Answer Happy

A 4-pole 3-phase, 50 Hz, Y-connected, non-salient pole synchronous motor has the following parameters: R = 1.25 22/phase; X5o = 12.50/phase @50 Hz The motor induced emf/phase at base speed, E, is 200 V. Vrated = 230 V/phase; Irated = 20 A/phase. The motor is driven from a current source inverter (CSI) which supplies three-phase sinusoidal currents of variable frequency to the motor. The switching of the inverter is synchronized with rotor position in such a way that the stator current phasor of each phase can be set at any arbitrary phase angle y with respect to the back emf phasor Ef of the corresponding phase. (a) Assuming that the motor is to be driven such that it develops its highest torque per ampere (MTPA) characteristic, calculate the amplitude of the stator current when the motor develops 80 Nm while operating at 700 rev/min. Sketch the per-phase phasor diagram of the motor for this condition of operation and indicate the Id and Ig components of the phase current. (b) Calculate the power developed by the motor for this condition of operation. (c) Calculate the power factor with which the motor will operate. (d) In order to improve the power factor of the drive, the commutation angle y of the stator current is advanced by 30°. In other words, the I phasor is set at 30° of lead angle with respect to the Esphasor. Calculate the stator current amplitude when the motor develops 80 Nm while operating at 700 rev/min. Sketch the phasor diagram for the motor for this condition of operation and indicate the Id and I values in this diagram. (e) Calculate the power factor with which the motor will now operate.