Electrical Drives Situational-Based MCQs - Advanced to Expert

You are designing a high-speed spindle motor for CNC. Which control method ensures precision and stability?

• Scalar control (V/f)

• Field-Oriented Control (FOC) with encoder feedback

• Open-loop PWM

• Phase-angle control

A high-speed drive exhibits oscillations during acceleration. What control strategy can help stabilize it?

• Increase PWM frequency

• Apply notch filter and feedforward control

• Use soft starter

• Use DTC

A traction motor requires torque boost during low-speed startup. Best solution?

• High rotor inertia

• Voltage boost at low frequency or flux compensation

• Phase reversal

• Pulse injection

Your regenerative elevator drive fails under peak load. Likely reason?

• Motor too large

• DC link overvoltage and inadequate braking resistor sizing

• Excessive slip

• Bad alignment

In sensorless vector control, what can cause instability at low speeds?

• Over-modulation

• Inaccurate rotor flux estimation due to low back EMF

• High V/f ratio

• Encoder noise

In a PMSM drive with FOC, what causes torque ripple at high speed?

• Demagnetization

• Improper current vector angle control

• Low frequency noise

• Low carrier modulation

A BLDC motor used in robotics stalls under sudden load. Recommended strategy?

• Increase speed

• Implement current limit and acceleration ramping

• Use DTC

• Bypass sensor

During motor coasting, you notice slow deceleration. What would improve braking performance?

• Lower frequency

• Short motor leads

• Dynamic braking using resistor or regenerative inverter

• Lower DC link voltage

For torque-sharing between motors on a conveyor, which approach is best?

• Equal V/f drive

• Master-slave vector control with load balancing

• DOL start

• Use star-delta

A servo drive overshoots position at every cycle. What tuning change helps?

• Reduce integral gain

• Increase derivative gain to damp response

• Increase proportional gain only

• Reduce encoder resolution