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Grid-interactive photovoltaic generation system with power quality control and energy saving

  • US 8,880,229 B2
  • Filed: 06/11/2008
  • Issued: 11/04/2014
  • Est. Priority Date: 05/30/2008
  • Status: Expired due to Fees
First Claim
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1. A grid-interactive photovoltaic generation system having power quality improvement and power saving functions, the system comprising:

  • a solar cell array for receiving solar light and generating predetermined power;

    a first inverter for converting the power, generated by the solar cell array, into power required by a grid line;

    a second inverter connected to the first inverter, and configured to step down power, which will be supplied to a load, to a predetermined voltage;

    a Maximum Power Point Tracking (MPPT)-Power Quality Control (PQC) integrated controller for performing control;

    in a nighttime mode of performing PQC in order to output high-quality power to the grid by controlling operation of the first inverter during a nighttime during which there is no solar light; and

    in a daytime mode of simultaneously performing both PQC in order to output improved quality power to the grid by controlling operation of the first inverter and MPPT in order to maximize power generated in a solar cell array by controlling operation of the first inverter during a daytime during which there is solar light; and

    a voltage controller for controlling operation of the second inverter so that a voltage, which will be supplied to the load, is stepped down to the predetermined voltage regardless of a presence of the solar light in order to save illumination power,wherein the second inverter is a Voltage Controlled Voltage Source Inverter (VCVSI) that is connected in series between a power source and the load,wherein saving of illumination power is realized by controlling the voltage applied to the load by operating the second inverter as the voltage controlled voltage source inverter (VCVSI) capable of directly controlling output voltage, thereby adjusting the output of the second inverter to equivalent AC voltage, andwherein the voltage of the load is adjusted to the predetermined voltage for the saving of illumination power by controlling a voltage Vx of a second transformer connected in series between the grid and the load, and a voltage command value V*x of the second inverter is calculated by a voltage controller in order to set an optimum illumination voltage VL capable of maximizing power saving while maintaining predetermined luminance and maintain and supply the voltage at a uniform level regardless of a level of a grid voltage Vg, and the relationship therebetween is expressed as follows;


    V*x=Vg

    V
    L,

    wherein an output voltage of the second inverter controlled based on the equation is output as the control voltage Vx through the second transformer connected to the second inverter and the load voltage VL predetermined for energy saving is maintained by controlling the control voltage Vx regardless of the level of the applied grid voltage.

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