Problems #5

1. The current vector control of synchronous reluctance motor drive has been classified as:

(1) Constant i_ds control

(2) Fast torque response control

(3) Maximum torque/Amp. Control

(4) Maximum power factor control

(a) Explain why current vector control cannot be defined as true vector control. How does it differ from open loop volts/Hz control? Does machine require damper winding in this drive?

(b)Compare the performance of the above control methods for the following:

· Stator flux variation

· Efficiency

· Torque response

· Power factor

· Operation at zero speed and field-weakening regions

2. Propose a stator flux oriented direct vector control scheme of synchronous reluctance motor drive and explain its operation. How does it generally differ from current vector control method?

3. An IPM synchronous machine is being used with a voltage-fed IGBT inverter to drive an electric vehicle. The drive operates in constant torque as well as constant power field-weakening regions. The stator flux in constant torque region is programmed as function of developed torque to improve light-load efficiency. The salient machine ratings are:

Rated power = 70 hp

No. of poles = 4

Base speed = 3394 rpm (at rated torque and flux)

(a) Explain the salient features of IPM machine drive compared to sinusoidal SPM machine drive. Why IPM is preferred for EV drive, but not the SPM?

(b)Give power circuit of the drive.

(c) Explain the advantages of stator flux programming in the constant torque region. Give a typical stator flux program as function of developed torque and explain how it works.

(d)Give a typical torque-speed curve of the drive and sketch the stator voltage (V_s) and stator flux (y_s) variation with frequency on the same curve at the full torque condition.

(e) Neglecting all the losses, calculate the rated torque and base frequency.

(f) Give a phasor diagram at the rated torque condition showing all the important variables.