6Detuning Effects in Induction Motor Vector Control

In vector control described in Chapters 4 and 5, we assumed that the induction machine parameters were known exactly. In practice, the estimated parameters may be off by a significant amount. This is particularly true of the rotor time constant τ_r (=L_r/R_r), which depends on the rotor resistance that increases significantly as the rotor heats up. In this chapter, we will calculate the steady-state error due to the incorrect estimate of the rotor resistance and also look at its effect on the dynamic response of vector-controlled drives [1,2].

6-1 Effect of Detuning Due to Incorrect Rotor Time Constant τ_r

We will define a detuning factor to be the ratio of the actual and the estimated rotor time constants as

(6-1) $c6-math-0001$

where the estimated quantities are indicated by the subscript “est.” To analytically study the sensitivity of the vector control to k_τ, we will simplify our system by assuming that the rotor of the induction machine is blocked from turning, that is, ω_mech = 0. Also, we will assume an open-loop system, where the command (reference) currents are $c6-math-5001$ and $c6-math-5002$ .