Inverters line-commutated

Note Since an inverter is not line commutated, the SCRs have a sw-iiching limitation and hence a limitation in frequency variation. When lliyrislors ai e to perform frcquenl switchings, CTOs are used In the inverter circuit. 

High-power inverters were initially developed for the long-distance transmission of power from a three-phase source to a remote three-phase sink using a DC overhead transmission line or cable. Early DC power transmission used mercury arc thyratrons (gas-filled values or tubes), which functioned in a manner very similar to the early types of thyristors. The on state of the valves was controllable, but the off state was determined by natural commutation made available by the sinusoidal voltages of the sink power system, see Reference 13. A brief description of three-phase inverters follows. 

Assume the inverter output line current consists of a 120° rectangle wave and that the commutation angle u is small enough to be ignored. The complete waveform has a harmonic content of,... 

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