Modelling and Analysis of SEPIC using DVR for Solar PV System

Modelling and Analysis of SEPIC using DVR for Solar PV System

Dr. S. N. V. Ganesh B. Gayatri Subhadra

Head of the Department Power Electronics Division Sri Sivani College of Engineering Sri Sivani College of Engineering

Chilakapalem Chilakapalem

Srikakulam (Dist.),India Srikakulam (Dist.),India

Abstract: Dynamic Voltage Restorer (DVR) is a series controller which has capability to control voltage profile at the load end under all operating conditions. The device is mainly used in distribution system with low and medium voltages. The controller has now much importance (due to its capability in maintaining power quality) as most of the loads are becoming very sensitive to power quality events like voltage sags, swells etc. However energy storage requirement has put limitations on high power rating of DVR. This project tries to find a solution to energy storage limitations: renewable sources. The project proposes modelling of PV array, Single Ended Primary Inductive Coil (SEPIC)/Boost converter for mitigating voltage disturbances using DVR. Performance of DVR will be investigated using motor load.

Keywords: Solar Photovoltaic, SEPIC, Power Quality, DVR

1. INTRODUCTION:

   Now a days electrical energy plays a major role in day to day life of humans. For giving the supply voltage to DVR, in this project renewable energy sources are used. In this project Solar

   represented by a current source connected parallel with diode as shown in Fig. 1.

   Fig 1: Electrical Model of a PV cell

   By writing the equation for the PV circuit using the Kirchhoffs current law for current is,

   Energy is used as a source of energy for supplying the supply

   =

   ……………(1)

   voltage to DVR. In this solar energy is converted into electrical energy. From the Photo Voltaic array we can get low voltage, so we have to increase this voltage. For this purpose Single Ended Primary Inductor Converter (SEPIC) is used in this project. SEPIC converter can acts as both Buck converter and Boost converter. It has a switching device MOSFET, by adjusting the

   gating signals of MOSFET we can get the desired output

   Where, is the light generated current in the cell

   is the voltage dependent current lost to recombination

   is the current lost due to shunt resistance The diode model equation is represented as,

   V IRS

   voltage. For the purpose of controlling PI controller is used in

   ID I 0 exp

   nV 1

   …………..(2)

   this converter. The output of the SEPIC converter is given to the DVR as input. When there is any voltage sags or swells the DVR injects the missing voltage. By connecting different loads we can find out the performance of the DVR. This work is done in MATLAB/SIMULINK.

2. PHOTO VOLTAIC SYSTEM:

   The Solar-PV cells are used to produce electricity by directly converting solar energy to electrical energy. Each solar cell is basically a p -n diode. As

   T

   Where, n is the diode ideality factor

   I0 is the diode saturation current

   VT is the thermal voltage

   Now, the equation for the PV module is expressed as,

   m m S S m m S S

   m m S S m m S S

   V I N R V I N R

   Im I L Io exp 1

   sunlight strikes a solar cell, the incident energy is converted directly into electrical energy without any

   nN

   SVT

   NS Rp

   mechanical effort. The voltage and current levels are produced from PV cells are very less, thus these PV cells are connected in series and parallel called modules and arrays to produce required voltage and current levels. The solar PV array is modelled by considering the output characteristics of PV panel which directly have relation with power converters which exists in the system. The solar PV cell is a non linear device which can be

   Where, NS is the identical number of series cells

   Vm is the module voltage and Im is the module current

   The equation (3) is simulated using MATLAB/Simulink and P-V and I-V characteristics are obtained. The operating curves shows that solar PV output power is function of solar irradiation. Fig. 2 shows I -V and P-V

   characteristics of a one PV module. The specification of a solar PV module for grid connected solar PV system is given in Table I.

   Design of SEPIC converter:

   For closed loop simulation we go for state space transfer function. For SEPIC the input to output relationship and associated signal state relationship can be represented as,

   VOUT

   Vin

   D

   (1 D)

   D2V

   I L1

   in

   (1 D)2 R

   V V L

   I L2

   C1 in

   D Vin

   (1 D) RL

   VC 2

   D Vin

   (1 D)

   Fig 2: PV and IV characteristics

   Now, duty cycle to output relationship can be expressed as,

   Where,

   V X S 3 X S 2 X S X

   6

   6

   7

   7

   out (S ) 1 2 3 4 *Vin

   Parameters	Values
   Irradiation	1000W/m2
   Short circuit current	5.45A
   Open circuit voltage	22.2V
   Current at Pmax	4.95A
   Voltage at Pmax	18V

   Parameters	Values
   Irradiation	1000W/m2
   Short circuit current	5.45A
   Open circuit voltage	22.2V
   Current at Pmax	4.95A
   Voltage at Pmax	18V

   D X 5

   S 4 X

   S 3 X

   S 2 X

   8 S X 9

   ..(4)

   1

   1

   X L1C1L2D 1.4557 *1011

   X 2 L1C1RL

   D2 7.3062 *1011

   Table 1: Parameters of the PV system

3. SEPIC:

   5

   5

   L

   L

   It is a converter which can converts the DC voltage from one level to another level that means it can

   X D2 L1 3.645*103

   3

   3

   4

   4

   X D2 R 21.573

   step-up or step-down the output voltage by varying the Duty cycle of the MOSFET. It has advantages like low component stresses, low energy storage requirements,

   X (1 D)2 L1C1L2R

   7.9128*1015

   compact in size and the efficiency also high compared to Buck-Boost converter. The circuit diagram of SEPIC is shown in fig.2;

   L11

   L11

   C1

   X (1 D)2 L1C1L2 3.966 *103

   6

   6

   X 7 (1 D)2 RL[L1C1(1 D)2 L2C2(1 D)2 L2C1(1 D)2 L1C2D2]

   8

   8

   9

   9

   L

   L

   DC Voltage Source

   m

   S

   m

   S

   g

   D

   g

   D

   Mosfet

   Diode

   R

   L2 C2

   X (1 D)2 [L2(1 D)2 L1D2 ] 8.6923*105

   Terminator

   X (1 D)4 R

   0.01601

   Fig .3. Circuit diagram of the SEPIC converter

   V out (S)

   V

   Y S 2 Y

   1 2

   1 2

   Y S 4 Y S 3 Y S 2 Y S Y

   ………(5)

   in 3 4 5 6 7

   Where,

   Y1 L2C1RL

   (1 D) 1.5443*108

   cost will depends on the power rating and other equipments.

   Y2 D(1 D)

   RL 3.8668

   DVR works independently on the type of fault or any event that happens in the syste, provided that the total

   Y3 L1C1L2C2RL

   3.4249 *1013

   system is remains constant and it is connected to the supply grid i.e., the line circuit breaker does not trip. For

   4

   4

   Y L1C1L2 1.7167 *1011

   L

   L

   5

   5

   Y R [L1C1(1 D)2 L2C2(1 D)2 L2C1(1 D)2 L1C2D2 ]

   7.5061*105

   most practical cases, a more economical design can be achieved by only compensating the positive and negative sequence components of the voltage disturbances seen at the input of the DVR. Because of infinite impedance the zero sequence component does not pass through the step- down transformer.The injected voltage of the DVR can be

   6

   6

   Y L1D2 L2(1 D)2 3.7622 *103

   expressed as,

   V

   V V

   …………..(8)

   Y R (1 D)2 0.69312

   inj

   La Sa

   L

   L

   By substi7tutingLthe L1, L2, C1, C2, R and D values we can get that input to output relationship,

   Where,

   VLa is the desired load voltage magnitude

   Vout

   1.5443*108S 2 3.8668

   VSa is the source voltage during disturbance

   (S)

   Vin 3.4249*103S 4 1.7167*1011S3 7.506*105S 2 3.7622*103S 0.69312

   The load current ILa is given by,

   …(6)

   PLa QLa

   V

   V

   I

   I

   La

   La

   …………..(9)

   By using the above transfer function we can get the desired output voltage.

   1. SIMULATION AND RESULTS

      The simulation circuit shown in below fig.3. Comprises of system with 3-phase programmable voltage source with an A.C voltage of 440V, 50Hz. Here, asynchronous machine is placed as a load replacing with the resistive load. Here, the fault is placed in the 3-phase programmable source with a time period of 0.3 to 0.4 in the total simulation time (0.5).

      Element	Value
      Supply Voltage	107V
      Inductor, L1	5.069mH
      Inductor, L2	5.069mH
      Capacitor, C1	668.13pF
      Capacitor, C2	665µF
      Diode Voltage drop, VD	0.8V
      Resistance, R	33.33
      Buck Output Voltage	52V
      Boost Output Voltage	602V

      Element	Value
      Supply Voltage	107V
      Inductor, L1	5.069mH
      Inductor, L2	5.069mH
      Capacitor, C1	668.13pF
      Capacitor, C2	665µF
      Diode Voltage drop, VD	0.8V
      Resistance, R	33.33
      Buck Output Voltage	52V
      Boost Output Voltage	602V

      A Vabc

      A Iabc

      N B B a

      b

      b

      C C c

      1. Vabc Tm

         Iabc A

      2. a m

         b B

      3. c C

   Table 2: SEPIC elements and its values

4. DYNAMIC VOLTAGE RESTORER:

DVR is a series controller which is used to compensate voltage sags and swells. DVR is used for short time faults

PV array

Continuous

Continuous

A B C

A B C

powergui

Three-Phase Programmable Voltage Source

g

+

+

+

A A A

s

–

s

–

C V S B B B

– C C

1. Vabc Iabc

2. a

   A1+ A1 B1+ B1 C 1+ C1

   A1+ A1 B1+ B1 C 1+ C1

   Gain2

   A2+ A2 B2+ B2 C 2+ C2

   A2+ A2 B2+ B2 C 2+ C2

   -K-

   Vabc

   PQ

   Iabc

   Scope5

   Asynchronous Machine pu Units

   only. DVR injects the voltage in phase to the supply. So,

   num(s)

   V

   1.2

3. b

C c

Discrete

3-phase

Instantaneous

that it can maintain a good power quality profile at the

den(s)

SEPIC

Gain1

PWM Generator Active & Reactive Power1

A B C

A B C

Unit Delay

load. DVR contains a Voltage Source Converter (VSC), an Energy Storage System, an Injection Transformer and a LC-Filter. In this VSC will convert the DC into AC and by this converting process it will produce some

harmonics. To reduce these harmonics we use an LC-

PV Array

Scope7

Scope1

node 10 node 10

Vabc (pu) Sin_Cos

node 10

1

Pulses Uref

z

Gain

-K-

A B C

A B C

Vabc Iabc

Scope3

PQ

Scope4

Filter and it doesnt allow harmonics across it. Filter is connected in between the VSC and Injection

Discrete

3-phase PLL1

Scope2

dq0

3-phase Instantaneous

Active & Reactive Power

Transformer. Injection Transformer will inject the voltage in series with the supply lines. Depending on the

A A Vabc

a

N B B

b

C C c

abc

sin_cos

dq0

abc

abc

sin_cos

-K-

Vabc

PQ

compensation the storage of energy will be stored and for energy storage capacitors and batteries are used. In this

Three-Phase Programmable Voltage Source1

sin_cos

dq0

Gain3

Iabc

3-phase Instantaneous

Scope6

DVR we use fast switches, due to these fast switching

operations we can get the desired output. By using fast switches the cost of the DVR will increases and the DVR

Active & Reactive Power2

Fig.4. Simulink model of the system with motor load

Source Voltage

Voltage in pu

Voltage in pu

1

0

-1

0 0.1 0.2 0.3 0.4 0.5

Voltage in pu

Voltage in pu

Load Voltage

1

0

-1

0 0.1 0.2 0.3 0.4 0.5

DVR injected Voltage

Voltage in pu

Voltage in pu

0.5

0

-0.5

0 0.1 0.2 0.3 0.4 0.5

Time (secs)

Fig .5. Output waveform of system with motor load in sag condition

VII. REFERENCES

1. Binod Kumar Padhi and Anirudha Narain, Controller Design For SEPIC Converter Using Model Order Reduction ASAR International Conference, Bangalore Chapter- 2013, ISBN: 978-81-927147-0-7.

2. R. W. Erickson and D. Makdimovic, Fundamental of Power Electronics, 2nd ed., Kluwer Academic Publishers, 2001.

3. Anwar Sahbela, Naggar Hassanb, Magdy M. Abdelhameedb, Abdelhalim Zekryb Experimental Performance Characterization of Photovoltaic Modules Using DAQ TerraGreen 13 International Conference 2013 – Advancements in Renewable Energy and Clean Environment.

4. Godsk Nielsen Design and Control of a Dynamic Voltage Restorer by John Copyright c 2002, ISBN: 87-89179-42-0.

5. A. P. Torres1, P. Roncero-Sanchez2, Design and Comparison of Two Control Strategies for Voltage-sag Compensation using Dynamic Voltage Restorers BY X.del Toro Garcia2, V. Feliu2. http://dx.doi.org/10.5755/j01.eee.19.6.4553.

6. M. Ramasamya*, S. Thangavelb Photovoltaic Based Dynamic

4

x 10

15

Power (W)

Power (W)

10

Source Power

Voltage Restorer with Outage Handling Capability Using PI Controller BY © 2011 Published by Elsevier Ltd.

5

0

-5

0 0.1 0.2 0.3 0.4 0.5

4

4

x 10 Load Power

15

Power (W)

Power (W)

10

5

0

-5

0 0.1 0.2 0.3 0.4 0.5

Time (secs)

Fig.6. Output power waveform of system with motor load in sag condition.

VI. CONCLUSION

In this project SEPIC modeling is presented briely. The open loop and closed loop simulations are presented. A DC 600V output is obtained from only 107V as input. It is observed by varying duty cycle and output also changes, duty cycle above 50% it operate as a boost converter and below 50% it act like a buck converter. A current input PV model is developed using Matlab/Simulink in modeling. By this model the I-V and P-V characteristics are obtained.

The project proposes modeling of PV array, Single Ended Primary Inductive Coil (SEPIC)/Boost converter for mitigating voltage disturbances using DVR. Performance of DVR was investigated.