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Ain shams University 3rd

year MechatronicsFaculty of Engineering Industrial Electronics

Electrical Power & Machines Dept 2010-2011

Sheet (4)

1) Answer the following questions.a) What are the main applications of ac voltage controllers?

b) Draw different circuits for realizing the single-phase full-wave ac voltage

controller and mention the main feature of each circuit.

c) Despite it is more expensive, the full-wave ac voltage controller is preferred

over half-wave one. Why?

d) Suggest suitable power semiconductor switches for phase-controlled and

PWM-controlled ac choppers. Support your selection by reasons.

e) What are the main limitations of ac voltage controllers?

2)For a single-phase ac voltage controller as in Fig. 1 and delay angle = /2, answerthe following questions.

a) Draw the output voltage, output current, and thyristor voltage waveforms.

b) Determine the rms output voltage, rms output current, and input power factor.

The load and supply information is:

R=10 ohms Vs = 120 V (rms) f=60 Hz.

3) The single-phase ac voltage controller of problem 2 is now supplying an RL-load.

The load is such that L = 2.5 mH and R = 2.5 ohms. For a delay angle =/2,

answer the following questions.

a) Draw the output voltage, thyristor voltage, and output current waveforms.

b) Determine the conduction angle and rms output voltage.c) Determine the rms output current and input power factor (use the trapezoidal

method of integration).

4) For a single-phase ac voltage controller as in Fig.1

a) Explain briefly the gate requirements of the SCRs.

b) Why is it good practice to use carrier frequency gating rather than sustained

continuous gate pulse in case of RL-load.

c) Draw the envelope of control characteristics.

d) If the measured output voltage was constant at 120 V (rms) for a firing angle

range of 0

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Figure 1

Figure 2

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Matlab/simulink simulation results for problem 3.