and 42 will operate at duty cycles from zero to 50 as commanded by a control circuit to provide the desired current or voltage regulation for the ac port the inclusion of switch 43 allows the ac port to act as a boost circuit in conjunction with inductor 51 when delivering energy from utility grid 66 to high frequency transformer 30 switch 43 also allows an efficient path for freewheeling inductor current when power is being delivered from transformer 30 to ac loads 64 or utility grid 66 without switch 43 a limited boost function can be had by simultaneously closing switches 41 and 42 causing transformer windings 33 and 34 to be short circuited and opening all bridge 20 switches this works well for two port converters but limits the transformer availability for converters with three or more ports because the transformer is unable to sink or source power at any port when windings 33 and 34 are shorted also anytime bridge 20 is not in conduction the operation of one port becomes dependent on the operation of other ports and the value of this power conversion approach is severely compromised the inclusion and function of switch 43 in the ac port is novel and part of this invention it should be noted that if power is flowing into the ac port inductor 51 acts as.