Sensor-less vector control of induction motor at low-speed operation using modular multilevel converter

ABSTRACT Modular Multilevel Converter (MMC) is widely known as one of the most promising topologies for high power medium voltage application. However, MMC is still limited when it comes to Variable Speed Drive (VSD) applications. The reasons behind this is the large fluctuations in the submodules capacitor voltages during low-speed constant torque operation. Thus, the feasibility of sensor-less vector control of MMC based variable speed drive is considered as a difficult task. This paper proposes a novel speed observer for MMC-based VSD suitable for low-speed operation. Speed estimation is carried out by using the stator currents and the input voltages. A discrete model where the rotor parameters do not change during a short sampling time is considered. An extensive simulation is carried out for verifying the closed loop operation of the proposed speed sensor -less MMC-based VSD.