Thyristor choppers using a bridge-connected capacitor for commutation

A thyristor d.c. chopper may utilise a capacitor connected within a bridge of four thyristors for forced commutation instead of the more common resonant LC circuit. Consideration is given to the main forms that such chopper circuits may take, and it is shown that, of the various modes of operation, three depend upon parallel-capacitor commutation, whereas one relies solely on series-capacitor commutation. It is concluded that choppers operated in the first three modes are easier to design than more conventional choppers, although, in general, their advantages are roughly balanced by their disadvantages, except for particular applications such as traction. The fourth mode results in a chopper having inherently safe commutation, even on considerable overload, and this offers a unique advantage over conventional choppers.