DC to AC inverter with single-switch bipolar boost circuit

Abstract

This invention improves the performance and lowers the cost of DC to AC inverters and the systems where these inverters are used. The performance enhancements are most valuable in renewable and distributed energy applications where high power conversion efficiencies are critical. The invention allows a variety of DC sources to provide power thru the inverter to the utility grid or directly to loads without a transformer and at very high power conversion efficiencies. The enabling technology is a novel boost converter stage that regulates the voltage for a following DC to AC converter stage and uses a single semiconductor switching device. The AC inverter output configuration is either single-phase or three-phase.

1. An apparatus for converting DC power from solar photovoltaic modules or other DC sources into AC power where said AC power is supplied to an electric utility grid and comprising; a bipolar DC input circuit with a center-tapped connection to ground or to the zero-voltage reference point of said electric utility grid, a DC to DC converter capable of boosting said bipolar DC input circuit voltages to higher bipolar DC output voltages with respect to ground or to the zero-voltage reference point of said electric utility grid and where said DC to DC converter uses a single semiconductor switch and a DC to AC converter which converts the output of said DC to DC converter into current regulated sine waves, synchronized with said electric utility grid voltage, in order to source power into said electric utility grid and where said DC to DC converter is further defined as comprising three input terminals designated plus, common and minus where there is a capacitor connected across the plus and common terminals and a capacitor connected across the common and minus terminals and where there is a top inductor connected between the plus input terminal and the collector or drain of a semiconductor switching device and also connected to the anode of a top diode and where there is a bottom inductor connected between the minus input terminal and the emitter or source of a semiconductor switching device and also connected to the cathode of a bottom diode and where the output of said DC to DC converter has at least two terminals designated positive and negative where there is a capacitive storage element between said positive and negative output terminals and where the cathode of said top diode is connected to the positive output terminal and where the anode of said bottom diode is connected to the negative output terminal. 
     
     
       2. A DC- to - DC converter comprising:      three input terminals designated plus, common and minus,        at least two terminals designated positive and negative,        a capacitor connected across the plus and common terminals,        a capacitor connected across the common and minus terminals,        a semiconductor switching device,        a top diode having a cathode connected to said positive output terminal,        a bottom diode having an anode connected to said negative output terminal,        a top inductor connected between said plus input terminal and the collector or drain of said semiconductor switching device and also connected to the anode of a top diode,        a bottom inductor connected between said minus input terminal and the emitter or source of said semiconductor switching device and also connected to the cathode of a bottom diode, and        a capacitive storage element between said positive and negative output terminals.     
     
     
       3. An inverter for coupling a photovoltaic array to a utility grid, the inverter comprising:
   a DC - to - AC converter coupled to the utility grid; and        a DC - to - DC converter coupled between the photovoltaic array and the DC - to - AC converter, the DC - to - DC converter including:      three input terminals designated plus, common and minus,        at least two terminals designated positive and negative,        a capacitor connected across the plus and common terminals,        a capacitor connected across the common and minus terminals,        a semiconductor switching device,        a top diode having a cathode connected to said positive output terminal,        a bottom diode having an anode connected to said negative output terminal,        a top inductor connected between said plus input terminal and the collector or drain of said semiconductor switching device and also connected to the anode of a top diode,        a bottom inductor connected between said minus input terminal and the emitter or source of said semiconductor switching device and also connected to the cathode of a bottom diode, and        a capacitive storage element between said positive and negative output terminals.       
     
     
       4. The inverter of  claim 3 , further comprising a current sensor disposed between said top inductor and said switching device.