POWER ELECTRONICS

Power Electronics

Power electronics is a subject or a field which combines the knowledge of Power (Electric Power), Electronics and Control System to process and control the flow of electric power by supplying voltages and currents in the form optimally suited for user load. Power engineering deals with the static and rotating power equipment for the generation, transmission and distribution of electric power. Electronics deals with the study of solid state semiconductor power devices and circuits for power conversion to meet the desired control objectives i.e. to control the output voltage and output power. So power electronics may be defined as the subject of applications of solid state power semiconductor devices for the control and conversion of electric power. The basic block diagram of power electronics is shown in fig 1 below.

Fig 1: Basic block diagram of Power Electronics

The main goal of power electronics is to convert the electrical energy from one form to another form and also to control the flow of energy from an electrical source to an electrical load with highest efficiency, high availability and high reliability with the lowest cost, smallest size and light weight. Power electronics deals with the study and design of Thyristorised power controllers for variety of applications like Heat Control, Light Illumination Control and Motor control – AC/DC motor drives used in industries. Today power electronics systems are widely spread for adapting energy to the load in many different cases in industries, transportation and household, e.g.

• ·         Power supply and electrical transmission e.g. high voltage DC lines(HVDC)
• ·         Electric drives in electric cars, trams, locomotives and many other cases
• ·         Electric drives in conveying devices, rolling mills, machine tools and others
• ·         Power supply for welding, electroplating and electrolysis
• ·         Power supply for consumer goods, e.g. switching mode power supply for computers, TV and many more other products, furthermore light dimming, speed control of fans, vacuum cleaners and many others electric appliances.

The main task of power electronics is to convert and control the electric power, i.e. for the control of electric power or power conditioning, the conversion of electrical power from one form to another form is necessary and the switching characteristics of power devices permits these conditions. The static power converters perform these functions of power conversions. A converter may be considered as a switching matrix. The four main forms of conversions are:

Ø  AC to DC Conversion (Rectification)

Ø  AC to AC Conversion (Phase Controlled Rectifiers)

Ø  DC to DC Conversions (DC Choppers)

Ø  DC to AC Conversions (Inverters)

                                              

Why Power Electronics

Power electronics is a technology associated with the efficient conversion, control and conditioning of electric power by static means from its available input form into the desired electrical output form. Power electronics is used for quality control of power supply i.e. better power factor and it makes the system 10-100 times smaller and lighter as well as 10 times more efficient power supply in comparison with previous technology used. The control design for different distributed energy system helps protect the system from damaging i.e. minimum damage will occur. It makes mobile phone last longer, makes hybrid cars practicable and helps make electric generation possible from sources ranging from solar cells on roof to nuclear reactor in rural areas. It has a potential to make a huge contribution to the low carbon economy - power savings on conventional electrical devices of 30-40% are here now, and there is more to come.

Fig 2: Power System employing one dc supply created from the mains and distributed individual power supplies for each subsystem

Some Applications of Power Electronics

·         Commercial Applications: Heating systems ventilating, Air conditioners, Central Refrigeration, Lighting, Computers and Office Equipments, Uninterruptible Power Supply (UPS), Elevators and Emergency Lamps.

·         Domestic Applications: Cooking Equipments, Lighting, Heating, AC, Refrigerators and Freezers, Personal Computers, Entertainment Equipments, UPS.

·         Industrial Applications: Pumps, Compressors, Blowers and Fans, Machine Tools, Arc Furnaces, Induction Furnaces, Lighting Control Circuits, Industrials Lasers, Induction Heating, Welding Equipments.

·         Aerospace Applications: Space Shuttle Power Supply System, Satellite Power System, Aircraft Power Systems.

·         Telecommunication: Battery chargers, Power Supplies (DC and UPS), Mobile Cell Phones Battery Chargers.

·         Transportation: Traction Control of Electric Vehicles, Battery Chargers for Electric Vehicle, Electric Locomotives, Street Cars, Trolley Buses, Automobile Electronics Including Engine Controls.

·         Utility System: High Voltage DC (HVDC) Transmission, Static VAR Compensation (SVC), Alternative Energy Sources (Wind, Photovoltaic), Fuel Cells, Energy Storage System, Induced Draft Fans and Boiler Feed Water Pumps.

Fig 3: Application of Power Electronics

Brief History of Power Electronics

The first power electronics device developed was the Mercury Arc Rectifier during the year 1900. Then the other power devices like metal tank rectifier, grid controlled vacuum tube rectifier, ignitron, phanotron, thyratron and magnetic amplifier were developed and used gradually for power control applications until 1950. The first Silicon Controlled Rectifier (SCR) or Thyristor was invented and developed by Bell Lab’s in 1956 which was the first PNPN triggering transistor. The second electronic revolution began in the year 1958 with the development of the commercial grade Thyristor by the General Electric (GE) Company, thus the new era of power electronics was born. After that many different types of power semiconductor devices and power conversion techniques have been introduced. The power electronic revolution is giving us ability to convert shapes and control large amounts of power.

Notes:

1. ·         Power electronics refers to control and conversion of electrical power by power semiconductor devices wherein these devices operate as switches.
2. ·         Advent of silicon-controlled rectifiers, abbreviated as SCRs, led to the development of a new area of application called the power electronics.
3. ·         Prior to the introduction of SCRs, mercury-arc rectifiers were used for controlling electrical power, but such rectifier circuits were part of industrial electronics and the scope for applications of mercury-arc rectifiers was limited.
4. ·         Once the SCRs were available, the application area spread to many fields such as drives, power supplies, aviation electronics & high frequency inverters.
5. ·         The main task of power electronics is to control and convert electrical power from one form to another.
6. ·         Power electronics has applications that span the whole field of electrical power systems, with the power range of these applications extending from a few VA/Watts to several MVA / MW.
7. ·         "Electronic power converter" is the term that is used to refer to a power electronic circuit that converts voltage and current from one form to another.