The solid state switches connected to fixed taps on a voltageinjecting transformer winding in a solid state step voltage regulator or load tap changing transformer are controlled synchronously to effectively insert the winding in series with the line for a variable number of half cycles, or preferably full cycles, of a base time interval. In addition to zero and full value voltage insertions, a variable portion of the full value voltage increment is injected in series with the line voltage without increasing the number of switches.