circuit Voltage,

Fractional Short Circuit Current, Matlab/Simulink, DSpace

DS1104

I INTRODUCTION

When a photovoltaic (PV) system is connected to the load,

the system will operate at the intersection of the I-V

characteristic of the photovoltaic and the load characteristic

To increase the effectiveness of photovoltaic system, the

photovoltaic system should be operated at the maximum

power point Maximum power point is not a fixed point

which depends on conditions of environmental temperature

and solar radiation Natural environmental conditions are very

volatile, so the MPPT controller for photovoltaic systems is

very essential The MPPT controller has an impact on the

DC-DC converter to inject maximum power at the output

before the system is connected to the load or DC-AC

converter for grid connection

Many MPPT algorithms have been studied and developed

([7], [9], [10]) such as Perturb and Observe (P & O),

Incremental conductance (IncCond), Fractional Open Circuit

Voltage, Fractional Short Circuit current or ANN based

algorithm ([6], [8]) to determine MPPT P & O algorithm is

often used in practice because it's simple to implement But

this algorithm does not specify MPP exactly when there is rapid change of solar radiation IncCond algorithm overcomes the disadvantages of P & O but the respond time is not fast ANN is a method to determine MPP quickly and accurately ANN algorithm would learn characteristics of a specific photovoltaic panels so when the photovoltaic system is changed, the algorithm must learn a new characteristic In the course of long-term use the characteristics of photovoltaic panel will be changed, resulting in inaccurate algorithm Improvements of MPPT algorithm have been researched and developed in [1-5], [11] Reference [11] proposes a two-stage algorithm that offers fast tracking in the first two-stage and fine tracking in the second stage This method remains a problem of determining VOC (Open Circuit Voltage)

This paper presents a new algorithm of MPPT based on improved IncCond algorithm combined with Fractional Short Circuit Current and Fractional Open Circuit Voltage algorithms This method will determine short circuit current if the photovoltaic system operates on the left of I-V characteristics or open circuit voltage if the system works on the right of I-V characteristics Then Fractional Short Circuit Current or Fractional Open Circuit Voltage algorithms will be implemented to put the power around the MPP quickly and then IncCond algorithm is used to determine the exact MPP The proposed algorithm not only identifies quickly and accurately the MPP, but also is not affected by the aging of the system in long term use

II THE NEW ALGORITHM

The proposed algorithm divides I-V characteristics into three domains: the left, the middle and the right domain as shown in Fig 1 According to initial conditions of whether the photovoltaic system is operating in the left or right domain, the algorithm will determine ISC or VOC

At the beginning, if the photovoltaic system operates in the left domain, the algorithm will determine the MPP based on the correspondent value of IREF Assume that in the left domain of the I-V characteristic, there is an almost linear IEEE PEDS 2011, Singapore, 5 - 8 December 2011

relationship between IMPP and ISC of the PV and the value of

ISC is determined in the first calculation cycles

) 1 ( 1 2

1 2

I I

I

sc

−

− +

In which

SC I K

REF

where K1 is a constant chosen at random with constant K1

= 0.75- 0.92 in Fractional Short Circuit Current algorithm In

the next calculation cycles, the photovoltaic system will

operate in the middle domain; Incremental conductance

algorithm is used to determine IREF so that it operates at MPP

At the beginning, if the photovoltaic system operates in the

right domain, the algorithm will determine MPP based on the

correspondent value of VREF Assume that in the right domain

of the I-V characteristic, there is a near linear relationship

between VMMP and VOC of the PV array and the value of VOC

is determined in the first calculation cycles

) 1 ( 1 2

1 2

V V V oc

−

− +

In which

OC V K REF

where: K2 is a constant chosen at random with constant K2

= 0.72: 0.78 in Fractional Open Circuit Voltage algorithm In the next calculation cycles, the photovoltaic system will operate in the middle domain; Incremental conductance algorithm is used to determine VREF so that it operates at MPP

When environmental conditions vary, the MPP will be changed by photovoltaic system, depending on the variance

of current value at the point of change, the algorithm will determine MPP according to the value of IREF or VREF The working principle of the proposed algorithm can be explained using a flowchart show in Fig 2

Let

V

I b dV

dI a

−

=

=

(5)

The algorithm for determining the value of IREF or VREF

being relative to ISC or VOC is shown in Fig.3

III SIMULATION RESULTS OF THE PROPOSED ALGORITHM

System model of the proposed algorithm is developed on Matlab/Simulink and SimPowerSystems

The photovoltaic system model consists of PV array, the buck - boost converter, load R and MPPT controller as shown

in Fig 4

Components of the system include:

PV Array: 01 module PV SX 3200 VOC = 30.8 V, ISC = 8.7

A (normal radiation);

DC-DC Converter: Buck-Boost Converter with parameters:

C1 = 2500µF, L = 1.5 mH, C2 = 5000µF;

Load : resistance load

1 Case 1: Simulation results of the time response of the proposed algorithm and traditional IncCond algorithm

Fig 1 I-V Characteristic of a photovoltaic cell

Fig 2 Flowchart of the proposed algorithm

Fig 3 Flowchart algorithm determines I REF or V REF

Irradiation and ambient temperature in the simulation are:

T = 250C and λ = 1 kW/m2

The proposed method tracks to the MPP faster than the

conventional IncCond algorithm The proposed algorithm

(Fig.5) reaches to the MPP in 0.02s, while the IncCond

algorithm (Fig.6) reaches to the MPP in 0.2s

2 Case 2: Ability of the proposed algorithm to response to the changes of the environmental temperature conditions

Irradiance is constant with λ = 1kW/m2

Ambient temperature in the simulation is:

− Time: t = 0s – 0.3 s: T = 250C

− Time: t = 0.3s – 0.55s: T = 350C

− Time: t = 0.55s – 1s: T = 300

C The response is shown in Fig.7 and Fig.8

3 Case 3: Ability of the proposed algorithm to response to the changes of solar irradiation

Ambient temperature is constant: T =250C Irradiation in the simulation is:

− Time: t = 0s – 0.4s: λ = 1 kW/m2

− Time: t=0.4s–0.8s: λ = 0.2 kW/m2

− Time: t=0.8s–1.2s: λ = 0.8 kW/m2

The response is shown in Fig.9 and Fig.10 Comparing with traditional algorithm, the proposed algorithm has faster response and higher accuracy in case of changing the environmental temperature or radiation intensity

IV EXPERIMENTAL RESULTS

The proposed algorithm is implemented on the experimental Kit DSpace DS 1104 to test the ability of the algorithm Components of the system include:

PV Array: 4 module PV H-Tech 13W VOC = 10.9 V, ISC = 1.2 A (radiation of lamp);

DC-DC Converter: Buck-Boost Converter with parameters:

C1 = 3900µF, L = 1.5 mH, C2 = 5000µF;

Load: resistance load;

Controller MPPT: Kit dSPACE DS1104 set on computer and can communicate with program MATLAB/Simulink The model is shown in Fig 11

to VREF

Information of photovoltaic system using proposed algorithm is demonstrated in Control Desk Proposed algorithm determine MPP according to VREF for 0.02s (Fig 12) The initial photovoltaic system operates at open circuit voltage and then immediately operates at maximum power point (Fig.13-14)

Fig 5 PV Power Response Curve

(the proposed algorithm)

Fig 6 PV Power Response Curve with Inc algorithm.

Fig 4 Block diagram of MPPT controller

0 0.2 0.4 0.6 0.8 1

140

160

180

Time (s)

Fig 7 Power Response Curve

with temperature changes (the

proposed algorithm)

Fig 8 P-V Curve with temperature changes (the proposed

algorithm)

Fig 9 PV Power Curve with

irradiation changes (the proposed

algorithm)

0 100 200

Voltage (V)

Fig.10 P-V Curve with irradiation changes (the proposed algorithm)

Fig 11 Experimental model using proposed algorithm

2 Case 2: Proposed algorithm determines MPP according

to IREF

Information of photovoltaic system using proposed

algorithm is demonstrated in Control Desk Proposed

algorithm determines MPPT according to IREF for 0.03s

(Fig.15) The initial photovoltaic system operates at short

circuit current and then immediately operates at maximum

power point (Fig.16-17)

3 Case 3: Traditional IncCond algorithm determines MPP

Information of photovoltaic system using IncCond

algorithm is demonstrated in Control Desk IncCond

algorithm determines MPPT according to VREF for 0.45s

(Fig.18) The initial photovoltaic system operates at open

circuit voltage and then step by step operates at maximum

power point (Fig.19-20) The proposed algorithm can

determine MPP accurately by both reference current and

voltage When there is a change in ambient temperature or radiation intensity, the proposed algorithm has good response, even at low radiation intensity (light sun)

V CONCLUSION

The proposed algorithm satisfies the two essential elements in determining MPP, which are fast and accurate response in case of rapid change of environmental conditions

of temperature and solar radiation, compared to traditional algorithms

The main utility of the algorithm:

− Not affected by the property of the photovoltaic

− No additional photovoltaic system to determine the open circuit VOC or short circuit current ISC

− Good response even when the solar irradiation is low

− Identify MPPT by the current and voltage, the calculation algorithm can be implemented easily in the DSP microcontroller in the future

ACKNOWLEDGMENT

The authors gratefully acknowledge the HCMUT – VNU (Vietnam) and Network-Based Automation Research Center

of University of Ulsan (Korea) for providing excellent supports and facilities

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