Solar array inverter with maximum power tracking

A power supply adapted to supply AC power to a utility grid, comprising:

• a DC power source comprising a plurality of distributed DC sources that are individually connected in cascade with respective upstream DC-DC converters, where each upstream DC-DC converter has an output, and the outputs are connected in parallel;
• a power converter that provides uni-polar output power through a single power stage of DC-DC conversion;
• an unfolding and output filtering grid interface that commutates and filters the uni-polar output power into AC current that is supplied to the utility grid;
• a system controller for
• controlling the waveform of the converter output current to be rectified sinusoidal in phase with the utility grid, and
• reducing the output power when the utility grid voltage exceeds a pre-determined threshold;
• wherein the power converter is a cascade connection of an input bulk capacitor, a line-filter for providing sufficient filtering of the converter input current, and the single power stage;
• each of the distributed DC sources includes a dedicated maximum power tracking control through the respective upstream DC-DC converter;
• the parallel-connected outputs of the upstream DC-DC converters provide DC power to the single power stage;
• and
• the system controller regulates the power source voltage at a fixed DC voltage.

A method of converting power from a DC power source into AC power, comprising:

• detecting the utility grid power ripple;
• sensing a current proceeding from the DC power source into a power conversion stage, wherein the output current of the power conversion stage is controlled by a control signal that possesses a rectified sinusoidal waveform of a proper amplitude;
• sensing a voltage across the DC power source;
• generating a power signal as a function of the product of the sensed current and the sensed voltage;
• detecting an AC power ripple from the power signal and an AC voltage ripple from the sensed voltage, each ripple appearing as an inherent result of operation of the power conversion stage;
• extracting a first dither signal from the AC power ripple, and a second dither signal from the AC voltage ripple;
• deriving a dither signal inherently available from the utility grid power ripple;
• and
• converting power from the DC power source into AC power, including:
• determining the proper tracking direction toward the maximum power point of the DC source, and
• providing inherent dithering as a result of regulating the sensed output current to track the rectified sinusoidal control signal, and
• deriving the proper amplitude of the rectified sinusoidal within the control signal through a three-input multiplier.

A power supply adapted to supply AC power, comprising:

• a DC power source having an output voltage VSA and an output current ISA;
• a first low-pass filter taking VSA as an input and providing a filtered voltage level VLP as an output;
• a second low-pass filter taking ISA as an input and providing a filtered current level ILP as an output;
• an analog multiplier taking filtered voltage level VLP and filtered current level ILP as inputs, and providing a scaled power output level PSA=k·VLP·ILP as an output, for a predetermined value k;
• a first analog differentiator taking filtered voltage level VLP as an input, and providing voltage derivative signal VacSA as an output;
• a second analog differentiator taking scaled power output level PSA as an input, and providing power derivative signal PacSA as an output;
• a set point searching means for searching for a set point voltage VSP as a function of the voltage derivative signal VacSA and power derivative signal PacSA;
• and
• a feedback means for controlling the DC power source output voltage VSA to track the voltage, being proportional to the set point voltage VSP, that eventually reaches and swings back and forth around the maximum power voltage of the DC power source.

A DC-to-AC power conversion system, comprising:

• a utility grid interface having two input terminals and two output terminals;
• a uni-directional switching bridge, comprising two upper uni-directional semiconductor switches and two lower uni-directional semiconductor switches, that takes the rectified converter output current IOUTas an input and provides AC output as inverter output current (IAC) feeding into the two input terminals of the utility grid interface, wherein each uni-directional semiconductor switch has an upper terminal and a lower terminal;
• a DC-DC converter output having positive and return terminals, where the positive terminal is connected to the upper terminals of the two upper uni-directional semiconductor switches within the switching bridge, and the return output terminal is connected to the lower terminals of the two lower uni-directional semiconductor switches within the switching bridge;
• a full bridge rectifier taking the signal between the two input terminals of the utility grid interface as input, and providing a positive output and a negative output;
• and
• an energy absorption device (730) electrically connected between the positive output and the negative output of the rectifier;
• wherein the DC-DC converter positive output terminal is connected to the positive output of the rectifier (720) through a forward-biased diode (D5);
• wherein each of the upper and lower uni-directional semiconductor switches comprises a diode and a semiconductor switch connected in series and has an upper terminal and a lower terminal;
• and
• wherein each semiconductor switch is a transistor selected from the group consisting of:
• a bipolar junction transistor (BJT),
• a metal-oxide semiconductor field effect transistor (MOSFET), and
• an insulated-gate bipolar junction transistor (IGBT).

A power supply adapted to provide AC power from a DC power source to a utility grid having a utility grid transmission line, comprising:

• a DC-DC power conversion stage
• having a converter output inductor and
• providing a rectified converter output current IOUT between a first conductor and a second conductor, where the voltage potential of the first conductor is at least about as great as the potential of the second conductor;
• a uni-directional switching bridge, comprising four or more uni-directional switches, that takes the rectified converter output current IOUT as an input and provides AC output as inverter output current (IAC) to the utility grid;
• a full-bridge rectifier that takes the AC output as its input and provides a fully rectified output between a positive terminal and a negative terminal;
• a transient energy absorption device (730, 930, 931) electrically connected between the positive terminal and the negative terminal;
• and
• a bleeding diode that provides a current path for a portion of
• excess energy stored in the converter output inductor and
• external transient energy coupled to or residual energy stored in the utility grid transmission line to be absorbed by the transient energy absorption device;
• wherein the excess inductive energy in the rectified converter output current IOUT is directed from the first conductor into the transient energy absorption network, and excess energy in forms of voltage surges produced from the utility grid is directed through the following devices:
• the bleeding diode,
• one or more of the semiconductor switches in the uni-directional switching bridge,
• the full-bridge rectifier, and
• the transient energy absorption device;
• wherein the external transient energy in forms of voltage surges produced from the utility grid is directed through the following devices:
• one of the semiconductor switches in the uni-directional switching bridge,
• the full-bridge rectifier, and
• the transient energy absorption device;
• and
• wherein the uni-directional switches each comprise a series connection between a diode and a semiconductor switch selected from the switch group consisting of a MOSFET, a BJT, and an IGBT.

A power supply adapted to provide AC power from a DC power source to a utility grid with energy transient absorption capability, comprising:

• a DC-DC uni-directional converter power stage having an AC converter output current IAC between a first conductor and a second conductor, where the voltage potential of the first conductor relative to the second conductor is sinusoidal and in-phase with the utility grid voltage, and comprising an output-coupled inductor having a first winding and a second winding;
• a first and a second uni-directional transient energy absorption network, each comprising a diode and a uni-directional transient absorber connected in series, the uni-directional transient energy absorption devices being connected in series with opposite polarity to provide bi-directional transient energy absorption;
• and
• wherein excess energy in the output-coupled inductor is directed through either
• a first diode, the first winding of the output-coupled inductor, a second diode, and the first uni-directional transient energy absorption network, or
• a third diode, the second winding of the output-coupled inductor, a fourth diode, and the second uni-directional transient energy absorption network;
• and
• excess energy from the utility grid is directed through either
• a first semiconductor switch and the first transient energy absorption network,
• a second semiconductor switch and the second transient energy absorption network;
• and
• wherein the first and second semiconductor switches have their respective paralleled or built-in body diodes for providing current paths for the excess energy from the utility grid to be absorbed by the first and the second transient energy absorption networks.