Consider the case in which the load on the synchronous motor in the field oriented torque-control system of Problem 11.13 is increased, and the motor begins to slow down. Based upon some knowledge of the load characteristic, it is determined that it will be necessary to raise the torque set point Tref from 50 percent to 80 percent of the motor-rated torque to return the motor to its rated speed.

a. If the field current were left unchanged at 14.0 A, calculate the values of quadrature-axis current, rms armature current, and motor line-to-line terminal voltage (in V and in per unit) which would result in response to this change in reference torque.

b. To achieve this operating condition with reasonable armature terminal voltage, the field-oriented control algorithm is changed to the unity power-factor algorithm described in the text prior to Example 11.9. Based upon that algorithm, calculate

(i) The motor terminal line-to-line terminal voltage (in V and in per unit).

(ii) The rms armature current.

(iii) The direct- and quadrature-axis currents, iD and iQ.

(iv) The motor field current.