Power Electronics Converters
Electronic power is the muscle of modern industry and power electronics makes its utilization smarter. Power electronics is solely concerned with the processing of electronic energy. The electric energy by itself is not useful to mankind. It must be converted to other energy forms such as heat, light, sound and mechanical energies, which are directly useful to human beings and society. The focus in power electronics is on conversion and control of energy. System Vies of Power Electronics Converters
Power converter system is a single-input single-output system. The source provides power, the converters convert it into a usable form to suit the sink where the power is utilized, that is, removed out of the system. The source is either a DC or another source, or a device where the electrical energy is converted into nonelectrical forms such as a motor. The voltage and current waveform on the source and the sides are either single phase or multiphase (usually three-phase). The converter system is
comprised of switches, reactive components L, C, and transformers. Switches include two terminal devices such as diodes and three-terminal devices such as transistor or thyristors (SCRs).
A more general power electronic converter system may contain more than one input and one or more output variables.
For simplifying the analysis of converter operation, the switches and other
components are assumed to be ideal, linear and invariant over the time of obligation. The switches are assumed to have unrestricted voltage or current carrying capabilities. Power electronic converters may be classified into four categories on the basis of the type of the source and the type of desired output characteristics. 1. DC to AC converter 2. AC to DC converter 3. DC to DC converter 4. AC to AC converter
AC to AC converter
The AC to AC converter takes power from an AC voltage or current source and delivers to a load. The output variable is a low distortion AC voltage or AC current of an equal or different frequency than the input AC source. The conversion may also involve single phase to multiphase or vice versa. The practical AC controller usually uses line frequency 50-60Hz voltage sources, single-phase or three-phase. The AC-AC converter where the output frequencies lower than the frequency of the source is called the cycle-converter in a cycle-converter is a simple fraction such as 1/3,1/5
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and so on of the source frequency. They are used in very high power industrial applications. The AC to AC converter with no change of frequency is referred to as the AC controller.
The output frequency is the same as the source frequency in a basis AC to AC converter topology. The switch is turned off at the end of each half period of the source waveform. The instant of turning on the switch relative to the AC source waveform determines the shape of the output voltage waveform, which in turn determines the RMS voltage at the output terminals.
A more complex AC to AC conversation is achieved by first converting the input AC to the DC and the DC to the AC of desired frequency, amplitude and number phases. Such a converting conversion, there is no restriction on the output frequency relative to the source frequency. Applications:
Light dimmers AC motor speed controls Voltage regulators Electronic tap changers VAR regulators Solid-state relays
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电力电子变换器-英文
