Modified switching schemes for direct torque controlled bldc motor drives

Abstract

The rapid development of power semiconductor devices has led to the increased use newlineof adjustable speed AC drives in a variety of industrial and locomotive applications. newlineThe efficiency of the drives can be improved by controlling the speed effectively newlineand thus leading to savings in energy. Among the AC machines, Permanent Magnet newline(PM) machines are receiving significant attention in drives applications owing to its newlinemerits in the rotor structure, simplicity in control, high torque/size ratio and noiseless newline newlineoperation. Permanent Magnet machines are structurally similar to synchronous ma- newlinechines with the wound rotor replaced by permanent magnets. Depending on the shape newline newlineof motor back EMF waveform, PM machines are classified as Permanent Magnet newlineSynchronous Motors (PMSM) with sinusoidal back EMF and Brush-Less Direct newlineCurrent (BLDC) Motors having trapezoidal back EMF. Although various strategies newlineexist to control AC motors, Direct Torque Control (DTC) promises to offer favorable newlinecontrol performance in varying the speed and torque of the machine over a wide newlinerange in addition to simplicity in the hardware realization. The absence of voltage newlinemodulation is exploited in DTC to achieve minimal torque response time. Apart newlinefrom the advantages, inherent torque and flux ripples during starting, occurrence of newlineswitching frequency variations and requirement of machine parameter values for newlineimplementing the algorithm are the problems associated with DTC. Normally two newline phase voltage vectors are used for the inverter switching for DTC fed BLDC due newlineto its constructional specialities. Hence, the switching vector table for the torque newline newlineincrement and decrement in DTC are formulated by satisfying the design consid- newlineerations. However, the reported works on DTC fed BLDC are not addressing the newline newlineproblem of switching frequency variations. newline