A. Power electronics refers to control and conversion of electrical power by power semiconductor devices wherein these devices operate as switches.
A. The main task of power electronics is to control and convert electrical power from one form to another.
AC to DC conversion: Rectifier is used for converting an AC voltage to a DC voltage. Rectifier applications: Variable speed dc drives, Battery chargers, DC power supplies and Power supply for a specific application like electroplating.
DC to AC conversion: Inverter circuit is used to convert DC voltage to an alternating voltage.
Inverter applications: Emergency lighting systems, AC variable speed drives, Un-interrupted power supplies and Frequency converters.
DC to DC conversion: A dc-to-dc converter circuit was called a chopper.
Chopper applications: DC drive, Battery charger and DC power supply.
AC to AC conversion: A cycloconverter converts an AC voltage to another AC voltage. Cycloconverter applications: It is rarely used. Can be used for controlling the speed of an AC traction motor
A. SCR or thyristor will have three regions of operations based on the mode in which the device is connected in the circuit.
Reverse blocking region: When the cathode of the thyristor is made positive with respect to the anode and no gate signal is applied. In this region SCR exhibits the reverse blocking characteristics similar to diode.
Forward blocking region: In this region the anode of the thyristor is made positive with respect to the cathode and no gate signal is applied to the thyristor. A small leakage current flow in this mode of operation of the thyristor.
Forward conduction region: when the forward voltage applied between the anode and cathode increases at particular break over voltage avalanche breakdown takes place and thyristor starts conducting current in forward direction. By this type of triggering the device damages the scr. Hence a gate signal is applied before the forward break over voltage to trigger the scr.
A. Holding current is the minimum current required to hold the SCR in forward conduction state. When the forward current becomes less than holding current (If< Ih ), SCR changes from forward conduction state to forward blocking state.
A. Latching current is the minimum current required to latch (turn on) the SCR from forward blocking state to forward conduction state.
A. Forward conduction losses
Loss due to leakage current during forward and reverse blocking
Switching losses at turn on turn off
Gate triggering loss
A. Forward voltage triggering
Gate Triggering
dv/dt triggering
Thermal triggering (Temperature Triggering)
Light triggering (Radiation triggering)
A. The angle between the zero crossing of the input voltage and the instant the SCR is fired is called as delay angle or firing angle.
A. The input power factor is improved. It prevents the output voltage from becoming negative. Load current waveform is also improved.
A. It is also known as frequency changer. It converts input power at one frequency to output power at another frequency with one stage conversion.
A. Step up cyclo-converter: In this output frequency is less than the input frequency.
Step down cyclo-converter: In this output frequency is more than the input frequency.
A. It is the one which converts fixed alternating voltage to a variable voltage without change in frequency.
A. A device which converts dc power into ac power at desired output voltage and frequency is called as Inverter.
A. Voltage Source Inverter
Current Source Inverter
A. It is the ratio of the on time of the chopper to total time period of the chopper.
D = Ton / [Ton + T off]
Humankind has become extremely dependent on electricity, without it we can’t run the household, keep…
[1] Define the term synchronous speed [Dec-2003] For synchronous machines there exists a fixed relationship…
We shared a lot of interview questions on electrical machines, power system and power electronics. Today we…
DIESEL POWER STATION A generating station in which diesel engine is used as the prime…
Q:Why syn. generators are used for the production of electricity? A:synchronous machines have capability to…
Hydro-electric Power Station A generating station which utilises the potential energy of water at a…