Solid State Drive Control Questions and Answers

Answer: C

Correct answer: no dc link at all

A matrix converter connects each output phase directly to each input phase through bidirectional switches, converting from one ac frequency to another in a single stage. The absence of a dc link removes the electrolytic capacitor, which is the component that most limits a conventional drive’s life, at the cost of a considerably more complex modulation problem.

Answer: D

The output cannot exceed about eighty-six per cent of the input voltage, and commutating between bidirectional switches without shorting the supply or open-circuiting the load needs careful multi-step sequencing. Those two obstacles have kept it out of general use.

Answer: A

Correct answer: more voltage steps and therefore less distortion

A multilevel inverter synthesises the output from several dc levels rather than two, so each step is smaller and the waveform approaches a sine more closely. Harmonic distortion falls, the rate of rise of voltage falls with it, and each device blocks only a fraction of the total - which is what makes the topology attractive at medium voltage.

Answer: B

Connecting the output to the capacitive mid-point through those diodes gives the third level, so each device sees only half the link voltage. Balancing the two capacitor voltages is the control problem such a topology brings.

Answer: C

Each cell contributes its own voltage step and the cells are summed in series, so many levels are available. Each cell needs an isolated dc source, which is why the topology suits drives fed from a multi-winding transformer or from batteries.

Answer: D

A machine at six or eleven kilovolts needs blocking voltages beyond a single practical device, and series connection with static and dynamic voltage sharing is difficult. Multilevel topologies divide the voltage by construction.

Answer: A

Switching devices in place of diodes let power flow either way, which gives regeneration, and also let the supply current be shaped to be nearly sinusoidal at unity power factor. Roughly doubling the front-end cost is what it takes.

Answer: B

Both benefits come from the same capability, since shaping the current and passing it either way are the same freedom. Where neither regeneration nor harmonic compliance is needed, the diode bridge remains the sensible choice.

Answer: C

Correct answer: the reference amplitude to the carrier amplitude

The modulation index is the ratio of the modulating signal to the triangular carrier, and it sets the fundamental output as a fraction of what the link can supply. Below one the relation is linear; above one the inverter over-modulates, gaining a little fundamental voltage at the cost of low-order harmonics.

Answer: D

Once pulses begin to be dropped, the output is no longer a faithful reproduction of the reference and harmonics at low multiples of the fundamental appear. Those harmonics produce torque ripple and extra loss in the machine.