Optimum size of dissipative nonlinear turn-off snubber

The use of voltage dependent, saturable capacitors as nonlinear turn-off snubbers for power electronic switches is discussed. Emphasis is placed on the optimum dissipative snubber configuration. The snubber capacitance is optimised in terms of minimum total energy losses (consisting of the stored energy in the capacitor, and the energy loss in the power switch during turn-off). By means of a computer analysis, which uses the exact capacitance-voltage curve of the nonlinear snubber capacitor, the needed energies are calculated and the results presented in clear graphical form. The computer simulation is also verified by means of an experimental measurement. From the results, it is evident that, from an energy point of view, the nonlinear capacitive snubber is always superior to the normal linear snubber. This conclusion is applicable to the stored energy in the capacitor, total energy losses, as well as to the minimum total energy loss