KR-102961775-B1 - STRING OPTIMA FOR DIAGNOSING IV CURVE FOR EACH STRING, SOLAR POWER GENERATION SYSTEM HAVING THE SAME, AND METHOD FOR CONTROLLING THEREFOR

KR102961775B1KR 102961775 B1KR102961775 B1KR 102961775B1KR-102961775-B1

Abstract

The present invention has the advantage of improving the overall power generation efficiency of a photovoltaic power generation system by generating a current-voltage characteristic curve (hereinafter referred to as a ‘curve’) for each of at least one string constituting a photovoltaic power generation system and controlling the power output based on the diagnosis results of the IV curve for each string. In addition, the present invention has the advantage of increasing the power output of a photovoltaic power generation system by analyzing the IV curve for each string to derive a maximum power point (MPP) for each string, and by resetting the global maximum power point (GMPP) based on a comparison between the power generation amount due to the global maximum power point (GMPP) tracked by the inverter and the power generation amount due to each maximum power point. Furthermore, the present invention has the advantage of being able to derive an accurate IV curve for each string by measuring the open-circuit voltage for each string and monitoring the change in input/output voltage according to the flow of current, thereby enabling the derivation of an accurate maximum power point (MPP) for each string.

Inventors

박기주
박재성
박세희
이경문

Assignees

주식회사 스마트파워

Dates

Publication Date: 20260508
Application Date: 20221118

Claims (15)

In a string optima connected between the output terminal of each of a plurality of solar cell strings constituting a photovoltaic power generation system and an inverter, An internal control unit that controls the operation of the string optima based on a preset control algorithm; A booster unit that boosts or bypasses the voltage supplied from the output terminal of a corresponding solar cell string; A first switch connected between the output terminal of the solar cell string and the booster unit, which is turned on/off by the control of the internal control unit; and It includes a second switch that is turned on/off by the control of the internal control unit to control the boosting voltage of the booster unit, and The above internal control unit When the first switch is turned off, the open-circuit voltage of the solar cell string is measured from the output terminal of the solar cell string, and when the first switch is turned on, the input/output voltage of the booster unit and the input/output current of the booster unit are monitored to generate an IV curve of the corresponding solar cell string, and then the IV curve is analyzed to derive the maximum power point (MPP) of the corresponding solar cell string. String Optima characterized by transmitting the derived result to an external control device that aggregates the maximum power points (MPPs) of each of the solar cell strings in order to cut off the output of the solar cell string with the lowest maximum power point (MPP) among the solar cell strings and reset the global maximum power point (GMPP) tracked by the inverter to a high value, and then controlling the on/off of the first switch by the control of the external control device to cut off or release the output of the corresponding solar cell string.
delete
In solar power generation systems, Multiple solar cell strings composed of multiple solar cell modules; A plurality of string optimas connected to the output terminals of each of the plurality of solar cell strings, boosting or bypassing the voltage supplied from the corresponding solar cell string to output, and generating an IV curve of the corresponding solar cell string and then analyzing the IV curve to derive the maximum power point (MPP) of the corresponding solar cell string; An inverter that derives a Global Maximum Power Point (GMPP) from the voltage output from each of the plurality of string optimas, tracks the Global Maximum Power Point (GMPP), converts the result into AC power, and connects to the grid; and It includes an integrated control unit that determines whether to operate each of the plurality of string optimas by comparing the amount of power generated by the above GMPP with the amount of power generated using a string-specific MPP, which is the MPP of each of the above solar cell strings. The above integrated control unit is, Each of the maximum power points (MPPs) for each of the above strings is compared to determine the first solar cell string with the lowest maximum power point (MPP), and the string optima connected to the output terminal of the first solar cell string is stopped. The above inverter A photovoltaic power generation system characterized by resetting the Global Maximum Power Point (GMPP) according to the operation change of the String Optima, and then tracking the reset GMPP, wherein the Global Maximum Power Point (GMPP) is reset based on the Maximum Power Point (MPP) of each of the remaining solar cell strings excluding the first solar cell string, and then tracking the reset GMPP.
In paragraph 3, the String Optima is An internal control unit that controls the operation of the string optima based on a preset control algorithm; A booster unit that boosts or bypasses the voltage supplied from the output terminal of a corresponding solar cell string; A first switch connected between the output terminal of the solar cell string and the booster unit, which is turned on/off by the control of the internal control unit; and It includes a second switch that is turned on/off by the control of the internal control unit to control the boosting voltage of the booster unit, and The above internal control unit When the first switch is turned off, the open-circuit voltage of the solar cell string is measured from the output terminal of the solar cell string, and A photovoltaic power generation system characterized by controlling the second switch to increase the amount of current flowing from the output terminal of the solar cell string to the booster unit when the first switch is turned on, monitoring the input/output voltage of the booster unit and the input/output current of the booster unit according to the change in the amount of current, deriving the current-voltage characteristics of the corresponding solar cell string as a result, and then generating the IV curve of the solar cell string.
In paragraph 4, the above internal control unit A photovoltaic power generation system characterized by analyzing the above IV curve to derive the maximum power point (MPP) of the corresponding solar cell string.
delete
delete
In paragraph 3, the integrated control unit A photovoltaic power generation system characterized by receiving the reset GMPP from the inverter and resuming the operation of the first solar cell string to boost the output voltage of the first solar cell string to the reset GMPP.
In paragraph 3, A storage unit for storing the above-mentioned IV curves for each string; and A photovoltaic power generation system characterized by further including a solar cell string diagnostic unit that analyzes the stored IV curve to identify the operating characteristics of the corresponding solar cell string and diagnoses whether there is a fault.
In Paragraph 9, A big data unit that generates big data by storing the solar irradiance and temperature corresponding to the IV curve for each string above together; and A photovoltaic power generation system characterized by further including a power generation prediction unit that predicts power generation per string by learning the correlation between solar irradiance and temperature and the IV curve for each string based on the above big data.
In a method for controlling the operation of a photovoltaic power generation system, A string-specific IV curve generation step of deriving string-specific current-voltage characteristics using a string optima connected to the output terminal of each of at least one solar cell string constituting the photovoltaic power generation system, and then generating an IV curve of the corresponding solar cell string; A step for deriving a maximum power point (MPP) per string by analyzing the above IV curves to derive the maximum power point (MPP) of the corresponding solar cell string; A GMPP derivation step for deriving a Global Maximum Power Point (GMPP) that the inverter of the photovoltaic power generation system tracks based on the Maximum Power Points (MPPs) for each string; A GMPP resetting step for resetting the GMPP by comparing the amount of power generated by the above GMPP with the amount of power generated using the above string-specific MPP; and A method for controlling a photovoltaic power generation system characterized by including a power generation stage that develops to follow the above-mentioned reset GMPP.
In Clause 11, the above-mentioned string-specific IV curve generation step is An open-circuit voltage measurement step of measuring the open-circuit voltage for each string at the output terminal of each of the solar cell strings after blocking the current flowing from the output terminal of each of the solar cell strings to the string optima; and A photovoltaic power generation system control method characterized by including a current-voltage characteristic derivation step of deriving current-voltage characteristics for each string by measuring the input voltage/output current/output voltage/output power of the string optima according to the change in the current amount while increasing the amount of current flowing from each of the output terminals of the solar cell strings to the corresponding string optima.
In Clause 11, the above GMPP reset step is A string blocking step of determining the first solar cell string having the lowest maximum power point (MPP) by comparing each of the maximum power points (MPPs) for each string, and blocking the power transmission path from the first solar cell string to the inverter; A GMPP modification step for changing the Global Maximum Power Point (GMPP) based on the Maximum Power Point (MPP) of each of the remaining solar cell strings excluding the first solar cell string; A string block release step for releasing the blockage of the power transmission path transmitted from the first solar cell string to the inverter when the above GMPP is changed; and A photovoltaic power generation system control method characterized by including a boosting step for boosting the output voltage of the first solar cell string to output the modified GMPP.
In Paragraph 11, A storage step for storing the above-mentioned IV curves for each string; and A method for controlling a photovoltaic power generation system characterized by further including a diagnostic step of analyzing the stored IV curve to identify the operating characteristics of the corresponding string and diagnosing whether there is a fault.
In Paragraph 14, A big data generation step for generating big data by storing the solar irradiance and temperature corresponding to the IV curve for each string together; and A method for controlling a photovoltaic power generation system characterized by further including a power generation prediction step that predicts the power generation amount for each string by learning the correlation between solar irradiance and temperature and the IV curve for each string based on the above big data.

Description

String Optima for Diagnosing IV Curves for Each String, Solar Power Generation System Equipped with the Same, and Method for Controlling Therefor The present invention relates to a photovoltaic power generation system, and more specifically, to a string optima constituting a photovoltaic power generation system and a method for controlling the output of a photovoltaic power generation system using the same. In general, solar power generation has the disadvantage of low power production efficiency compared to its high generation cost. However, as environmental demands for a reduction in fossil energy and pollution-free environments increase, much research is currently being conducted to improve the efficiency of solar power generation. Currently, the proportion of electrical energy that can be converted from the sun through solar cells is only about 15–20% of the total solar energy. Specifically, since the output of a solar cell that generates solar power is very small, multiple solar cells are connected in series to form a photovoltaic module (PV Module, PhotoVoltanic Module) in order to obtain the required output, and the said solar cell modules are connected again in series or parallel to form a photovoltaic array (PV Array). The voltage of a solar cell array is proportional to the number of series-connected solar cell modules, and the current of a solar cell array is proportional to the number of parallel-connected lines. On the other hand, solar power generation devices face difficulties in providing a stable electricity supply compared to other power generation methods because the output of the solar cells varies depending on the surrounding environment. In other words, solar power generation devices have the characteristic that the voltage and current of the solar cells change non-linearly depending on surrounding conditions such as solar irradiance, temperature, and clouds. To address the low efficiency and unstable power supply of these solar cells, the most fundamental solution is to improve efficiency by enhancing the performance of the solar cells themselves; however, significant improvement is difficult with current technology. Therefore, to enhance the competitiveness of solar power generation, while it is important to improve efficiency by enhancing the performance of power generation devices, a system capable of stably maintaining maximum output is required to sustain efficiency, and Maximum Power Point Tracking (MPPT) control is essential to produce maximum output. Typically, such MPPT control is performed at the inverter stage of the photovoltaic power generation system, but in this case, there was a problem where the efficiency was relatively reduced because the output voltages of the string optima were not equal to each other. Accordingly, Korean Registered Patent No. 10-2412303 discloses a string optima capable of effectively resolving solar cell output imbalance and enabling stable electricity supply by further performing string MPPT control that tracks an equal voltage on a string-by-string basis using the current value of each string of the solar cell array prior to the inverter control MPPT performed at the inverter stage, thereby effectively resolving the output imbalance of the solar cell due to environmental factors and stably maintaining the maximum output of the solar cell, and by having string optimas corresponding to each of the solar cell strings mutually share the output current of each of the corresponding solar cell strings and boost the output current of the solar cell string with a low output current based on the result, and discloses a photovoltaic power generation system applying the same. According to the above patent, there is an advantage in that the solar cell output imbalance can be effectively resolved by boosting the current value of each string and then controlling the operation of the booster unit so that the voltage corresponding to the boosted current value follows the equal voltage. However, in a photovoltaic power generation system comprising at least one string that follows a different MPP, this conventional technology had a problem in that it could not efficiently utilize the generated power of the string whose MPP was greater than the Global Max Power Point (GMPP). For example, as illustrated in FIG. 1, in the case of a photovoltaic power generation system including String #1 with an MPP of 760V, String #2 with an MPP of 750V, and String #3 with an MPP of 550V, when considering the total power generated by the photovoltaic power generation system, the GMPP that the inverter follows is typically determined to be 550V. In this case, some of the power generated by String #1 (A) (i.e., 210V * 10A = 2.1kW) and some of the power generated by String #2 (B) (i.e., 200V * 10A = 2kW) are not output, and as a result, there was a problem in that the power generated by each string could not be used efficiently. FIG. 1 is a diagram illustrating the relationship betwe