Question 5.1: The motor model developed earlier, with the d-axis aligned w......
The motor model developed earlier, with the d-axis aligned with \vec{\lambda}_r, can be used to model induction machines where vector control is not the objective. To illustrate this, we will repeat the simulation of Example 3-3 of a line-fed motor using this new motor model (which is much simpler) and compare simulation results of these two examples.
We need to recalculate initial flux values because now the rotor flux linkage is completely along the d-axis. This is done in a MATLAB file EX5_1calc.m on the accompanying website. The initial part in this file is the same as in EX3_1.m (used in Example 3-3), in which the initial values of the angles thetar and thetas for \vec{\lambda}_r and \vec{\lambda}_s are calculated with respect to the d-axis aligned to the stator a-axis with θ_{da}(0) = 0. In the present model, with the d-axis aligned with \vec{\lambda}_r, the rotor flux linkage angle is zero, and the stator flux linkage angle with respect to the d-axis equals (thetas—thetar) in terms of their values in EX3.1m.
The Simulink schematic for this example is called EX5_1.mdl (included on the accompanying website) and its top-level diagram is shown in Fig. 5-5. The resulting torque and speed plots due to a load torque disturbance in this line-fed machine are plotted in Fig. 5-6, which are identical to the results obtained in Example 3-3.
