DESIGN AND ANALYSIS OF INTERLEAVED BOOST CONVERTER FOR ...ijcns.com/pdf/ijpcscvol5no2-6.pdf ·...

International Journal of Power Control and Computation(IJPCSC) Vol5.No.2 2013 pp 34-41

available at: www.ijcns.com Paper Received :05-05-2013

Paper Accepted:28-05-2013 Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami

Editor : Prof. P.Muthukumar

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DESIGN AND ANALYSIS OF INTERLEAVED BOOST CONVERTER FOR PHOTOVOLTAIC MODULE

K.E.Lakshmi Prabha1, Thangapandian.R2 Assistant Professor1, PG Student2

Karpaga Vinayaga College of Engineering and Technology1, 2 [email protected], [email protected]

Abstract- Solar energy is derived from solar radiations that are replaced constantly. An appropriate DC-DC converter is suggested for very effective solar energy systems. Interleaved Boost Converter (IBC) concept is used in this paper for photovoltaic module applications. The advantages of interleaved boost converter related to the conventional boost converter are low input current ripple, high efficiency, faster transient response, reduced electromagnetic emission and improved reliability. This paper focuses on a two-phase IBC's with (i) the front end inductors magnetically coupled (ii) uncoupled inductors and (iii) inversely coupled inductors performance have been analyzed and related for three types of IBC. Based on the output voltage ripple, input current ripple and inductor current ripple of the three types of converters are compared. The waveforms of input, inductor current ripple and output voltage ripple are achieved using MATLAB/Simulink. From the simulation results, the best of the three types of IBC is concluded. Keywords: DC-DC Converter, Uncoupled, Directly coupled, inversely coupled, ripple.

I. INTRODUCTION

For many years, fossil fuel has been the primary source of energy. However, there is a limited supply of these fuels on Earth and they are being used much more rapidly than they are being created. Eventually, they will run out. In addition, because of safety concerns and waste disposal problems, renewable energy is definitely the solution since such technology is “clean” or “green” because they produce few if any, pollutants. The world trend nowadays is to find a non-depletable and clean source of energy. The most effective and harmless energy source is probably solar energy, which for many applications is so technically straightforward to use. With the exception of nuclear and geothermal, all forms

of energy used on Earth originate from the sun’s

energy. Solar energy is considered one of the most promising energy sources due to its infinite power. Thus modern solar technologies have been penetrating the market at faster rates. The solar technology that has the greatest impact on our lives is photovoltaic. Not in terms of the amount of electricity it produces, but because of the fact that photovoltaic cells – work silently, not polluting – can generate electricity wherever sun shines, even in places where no other form of electricity can be obtained. The word Photovoltaic is a combination of the Greek word for light and the name of the physicist AlessandroVolta It detect the direct conversion of sunlight into electricity by means of solar cells. The proper converter is designed for photovoltaic module applications. The Interleaved boost converter has high voltage step up, reduced output voltage ripple, low switching loss, faster transient response. Also, the steady-state voltage ripples at the output capacitors of IBC are reduced. Although IBC topology has more inductors increasing the complexity of the converter correlated to the classical boost converter it is chosen because of the low ripple content in the input and output sides. In order to decrease this complexity, this paper considers the aids of coupled, uncoupled and inversely inductors for IBC. Complete analysis has been done to study the ripple content of all the three types of the converter. The proper IBC for photovoltaic module application is suggested. Switching pulses are generated using pulse generator.

II. BLOCK DIAGRAM

The block diagram representation of proposed system is shown in figure1.





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Fig. 1 Block Diagram Representation of Proposed System

In this proposed system, the sunlight is incident on the solar panel or module, and then the dc voltage is produced. This voltage is fed into the interleaved boost converter for step up the dc voltage. For e.g. 12V to 70V. The Controller is used for generating the control signals to turn on/off of the power switches present in the converter circuit to get the desired output voltage. The output voltage of the DC-DC converter is given to the filter circuit for regulating the dc voltage. This regulated dc output is given to the dc load. This proposed system consists of following components. They are Photovoltaic module, Interleaved Boost Converter, Controller, DC filter, DC load.

A. Photovoltaic Arrangement Photovoltaic Cell

PV cells are made of semiconductor materials, such as silicon. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current - that is, electricity. This electricity can then be used to power a load. A PV cell can either be circular or square in construction. Photovoltaic Module

Due to the low voltage generated in a PV cell (around 0.5V), several PV cells are connected in series (for high voltage) and in parallel (for high current) to form a PV module for desired output. Separate diodes may be needed to avoid reverse currents, in case of partial or total shading, and at night. The p-n junctions of mono-crystalline silicon cells may have adequate reverse current characteristics and these are not necessary. Reverse currents waste power and can also

lead to overheating of shaded cells. Solar cells become less efficient at higher temperatures and installers try to provide good ventilation behind solar panels. Photovoltaic Array

The power that one module can produce is not sufficient to meet the requirements of home or business. Most PV arrays use an inverter to convert the DC power into alternating current that can power the motors, loads, lights etc. The modules in a PV array are usually first connected in series to obtain the desired voltages; the individual modules are then connected in parallel to allow the system to produce more current.

B. Interleaved Boost Converter

Interleaved boost converter has been studied in recent years with the goal of improving power converter performance in terms of efficiency, size, conducted electromagnetic emission, and transient response. The benefits of interleaving include high power capability, modularity, and improved reliability. Interleaving add benefits such as reduced ripple current in both input and output circuits. Higher efficiency is realized by splitting the output current into ‘n’ paths, substantially reducing I2R losses and inductor losses. In addition, interleaving is also employed to reduce the input current ripple, and therefore to minimize the size of the input filter that would be relatively large if a single boost converter was used.

C. Controller

In this system, micro controller is used for generating the control signal depends upon the applications. This control signals are used to turn on/off of the power switches present in the converter circuit to get the desired output voltage.

D. Dc Filter

This filter is used to reduce the ripple content present in the output voltage of the converter. The capacitor is widely used for dc filter. In addition to that the inductor and the capacitors serve as voltage sources to extend the voltage gain and to reduce the voltage stress on the switch. This regulated dc output is given to the dc load.

III. INTERLEAVED BOOST CONVERTER

A two-phase interleaved boost converter is usually employed in high input-current and high input-to-output voltage conversion applications. The circuit diagrams of the two phase interleaved boost converter with uncoupled, directly coupled, inversely coupled IBC are shown in figure 2 to 4.

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Fig.2 Circuit Diagram for two phase uncoupled IBC

Fig.3 Circuit Diagram for two phase coupled IBC The two phases of the converter are driven 180 degrees out of phase, this is for the reason that the phase shift to be provided depends on the number of phases given by 360/n where n stands for the number of phases.

Fig. 4 Circuit Diagram for two phase inversely coupled IBC Operation of Interleaved Boost Converter:

There are two modes of operation in two phase interleaved boost converter for renewable energy applications such as photovoltaic module, fuel cell. They are, i) Mode 1operation ii) Mode 2 operation

Mode 1 Operation: (0 ≤ t < t1)

At t =0, the gate pulse is given to the switch ‘S1’ of the first phase. Then the switch ‘S1’ is turned on, the current across the inductor L1 rises linearly. At the same time, the switch ‘S2’ in the second phase is turned off and the energy stored in the inductor L2 is transferred to the load through the output diode D2. In this time interval, the diode D1 in the first phase is in reverse bias condition. The circuit operation for Mode-1 is shown in figure 5.

Fig.5 Current paths of IBC in Mode-1 At time t0, S1 is closed. The current in the inductor L1 starts to rise while L2 continues to discharge. The rate of change of iL2 is approximately given by,

Mode 2 Operation: (t1 ≤ t < t2)

At t = t1, the gate pulse is given to the switch ‘S2’ of the first phase. Then the switch ‘S2’ is turned on, the current across the inductor L2 rises linearly. At the same time, the switch ‘S1’ in the first phase is turned off and the energy stored in the inductor L1 is transferred to the load through the output diode D1. In this time interval, the diode D2 in the second phase is in reverse bias condition. The circuit operation for Mode-2 is shown in figure 6.

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Fig.6 Current paths of IBC in Mode-2 At time t1, S2 is closed. The current in the inductor L2 starts to rise while L1 continues to discharge. The rate of change of iL1 is approximately given by,

IV. DESIGN PROCEDURE FOR IBC The interleaved boost converter design

involves the selection of the number of phases, the inductors, the output capacitor, the power switches and the freewheeling diodes. Both the inductors and diodes should be identical in all the channels of an interleaved design. In order to select these components, it is necessary to know the duty cycle range and peak currents. Since the output power is channeled through ‘n’ power paths where ‘n’ is the number of phases, a good starting point is to design the power path components using 1/n times the output power. The various stages involved in designing interleaved boost converter are Selection of number of phases Selection of duty ratio Selection of power devices Design of inductor Design of output filter

A. Selection of number of phases It has been observed that the ripple in the input

current decreases with increase in the number of phases. On the other hand, the cost and complexity of the circuit also increases. So, a compromise had to be made between them. In this paper, the number of phases was chosen to be two to reduce the ripple content without increasing the cost drastically. The number of inductors, switches and diodes are same as the number of phases and switching frequency is same

for all the phases. The switching pattern for interleaved boost converter is shown in Fig.7.

Fig.7.Switching pattern for two phase IBC

B. Selection of duty ratio

Duty ratio also aids in ripple reduction and hence it has to be selected carefully. From the plot of the input current ripple versus the duty ratio, it can be found that for an N-phase IBC, the ripple can be zero at particular values of duty ratio. The input current ripple for various duty ratios are shown in figure 8.

Fig.8 Input current ripple with duty ratio For a 2-phase converter, the ideal duty ratio at which the ripple is zero is 0.5. C. Selection of power semiconductor switches

The semiconductor device chosen for constructing the two phase interleaved boost converter is the IGBT. The main benefits of IGBT are lower on-

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state resistance, lower conduction losses and high switching operation. The maximum voltage across the switching devices is given by

(3)

Where Vin is the input voltage, K is the duty ratio of the converter. The diode has less forward voltage, high reverse breakdown voltage and less reverse recovery. D. Selection of Inductors

Design of inductance is very important in boost topologies so that the inductor is sized correctly. The design of inductors for uncoupled and directly coupled IBC is explained as follows: 1. Design of uncoupled inductor

The value of the inductance is given by, (4)

2. Design of coupled inductor

The expression for equivalent inductance of directly coupled IBC is given by,

(5)

Where, Vin represents input voltage, K represents duty ratio. To find out the values of mutual inductance (Lm), the input current is calculated using the input voltage and power. The value of mutual inductance ‘Lm’ is given by,

Lm = α L (6)

Where, α represents coupling coefficient Therefore, the overall input current ripple is derived as

(7)

From the above equations it is clear that increasing the value of the coupling coefficient can effectively reduce the input current ripple, but the phase current ripple is increased. Therefore, the value of coupling coefficient is carefully chosen as 0.61, so that the input current ripple is reduced and the phase current ripples are within the limits. 3. Design of inversely coupled inductor

The self-inductance value for inversely coupled is obtained from the equation is given by,

The value of mutual inductance is given by,

(9)

E. Design of Output Filter A capacitor filter is needed at the output to

limit the peak to peak ripple of the output voltage. The capacitance of the output filter is function of the duty cycle, frequency and minimum load resistance during maximum load. For 5% output voltage ripple, the value of the capacitance is given by the formula,

(10)

Where, R represents the load resistance, Vo represents the output voltage and T represents the switching period.

V. SIMULATION RESULTS

As per the design equations, a two phase interleaved boost converter with uncoupled, directly coupled and inversely coupled inductors are simulated in MATLAB/SIMULINK .The values for uncoupled IBC are L=2.5mH, C=78µF, f=2KHz.and R=3.2Ω.The output voltage is Vo=72V, for an input Vin=12V. The values used for directly and inversely coupled IBC are summarized as Vin = 12V, R = 3.2Ω, C =78uF, fs=2kHz, Lm = 7mH, Lkl = Lk2 =4.3mH, Vo =67v, K=0.5and a = 0.61 for directly coupled.

Fig.9 Input voltage waveform of two phase uncoupled IBC

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Fig.10 Switching pattern for two phase IBC

Fig.11 Inductor current waveform for

uncoupled IBC

Fig.12 Output Voltage waveform for uncoupled IBC

Fig.13 Inductor current waveform for coupled IBC

Fig.14 Output Voltage waveform for coupled IBC

Fig.15 Inductor current waveform for inversely

coupled IBC

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Fig.16 Output Voltage waveform for inversely coupled IBC

From the results we conclude that the inductor ripple is smaller for inversely coupled compared to the others, still the input current ripple is greater for inversely coupled IBC. We distinguish that whenever the inductor current ripple is less, efficiency is more. The higher value of input current ripple of inversely coupled is not apt for certain applications. This higher current ripple can be reduced by selecting correct value of duty ratio and coupling coefficient. The results show that the directly coupled IBC provides a reduced input current ripple which is best suitable for photovoltaic module applications.

VI. CONCLUSION

Interleaved boost converter has so many merits and is a proper converter for renewable energy applications. Three cases of IBC using uncoupled, coupled and inversely coupled inductor have been considered for renewable energy applications. Their design equations have been presented and performance parameters of all three cases have been related using simulation. It is demonstrated that the directly coupled interleaved DC-DC converter efficiently reduces the overall current ripple related to that of uncoupled inductors. Therefore directly coupled IBC is a right choice for photovoltaic module.

REFERENCES

[1] Choe, G.Y; Kang,H.S; Lee, B.K; and Lee, W.L. "Design consideration of Interleaved Converters for

fuel cell applications", in Proc. International conference on Electrical machines and Systems, Seoul, 2007, pp.238 -243. [2] Kosai, H; McNeal, S; Page, .A; Jordan, B; Scofield, J; and Ray.B. "Characterizing the effects of inductor coupling on the performance of an interleaved boost converter," in Proc. CARTS USA 2009, 2009, pp. 237-251. [3] Shin,H.B; Park,J.G; Chung, S.K; Lee, .H.W; and Lipo, T.A. "Generalized Steady-State Analysis of Multiphase Interleaved Boost Converter with Coupled Inductors," in Proc. IEE Electronics Power Application, Vol. 152, No. 3, 2005, pp. 584-594. [4] Lee, .P; Lee, .Y; Cheng, .DKW; and Liu, X. "Steady-state analysis of an interleaved boost converter with coupled inductors", IEEE Trans. on Industrial Electronics, 47, 2000, pp. 787-795. [5] Dahono, P.A; Riyadi, S; Mudawari, A; and Haroen, Y."Output ripple analysis of multiphase DC-DC converter", in Proc. IEEE International Conference on Power Electrical and Drive Systems, Hong Kong, 1999. [6] Veer chary, M; Senjyu, T; and Uezato, K. "Small-signal analysis of interleaved dual boost converter", International Journal of circuit theory and applications, Vol.29, Issue 6, 2001, pp. 575 -589. [7] Laszlor, H; Brian, T; Irving, M; Milan and Jovanovic “Closed Loop Control Methods for Interleaved DCM/CCM Boundary Boost PFC Converters," in Proc. IEEE Applied Power Electronics Conference, 2009, pp. 991-997. [8] Thou thong, P; Sethakul,P; Rael,S; and Davat,B. "Design and implementation of 2- phase interleaved boost converter for fuel cell power source," in Proc. International Conference on Power Electronics, Machines, and Drives, PEMD 2008, pp. 91-95. [9]M.Harinee, V.S.Nagarajan, Dimple, R.Seyezhai, Dr.B.L.Mathur. “Modeling and design of fuel cell based interleaved boost converter". Electrical Energy Systems (ICEES), 2011 1st International Conference on Year: 2011, pp. 72 - 77 [10] R. Seyezhai and B.L. Mathur "Analysis, Design and Experimentation of Interleaved Boost Converter for Fuel Cell Power Source" International Journal of Research and Reviews in Information Sciences (IJRRlS) Vol. 1, No. 2, June 2011 ISSN: 2046-6439 Copyright © Science Academy Publisher, United Kingdom [11] P. A. Dahono, S. Riyadi, A. Mudawari, and Y. Haroen, "Output ripple analysis of multiphase DC-DC converter," IEEE Power Elect. and Drive Systems (PEDS), pp.626-631, 1999.

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[12] Y. Hu et aI, "Characteristics analysis of two-channel interleaved boost converter with integrated coupling inductors," in Proc. IEEE Power Electronics Specialists Con!, Jun. 2006. [13] Xu, .H; Qiao, .E; Guo, .X; Wen, .X; and Kong, L. "Analysis and Design of High Power Interleaved Boost Converters for Fuel Cell Distributed Generation System", in Proc. IEEE Power. [14] Wai, R.J; and Duan; .R.Y. "High step-up converter with coupled-inductor," IEEE Trans. Power Electronics, Vol. 20, No.5, pp. 1025-1035, 2005. [15] Huber, L; Brian, T; Irving, and Jovanovic, .M.M. "Closed Loop Control Methods for Interleaved DCM/CCM Boundary Boost PFC Converters," in Proc. IEEE Applied Power Electronics Conference and Exposition, APEC 2009, pp. 991-997, 2009.

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