A PWM current-source rectifier with active damping for high power medium voltage applications

A digitally implemented active damping technique is proposed for high-power, medium-voltage (2300 V to 7200 V) PWM current-source rectifiers (PWM-CSR). The rectifier requires an LC filter connected at its input terminals. The damping of the LC filter is dependent on the power system characteristics, and the resonant frequency changes with the power system impedance. Moreover the lightly damped LC filter can cause oscillations during system transients if not adequately damped. These issues are traditionally addressed at the design stage by properly choosing the filter resonant frequency. This paper proposes a damping method accounting for the limitations of the power semiconductor switching frequency (typically around 500 Hz), and limits the dependency on the power system and the design of the LC filter. The proposed active damping scheme combined with the improved space vector PWM technique can effectively solve the above mentioned problems. The concept of the active damping control is introduced, and the principle of the PWM switching pattern is discussed. Experimental results based on a 10 kVA prototype are provided. It is demonstrated that the proposed rectifier can effectively reduce the line current distortion and improve the system stability. It has the potential to protect the switching devices from over-voltage stress caused by the LC resonance as well.