Photovoltaic system capable of controlling relay for each string

Abstract

The present invention relates to a photovoltaic system, and more particularly to a photovoltaic system capable of controlling a relay for each string, wherein: respective strings and an inverter of the photovoltaic system are connected by relays so as to enable individual controlling; and even when an abnormality in insulation resistance occurs in a string, only a relay of the string in which the abnormality has occurred is made open until a worker arrives, without having to stop the overall operation of the photovoltaic system, thereby making efficient power generation possible.

Description

Solar power generation system capable of relay control per string

[0001] The present invention relates to a photovoltaic power generation system, and more specifically, to a photovoltaic power generation system capable of string-by-string relay control, in which individual control is achieved by connecting each string of the photovoltaic power generation device and the inverter via a relay, and even when an insulation resistance abnormality occurs in each string, efficient power generation is possible by opening only the relay of the abnormal string without having to stop the entire operation of the photovoltaic power generation device until a worker visits.

[0002] Solar power generation, a sector of renewable energy, has recently seen a surge in demand due to its numerous advantages, and technologies aimed at increasing generation efficiency have also advanced significantly. In particular, solar power generation devices are currently being installed in various forms, including on building rooftops and on water, as well as in Building Integrated Photovoltaics (BIPV) systems that are integrated with the building itself.

[0003] Solar power generation devices must be constantly exposed to the sun for high efficiency and pose a high fire risk due to the heat generated by power generation; in particular, the decrease in insulation resistance is identified as a major cause of fire.

[0004] Therefore, it is necessary to frequently measure and check the insulation resistance of a photovoltaic power generation device. To this end, as described in the patent document below, a technician is instructed to periodically visit the site to measure the insulation resistance and check whether it exceeds a standard value. If an abnormality occurs in the insulation resistance, the operation of the photovoltaic power generation device is stopped, and a technician is instructed to visit the site to conduct an inspection.

[0005] Consequently, conventionally, there were problems such as the necessity of a technician's visit requiring a large workforce and inconvenience in management, as well as the inability to operate the solar power generation system until the technician arrived.

[0006] In addition, for photovoltaic power generation devices connected to the general power grid, the power generated by the devices is sent back into the grid during times of low power usage, such as on weekends or holidays in offices or factories, thereby disrupting the grid power. To prevent this, KEPCO installs reverse power relays and trips the circuit breaker to disconnect the connection with the consumer when power is sent back. In such cases, the manager is required to turn the circuit breaker back on during weekdays to receive power from the grid again, which is causing difficulties in management.

[0007] (Patent Document) Registered Patent Publication No. 10-1529476 (Registered June 11, 2015) "Insulation Resistance Monitoring System for Solar Module Strings"

[0008] The present invention has been devised to solve the above-mentioned problems,

[0009] The present invention aims to provide a photovoltaic power generation system capable of string-specific relay control, which enables individual control by connecting each string of a photovoltaic power generation device and an inverter with a relay, and allows for efficient power generation by opening only the relay of the faulty string without having to stop the entire operation of the photovoltaic power generation device until a worker visits, even if an insulation resistance abnormality occurs in each string.

[0010] The present invention aims to provide a photovoltaic power generation system capable of string-by-string relay control, which enables frequent measurement of insulation resistance and rapid prevention of fire and safety accidents by selectively opening the relay remotely to measure insulation resistance.

[0011] The present invention aims to provide a photovoltaic power generation system capable of string-by-string relay control, which prevents reverse transmission of generated power by setting periods such as weekends and holidays when power usage is low and automatically opening the relay, thereby eliminating the inconvenience of having to manually raise the circuit breaker again when the reverse power relay trips.

[0012] The present invention aims to provide a photovoltaic power generation system capable of string-by-string relay control, which can increase the convenience and accuracy of control by automatically setting the opening time of the relay according to the power usage pattern.

[0013] The present invention aims to provide a photovoltaic power generation system capable of string-by-string relay control, which prevents reverse transmission of generated power while enabling electricity bill savings through the use of photovoltaic power even on weekends and holidays by analyzing power consumption and setting the number of relays to be opened.

[0014] The present invention is implemented by an embodiment having the following configuration to achieve the aforementioned objective.

[0015] According to one embodiment of the present invention, a photovoltaic power generation system capable of string-specific relay control according to the present invention comprises a photovoltaic power generation device that produces power by solar energy and a management server that controls the operation of the photovoltaic power generation device, wherein the photovoltaic power generation device comprises a plurality of photovoltaic modules connected in series and a plurality of strings installed in parallel; an inverter that converts power output from each string and supplies it to a grid and a load; and a plurality of relays formed between each string and the inverter to control the connection between each string and the inverter, wherein the management server individually opens the relays connected to each string to allow for the measurement of insulation resistance, and adjusts the connection of the relays according to the measurement result of the insulation resistance.

[0016] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the management server includes an insulation resistance measuring unit that enables the insulation resistance of each string to be measured, and the insulation resistance measuring unit includes a string determination module that determines a string to be measured for insulation resistance, a relay opening module that opens a relay connected to the string determined by the string determination module, and a measurement instruction module that instructs the measurement of the insulation resistance of the string in which the relay is opened.

[0017] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the management server includes an insulation resistance diagnosis unit that diagnoses the insulation resistance status of each string according to the measurement result by the insulation resistance measurement unit, and the insulation resistance diagnosis unit includes an abnormality detection module that detects an abnormality in the insulation resistance of each string and an open-holding module that maintains the relay of the string in which the abnormality was detected in an open state.

[0018] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the management server includes a relay control unit that automatically adjusts the opening and closing of relays connected to each string, and the relay control unit includes an opening time setting module that sets the opening time of a relay connected to each string, a connection time setting module that sets the connection time of each opened relay, and an automatic opening and closing operation module that automatically operates the relays according to the set opening and connection times.

[0019] According to another embodiment of the present invention, in a photovoltaic power generation system capable of string-by-string relay control according to the present invention, the management server includes a control setting unit that sets information related to the operation of the relay by the relay control unit, and the control setting unit is characterized by determining the timing of opening and closing the relay according to the power usage pattern of the load connected to the photovoltaic power generation device.

[0020] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the control setting unit comprises: a reference time setting module for setting a reference time having a power generation amount greater than a certain amount; a usage collection module for collecting power consumption information of a load during the set reference time; a usage pattern analysis module for analyzing the pattern of collected power consumption by unit period; a reference usage setting module for setting a reference power consumption amount for a unit period; and a target time extraction module for extracting a target time to open a relay when the power consumption within the set reference time is less than the reference power consumption amount as a result of analyzing the power consumption pattern.

[0021] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the reference time setting module comprises a power generation amount collection module that collects power generation amount information of a photovoltaic power generation device, a power generation pattern analysis module that analyzes the pattern of power generation amount, a reference value setting module that sets a reference value for power generation amount, and a reference time determination module that determines a time having a power generation amount greater than or equal to the reference value as a reference time.

[0022] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the control setting unit is characterized by including an operating range setting module that sets the number of operating strings according to the amount of power generated and the amount of power consumed for the target time when the relays are opened, and a connection adjustment module that adjusts the connection of relays for the set number of strings.

[0023] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the connection adjustment module comprises: a connection information collection module that collects connection information of relays for each string; a capacity information collection module that collects output capacity information of each string; a power generation loading module that retrieves power generation information of each string; a usage index calculation module that calculates a usage index based on the ratio of cumulative power generation to capacity of each string; a usage index comparison module that compares the usage indices of each string; and a relay selection module that selects a number of strings set by the operation range setting module in order of highest usage index.

[0024] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the management server includes a module imbalance diagnosis unit that diagnoses imbalance between photovoltaic modules within the string, and the insulation resistance measurement unit is characterized by performing an insulation resistance measurement when the imbalance is diagnosed as a decrease in insulation resistance by the module imbalance diagnosis unit.

[0025] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the module imbalance diagnosis unit comprises a voltage imbalance calculation unit that calculates the degree of imbalance regarding the voltage between modules constituting the string, a fluctuation abnormality calculation unit that calculates the degree of abnormality according to voltage and current fluctuations of the string, and an imbalance detection unit that detects imbalance between modules of the string according to the degree of voltage imbalance and the degree of fluctuation abnormality, wherein the voltage imbalance calculation unit comprises a string voltage measurement module that measures the voltage of power output from the string, a module voltage measurement module that measures the voltage at one specific module within the string, and a voltage imbalance coefficient calculation module that calculates a voltage imbalance coefficient indicating the degree of voltage imbalance between modules by subtracting the value obtained by multiplying the number of photovoltaic modules included in the string by the voltage of the specific module from the string voltage.

[0026] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the voltage imbalance calculation unit includes a voltage imbalance diagnosis module that compares the voltage imbalance coefficient calculated by the imbalance coefficient calculation module with a reference value and diagnoses the voltage imbalance between modules and executes a fluctuation abnormality calculation unit when the reference value is exceeded; and the fluctuation abnormality calculation unit includes a voltage measurement module that measures the voltage output from the string for a certain period of time, a current measurement module that measures the current output from the string for a certain period of time, and a power fluctuation coefficient calculation module that calculates the value of the ratio of voltage change amount to current change amount for the ratio of voltage to current per unit time for a certain period of time and calculates a power fluctuation coefficient indicating the degree of fluctuation of voltage and current by the average value.

[0027] According to another embodiment of the present invention, in a photovoltaic power generation system capable of string-by-string relay control according to the present invention, the fluctuation abnormality calculation unit is characterized by including a coefficient adjustment module that increases the scale while changing the standard for the steady state of the power fluctuation coefficient to 0.

[0028] According to another embodiment of the present invention, in a photovoltaic power generation system capable of string-by-string relay control according to the present invention, the coefficient adjustment module is characterized by adjusting the power fluctuation coefficient according to Equation 3 to calculate the final power fluctuation coefficient. (Equation 3) Pf = (1-Pd)*10 (wherein Pf is the adjusted power fluctuation coefficient, Pd is the initial power fluctuation coefficient)

[0029] According to another embodiment of the present invention, in a photovoltaic power generation system capable of relay control per string according to the present invention, the imbalance detection unit comprises a voltage imbalance coefficient loading module that retrieves a voltage imbalance coefficient, a power fluctuation coefficient loading module that retrieves a power fluctuation coefficient, an imbalance index calculation module that calculates an imbalance index indicating the degree of imbalance in output between modules by multiplying the voltage imbalance coefficient and the power fluctuation coefficient, and an abnormal information diagnosis module that diagnoses an abnormal state due to output imbalance between modules of the string according to the calculated imbalance index.

[0030] According to another embodiment of the present invention, in a photovoltaic power generation system capable of string-by-string relay control according to the present invention, the abnormal information diagnosis module is characterized by diagnosing module damage, shading, or contamination when the imbalance index is positive, and diagnosing PID, cell cracking, or insulation resistance degradation when the imbalance index is negative.

[0031] The present invention can achieve the following effects through the combination and usage relationship of the embodiments described above and the configuration described below.

[0032] The present invention has the effect of enabling efficient power generation by connecting each string of a photovoltaic power generation device and the inverter with a relay to enable individual control, and by opening only the relay of the faulty string without having to stop the entire operation of the photovoltaic power generation device until a worker visits, even if an insulation resistance abnormality occurs in each string.

[0033] The present invention has the effect of enabling the measurement of insulation resistance at any time by selectively opening a relay remotely to measure insulation resistance, thereby enabling the rapid prevention of fire and safety accidents.

[0034] The present invention has the effect of preventing reverse transmission of generated power by setting periods such as weekends and holidays when power usage is low so that the relay is automatically opened, thereby eliminating the inconvenience of having to manually raise the circuit breaker again when the reverse power relay trips.

[0035] The present invention has the effect of increasing the convenience and accuracy of control by automatically setting the opening time of a relay according to the power usage pattern.

[0036] The present invention has the effect of enabling electricity bill savings through the use of solar power generation even on weekends and holidays, while preventing reverse transmission of generated power by analyzing power consumption and setting the number of relays to be opened.

[0037] FIG. 1 is a configuration diagram of a photovoltaic power generation system capable of string-by-string relay control according to an embodiment of the present invention.

[0038] Figure 2 is a block diagram showing the configuration of a management server.

[0039] FIG. 3 is a block diagram showing the configuration of the insulation resistance measuring unit.

[0040] Figure 4 is a block diagram showing the configuration of the insulation resistance diagnostic unit.

[0041] Figure 5 is a graph showing an example of insulation resistance measurement.

[0042] FIG. 6 is a block diagram showing the configuration of the relay control unit

[0043] FIG. 7 is a block diagram showing the configuration of the control setting unit

[0044] FIG. 8 is a block diagram showing the configuration of a reference time setting module.

[0045] FIG. 9 is a block diagram showing the configuration of a connection adjustment module.

[0046] FIG. 10 is a block diagram showing another configuration of a management server.

[0047] FIG. 11 is a block diagram showing the configuration of the module imbalance diagnosis unit.

[0048] FIG. 12 is a reference diagram showing an example of voltage measurement by the voltage imbalance calculation unit.

[0049] Figure 13 is a graph showing an example of voltage change according to string condition.

[0050] Figure 14 is a reference diagram showing the operating point on the IV curve according to the unbalance index.

[0051] FIG. 15 is a block diagram showing the configuration of the power generation prediction unit.

[0052] FIG. 16 is a block diagram showing the configuration of the fault diagnosis unit

[0053] FIG. 17 is a reference diagram showing an IV graph used by the fault diagnosis unit.

[0054] Explanation of symbols used in drawings

[0055] 1: Solar power generation device 11: String

[0056] 12: Relay 13: Inverter

[0057] 14: Control Module 3: Management Server

[0058] 31: Insulation resistance measuring unit 32: Insulation resistance diagnostic unit

[0059] 33: Relay control unit 34: Control setting unit

[0060] 35: Module Imbalance Diagnosis Unit 36: Power Generation Prediction Unit

[0061] 37: Power Generation Measurement Unit 38: Fault Diagnosis Unit

[0062] Hereinafter, preferred embodiments of a photovoltaic power generation system capable of string-by-string relay control according to the present invention will be described in detail with reference to the attached drawings. In describing the present invention below, if it is determined that a detailed description of known functions or configurations may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, terms such as "...part," "...module," etc., described in the specification refer to a unit that processes at least one function or operation, and this may be implemented in hardware, software, or a combination of hardware and software.

[0063] A photovoltaic power generation system capable of string-by-string relay control according to one embodiment of the present invention is described with reference to FIGS. 1 to 9. The photovoltaic power generation system includes a photovoltaic power generation device (1) that produces power by solar energy, and a management server (3) that controls the operation of the photovoltaic power generation device (1).

[0064] In particular, the solar power generation device (1) is configured such that a plurality of strings (11), in which solar modules are connected in series, are connected in parallel, and each string (11) is connected to an inverter (13) through an individual relay (12). Accordingly, power produced from each string (11) can be selectively transferred to the inverter (13) to be supplied to a load or grid, and in particular, through individual control of the relay (12), only a specific relay (12) can be opened to measure the insulation resistance of the string (11). Through this, the present invention allows the insulation resistance of the string (11) to be measured and an abnormal condition checked by opening only a specific relay (12) at any time regardless of the power generation status of the solar power generation device (1), and if an abnormality in insulation resistance is detected, only the relay (12) of the corresponding string (11) can be opened, thereby enabling continuous operation without the need to stop the operation of the entire solar power generation device (1) before a manager visits. Accordingly, the present invention can enable efficient power supply without stopping the operation of the photovoltaic power generation device (1) while reducing the risk of fire through rapid diagnosis of insulation resistance. To this end, the photovoltaic power generation device (1) may include a control module (14) connected to a management server (3) via wired or wireless communication, and may transmit and receive various information with the management server (3) and control the operation of the photovoltaic power generation device (1) according to the information transmitted by the management server (3).

[0065] The above management server (3) is configured to control the operation of the solar power generation device (1), enabling remote control of the operation of the solar power generation device (1). The above management server (3) can be connected to the solar power generation device (1) via wired or wireless communication, and can control the operation of the solar power generation device (1) by receiving control information through the operation of various terminals such as PCs and smartphones. In particular, the above management server (3) can control the opening and closing of the relay (12) to measure the insulation resistance within the solar power generation device (1), and can diagnose the insulation resistance status of each string (11) using the measured insulation resistance. In addition, as previously discussed in the background technology, there is a problem where power is reversed back into the grid on weekends and holidays when power usage is low. Therefore, power is cut off using a reverse relay circuit breaker, and the manager repeatedly performs the task of reconnecting the circuit breaker. To resolve this inconvenience, the management server (3) automatically adjusts the opening and closing of the relay (12) according to a set time, thereby preventing power reversed back into the grid without the manager's intervention. Furthermore, the management server (3) can analyze the power usage pattern on weekends and holidays when the relay (12) is open and set the number of relays (12) connected to enable power supply through the solar power generation device (1). To this end, the management server (3) may include an insulation resistance measurement unit (31), an insulation resistance diagnosis unit (32), a relay control unit (33), and a control setting unit (34).

[0066] The insulation resistance measuring unit (31) is configured to measure the insulation resistance of each string (11) and instructs the insulation resistance to be measured by an insulation resistance measuring facility formed within the photovoltaic power generation device (1). In particular, the insulation resistance measuring unit (31) may enable insulation resistance measurement by designating a string (11) to measure insulation resistance and opening a relay (12) connected to the corresponding string (11). To this end, the insulation resistance measuring unit (31) may include a string determination module (311), a relay opening module (312), and a measurement instruction module (313).

[0067] The string determination module (311) above is configured to determine the string to be measured for insulation resistance, and can sequentially measure the insulation resistance at set times.

[0068] The above relay opening module (312) is configured to open the relay (12) of the string to be measured for insulation resistance, and to open the relay (12) of the string determined by the string determination module (311). Accordingly, the above relay opening module (312) can open the relay (12) individually according to a set sequence so that the insulation resistance can be measured.

[0069] The above measurement indicator module (313) is configured to indicate the measurement of insulation resistance, and can enable the measurement of insulation resistance to be performed for the string (11) in which the relay (12) is opened by the above relay opening module (312).

[0070] The insulation resistance diagnosis unit (32) is configured to diagnose the insulation resistance status of each string, and can detect abnormal conditions using the insulation resistance of each string measured by the insulation resistance measurement unit (31). The insulation resistance diagnosis unit (32) can detect abnormal conditions by comparing the insulation resistance measured for each string with a reference value, but insulation resistance is greatly affected by environmental factors such as humidity, and if the insulation resistance drops below the reference value, it is already exposed to the risk of fire, so there is a problem that it is difficult to prevent the risk of fire in advance by comparing with the reference value. Therefore, the insulation resistance diagnosis unit (32) monitors the change in insulation resistance while applying voltage for a certain period of time and diagnoses the decrease in insulation resistance according to the change in state, thereby enabling accurate diagnosis of the decrease in insulation resistance even in various environments and local defects. In addition, the insulation resistance diagnostic unit (32) can continue to supply power from sunlight by keeping only the relay (12) of the corresponding string open until an administrator performs an inspection, without the need to stop the operation of the entire solar power generation device (1) when an abnormality in the insulation resistance of the string is detected. To this end, the insulation resistance diagnostic unit (32) may include a voltage application module (321), a voltage adjustment module (322), an insulation resistance measurement module (323), a kick index calculation module (324), an abnormality detection module (325), and an open maintenance module (326).

[0071] The above voltage application module (321) is configured to apply voltage to a string for measuring insulation resistance, and can apply voltage for a certain period of time, for example, 10 minutes.

[0072] The above voltage adjustment module (322) is configured to adjust the voltage applied by the voltage application module (321), and can measure changes in insulation resistance under various voltage conditions by increasing the voltage in steps. For example, the above voltage adjustment module (322) can increase the voltage in steps from 100V to 500V.

[0073] The insulation resistance measuring module (323) is configured to measure insulation resistance during a certain period of time when voltage is applied. For example, when voltage is applied for 10 minutes, insulation resistance can be measured at 1-second intervals. Additionally, when insulation resistance is measured while increasing the voltage stepwise by the voltage adjustment module (322), insulation resistance can be measured each time the voltage is increased.

[0074] The above kick index calculation module (324) is configured to calculate a kick index indicating the degree of change in insulation resistance. If the insulation resistance measured in units of time or voltage by the insulation resistance measurement module (323) does not change linearly, but rather has a large range of change or a rapid change as shown in FIG. 5, it can be determined that the insulation resistance has decreased. Accordingly, the above kick index calculation module (324) can calculate the degree of change in insulation resistance on average as a kick index. It can also calculate a time kick index regarding the degree of change per unit time when a constant voltage is applied for a certain period, and a voltage kick index regarding the degree of change each time the voltage is changed when the voltage is applied while adjusting it step by step for a certain period. At this time, the time kick index can be calculated by the following (Equation 1), and the voltage kick index can be calculated by the following (Equation 2).

[0075] (Mathematical Formula 1)

[0076]

[0077] (Mathematical Formula 2)

[0078]

[0079] The above abnormality detection module (325) is configured to detect an abnormal state due to a decrease in insulation resistance, and may detect an abnormal state by comparing the measured insulation resistance with a reference value if it is less than the reference value, or may determine that a state of danger has occurred due to a decrease in insulation resistance if the time kick index or voltage kick index calculated by the above kick index calculation module (324) exceeds a set value.

[0080] The above-mentioned open-maintaining module (326) is configured to maintain the open state of the relay (12), and when an abnormal state regarding the insulation resistance of the string (11) is detected by the above-mentioned abnormality detection module (325), the relay (12) is maintained in the open state. Accordingly, the above-mentioned open-maintaining module (326) can prevent the occurrence of fire, etc. due to an abnormality in insulation resistance, and can maintain efficient power generation by opening only the relay (12) of the string where the abnormality occurred and continuing the operation of the solar power generation device (1).

[0081] The relay control unit (33) is configured to automatically control the opening and closing of the relay (12), and can automatically control the opening and closing of the relay (12) according to a set time, and can also control the opening and closing of the relay (12) connected to each string (11) individually. In particular, the relay control unit (33) can automatically open the relay (12) to prevent power from being transmitted backward when power usage is low, such as on weekends or holidays, as described above, and reconnect the relay (12) when power usage increases. To this end, the relay control unit (33) may include an opening time setting module (331), a connection time setting module (332), and an automatic opening and closing operation module (333).

[0082] The above-mentioned opening time setting module (331) is configured to set the time when the relay (12) opens, and the opening time can be set to coincide with the start of times such as weekends and holidays when power usage is low. The above-mentioned opening time setting module (331) can set and save the opening time manually according to the operation of a manager terminal, etc., or the opening time can be set automatically according to the power usage pattern of the load in the above-mentioned control setting unit (34).

[0083] The above connection timing setting module (332) is configured to set the time for the relay (12), which was opened at the time set by the above opening timing setting module (331), to be reconnected, and the connection timing can be set to coincide with weekdays when power usage increases. The above connection timing setting module (332) can set the connection timing manually, like the opening timing setting module (331), or be set automatically by the control setting unit (34).

[0084] The above automatic opening / closing operation module (333) is configured to automatically open / close the relay (12) according to a set time, and can transmit a control command to the above control module (14) to enable the opening / closing of the relay (12).

[0085] The above control setting unit (34) is configured to set information related to the operation of the relay (12) by the above relay control unit (33), and the timing of opening and closing the relay (12) can be automatically set according to the power usage pattern of the load connected to the photovoltaic power generation device (1). Since the problem of power reverse transmission may occur only during daytime hours when there is a power generation amount of a certain amount or more, the above control setting unit (34) analyzes the power usage pattern of the load for that time period, and can set the time period when power usage is low during the time period when power reverse transmission may occur with a power generation amount as the time period when the relay control unit (33) opens the relay (12). In addition, the above control setting unit (34) can supply power by connecting only some strings of relays to supply power to the photovoltaic power generation device (1) even during the time period when the relay (12) is opened, thereby preventing power reverse transmission while enabling efficient power usage. To this end, the control setting unit (34) may include a reference time setting module (341), a usage collection module (342), a usage pattern analysis module (343), a reference usage setting module (344), a target time extraction module (345), an operation range setting module (346), and a connection adjustment module (347).

[0086] The above reference time setting module (341) is configured to set a reference time for which the relay (12) needs to be opened, and sets a time period when there is a concern about power backflow due to the generation of a certain amount or more of power. The above reference time setting module (341) may manually set a daytime period when power generation occurs by sunlight, or it may automatically set the reference time by analyzing the power generation pattern. To this end, the above reference time setting module (341) may include a power generation amount collection module (341a), a power generation pattern analysis module (341b), a reference value setting module (341c), and a reference time determination module (341d).

[0087] The above power generation collection module (341a) is configured to collect power generation information of the solar power generation device (1), and can collect power generation information for a certain period.

[0088] The above power generation pattern analysis module (341b) is configured to analyze the change pattern of power generation, for example, to analyze the change pattern of power generation by time, and to calculate the average power generation by time period based on the analyzed result.

[0089] The above reference value setting module (341c) is configured to set a reference value for the amount of power generated that may be subject to power reverse transmission, and can set a reference amount of power generated in hours.

[0090] The above reference time determination module (341d) is configured to determine the reference time for opening and closing the relay (12), and can determine the time period in which the average power generation amount per time period is greater than or equal to the reference value set by the reference value setting module (341c) based on the analysis result by the power generation pattern analysis module (341b) as the reference time.

[0091] The above usage collection module (342) is configured to collect information regarding the power usage of a load, and collects power usage information during a reference time set by the above reference time setting module (341). The above usage collection module (342) may collect power usage information manually entered through a manager terminal, etc., or may automatically measure and collect power usage through a separate device.

[0092] The above usage pattern analysis module (343) is configured to analyze the pattern of collected power usage and can analyze power usage by unit period, for example, can analyze the pattern of daily power usage and calculate the daily average power usage for a reference time. However, the above usage pattern analysis module (343) is not limited to this, and can analyze power usage by setting various unit periods such as by hour or by month.

[0093] The above standard usage setting module (344) is configured to set a standard value for power usage that is at risk of reverse power transmission, and sets a standard value for power usage that is low enough to cause a risk of reverse transmission for a standard time per unit period. At this time, the above standard usage setting module (344) may set a standard value for power usage at which reverse transmission may occur by considering the amount of power generated per unit period.

[0094] The target time extraction module (345) is configured to extract a target time for opening the relay (12) by the relay control unit (33), and can extract a target time for opening the relay (12) for a time when the power consumption of the load for a reference time is less than the reference value set by the reference consumption setting module (344). At this time, if the extracted target time is consecutive on a daily basis, the target time extraction module (345) can select the entire number of such days as the target time to ensure that the relay (12) is opened. For example, if Saturday and Sunday are extracted as consecutive target times, the entire Saturday and Sunday can be selected as the target time to ensure that the relay (12) remains continuously open without opening or closing in between. Additionally, if the target time is extracted over an entire month, such as during a vacation, the relay (12) may remain continuously open during the vacation period. Accordingly, the relay control unit (33) can be operated according to the time extracted by the target time extraction module (345) to automatically open and close the relay (12).

[0095] The above operating range setting module (346) is configured to set the number of relays (12) that are opened and closed. It may be possible to open all relays (12) for the extracted target time to prevent reverse transmission, but in some cases, some power usage may occur even on weekends or holidays when power usage is low. Accordingly, some relays (12) may be connected to supply power by the solar power generation device (1). At this time, the above operating range setting module (346) may set the minimum number of strings capable of supplying power to the load according to the amount of power generated and the amount of power used analyzed by the power generation pattern analysis module (341b) and the usage pattern analysis module (343).

[0096] The above connection adjustment module (347) is configured to adjust the connection of relays (12), and determines and adjusts the relays (12) to be connected while connecting a number of relays (12) set by the above operation range setting module (346). The above connection adjustment module (347) enables the lifespan of the photovoltaic power generation device (1) to be extended through the even use of each string (11), and to this end, determines the relays (12) to be connected by identifying the usage level of each string (11). The above connection adjustment module (347) may include a connection information collection module (347a), a capacity information collection module (347b), a power generation amount loading module (347c), a usage index calculation module (347d), a usage index comparison module (347e), and a relay selection module (347f).

[0097] The above connection information collection module (347a) is configured to collect connection information of the relay (12) for each string (11), and collects information that each string (11) is connected to the inverter (13) to supply power generated according to the opening and closing of the relay (12).

[0098] The above capacity information collection module (347b) is configured to collect power generation capacity information of each string, and can collect power generation capacity information of the string by considering the specifications of the photovoltaic module constituting each string.

[0099] The above power generation loading module (347c) is configured to retrieve power generation information for each string, and the relay (12) is connected to retrieve information regarding the power generation amount supplied.

[0100] The above usage index calculation module (347d) is configured to calculate a usage index indicating the degree of use of each string (11), and, for example, can calculate the usage index according to the ratio of the accumulated power generation loaded by the power generation loading module (347c) to the power generation capacity of the string collected by the capacity information collection module (347b).

[0101] The above usage index comparison module (347e) is configured to compare the usage index of each string, and through the comparison of the usage index, the relay (12) to be connected during the target time can be selected.

[0102] The above relay selection module (347f) is configured to select relays (12) to be connected for power supply by string (11) within the target time for opening relays (12), and selects a number of relays (12) set by the above operation range setting module (346), and selects relays (12) in order of lowest usage index as a result of comparison by the usage index comparison module (347e).

[0103] A photovoltaic power generation system capable of relay control per string according to another embodiment of the present invention is described with reference to FIGS. 10 to 17. The photovoltaic power generation system capable of relay control per string may additionally include a module imbalance diagnosis unit (35) in which a management server (3) diagnoses imbalance between modules within a string, a power generation prediction unit (36) that predicts the power generation amount per string of a photovoltaic power generation device, a power generation measurement unit (37) that measures the power generation amount of the current string in real time, and a fault diagnosis unit (38) that diagnoses the type of fault of the string using the area on the IV coordinate plane according to the predicted power generation amount and the measured power generation amount.

[0104] In this embodiment, the photovoltaic power generation system can diagnose an unbalanced state between photovoltaic modules within the string, and if a decrease in insulation resistance is suspected while the unbalanced state is diagnosed, the insulation resistance can be diagnosed to enable efficient operation of the system.

[0105] In addition, the above photovoltaic power generation system can diagnose a decrease in power generation of the string, and in addition to comparing the existing predicted power generation with the current power generation, it can identify the type of fault by using the area on the IV coordinate plane, thereby enabling a more rapid response to the decrease in power generation, and if the cause of the decrease in power generation is suspected to be insulation resistance, a precise diagnosis of the insulation resistance can be performed by the insulation resistance diagnosis unit (32).

[0106] The module imbalance diagnosis unit (35) is configured to diagnose imbalances between solar modules within a string, and diagnoses imbalances in performance caused by failure, damage, aging, etc. The module imbalance diagnosis unit (35) may be configured to perform diagnosis in real time at regular intervals, or it may be executed when a decrease in power generation is diagnosed by the failure diagnosis unit (38). In particular, the module imbalance diagnosis unit (35) can improve the accuracy of the diagnosis by comprehensively considering the degree of voltage imbalance between solar modules and the degree of voltage fluctuation to diagnose the imbalance state. In other words, the module imbalance diagnosis unit (35) detects the degree of voltage mismatch between solar modules and, in addition, considers the degree of voltage fluctuation in the diagnosis of the imbalance state. The inverter of the string performs maximum power point tracking (MPPT) to find the maximum output point and fluctuate the voltage and current. In a normal state, the voltage and current fluctuate within a certain range, but when an imbalance occurs between solar modules, the fluctuation range of the voltage and current exceeds a certain range and becomes larger or smaller. By reflecting this to diagnose the imbalance state, the accuracy of the diagnosis can be further improved. To this end, the module imbalance diagnosis unit (35) may include a voltage imbalance calculation unit (351), a fluctuation abnormality calculation unit (352), and an imbalance detection unit (353).

[0107] The above voltage imbalance calculation unit (351) is configured to calculate the degree of voltage imbalance between solar modules within a string, specifically using the voltage output from the string and the voltage measured from a specific module within the string. Conventionally, to detect voltage imbalance between modules within a string, it was necessary to measure and compare the voltages of each module, but this resulted in increased installation and maintenance costs. Therefore, the above voltage imbalance calculation unit (351) calculates the degree of voltage imbalance by comparing the voltage of the string with the value obtained by multiplying the voltage of a specific module by the number of modules, thereby simplifying installation and maintenance and reducing costs and time. In other words, if there is no imbalance between solar modules, the voltage of the string will be equal to the value obtained by multiplying the voltage of a specific module by the number of modules, so the degree of voltage imbalance can be calculated based on that difference. To this end, the voltage imbalance calculation unit (351) may include a string voltage measurement module (351a), a module voltage measurement module (351b), a voltage imbalance coefficient calculation module (351c), and a voltage imbalance diagnosis module (351d).

[0108] The string voltage measurement module (351a) is configured to measure the voltage output from the string, and as shown in FIG. 12, the voltage can be measured at the output terminal of the string.

[0109] The above module voltage measuring module (351b) is configured to measure the voltage of a specific module within a string, and measures the voltage of only one of the multiple solar modules included in the string, and, for example, can measure the voltage of the module at the final stage.

[0110] The above voltage imbalance coefficient calculation module (351c) is configured to calculate a voltage imbalance coefficient indicating the degree of voltage imbalance of modules within a string, and can calculate the voltage imbalance coefficient by subtracting the value obtained by multiplying the voltage of a specific module by the number of modules from the string voltage. Therefore, the greater the degree of voltage imbalance between modules within a string, the larger the voltage imbalance coefficient.

[0111] The above voltage imbalance diagnosis module (351d) is configured to diagnose the voltage imbalance state of the string when the voltage imbalance coefficient exceeds a set reference value, and can execute the fluctuation abnormality calculation unit (352) when the voltage imbalance state is diagnosed.

[0112] The above-mentioned fluctuation abnormality calculation unit (352) is configured to calculate the degree of abnormality regarding voltage fluctuation of the string, and represents the degree of voltage fluctuation as a numerical value to be reflected in the calculation of the degree of imbalance. As described above, in the case of a normal state as shown in FIG. 13, the string continues to track the maximum power point while maintaining voltage fluctuations within a certain range as shown in ①, but if it shows a fluctuation range that is too large or too small, deviating from the voltage fluctuation range as shown in ② and ③, it is determined to be an abnormal state of fluctuation, and the degree thereof is calculated. In addition, the above-mentioned fluctuation abnormality calculation unit (352) adjusts the scale and reference value to calculate the degree of imbalance by linking the degree of abnormality of voltage fluctuation with the voltage imbalance coefficient. To this end, the above-mentioned fluctuation abnormality calculation unit (352) may include a voltage measurement module (352a), a current measurement module (352b), a power fluctuation coefficient calculation module (352c), and a coefficient adjustment module (352d).

[0113] The above voltage measurement module (352a) is configured to measure the voltage output from the string, and measures it for a certain period of time to calculate the degree of change per unit time.

[0114] The above current measurement module (352b) is configured to measure the current output from the string, and measures it for a certain period of time like voltage to calculate the degree of change with respect to voltage.

[0115] The power fluctuation coefficient calculation module (352c) is configured to calculate a power fluctuation coefficient that indicates the degree of fluctuation in voltage and current, and calculates the degree of change in voltage and current per unit time. For example, the power fluctuation coefficient calculation module (352c) can calculate the power fluctuation coefficient by dividing the ratio of the voltage and current change range by the ratio of the voltage and current magnitudes as shown in (Equation 3) below. If there is no imbalance between modules, the power fluctuation coefficient will have a value close to 1, if the voltage change range is large, it will have a value less than 1, and if the voltage change range is small, it will have a value greater than 1.

[0116] (Mathematical Formula 3)

[0117]

[0118] (I, V = Current, Voltage / dI, dV = Fluctuation range of current, voltage)

[0119] In this case, a large voltage fluctuation range indicates that a specific module has deteriorated or that the power generation has decreased due to odors, pollution, etc., and signifies a state in which the voltage is changed significantly as shown in ② of FIG. 13 to find the maximum power point by the MPPT algorithm of the inverter. Additionally, a small voltage fluctuation range resulting in a power fluctuation coefficient greater than 1 signifies a case in which the voltage change is almost negligible compared to the current change as shown in ③ of FIG. 13, indicating a state in which the power generation performance of the module is significantly reduced. The power fluctuation coefficient calculation module (352c) can calculate the power fluctuation coefficient for unit time periods of, for example, 5 seconds or 10 seconds, and can determine the final power fluctuation coefficient using the average value of the power fluctuation coefficients for unit time periods over a certain period.

[0120] The coefficient adjustment module (352d) is configured to adjust the final power fluctuation coefficient calculated by the power fluctuation coefficient calculation module (352c) to be linked with the voltage imbalance coefficient, converting the standard of the steady state from 1 to 0 and increasing the scale, and can calculate the adjusted power fluctuation coefficient according to the following (Equation 4).

[0121] (Mathematical Formula 4)

[0122] Pf = (3-Pd)*10

[0123] (Here, Pf is the adjusted power change coefficient, and Pd is the final power change coefficient)

[0124] Therefore, in a steady state where there is no imbalance between modules, the adjusted power fluctuation coefficient becomes 0, and power fluctuation coefficients less than 1 are converted into positive numbers, and power fluctuation coefficients greater than 1 are converted into negative numbers.

[0125] The above imbalance detection unit (353) is configured to detect the imbalance state of the modules within the string, and calculates the degree of imbalance between modules by reflecting the degree of voltage imbalance calculated by the voltage imbalance calculation unit (351) and the degree of voltage fluctuation abnormality calculated by the fluctuation abnormality calculation unit (352), and in particular, the cause of the module imbalance can be diagnosed according to the calculated degree of imbalance. To this end, the above imbalance detection unit (353) may include a voltage imbalance coefficient loading module (353a), a power fluctuation coefficient loading module (353b), an imbalance index calculation module (353c), and an abnormal information diagnosis module (353d).

[0126] The above voltage imbalance coefficient loading module (353a) is configured to load the voltage imbalance coefficient calculated by the above voltage imbalance calculation unit (351), and loads the voltage imbalance coefficient calculated by the above voltage imbalance coefficient calculation module (351c).

[0127] The power fluctuation coefficient loading module (353b) is configured to load the power fluctuation coefficient calculated by the fluctuation anomaly calculation unit (352), and loads the power fluctuation coefficient adjusted by the coefficient adjustment module (352d).

[0128] The above-mentioned imbalance index calculation module (353c) is configured to calculate an imbalance index indicating the degree of imbalance between modules, and can calculate the imbalance index by multiplying the voltage imbalance coefficient and the power fluctuation coefficient.

[0129] The above-mentioned abnormal information diagnosis module (353d) is configured to diagnose the imbalance state between modules according to the imbalance index, and can diagnose the imbalance state when the imbalance index exceeds a set value. Since the imbalance index is the product of the degree of voltage imbalance and the degree of abnormal fluctuation, a larger absolute value indicates a more severe degree of imbalance. Since the power fluctuation coefficient is calculated as positive or negative depending on the power fluctuation state, a positive imbalance index indicates a state where the voltage change is large, and a negative imbalance index indicates a state where the voltage change is small and the current change is large. Therefore, as shown in FIG. 14, if the imbalance index is positive, it means that it is operating to the left (ⓐ) of the normal maximum power point, which means that the series resistance has increased, and damage, shading, or contamination of the module may be suspected. Also, if the imbalance index is negative, it means that it is operating to the right (ⓑ) of the normal maximum power point, which means that the parallel resistance has decreased, which means that leakage current, cell cracking, or insulation resistance degradation may be suspected. Accordingly, it is possible to accurately diagnose the imbalance between modules, simultaneously identify the cause, and enable a rapid response. In this case, if the imbalance index is negative and a decrease in insulation resistance is suspected, the insulation resistance diagnosis unit (32) can be configured to operate automatically at a set time.

[0130] The above power generation prediction unit (36) is configured to predict the power generation of a solar power generation facility, and can predict the power generation for each string. In particular, the above power generation prediction unit (36) can increase the accuracy by predicting the power generation by reflecting the specifications and characteristics of each solar module, IV curve data, environmental information, and degradation rate. To this end, the above power generation prediction unit (36) may include a specification information collection module (361), a number information collection module (362), a power generation information collection module (363), an environmental information collection module (364), a solar radiation information collection module (365), a temperature information collection module (366), a degradation rate calculation module (367), and a predicted power generation module (368).

[0131] The above specification information collection module (361) is configured to collect specification information of a solar module included in a string, and can collect and store manufacturer and item information in advance.

[0132] The above count information collection module (362) is configured to collect information on the number of solar modules included in the string, and can generate prediction information by summing the predicted power generation information for each solar module according to the number of solar modules.

[0133] The above-mentioned power generation information collection module (363) is configured to collect information regarding the number of days of power generation of a solar power module, and can calculate and collect information regarding the number of days of power generation by accumulating and storing information on power generation since the time of installation.

[0134] The above environmental information collection module (364) is configured to collect environmental information around the solar module, and can collect information regarding temperature, humidity, etc.

[0135] The above-mentioned solar radiation information collection module (365) is configured to collect solar radiation information reaching the solar module, and can predict the amount of power generated using IV curve data based on the collected solar radiation.

[0136] The above temperature information collection module (366) is configured to collect module temperature information of a solar module, and can collect temperature information measured by a sensor installed in each solar module.

[0137] The above degradation rate calculation module (367) is configured to calculate a degradation rate indicating the degree of degradation of a solar module, and calculates the degradation rate according to the power generation day information collected by the above power generation information collection module (363) by reflecting the degree of degradation per day determined by the characteristics of the specifications of the solar module.

[0138] The above-mentioned predicted power generation module (368) is configured to predict the power generation of a string, and the prediction of power generation is made by considering IV curve data, environmental information, and degradation rate according to solar irradiance and module temperature. The prediction of power generation based on IV curve data and environmental information can be made experimentally or by analyzing measurement information collected from a photovoltaic power generation facility. For example, a correlation can be derived by learning by reflecting environmental information and degradation rate to the power generation based on IV curve data provided by the manufacturer of each photovoltaic module, and the power generation can be predicted using the derived correlation.

[0139] The above power generation measurement unit (37) is configured to measure the power generation of each string, and can calculate the power generation by measuring the voltage and current output from each string.

[0140] The fault diagnosis unit (38) described above is configured to diagnose a fault caused by a decrease in power generation, and diagnoses the decrease in power generation based on the difference between the predicted power generation and the measured power generation. In particular, it is configured to detect the type of fault that causes the decrease in power generation based on the area of ​​the region connecting the location on the IV coordinate plane according to the power generation and the point representing the short-circuit current and open-circuit voltage. To this end, the fault diagnosis unit (38) may include a power generation decrease diagnosis module (381), an Isc area calculation module (382), a Voc area calculation module (383), an area comparison module (384), and a fault cause detection module (385).

[0141] The above power generation degradation diagnosis module (381) is configured to diagnose a decrease in power generation, and diagnoses a decrease in power generation when the measured power generation falls short of the predicted power generation to a certain degree or more, and enables the detection of the cause of the decrease in power generation by using the area of ​​the region on the IV coordinate plane.

[0142] The above Isc area calculation module (382) is configured to calculate the area of ​​the Isc region formed by a point on the IV coordinate plane representing the predicted power generation and the measured power generation and a point (Isc) representing the short-circuit current, and calculates the area of ​​∆a in the graph shown in FIG. 17. The area of ​​∆a is an area that occurs according to the difference between the predicted power generation and the measured power generation, and a large area of ​​∆a means a decrease in current, that is, an increase in the series resistance on the string.

[0143] The above Voc area calculation module (383) is configured to calculate the area of ​​the Voc region formed by a point on the IV coordinate plane representing the predicted power generation and the measured power generation and a point (Voc) representing the open-circuit voltage, and calculates the area of ​​∆b in the graph shown in FIG. 17. The area of ​​∆b is also an area that occurs according to the difference between the predicted power generation and the measured power generation, and a large area of ​​∆b means a decrease in voltage, that is, a decrease in parallel resistance in the string.

[0144] The above area comparison module (384) is configured to compare the areas of the Isc area (∆a) and the Voc area (∆b), and depending on which area is larger, it is possible to determine whether the cause of the decrease in power generation is due to an increase in series resistance or a decrease in parallel resistance.

[0145] The fault cause detection module (385) is configured to detect the cause of the decrease in power generation based on the comparison result by the area comparison module (384). If the area of ​​the Isc region (∆a) is larger than the area of ​​the Voc region (∆b), it can be seen that the decrease in power generation is caused by an increase in series resistance, such as the cable connection condition, line condition, or shading within the module. If the area of ​​the Isc region (∆a) is smaller than the area of ​​the Voc region (∆b), it can be seen that the decrease in power generation is caused by a decrease in parallel resistance, such as leakage current, cell cracking, or a decrease in insulation resistance. In this case, the insulation resistance diagnosis unit (32) can be activated. Accordingly, rapid inspection and response to the decrease in power generation can be performed based on the result detected by the fault cause detection module (385).

[0146] Although the applicant has described various embodiments of the present invention above, such embodiments are merely examples of implementing the technical concept of the present invention, and any modification or alteration that implements the technical concept of the present invention should be interpreted as falling within the scope of the present invention.

Claims

1. A photovoltaic power generation device that produces electricity by solar energy, and a management server that controls the operation of the photovoltaic power generation device, and The above-mentioned solar power generation device is, A plurality of photovoltaic modules are connected in series and a plurality of strings are installed in parallel; an inverter that converts power output from each string and supplies it to the grid and load; and a plurality of relays formed between each string and the inverter to regulate the connection between each string and the inverter; comprising The above management server is, A photovoltaic power generation system capable of string-specific relay control, characterized by individually opening relays connected to each string to measure insulation resistance and adjusting the connection of the relays according to the measurement results of the insulation resistance.

2. In claim 1, the management server It includes an insulation resistance measuring unit that enables the insulation resistance of each string to be measured, and The insulation resistance measuring unit above is, A photovoltaic power generation system capable of relay control per string, characterized by including a string determination module for determining a string to measure insulation resistance, a relay opening module for opening a relay connected to the string determined by the string determination module, and a measurement indication module for indicating the measurement of insulation resistance of the string in which the relay is opened.

3. In Clause 2, the management server It includes an insulation resistance diagnostic unit that diagnoses the insulation resistance status of each string according to the measurement result by the insulation resistance measuring unit above, and The insulation resistance diagnostic unit above is, A photovoltaic power generation system capable of string-specific relay control, characterized by including an abnormality detection module that detects an abnormality in the insulation resistance of each string, and an open-holding module that maintains the relay of the string in which the abnormality is detected in an open state.

4. In claim 1, the management server It includes a relay control unit that automatically adjusts the opening and closing of relays connected to each string, and The above relay control unit is, A photovoltaic power generation system capable of string-specific relay control, characterized by including an opening time setting module for setting the opening time of a relay connected to each string, a connection time setting module for setting the connection time of each opened relay, and an automatic opening / closing operation module for automatically operating the relay according to the set opening and connection times.

5. In Clause 4, the management server It includes a control setting unit that sets information related to the operation of the relay by the above relay control unit, and A photovoltaic power generation system capable of string-by-string relay control, characterized in that the above-described control setting unit determines the opening and closing timing of the relay according to the power usage pattern of the load connected to the photovoltaic power generation device.

6. In claim 5, the control setting unit A photovoltaic power generation system capable of relay control per string, characterized by comprising: a reference time setting module for setting a reference time having a power generation amount of at least a certain level; a usage collection module for collecting power consumption information of a load during the set reference time; a usage pattern analysis module for analyzing the pattern of collected power consumption by unit period; a reference usage setting module for setting a reference power consumption amount for a unit period; and a target time extraction module for extracting a target time to open a relay when the power consumption within the set reference time is less than the reference power consumption amount as a result of analyzing the power consumption pattern.

7. In Clause 6, the reference time setting module is A photovoltaic power generation system capable of relay control per string, characterized by including a power generation collection module for collecting power generation information of a photovoltaic power generation device, a power generation pattern analysis module for analyzing the pattern of power generation, a reference value setting module for setting a reference value for power generation, and a reference time determination module for determining a time when power generation is greater than or equal to the reference value as a reference time.

8. In claim 6, the control setting unit A photovoltaic power generation system capable of relay control per string, characterized by including an operating range setting module that sets the number of operating strings according to the amount of power generated and the amount of power consumed for the target time when the relay is opened, and a connection adjustment module that adjusts the connection of relays for the set number of strings.

9. In claim 8, the connection adjustment module is A photovoltaic power generation system capable of relay control per string, characterized by comprising: a connection information collection module for collecting connection information of relays for each string; a capacity information collection module for collecting output capacity information of each string; a power generation loading module for retrieving power generation information of each string; a usage index calculation module for calculating a usage index based on the ratio of cumulative power generation to capacity of each string; a usage index comparison module for comparing usage indices of each string; and a relay selection module for selecting a number of strings set by the operation range setting module in order of highest usage index.

10. In Clause 2, the management server It includes a module imbalance diagnosis unit that diagnoses imbalance between photovoltaic modules within a string, and The insulation resistance measuring unit above is, A photovoltaic power generation system capable of string-by-string relay control, characterized by performing insulation resistance measurement when an imbalance caused by a decrease in insulation resistance is diagnosed by the above-mentioned module imbalance diagnosis unit.

11. In claim 10, the module imbalance diagnosis unit It includes a voltage imbalance calculation unit that calculates the degree of voltage imbalance between modules constituting a string, a fluctuation abnormality calculation unit that calculates the degree of abnormality due to voltage and current fluctuations of the string, and an imbalance detection unit that detects imbalance between modules of the string according to the degree of voltage imbalance and the degree of fluctuation abnormality. The above voltage imbalance calculation unit is, A photovoltaic power generation system capable of relay control per string, characterized by including a string voltage measurement module for measuring the voltage of power output from a string, a module voltage measurement module for measuring the voltage at a specific module within the string, and a voltage imbalance coefficient calculation module for calculating a voltage imbalance coefficient indicating the degree of voltage imbalance between modules by subtracting the value obtained by multiplying the number of photovoltaic modules included in the string by the voltage of the specific module from the string voltage.

12. In claim 11, the voltage imbalance calculation unit is It includes a voltage imbalance diagnosis module that compares the voltage imbalance coefficient calculated by the above-mentioned imbalance coefficient calculation module with a reference value, diagnoses voltage imbalance between modules if it exceeds the reference value, and executes a fluctuation abnormality calculation unit. The above fluctuation abnormality calculation unit is, A photovoltaic power generation system capable of relay control per string, characterized by including a voltage measuring module that measures a voltage output from a string for a certain period of time, a current measuring module that measures a current output from a string for a certain period of time, and a power fluctuation coefficient calculation module that calculates a power fluctuation coefficient indicating the degree of fluctuation of voltage and current by calculating the value of the ratio of voltage change amount to current change amount for the ratio of voltage to current per unit time for a certain period of time and the average value.

13. In Clause 12, the above fluctuation abnormality calculation unit A photovoltaic power generation system capable of string-by-string relay control, characterized by including a coefficient adjustment module that increases the scale while changing the standard for the steady state of the power fluctuation coefficient to zero.

14. In claim 13, the coefficient adjustment module A photovoltaic power generation system capable of string-by-string relay control, characterized by calculating the final power fluctuation coefficient by adjusting the power fluctuation coefficient according to mathematical formula 3. (Mathematical Formula 3) Pf = (1-Pd)*10 (Here, Pf is the adjusted power variation coefficient, and Pd is the initial power variation coefficient) 15. In claim 13, the imbalance detection unit A photovoltaic power generation system capable of relay control per string, characterized by including a voltage imbalance coefficient loading module for retrieving a voltage imbalance coefficient, a power fluctuation coefficient loading module for retrieving a power fluctuation coefficient, an imbalance index calculation module for calculating an imbalance index representing the degree of output imbalance between modules by multiplying the voltage imbalance coefficient and the power fluctuation coefficient, and an abnormal information diagnosis module for diagnosing an abnormal state due to output imbalance between modules of the string according to the calculated imbalance index.

16. In claim 15, the above abnormal information diagnosis module is A photovoltaic power generation system capable of string-by-string relay control, characterized by diagnosing module damage, shading, or contamination when the imbalance index is positive, and diagnosing PID, cell cracking, or insulation resistance degradation when the imbalance index is negative.

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