Control strategies for direct torque control using discrete pulse modulation

A scheme for direct torque control of AC machines using discrete pulse modulated inverters, such as the resonant DC link inverter, is presented. A unique feature of the control method presented is that only one current sensor in the DC link is required. Excellent control of torque, stator flux and motor current waveshapes is obtained without affecting the high dynamic performance associated with the direct self-control of machines. A control that does not use the zero voltage vector is defined, and an observer is proposed for estimation of the motor current using only one current sensor in the DC link. A direct bang-bang (sliding mode) torque controller is then derived on the basis of this current observer. Experimental verification of simulation results on a resonant DC link inverter drive with a switching frequency of 27 kHz is included. The inverter switching scheme is implemented using a real-time Motorola DSP56000 digital signal processor-based controller.<>