Enhanced inverter switching for fast response direct torque control[of induction motor drives]

摘要

In classical direct torque control (DTC), an inverter switchingnevent can occur once in each control update period. Because the naturenof the inverter switching event is unconstrained, it is essential tonlimit the inverter switching frequency, and hence the control updatenperiod, to ensure that under no circumstances is the allowable switchingnfrequency of any individual power device exceeded. Consequently thenswitching capability of individual power devices is generallynunder-utilized, and the control scheme produces high levels of ripple innthe motor current and torque. This paper describes a new strategy forndevice switching and voltage vector selection in DTC. The basis of thenstrategy is an increase in the control update frequency, while limitingnthe switching rate of each inverter leg. Although the rate at whichndevice switching events may occur is unchanged, the higher controlnupdate frequency leads to higher resolution timing of switching events.nThe advantages of the strategy, demonstrated by experimental results onna 3 kW induction motor drive, are a significant reduction in thensteady-state torque ripple as well as a faster transient response