The transfer function of an ideal derivative controller is:
Answer: A
A derivative controller has transfer function Gc(s) = Kd·s, where Kd is the derivative gain. It provides leading phase.
Q.122Easy
For a system G(s) = K(s+2)/[s(s+1)(s+3)], the number of asymptotes in root locus is:
Answer: B
Number of asymptotes = |poles - zeros| = |3 - 1| = 2. Three poles, one zero gives 2 asymptotes.
Q.123Easy
In digital control systems, the sampling theorem requires sampling frequency to be:
Answer: A
Nyquist sampling theorem: fs > 2·fmax to avoid aliasing. The sampling frequency must be at least twice the highest frequency component.
Q.124Easy
A second-order system has natural frequency ωn = 10 rad/s and damping ratio ζ = 0.5. The peak overshoot percentage is approximately:
Answer: A
Using the formula for peak overshoot: Mp = exp(-ζπ/√(1-ζ²)) × 100 = exp(-0.5π/√0.75) × 100 ≈ 16.3%. This is independent of ωn.
Q.125Easy
A PID controller Gc(s) = Kp + Ki/s + Kd·s is applied to a process. Which parameter adjustment would primarily reduce steady-state error without affecting transient response significantly?
Answer: B
The integral term (Ki) directly addresses steady-state error by accumulating past errors. Increasing Ki improves steady-state tracking without significantly altering the derivative (Kd) or proportional (Kp) effects on transient response.
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Q.126Easy
Which of the following is a unidirectional device in power electronics?
Answer: D
Both diodes and thyristors are unidirectional devices that conduct current in only one direction. MOSFETs are bidirectional.
Q.127Easy
The forward voltage drop across a silicon diode at room temperature is approximately:
Answer: B
Silicon diodes have a typical forward voltage drop of 0.6-0.7 V at room temperature. Germanium diodes have ~0.3 V.
Q.128Easy
Which device is used to convert DC to AC power?
Answer: B
An inverter converts DC power to AC power. Rectifiers do the opposite (AC to DC). Choppers convert DC to DC.
Q.129Easy
The peak inverse voltage (PIV) rating of a diode is important to prevent:
Answer: B
PIV rating defines the maximum reverse voltage a diode can withstand without breaking down. Exceeding this causes reverse breakdown and device failure.
Q.130Easy
In MOSFET, the gate-source voltage at which current starts to flow is called:
Answer: B
Threshold voltage (Vth) is the gate-source voltage required to create an inversion layer and allow current flow in MOSFET.
Q.131Easy
In a buck converter, the output voltage is always:
Answer: A
A buck converter steps down the input voltage. The output voltage Vo = D×Vin where D is the duty cycle (0 < D < 1), making output always less than input.
Q.132Easy
The maximum frequency of a thyristor is typically limited by:
Answer: B
Turn-off time (tq) determines the minimum period required between successive gate pulses, thus limiting the maximum operating frequency of thyristors.
Q.133Easy
A PWM inverter with sinusoidal modulation produces output voltage with:
Answer: B
Sinusoidal PWM produces a voltage waveform containing the fundamental frequency plus high-frequency harmonics that can be filtered out.
Q.134Easy
The presence of freewheeling diode in a DC motor drive is essential because it:
Answer: A
The motor inductance tends to maintain current flow. The freewheeling diode provides a path for this current when the main switch is off, preventing voltage spikes.
Q.135Easy
In a boost converter operating in continuous conduction mode (CCM), if the duty cycle is 0.5 and input voltage is 12V, what is the output voltage?
Answer: A
For a boost converter, Vo/Vin = 1/(1-D). With D=0.5, Vo = 12/(1-0.5) = 24V
Q.136Easy
Which of the following devices is a unidirectional switch in power electronics?
Answer: A
A diode conducts only in one direction (forward bias), making it a unidirectional switch
Q.137Easy
In a half-bridge inverter, what is the minimum number of switches required to generate AC output from DC source?
Answer: A
A half-bridge inverter requires 2 switches (typically with 2 diodes) to generate AC output from a DC source
Q.138Easy
What is the primary purpose of a freewheeling diode in a buck converter?
Answer: B
The freewheeling diode provides a continuous path for the inductor current during the switch OFF period, preventing voltage spikes
Q.139Easy
In a three-phase full-bridge inverter, the total number of thyristors required is:
Answer: C
A three-phase full-bridge inverter requires 6 thyristors (2 per phase) to generate three-phase AC output
Q.140Easy
In a buck-boost converter, the polarity of output voltage compared to input is:
Answer: B
A buck-boost converter produces an output voltage of opposite polarity to the input voltage, with magnitude |Vo| = Vin × D/(1-D)
