Unity-Power-Factor PWM Converter with DC Ripple Compensation.

Abstract

The generation of harmonics and their subsequent propagation into power line is a topic of increasing concern to power supply authorities. To prevent obstacles on the power system, Unity-Power-Factor PWM converter is going to apply to AC-DC power conversion plant. However, PWM converter, especially at single phase circuit, has some serious defects, that is low frequency ripple current which flows into the DC line and low frequency ripple voltage which appears on the DC output In usual case, it is necessary to connect a very large capacitor or a passive L-C resonant circuit to the DC line for the reduction of low frequency ripple voltage. However, in case of the Batteries are connected with the DC output, most of the DC ripple current flows into the Battery even if previous circuits are used because the impedance of the Battery is very low compared with that of previous circuit. The low frequency ripple current cause power loss on the Battery and the temperature has risen. It is well known that the life of the Battery is deeply influenced by the temperature. The ripple current, therefore, should be reduced to as possible as low.To accomplish the reduction of the low frequency ripple current, a novel topology of the PWM rectifier is presented in this paper. The main circuit is constituted by adding only a pair of switching devices to conventional PWM converter circuit. With simple control technique, the ripple energy on the DC line is converted into the stored energy on the input AC capacitors though the additional switches. The theoretical characteristics are obtained by using statespace-averaging-method. The effect of the ripple reduction is confirmed by experiments using a bread board set-up.