Solid State Drive Control Questions and Answers

Answer: A

Carrier-based and vector-based modulators are the two families, and both end with a set of on and off times for each device in each interval. The pattern is recomputed every switching period from the controller's voltage demand.

Answer: B

Solving for the angles that null the fifth, seventh and eleventh, say, gives a very low switching frequency with acceptable distortion. It suits large drives where each switching is expensive and the angles can be precomputed and stored in a table.

Answer: C

Dithering the switching instants turns a pure tone into a broadband hiss, which is far less objectionable even at the same total energy. It also spreads conducted emission, which can help with compliance at particular frequencies.

Answer: D

Correct answer: a line reactor, a multi-pulse arrangement or an active front end

Supply distortion is created by the rectifier drawing current in pulses, so the remedy must act on the input stage. A line reactor smooths the pulses, a twelve or eighteen pulse arrangement cancels the lower harmonics between phase-shifted bridges, and an active front end draws a sinusoidal current outright. Nothing on the inverter side affects it.

Answer: A

Two six-pulse bridges fed thirty degrees apart draw those harmonics in antiphase, so they cancel in the transformer primary. The eleventh and thirteenth survive, and an eighteen- or twenty-four-pulse arrangement pushes the residue higher still.

Answer: B

The current is roughly in phase with the voltage but far from sinusoidal, so the displacement factor is good while the distortion factor is not. A phase-controlled rectifier is the reverse case, with a displacement factor that falls with firing angle.

Answer: C

Lowering the frequency faster than the load will slow makes the machine generate into the link, and with a diode front end the voltage climbs. Lengthening the deceleration ramp, or fitting a braking chopper, is the remedy.

Answer: D

Correct answer: a fault in the output wiring or the machine

An overcurrent trip at every start, immediately, points to a short or an earth fault on the output rather than to anything about the drive’s settings or environment. A ramp that is too aggressive would trip after some acceleration, and thermal problems trip on temperature after a period of running rather than at once.

Answer: A

Thermal trips integrate current over time, so a delayed trip is the signature of a genuine overload rather than a fault. Checking the mechanical load and the drive's current limit settings is the sensible starting point.

Answer: B

Correct answer: a replacement drive must be configured identically

A drive out of the box carries default parameters, and a replacement fitted without the commissioned settings will not run the machine correctly and may damage it. The parameter set is therefore part of the plant record, backed up and stored with the drawings, and a good deal of commissioning time is saved by having it.