Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Section 1
Choose the correct answer of the following (any seven) :
The most suitable device for high frequency inversion in SMPS is
As compared to power MOSFET, a BJT has
In a thyristor-controlled rectifier, the firing angle of thyristor is to be controlled in the range of
In a single-phase full converter, if load current is and ripple free, then average and r.m.s. values of thyristor current are
Match the type of commutation in List-I with their alternative names in List-II and tick the correct answer from the codes given below : List-I (Type of Commutation): A. Class A, B. Class B, C. Class C, D. Class D List-II (Alternative Name): 1. Voltage commutation, 2. Parallel-capacitor commutation, 3. Complementary-impulse commutation, 4. Self-commutation, 5. Natural commutation, 6. Current commutation
For a step-down d.c. chopper operating with discontinuous load current, what is the expression for the load voltage? (where is duty ratio of chopper)
In d.c. choppers, the waveforms for input and output voltages are
A single-phase, voltage source, square wave inverter feeds a pure inductive load. The waveform of the current will be
A single-phase inverter has square wave output voltage. What is the percentage of the fifth harmonic component in relation to the fundamental component?
The most suitable solid-state converter for controlling the speed of the three-phase cage motor at 25 Hz is
Show that the fundamental r.m.s. value of per-phase output voltage of low-frequency for an m$-pulse cycloconverter is given by $V_{or} = V_{ph}(m/\pi)\sin(\pi/m)
Shown in figure below the resonant pulse commutation (or class B commutation) circuit has and . Initial voltage across capacitor is . For a constant load current of 300 A, calculate- (i) conduction time for the auxiliary thyristor; (ii) voltage across the main thyristor when it gets commutated; (iii) the circuit turn-off time of the main thyristor.
Explain the I-V characteristics of a thyristor. Label the various voltages, currents and the operation modes.
A 3-phase full-converter delivers a ripple free load current of 10 A with a firing delay of . The input voltage is 3-phase, 400 V, 50 Hz- (i) draw the waveform of source current and write the expression of Fourier series; (ii) calculate input power factor and THD.
A single-phase full-bridge inverter is connected to a d.c. source . Resolve the output voltage wave shape into Fourier series.
Describe the operation of a single-phase two-pulse mid-point converter with relevant voltage and current waveforms.
For type-A chopper connected to RLE load, write the basic voltage equations and derive the expression for the maximum and minimum value of load current in terms of source voltage .
Hence show that the expression for per unit ripple in the load current of a type-A chopper (Question No. 5(a)) is given by . Where .
A 1-phase full-converter delivers ripple current to RL load with . The source voltage is 230 V, 50 Hz. For a firing angle of , calculate- (i) rectification efficiency; (ii) voltage ripple factor; (iii) THD.
Describe the switching characteristics of power SCR.
Explain the constructional details and working of n-channel power MOSFET.
Describe the switching characteristics of power MOSFETs.
With the help of equivalent circuit, obtain the nature of waveform of phase voltage of a star-connected resistive load fed from a three-phase DC to AC bridge-inverter operating in conduction mode.
Discuss the principle of operation of following choppers, with necessary circuit diagram and waveforms : (a) Step-down chopper (b) Step-up chopper Give comments on chopping frequency.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Section 1
Choose the correct alternative from any seven of the following :
If the peak value of an applied voltage in a full-wave rectifier is , the peak inverse voltage of diode is
If a 50 Hz a.c. signal is fed to a rectifier, the ripple frequency of output voltage waveform for full bridge rectifier is
Which of the following devices should be used as a switch in a low-power switched-mode power supply?
A single-phase full bridge diode rectifier delivers a load current of 10 A, which is ripple free. Average and RMS values of diode currents respectively are
A 3-phase half-wave diode rectifier feeds a load of . For an input supply of 400 V, 50 Hz, the power delivered to the load is
A step-up chopper has as the source voltage and as the duty cycle. The output voltage of this chopper is given by
A chopper circuit is fed with an input voltage of , delivers a load power of 16 W. For a chopper efficiency of 0.8, the input current is
In single pulse modulation of PWM inverters, third harmonic can be eliminated if pulse width is equal to
A single-phase a.c. voltage controller has input voltage of 240 V, 50 Hz and a load of . For 3 cycles on and 2 cycles off, the load would consume a power of
A 3-phase to 1-phase conversion device employs a 6-pulse bridge cycloconverter. For an input voltage of 200 V per phase, the fundamental RMS value of output voltage is
Derive the relation for average output voltage, RMS output voltage and voltage ripple factor of 1-phase full-wave uncontrolled bridge rectifier.
A 1-phase full-wave bridge rectifier circuit fed from a supply. It consists of four diodes, a load resistance and a very large inductance so that the load current is constant. Determine the (i) average output voltage, (ii) average output current, (iii) average value of diode current, (iv) RMS value of diode current, (v) RMS value of input current, (vi) d.c. output power and (vii) input power factor.
Compare at least 8 performance parameters of 1-phase and 3-phase uncontrolled rectifiers.
A 1-phase heater is connected across 1-phase supply through a diode. Calculate the power delivered to the heater element. Find the (i) peak, average and RMS values of diode current and (ii) input power factor.
A d.c.-d.c. converter is connected to a source with an inductive load and . A freewheeling diode is also connected across load. Assume the load current varies from 10 A to 15 A. Find the time ratio of d.c.-d.c. converter.
Explain the operation of class A chopper with neat waveforms.
A single-phase half bridge inverter connected to source feeds a resistive load of . Determine the following : (i) Fundamental RMS output voltage and total output power (ii) Average and peak current through each thyristor (iii) Input power factor and distortion factor (iv) Total harmonic distortion and harmonic factor for lowest order harmonic
Explain a.c. voltage control and series inverter control in single-phase inverters.
Write the applications of current source inverters. What is the condition to get sinusoidal output wave of the current source inverter?
A single-phase bridge inverter fed from is connected to load and . Determine the power delivered to load in case the inverter is operating at 50 Hz with- (i) square-wave output; (ii) quasi-square-wave output with an on period of 0.5 of a cycle; (iii) two symmetrically spaced pulses per half cycle with an on period of 0.5 of a cycle.
A single-phase voltage controller has input voltage of 230 V, 50 Hz and a load of . For 6 cycles on and 4 cycles off, determine the- (i) RMS output voltage; (ii) input power factor; (iii) average and RMS thyristor currents.
Draw the phasor diagram of a highly inductive series R-L-C circuit when excited with a sinusoidal voltage source.
A single-phase to single-phase mid-point cycloconverter is delivering power to a resistive load . The supply transformer has turns ratio of 1:1:1. The frequency ratio is . The firing angle delays for all the four SCRs are the same. Sketch the variations of the following waveforms for and : (i) Supply voltage (ii) Output current (iii) Supply current
Explain the operating principle of 1-phase to 1-phase step-up cycloconverter with the help of mid-point and bridge-type configurations. Illustrate your answer with appropriate circuit and waveforms. The conduction of various thyristors must also be indicated on the waveforms.
Discuss two-transistor analogy of a thyristor. Derive an expression for the anode current and discuss therefrom the turn on mechanisms of a thyristor.
Explain the UJT as relaxation oscillator.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct answer of the following (any seven):
It is preferable to use a train of pulse of high frequency for gate triggering of SCR in order to reduce
Reverse recovery current in a diode depends upon
In a 3-phase full-wave a.c. to d.c. converter, the ratio of output-ripple frequency to the supply-voltage frequency is
A fully controlled natural commutated 3-phase bridge rectifier is operating with a firing angle $ \alpha = 30^{\circ} $. The peak to peak voltage ripple expressed as a ratio of the peak output d.c. voltage to the output of the converter bridge is
Natural commutation of a thyristor takes place when
A four-quadrant chopper cannot be operated as
A boost regulator has an input voltage of 5 V and the average output voltage of 15 V. The duty cycle is
PWM switching is preferred in voltage source inverter for the purpose of
Compared to a single-phase half-bridge inverter, the output power of a single-phase full-bridge inverter is higher by a factor of
How many switches are used to construct a 3-phase to 3-phase cycloconverter?
Q.2 Solve both questions :
A single-phase bridge-type cycloconverter feeds a load R. For an output frequency equal to one-third of the input frequency, sketch output voltage waveform for a firing angle of about $ 30^{\circ} $. Also derive an expression for the r.m.s. output voltage.
Explain the processes of $ dv/dt $ triggering and temperature triggering.
Q.3 Solve both questions :
A 3-phase bridge inverter delivers power to a resistive load from a 450 V d.c. source. For a
star-connected load $ 10~\Omega $ per phase, determine the following for $ 120^{\circ}
$
mode of operation:
(i) r.m.s. value of output phase and line voltages
(ii) r.m.s. value of transistor current
(iii) r.m.s. value of load current
(iv) Load power
Describe the structural features of power diodes. How do these differ from signal diodes?
Q.4 Solve both questions :
A single-phase full-converter delivers a constant load current $ I_0 $. Express its source current in Fourier series.
Derive the expressions for the following performance parameters with the help of waveforms and Fourier series expression in Question No. 4(a): Input displacement factor, Current distortion factor, Power factor, Total harmonic distortion, Voltage ripple factor, Active and Reactive power inputs.
Q.5 Solve both questions :
A battery is charged through a resistor R. If $ v_s = 220\sqrt{2} \sin \omega t $, $ E = 100 \text{ V} $ (d.c.) and $ R = 20~\Omega $, calculate the battery charging current and power supplied to the battery.
Write down any four applications of cycloconverters.
Q.6 Solve both questions :
Discuss with relevant waveforms, class-B (resonant-pulse commutation) type of commutation employed for thyristor circuits.
What are forward blocking losses and gate power loss in a thyristor?
Q.7 Solve both questions :
For step-down chopper circuit, source voltage $ V_s = 220 \text{ V} $, chopping period $ T
=
2000~\mu s $, on period $ = 600~\mu s $, load circuit parameters $ R = 1~\Omega $,
$
L = 5 \text{ mH} $ and $ E = 24 \text{ V} $.
(i) Find whether load current is continuous or not.
(ii) Calculate the value of average output current.
(iii) Compute the maximum and minimum values of steady state output currents.
Draw the circuit diagram of step-down chopper, also draw the waveforms of source voltage $ V_s $ and output voltage $ V_0 $ for duty ratio $ \alpha = 0.4 $ and time period $ T = 10~\mu s $.
Q.8 Solve both questions :
Describe unipolar-voltage switching in a single-phase full-bridge inverter by suitable waveforms for carrier wave, reference wave and output voltage. Show the turn-on and turn-off of various switches in waveforms.
Justify why it is called unipolar-voltage switching inverter or three-level PWM inverter.
Q.9 Solve both questions :
Explain the operation of boost converter with voltage and current waveforms across the boost inductor. Assume continuous conduction.
Derive its output voltage equation in terms of duty cycle and input voltage.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct answer of the following (any seven):
It is preferable to use a train of pulse of high frequency for gate triggering of SCR in order to reduce
Reverse recovery current in a diode depends upon
In a 3-phase full-wave a.c. to d.c. converter, the ratio of output-ripple frequency to the supply-voltage frequency is
A fully controlled natural commutated 3-phase bridge rectifier is operating with a firing angle $ \alpha = 30^{\circ} $. The peak to peak voltage ripple expressed as a ratio of the peak output d.c. voltage to the output of the converter bridge is
Natural commutation of a thyristor takes place when
A four-quadrant chopper cannot be operated as
A boost regulator has an input voltage of 5 V and the average output voltage of 15 V. The duty cycle is
PWM switching is preferred in voltage source inverter for the purpose of
Compared to a single-phase half-bridge inverter, the output power of a single-phase full-bridge inverter is higher by a factor of
How many switches are used to construct a 3-phase to 3-phase cycloconverter?
Q.2 Solve both questions :
A single-phase bridge-type cycloconverter feeds a load R. For an output frequency equal to one-third of the input frequency, sketch output voltage waveform for a firing angle of about $ 30^{\circ} $. Also derive an expression for the r.m.s. output voltage.
Explain the processes of $ dv/dt $ triggering and temperature triggering.
Q.3 Solve both questions :
A 3-phase bridge inverter delivers power to a resistive load from a 450 V d.c. source. For a
star-connected load $ 10~\Omega $ per phase, determine the following for $ 120^{\circ}
$
mode of operation:
(i) r.m.s. value of output phase and line voltages
(ii) r.m.s. value of transistor current
(iii) r.m.s. value of load current
(iv) Load power
Describe the structural features of power diodes. How do these differ from signal diodes?
Q.4 Solve both questions :
A single-phase full-converter delivers a constant load current $ I_0 $. Express its source current in Fourier series.
Derive the expressions for the following performance parameters with the help of waveforms and Fourier series expression in Question No. 4(a): Input displacement factor, Current distortion factor, Power factor, Total harmonic distortion, Voltage ripple factor, Active and Reactive power inputs.
Q.5 Solve both questions :
A battery is charged through a resistor R. If $ v_s = 220\sqrt{2} \sin \omega t $, $ E = 100 \text{ V} $ (d.c.) and $ R = 20~\Omega $, calculate the battery charging current and power supplied to the battery.
Write down any four applications of cycloconverters.
Q.6 Solve both questions :
Discuss with relevant waveforms, class-B (resonant-pulse commutation) type of commutation employed for thyristor circuits.
What are forward blocking losses and gate power loss in a thyristor?
Q.7 Solve both questions :
For step-down chopper circuit, source voltage $ V_s = 220 \text{ V} $, chopping period $ T
=
2000~\mu s $, on period $ = 600~\mu s $, load circuit parameters $ R = 1~\Omega $,
$
L = 5 \text{ mH} $ and $ E = 24 \text{ V} $.
(i) Find whether load current is continuous or not.
(ii) Calculate the value of average output current.
(iii) Compute the maximum and minimum values of steady state output currents.
Draw the circuit diagram of step-down chopper, also draw the waveforms of source voltage $ V_s $ and output voltage $ V_0 $ for duty ratio $ \alpha = 0.4 $ and time period $ T = 10~\mu s $.
Q.8 Solve both questions :
Describe unipolar-voltage switching in a single-phase full-bridge inverter by suitable waveforms for carrier wave, reference wave and output voltage. Show the turn-on and turn-off of various switches in waveforms.
Justify why it is called unipolar-voltage switching inverter or three-level PWM inverter.
Q.9 Solve both questions :
Explain the operation of boost converter with voltage and current waveforms across the boost inductor. Assume continuous conduction.
Derive its output voltage equation in terms of duty cycle and input voltage.
Instructions:
- The marks are indicated in the right-hand margin.
- There are EIGHT questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Answer any seven of the following:
Draw the symbols of BJT, MOSFET and SITH.
The reverse recovery time of a diode is $ t_{rr} = 3~\mu s $ and the rate of fall of the diode current is $ di/dt = 30 \text{ A}/\mu s $. Determine the stored charge $ Q_{RR} $ in reverse recovery zone.
What is the softness factor of diodes?
Explain forward-biased safe operating area (FBSOA) of BJT.
Define distortion factor (DF).
A step-up d.c.-d.c. converter has input voltage $ V_s = 10 \text{ V} $, inductance $ L = 1 \text{ mH} $, duty ratio $ d = 0.5 $ and time period $ T = 1 \text{ ms} $. Find the peak-to-peak ripple current in inductor.
The H-bridge inverter has an R-L-C load with $ R = 10~\Omega $, $ L = 31.5 \text{ mH} $ and $ C = 112~\mu F $. The inverter frequency is $ f_0 = 60 \text{ Hz} $ and d.c. input voltage is $ V_s = 220 \text{ V} $. Find the output fundamental r.m.s. voltage.
Find the line-to-line r.m.s. voltage of three-phase inverter operating in $ 180^{\circ} $ conduction mode if d.c. input voltage $ V_s = 220 \text{ V} $.
Explain dynamic current sharing in parallel operation of thyristors.
The full converter is connected to a 120 V, 60 Hz supply. The load current $ I_a = 8 \text{ A} $ is continuous and its ripple content is negligible. If the delay angle is $ \alpha = \pi/3 $, calculate power factor.
Q.2 Solve both questions :
The three-phase bidirectional delta-connected controller has a resistive load of $ R = 10~\Omega $. The line-to-line voltage is $ V_s = 208 \text{ V} $ (r.m.s.), 60 Hz and the delay angle is $ \alpha = 2\pi/3 $. Determine the r.m.s. output voltage $ V_0 $, the input PF and the r.m.s. current of a thyristor $ I_R $.
Explain three-phase full-wave delta-connected controller with various waveforms.
Q.3 Solve both questions :
A single-phase half-wave converter is operated from a 120 V, 60 Hz supply and the resistive load is $ R = 10~\Omega $. If the average output voltage is 50% of the maximum possible output voltage, calculate the delay angle, the r.m.s. and average output currents.
Explain three-phase full converter with R-L load with various waveforms.
Q.4 Solve both questions :
Explain two-transistor model of a thyristor.
A single-phase half-bridge inverter has resistive load of $ R = 5~\Omega $ and the d.c. input voltage is $ V_s = 100 \text{ V} $. Determine the r.m.s. output voltage at the fundamental frequency $ V_{01} $ and the output power $ P_0 $.
Q.5 Solve both questions :
A single-phase full-bridge inverter is operated at 1 kHz and uses a uniform PWM with four pulses per half-cycle for voltage control. Plot the fundamental component, distortion factor and THD against the modulation index M.
The bridge inverter has an R-L-C load with $ R = 10~\Omega $, $ L = 31.5 \text{ mH} $ and $ C = 112~\mu F $. The inverter frequency is $ f_o = 60 \text{ Hz} $ and d.c. input voltage is $ V_s = 220 \text{ V} $. Calculate the r.m.s. load current at the fundamental frequency $ I_{o1} $ and the THD of the load current.
Q.6 Solve both questions :
The buck converter has d.c. input voltage $ V_s = 110 \text{ V} $, average load voltage $ V_a = 80 \text{ V} $ and average load current $ I_a = 15 \text{ A} $. The chopping frequency is $ f = 10 \text{ kHz} $. The peak-to-peak ripples are 5% for load voltage, 2.5% for load current and 10% for filter $ L_e $ current. Determine the values of $ L_e $, $ L $, $ C_e $.
Write on the steady state analysis of buck converter.
Q.7 Solve both questions :
Explain briefly about Cuk-converter.
The buck-boost regulator has an input voltage of $ V_s = 12 \text{ V} $. The duty cycle $ k = 0.25 $ and the switching frequency is 25 kHz. The inductance $ L = 150~\mu\text{H} $ and filter capacitance $ C = 220~\mu\text{F} $. The average load current $ I_a = 1.25 \text{ A} $. Determine the peak-to-peak output voltage ripple $ \Delta V_c $ and the peak-to-peak ripple current of inductor $ \Delta I_L $.
Q.8 Write brief notes on any two of the following:
Instructions:
- The marks are indicated in the right-hand margin.
- There are EIGHT questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Answer any seven of the following:
Draw the symbols of BJT, MOSFET and SITH.
The reverse recovery time of a diode is $ t_{rr} = 3~\mu s $ and the rate of fall of the diode current is $ di/dt = 30 \text{ A}/\mu s $. Determine the stored charge $ Q_{RR} $ in reverse recovery zone.
What is the softness factor of diodes?
Explain forward-biased safe operating area (FBSOA) of BJT.
Define distortion factor (DF).
A step-up d.c.-d.c. converter has input voltage $ V_s = 10 \text{ V} $, inductance $ L = 1 \text{ mH} $, duty ratio $ d = 0.5 $ and time period $ T = 1 \text{ ms} $. Find the peak-to-peak ripple current in inductor.
The H-bridge inverter has an R-L-C load with $ R = 10~\Omega $, $ L = 31.5 \text{ mH} $ and $ C = 112~\mu F $. The inverter frequency is $ f_0 = 60 \text{ Hz} $ and d.c. input voltage is $ V_s = 220 \text{ V} $. Find the output fundamental r.m.s. voltage.
Find the line-to-line r.m.s. voltage of three-phase inverter operating in $ 180^{\circ} $ conduction mode if d.c. input voltage $ V_s = 220 \text{ V} $.
Explain dynamic current sharing in parallel operation of thyristors.
The full converter is connected to a 120 V, 60 Hz supply. The load current $ I_a = 8 \text{ A} $ is continuous and its ripple content is negligible. If the delay angle is $ \alpha = \pi/3 $, calculate power factor.
Q.2 Solve both questions :
The three-phase bidirectional delta-connected controller has a resistive load of $ R = 10~\Omega $. The line-to-line voltage is $ V_s = 208 \text{ V} $ (r.m.s.), 60 Hz and the delay angle is $ \alpha = 2\pi/3 $. Determine the r.m.s. output voltage $ V_0 $, the input PF and the r.m.s. current of a thyristor $ I_R $.
Explain three-phase full-wave delta-connected controller with various waveforms.
Q.3 Solve both questions :
A single-phase half-wave converter is operated from a 120 V, 60 Hz supply and the resistive load is $ R = 10~\Omega $. If the average output voltage is 50% of the maximum possible output voltage, calculate the delay angle, the r.m.s. and average output currents.
Explain three-phase full converter with R-L load with various waveforms.
Q.4 Solve both questions :
Explain two-transistor model of a thyristor.
A single-phase half-bridge inverter has resistive load of $ R = 5~\Omega $ and the d.c. input voltage is $ V_s = 100 \text{ V} $. Determine the r.m.s. output voltage at the fundamental frequency $ V_{01} $ and the output power $ P_0 $.
Q.5 Solve both questions :
A single-phase full-bridge inverter is operated at 1 kHz and uses a uniform PWM with four pulses per half-cycle for voltage control. Plot the fundamental component, distortion factor and THD against the modulation index M.
The bridge inverter has an R-L-C load with $ R = 10~\Omega $, $ L = 31.5 \text{ mH} $ and $ C = 112~\mu F $. The inverter frequency is $ f_o = 60 \text{ Hz} $ and d.c. input voltage is $ V_s = 220 \text{ V} $. Calculate the r.m.s. load current at the fundamental frequency $ I_{o1} $ and the THD of the load current.
Q.6 Solve both questions :
The buck converter has d.c. input voltage $ V_s = 110 \text{ V} $, average load voltage $ V_a = 80 \text{ V} $ and average load current $ I_a = 15 \text{ A} $. The chopping frequency is $ f = 10 \text{ kHz} $. The peak-to-peak ripples are 5% for load voltage, 2.5% for load current and 10% for filter $ L_e $ current. Determine the values of $ L_e $, $ L $, $ C_e $.
Write on the steady state analysis of buck converter.
Q.7 Solve both questions :
Explain briefly about Cuk-converter.
The buck-boost regulator has an input voltage of $ V_s = 12 \text{ V} $. The duty cycle $ k = 0.25 $ and the switching frequency is 25 kHz. The inductance $ L = 150~\mu\text{H} $ and filter capacitance $ C = 220~\mu\text{F} $. The average load current $ I_a = 1.25 \text{ A} $. Determine the peak-to-peak output voltage ripple $ \Delta V_c $ and the peak-to-peak ripple current of inductor $ \Delta I_L $.
Q.8 Write brief notes on any two of the following:
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Section 1
Choose the correct option of the following (any seven) :
A single-phase fully controlled thyristor bridge AC-DC converter is operating at a firing angle of and an overlap angle of with constant DC output current 20 A. The fundamental power factor at input AC mains is
A UJT used for triggering an SCR has the supply voltage of . The intrinsic standoff ratio is 0.82. The bias voltage required to conduct the UJT is
The average on state current for an SCR is 30 A for a resistive load. If an inductance of 7 mH is included in the load, then average on state current would be
Analysis of voltage waveform of a single-phase bridge converter shows that it contains $x$% of 6th harmonic. The 6th harmonic content of the voltage waveform of a 3-phase bridge converter would be
A thyristor is triggered by a pulse train of 5 kHz. The duty ratio is 0.4. If the allowable average power is 100 W, then the maximum allowable gate drive power is
An SCR has an anode supply voltage of 200 V r.m.s., 50 Hz applied through a 100 ohm resistor and fired at an angle of . Assume no voltage drop, the output r.m.s. voltage is
In a 3-phase half-wave diode rectifier, if is the maximum value of per phase voltage, then each diode is subjected to peak inverse voltage of
A half-controlled single-phase bridge rectifier is supplying an R-L load. It is operated at a firing angle and the load current is continuous. The fraction of cycle that the freewheeling diode conduct is
A half-wave rectifier circuit with a capacitive filter is connected to 200 volts, 50 Hz AC line. The output voltage across the capacitor should be approximately
A 3-phase bridge rectifier charges a 240 V battery. The rectifier is given a 3-phase, 230 V supply. The current limiting resistance in series with the battery is of . The average value of battery charging current is
Explain the fully-controlled rectifier with R-L load with neat conduction waveforms.
Draw the V-I characteristics of SCR and explain various modes of operation.
Discuss about power MOSFET and its characteristics.
If the half-wave controlled rectifier has a purely resistive load of and the delay angle is , determine the-
rectification efficiency;
form factor;
ripple factor;
transformer utilization factor;
peak inverse voltage for SCR .
Draw and explain the equivalent circuit and V-I characteristics of the UJT in detail.
Compare the R firing circuit and R-C firing circuit.
For a single-phase quasi square wave inverter having resistive load, derive an expression for (i) r.m.s. output voltage, (ii) r.m.s. output current and (iii) load power.
A 3-phase bridge inverter is operated from 200 V DC supply in mode. Determine (i) r.m.s. output voltage, (ii) r.m.s. value of fundamental component of line voltage.
A DC chopper circuit connected to a 100 V DC source supplies an inductive load having 40 mH in series with a resistance of . A freewheeling diode is placed across the load. The load current varies between the limits of 10 A and 12 A. Determine the time ratio of the chopper.
Describe the principle of operation of step-down chopper or buck converter.
Explain the time ratio control and current limit control of DC choppers.
Explain the bidirectional AC voltage controller with R-load.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct option (any seven):
The number of p-n junctions in a thyristor is
When a thyristor gets turned on, the gate drive
Once SCR starts conducting a forward current, its gate loses control over
In a single-phase full converter, for continuous conduction, each pair of SCRs conduct for
Commutation overlap in the phase-controlled a.c. to d.c. converters is due to
A converter which can operate in both 3-pulse and 6-pulse modes is a
In a 3-phase semi-converter, the three SCRs are triggered at an interval of
In single-pulse modulation of PWM inverters, third harmonic can be eliminated if pulse width is equal to
In d.c. choppers, the waveforms for input and output voltages are
In a 1-phase to 1-phase step-down cycloconverter
Q.2 Solve both questions :
Explain the two-transistor model of a thyristor.
Sketch switching (or dynamic) characteristics of a thyristor during its turn-on and turn-off processes. Show the variation of voltage across the thyristor and current through it during these two dynamic processes.
Q.3 Solve this question :
Describe a 1-phase full-wave diode-bridge rectifier with a circuit diagram and relevant waveforms for load R. Hence, derive expressions for average and r.m.s. values of output voltage and obtain therefrom voltage ripple factor (VRF), form factor (FF) and rectifier efficiency.
Q.4 Solve both questions :
Enumerate the various techniques by which thyristors can be triggered into conduction.
Explain the working principle of snubber circuit used for protection of thyristor.
Q.5 Solve both questions :
Discuss the principle of working of a three-phase inverter with an appropriate circuit diagram. Draw phase and line voltage waveforms on the assumption that each thyristor conducts for $ 120^{\circ} $ and the resistive load is star-connected.
A three-phase bridge inverter delivers power to a resistive load from a 450 V d.c. source. For a star-connected load of $ 10~\Omega $ per phase with $ 120^{\circ} $ mode of operation, calculate the following: (i) r.m.s. value of load current (ii) r.m.s. value of thyristor current (iii) Load power.
Q.6 Solve both questions :
What is meant by step-up chopper? Explain its operation. Sketch the input voltage, input current, output voltage and output current waveforms. State the various assumptions made.
A d.c. chopper is fed from 100 V d.c. Its load voltage consists of rectangular pulses of duration 1 msec in an overall cycle time of 3 msec. Find the average output voltage and ripple factor for this chopper.
Q.7 Solve both questions :
What is an a.c. voltage controller? List some of its industrial applications. Enumerate its merits and demerits.
A 3-phase half-wave controlled converter is fed from 3-phase, 400 V, 50 Hz source and is connected to load taking a constant current of 36 A. Thyristors have a voltage drop of 1.4 V. Find out the average value of load voltage for firing angle of $ 30^{\circ} $ and $ 60^{\circ} $.
Q.8 Solve this question :
Describe the modified McMurray-Bedford half-bridge single-phase inverter with relevant voltage and current waveforms. The working of this inverter may be explained in certain well-defined modes. Enumerate the simplifying assumptions made.
Q.9 Solve this question :
A single-phase bridge-type cycloconverter has input voltage of 230 V, 50 Hz and load of $ R=10~\Omega $. Output frequency is one-third of input frequency. For a firing angle delay of $ 30^{\circ} $, calculate (a) r.m.s. value of output voltage, (b) r.m.s. current of each converter, (c) r.m.s. current of each thyristor and (d) input power factor.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct option (any seven):
The number of p-n junctions in a thyristor is
When a thyristor gets turned on, the gate drive
Once SCR starts conducting a forward current, its gate loses control over
In a single-phase full converter, for continuous conduction, each pair of SCRs conduct for
Commutation overlap in the phase-controlled a.c. to d.c. converters is due to
A converter which can operate in both 3-pulse and 6-pulse modes is a
In a 3-phase semi-converter, the three SCRs are triggered at an interval of
In single-pulse modulation of PWM inverters, third harmonic can be eliminated if pulse width is equal to
In d.c. choppers, the waveforms for input and output voltages are
In a 1-phase to 1-phase step-down cycloconverter
Q.2 Solve both questions :
Explain the two-transistor model of a thyristor.
Sketch switching (or dynamic) characteristics of a thyristor during its turn-on and turn-off processes. Show the variation of voltage across the thyristor and current through it during these two dynamic processes.
Q.3 Solve this question :
Describe a 1-phase full-wave diode-bridge rectifier with a circuit diagram and relevant waveforms for load R. Hence, derive expressions for average and r.m.s. values of output voltage and obtain therefrom voltage ripple factor (VRF), form factor (FF) and rectifier efficiency.
Q.4 Solve both questions :
Enumerate the various techniques by which thyristors can be triggered into conduction.
Explain the working principle of snubber circuit used for protection of thyristor.
Q.5 Solve both questions :
Discuss the principle of working of a three-phase inverter with an appropriate circuit diagram. Draw phase and line voltage waveforms on the assumption that each thyristor conducts for $ 120^{\circ} $ and the resistive load is star-connected.
A three-phase bridge inverter delivers power to a resistive load from a 450 V d.c. source. For a star-connected load of $ 10~\Omega $ per phase with $ 120^{\circ} $ mode of operation, calculate the following: (i) r.m.s. value of load current (ii) r.m.s. value of thyristor current (iii) Load power.
Q.6 Solve both questions :
What is meant by step-up chopper? Explain its operation. Sketch the input voltage, input current, output voltage and output current waveforms. State the various assumptions made.
A d.c. chopper is fed from 100 V d.c. Its load voltage consists of rectangular pulses of duration 1 msec in an overall cycle time of 3 msec. Find the average output voltage and ripple factor for this chopper.
Q.7 Solve both questions :
What is an a.c. voltage controller? List some of its industrial applications. Enumerate its merits and demerits.
A 3-phase half-wave controlled converter is fed from 3-phase, 400 V, 50 Hz source and is connected to load taking a constant current of 36 A. Thyristors have a voltage drop of 1.4 V. Find out the average value of load voltage for firing angle of $ 30^{\circ} $ and $ 60^{\circ} $.
Q.8 Solve this question :
Describe the modified McMurray-Bedford half-bridge single-phase inverter with relevant voltage and current waveforms. The working of this inverter may be explained in certain well-defined modes. Enumerate the simplifying assumptions made.
Q.9 Solve this question :
A single-phase bridge-type cycloconverter has input voltage of 230 V, 50 Hz and load of $ R=10~\Omega $. Output frequency is one-third of input frequency. For a firing angle delay of $ 30^{\circ} $, calculate (a) r.m.s. value of output voltage, (b) r.m.s. current of each converter, (c) r.m.s. current of each thyristor and (d) input power factor.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Section 1
Choose the correct option (any seven) :
In the SCR structure, the gate terminal is located
The latching current is ________ the holding current.
When a diode is connected in series with an AC source and R load, the conduction time per cycle is
In a single-phase half-wave circuit with RL load and a freewheeling diode, the freewheeling period is
A three-phase three-pulse M-3 type controlled converter has firing angle for one of the SCRs set as . This SCR would start conducting at
Find the output voltage for a step-up chopper when it is operated at a duty cycle of 50% and .
In the mode VSI, ________ devices conduct at a time.
In AC voltage controllers, the
The single-phase bridge-type cyclo-converter uses ________ number of SCRs.
A single full converter alone can give a
Describe the different modes of operation of a thyristor with the help of its static V-I characteristic.
With the help of a neat diagram, explain the two-transistor analogy of an SCR.
Explain the working of an oscillator employing an UJT. Derive expression for the frequency of triggering.
A relaxation oscillator using a UJT is to be designed for triggering an SCR. The UJT has the following data : $\eta = 0.72$, , , , , Normal leakage current with emitter open . The firing frequency is . For , compute the values of and .
A single-phase half-wave controlled converter is operated from a supply. Load resistance . If the average output voltage is 25% of the maximum possible average output voltage, determine- (i) firing angle; (ii) r.m.s. and average output currents; (iii) average and r.m.s. SCR currents.
Explain the operation of single-phase half-controlled bridge converter (symmetrical configuration) with resistive load along with suitable waveforms. Also derive the expressions for average load voltage, average load current and RMS load voltage.
A three-phase fully controlled converter is connected to a resistive load. Show that the average output voltage is given by : , for and $E_{dc} = \frac{3}{2\pi} E_m [1 + \cos(\alpha + \frac{\pi}{6})]$, for
With the help of neat circuit diagram and associated waveforms, explain the operation of single-phase half-bridge voltage-source inverter with resistive load.
The single-phase half-bridge inverter has a resistive load of and the center-tap DC input voltage is . Compute- (i) RMS value of the output voltage; (ii) fundamental component of the output voltage waveform; (iii) first five harmonics of the output voltage waveform; (iv) RMS power consumed by the load.
Draw the schematic of step-down and step-up choppers and derive an expression for output voltage in terms of duty cycle for a step-up and step-down choppers.
Draw the schematic of class E chopper and explain the working of the same.
Describe the basic principle of working of a single-phase to single-phase cycloconverter for both continuous and discontinuous conductions for a bridge-type cycloconverter. Mark the condition of various thyristors also.
For a single-phase full-wave a.c. voltage controller feeding a resistive load, draw the waveforms of source voltage, gating signals, output voltage, source and output currents and voltage across SCRs. Describe its working with reference to the waveforms drawn.
A single-phase full-wave a.c. voltage controller feeds power to a resistive load of from source. Determine the peak values of average and RMS thyristor currents for any firing angle .
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct option (any seven):
A single-phase one pulse diode rectifier is feeding an RL load with freewheeling diode across the load. For conduction angle $ \beta $, the main diode and freewheeling diode would, respectively, conduct for
When a thyristor is forward biased, the number of blocked p-n junctions is
During forward blocking state, a thyristor is associated with
When a UJT is used for triggering an SCR, the wave shape of the voltage obtained from UJT circuit is a
In a commutation circuit employed to turn off an SCR, satisfactory turn-off is obtained when
A step-up chopper has $ V_s $ as the source voltage and $ \alpha $ as the duty cycle. The output voltage for this chopper is given by
In an inverter with fundamental output frequency of 50 Hz, if third harmonic is eliminated, then the frequencies of other components in the output voltage wave, in Hz, would be
A cycloconverter is a frequency converter from
1. higher to lower frequency with one-stage conversion
2. higher to lower frequency with two-stage conversion
3. lower to higher frequency with one-stage conversion
4. AC at one frequency to DC and then DC to AC at different frequencies
From these, the correct statement(s) is/are
If, for a single-phase half-bridge inverter, the amplitude of output voltage is $ V_s $ and the output power is P, then their corresponding values for a single-phase full-bridge inverter are
In DC choppers, the waveforms for input and output voltages are respectively
Q.2 Solve both questions :
Briefly discuss the V-I characteristic of SCR.
Explain the turn-on and turn-off characteristics of SCR with neat waveforms.
Q.3 Solve both questions :
Explain the operation of three-phase half-wave controlled converter for a firing angle less than $ 30^{\circ} $ and feeding R load. Also derive the expression for its average output voltage.
The specification sheet for an SCR gives maximum rms on-state current as 35 A. If this SCR is used in a resistive circuit, compute average on-state current rating for half sine wave current for conduction angle of $ 180^{\circ} $.
Q.4 Solve both questions :
Explain the effect of source inductance in the operation of single-phase fully controlled converter.
With neat circuit diagram and waveform, explain the working principle of single-phase AC voltage controller with R-L load.
Q.5 Solve both questions :
Explain the principle of operation of three-phase inverter with $ 180^{\circ} $ conduction mode with necessary waveforms and circuit.
A step-up chopper has input voltage of 220 V and output voltage of 660 V. If the conducting time of thyristor-chopper is 100 $ \mu\text{s} $, compute the pulse width of output voltage. In case output-voltage pulse width is halved for constant frequency operation, find the average value of new output voltage.
Q.6 Solve both questions :
Explain the two-transistor analogy of a thyristor.
Discuss the various mechanisms that can be used to trigger thyristors.
Q.7 Solve both questions :
Discuss the operation of step-up chopper and prove that its output voltage is greater than input voltage.
Snubber circuit for an SCR should primarily consist of capacitor only. But, in actual practice, a resistor is used in series with capacitor. Discuss.
Q.8 Solve both questions :
With neat circuit diagram and waveform, explain the operating principle of 1-$\phi$ to 1-$\phi$ step down mid-point type cycloconverter, with continuous load current. Assume the loads to be R and L in series.
A single-phase half-wave AC voltage controller feeds a load of $ R=20~\Omega $ with an input voltage of 230 V, 50 Hz. Firing angle of thyristor is $ 45^{\circ} $. Determine: (i) rms value of output voltage; (ii) average input current.
Q.9 Solve this question :
Briefly discuss the different types of PWM schemes available for voltage control in an inverter.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct option (any seven):
A single-phase one pulse diode rectifier is feeding an RL load with freewheeling diode across the load. For conduction angle $ \beta $, the main diode and freewheeling diode would, respectively, conduct for
When a thyristor is forward biased, the number of blocked p-n junctions is
During forward blocking state, a thyristor is associated with
When a UJT is used for triggering an SCR, the wave shape of the voltage obtained from UJT circuit is a
In a commutation circuit employed to turn off an SCR, satisfactory turn-off is obtained when
A step-up chopper has $ V_s $ as the source voltage and $ \alpha $ as the duty cycle. The output voltage for this chopper is given by
In an inverter with fundamental output frequency of 50 Hz, if third harmonic is eliminated, then the frequencies of other components in the output voltage wave, in Hz, would be
A cycloconverter is a frequency converter from
1. higher to lower frequency with one-stage conversion
2. higher to lower frequency with two-stage conversion
3. lower to higher frequency with one-stage conversion
4. AC at one frequency to DC and then DC to AC at different frequencies
From these, the correct statement(s) is/are
If, for a single-phase half-bridge inverter, the amplitude of output voltage is $ V_s $ and the output power is P, then their corresponding values for a single-phase full-bridge inverter are
In DC choppers, the waveforms for input and output voltages are respectively
Q.2 Solve both questions :
Briefly discuss the V-I characteristic of SCR.
Explain the turn-on and turn-off characteristics of SCR with neat waveforms.
Q.3 Solve both questions :
Explain the operation of three-phase half-wave controlled converter for a firing angle less than $ 30^{\circ} $ and feeding R load. Also derive the expression for its average output voltage.
The specification sheet for an SCR gives maximum rms on-state current as 35 A. If this SCR is used in a resistive circuit, compute average on-state current rating for half sine wave current for conduction angle of $ 180^{\circ} $.
Q.4 Solve both questions :
Explain the effect of source inductance in the operation of single-phase fully controlled converter.
With neat circuit diagram and waveform, explain the working principle of single-phase AC voltage controller with R-L load.
Q.5 Solve both questions :
Explain the principle of operation of three-phase inverter with $ 180^{\circ} $ conduction mode with necessary waveforms and circuit.
A step-up chopper has input voltage of 220 V and output voltage of 660 V. If the conducting time of thyristor-chopper is 100 $ \mu\text{s} $, compute the pulse width of output voltage. In case output-voltage pulse width is halved for constant frequency operation, find the average value of new output voltage.
Q.6 Solve both questions :
Explain the two-transistor analogy of a thyristor.
Discuss the various mechanisms that can be used to trigger thyristors.
Q.7 Solve both questions :
Discuss the operation of step-up chopper and prove that its output voltage is greater than input voltage.
Snubber circuit for an SCR should primarily consist of capacitor only. But, in actual practice, a resistor is used in series with capacitor. Discuss.
Q.8 Solve both questions :
With neat circuit diagram and waveform, explain the operating principle of 1-$\phi$ to 1-$\phi$ step down mid-point type cycloconverter, with continuous load current. Assume the loads to be R and L in series.
A single-phase half-wave AC voltage controller feeds a load of $ R=20~\Omega $ with an input voltage of 230 V, 50 Hz. Firing angle of thyristor is $ 45^{\circ} $. Determine: (i) rms value of output voltage; (ii) average input current.
Q.9 Solve this question :
Briefly discuss the different types of PWM schemes available for voltage control in an inverter.
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct option (any seven):
When an SCR is reverse biased
An R-C snubber circuit is used to protect a thyristor against
A single-phase semiconverter is feeding a highly inductive load and has free-wheeling diode across the load. The waveshapes of output voltage and output current
A single-phase half-wave rectifier is feeding a resistive load. Input voltage $ v = V_m \sin \omega t $. The output d.c. voltage is $ V_{dc} $ and output r.m.s. voltage is $ V_{r.m.s.} $. If firing angle is $ 180^{\circ} $, $ V_{dc} $ and $ V_{r.m.s.} $ respectively are
In a step-down chopper using pulse-width modulation $ T_{on} = 3 \times 10^{-3} \text{ s} $ and $ T_{off} = 1 \times 10^{-3} \text{ s} $. The chopping frequency is
In a three-phase full-wave regulator feeding a star-connected resistance load the input voltage is 400 V line to line. The firing angle is $ 160^{\circ} $. The line to line output voltage would be
Assertion (A): An inverter does not require forced commutation. Reason (R): A series inverter is a forced commutation inverter.
A three-phase bridge inverter is fed by 400 V battery. The load is star-connected and has a resistance of $ 10~\Omega $ per phase. The peak value of load current is
The waveshape of output voltage of half-bridge inverter is
In dielectric heating, the thyristor circuits consist of
Q.2 Solve both questions :
Discuss some of the advantages and disadvantages of power electronic converters.
Define latching and holding currents as applicable to an SCR. Show these on the V-I characteristics.
Q.3 Solve both questions :
Why are $ dv/dt $ and $ di/dt $ protections in case of thyristor important?
An SCR operating from a peak supply voltage of 400 V has the following specifications: Repetitive peak current $ I_p = 200 \text{ A} $, $ (di/dt)_{max} = 50 \text{ A}/\mu\text{s} $, $ (dv/dt)_{max} = 200 \text{ V}/\mu\text{s} $. Choosing a factor of safety of 2 for $ I_p $, $ (di/dt)_{max} $ and $ (dv/dt)_{max} $, design a suitable snubber circuit. The minimum value of load resistance is 10 ohms.
Q.4 Solve both questions :
Explain the principle of phase control with suitable diagram and waveform.
Discuss in detail three-phase full converter with R-L-E load with suitable diagram and waveform.
Q.5 Solve both questions :
What is inverter? List a few industrial applications of inverter.
Discuss in detail three-phase 120 degree mode voltage source inverter.
Q.6 Solve both questions :
Describe the principle of d.c. chopper operation.
Derive an expression for its average d.c. output voltage.
Q.7 Solve both questions :
Describe integral cycle control type a.c. voltage controller.
Enumerate the merits and demerits of a.c. voltage controller.
Q.8 Solve both questions :
Draw the basic integrated structure and the V-I characteristics of a TRIAC and briefly explain its principle of working.
Briefly explain the working of an oscillator employing a UJT. Derive the expressions for the frequency of triggering firing angle delay in terms of $ \eta $, and the charging resistance values.
Q.9 Write short notes on any two of the following:
Instructions:
- The marks are indicated in the right-hand margin.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Q.1 Choose the correct option (any seven):
When an SCR is reverse biased
An R-C snubber circuit is used to protect a thyristor against
A single-phase semiconverter is feeding a highly inductive load and has free-wheeling diode across the load. The waveshapes of output voltage and output current
A single-phase half-wave rectifier is feeding a resistive load. Input voltage $ v = V_m \sin \omega t V_{dc} V_{r.m.s.} 180^{\circ} V_{dc} V_{r.m.s.} $ respectively are
In a step-down chopper using pulse-width modulation and . The chopping frequency is
In a three-phase full-wave regulator feeding a star-connected resistance load the input voltage is 400 V line to line. The firing angle is . The line to line output voltage would be
Assertion (A): An inverter does not require forced commutation. Reason (R): A series inverter is a forced commutation inverter.
A three-phase bridge inverter is fed by 400 V battery. The load is star-connected and has a resistance of per phase. The peak value of load current is
The waveshape of output voltage of half-bridge inverter is
In dielectric heating, the thyristor circuits consist of
Q.2 Solve both questions :
Discuss some of the advantages and disadvantages of power electronic converters.
Define latching and holding currents as applicable to an SCR. Show these on the V-I characteristics.
Q.3 Solve both questions :
Why are and protections in case of thyristor important?
An SCR operating from a peak supply voltage of 400 V has the following specifications: Repetitive peak current , , $ (dv/dt){max} = 200 \text{ V}/\mu\text{s} I_p $, $ (di/dt){max} (dv/dt)_{max} $, design a suitable snubber circuit. The minimum value of load resistance is 10 ohms.
Q.4 Solve both questions :
Explain the principle of phase control with suitable diagram and waveform.
Discuss in detail three-phase full converter with R-L-E load with suitable diagram and waveform.
Q.5 Solve both questions :
What is inverter? List a few industrial applications of inverter.
Discuss in detail three-phase 120 degree mode voltage source inverter.
Q.6 Solve both questions :
Describe the principle of d.c. chopper operation.
Derive an expression for its average d.c. output voltage.
Q.7 Solve both questions :
Describe integral cycle control type a.c. voltage controller.
Enumerate the merits and demerits of a.c. voltage controller.
Q.8 Solve both questions :
Draw the basic integrated structure and the V-I characteristics of a TRIAC and briefly explain its principle of working.
Briefly explain the working of an oscillator employing a UJT. Derive the expressions for the frequency of triggering firing angle delay in terms of , and the charging resistance values.
Q.9 Write short notes on any two of the following:
Instructions:
- The questions are of equal value.
- There are NINE questions in this paper.
- Attempt FIVE questions in all.
- Question No. 1 is compulsory.
Section 1
Choose the correct answer (any seven) :
Power electronic device with poor turn-off gain is
It is preferable to use a train of pulse of high frequency for gate triggering of SCR in order to reduce
In a fully-controlled converter, the load voltage is controlled by which of the following quantity?
In a single-phase full-wave controlled bridge rectifier, minimum output voltage and maximum output voltage are obtained at which conduction angle?
In the continuous conduction mode, the output voltage waveform does not depend on
A step-down chopper is operated in the continuous conduction mode in steady state with a constant duty ration . If is the magnitude of the d.c. output voltage and is the magnitude of the d.c. input voltage, the ratio is given by
In a single-pulse modulation PWM inverter, third harmonics can be eliminated if the pulse-width is made equal to
In case of voltage-source inverter, free-wheeling can be needed for the load of
PWM switching is preferred in voltage-source inverters for the purpose of
Compared to a single-phase half-bridge inverter, the output power of a single-phase full-bridge inverter is higher by a factor of
Circuit of given Fig. 1, employing resonant-pulse commutation (or class-B commutation) has and . Initial voltage across capacitor is , for a constant load current of 300 A, calculate-
conduction time for the auxiliary thyristor;
voltage across the main thyristor when it gets commutated;
the circuit turn-off time for the main thyristor.
What is complementary impulse commutation?
A d.c. battery is charged through a resistor as shown in Fig. 2. Derive an expression for the average value of charging current in terms of On the assumption that SCR is fired continuously-
for an a.c. source voltage of , find the value of average charging current for and $E = 150\text{V}$;
find the power supplied to battery and that dissipated in the resistor;
calculate the supply p.f.
A single-phase full-converter bridge is connected to RLE load. The source voltage is . The average load current of 10 A is constant over the working range for and .
Compute the firing angle delay for .
Compute the firing angle delay for . Indicate which source is delivering power to load in parts (a) and (b). Sketch the time variations of output voltage and load current for both the parts.
In case output current is assumed constant, find the input p.f. for both the parts (a) and (b).
For type-A chopper of Fig. 3, DC source voltage , load resistance . Take a voltage drop of 2 V across chopper when it is on, for a duty cycle of 0.4, calculate-
the average and r.m.s. values of output voltage;
the chopper efficiency.
What is meant by step-up chopper? Explain its operation.
A step-down chopper, fed from is connected to RL load with and , chopper frequency is and duty cycle is 0.5. Calculate-
the minimum and maximum value of load current;
the maximum value of ripple current;
the average and r.m.s. values of load current;
the r.m.s. value of chopper current.
With the help of equivalent circuit, obtain the nature of waveform of phase voltage of a star-connected resistive load fed from a three-phase DC to AC bridge-inverter operating in conduction mode.
Describe the working of single-phase full-bridge inverter.
A single-phase full-bridge inverter has R-L-C load of and . The DC input voltage is and the output frequency is . Find an expression for load current up to fifth harmonic. Also calculate- (i) the r.m.s. value of fundamental load current; (ii) the power absorbed by load and the fundamental power.
Sketch static I-V characteristics of a thyristor. Label the various voltages, currents and the operating modes on this sketch.
SCR with a rating of and are available to be used in a string to handle and . Calculate the no. of series and parallel units required in case derating factors are (i) 0.1 and (ii) 0.2.