High Power Motor Drives Based On Hybrid Multilevel Converters and Direct Torque Control

A new control set of the single dc source hybrid (cascaded) multilevel converter topologies for high power motor drives is proposed in the paper. First, it guarantees that the main and auxiliary converters switch at the pure fundamental frequency (IGCT) and PWM frequencies (IGBT), respectively. Compared to the previous research, the new control set has much less computational burden and offers more straightforward and robust capacitor voltage control for the hybrid (cascaded) inverter cell without dc sources. At the same time, it tracks the fast changing motor drive reference voltage magnitude and frequency instantaneously. Therefore, it is readily integrated into the motor drive controls with fast dynamics, such as direct torque control as used in this work. Several practical issues in its implementation, such as capacitor voltage ripple, capacitor precharging and initial stator flux buildup, are analyzed in detail. Finally, detailed simulation results and lab data verify the proposed control.