Double Closed-loop Control of Three-Phase Five-level PWM Current Source Inverter

A direct type multilevel current source inverter (CSI) and its closed-loop strategy are studied in this paper. In the three phase static symmetric axes (a, b, c), parameters on the AC side of the three phase five-level CSI are time-variant AC variables, which is a difficult point in the designing of control system. So a direct current control method based on the synchronous rotational axes (d, q, 0) is proposed. This strategy transforms AC variables in the three-phase static symmetric axes into direct values in the synchronous rotational axes (d, q, 0), so the problem of controlling the AC variables is transformed into adjusting the direct values. This control strategy has little influence over changes of system parameter, it suit well with linear system and nonlinear system. Simulations are carried out with software PSIM to confirm feasibility of the proposed control method.