A PWM inverter produces an output frequency of 50Hz with a carrier frequency of 10kHz. What is the modulation index if the peak modulating signal is 0.8V and the peak carrier signal is 1V?

The correct answer is C: 0.8. Modulation index m = Vm/Vc = 0.8/1 = 0.8, where Vm is peak modulating signal and Vc is peak carrier signal.

A 3-phase induction motor draws 50 A at 0.8 power factor lagging from 400 V supply. The input power is approximately:

The correct answer is B: 27.71 kW. P = √3 × V × I × cosφ = 1.732 × 400 × 50 × 0.8 = 27,712 W ≈ 27.71 kW

In a 8-bit barrel shifter, how many control bits are required to specify any shift amount?

The correct answer is B: 3 bits. For an 8-bit barrel shifter, 3 control bits can specify 2^3 = 8 different shift positions (0 to 7), covering all possible shifts.

The commutation of a thyristor in a circuit means:

The correct answer is C: Turning it off by making anode current zero. Commutation is the process of turning off a thyristor by reducing anode current to below holding current value (natural commutation in AC circuits or forced commutation in DC).

A combinational circuit has 6 input variables. The minimum number of rows required in its truth table is:

The correct answer is B: 64. For n input variables, truth table rows = 2^n. For 6 inputs: 2^6 = 64 rows.

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Electrical Engg (EEE)
Control Systems

Electrical machines, power systems, circuits

53 Q 7 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 53

Topics in Electrical Engg (EEE)

All Circuit Analysis 100 Electrical Machines 100 Power Systems 100 Control Systems 100 Power Electronics 100 Electrical Measurements 40 Digital Electronics 100

Q.21 Medium Control Systems

A system exhibits steady-state error of 0.2 for unit ramp input with loop gain K = 50. The static velocity error constant is:

A 5 sec⁻¹

B 10 sec⁻¹

C 2.5 sec⁻¹

D 20 sec⁻¹

Correct Answer: A. 5 sec⁻¹

EXPLANATION

For ramp input, ess = 1/Kv. Given ess = 0.2, therefore Kv = 1/0.2 = 5 sec⁻¹

Test

Q.22 Medium Control Systems

For a unity feedback control system with G(s) = 10/[s(s+5)], the static velocity error constant Kv is:

A 2 sec⁻¹

B 10 sec⁻¹

C 50 sec⁻¹

D 5 sec⁻¹

Correct Answer: A. 2 sec⁻¹

EXPLANATION

Kv = lim(s→0) s·G(s) = lim(s→0) s·10/[s(s+5)] = 10/5 = 2 sec⁻¹

Test

Q.23 Medium Control Systems

In a compensated system, if phase margin PM = 30° and gain margin GM = 8 dB, this indicates:

A Excellent stability with fast response

B Marginal stability with oscillatory response

C Good stability with acceptable transient response

D Poor stability requiring redesign

Correct Answer: C. Good stability with acceptable transient response

EXPLANATION

PM = 30° is acceptable (typically 30-60°), GM = 8 dB (>6 dB threshold) indicates good gain stability. Both margins suggest satisfactory performance

Test

Q.24 Medium Control Systems

In a unity feedback system, increasing loop gain K generally:

A Increases steady-state error and decreases stability margins

B Decreases steady-state error but may reduce stability margins

C Increases both steady-state error and stability

D Has no effect on steady-state error

Correct Answer: B. Decreases steady-state error but may reduce stability margins

EXPLANATION

Higher K reduces ess proportionally but shifts root locus rightward, potentially crossing into RHP, thus reducing stability margins

Test

Q.25 Medium Control Systems

A system has poles at -2±j3. The natural frequency and damping ratio are approximately:

A ωn = √13, ζ = 0.55

B ωn = √13, ζ = 1.45

C ωn = 5, ζ = 0.4

D ωn = 3, ζ = 0.67

Correct Answer: A. ωn = √13, ζ = 0.55

EXPLANATION

ωn = √(4+9) = √13 ≈ 3.6 rad/s, ζ = 2/√13 ≈ 0.55

Test

Q.26 Medium Control Systems

Which compensator is preferred for improving steady-state error without significantly affecting transient response?

A Lead compensator

B Lag compensator

C PID controller

D Proportional controller

Correct Answer: B. Lag compensator

EXPLANATION

Lag compensator increases DC gain significantly, improving steady-state error, while its phase lag is restricted to lower frequencies, minimizing transient effects

Test

Q.27 Medium Control Systems

For an underdamped second-order system, the relationship between settling time ts and damping ratio ζ is:

A ts ∝ 1/ζ

B ts ∝ ζ

C ts ∝ 1/(ζωn)

D ts ∝ ωn/ζ

Correct Answer: C. ts ∝ 1/(ζωn)

EXPLANATION

Settling time ts ≈ 4/(ζωn) for 2% criterion, thus ts ∝ 1/(ζωn)

Test

Q.28 Medium Control Systems

In state-space representation, if eigenvalues of A matrix are at s = -1, -2, -3, the system is:

A Unstable and uncontrollable

B Stable but may be uncontrollable

C Stable and controllable

D Marginally stable

Correct Answer: B. Stable but may be uncontrollable

EXPLANATION

Stability depends only on eigenvalue locations (all in LHP = stable). Controllability requires rank[B AB A²B] = n, which eigenvalues alone don't determine

Test

Q.29 Medium Control Systems

A lead compensator Gc(s) = K(s+a)/(s+b) where b > a provides maximum phase lead at frequency:

A ωm = √(ab)

B ωm = (a+b)/2

C ωm = a·b

D ωm = b/a

Correct Answer: A. ωm = √(ab)

EXPLANATION

For lead compensator, maximum phase lead occurs at ωm = 1/√(τ₁τ₂) where τ₁ = 1/a and τ₂ = 1/b, giving ωm = √(ab)

Test

Q.30 Medium Control Systems

What is the effect of adding a pole at the origin to a stable open-loop system?

A Increases phase margin, decreases gain margin

B Decreases phase margin, increases gain margin

C Decreases both phase and gain margins

D Increases both margins equally

Correct Answer: C. Decreases both phase and gain margins

EXPLANATION

Adding a pole at origin adds -90° phase shift at all frequencies, decreasing phase margin. It also reduces high-frequency gain, decreasing gain margin

Test

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