Centralized Control of Modular Multi Rectifier for Motor Drive Applications under Unbalanced Grid

A centralized control scheme is proposed for modular multi rectifier system as a popular front-end rectifier solution for the industrial application where multiple motors are supplied by the Silicon Controlled Rectifier (SCR). Normally under conventional balanced grid voltage, the input current distortions can be improved by implementing the appropriate SCR firing angles in each unit. However, the three-phase grid voltage may be either amplitude or phase angle unbalanced, which deteriorate the performance of the conventional harmonic mitigation method. In order to remedy this issue, the three-phase total input currents 3rd harmonic components are extracted and included in the closed-loop control using PI controller, and a reset unit with the input of inductor current is adopted to reset the integrator. The proposed control strategy is able to obtain the appropriate SCR firing angle compensation, and then consequently achieve harmonics improvement in the input current under unbalanced grid voltage. Simulation results based on PLECS and experimental results have validated the effectiveness of the proposed improved control strategy under unbalanced grid voltage.