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

• Current Assignee: Industry-Academic Cooperation Foundation, Kunsan National University (Kunsan National University)
• Original Assignee: Industry-Academic Cooperation Foundation, Kunsan National University (Kunsan National University)
• Inventors: Lee, Seong Ryong
• Primary Examiner(s): Ali, Mohammad
• Assistant Examiner(s): Booker, Kelvin
• Application Number:
  US12/991,595
• Publication Number:
  US 20110088748A1
• Time in Patent Office: 2,337 Days
• Field of Search: None
• US Class Current: 700/295
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/1814 wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
• CPC Class Codes: H02J 3/1842 wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02M 1/0093 wherein the output is created by adding a regulated voltage to or subtracting it from an unregulated input
• CPC Class Codes: H02M 5/293 using semiconductor devices only
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

Disclosed here is a grid-interactive photovoltaic generation system having power quality improvement and power saving functions. The grid-interactive photovoltaic generation system includes a solar cell array, a first inverter, and a second inverter. The solar cell array receives solar light and generates predetermined power. The first inverter converts the power, generated by the solar cell array, into power required by a grid line. The second inverter is connected to the first inverter, and steps down power, which will be supplied to a load, to an appropriate voltage.

Claims

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, and

wherein 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 V_L 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 V_g, and the relationship therebetween is expressed as follows;

V*x=V_g−

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 V_L predetermined for energy saving is maintained by controlling the control voltage Vx regardless of the level of the applied grid voltage.

2. The grid-interactive photovoltaic generation system as set forth in claim 1, wherein the first inverter is a Current Controlled Voltage Source Inverter (CCVSI) that is connected in parallel to a grid input power source.

3. The grid-interactive photovoltaic generation system as set forth in claim 1, wherein the first inverter and the second inverter are connected in parallel to a power source comprising the solar cell array.

4. The grid-interactive photovoltaic generation system as set forth in claim 1, wherein, in the nighttime mode of performing PQC, an improvement of power quality including an improvement of a power factor and a reduction in harmonics is performed using a predetermined equation.

5. The grid-interactive photovoltaic generation system as set forth in claim 1, wherein, in the daytime mode, both a MPPT control unit and a PQC unit simultaneously operate because maximum power point tracking (MPPT) control based on the solar light must be considered, with a result that both the MPPT of photovoltaic generation and the improvement of the power quality of the grid are performed using a predetermined equation.