A single-phase full wave fully controlled SCR bridge rectifier with RL load in continuous conduction mode has a pure DC load current of 50A, where the supply voltage is 230V 50Hz, Sketch the circuit diagram with all circuit components.

Question 1: Single- Phase Controlled Rectifier with Inductive Load [30 Marks]

(a) A single-phase full wave fully controlled SCR bridge rectifier with RL load in continuous conduction mode has a pure DC load current of 50A, where the supply voltage is 230V 50Hz, Sketch the circuit diagram with all circuit components.

[5 Marks]

Answer:

(b) If the load inductive reactanceωL>>R, the firing angle of SCR for positive half cycle is 60° and the firing angle of SCRs for negative half-cycle is 240°. Determine: i) the average value of the output voltage; (ii) the rectification efficiency; (iii) the form factor;(iv) the ripple factor and (v) Peak Reverse Voltage (PRV) of each SCR.

i) the average value of the output voltage [8 marks]

Answer:

ii)the rectification efficiency [2 marks]

Answer:

(iii) the form factor [2 marks]

Answer:

(iv) the ripple factor [2 marks]

Answer:

(v) Peak Reverse Voltage (PRV) of each SCR. [2 marks]

Answer:

(c) Explain the TWO effects of placing a FWD diode across the load. [4 marks]

Answer:

(d) Sketch the aligned (i) supply voltage waveform (ii) the output voltage waveform and (iii)the output current waveform, for one cycle of the input waveform. Label the amplitudes and angles clearly.

[5 Marks]

Answer:

Question 2: Switching Regulator [26 Marks]

(a) State the methods for ripple current reduction. [4 Marks]

Answer:

(b) A Boost switching regulator operates at a frequency of 1 kHz. The source voltage is 50 V DC and the load resistance is 2Ω. Itsefficiency is 90%. If the average value of the load current is 100A. Determine: (i)the power dissipated by the load; (ii) the load voltage; (iii) the duty cycle; (ii) the average value of source current and (iv) the average value of the switch current. [12 Marks]

Answer:

(c) An inverting switching regulator operates at a frequency of 1kHz. The source voltage is100V and the load resistance is 3Ω. If the average value of the load current is 100A, determine: (i) the Dc voltage across the load; (ii) the average power dissipated by the load; (iii) the duty cycle of the switching waveform; (iv) the input power from the source if the efficiency of the regulator is 90%; (v) the average value of source current. [10 Marks]

Answer:

Question 3: Three-Phase Uncontrolled Rectifier [16 Marks]

A three-phase full wave uncontrolled rectifier is operated from a 415V 50Hz Supply and the load resistance is 40Ω. Determine (i) the average output voltage (ii) the RMS output voltage (iii) the Dc load current (iv) the RMS load current (v) efficiency (vi) form factor (vii) ripple factor (viii) peak inverse voltage of each diode. [16 Marks]

Answer:

Question 4: DC-to-AC Inverter [28 Marks]

(a) Sketch the half bridge voltage inverter circuit diagram with all circuit components. [6 marks]

Answer:

(b) Fill up the following table condition for the half bridge voltage inverter circuit diagram circuit. [4 marks]

S1 S2 V0 Reason
0 0
0 1
1 0
1 1

(c) Sketch the (i) supply voltage waveform (ii) the output voltage waveform and (iii) the output current waveform, (iv) one switch current waveform (v) one diode current waveform for one cycle of the input waveform for half bridge voltage inverter circuit diagram. Label the amplitudes and time periods clearly. [5 marks]

Answer:

(d) Describe TWO different features of 120° and 180° conduction mode three-phase bridge inverters with a Y-connected balanced resistive load. [8 marks]

Answer:

(e) A three-phase bridge inverter supplies a Y-connected resistive load with 20Ω per phase and 30 Ω total resistance. The DC source voltage is 900V and the inverter operates in 180° conduction mode. Determine: (i) the source current; (ii) the average power absorbed by the load; (iii) the RMS value of output phase voltage; and (iv) the RMS value of output line voltage. [5 marks]

(i) the source current

(ii) the average power absorbed by the load

(iii) the RMS value of output phase voltage;

(iv) the RMS value of output line voltage.

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