Application of cascaded H-bridge multilevel inverter in the speed regulation of medium- and high-voltage asynchronous motor

Medium- and high-voltage motors are characterized by high power and large inertia, and are widely used in industrial frequency conversion. The cascaded H-bridge multilevel (CHB-ML) inverter adopts a modular design concept to realize high-voltage and high-power functions by cascading multiple identical low-voltage conversion units. Moreover, the harmonic content of the output current of the inverter is small. For this purpose, a multilevel inverter consisting of eight H-bridge inverter units cascaded in each phase is introduced to drive medium- and high-voltage asynchronous motors for starting and frequency regulation. The carrier phase-shifted sinusoidal pulse-width modulation technique, DC voltage equalization control of power unit, and speed sensorless vector control strategy based on a voltage–current hybrid chain observer are mainly introduced. The simulation and experimental results of the real-time digital simulation system (RTDS) of the asynchronous motor dragged by the inverter verify that the CHB-ML inverter with the proposed control strategy has good starting and frequency regulation performance. These findings provide a technical guarantee for the field of medium- and high-voltage high-power drives.