Motor drives

Abstract

Direct-current motors are extensively used in variable-speed drives and position-control systems where good dynamic response and steady-state performance are required. Depending on the application requirements, the power converter for a dc motor may be chosen from a number of topologies. The ac induction motor is by far the most widely used motor in the industry. Traditionally, it has been used in constant and variable-speed drive applications that do not cater for fast dynamic processes. When an induction motor is driven from an ideal ac voltage source, its normal operating speed is less than 5% below the synchronous speed, which is determined by the ac source frequency and the number of motor poles. The motor voltage waveforms are determined by the load. These waveforms are more nearly sinusoidal than the current waveforms. The thyristor converter supplying the quasi-square current waveforms to the motor has firing-angle control, in order to regulate the dc-link current to the inverter. In spindle and other variable-speed drive applications, where the lowest speed of operation is not less than a few hundred revs/min, it may be possible to obtain the switching signals for the inverter from the motor back-emf, thus dispensing with rotor-position sensors. © 2011 Elsevier Inc. All rights reserved.