ABSTRACT:

In this paper a AC-DC converter has been proposed for DC voltage regulation which can be used for dc motor drive, battery charging applications, etc. The conventional converter comprises two stages. The first stage is the diode bridge rectifier and the second stage is DC-DC buck converter. The two stages are coupled by a dc-link capacitor which also eliminate the ripple present in the output of the rectifier. The two stages are combined by increasing a Switch and decreasing number of diodes and eliminating the dc link capacitor. A feedback control system, based on PWM technique, has been designed which regulates its load voltage. The simulation work is carried out using MATLAB/SIMULINK.

INTRODUCTION

Day by day, application of single phase ac to dc conversion system are increasing with the increasing requirements for dc power. Most of the applications requires power ranging from 12V to 400V of dc supply. A large number of applications involves the use of dc motors. Therefore, it is necessary to have a efficient power conversion system. Here, the designed two stage ac to dc converter is unidirectional and is used to control the speed of a dc motor. To control the speed of motor, the output of the buck converter must be regulated, which can be achieved by an efficient feedback control loop. However, the design of an efficient feedback loop is not easy as its performance is significantly affected by the disturbances. These disturbances are basically created by load variations, changes in input voltage, and electromagnetic interference, which is caused by the switching operations of semiconductor devices such as MOSFETs, transistors and diodes. Therefore, to obtain the desired output voltage, the feedback control system must have a high disturbance rejection ability. Many researchers have proposed different control schemes such as predictive control, adaptive control, sliding mode control and fuzzy logic control which lead to improvement in performance of feedback control system. In this paper, authors have implemented PWM control technique because of its simplicity. Also, to achieve the high conversion efficiency, the efficiency of rectifier as well as dc-dc converter should be high. Therefore, in the proposed model, fast recovery diodes has been used in the dc-dc converter which result in reduced voltage drop across diode and hence, increased converters efficiency. The lower value of selected switching frequency also results in lower switching losses and further increases the buck converter efficiency. The control method, dc capacitor design and ac inductor design are discussed in this paper. Supplying other components of the circuit like ramp generator, amplifier and comparator, which operates at low-voltage, from the output of the rectifier is the another concern.

PROBLEM STATEMENT

In this, a two stage converter is combined to propose a single stage AC-DC converter in order to reduce the components used. A PWM based dc voltage control circuit is used for load voltage regulation. The power factor and efficiency of both conventional and proposed converters are compared based on the simulation results. The converter design procedure is also explained in this work.