Gate Drive circuit for three phase fully controlled converter
Gate Drive Circuit for three phase fully controlled converter:
Fig: Triggering circuit for single phase converter (a)circuit diagram (b) phaser diagram (c)Waveforms
- In either single or three phase converters
- To get,
- A phase shift network is used to obtain a waveform leading vi by 90º. The output of the phase shift waveform (and its inverse) is compared with vc. The firing pulse is generated at the point when these two waveforms are equal.
- At-this instant
Therefore, this method of generation of converter firing pulses is called “inverse cosine” control.
- The output of the phase shift network is called carrier waveform. The signal transformer uses three single phase transformer each of which has two secondary windings.
- The primary windings are connected in delta while the secondary windings are connected in zigzag. T2 is fired α angle after the positive going zero crossing of vbc. Therefore, to implement inverse cosine the carrier wave for T2 must lead vbc by 90º. This waveform is obtained from zigzag connection of the winding segments a1a2 and c1c2
- The voltage across each zigzag phase can be used to fire two thyristors belonging to the same phase leg using a circuit similar to the triggering circuit for single phase converter. The phase shift network will not be required in this case.