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1. A modulation control scheme for a photovoltaic system charge controller to control charging of a battery bank with electrical power from a high voltage photovoltaic (PV) array, comprising
a photovoltaic system charge controller including a dual active bridge DC to DC converter having a first bridge with four MOSFET switches, a second bridge with four MOSFET switches, and a transformer electrically connecting said first and second bridges and having a total leakage inductance Ltot and a turn ratio n, said first bridge receiving electrical input V1 from the high voltage photovoltaic array and said second bridge delivering electrical output Vout of appropriate voltage to charge the battery bank; and a modulation control scheme for selectively controlling on and off actions of said switches to control electrical power flow through said converter in a minimum root mean square M-RMS mode of operation to minimize conduction losses and a full zero-voltage switching F-ZVS mode of operation to minimize switching losses, said M-RMS mode of operation having an operating range divided into five main M-RMS operating regions and four transition M-RMS operating regions respectively located between adjacent main M-RMS operating regions based on the value of a voltage component Vtrnf corresponding to the voltage differential V1−Vout/n, said F-ZVS mode of operation having an operating range divided into seven main F-ZVS operating regions and six transition F-ZVS operating regions respectively located between adjacent main F-ZVS operating regions based on the value of Vtrnf, each of said operating regions having switching semi-cycles divided into a plurality of intervals, said modulation control scheme controlling said switches in a first main M-RMS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a charging interval during which a voltage component Vtrnf corresponding to V1 is applied across Ltot, a transfer interval during which Vtrnf is applied across Ltot and an idling interval during which a voltage component Vidln corresponding to zero-voltage is applied across Ltot while the transformer primary current is zero, a first transition M-RMS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a charging interval and a transfer interval wherein transformer primary current reaches zero at the end of the transfer interval, a second main M-RMS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval during which a voltage component Vcirc corresponding to V1+Vout/n is applied across Ltot, a charging interval and a transfer interval wherein transformer primary current reaches zero at the end of the transfer interval, a second transition M-RMS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current reaches zero at the end of the transfer interval, a first aspect of a third main M-RMS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current is not at zero at the end of the transfer interval, a second aspect of the third main M-RMS operating region in which Vtrnf is zero and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current is constant and not zero during the transfer interval, a third aspect of the third main M-RMS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current is not zero at the end of the transfer interval, a third transition M-RMS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current is zero at the end of the circulating interval, a fourth main M-RMS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval, a transfer interval and a discharging interval during which a voltage component Vdsch corresponding to Vout/n is applied across Ltot wherein transformer primary current reaches zero at the end of the circulating interval, a fourth transition M-RMS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a discharging interval and a transfer interval wherein transformer primary current reaches zero at the end of the discharging interval, a fifth main M-RMS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a transfer interval, a discharging interval and an idling interval wherein transformer primary current reaches zero at the end of the discharging interval, a first main F-ZVS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval, a charging interval, a freewheeling interval, during which a voltage component Vfreew corresponding to zero-voltage when transformer primary is not zero is applied across Ltot, and a discharging interval wherein transformer primary current reaches a selected circulating primary current value Ix at the ends of the circulating and discharging intervals, a first transition F-ZVS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval and a charging interval wherein transformer primary current reaches Ix at the ends of the circulating and discharging intervals, a second main F-ZVS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval, a charging interval, a transfer interval and a discharging interval wherein transformer primary current reaches Ix at the ends of the circulating and discharging intervals, a second transition F-ZVS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval, a charging interval and a transfer interval wherein transformer primary current reaches Ix at the ends of the circulating and transfer intervals, a third main F-ZVS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval, a charging interval and a transfer interval wherein transformer primary current reaches Ix only at the end of the transfer interval, a third transition F-ZVS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current reaches Ix at the end of the transfer interval, a first aspect of a fourth main F-ZVS operating region in which Vtrnf is negative and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current reaches a current value Ip2 at the end of the circulating interval and reaches a current value Ip1, less than Ip2, at the end of the transfer interval, a second aspect of the fourth main F-ZVS operating region in which Vtrnf is zero and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current is at Ip1 throughout the transfer interval, a third aspect of the fourth main F-ZVS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current reaches Ip1 at the end of the circulating interval and reaches Ip2 at the end of the transfer interval, a fourth transition F-ZVS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval and a transfer interval wherein transformer primary current reaches Ix at the end of the circulating interval and reaches a current value Ip, greater than Ix, at the end of the transfer interval, a fifth main F-ZVS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval, a transfer interval and a discharging interval wherein transformer primary current reaches Ip2 at the end of the transfer interval and reaches Ip1 at the end of the discharging interval, a fifth transition F-ZVS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval, a transfer interval and a discharging interval wherein transformer primary current reaches Ix at the end of the circulating interval, reaches Ip at the end of the transfer interval and reaches Ix at the end of the discharging interval, a sixth main F-ZVS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval, a charging interval, a transfer interval and a discharging interval wherein transformer primary current reaches Ix at the end of the circulating interval, reaches Ip1 at the end of the charging interval, reaches Ip2 at the end of the transfer interval and reaches Ix at the end of the discharging interval, a sixth transition F-ZVS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval, a charging interval and a discharging interval wherein transformer primary current reaches Ix at the end of the circulating interval, reaches Ip at the end of the charging interval and reaches Ix at the end of the discharging interval, and a seventh main F-ZVS operating region in which Vtrnf is positive and each switching semi-cycle consists in sequence of a circulating interval, a charging interval, a freewheeling interval and a discharging interval wherein transformer primary current reaches Ix at the end of the circulating interval, reaches Ip at the end of the charging interval, remains at Ip during the freewheeling interval and reaches Ix at the end of the discharging interval. |
