A flux balancer for phase shift ZVS DC-DC converters under transient conditions

Under transient conditions the transformer flux of a phase shift controlled ZVS DC-DC converter may be driven deep into saturation. The conditions under which this will occur as well as the severity of this problem are analyzed and a prediction model is presented. With this information the transformer may be over dimensioned in order to prevent saturation from occurring. A circuit which modifies the duty cycle command under transient conditions is also presented. This circuit maintains flux balance and eliminates transformer saturation. Experimental results are presented which clearly show the problem as well as how it is eliminated with the proposed circuit.