Electrical Drives Quiz - Intermediate Level

In vector control of an induction motor, what is the role of rotor flux orientation?

• To align torque with slip

• To decouple torque and flux control

• To reduce harmonics

• To enable synchronous braking

You’re implementing closed-loop speed control in a DC motor. What component is essential for feedback?

• Capacitor

• Tachogenerator or encoder

• Contactor

• Resistor

A VFD drive connected to an induction motor is producing torque ripple. Most likely cause?

• High modulation index

• Improper carrier frequency

• Zero slip

• Low temperature

In regenerative braking using a four-quadrant chopper drive, which component manages power flow back to the supply?

• Freewheeling diode

• Step-down converter

• Reversible switch matrix or controlled bridge

• MOV

In a multi-motor hoisting system, speed mismatches are observed. What solution ensures equal torque sharing?

• Separate VFDs with encoder feedback and master-slave synchronization

• Same rated power

• Increase slip

• Use one large motor

Why is field weakening used in high-speed operation of drives?

• To reduce voltage

• To increase field flux

• To allow operation beyond base speed at constant power

• To improve starting torque

A synchronous motor lags at light load. How can you correct power factor?

• Use damper windings

• Increase stator current

• Increase excitation (over-excited mode)

• Increase rotor resistance

Which modulation strategy in inverters improves motor efficiency and reduces THD?

• Square wave

• Harmonic injection

• Sinusoidal PWM (SPWM)

• Cycloconverter

In field-oriented control, what quantity is transformed to dq reference frame?

• Voltage only

• Current and voltage

• Phase currents and rotor flux

• Speed only

Why is slip important in an induction motor under load?

• It reduces starting torque

• It allows rotor to generate torque

• It increases power factor

• It controls frequency