JNTU
JNTU B.Tech III POWER ELECTRONICS Previous Question Paper (March - 2024 - R13)
i) Question paper consists of Part A, Part B.
ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions.
iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Define Latching and holding current of SCR.
Answer
Latching current is the minimum anode current required to maintain the SCR in the ON state immediately after it has been triggered and the gate signal is removed. Holding current is the minimum anode current below which the SCR turns OFF from the conducting state.
What are the applications of power MOSFET and power IGBT?
Answer
Power MOSFETs are used in high-frequency switching applications such as SMPS, DC-DC converters, and motor drives for low-power ratings. Power IGBTs are used in high-voltage, high-current applications such as induction heating, traction motor drives, and large-scale UPS systems due to their superior conduction characteristics.
What is active power input of single phase full converter at α = 60°?
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Give the list of applications of three phase controlled converters.
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Explain duty cycle in step up chopper operation.
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Explain the principle of current limit control in case of choppers.
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What type of gating signal is used in single phase ac voltage controller with RL load?
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Compare turn off mechanism of TRIAC and Thyristor.
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What assumptions are considered for the operation of inverters?
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What are the advantages of PWM control?
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Part B
What is power MOSFET? What are the types of power MOSFET? Write the difference between general purpose MOSFET and power MOSFET.
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Describe the basic behavior of thyristor using a two-transistor model.
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Draw the V-I characteristics of a power IGBT and explain different operating regions.
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Draw dynamic characteristics of SCR during turn off. Explain how turn off process can be carried out?
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What is phase angle controlled technique? Explain the operation of single – phase angle controlled rectifier. Derive the expression for average dc output voltage. Draw the relevant waveforms.
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Write the advantage of freewheeling diode in single–phase half–wave controlled rectifier with RL load.
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Draw the circuit diagram of 3 – phase half –wave controlled rectifier with RL load and explain its operating principle with voltage and current waveforms. Determine the following parameters for RL load with firing angle α = 30°: a) dc output voltage b) Average dc load current c) rms output voltage d) rms load current e) Ripple factor.
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Explain the operating principle of dc chopper with a suitable diagram. Draw the voltage and current waveforms of chopper. Derive expressions for average output voltage and rms output voltage.
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Explain the operating principle of AC chopper with a suitable diagram.
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A class-A chopper circuit has a load resistance of 100 ohms, capacitance of 10 micro farads and inductance of 10 mH. Find the time for which thyristor will remain in ON state. What will be the turn ON time if the load resistance is decreased to 25 ohms?
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Describe the V-I characteristics of TRIAC and modes of operation.
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Describe working of Single Phase AC-AC regulators with R load only and draw the relevant waveforms.
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Explain the Principle of operation of Single phase mid - point cyclo-converters with Resistive and inductive load.
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A single phase ac voltage controller is connected with a load of R = 10 Ω with input voltage of 230 V, 50 Hz supply. If the firing angle of SCR is 90°, calculate, rms value of output voltage, power delivered to load, average value of thyristor current and input power factor?
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What are pulse width modulated inverters? What are the different PWM techniques used in inverter?
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Explain the working of a 1-phase full bridge Inverter with RL load. Draw the relevant output waveforms.
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With the help of a neat circuit diagram and waveforms, explain the operation of 3-phase bridge inverter with R load.
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Compare 180° and 120° conduction mode of 3-ϕ transistorized bridge inverter.
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