Parallel Coupling and Stability Analysis of Three-phase Current-source PWM Rectifiers in Weak Grid Environments

Three-phase current-type PWM rectifiers generate current pulses due to the specific commutations and control strategies. As a result, CLC-type filters are inserted between the input grid and rectifiers. Moreover, for the cases of weak grids with large grid impedances, parallel connected rectifiers may be unstable because of the resonances caused by the coupled filters and grid impedance. This paper investigates the scheme and mathematical model for paralleled current-type PWM rectifiers. It is shown that the system may become resonant through the standard connected point voltage. The active damping is proposed based on the estimation of the capacitor voltage with the output current, and system stability can be guaranteed. The effectiveness of the proposed active damping is verified through simulations and experiments.