DIRECT TORQUE CONTROL OF INDUCTION MACHINES USING SPACE VECTOR MODULATION

This paper describes a control scheme for direct torque and flux control of induction machines based on the stator flux field-orientation method. With the proposed predictive control scheme, an inverter duty cycle has directly calculated each fixed switching period based on the torque and flux errors, the transient reactance of the machine, and an estimated value of the voltage behind the transient reactance. The paper describes a method by which a voltage space vector can be calculated in order to control the torque and flux directly in a deadbeat fashion. The inverter duty cycle can then be calculated using the space vector PWM technique. With this scheme, the requirement of a separate current regulator and proportional-integral (PI) control of the flux, torque, and/or current error is eliminated, thereby improving transient performance. An alternative modulation scheme is presented in which transient performance is improved by specifying the inverter switching states a priori, then calculating the required switching instants to maintain deadbeat control of the flux while reducing the torque error during the entire switching interval. A similar approach is used for a transient in the flux. The implementation of the control scheme using DSP-based hardware is described, with complete experimental results given.