A Study on the Operation Limits on the 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 the obstacles on the power system, Unity-Power-Factor PWM converter is going to apply to AC-DC power conversion circuit. However, PWM converter, especially at single phase circuit, has some serious defects, that is low frequency ripple current which flows into the battery connected to the DC output or low frequency ripple voltage which appears on the DC output capacitor. Especially, in case of the batteries are connected with the DC output, the low frequency ripple current flows into the battery and cause power loss on the battery. The power loss cause high temperature of the battery and shortens the life of it. To accomplish the reduction of the low frequency ripple current, the authors have been proposed a novel topology of the PWM rectifier and reported its operation principles. In this paper, the operation limit influenced by the circuit parameters, especially capacitance of the input capacitor, is discussed. It is shown that the operation limit can be estimated based on the calculation of the ripple energy that is stored in the input capacitors. By adopting the ripple energy expression on both the input capacitor and the DC output, the limitation for the DC ripple reduction can be clearly expressed. The calculated results agree well with that of the experimental results. The proposed calculation technique is useful for the practical design of the proposed PWM converter.