Power electronics deals with applying electronic principles to power-level situations rather than signal-level. It involves devices like power diodes, thyristors (SCRs), and transistors (BJT, MOSFET, IGBT) that can control high currents and voltages. A thyristor maintains conduction below its holding current and latches on above its latching current. Snubber circuits protect thyristors from high dv/dt. Controlled rectifiers use thyristors to vary DC output voltage. Choppers vary DC voltage using switching circuits. Inverters convert DC to AC. AC voltage controllers vary AC output voltage using phase control or on-off control of thyristors. Cycloconverters directly convert AC power

1. Power electronics 2 marks
1. What is power electronics?
Ans:Power electronics is a subject that concerns the applications electronics principles into
situations that are rated at power level rather than signal level. It may be defined as a subject
deals with the apparatus and equipment working on the principle of electronics but at rated
power level.
2. Classify power semiconductor devices give examples.
And:Diodes: power diodes
Thyristors: SCR
Control switches: BJT, MOSFET and IGBT
3 Define latching current of SCR.
Ans:The latching current is defined as the minimum value of anode current which it must
attain during turn on process to maintain conduction when gate signal is removed.
4.Define holding current.
Ans:The holding current is defined as the minimum value of anode current below which it must
fall to for turning off the thyristor.
5.What are the different methods to turn on the thyristor?
Ans:Forward voltage triggering, Gate triggering, dv/dt triggering, temperature triggering & light
triggering
6What is the use of snubber circuit?
Ams:It consists of a series combination of a resistor and a capacitor in parallel with the
thyristors. It is mainly used for dv / dt protection.
7.Difference between power Diode and signal
8.What losses occur in a thyristor during working conditions?

2. Ans:Forward conduction losses
Loss due to leakage current during forward and reverse blocking.
Switching losses at turn-on and turn-off.
Gate triggering loss.
9.What are the types of power transistors?
Ans:1Bipolar Junction Transistor (BJT)
2.Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
3.Insulated Gate Bipolar Transistor (IGBT)
10.What are the draw backs of GTO?
Ans:1. Magnitude of latching and holding currents is more.
2. On state voltage drop and the associated loss is more
3. Due to multi cathode structure of GTO, triggering gate current is higher than the required for a
conventional thyristor.
Unit2 2marks
1.what is rectification and the classification of rectifier
Ans.Rectification is the process of converting alternating current (AC) which reverses its
direction periodically to direct current (DC) which flows only in one direction.
The Different Types of Rectifiers
Single Phase & Three Phase Rectifiers.
Half Wave & Full Wave Rectifiers.
Bridge Rectifiers.
Uncontrolled & Controlled Rectifiers.
2.Mention some of the applications of controlled rectifier.
Ans:1Steel rolling mills, printing press, textile mills and paper mills employing dc motor drives.
2.DC traction
3.chemical and electro-metallurgical process
4.Portable hand tool drives
5.Magnet power supplies
6.HVDC
3.Give any two differences single phase full and semi converter?

3. Ans:
Full Converter
Half controlled converter
1.
Thyristors only
Mixture of diodes and thyristors
2.
Two Quadrant Converter
One Quadrant converter
3.
Power factor is less
power factor is more
4.Define the term voltage ripple factor and current ripple factor.
Ans.It is the ratio of the net harmonic content of the output voltage to the average output
voltage.
5.What is dual converter?
Ans: It consists of two similar single phase or three phase fully controlled converter which are
connected in parallel at the input side and are connected inverse parallel at the output side.
6.Write any four parameters of phase controlled converter?
Ans1.Input displacement factor.
2.Input power factor.
3.Input harmonic factor.
4.Current ripple factor
7.What is the function of freewheeling diodes in controlled rectifier?
Ans:1.It prevents the output voltage from becoming negative.
2.The load current is transferred from the main thyristors to the freewheeling diode, thereby
allowing all of its thyristors to regain their blocking states.
8.What are the advantages of freewheeling diodes in a controlled rectifier?
Ans :1.Input power factor is improved.
2 .Load current waveform is improved and thus the load performance is better.
3.Load current waveform is improved and thus the load performance is better.

4. 9.What is meant by delay angle?
Ans:The delay angle is defined as the angle between the zero crossing of the input voltage and
the instant the thyristor is fired.
10.What is mean by full converter?
Ans: A fully controlled converter uses thyristors only and there is a wider control over the level
of dc output voltage. It is also known as two quadrant converter.
Unit:3. 2marks
1.What is meant by dc chopper?
Ans:A dc chopper is a high speed static switch used to obtain variable dc voltage from a constant
dc voltage.
2.What are the applications of dc chopper?
Ans:1.Battery operated vehicles
2.Traction motor control in electric traction
3.Trolley cars
4.Marine hoists
5.Mine haulers
6.Electric braking.
3.What is meant by step-up and step-down chopper?
Ans:1.In a step- down chopper or Buck converter, the average output voltage is less than the
input voltage.2. In a step- up chopper or Boost converter, the average output voltage is more than
the input voltage.
4.What is meant by duty-cycle?
Ans.Duty cycle is defined as the ratio of the on time of the chopper to the total time period of the
chopper. It is denoted by α.
5.What are the two types of control strategies?
Ans:1.Time Ratio Control (TRC)
2.Current Limit Control method (CLC)
6.What is meant by PWM control in dc chopper?

5. Ans:In this control method, the on time Ton is varied but chopping frequency is kept constant.
The width of the pulse is varied and hence this type of control is known as Pulse Width
Modulation (PWM).
7.What are the different types of chopper with respect to commutation process?
Ans:1.Voltage commutated chopper.
2.Current commutated chopper.
3.Load commutated chopper.
8.Write down the expression for the average output voltage for step down and step up chopper.
Ans::Average output voltage for step down chopper is VO = α VS. Average output voltage for
step up chopper is VO = α VS x [1/ ( 1- α )].
9.What are the advantages of load commutated chopper?
Ans::1.Commutating inductor is not required.
2.It is capable of commutating any amount of load current.
3.It can work at high frequencies in the order of kHz.
4.Filtering requirements are minimal.
10.What is two quadrant chopper?
Ans::A DC chopper can be operate in the I and II quadrant as well as I and IV quadrant.
Uint:4. 2marks
1.What is meant by inverter?list few industrial applications of inverter.
Ans;A device that converts dc power into ac power at desired output voltage and frequency is
called an inverter.
1.Adjustable speed drives
2.Induction heating
3.Stand-by aircraft power supplies
4.UPS
5.HVDC transmission
2.what are line commutated inverter?

6. Ans:Line Commutated Inverter is an inverter that is tied to a power grid or line. The
commutation of power (conversion from direct current to alternating current) is controlled by the
power line, so that, if there is a failure in the power grid, the photovoltaic system cannot feed
power into the line.
3.What is the main classification of inverter?
Ans:1.Voltage Source Inverter
2.Current Source Inverter
4.What is meant a series inverter?
An inverter in which the commutating elements are connected in series with the load is called a
series inverter.
5.What is meant a parallel inverter?
An inverter in which the commutating elements are connected in parallel with the load is called a
parallel inverter.
6.What is meant by McMurray inverter?
Ans::It is an impulse-commutated inverter, which relies on LC circuit and an auxiliary thyristor
for commutation in the load circuit.
7.What are the different types of PWM methods for voltage control within inverter?
Ans::1.Single pulse width modulation
2.Multiple pulse width modulation
3.Sinusoidal pulse width modulation
8.What is meant by PWM control?
Ans.In this method, a fixed dc input voltage is given to the inverter and a controlled ac output
voltage is obtained by adjusting the on and off periods of the inverter components. This is the
most popular method of controlling the output voltage and this method is termed as PWM
control.
9.How is the inverter circuit classified based on commutation circuitry?
Ans.1.Line commutated inverters.
2.Load commutated inverters.
3.Self commutated inverters.

7. 4.Forced commutated inverters.
10.Define the term inverter gain.
Ans:It is defined as the ratio of the AC output voltage to DC input voltage.
UNIT 5. 2marks
1.What does ac voltage controller mean?
Ans:It is device, which converts fixed alternating voltage into a variable voltage without change
in frequency.
2. What are the applications of phase controlled converter or ac voltage controller.
Ans;:1.Domestic and industrial heating
2.Lighting control
3.Speed control of single phase and three 4.phase ac motors
5.Transformer tap changing.
3.What are the advantages of ac voltage controllers?
Ans:1.High efficiency
2.Flexibility in control
3.Less maintenance
4.. What are the two methods of control in ac voltage controllers?
Ans:1.ON-OFF control
2.Phase control
5.what is the difference between On Off control and phase control
Ans.ON-OFF control: In this method, the thyristors are employed as switches to connect the load
circuit to the source for a few cycles of the load voltage and disconnect it for another few cycles.
Phase control: In this method, thyristor switches connect the load to the ac source for a portion of
each half cycle of input voltage.
6.What is meant by cyclo-converter?

8. Ans:It converts input power at one frequency to output power at another frequency with
one-stage conversion. Cycloconverter is also known as frequency changer.
7.What are the two types of cyclo-converters?
Ans: a. Step-up cyclo-converters.
b. Step-down cyclo-converters.
8.What is meant by step-up cyclo-converters?
In these converters, the output frequency is less than the supply frequency.
9.What is meant by step-down cyclo-converters?
In these converters, the output frequency is more than the supply frequency.
10 .Same as 9 questions