Practical issues in the design of active rectifiers for AC drives with reduced DC-link capacitance

For AC drives with an active front-end boost rectifier, the DC-link voltage can be regulated with fast dynamic control and made immune to line and load variations. Hence, it is possible to reduce the DC-link capacitance and use film capacitors instead of electrolytics, thus improving the life expectancy of the drive. Typically, active rectifier control includes load power feed-forward to enhance the response of the DC voltage regulating loop to load transients. In this paper, it is shown that under certain load transients encountered in practice, the rise of the DC bus voltage is inevitable and cannot be mitigated by control. It is also shown that with power feedforward control, the limited sampling rate of the pulse-width-modulated DC link current in a practical system affects the quality of the input line currents. Detailed design and stability analysis and experimental results under several practically encountered situations are presented.