Novel and Simple Current-Ripple Calculation of LCL Filter for Parallel-Connected Three-Phase PWM Rectifiers

This paper proposes a simple current-ripple calculation on the source side of the LCL filter for three-phase pulse width modulated (PWM) rectifiers and the parallel-connected PWM rectifiers. Per-phase-base equivalent-circuits of the LCL filter for PWM rectifiers and parallel-connected three-phase PWM rectifiers are derived theoretically. The transfer function between the output voltages of three-phase PWM rectifiers and parallel-connected three-phase PWM rectifiers and the source-side ripple currents is derived using the superposition principle, and then Bode plots are drawn. Then, the amplitude ratio of source-side harmonic currents to the output voltages of three-phase PWM rectifiers and the parallel-connected three-phase PWM rectifiers is easily calculated from the Bode plots. A digital computer simulation is implemented to confirm the validity and high practicability of the proposed current-ripple calculation of LCL filter using PSIM software. Simulation results demonstrate that the current-ripple calculated with the Bode plots agrees well with the simulation results. It is, therefore, concluded that the proposed current-ripple calculation of the LCL filter is useful for three-phase PWM rectifiers and parallel-connected three-phase PWM rectifiers.