A Low-Switching-Frequency Discrete-Time Model and Control Strategy for NPC Three-Level Inverter-Fed Dual Three-Phase PMSM Drives

In this paper, the discrete-time model and control strategy are studied for a neutral-point-clamped three-level (NPC-3L) inverter-fed dual three-phase permanent-magnet synchronous machines (PMSM) drive with low switching frequencies. The precise discretization with the Laplace transform is proposed and compared with two different Euler-method based discretization methods. Based on the discrete-time model, the deadbeat control scheme combined with the space vector pulse width modulation (SVPWM) is established. The delay existing in the control loop is compensated by one-step current prediction. Coordinate transformation compensation based on the principle of voltage-second balance is conducted to ensure the effects of the voltage vectors synthesized by the inverters in the stationary frame are the same as those of the ideal reference voltage vectors in the synchronous rotating frame. Simulation results have been given to verify the validity of the proposed discrete-time modeling method and control schemes.