Concept of Power Electronics - Electrical Engineering (EE) PDF Download

What is Power Electronics?

• Power electronics belongs partly to power engineers and partly to electronics engineers. engineering is mainly concerned with the generation, transmission, distortion and utilization of electric energy at high efficiency.
•  Electronics engineering, on the other hand, is guided by distortion -less production, transmission, and reception of data and signals of high efficiency.

Important Power Electronic Devices

Apparatus associated with power engineering is biased mainly on electromagnetic principles whereas that in electronics engineering is based upon physical phenomena in vacuum, gasses/vapors, and semiconductors. Power electronic converters (or circuits ) can be classified into six types under:

1. Diode rectifiers 

Diode Rectifier

• A diode rectifier circuit converts AC input voltage into a fixed DC voltage. The input voltage may be single-phase or three-phase. 
• Diode rectifiers find wide use in electric traction, battery charging, electroplating, electrochemical processing, power supplies, welding, and uninterruptible power supply (UPS) systems.

2. AC to DC Converter (phase-controlled rectifiers) 

Phase Controlled Rectifier

• These convert constant voltage to line voltage for their commutation, as such these converters. Phase-controlled converters may be fed from 1-phase or 3-phase source. 
• These are used in DC drives, metallurgical and chemical industries, excitation systems for synchronous machines, etc.

3. DC to DC converters (Choppers)

DC-DC Converter

• A DC chopper converts fixed DC input voltage to a controllable DC output voltage. The chopper circuits required force, or load commutation to turn off the thyristors.
• For lower-power circuits, thyristors are replaced by power transistors. 
• Classification of chopper circuits depends upon the type of commutation and also on the direction of power flow. choppers find wide applications in DC drives, subway cars, trolley trucks, battery-driven vehicles, etc.

4. DC to AC converters (Inverters)

Inverter

• An inverter converts fixed DC voltage to a variable AC voltage. The output may be a variable voltage and variable frequency. 
• These converters used line, load, or forced commutation to turn -off the thyristors. Inverters find wide use in induction-motor and synchronous-motor drives, induction heating, UPS, HVDC transmission, etc. 
• At present, conventional thyristors are also being replaced by GTOs in high-power applications and by power transistors in low-power applications.

5. AC to AC converters

These convert fixed AC input voltage into variable AC output voltage. They are of two types under

(a) AC Voltage  controllers  (AC voltage regulators):

• These converter circuits convert fixed AC voltage directly to a variable AC voltage at the same frequency.
• AC voltage controllers employ two thyristors in anti-parallel or a triac. Turn-off of both devices is obtained by line commutation. 
• The output voltage is controlled by varying the firing angle delay. AC voltage controllers are widely used for lighting control, speed control of fans, pumps etc.

(b) Cycloconverters: 

• These circuits convert input power at one frequency to output power at a different frequency through one-stage conversion, Line commutation is more common in these converters, though forced and load-commutated cycloconverters are also employed.
• These are primarily used for slow-speed large AC drives like rotary kilns etc.

6. Static switches 

• The power semiconductor devices can operate as static switches or contractors. Static switches possess many advantages over mechanical and electromechanical circuit breakers. 
• Depending upon the input supply, the static switches are called AC static switches or DC static switches.