A New Isolated Bidirectional Buck-Boost PWM Converter

Abstract

In this paper, a new isolated dc-dc bidirectional converter is introduced. This

converter consists of flyback and forward transformers and only one switch in

primary side and one switch in secondary side of transformers. In this converter

energy transfers to the output in both on and off switch states and controlled by

PWM signal. Therefore implementation of control circuits is easy. Also this

converter operates over a wide input voltage range. Theoretical analysis is

presented and computer simulation and experimental results verify the converter

analysis.

Keywords: Bi directional, dc-dc converter, buck boost,

PWM, flyback, forward.

INTRODUCTION

Bidirectional dc-dc converters provide the function of transfer of power between two dc

sources in either direction. These converters are used vastly in industrial applications

such as DC uninterruptible power supplied (UPS), battery chargers, electric vehicles and

etc. Various topologies are introduced for these applications. Some bidirectional

converters were developed base on basic PWM topologies by replacing the diodes and

switches with bidirectional current switches. Early papers describe some commonly used

topologies of bidirectional PWM dc-dc converter including Buck-Boost, Cuk, Push-Pull

and full bridge. These converters are obtained by adding an anti-parallel diode to the

switch (if it is non already exist) and replace a switch with diode. Therefore the load can

be replaced by a DC voltage source and power can flow in either direction.

PROPOSED SYSTEM

In this paper, A new bidirectional dc-dc converter is introduced. This converter has some

advantage in comparison with conventional bidirectional dc-dc converter such as flyback

converters. This converter transfers energy to the output in both on and off switch states.

Also this converter can operate buck boost in either direction therefore it can operate

under wide range variation of voltage source. Furthermore this converter controlled by

PWM signal and it have minimum active switch in power stages. Since the output current

in forward mode is continues, the power density of converter is high.

The Proposed Converter

Circuit description

The proposed converter is shown in Fig. 1. S1 and S2 are the main switches and Cb is

balancing capacitor. T1 and T2 are the flyback and forward transformers respectively.

Also D1 and D2 are the anti-parallel diodes of S1 and S2 respectively. VLm1 is voltage

across magnetizing inductor of flyback transformer (Lm1) and VLm2 is voltage across

magnetizing inductor of forward transformer (Lm2). V1 and V2 are the primary side and

secondary side source of the converter.

Operation principle

a) Converter Operation

In order to simplify the steady state analysis the 1st Power Electronic & Drive Systems &

Technologies Conference following assumptions are made.

• All parasitic components are neglected.

• V1 and V2 can be considered constant in a switching cycle.

b) Forward mode

In this mode the switch S1 on the primary side is gate while S2 is not switched at all. The

proposed circuit in this mode has two distinct operating stages in one switching cycle.

c) Backward mode

In this mode the switch S2 on the secondary side is gated while S1 is not switched at all.

Proposed converter in this mode has two operating stages in a switching cycle.

ADVANTAGES

A new bidirectional dc-dc converter is introduced. This converter transfer’s energy to the

output in both on and off switch states in forward mode and in this converter the output

current is continuous. Therefore power density of converter is high. Also this converter

can operate buck-boost in either direction therefore it can operate under wide range

variation of voltage source. Furthermore this converter controlled by PWM signal and it

have minimum active switch in power stages.

Hardware Requirements

Inductors, capacitors, transistors, diodes, and Triggering circuits.

Software Requirements

PSIM/MULTISIM Tools for simulation.

Windows Xp: Service pack 2