High Step up Interleaved Converter with Voltage Multiplier Module

International Journal of Engineering Trends and Technology (IJETT) – Volume 22 Number 11 April 2015

High Step up Interleaved Converter with Voltage

Multiplier Module

Remya.M.S

#1

, Susmi.K.M

#2

, Meera.G

#3

#

PG Students, Power electronics, EEE, Calicut university

Vidya Academy of Science and Technology, Thrissur, Kerala, India

Abstract

— A High step-up converter suitable for renewable energy system is designed in this paper. Using a conventional interleaved boost converter, accompanied by a voltage multiplier module composed of switched capacitors and coupled inductors, high step-up gain is obtained without operating at extreme duty ratio. The topology of the proposed converter reduces the current stress. The topology constrains the input current ripple, and hence the conduction loss reduces. The circuit also increases the lifetime of the source. Because of the lossless passive clamp performance, the leakage energy can be recycled to the output terminal. This leads to the reduction in large voltage spikes across the switches and improvement in the overall efficiency.

The low voltage stress enables the use of low-voltage-rated

MOSFETs for reductions of conduction losses and cost. The circuit with 12-V input voltage and 100-W output power was simulated using Matlab simulink and an output voltage of 110-V was obtained.

Keywords

— Coupled Inductor, Switched Capacitor, Voltage

Multiplier Module.

I.

I NTRODUCTION

In present scenario renewable energy is progressively more valued and employed worldwide because of energy shortage and environmental contamination. The output voltage obtained from the renewable energy systems is very low. So, for many renewable energy applications like photovoltaic systems, fuel cells, wind power generation high step-up dc/dc converters have been used. Such systems transform the low voltage energy from the renewable resources into high voltage via a step-up converter. The dc dc converter converts the energy into electricity using a grid-bygrid inverter or a dc micro grid. A two-stage converter with cascade structure may be required for step-up gain for high step-up conversion. But this will lead to reduction in the efficiency and increase in cost. This indicates that, a high stepup converter is an important stage in the system as it requires sufficiently high step-up conversion and high efficiency. The drawback with the conventional step-up converters, such as boost converter and flyback converters is low step-up conversion with increase in efficiency because of the leakage inductance or resistances of elements. Hence, the voltage stresses are large. The conventional interleaved boost converter is suitable for high power applications and power factor correction. But this converter has the major drawback of limited step-up gain and the high voltage stresses on semiconductor components which is equal to the output voltage. Hence, based on the above considerations, modifying a conventional interleaved boost converter for high step-up and high-power application is a suitable approach. The addition of switched capacitors into interleaved boost converter circuit may make the voltage gain to reduplicate, but the step-up voltage gain is limited as no coupled inductors are used. Conversely, on integrating coupled inductors into an interleaved boost converter circuit, the voltage gain may increase. Since switched capacitors are not used, it causes the step up voltage gain to be ordinary. Thus, the use of coupled inductors and switched capacitors together is a better concept.

High step-up gain, high efficiency, and low voltage stress are obtained even for high-power applications using such circuits.

The proposed converter is the integration of voltage multiplier module with the conventional interleaved boost converter. Coupled inductors and switched capacitors together constitute the voltage multiplier module. The design of the coupled inductors can be used to extend step-up gain and higher voltage conversion ratio is offered by the switched capacitors. Moreover, the energy stored in the magnetizing inductor will transfer via three respective paths when one of the switches turns off and thus current distribution decreases.

Hence, the conduction losses decrease because of low effective current. The currents through some diodes decrease to zero before they turn off and hence diode reverse recovery losses are also reduce. The objective of this paper is to develop a converter with low switching losses, reduced voltage and current stress and reduced conduction loss. The leakage inductance of the isolation transformer, resulting in high voltage spike during switching transition is a major issue.

The freewheeling current due to the leakage inductance will increase the conduction losses and reduce the duty cycle. A notable approach is to pre charge the leakage inductance and to raise its current level up to that of the current-fed inductor, thus reducing their current difference and voltage spikes. As the current level varies with variation in the load, it is difficult to tune the switching timing diagram to match these two currents. Thus, a passive or an active clamp circuit is required.

II.

C IRCUIT OPERATING PRINCIPLE

The objective of this work is to obtain high step-up gain without operating at an extreme duty ratio through voltage multiplier module composed of switched capacitor and coupled inductor. Also to reduce input current ripple which in turns reduce conduction losses and to eliminate voltage spike produced across the switching devices. The proposed high step-up interleaved converter is shown in Fig. 1.

ISSN: 2231-5381 http://www.ijettjournal.org

Page 498


Fig. 1 Circuit diagram

The voltage multiplier module consists of two coupled inductors and two switched capacitors. It is inserted between the conventional interleaved boost converter to form a modified boost flyback forward interleaved structure. When the switches turn off in steps, the phase with the switch in

OFF position act as a fly back converter, and the other phase with the switch is ON position act as a forward converter. The turns of primary windings of the coupled inductors is N p

and is used to decrease the input current ripple, and the secondary windings of the coupled inductors with N s

turns are connected in series to adjust the voltage gain. The coupled inductors have equal turns ratio. The coupling references of the inductors are denoted as " ." and " * ".

Fig. 2 describes the equivalent circuit of the proposed converter. Lm1 and Lm2 are the magnetizing inductors. LK1 and LK2 represent the leakage inductors and Ls represent the series leakage inductors in the secondary side. S1 and S2 denote the power switches.

Fig -3: Steady state waveform of proposed converter

The switched capacitors and the output capacitors are represented as Cc1, Cc2 and C1, C2, C3 respectively. The clamp diodes are denoted by Dc

1

and Dc2. The output diodes for the boost operation with switched capacitors are represented as Db1 and Db2 and the output diodes for flyback forward operation are represented as Df1 and Df2

.

The turns ratio is defines as n and that equals to N s

/N p

. The circuit analysis is made on the basis of continuous conduction mode

(CCM) of operation. The Fig. 3 shows the steady waveform of the proposed converter.

III.

M ODES OF O PERATION

A.

Mode 1

. Fig. 2 Equivalent circuit of proposed converter


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Fig. 5. Equivalent circuit for Mode 2 operation

Fig. 4 Equivalent circuit of proposed converter

Mode 1 [t0, t1]: At t = t0, the power switch S2 is in ON state, and S1 begins to turn on. Magnetizing inductors Lm1 and

Lm2 will be charging. The polarity of magnetizing inductors reverse biases the diodes Dc1, Dc2, Db1, Db2, and Df1 , as shown in Fig. 4. The series leakage inductor Ls release the stored energy to the output terminal via fly back forward diode Df2 and its current reduces to zero. The magnetizing inductor Lm1 keeps on transferring energy to the secondary side of coupled inductors. The current through the leakage inductor LK1 increases linearly and that through the leakage inductor LK2 decreases linearly.

B.

Mode 2

Mode 2 [t1, t2]: At t = t1, both of the power switches S1 and

S

2

remains in ON position. The magnetizing inductors Lm1 and Lm2 are charging as shown in Fig. 5. The polarity of the magnetizing inductors cause the diodes Db1, Db2, Dc1, Dc2 to be reverse biased. The series inductor Ls has completely discharged, and hence diode Df2 gets naturally turned OFF.

Both currents through leakage inductors LK1 and LK2 are increasing linearly due to charging by input voltage source V in

.

C.

Mode 3

Mode 3 [t2, t3]: At t = t2, the power switch S1 is in ON state, and S2 begins to turn OFF, magnetizing inductors Lm1 will be charging and Lm2 will be discharging. The reversed polarity of Lm2 cause diodes Dc2 and Db2 forward biased.

The equivalent circuit is as shown in Fig. 6. The energy stored in Lm2 is transferred to the secondary side of coupled inductor. The current through the series leakage inductor Ls flows to the output through the output capacitor C3 and the fly back forward diode Df1. The voltage stress on the switch S2 is clamped by the clamp capacitor Cc1 thereby reducing the voltage stress.

Fig. 6 Equivalent circuit for Mode 3 operation


Page 500


D.

Mode 4



Mode 4 [t3, t4]: At t = t3, the power switch S1 is in ON state, and S2 is in OFF state, magnetizing inductors Lm1 will be charging and Lm2 has completely discharged .The diode Dc2 turns OFF naturally, and this reduces the reverse recovery loss across the diode. The series leakage inductor Ls is charging through fly back diode Df1. The circuit state is shown in Fig.

7.

F.

Mode 6

Mode 6 [t5, t6]: At t = t5, both of the power switches S1 and

S2 remain in ON position, and the magnetizing inductors Lm1 and Lm2 are charging as shown in Fig. 9. The polarity of the magnetizing inductors cause the diodes Db1 , Db2, Dc1, Dc2 to be reverse biased. The series inductor Ls discharges completely. So the diode Df2 gets turned OFF naturally. Both currents through leakage inductors LK1 and LK2 are increasing linearly.

E.

Mode 5

Mode 5 [t4, t5]: At t = t4, the power switch S1 remains in ON state, and S2 begins to turn ON, magnetizing inductors Lm1 and Lm2 are charging. The polarity of magnetizing inductors reverse biases the diodes as it is shown in fig 8. The magnetizing inductor Lm2 transfer energy to the secondary side of the coupled inductors. The series leakage inductor Ls is discharging through diode Df1 and C3 reducing current i

Ls to zero.



Page 501


G.

Mode 7

Fig. 11 Equivalent circuit for Mode 8 operation stress.


Mode 7 [t6, t7]: At t = t6, the power switch S2 is in ON state, and S1 begins to turn OFF, magnetizing inductors Lm1 will be discharging and Lm2 will be charging. The reversed polarity of Lm1 cause diodes Dc1 and Db1 to be forward biased. The current flow direction is as shown in Fig. 10. The energy stored in Lm1 is transferred to the secondary side of coupled inductor. Current through series leakage inductor Ls flows to the output through the output capacitor C2 and the fly back forward diode Df2. The voltage stress on switch s

1

is clamped by clamp capacitor Cc2 thereby reducing the voltage

H.

Mode 8

Mode 8 [t7, t8]: At t = t7, current i

Dc1

has naturally decreased to zero due to magnetization current distribution. Hence conduction losses and diode reverse recovery losses are reduced. All the power switches and diodes remains in same state as in previous mode as shown in Fig 11.

IV.

S IMULATION

The simulation diagram for closed loop operation is shown in Fig-12. The output voltage adjusts to a constant voltage for slight variations in the supply voltage. The simulation parameters are

Input voltage V in

= 12V

Output voltage V o

= 110V

Switching frequency f s

=40 kHz

Duty cycle D=0.7

Magnetizing inductors Lm =Lm2 =133 µH

Output capacitor C1=470 µF

Output capacitor C2=C

3

=220 µF

Clamp capacitors Cc1=Cc2=220 µF

Turns Ratio n=1

Load resistance R=140 Ω

ISSN: 2231-5381

Fig.12 Simulation Diagram

The gating signal applied to switches S1 & S2 are as shown in

Fig 13. http://www.ijettjournal.org

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R EFERENCES

[1] Kuo - Ching Tseng and Chi- Chih Huang, High StepUp High

Efficiency Interleaved Converter with Voltage Multiplier Module for

Renewable Energy System, IEEE Transactions on Industrial

Electronics, VOL. 61, NO.3, Mar. 2014.

[2] C.M.Lai, C.T.Pan, and M.C.Cheng, High Efficiency Modular High

StepUp Interleaved Boost Converter for DC Micro Grid Applications,

IEEE Transactions. Industrial Appl.,vol. 48, no. 1, pp. 161171,

Jan./Feb. 2012.

[3] W.Li, Y.Zhao, J.Wu, and X.He, Interleaved High StepUp Converter with Winding Cross Coupled Inductors and Voltage Multiplier Cells,

IEEE Transactions. Power Electronics., vol. 27, no.1, pp.133143,

Jan.2012

Fig.13 Pulse Pattern

The output voltage waveform obtained for 12V input is as shown in Fig 14.The simulation results provide an output voltage of 108V.

Fig.14 Output voltage waveform

V.

C ONCLUSIONS

Often for renewable energy applications a low voltage is obtained from the renewable energy sources. It has to be boosted up to a higher voltage level in order to be used by the consumer. There exists a wide range of step up converters. In this work a high step up high efficiency converter is designed for a given output power, voltage and input voltage. It works on the principle of voltage multiplier.

The circuit is designed and simulated using Matlab simulink

2009b.

A CKNOWLEDGMENT

I wish to record my indebtedness and thankfulness to all those who helped me prepare this report titled ” HIGH

STEP-UP INTERLEAVED CONVERTER WITH

VOLTAGE MULTIPLIER MODULE FOR RENEWABLE

ENERGY APPLICATIONS ” and present it in a satisfactory way.


Page 503

High Step up Interleaved Converter with Voltage Multiplier Module

High Step up Interleaved Converter with Voltage

Multiplier Module

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