Design of cosine control firing circuit using sinusoidal oscillator

Abstract

The theme of dissertation is to design & implement the firing circuit for a converter. The idea behind our dissertation is to use cosine signal for the firing circuit which has several advantage. The various circuits like UJT relaxation oscillator triggering, RC triggering & Ramp triggering etc undergoes the problem of limited firing angle. But Cosine Firing Scheme (CFS) can be implemented for the very precise control of firing angle. Another advantage of CFS is that it can be controlled digitally using microcontrollers. Thus can be used for the closed loop circuit. For giving the AC supply of 6-0-6 V earlier we are using the Centre tap transformer which makes the circuit bulky and also the overall cost of the firing circuit is high. Instead of Centre tap transformer we are using sinusoidal oscillator which has a high frequency in the firing circuit and its cost is cheaper than transformer and easily available and the bulkiness of the firing circuit reduces. In the earlier research the voltage which we get at the pulse transformer doesn’t have the high frequency therefore so there will be delay to turnon the thyristor. For designing the firing circuit we are using digital & analog component such as SCRs, BJTs, MOSFETs, 1-phase converter comparator, Monoshot, SR flip flop, 555 timer, opamp etc. The model is simulated on Multisim software and implemented on bread board for its real time implementation and several results are obtained on oscilloscope.