Comparison of Perturb & Observe and Ripple ... - IEEE Xplore

t 1s IEEE International Conference on Power Electronics, Intelligent Control and Energy Systems (ICPEICES-2016)

Comparison of Perturb & Observe and Ripple Correlation Control MPPT Algorithms for PV Array 3 4 2 l Akankshi Trivedi , Ankit Gupta , Rupendra Kumar Pachauri and Yogesh K. Chauhan

1,2,3Electrical Engineering D epartment, School of Engineering, Gautam Buddha University, Greater Noida, India E- mail: [email protected]@gmail.com. [email protected], [email protected],

Ripple correlation technique [12, 13], these ripples are utilized as input to the MPPT. This can be interpreted as the perturbation for the observation in change in power. The RCC can be assumed as the conventional P&O with perturbation as the inherent ripple content. The analog and digital implementations of the technique are reported which would result in the cost reduction and improved efficiency [14]. In discrete- RCC , suitable variables should be sampled at appropriate time which would result in increased complexity. The rate of convergence of perturb and observe algorithm varies [15] with different loads and weather conditions. Also, in conventional P&O, parameter tuning capability is not present. These algorithms are implemented individually and proper comparative analysis is not discussed. Also, any analysis not had been done on basis of rate of convergence with change in atmospheric conditions By motivation of above literature review, the novelty of this paper is to present a comparative study of Perturb and Observe algorithm with Ripple C orrelation control.

Abstract-The maximum power point tracking (MPPT) techniques are used to gain maximum power through solar PV system. Therefore, the research is creating to design a more effective and efficient MPPT to achieve maximum power transfer to the load. In this context, two MPPT techniques, i.e. Perturb and Observe (P&O) and Ripple correlation control (RCC) are implemented. Both the MPPT techniques are investigated. In terms of transient response, the

models

are

developed

in

MATLABI

Simulink

environment. The performance is investigated under variable irradiation conditions and found satisfactory for both the techniques. Keywords-Boost Converter; Perturb and Observe; Ripple Correlation; Solar PV; Maximum Power Point Tracking

I. INTRODUCTION With the advancement of technology and demand of energy, the fossil fuels are decreasing exponentially and hence the utilization of renewable energy (RE) is required. Solar energy is suitable RE but the continuously changing weather conditions and low efficiency builds the challenges. To obtain the PV's maximum power irrespective of the weather conditions, a maximum power tracking system is required to extract the maximum power from the solar PV system [1]. The mathematical modeling of PV system had been done [2,3] and observed that due to variation of atmospheric temperature and irradiation level, the operating voltage and current varies and hence power varies. MPPT techniques are required to obtain maximwn power The most common maximwn power tracking techniques include perturb and observe, hill climbing, incremental conductance under different types of converters. No algorithm can be claimed best as they may vary with respect to simplicity, cost effectiveness, speed of convergence, implementation etc [4- 8 ]. Perturb and Observe algorithm operates on the change in output power with change in voltage. The tracking system continuously increment or decrement the duty ratio. The voltage is perturbed and change in voltage with respect to change in power is observed. The step size for perturbation is fixed and provided by external source [8- 11]. Inherent ripples present due to power electronic converter system. In 978-1-4673-8587-9/16/$31.00 ©2016 IEEE

II.

SYSTEM DESCRIPTION

The system comprises mainly four parts as (a) PV system (b) MPPT methods (i) Perturb and Observe (ii) Ripple C orrelation (c) DC-DC boost converter (d) DC resistive load.

V

I

PV Array

f-------1 DC-DC Boost Converter

Fig. 1: Schematic Diagram of Proposed System

Moreover this paper is organized as the modeling of photovoltaic system is reported in section 3. In section 4. power electronics interface is discussed then the results and discussion part is discussed in section 5. Furthennore section 6 concludes the entire paper. [1)


III.

Basic MPPT algorithm consists of perturb and observe algorithm the change in power is continuously observed with respect to change in voltage. Initially the operated voltage is incremented and hence compared to its previous value and then observed whether power is incremented or not. If the power is also incremented then the positive perturbation is provided and voltage is again increased until power starts decreasing but if increase in voltage results in decrease in power compared to previous one, then the perturbation direction is reversed. The perturbation is provided externally to the MPPT. Large perturbation step size results in large oscillation whereas small perturbation would result slower rate of convergence.

MODELLING OF PHOTOVOLTAlC SYSTEM

The equation describing characteristics of solar panel is: q(Vm+I mR S) ) _I 1=1 p- I0 exp( akTNs Isc+K1(T-Tn) I = (V +K 2 (T-Tn) ) q exp( oc )

[

]

the

behavior

and

(1)

0

(2)

kaTNs

G Ip=«T-Tn) K1+la) Gn

(3) Rs

+

B.

Ripple Correlation

p *

p Fig. 2: Single Diode Model of Practical Photovoltaic Device Including Parallel and Series Resistance

Where, Ip=C urrent generated from solar irradiation. Id= Shockley diode equation 10= R everse saturation current Vm=array output voltage Im=array output current T= Temperature in Kelvin G=Solar irradiation in W1m2 IV.

Fig. 4: PV Array Average Power and Current

The boost converter input current iL consist a combination of dc component IL and ripple component ir. Input current iL is adjusted according to irradiation and temperature level and hence output power is obtained is the combination of ripple and average component. The average component P varies non linearly with dc component of inductor current as shown in the Fig. 4. The main objective is to track IL towards IL* at which maximum average power is obtained. The input inductor current and array power can be correlated in order to determine whether IL* is below or above IL. When IL is below IL*, current ripple and power ripple are in phase and current ripple imposed along the curve which leads the dpldt x diLidt positive whereas when IL is above IL*, the product of dpldt and diLidt is negative [12].

MAXIMUM POWER POINT TRACKING METHODS

M aximum power is tracked in solar photovoltaic panel by Perturb and Observe technique and R ipple correlation control technique. A.

Perturb and Observe Technique

diL dp * >0 . IL 1L dt dt

-

(4)

(5)

R ipple component can be separated from the dc component using high pass filter. The cutoff frequency of filter must be less than the ripple frequency. High pass filter can be equivalent represented using differentiator circuit.

Fig. 3: Perturb and Observe Flowchart [21


Basically in ripple correlation the time derivatives of power and current are calculated which is non zero due to the presence of inherent ripples present due to converter switching. Given conclusion can be drawn: d=k

f diL �t . dt . dt

•

•

(6 )

Where k=gain, p=total power flow this will lead to RCC law.

•

•

Fig. 5: Block Diagram of Ripple Correlation Control

V. DC-DC

PV Array

On increasing the solar irradiation level, the maximum current increases which would result in increase maximum power. There will be negligible increase in open circuit voltage. On decreasing the solar irradiation level, the maximum current decreases which would result in decrease maximum power. There will be negligible decrease in the open circuit voltage. On increasing the operating temperature, the open circuit voltage decreases which would result in decrease in maximum power. There will be negligible change in short circuit current. On decreasing the operating temperature, the open circuit voltage increases which would result in increase in maximum power. There will be negligible change in short circuit current. 350

BOOST CONVERTER

- --. - s = 1000 x

--..-- s = 800 x

o

Switch

Fig. 6: PV Array Connected Boost Converter

10

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:: ·:=: :�==: : : : : : : L: : : : : : : : :L. . . . . ��:�� ::: �::ow��rri' � �� ::::::=r:: ::� . OL-______

Vout =----!.!!.... (7) I-D Where Vout is the output voltage of the boost converter, Yin is the input voltage of the boost converter which is the same as the output voltage of solar panel, D is the duty ratio provided by the MPPT controller.

__

40

_25°C

200

150 100 50

RESULTS AND DISCUSSION

o

Performance of P&O and RCC MPPT methods assisted of PV system is summarized as • I- V and P- V C haracteristics of PV array. • Steady state analysis of PV array. • Dynamic response of PV array assisted by P&O and RCC MPPT algorithm A.

20 Voltage (V) (a) _. __ .-

To track the maximum power from the solar panel, boost converter can be used as the power electronic interface between the solar panel and load. The boost converter enhances the input voltage according to the duty ratio provided by the MPPT controller. The input voltage and output voltage are related by:

VI.

Wlrrf

Wlrrf

8

16

24

Voltage (V)

(C)

32

10 ,-------.--, , , ,

I�

Characteristics a/Solar Photovoltaic Array

As the non- linear V- I and P- V characteristics are obtained of the solar photovoltaic system. On different irradiation and temperature, the change in maximum power and open circuit voltage is observed respectively. It can be concluded that the

, , ,

, , ,

i�� l I �\ o

10

20

Voltage (V)

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(d) Fig. 7: (a) to (d) P-V and I-V Characteristics at Different Irradiation and Temperature Level

[31


B.

Steady State Analysis of Photovoltaic Array 300 r-----�----�--�

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Time (Sec)

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.mmmmm.,.m·I �&O · · · · · · · · · · · · · · · · · · · ·1RCC.I �·T· · · · · · · · · t· · · · · · · · · T· · ·

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(e) Fig. 8: (a) - (e) Output Power, Current and Voltage of PV Array without MPPT

2.5

Time (sec)

3.5

4.5

(e) Fig. 9: Comparision of Output Current, Voltage and Power under P&O and RCC MPPT

In steady state, when the solar is connected directly to the load without any MPPT tracker, the constant power, voltage and current are observed with reduced magnitude. To track the maximum power that can be extracted from the solar panel, MPPT techniques are used. The obtained power is 67.6 W at 3 1.8 V and 2.12 A. C.

_

VII.

CONCLUSION

In this paper, P&O and RCC MPPT techniques are implemented to extract the maximum power from the solar panel. The transient and steady state analysis has been carried out for both the techniques and it can be concluded as: • Increase in irradiation level would result in increase in operating current, consequently maximum power increases and decrease in irradiation level would result in decrease in operating current, consequently maximum power decreases. • Increase in temperature would result in decrease in operating voltage consequently maximum power decreases and decrease in temperature would result in increases in operating voltage consequently maximum power increases. • The tracking of maximum power in different irradiation level in both perturb and observe and ripple correlation control technique are observed and found satisfactory.

Dynamic Response of P V Array Assisted by P &0

andR C C

P&O and RCC MPPT techniques are operated under two different irradiation level. At t=1.5s, the irradiation level changes from 1000 W/m2 to 600 W/m2.This would result in change in operating current, therefore maximum power is changes. Both are MPPT techniques tracks the change in power. It is observed that there is negligible change in operating voltage. At 1000 W/m2, the operating power was 200 W at 27 V and change in irradiation level results in 118 W of power at 26 V. The duty ratio of both the techniques are being compared for 1000 W1m2 irradiation and it is observed that the rate of convergence of ripple correlation control technique is greater than perturb and observe technique. [41

t 1s IEEE International Conference on Power Electronics, Intelligent Control and Energy Systems (ICPEICES-2016) • •

[4J

RCC results in greater rapid response and lower settling time compared to the P&O. The rate of convergence of RCC is found to be greater than the P&O. By taking very small step size, the ripple content in P&O and RCC is found to be nearly equal.

[5J

[6J

TABLE I: COMPARISON OF P & 0 AND RCC MPPT MPPT Technique Tuning Parameter Cost Effectiveness Tracking Time Complexity Level Ripple Content

P&OMPPT No Expensive 0.3 s More More

RCCMPPT Yes Inexpensive 0.2 s Less Less

[7J

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ApPENDIX: SPECIFICATIONS OF PV ARRAY Operating Parameters Short circuit current,Isc Current coefficient,Kt Nominal Temperature,Tn Open circuit voltage,Voc Voltage coefficient,K, electronic charge,q Boltzmann constant,k Diode ideality constant, a Light generated current at nomial conditions,la Series connected cells,Ns Nomiallrradiation,Gn Variation in Irradiation

Values 8.21 A 0.0032 NK 25°C 32.9 V -0.2130 V/K 1.6021x 10' C l.3806x I0'" J/K 1.2 8.214 A

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54 1000 W/m' 600-1000 W/m'

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