Power Electronics refers to the process of controlling the flow of current and voltage and converting it to a form that is suitable for user loads. The most desirable power electronic system is one whose efficiency and reliability is 100%.
A power electronic system converts electrical energy from one form to another and ensures the following is achieved −
- Maximum efficiency
- Maximum reliability
- Maximum availability
- Minimum cost
- Least weight
- Small size
Applications of Power Electronics are classified into two types − Static Applications and Drive Applications.
Static Applications
This utilizes moving and/or rotating mechanical parts such as welding, heating, cooling, and electro-plating and DC power.
Drive Applications
Drive applications have rotating parts such as motors. Examples include compressors, pumps, conveyor belts and air conditioning systems.
Power Electronics - Linear Circuit Elements
Linear circuit elements refer to the components in an electrical circuit that exhibit a linear relationship between the current input and the voltage output. Examples of elements with linear circuits include −
- Resistors
- Capacitors
- Inductors
- Transformers
Silicon Controlled Rectifier
A silicon controlled rectifier or semiconductor-controlled rectifier is a four-layer solid-state current controlling device. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor.
SCRs are mainly used in electronic devices that require control of high voltage and power. This makes them applicable in medium and high AC power operations such as motor control function.
Power Electronics - TRIAC
The acronym TRIAC stands for Triode for Alternating Current. A TRIAC is a semiconductor device with three terminals that control the flow of current, thus the name Triac. Unlike SCR, TRIAC is one directional while SCR is bi-directional.
It is ideal for operation utilizing AC power for switching purposes since it can control current flow for both halves in an alternating current cycle. This explained clearly in the diagram below.
Power Electronics - BJT
A Bipolar Junction Transistor (BJT) is a transistor whose operation depends on the contact made by two semiconductors. It can act as a switch, amplifier or oscillator. It is known as a bipolar transistor since its operation requires two types of charge carriers (holes and electrons). Holes constitute the dominant charge carriers in P-type semiconductors while electrons are the main charge bearers in N-type semiconductors.
Power Electronics - MOSFET
Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is a type of transistor used to switch electronic signals. It has four terminals namely; source (S), Drain (D), Gate (G) and Body (B).The MOSFET’s body is normally connected to the terminal of the source(S), which results in three-terminal device similar to other field effect transistors (FET). Since these two main terminals are usually interconnected via short circuit, only three terminals are visible in electrical diagrams.
Power Electronics - Pulse Converters
A phase controlled converter converts AC to DC energy (line commutated). In other words, it is used in the conversion of fixed-frequency and fixed-voltage AC power into variable DC voltage output. It is expressed as
- Fixed Input − Voltage, frequency and AC power
- Variable output − DC voltage output
Power Electronics - Dual Converters
Dual converters are mainly found in variable speed drives (VFDs). In a
dual converter, two converters are linked together back to back. The operation
of a dual converter is explained using the diagram below. It is assumed that −
·
A dual converter is an ideal one (gives pure DC output)
at its terminals.
·
Each two-quadrant converter is a controlled DC source in
series with a diode.
·
Diodes D1 and D2 show the unidirectional flow of current.
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