Problems #6

1. (a) Explain clearly why a trapezoidal PMSM drive with self-control should be defined as electronically commutated dc motor (ECM) or brushless dc motor (BLDM). What are the exact differences between ECM and conventional dc motor?

(b) Since all the synchronous machine drives with self control have dc machine property, explain justification of defining trapezoidal PMSM drive as BLDM.

(c) A ECM is being controlled to regulate phase current by hysteresis-band PWM method. Explain the operation with the help of voltage and current waveforms.

(d) Show that phase current is proportional to developed torque.

(e) Why absolute position sensor is needed for the control?

2. Discuss the operation of the following converter topologies used with a BLDCM drive:

(a) Split Supply Converter Topology,

(b) C-Dump Topology

3. Discuss a scheme to control speed of a BLDM in PWM Feedback mode.

4. Discuss the merits and limitations of the BLDM drive. Also explain how torque pulsation may be reduced for this drive.