Delta current control for vector controlled permanent magnet synchronous motors

For the delta controller, the delta frequency must be chosen with respect to the required characteristics of torque, peak current, and the average switching frequency of the inverter power transistors. These characteristics are studied experimentally, using computer simulation and with mathematical analysis, with respect to the variables of delta frequency, DC supply voltage, and the reference current magnitude. At low delta frequencies, there is an exponential increase in the mean torque and peak current. An approximate analytical expression is given to predict the delta frequency at which this operating region commences. The effect of the motor speed on the torque is shown to enable the minimum required supply voltage to be chosen, and the upper bound on the delta frequency is shown to be determined by the maximum acceptable average switching frequency