A Simple Overmodulation Strategy in Direct Torque Control of Induction Machines

A fast dynamic torque and high speed operations are so important especially in electric vehicle applications. In principle, there are two approaches to obtain these conditions. One is the use of mechanical gears and the other one is the use of overmodulation strategy. Through overmodulation strategy, the inverter voltage can be increased beyond its linear modulation range, thus full utilization of DC-linked voltage is achieved. This paper presents a simple overmodulation strategy that is well- suited in a constant frequency torque controller-based of direct Torque control (DTC) of induction motor drives. The simple overmodulation strategy is constructed based on torque and flux errors and flux position which are readily available; as required in conventional DTC scheme. The simulation results showed that the drive system is capable of operating in overmodulation and field weakening regions without resolving to the common approach of space vector modulation (SVM) based approach.