A digital signal processing approach to real-time AC motor modeling

Discrete-time computational models of squirrel-cage AC motors are derived and analyzed for the purpose of advanced motor control. The starting point is a continuous-time model defined by a pair of simultaneous complex-coefficient differential equations. Discrete-time models are derived using both the bilinear transformation and the forward-difference approximation. The exact dependence between stability and the minimum sampling rate in the forward-difference approach is shown. The responses of the two discretized models are compared using real-world motor parameters. Using the forward difference method, a more compact implementation is obtained (although a higher sampling rate is required) as compared to the bilinear transformed model of equivalent performance and 2.7 times higher computational complexity. A 16/24-b DSP-ASIC coprocessor prototype implementing the AC motor model is introduced