JP2017161483A - Ground fault detection device, control method and control program thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce standby time for ground fault detection.SOLUTION: A time constant estimation section (23) calculates a reference time constant by using a measured value of a parasitic capacitance (95) measured by a parasitic capacitance measurement section (21) and a reference value of a round fault resistance (90). A ground fault determination section (24) determines if there is any ground fault based on the reference time constant which is calculated by the time constant estimation section (23) and measurement time and the measured value of the ground fault resistance (90) from the resistance measurement section (22).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ground fault detection device that detects a ground fault in a power generation system such as a solar cell string.

  The solar power generation system includes a solar cell array, and the solar cell array is configured by connecting a plurality of solar cell strings in parallel, and each solar cell string is configured by connecting a plurality of solar cell modules in series. Yes. As an example, DC power generated in each solar cell string is converted into appropriate DC power and / or appropriate AC power by a power conditioning system (PCS).

  The electric circuit of the solar cell string is electrically insulated (hereinafter simply referred to as “insulation”) with an arbitrary sealing material. However, if for some reason, the insulation resistance between a certain point in the electric path of the solar cell string and the ground decreases, a ground fault occurs at that point.

  Therefore, conventionally, a solar power generation system is provided with a ground fault detection device that detects a ground fault as disclosed in Patent Document 1. Specifically, the ground fault detection device of Patent Document 1 measures a voltage change or a current change in a closed circuit formed by a solar cell string, a ground fault resistance, and a ground fault detection device. Judgment is made.

JP 2012-119382 A (released on June 21, 2012)

  In general, the measured value for detecting a ground fault becomes a steady value via a transient value due to the ground capacitance of the photovoltaic power generation system (hereinafter abbreviated as “ground capacity”). It is necessary to wait for detection of a fault. In particular, when the solar cell array is configured on a large scale by increasing the number of solar cell modules or increasing the number of solar cell strings, the conductors connecting the solar cell strings become longer or included in the solar cell array. The total area of the solar cell module to be increased. Thereby, the ground capacity in the photovoltaic power generation system increases, and the standby time for waiting for detection of a ground fault becomes longer.

  With respect to this problem, in Patent Document 1, a solar cell string whose ground fault is detected is disconnected (separated) from the photovoltaic power generation system. Thereby, since the ground capacity which affects ground fault detection is limited to the thing regarding a solar cell string, the said standby | waiting time can be shortened.

  However, in the case of Patent Document 1, a ground fault is detected for a certain solar cell string, and this is performed for all the solar cell strings included in the photovoltaic power generation system. Therefore, the total value of the standby time in the photovoltaic power generation system still remains long.

  Accordingly, an object of the present invention is to provide a ground fault detection device, a ground fault detection method, and the like that can shorten the standby time for standby detection of a ground fault in a power generation system such as a solar battery string. .

  In order to solve the above-described problem, a ground fault detection apparatus according to the present invention is a ground fault detection apparatus for detecting a ground fault in a power supply system including a DC power source for generating or charging / discharging, and the ground fault detection apparatus according to the present invention A capacitance acquisition unit that acquires a capacitance value, a resistance reference value setting unit that sets a reference value of a ground fault resistance of the power supply system in a state where no ground fault occurs, a value of the ground capacitance, and the ground fault resistance A time constant estimator for estimating a reference time constant using the reference value, and a measurement value for detecting the ground fault, wherein the measurement value transiently changes depending on the time constant of the power supply system. A measurement unit that measures and acquires a transient value and a measurement time; and a ground fault determination unit that determines the presence or absence of the ground fault based on the reference time constant, the transient value of the measurement value, and the measurement time. It is characterized by that.

  According to the above configuration, the reference time constant is calculated using the value of the ground capacity in the power supply system and the reference value of the ground fault resistance in a state where no ground fault occurs. Thereby, a determination value for the reference value of the measurement value is estimated from the time constant of the reference, a transient value of the measurement value, and the measurement time, and the estimated determination value and a predetermined threshold corresponding to the measurement value Can be determined whether or not the ground fault exists. Alternatively, a threshold value at the measurement time is obtained from the reference time constant, a predetermined threshold value corresponding to the measurement value, and the measurement time, and the threshold value at the measurement time is compared with a transient value of the measurement value. Thus, the presence or absence of the ground fault may be determined.

  Therefore, in order to determine the presence or absence of the ground fault, there is no need to wait until the steady value of the measured value is acquired, and as a result, the standby time for waiting for the detection of the ground fault can be shortened compared to the conventional case. it can.

  By the way, as a reference value of the ground fault resistance in a state where no ground fault has occurred, a measured value measured in the past in the state, a calculated value calculated from a positional relationship between the power supply system and the ground, There are predetermined values such as a threshold value for determining the presence or absence of an entanglement.

  On the other hand, the reference value of the ground capacity can be estimated from the internal structure of the power supply system, the positional relationship between the power supply system and the ground, and the like. However, the ground capacity varies depending on the environment of the power supply system, such as humidity and temperature.

  Therefore, the capacity acquisition unit may acquire the value of the ground capacity by measurement. Specifically, the value of the ground capacity can be obtained by measuring the open circuit voltage, current, etc. of the power supply system.

  Alternatively, it further includes an information acquisition unit that acquires information on the environment of the power supply system, and the capacity acquisition unit corrects the reference value of the ground capacity based on the information acquired by the information acquisition unit. The value of the ground capacity may be acquired. In this case, since the value of the ground capacity corresponding to the environment is acquired, the ground fault can be detected with high accuracy.

  A control method for a ground fault detection device according to the present invention is a control method for a ground fault detection device for detecting a ground fault in a power supply system including a DC power source for generating or charging / discharging, and a value of a ground capacity of the power supply system A capacitance acquisition step of acquiring a reference value, a resistance reference value setting step of setting a reference value of a ground fault resistance of the power supply system in a state where a ground fault has not occurred, a value of the ground capacitance and a reference value of the ground fault resistance A time constant estimating step for estimating a reference time constant, and a measured value for detecting the ground fault, the transient value of the measured value transiently changing according to the time constant of the power supply system, and A measurement step of measuring and acquiring a measurement time, and a ground fault determination step of determining the presence or absence of the ground fault based on the reference time constant, the transient value of the measurement value, and the measurement time. It is said.

  According to said method, there exists an effect similar to the said ground fault detection apparatus.

  The ground fault detection apparatus according to the present invention may be realized by a computer. In this case, the ground fault detection apparatus is realized by a computer by causing the computer to operate as each unit included in the ground fault detection apparatus. The control program for the fault detection apparatus and the computer-readable recording medium on which the control program is recorded also fall within the scope of the present invention.

  The ground fault detection device according to the present invention calculates the reference time constant using the value of the ground capacity in the power supply system and the reference value of the ground fault resistance in a state where no ground fault has occurred. There is no need to wait until a steady value of a measurement value for detecting a fault is obtained, and as a result, the standby time for waiting for the detection of the ground fault can be shortened as compared with the prior art.

It is a block diagram which shows the schematic structure of the solar energy power generation system which concerns on Embodiment 1 of this invention. It is a graph which illustrates the relationship between the measured value of ground fault resistance, and measurement time. It is a graph which shows the mode of the time change of the measured value of ground fault resistance. It is a block diagram which shows schematic structure of the solar energy power generation system which concerns on Embodiment 2 of this invention.

Embodiment 1
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram illustrating a schematic configuration of a photovoltaic power generation system 100 according to the first embodiment. First, the configuration of the photovoltaic power generation system 100 will be described with reference to FIG.

(Solar power generation system 100)
As shown in FIG. 1, the photovoltaic power generation system 100 includes a solar cell string 10, a ground fault detection device 20, a breaker 30, and a PCS 40. The solar cell string 10 is connected to the PCS 40 via the ground fault detection device 20 and the breaker 30.

  The solar cell string 10 is configured by connecting a plurality of (for example, 10 to 20) solar cell modules 11 in series. Each solar cell module 11 includes a plurality of solar cells connected in series, and is formed in a panel shape. Thus, the solar cell string 10 is a power generator that receives light (for example, sunlight) and generates DC power.

  The solar cell string 10 is connected to the ground fault detection device 20 via the electric paths 15a and 15b. The ground fault resistance 90 is a resistance formed between the electric paths 15a and 15b of the solar cell string 10 and the ground. The parasitic capacitance 95 is a ground capacitance formed between the solar cell string 10 and the ground.

  In FIG. 1, only a part of the ground fault resistance 90 and the parasitic capacitance 95 are illustrated for simplicity. As shown in FIG. 1, the solar cell string 10 is connected to the ground via a ground fault resistor 90 and a parasitic capacitance 95. In FIG. 1, the resistance value of the ground fault resistor 90 is shown as Rz, and the parasitic capacitance 95 is shown as the capacitance Cg.

  In FIG. 1, only one solar cell string 10 is illustrated for simplicity. However, the actual photovoltaic power generation system 100 includes a solar cell array including a plurality of solar cell strings 10, and a breaker 30 is provided for each solar cell string 10. A fuse may be provided instead of the breaker 30.

  Further, as shown in FIG. 1, the ground fault detection device 20 may be configured to be provided between the solar cell string 10 and the breaker 30, or the two electric circuits 15 a and 15 b of the solar cell string 10. Alternatively, two probes may be attached to each other. In the former case, the number of ground fault detection devices 20 is required by the number of solar cell strings 10, but it is possible to save the user from attaching the probe. In the latter case, only one ground fault detection device 20 is required, but the user needs to attach the probe.

  In addition, you may incorporate the ground fault detection apparatus 20 and the breaker 30 in the DC circuit part of PCS40. In particular, in the case of a PCS in which electric power from a plurality of solar cell strings 10 can be individually input, inspection for each solar cell string 10 can be performed by incorporating the ground fault detection device 20 and the breaker 30 in the PCS. .

  The ground fault detection device 20 includes a parasitic capacitance measurement unit 21 (capacitance acquisition unit), a resistance measurement unit 22 (measurement unit), a time constant estimation unit 23 (resistance reference value setting unit, time constant estimation unit), and a ground fault determination unit. 24. As will be described below, the ground fault detection device 20 functions as an inspection device that inspects the solar cell string 10. Specific operation of the ground fault detection device 20 will be described later.

  The breaker 30 is a circuit breaker that manually interrupts the current from the solar cell string 10 to the PCS 40.

  The PCS 40 is a power conversion device that converts DC power supplied from the solar cell string 10. As an example, the PCS 40 includes a DC / DC converter and a DC / AC converter (not shown). The DC / DC converter is a circuit that converts DC power into predetermined DC power (DC / DC conversion), and is, for example, a step-up chopper.

  As an example, the DC / DC converter converts the DC power supplied from the solar cell string 10 into DC power having a higher voltage. Then, the DC power converted in the DC / DC converter is supplied to the DC / AC converter.

  The DC / AC converter is a circuit that converts DC power supplied from the DC / DC converter into AC power (DC / AC conversion), for example, an inverter. As an example, the DC / AC converter converts DC power into AC power having a frequency of 60 Hz. Then, the AC power converted in the DC / AC converter is supplied to a load device (not shown) outside the photovoltaic power generation system 100.

  Thus, by providing the PCS 40, the DC power generated in the solar cell string 10 can be converted into AC power having a predetermined voltage and frequency according to the specifications of the load device. In addition, when the voltage and frequency of the alternating current power converted in PCS40 are the same as an electric power system (not shown), the said alternating current power may be supplied to an electric power system.

  In addition, when the above-mentioned load apparatus can receive direct-current power, it is not necessary to perform DC / AC conversion. Further, when DC / DC conversion is not necessary, a load device may be provided in the solar power generation system 100 instead of the PCS 40.

(Transient time change of measured value of ground fault resistance)
As shown in FIG. 1, when a ground fault occurs in the solar cell string 10, a ground fault current I is generated in a closed circuit formed by the solar cell string 10, the ground fault resistor 90, and the ground fault detection device 20. Flows. Therefore, Rz = V / I can be measured by measuring the ground fault current I in a state where a predetermined DC voltage (constant voltage) V is applied to the ground fault resistor 90.

  However, a charging current flows through the parasitic capacitance 95 until the charging of the parasitic capacitance 95 is completed. Hereinafter, the charging current is expressed as Ig. Here, assuming that the current flowing through the ground fault resistor 90 is Iz, the ground fault current I is expressed as I = Iz + Ig.

  In the parasitic capacitance 95, when a voltage is applied, a large charging current Ig flows first, and then the charging current Ig gradually decreases (transiently). When the parasitic capacitance 95 is completely charged, the charging current Ig is 0. It becomes. Specifically, the charging current Ig decreases exponentially under the time constant τ = Cg × R0.

  As will be described later, R0 is a true value of the resistance value Rz. As an example, when Cg = 0.3 μF and R0 = 100 MΩ, τ = 0.3 μF × 100 MΩ = 30 s.

As an example, the ground fault current I = I (t) is expressed by the following formula (1),
I (t) = I0 × {1 + exp (−t / τ)} (1)
Represented by Here, I0 is a constant. T is the measurement time. Specifically, t is an elapsed time since the voltage V is applied to the ground fault resistance 90 (that is, an elapsed time from the start of measurement of the ground fault resistance 90).

  Referring to Equation (1), in order to measure the steady value I0 of the ground fault current I (in other words, the true value R0 of the resistance value Rz) with high accuracy, the measurement time is compared with the time constant τs. It will be understood that it is necessary to ensure a sufficiently long length.

Further, the measured value R = R (t) of the resistance value Rz is expressed by the following equation (2),
R (t) = V ÷ [I0 × {1 + exp (−t / τ)}] (2)
Represented by Referring to the equation (2), it can be understood that the transient time change of the measured value R (t) is defined by the time constant τ as well as the ground fault current I (t). Here, the steady value R0 of the resistance value Rz is R0 = V / I0. This R0 is the true value of the resistance value Rz.

  Strictly speaking, R0 includes a ground fault resistance and an internal resistance in the ground fault detection device 20. In practice, the solar cell string 10, the ground fault detection device 20, and the circuit (PV system circuit) of the photovoltaic power generation system including the ground are not simple CR circuits. Therefore, it is desirable to calculate the coefficient by adding an appropriate coefficient to the exponential function and fitting it to the actual PV system circuit.

  FIG. 2 is a graph illustrating the relationship between the measurement value R and the measurement time. In the graph of FIG. 2, the vertical axis represents the measured value, and the horizontal axis represents the measurement date. FIG. 2 shows graphs when the measurement time (ie, t) is “50 ms”, “1 s”, “4 s”, and “10 s”, respectively.

  Referring to FIG. 2, when the measurement time is short (when the measurement time is other than 10 s), the measurement value R (transient value) is measured as a value sufficiently lower than the true value R0 (steady value). It is understood. This is because the measurement time is shorter than the time until the measurement value R reaches a steady value.

  In addition, referring to FIG. 2, it can be understood that the measurement value varies depending on the measurement date even when the measurement time is the same. This is because the capacitance Cg of the parasitic capacitance 95 changes depending on the ambient environment (particularly humidity) of the site where the solar cell string 10 is disposed.

  For example, when the humidity is high, the amount of water contained between the solar cell string 10 and the ground is large, so that the capacitance Cg increases. Further, when moisture adheres to the surface of the solar cell module 11, the capacitance Cg increases due to the influence of the moisture. For this reason, the measurement time for measuring the true value R0 becomes longer as the time constant τ increases.

  The capacitance Cg also varies depending on the type and arrangement state of the power cables (electric paths 15a and 15b) connected to the solar cell string 10. In addition, the capacitance Cg varies depending on the size of the solar cell string 10, the type of solar cell, the ambient temperature, and the like.

  FIG. 3 is a graph showing how the measured value R changes with time. In the graph of FIG. 3, the vertical axis represents the measured value R, and the horizontal axis represents time t. As shown in FIG. 3, at t = 0, R (0) = Ri, and at t = τ, R (τ) = Rτ. Note that, according to the above equation (2), Ri = R0 / 2 and Rτ = R0 / {1 + exp (−1)} ≈0.73R0. However, in actual measurement, Ri and Rτ depend on the electrical characteristics of the photovoltaic power generation system 100.

(Estimation of ground fault resistance in the ground fault detection device 20)
As described above, in the photovoltaic power generation system 100, in order to measure the true value R0, a relatively long measurement time is required. Therefore, the inventor of the present application newly arrived at the technical idea of shortening the measurement time of the ground fault resistance by estimating the reference time constant τ instead of measuring the true value R0 itself. .

  Next, a specific configuration of the ground fault detection device 20 will be described, and a method for estimating the reference time constant τ will be described. As described below, in the present embodiment, the capacitance Cg is measured in advance, and the reference time constant τ0 is estimated based on the measurement result.

  In the ground fault detection device 20, the parasitic capacitance measuring unit 21 measures the capacitance Cg. Further, the resistance measuring unit 22 measures the measurement value R. The parasitic capacitance measuring unit 21 and the resistance measuring unit 22 may be mounted by, for example, a known LCR meter. Moreover, the measurement in the parasitic capacitance measurement part 21 and the resistance measurement part 22 is realizable using the method of a disconnection measurement, for example. Note that the method for measuring disconnection is well known as described in Japanese Patent No. 4604250 and the description thereof is omitted.

  First, the parasitic capacitance measurement unit 21 measures the capacitance Cg in advance before the operations of the resistance measurement unit 22, the time constant estimation unit 23, and the ground fault determination unit 24. The capacitance Cg may be obtained by correcting the past data from the measured value, the design value, past data, a combination thereof, and an equivalent circuit of the system.

  The time constant estimation unit 23 estimates a reference time constant τ0. Note that a predetermined reference value Rst is preset in the time constant estimation unit 23. The reference value Rst may be appropriately set by the designer of the photovoltaic power generation system 100 as a value necessary for the ground fault resistance 90 to satisfy sufficient insulation performance (so that the ground fault current I does not become excessive). . Examples of the predetermined reference value Rst include a threshold value for determining the presence or absence of a ground fault, a measured value of the true value R0 in a past state where no ground fault has occurred, and the solar cell string 10 and the ground. Examples include calculated values calculated from the positional relationship.

  Specifically, the time constant estimation unit 23 calculates the reference time constant τs as τs = Cg × Rst. This time constant τs may be understood to be a provisional time constant (provisional value of the time constant τ) set using the capacitance Cg and the reference value Rst. In the present embodiment, a case where Rst = 5 MΩ is considered. In this case, τs = 0.3 μF × 5 MΩ = 1.5 s.

  As described above, if the capacitance Cg is measured by the parasitic capacitance measuring unit 21, the reference time constant τs can be calculated using the capacitance Cg and the reference value Rst. That is, even if the true value R0 is not known, it is possible to estimate a time constant that can be used to determine the presence or absence of a ground fault.

  Subsequently, the time constant estimation unit 23 uses the reference value Rst, the reference time constant τs, the measurement time T of the ground fault resistance 90 from the resistance measurement unit 22, and the equation (2), t = T A transient reference value Rst (T) at is calculated.

  The ground fault determination unit 24 detects a ground fault in the solar cell string 10. Specifically, the ground fault determination unit 24 measures the transient reference value Rst (T) (threshold value) calculated by the time constant estimation unit 23 and the ground fault resistance 90 at t = T. By comparing the magnitude relationship with the value R (T), it is determined whether or not a ground fault has occurred. More specifically, the ground fault determination unit 24 determines that the measured value R (T) is greater than or equal to the transient reference value Rst (T) (that is, R (T) ≧ Rst (T)). Determines that no ground fault has occurred. On the other hand, when the measured value R (T) is smaller than the transient reference value Rst (T) (that is, when R (T) <Rst (T)), the ground fault determination unit 24 has a ground fault. Is determined to have occurred.

(Effect of the photovoltaic power generation system 100)
According to the photovoltaic power generation system 100 of the present embodiment, a transient reference value of the ground fault resistance 90 in a relatively short time can be estimated. Therefore, it is not necessary to continue the measurement of the ground fault resistance 90 for a time sufficiently longer than the above-described time constant τ, so that the measurement time of the ground fault resistance 90 can be shortened.

  Moreover, since the presence or absence of the occurrence of the ground fault in the solar cell string 10 can be determined based on the transient reference value of the ground fault resistance 90, the time required for the ground fault detection can be shortened. Furthermore, even if the environment of the solar cell string 10 changes, the measured value of the capacitance Cg changes in accordance with the change, so it is possible to accurately determine whether or not the ground fault has occurred.

  By the way, the earth leakage breaker (not shown) which prevents the earth leakage from PCS40 to the external load apparatus (or system | strain) may be provided in the alternating current side of PCS40. Specifically, the earth leakage breaker performs a breaking operation by judging that an earth leakage has occurred when a current of a predetermined value or more flows for a predetermined time (for example, 0.1 seconds). ). That is, the leakage breaker stops the electrical output from the PCS 40 to the external load device (or system) when a current of a predetermined value or more flows for a predetermined time.

  Therefore, the ground fault determination unit 24 may estimate the transient reference value I0st (T) of the ground fault current I by I0st (T) = V / Rst (T). Here, examples of the voltage V include the ground voltage of the solar cell string 10. Further, as an example of the resistance reference value Rst, a resistance value allowed for the predetermined time of the earth leakage breaker can be cited.

  And the ground fault determination part 24 may determine whether the transient reference value I0st (T) of the ground fault current I is more than the said predetermined value of the said earth-leakage breaker. As described above, the ground fault determination unit 24 can be provided with a function of estimating whether the leakage breaker trips based on the transient reference value I0st (T) of the ground fault current I.

(Additional notes)
In the above embodiment, the ground fault detection device 20 determines the presence or absence of a ground fault using a predetermined reference value Rst that is set in advance. However, the ground fault detection device 20 is set to the predetermined reference value Rst. May be corrected by adding the internal resistance and the presence or absence of a ground fault may be determined using the corrected reference value Rst.

  Moreover, in the said embodiment, although the transient reference value Rst (T) in t = T is made into threshold value Rth (T) for determining the presence or absence of generation | occurrence | production of a ground fault in the ground fault determination part 24, to this, It is not limited. For example, the threshold value Rth (T) may be a value obtained by adding an arbitrary margin in consideration of safety or measurement error to the transient reference value Rst (T).

  Further, in the above embodiment, the transient reference value Rst (T) of the ground fault resistance 90 is calculated, and the calculated transient reference value Rst (T) is compared with the measured value R (T). Although the presence or absence of the entanglement is determined, the present invention is not limited to this. For example, a value for determining the presence / absence of a ground fault using the reference time constant τs, the measurement time T and the measured value R (T) of the ground fault resistance 90 from the resistance measurement unit 22, and the equation (2). The determination value Res of the ground fault resistance 90 as described above may be calculated, and the presence / absence of a ground fault may be determined by comparing the calculated determination value Res and the reference value Rst.

[Embodiment 2]
The second embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as those described in the embodiment are given the same reference numerals, and descriptions thereof are omitted.

(Solar power generation system 200)
FIG. 4 is a block diagram illustrating a schematic configuration of the photovoltaic power generation system 200 according to the second embodiment. The solar power generation system 200 is obtained by replacing the ground fault detection device 20 with the ground fault detection device 20a in the solar power generation system 100 of the first embodiment.

  Further, the ground fault detection device 20a is obtained by replacing the parasitic capacitance measurement unit 21 with a parasitic capacitance estimation unit 25 (information acquisition unit, capacitance acquisition unit) in the ground fault detection device 20 of the first embodiment. As will be described below, the parasitic capacitance estimation unit 25 has a function of estimating the capacitance Cg.

  That is, the photovoltaic power generation system 200 of the present embodiment is different from the photovoltaic power generation system 100 of the first embodiment in that the capacitance Cg is estimated instead of measuring the capacitance Cg each time.

  In the parasitic capacitance estimation unit 25, an initial value Cgi (reference value) of the capacitance Cg is set in advance. As an example, the initial value Cgi is set based on the result of measuring the capacitance Cg in the solar power generation system 200 in advance. The initial value Cgi may be calculated from the positional relationship between the solar cell string 10 and the ground.

  The initial value Cgi may be set based on a result of measuring the capacitance Cg in advance in the same type of solar power generation system as the solar power generation system 200. In addition, the initial value Cgi is a photovoltaic power generation such as the type of the solar battery cell, the type of the power cable, and the size of the solar battery string 10 with respect to the result of previously measuring the capacitance Cg in the reference solar power generation system. It may be set based on information of members constituting the system 200. Moreover, the initial value Cgi may be changeable by the user of the photovoltaic power generation system 200.

  And the parasitic capacitance estimation part 25 acquires the environmental information which is the information used for estimation of the electrostatic capacitance Cg. The environmental information may be information indicating, for example, at least one of temperature and humidity of a site where the solar power generation system 200 is installed. As an example, the parasitic capacitance estimation unit 25 is connected to a thermometer or a hygrometer (not shown) provided at the site. In this case, the parasitic capacitance estimation unit 25 can acquire the temperature or humidity value as environmental information from each of the thermometer and the hygrometer.

  The parasitic capacitance estimation unit 25 may be connected to the Internet. In this case, the parasitic capacitance estimation unit 25 can acquire the temperature or humidity value at the site as environmental information from the weather information provided on the Internet.

  And the parasitic capacitance estimation part 25 calculates the estimated value Cge of the electrostatic capacitance Cg by correct | amending the initial value Cgi based on environmental information. Hereinafter, for the sake of simplicity, a case where the estimated value Cges is calculated based only on the site humidity h will be described as an example.

  First, a correction function f (h) that is a function of the humidity h is preset in the parasitic capacitance estimation unit 25. As an example, the correction function f (h) is obtained by interpolating data indicating a relationship between humidity and capacitance measured in advance in the photovoltaic power generation system 200 using a known interpolation method. It may be a thing. Further, the correction function f (h) may be a continuous function with respect to the humidity h, or may be a discrete function (eg, a step function). In addition, since the capacitance of the resin usually increases almost in proportion to the relative humidity, as an example, the correction function f (h) may be f (h) = kh. Here, k is a constant.

And the parasitic capacitance estimation part 25 is the following formula | equation (3),
Cges = Cgi × f (h) (3)
To calculate the estimated value Cges. According to Expression (3), it is possible to calculate the estimated value Cges according to the change in the humidity h.

  In the present embodiment, the time constant estimation unit 23 calculates a reference time constant τs as τs = Cges × Rst. That is, the time constant estimating unit 23 calculates the reference time constant τs using the estimated value Cges instead of the measured value of the capacitance Cg. Thereafter, the time constant estimation unit 23 and the ground fault determination unit 24 perform the same processing as in the first embodiment.

  By the way, it is known that the parasitic capacitance changes due to moisture adhering to the solar cell panel. Therefore, precipitation can be added to the environmental information.

  In addition, various materials have a characteristic (temperature characteristic) in which the capacitance changes according to a temperature change, but it is known that the temperature characteristic varies depending on the material. Therefore, when the temperature is included in the environmental information, the temperature characteristic data of the solar cell panel material may be added to the environmental information. That is, the value of the capacitance Cg may be corrected by further using temperature characteristic data of the solar cell panel material.

(Effect of the photovoltaic power generation system 200)
According to the photovoltaic power generation system 200 of the present embodiment, even if the environment of the solar cell string 10 changes, the environmental information changes according to the change, and the value of the capacitance Cg is set according to the changed environmental information. Since it correct | amends, the presence or absence of generation | occurrence | production of the said ground fault can be determined accurately. Further, since it is not necessary to measure the value of the capacitance Cg each time, the transient reference value Rst (T) of the ground fault resistance 90 can be estimated more easily. Therefore, it is possible to improve user convenience.

[Example of software implementation]
The control blocks (particularly the ground fault detection devices 20 and 20a) of the photovoltaic power generation systems 100 and 200 may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or a CPU (Central It may be realized by software using a Processing Unit.

  In the latter case, the photovoltaic power generation systems 100 and 200 include a CPU that executes instructions of a program that is software that realizes each function, and a ROM (Read Only Memory) or a storage device (these are referred to as “recording media”), a RAM (Random Access Memory) for expanding the program, and the like. Then, the computer (or CPU) reads the program from the recording medium and executes it to achieve the object of the present invention. As the recording medium, a “non-temporary tangible medium” such as a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used. The program may be supplied to the computer via an arbitrary transmission medium (such as a communication network or a broadcast wave) that can transmit the program. The present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  Moreover, in the said embodiment, although this invention is applied to a solar power generation system, it is not limited to this, This invention is applicable to the arbitrary power supply systems provided with DC power supply. As the DC power source, in addition to the photovoltaic power generation device, a fuel cell device capable of obtaining electric energy (DC power) using hydrogen fuel by an electrochemical reaction between hydrogen fuel and oxygen in the air, Examples include a storage battery that stores (charges and discharges) electric energy, and a capacitor such as a capacitor.

DESCRIPTION OF SYMBOLS 10 Solar cell string 20, 20a Ground fault detection apparatus 21 Parasitic capacitance measurement part (capacity acquisition part)
22 Resistance measurement unit (measurement unit)
23 Time constant estimation unit (resistance reference value setting unit, time constant estimation unit)
24 Ground fault determination unit 25 Parasitic capacitance estimation unit (information acquisition unit, capacitance acquisition unit)
90 Ground fault resistance 95 Parasitic capacitance 100,200 Solar power generation system

Claims (7)

A ground fault detection device for detecting a ground fault in a power supply system having a DC power source for generating or charging / discharging,
A capacity acquisition unit for acquiring a value of a ground capacity of the power supply system;
A resistance reference value setting unit for setting a reference value of a ground fault resistance of the power supply system in a state where a ground fault has not occurred;
A time constant estimating unit that estimates a reference time constant using the value of the ground capacity and the reference value of the ground fault resistance;
A measurement unit for detecting the ground fault, a measurement unit that measures and acquires a transient value and a measurement time of a measurement value that changes transiently according to a time constant of the power supply system;
A ground fault detection device comprising: a ground fault determination unit that determines the presence or absence of the ground fault based on the reference time constant, the transient value of the measurement value, and the measurement time.   The ground fault determination unit estimates a determination value for the reference value of the measurement value from the reference time constant, the transient value of the measurement value, and the measurement time, and corresponds to the estimated determination value and the measurement value The ground fault detection device according to claim 1, wherein the presence or absence of the ground fault is determined by comparing with a predetermined threshold value.   The ground fault determination unit obtains a threshold value in the measurement time from the reference time constant, a predetermined threshold value corresponding to the measurement value, and the measurement time, and a threshold value in the measurement time and a transient value of the measurement value The ground fault detection device according to claim 1, wherein the presence / absence of the ground fault is determined by comparing.   The ground fault detection device according to any one of claims 1 to 3, wherein the capacity acquisition unit acquires the value of the ground capacity by measurement. An information acquisition unit for acquiring information on the environment of the power supply system;
The said capacity | capacitance acquisition part acquires the value of the said ground capacity | capacitance by correct | amending the reference value of the said ground capacity | capacitance based on the information which the said information acquisition part acquired. The ground fault detection apparatus of any one of Claims.   A control program for causing a computer to function as the ground fault detection device according to claim 1, wherein the control program causes the computer to function as each unit. A control method for a ground fault detection device for detecting a ground fault in a power supply system including a DC power source for generating or charging / discharging,
A capacity acquisition step of acquiring a value of a ground capacity of the power supply system;
A resistance reference value setting step for setting a reference value of a ground fault resistance of the power supply system in a state where a ground fault has not occurred;
A time constant estimating step of estimating a reference time constant using the value of the ground capacity and the reference value of the ground fault resistance;
A measurement value for detecting the ground fault, a measurement step of measuring and acquiring a transient value and a measurement time of a measurement value that changes transiently according to a time constant of the power supply system,
And a ground fault determination step of determining the presence or absence of the ground fault based on the reference time constant, the transient value of the measurement value, and the measurement time.

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