Study the Performance of Solar PV Array under Partial ...

Jour of Adv Research in Dynamical & Control Systems, Vol. 10, 04-Special Issue, 2018

Study the Performance of Solar PV Array under Partial Shadow using DC- DC Converter Shaik Ilahi,Student, Department of Electrical and Electronics Engineering,K L E F M.Seetha Ramaiah, Student, Department of Electrical and Electronics Engineering, K L E F. T. Vijay Muni, Department of Electrical and Electronics Engineering, Koneru Lakshmaiah Education Foundation, Vaddeswaram, Guntur, Andhra Pradesh, India. K.Ganesh Naidu, Student, Department of Electrical and Electronics Engineering, K L E F. Abstract---Solar PV module is the power generation unit for photovoltaic. The paper deals with the solar PV array under partial shading condition using dc-dc converter with MPPT technique incremental conductance method. The main aim is to maintain the constant load at the grid side. Sun Power SPR-305-WHT-U solar panel is taken as reference. Sometimes on solar panel partial shadow may occur within that duration we get the low voltage and output power will decreases, with in that time also have to maintain the constant voltage, for that we are using the boost converter.In this MPPT is used to maintain impedances, while taking the Pmax solar impedance must match with the load (or) grid to maintain constant voltage .The duty ratio is changed time to time and to maintain the constant output voltage to system.Here the Bypass diode is replaced by boost converter using MPPT technique. Keywords---Boost converter; Solar panel; MPPT technique; Partial shadow effect.

I

Introduction

In day to day life the people are consuming the power in large quantity, so the power demand is very high in these days. Due to lake of resources the people cannot meet the demand, so by using renewable energy resources like solar and wind energy the demand can be met by the people. Solar energy is the primary source in renewable resources. Solar energy is used as generating unit or grid connected unit. If grid is near to solar we can directly connect to grid. In some urban areas grid is far away, so people can used solar energy as generating unit. Due to partial shading we get low voltage and low output power. So, to reduce this disadvantage so in his paper we are maintaining constant voltage and power to grid. This is done by using boost converter with MPPT technique with incremental conductance method [1]. Here tracking the maximum power is main purpose [2].In some applications there are curved roofs, flat roofs so we have to use flexible photovoltaic pv modules. To maximize the power of flexible photovoltaic pv modules a scanning window technique is used.When conductance is greater than zero then power increases. When conductance is less than zero then power decreases [3]. Under partial shadow effect the P-V and IV curves will decrease when compare to normal conditions [4]. The purpose of boost converter is it step up the output voltage of pv cells which is low [5].It consists of current Source, diode, resistor which are connected in parallel and all these are connected series with resistance [6]. The main objective of the 3-level inverter is to converter DC to AC. In the project the output power of solar panel is DC, so we are using inverter to convert it to AC because to get output power of grid. This is mainly used for high voltage direct current transmission lines.

Modeling Of System a) MAXIMUM POWER POINT TRACKING MPPT is implemented by using incremental conductance method. Here the pulses are given by pulse generator using PWM technique. The duty ratio is changed by MPPT and gives to pulse generator by this we get pulses. The incremental conductance method is built by using matlab code in matlab. In the incremental conductance method, the controller measures changes in photovoltaic array voltage and current using which the effect of change in voltage is predicted. If we use perturb and observe method, it can’t track the maximum power point ISSN 1943-023X Received: 5 Mar 2018/Accepted: 10 Apr 2018

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very quickly.but incremental conductance method can track changing conditions very quickly. When conductance is greater than zero then power increases at that time voltage also have to increase. When conductance is less than zero then power decreases at that time voltage have to decrease. So this method is preferred.The figure 2 shows the flow chart of incremental and conductance method. b) INCREMENTAL CONDUCTANCE METHOD At the instant of k voltage(v) and current(i) values are measured.Now the value of (delta)V and (delta)I values are calculated from the equation V(k)-V(k-1) and I(K)-I(k-1).Now the value of delta(v) is accessed to be zero. if the value of (delta)V and (delta)I are zero. then it is in the normal condition and once again the values are measured.Else if (delta)V value is not equal to zero then the value of ratio for the values of (delta)I and (delta)V are equated to (-I/V) and once again values of I and V are measured.If the value of ratio (delta)I and (delta)V is greater than –I/V then the operation of decreasing the value of Vreference is done.Else the value ratio of (delta)I and (delta)V is less than -I/V then the operation of increasing the value of Vreference is done.When the value of (delta)V is equal to zero and the value of delta I is not equal to zero then the value of Vreference is decreased else delta I is equated to zero then the value of Vreference is increased. P = V*I(1)

(2) Maximum power

(3)

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INPUT V(k) AND I(k)

∆V = V(k) - V(k-1) ∆I = I(k) - I(k-1)

Yes

No

∆I/∆V = -I/v

Yes

∆I = 0

No

No

∆I/∆V >-I/V Yes Decrease Vref

Yes

∆V = 0

∆I = 0 No

No

Yes Decrease Vref

Increase Vref

Increase Vref

RETURN

Fig.1: Flow chart of incremental conductance algorithm The electromagnetic launchers are generally classified into two different types, they are the rail guns and the coil guns where each has its own importance in different applications. The rail guns are generally used in applications which require to displace the launchers of small masses with a higher terminal velocity whereas coil guns are used in applications which require launchers of greater masses to be displaced with relatively low speeds. Both the names of the launchers will describe or give the basic idea of their working principle, the rail gun will generally consists of two parallel conducting rails along which the projectile is driven, these rails are energized by a DC source. The performance analysis of the rail guns was discussed in [1] using finite element method and the various methods that can be implemented in improving the efficiency of the rail guns was discussed in [2]-[4].The design parameters and the various aspects related to the rail dimensions was discussed in [5] and the power supply for the rail guns using switched inductor based pulsed method was proposed in [6].The evolution of coil gun began later than that in rail guns. In the electromagnetic propulsion based coil gun system, the projectile is propelled by the electromagnetic force caused by the electric current that will be energizing the electromagnetic solenoid coils. There are different forms in which a coil gun occurs but the basic operation of these is fundamentally the same. The coil guns are generally classified into two types based upon their operation as synchronous and induction coil guns and the coil gun electromagnetic launchers are generally classified as synchronous co-axial launchers,travelling wave launchers, induction coil launchers [7],single stage launchers. The comparison among the types of the electromagnetic launchers was discussed in [8].

II Proposed Methodology a) BOOST CONVERTER Here figure 2 shows the circuit diagram of DC-DC converter that is boost converter. the boost converter main purpose is to step up the voltage level that means it doubles or makes more than double the output voltage of solar panel. The operation of this converter is when switch is in ON condition the current flows from source to inductor, switch and to source that means it flows in form of loop. When switch is in off condition the current flows from source to inductor, diode, capacitor and load. The DC output voltage is obtained by adding input voltage and inductor voltage. The output voltage of the boost converter is given by the equation 4.

(4)

The duty ratio of the boost converter is given by the equation 5. ISSN 1943-023X Received: 5 Mar 2018/Accepted: 10 Apr 2018

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(5)

The output voltage in terms of input voltage and duty cycle is given by the equation 6. (6) The main moto of this paper being to set the value of D. so we are using boost converter to set the value of the D. it is Clear that the value of output voltage can be adjusted from the values of Input which are being provided in and also from the output equation boost converter it is possible to vary the value of the D. Depending upon the values which are given input with the help of the algorithm in the figure 2 It is possible to control the D by which the value of output voltage result is decided (eqn5) as the Solar irradiance is not a constant value,output voltage is Varying continuously so the amount of output voltage should be kept constant. this is achieved by using boost converter or and three level inverter in boost converter by controlling d and taking the input values from the converter and MPPT arranged incremental methods transient voltage,V d are decided.

PWM

MPPTINCRIMENT AL METHOD

D(duty cyclle) Pulses

Q4 Q8

Q4 Q10

Q4

Q3

Q5 Q3

Q5 Q3

Q5

Q11

Q4

Q12

Q4 Q13

Q4

Q3

Q5

Q3

Q5 Q3

Q5

LOAD

Ipv Q1 C1

SOLAR PV ARRAY

Q2

BOOST CONVERTER

r

y

AC AC

b

AC

Fig 2: -schematic diagram b) THREE LEVEL INVERTER Here the solar output is DC, so the inverter converts to AC then us get AC output waveforms from the DC. As irradiance of sun fluctuates the amount of irradiance fall on solar panel also fluctuates because constant DC voltage is not available.To provide constant output DC voltage which is essential part for inverter to deliver clean sine output AC voltage.It is necessary to maintain a constant DC voltage which has been successfully attained by using boost converter and algorithm fig [2]. Now conversion of dc voltage to ac voltage is can be done by using numerous inverters.but 3 level H bridge inverter occupies its stance.In solar DC to AC conversion H bridge has several input DC voltages emerging Cascaded h bridge multilevel inverter with sinusoidal PWM techniquehas very less amount of THD and selected waveform pattern harmonic spectrum,noise in output voltage.More over the quality of that time switching in H bridge gives accurate sinewave because of all above readings H bridge is opted as inverter in this paper. In photovoltaic array the PV modules are connected in series and parallel according to our power and voltage values. It consists of current source, diode, resistor which are connected in parallel and all these are connected series with resistance. Here the parallel resistance represents leakage current and series resistance represents voltage drop. The parallel and series ISSN 1943-023X Received: 5 Mar 2018/Accepted: 10 Apr 2018

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Resistances can be neglected because these are very small. The figure 3 indicates the equivalent circuit diagram of solar cell. The table 1 indicates the solar panel ratings.The table shows the specifications and ratings of solar panel .The equivalent circuit of solar cell.

Ii

Ipv

Rs Ish

Id D Rsh

Fig3: - solar cell The output current of solar cell is given by the equation 7.

(7)

Ipv = Ii - Id – Ish

The diode current is given by the equation

   Vd  I d  I o  exp    1  (8)  VT    The open circuit of solar cell is given by the equation 9.

V oc 

kT  IL  ln   1  (9) q  Io 

Here K is Boltzmann’s constant. T is temperature, q is electron charge, and Io is saturation current. The solar cell output depends on irradiance and temperature. Here solar irradiance and Temperature is connected to solar panel. Here the solar irradiance is varied due to partial shadow and temperature is kept constant. The PV array is connected to boost converter by in which MPPT is implemented by using incremental and conductance method. Here the pulses are given by pulse generator. The duty ratio is changed by itself and gives to pulse generator by this we get pulses using pwm technique. The incremental and conductance method is built by using mat lab code in mat lab. In the incremental conductance method, the controller measures changes in photovoltaic array voltage and current this can predict the effect of change in voltage. If we use perturb and observe method, it can’t track the changing condition very quickly, but incremental conductance method can track changing conditions very quickly. So this method is preferred. The solar panel Ratings are given below in following table 1. Table1: Panel ratings Specification Maximum Power (W) Voltage at maximum power (Vmp)

Ratings 305.226 54.7

Current at maximum power (Imp) Open circuit voltage (Voc)

5.58 64.2

Short circuit current (Isc) Cells per module (Ncell)

5.9 96

III Results And Discussion ISSN 1943-023X Received: 5 Mar 2018/Accepted: 10 Apr 2018

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Fig 4: - IV Curve

Fig 5:- PV curves


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Fig 6:- IV and PV curves of solar cell The above figure shows the graph between current vs voltage and power vs voltage.The IV curve indicates that current starts from some point and it is constant to some extent and slowly decreases to zero.The PV curve indicates that power starts from zero and goes on increasing and slowly decreases to zero

Fig 7:-boost converter The above figure shows the output voltage of boost converter.It is boosted up to 1 sec.From graph it is observed that voltage is around 790.Is this region from 0 to 0.1 voltage is transient and this transient state could heavily affect the conversion of DC to AC inverter.After transient state a steady state is observed. But even though the voltage seems to be stable because of some uncertainty.The voltage is not constant and some deviation can be observed from 0.7 to 0.9.


1012


Fig 8:- 3-level inverter graph The above figure shows the output voltage waveform of three level inverter.The voltage is tripping from -1000 to 1000 and around 700.The time duration is 0 to 1 sec.At 0.5 sec the voltage is in transient condition and after 0.5 to 1sec it is in steady state.

Fig 9:- output voltage and current graphs with time The above figure shows the output voltage and output current waveforms of the grid.The grid is AC, so we get sinusoidal wave form.The figure shows the output waveforms of voltage and current.Here the output of voltage is constant, and we can’t control the voltage.The current Is also in sinusoidal waveform.At the initial stage the current is in transient condition and after some time it will comes to steady state.

IV Conclusion A model in MATLAB/Simulink for solar pv cells to decrease the effect of voltage fluctuations due to partial shadow in successfully removed using boost converter with MPPT technique and a special algorithm. That would constantly monitor the output of this PV panel. Thus, by providing constant to supply DC voltage to inverter H bridge there by delivering output sinusoidal waveform which could be converted to grid which reduce effect of old model photovoltaic partial shadow effect. The output of Simulink model is constant voltage and adversely transient less current always small amount of transient is observed at initial stage which is less than 0.1 second it is steady state after that. For the more this model would provide a great effective tool to minimize the extreme voltage fluctuations for voltage fluctuations for even small changes of irradiance. In addition to that usage of MPPT technique ensures ISSN 1943-023X Received: 5 Mar 2018/Accepted: 10 Apr 2018

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that maximum power is always must to be available at the grid side. This model could be sufficient installed in individual homes.

V References [1] T.Esram, P.L.Chapman,”comparison of photovoltaic array power point tracking techniques”, IEEE Trans. on energy conversion. [2] DivyaTeja Reddy Challa1, Raghavendra, „ Implementation of Incremental Conductance MPPT [3] B. Liu, S. Duan, F. Liu, and P. Xu: Analysis and improvement of maximum power point tracking algorithm based on incremental conductance method for photovoltaic array. In Proc. IEEE PEDS, 2007, [4] A. Barchowsky, J. P. Parvin, G.F. Reed, M. J. Korytowski, B.M. Grainger, “A Comparative Study of MPPT Methods for Distributed Photovoltaic Generation”, Conference Publications, Innovative Smart Grid Technologies (ISGT), 2012 IEEE PES, 2012 [5] Bratcu, A.I. Munteanu, I.Bacha, S. Picault, D. ; Raison, B. , “Cascaded Dc-Dc Converter Photovoltaic Systems: Power optimization Issues” Industrial Electronics, IEEE Transactions [6] .R.Sridhar, S.Jeevanantham,S.S.Dash,N.ThamizhSelvan,”united MPPT Controller for Partial Shaded Panel in a Photovoltaic Array”,International Journal of Automation and Computing.


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