A NEW SWITCHING PATTERN FOR DIRECT TORQUE CONTROL OFA PERMANENT MAGNET SYNCHRONOUS MOTOR DRIVE

Abstract

This paper aims to enhance the performance of the direct torque control (DTC) of a permanent magnet synchronous motor drive. Direct torque control has several advantages such as fast transient response, less parameter dependence. It has no need either to pulse width modulation, current control loop or to speed sensor. However, the high torque and flux ripples content are considered one of the main problems of DTC. The two band hysteresis comparators of the torque and flux are the main reason beyond this problem. The inverter state does not change until the hysteresis outputs change. The slow change in the hysteresis output causes slow change in the inverter states which in turn increases the ripple content in motor torque. In this paper, a new switching pattern using non-hysteresis controllers and new look up table are proposed. Three band flux controller and five band torque controller are used instead of the conventional two band controllers. Zero and active voltage vectors are inserted into the conventional lookup table. The proposed technique neither needs additional measurements nor space vector modulation techniques. Simulation works are carried out to compare the performance of classical and proposed techniques. The torque, flux, current, and speed waveforms of the proposed and classical schemes are compared.