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Chopper Control - Essay Example
Author : ydonnelly
Pages 12 (3012 words)
There are two forms of electrical energy supplies namely; AC (Alternating Current) and DC (Direct Current). In Ac power supplies both the voltage and the current vary in magnitude with time whereas in DC power supplies both the voltage and the current are constant i.e…
Converters can be made using different technologies which depend on; the type of semiconductor devices used and the power ratings of the load. Several semi conductor devices are used such as the diodes, Thyristors, Triacs, GTO (gate turn off) among others (Gureich, 2008).
Thyristor or Silicon Controlled Rectifiers (SCRs) have been the traditional workhorses for bulk power conversion and control in industry. The Thyristor came from its gas tube equivalent, thyratron. Often it is a family name that includes SCRs, Triac, GTO, MCT and IGCT. A Thyristor is a controlled rectifier where the unidirectional current flow from anode to cathode is initiated by a small signal current from gate to cathode. Thyristors are classified as standard or slow-phase-control-type and fast switching, voltage fed inverter type (Ulrich et al, 1998).
Initially, when forward voltage is applied across a device, the off-state, or static dv / dt, must be limited so that it does not switch on spuriously. The dv / dt creates displacement current in the depletion layer capacitance of the middle junction, which induces emitter current in the component transistors and causes switching action (Dorf, 1997). When the device turns on; the anode current di / dt can be excessive, which can destroy the device by heavy current concentration. ...