A Grid-Tied AC Drive Using a Multilevel Topology Obtained from the Nine-Switch Converter

Nine-switch inverters, has been widely used in several power systems applications, especially for a dual motor or six-phase machine. Due to their interesting features such as the reduced switch number, this structure has been extended to multilevel topologies. Among the several multilevel topologies, the active-neutral-point-clamped (ANPC) based nine-switch multilevel converter (ANPC-NSMC) has been one of the interesting solutions. In this paper, instead of using this topology for a dual motor or six-phase motor, it is proposed a back-to-back application. In this way, one of the outputs is connected to the grid, while the other output is connected to the three-phase motor. However, for drives a closed loop control is needed. Therefore, a field-oriented controller and a model predictive control (MPC) strategy to control this AC drive is also proposed. The MPC will be used for closed loop current control, as well as for mitigation of the capacitor voltages imbalance. This optimal predictive controller allows the minimization of a cost functional weighing three criteria, the tracking errors of the three-phase AC currents of each side, as well as the two capacitors voltage imbalance. The performance of the proposed control strategy will be verified and discussed through several simulations results.