Damping of PWM Current-Source Rectifier Using a Hybrid Combination Approach

An LC filter is normally required at the input of a PWM current source rectifier (CSR), to assist the commutation of switching devices and to mitigate the line current harmonics. To dampen the LC resonance introduced by the input filter, an effective damping method is proposed in this paper by using a hybrid combination of the virtual harmonic resistive damper and a three-step control signal compensator. The virtual harmonic resistor, which is immune to the system parameter variations, can dampen the LC resonance caused by the external disturbance or control command changes without affecting the fundamental power flow. But the high pass filter used for fundamental component elimination leads to poor dynamics. Therefore a three-step compensator is designed and is simply inserted in the DC current closed-loop control path which can effectively eliminate the resonance within the control loop by shaping the modulation signal. Compared to the two-step Posicast controller, the proposed three-step compensator has significant implementation advantages in medium voltage CSR, where a low switching frequency is needed. By using a hybrid combination approach, the dynamics of the virtual harmonic resistor can be improved with the transient overshoot mitigated by the three-step compensator. At the same time, the parameter sensitivity of the three-step compensator can be reduced, as any residual resonant oscillations can be dampened by the virtual resistor. Simulation and experimental results are provided to verify the effectiveness of the proposed approach.