Abstract: A modulation control scheme for a series-connected dual active bridge (DAB) DC to DC converter in a maximum power point tracking charge controller used in a photovoltaic system controls operation of the converter in a forward direction power flow mode to control charging of a battery bank with electricity produced by the photovoltaic array. The modulation control scheme is also capable of operating the converter in a reverse direction power flow mode to control the flow of electricity from the battery bank to a DC load. The modulation control scheme divides the converter's operating range in each mode into five main cases of minimum root mean square (M-RMS) operating regions and seven main cases of full zero-voltage switching (F-ZVS) operating regions, as well as transition operating regions between adjacent main cases, based on applicable power level and value of voltage differential.