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KR-102959108-B1 - GRIDFORMING TYPE CURTAILMENT CONTROL SYSTEM AND METHOD

KR102959108B1KR 102959108 B1KR102959108 B1KR 102959108B1KR-102959108-B1

Abstract

The present invention relates to output limiting control technology for photovoltaic power generation, and more specifically, to a grid-forming type output limiting control system and method linked with a photovoltaic inverter. According to the present invention, inertia control, which is impossible with conventional photovoltaic inverters, can be performed more continuously by linking with a grid-forming inverter, and there is an effect of efficiently managing and utilizing existing photovoltaic inverter facilities.

Inventors

  • 강지성

Assignees

  • ㈜한국그리드포밍

Dates

Publication Date
20260511
Application Date
20231010

Claims (10)

  1. In a grid-forming type output limiting control system, A solar inverter that converts direct current electricity generated from solar panels into alternating current electricity; A gridforming inverter connected in parallel with the above-mentioned solar inverter to perform voltage source control in the power grid; and A DC linkage device that connects the DC circuit of the solar inverter and the DC circuit of the gridforming inverter through a switch, The above DC connection device is When the DC voltage of the grid-forming inverter is formed to be higher than the DC voltage of the solar inverter, the switch is opened (off) so that the DC circuit of the solar inverter and the DC circuit of the grid-forming inverter are not connected, When the DC voltage of the grid-forming inverter is lower than the DC voltage of the solar inverter, the switch is turned on so that the DC circuit of the solar inverter and the DC circuit of the grid-forming inverter are connected. The above gridforming inverter is A gridforming communication unit that receives a power system disconnection signal of the above-mentioned solar inverter due to a power grid disturbance; and When the above power system disconnection signal is received, The DC voltage of the grid-forming inverter is lowered from the normal voltage set point to the adjusted DC voltage set point so that the above DC linkage device is turned on, and After the above DC linkage device is turned on, the adjustment DC voltage set point is controlled so that it does not exceed the open-circuit voltage (Voc) of the solar panel, and A gridforming type output limiting control system comprising a gridforming control unit that controls the solar panel to operate at an operating point outside the maximum power point at the above-mentioned adjustment DC voltage set point.
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  3. In paragraph 1, A grid-forming type output limiting control system further comprising an energy storage device connected to the grid-forming inverter, which releases stored energy through the grid-forming inverter when a disturbance occurs in the power grid.
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  6. In paragraph 1, The above gridforming communication unit Receive more commands to limit the output of solar power generation from the outside, The above grid forming control unit When the above output restriction command is received, The DC voltage of the grid-forming inverter is lowered from the normal voltage set point to the output-limiting DC voltage set point so that the above DC linkage device is turned on, and Control to reduce solar output by causing the solar panel to operate at an operating point outside the maximum power point at the above output-limiting DC voltage set point. Gridforming type output limiting control system.
  7. In paragraph 1, The above grid forming control unit In the event of receiving an urgent output limiting command from an external source, or when it is determined that output limiting is necessary for system stabilization, A gridforming type output limiting control system that increases the AC output voltage of the gridforming inverter applied to the power grid to above the overvoltage relay cutoff setting value of the solar inverter, thereby tripping the solar inverter from the power system.
  8. A gridforming type output limit control method performed in a gridforming type output limit control system comprising: a solar inverter that converts direct current electricity generated from a solar panel into alternating current electricity; a gridforming inverter that is connected in parallel with the solar inverter and performs voltage source control on the power grid; and a DC connection device that connects the DC circuit of the solar inverter and the DC circuit of the gridforming inverter. A step of receiving a power grid disconnection signal from the solar inverter due to a power grid disturbance; When the above disconnection signal is received, a step of lowering the DC voltage of the grid forming inverter from the normal voltage set point to the adjusted DC voltage set point so that the DC linkage device is turned on; A step of connecting the DC circuit of the solar inverter and the DC circuit of the grid forming inverter by turning on the switch of the DC linkage device as the DC voltage of the grid forming inverter is formed to be lower than the DC voltage of the solar inverter; After the above DC linkage device is turned on, the step of setting the adjustment DC voltage set point so that the adjustment DC voltage set point does not exceed the open-circuit voltage (Voc) of the solar panel; and A grid-forming type output limiting control method comprising the step of controlling the solar panel to operate at an operating point outside the maximum power point by performing voltage source control at the above-mentioned adjustment DC voltage set point.
  9. In paragraph 8, A step in which a DC linkage device connecting the solar inverter and the grid forming inverter is turned on when the DC voltage of the grid forming inverter is lower than the DC voltage of the solar inverter, thereby connecting the solar inverter and the grid forming inverter; and A grid-forming type output limiting control method further comprising the step of controlling the output of a solar power plant at a predetermined DC voltage set point by DC-linking the grid-forming inverter with the solar power plant.
  10. In paragraph 8, In the event that an urgent output limit command is received from an external source or it is determined that output limiting is necessary for system stabilization, A grid-forming type output limiting control method further comprising the step of increasing the AC output voltage of the grid-forming inverter applied to the power grid to above the overvoltage relay cutoff setting value of the solar inverter to disconnect the solar inverter from the power system.

Description

Gridforming Type Curtailment Control System and Method The present invention relates to output limiting control technology for photovoltaic power generation, and more specifically, to a grid-forming type output limiting control system and method linked with a photovoltaic inverter. In accordance with global carbon reduction policies, the expansion of renewable energy generation and the reduction of thermal power plants are being steadily pursued. However, as inverter-based power generation facilities equipped with power electronics to convert renewable energy increase, "Weak Grid Issues" are emerging, characterized by a weakening of the power grid's ability to maintain voltage and frequency. Furthermore, the robustness of the power grid is deteriorating as renewable energy increases. Meanwhile, if a solar power plant receives an output limit order, it can respond by storing the generated energy in batteries, operating at reduced output, or shutting down the plant. However, first, storing energy in batteries is only possible if batteries are installed, making it unsuitable for existing power plants without batteries to respond to output limit orders. Second, operating at reduced output is only feasible with smart inverters among current source control inverters, and most currently installed solar inverters lack the capability to operate in this mode. Third, while shutting down the plant is the only practical option, it results in direct economic damage to the plant owner because solar energy cannot be sold during the shutdown period. In an environment where renewable energy is increasing day by day, existing solar power plants have had difficulty responding to stability issues other than tripping from the power grid or shutting down the plant due to output restrictions. The background technology of the present invention is disclosed in Korean Registered Patent No. 10-2320750. FIG. 1 is a drawing for explaining a grid-forming type output limiting control system according to one embodiment of the present invention. FIG. 2 is a block diagram of a grid-forming inverter coupled with a solar inverter according to one embodiment of the present invention. FIG. 3 is a diagram illustrating the relationship between the output and voltage of a photovoltaic power generation according to one embodiment of the present invention. FIGS. 4 and 5 are drawings for explaining a grid-forming type output limit control method according to a first embodiment of the present invention. FIGS. 6 and 7 are drawings for explaining a grid-forming type output limit control method according to a second embodiment of the present invention. FIGS. 8 and 9 are drawings for explaining a grid-forming type output limit control method according to a third embodiment of the present invention. FIG. 10 is a diagram illustrating the results of a grid-forming type output limit control simulation according to a first embodiment of the present invention. FIGS. 11 and 12 are drawings for explaining the results of a grid-forming type output limit control simulation according to a second embodiment of the present invention. FIG. 13 is a diagram illustrating the results of a grid-forming type output limit control simulation according to a third embodiment of the present invention. The present invention is susceptible to various modifications and may have various embodiments. Specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. In describing the present invention, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions would unnecessarily obscure the essence of the invention. Furthermore, singular expressions used in this specification and claims should generally be interpreted as meaning "one or more" unless otherwise stated. The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals. FIG. 1 is a drawing for explaining a grid-forming type output limiting control system according to one embodiment of the present invention. Referring to FIG. 1, the grid-forming type output limit control system includes a solar inverter (100), a grid-forming inverter (200), a DC connection device (300), and an energy storage device (400). The solar inverter (100) converts direct current electricity generated from the solar panel into alternating current electricity. T