Simulation Study on Four-quadrant Cascade Multilevel Inverter Based on AC Voltage Sensorless Simple Cell

This paper proposes an AC voltage sensorless simple four-quadrant structure which can be used in cascade multilevel inverter. The AC input voltages of every cell in combination with the AC filter inductors can be assumed to be quantities related to a virtual AC motor. The AC input voltages are induced by a virtual air-gap flux (VF). Using VF for instantaneous powers estimation, the AC input voltages need not to be detected and the AC voltage sensors are removed. Through transforming the outputs of the controllers of both active and reactive powers into two-phase static coordinates, the traditional SVPWM is used in direct power control (DPC) strategy, thus constant frequency VF-DPC is realized. The proposed simple structure has the merits as follows: fewer sensors, stranger ant-jamming ability, better static and dynamic control performance, bidirectional power flowing freely, and lower harmonic of both the input and output currents. The simulation results indicate its validity and feasibility.