International Journal of Conceptions on Electrical and Electronics Engineering Vol. 2, Issue. 1, April 2014; ISSN: 2345 - 9603

33 | 7 1

Design of DC-DC converter based on CUK topology for PV system

Chirag Patel and Prof. H N Prajapati Electrical Engineering Department

L.D.R.P. – I.T.R. Gandhinagar, India.

chirag3.31891@yahoo.in and profprajapati@hotmail.com

Abstract— Photovoltaic power systems are becoming increasingly prevalent in distribution and generation systems. Many nations are installing significant solar power capacity in their grids as a supplement or alternative to other power sources. This project presents PV module with CUK converter for electrical applications especially for dc load application. In this paper the cuk converter and PV system is simulated AND hardware is made for it and results are presented.

Keywords- Solar PV module, Cuk converter, Matlab Simulink

I. INTRODUCTION A PV module is simulated and output is given to cuk

converter. A cuk converter proposed for analyzing the performance of photovoltaic system is only for smooth operation for dc output. In the proposed cuk converter, the conduction losses and switching losses are reduced. The switching techniques are to provide smooth transition of voltage and current at input and output. So, the conversion efficiency of the PV system is improved and the load meeting the dynamic energy requirement is in an efficient way. It has an advantage over other converting topologies since they enable low voltage ripple on both the input and the output sides of the converter. Then, the different operation mode of proposed cuk converter is analyzed at different operating condition. The proposed cuk converter implemented in MATLAB simulation platform and the output performance is analyzed in this report. The input and output result is shown in this project report. [11]

II. THE NON ISOLATED CUK CONVERTER There are variations on the basic Cuk converter. For

example, the coils may share single magnetic core, which drops the output ripple, and adds efficiency. Because the power transfer flows continuously via the capacitor, this type of switcher has minimized EMI radiation. [1] The Cuk converter enables the energy flow bidirectionally, by adding a diode and a switch. The basic circuit of a Cuk converter is shown in Fig.1 and as you can see it has an additional inductor and capacitor. The circuit configuration is in some ways like a combination of the buck and boost converters, although like the buck-boost circuit. It delivers an inverted output. Note that virtually all of the output current must pass through C1, and as ripple current. So C1 is usually a large electrolytic with a high ripple current rating and low ESR (equivalent series

resistance), to minimize losses. When switch is turned on, current flows from the input source through L1 and MOSFET, storing energy in L1. Magnetic field. Then when MOSFET is turned off, the voltage across L1 reverses to maintain current flow.

Figure1. BASIC CUK CONVERTER CIRCUIT

As in the boost converter current then flows from the input source, through L1 and diode, charging up C1 to a voltage somewhat higher than Vin and transferring to it some of the energy that was stored in L1. Then when MOSFET is turned on again, C1 discharges through via L2 into the load, with L2 and C2 acting as a smoothing filter. [7]

= −( )

III. CONTINUOUS CONDUCTION MODE In steady state, the energy stored in the inductors has to

remain the same at the beginning and at the end of a commutation cycle. The energy in an inductor is given by:

E = 퐿퐼 This implies that the current through the inductors has to

be the same at the beginning and the end of the commutation cycle.

VL = 퐿

International Journal of Conceptions on Electrical and Electronics Engineering Vol. 2, Issue. 1, April 2014; ISSN: 2345 - 9603

34 | 7 1

As the evolution of the current through an inductor is related to the voltage across it:

It can be seen that the average value of the inductor voltages over a commutation period have to be zero to satisfy the steady-state requirements. If we consider that the capacitors C and Co are large enough for the voltage ripple across them to be negligible, the inductor voltages become higher or lesser as describe below.

1. In the off-state, inductor L1 is connected in series with Vi and C Therefore. As the 푉L푖 = 푉푖 − 푉푐 diode D is forward biased (we consider zero voltage drop), L2 is directly connected to the output capacitor. VL2 = Vo

2. In the on-state, inductor L1 is directly connected to the input source. Therefore. 푙1 = 푉푖 Inductor L2 is connected in series with C and the output capacitor, so 푉푙2 = 푉표 + 푉푐

IV. SOLAR PHOTO VOLTAIC SYSTEM Solar or photovoltaic (PV) cells are made up of materials that turn sunlight into electricity. PV cells are composed of layers of semiconductors such as silicon. Energy is created when photons of light from the sun strike a solar cell and are absorbed within the semiconductor material. This excites the semiconductor’s electrons, causing the electrons to flow, and creating a usable electric current. The current flows in one direction and thus the electricity generated is termed direct current (DC).

Figure 2. PV PANEL

The shown panel is simulated in MATLAB and results are taken. The above panel is also tested on different irradiation of solar. For solar system the results are taking on 1000 푊

푚 This irradiation is according to standard. The open circuit voltage and short circuit current was measured by standard equipment. The simulation of PV panel in MATLAB is shown In figure 3 and the results of voltage and current on 1000 irradiation is shown in figure 4.

Figure 3. SIMULATION OF PV PANEL

Figure 4. VOLTAGE AND CURRENT OF PV PANEL

IRRADI-ATION

Voc

Isc

Vm

Im

1000

21.60V

2.27A

17.60V

2.05A

800

21.29V

1.81A

17.55V

1.61A

600

20.89V

1.36A

17.44V

1.19A

400

20.32V

0.98A

17.19V

0.76A

200

19.36V

0.45A

15.66V

0.35A

Solar panel is making with the help of thirty six cells in series combination. The rating of solar panel is 12V and 30W. The different results are presented here for different radiation of sun light. The testing was made on testing machine which make the test of solar panel on different radiation. The rating of

panel is decided on 1000 radiation.

International Journal of Conceptions on Electrical and Electronics Engineering Vol. 2, Issue. 1, April 2014; ISSN: 2345 - 9603

35 | 7 1

V. OPEN LOOP SIMULATION OF CUK CONVERTER The measurement devices connected in the basic circuit for measure the different parameter of cuk converter operation. This parameter remain constant for buck as well as in boost operation of this converter. The switching frequency and input voltage is same for buck operation and for boost operation.

Figure 5. THE SIMULATION CIRCUIT IN MATLAB

The input of cuk converter is the output of PV panel. Here

the pulse generator is use for Mosfet switching. The cuk converter is give buck operation as well as boost operation.

VI. BUCK OPERATION OF CUK CONVERTER

The buck operation is taken for different duty cycle but the best result is achieved at 45% duty cycle. Input voltage is 21.60V here the switching frequency is 5kH and the result is only for 45% duty cycle. The Output voltage is -16.69V. The negative sign shows the inverted output of cuk converter. Figure 6 shows the output voltage waveform. Figure 7 is waveform of current for 45% duty

Figure 6. OUTPUT VOLTAGE

cycle. The variation is negligible and it is stable in less time compare to other outputs. The ripple in output voltage and current is very less and smooth which is good for any DC load application.

Figure 7. OUTPUT CURRENT

The input power of cuk converter is 36.12W and output

power is 18.53W for buck operation of cuk converter. The output power is approximately half of input power. By changing its duty cycle we can regulate the power but the optimum output of cuk converter is at 45% duty cycle.

VII. BOOST OPERATION OF CUK CONVERTER The boost operation of cuk converter is achieved at higher than 50% duty cycle. Here the result of 63% duty cycle is presented for boost operation.

Figure 8. OUTPUT VOLTAGE FOR 63% DUTY CYCLE

International Journal of Conceptions on Electrical and Electronics Engineering Vol. 2, Issue. 1, April 2014; ISSN: 2345 - 9603

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Figure 9. OUTPUT CURRENT FOR 63% DUTY CYCLE

The output voltage is -37.94V. Here the negative sign is for inverted output of cuk converter. The output current for boost operation is -2.52A. The output is very smooth and stable in less time. It take less than 0.09sec for become stable. Input power is 36.12W and output power is 95.60W for boost operation of cuk converter.

VIII. HARDWARE OF CUK CONVERTER

Figure 9. HARDWARE OF CUK CONVERTER

The hardware of cuk converter is prepared for 30W system and it is work properly and best output is achieved at 45% duty cycle for buck operation. And for boost operation the best result is achieved at 63% duty cycle.

The table of hardware result is presented here and compare with other duty cycles.

Here the voltage fluctuation is measured by DSO and calculation for fluctuation is carried out. The buck and boost operation of cuk converter is achieved but we got negative output. The inverted output is basic property of cuk converter.

DUTY

CYCLE

SWITCHING

FREQUENCY

INPUT

VOLTAGE

OUTPUT

VOLTAGE

VOLTAGE FLUCTUATE

20% 5kHz 18.54 V - 3.53 V 1.52%

45 % 5kHz 18.69 V - 17.33 V 1.12%

63 % 5kHz 18.53 V - 45.28 V 1.52%

65% 5kHz 18.51 V - 53.56 V 1.67%

VIII. CONCLUSION By performing the simulation of cuk converter it is

concluded on the basis of system performance that the output of cuk converter is change with duty cycle. The buck and boost operation is achieved in cuk converter by changing the duty cycle. Cuk converter gives buck operation for less than 50% duty cycle and gives boost operation for more than 50% duty cycle. It is found by system performance that the best performance of cuk converter is at 45% duty cycle for buck operation and 63% duty cycle for boost operation. At this duty cycle the output voltage regulation is minimum, the ripple in output is very less and output is becomes stable in less time compare to other outputs. The hardware result shows the best result of cuk converter.

REFERENCES [1] R.sriranjani, A.Shree Bharathi, S.Jayalalitha, “Design of Cuk

converter Powered by PV array” 6(5):793-796, sept 2013

[2] Neeraj Tiwan, D. Bhagwan Das(IJATER), “MPPT controller for photo voltaic system using Cuk DC/DC converter” volume 2, Issue3, 165-169,2012

[3] Lekshmy Rajan U, R.Pradeep, “Performance Analysis of Maximum Power Point Tracking based Photovoltaic Module with Cuk Converter for Electrical Applications”. Volume 1, issue 1, April 2013

[4] M. manikanda prabhu, Dr. A. Manivanna “Modeling and Performance Analysis of PV Panel Using Incremental conductance Maximum Power Point Tracking” Volume 2, Issue 3, March, 2013

[5] Cuk,S.: Coupled inductor and integrated magnetics techniques in power electronics. Proceeding, of IECE, japan, 1983.pp. 347-352

[6] M.Vaigundamoorthi, R.Ramesh, “Experimental Investigation of Chaos in Input Regulated Solar PV Powered Cuk Converter” Volume 43– No.10, 0975 – 8887, April 2012

[7] K.Kavitha*, Dr. Ebenezer Jeyakumar, “A Synchronous Cuk Converter Based Photovoltaic Energy System Design and Simulation” International Journal of Scientific and Research Publications, Volume 2, Issue 10, October 2012

[8] Electronics Handbook Devices, Circuits, And Applications Third Edition By Muhammad H. Rashid, Ph.D.