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In dc choppers and variable frequency inverters, the commutation of the conducting thyristors must be achieved. In most of the techniques used for commutation, the stored energy in the commutation capacitor at the end of the commutation is higher than the initial stored energy. This paper describes a commutation scheme which uses an energy recovery transformer to feed back the excess energy to the dc supply. The differential equations for the different modes of operation of the commutation system are derived. The solutions of the equations are used to optimize the system for minimum stored energy. Effects of the leakage inductance and turns ratio of the energy recovery transformer are also considered.