Insulation resistance measurement device and method for measuring insulation resistance

Abstract

To provide an insulation resistance measurement device capable of measuring an insulation resistance.SOLUTION: An insulation resistance measurement device comprises: a first terminal; a second terminal; a discharge circuit that is connected between the first terminal and the second terminal; a voltage measurement unit that measures the voltage between the first terminal and the second terminal; a current measurement unit that measures the current flowing between the first terminal and the second terminal; a voltage application circuit that applies a voltage between the first terminal and the second terminal; and a control circuit that, in a first state in which the voltage application circuit does not apply the voltage and the discharge circuit is connected between the first terminal and the second terminal, acquires a first voltage value and a first current value from the voltage measurement unit and the current measurement unit, respectively, and disconnects the discharge circuit from at least one of the first terminal and the second terminal after having acquired the first voltage value and the first current value when a first value and a second value satisfy a prescribed condition, the first value being calculated on the basis of a voltage change amount in a prescribed period for the voltage value acquired from the voltage measurement unit, and the second value being calculated on the basis of the current value acquired from the current measurement unit or a current change amount in the prescribed period for said current value, and, in a second state in which the application voltage is applied by the voltage application circuit, acquires a second voltage value and a second current value from the voltage measurement unit and the current measurement unit, respectively, and calculates an insulation resistance on the basis of the first voltage value, the first current value, the second voltage value, and the second current value.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an insulation resistance measuring device and an insulation resistance measuring method. [Background technology]

[0002] For example, when measuring the ground insulation resistance of a solar cell, a method is known in which a discharge circuit is connected between the ground terminal and the positive or negative terminal of the solar cell, and the voltage and current between the terminals are measured without applying a voltage between the terminals, and then the discharge circuit is electrically separated from the terminals, and a voltage is applied between the terminals to measure the voltage and current between the terminals (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-99223 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a capacitance to the earth between the ground terminal and the positive or negative terminal of a solar cell. To measure the insulation resistance with high accuracy, the charge accumulated in the capacitance to the earth must be discharged before measuring the insulation resistance. For this reason, a discharge resistor is connected between the ground terminal and the positive or negative terminal of the solar cell, and then insulation resistance measurement begins after a certain waiting time has elapsed. However, if the charge accumulated in the capacitance to the earth is small, measurement does not begin during the waiting time even though the capacitance to the earth has been discharged, resulting in wasted time. If the charge accumulated in the capacitance to the earth is large, insulation resistance measurement begins before the capacitance to the earth is discharged, reducing the accuracy of the insulation resistance measurement.

[0005] An object of the present disclosure is to provide an insulation resistance measuring device and an insulation resistance measuring method that are capable of appropriately measuring insulation resistance. [Means for solving the problem]

[0006] According to an embodiment of the present disclosure, an insulation resistance measuring device includes a first terminal, a second terminal, a discharge circuit connected between the first terminal and the second terminal, a voltage measurement unit that measures a voltage between the first terminal and the second terminal, a current measurement unit that measures a current flowing between the first terminal and the second terminal, a voltage application circuit that applies an application voltage between the first terminal and the second terminal, and a first value calculated based on an amount of change in voltage over a predetermined period of time in a voltage value acquired from the voltage measurement unit, a current value acquired from the current measurement unit, or a previous value in a first state in which the voltage application circuit does not apply the application voltage and the discharge circuit is connected between the first terminal and the second terminal. and a control circuit that, when a second value calculated based on a current change amount for a predetermined period of time of the current value satisfies a predetermined condition, acquires a first voltage value and a first current value from the voltage measurement unit and the current measurement unit, respectively; after acquiring the first voltage value and the first current value, disconnects the discharge circuit from at least one of the first terminal and the second terminal and applies the application voltage to the voltage application circuit, acquires a second voltage value and a second current value from the voltage measurement unit and the current measurement unit, respectively; and calculates a first insulation resistance between the first terminal and the second terminal based on the first voltage value, the first current value, the second voltage value, and the second current value.

[0007] According to an embodiment of the present disclosure, in a first state in which no applied voltage is applied between a first terminal and a second terminal and a discharge circuit is connected between the first terminal and the second terminal, when a first value calculated based on a voltage change over a predetermined period of time in a voltage value acquired from a voltage measurement unit that measures the voltage between the first terminal and the second terminal, a current value acquired from a current measurement unit that measures the current flowing between the first terminal and the second terminal, or a second value calculated based on a current change over a predetermined period of time in the current value satisfies a predetermined condition, a first voltage value and a first current value are acquired from the voltage measurement unit and the current measurement unit, respectively. After acquiring the first voltage value and the first current value, in a second state in which the discharge circuit is disconnected from at least one of the first terminal and the second terminal and the applied voltage is applied between the first terminal and the second terminal, a second voltage value and a second current value are acquired from the voltage measurement unit and the current measurement unit, respectively. The insulation resistance between the first terminal and the second terminal is calculated based on the first voltage value, the first current value, the second voltage value, and the second current value. [Effects of the Invention]

[0008] According to the present disclosure, insulation resistance can be measured appropriately. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a device under test in which the first embodiment is used. [Figure 2] FIG. 2 is a block diagram of the insulation resistance measuring device according to the first embodiment. [Figure 3] 3(a) and 3(b) are equivalent circuit diagrams of the first and second states in the first embodiment. [Figure 4] FIG. 4 is a diagram showing voltage values ​​with respect to time in the first state. [Figure 5] FIG. 5 is a flowchart showing the operation of the control circuit in the first embodiment. [Figure 6] FIG. 6 is a flowchart showing the operation of the control circuit in the first modification of the first embodiment. [Figure 7] FIG. 7 is a block diagram of an insulation resistance measuring device according to the second embodiment. [Figure 8] FIG. 8 is a flowchart showing the operation of the control circuit in the second embodiment. [Figure 9] FIG. 9 is a flowchart showing the operation of the control circuit in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following embodiments are examples for embodying the technical ideas of the invention, and the present disclosure is not limited to the described configurations and numerical values. In each drawing, the same components are denoted by the same reference numerals, and duplicate explanations may be omitted as appropriate.

[0011] (First embodiment) FIG. 1 is a block diagram of a solar cell system in which the first embodiment is used. As shown in FIG. 1, the solar cell system 110 includes a solar cell string 40, a connection box 44, and a load 46. The solar cell string 40 includes a plurality of units, each of which includes a solar cell 41 (photovoltaic: PV) and a diode 42 connected in parallel, connected in series between a positive terminal P and a negative terminal N. The connection box 44 includes switches 45p and 45n. The switch 45p electrically connects or disconnects the positive terminal P and the load 46. The switch 45n electrically connects or disconnects the negative terminal N and the load 46. The load 46 is, for example, a downstream power supply system. An insulation resistance Rn and a capacitance to the ground Cn exist between the negative terminal N and the ground. An insulation resistance Rp and a capacitance to the ground Cp exist between the positive terminal P and the ground. The capacitances to the ground Cn and Cp increase as the voltage of the solar cell string 40 increases. The capacitances to the ground Cn and Cp are, for example, 0.1 μF to 10 μF. The insulation resistances Rn and Rp are, for example, 1 MΩ to 1000 MΩ.

[0012] As shown in FIG. 1 , when measuring insulation resistance Rn using insulation resistance measuring device 100, first, switches 45p and 45n of junction box 44 are disconnected. Terminal T1 of insulation resistance measuring device 100 is connected to ground terminal E in junction box 44. Then, terminal T2 is connected to negative terminal N in junction box 44. The insulation resistance measuring device 100 measures insulation resistance Rn. Then, when measuring insulation resistance Rp, terminal T2 of insulation resistance measuring device 100 is connected to positive terminal P in junction box 44 with switches 45p and 45n disconnected. The insulation resistance measuring device 100 measures insulation resistance Rp. Note that insulation resistances Rn and Rp are connected in parallel between ground terminal E and negative terminal N. Therefore, it is possible to measure at least one of insulation resistances Rn and Rp. In the following explanation, the parallel-connected insulation resistances Rn and Rp when measuring between the negative terminal N and the ground terminal E will be collectively referred to as the insulation resistance RN, and the parallel-connected insulation resistances Rp and Rn when measuring between the positive terminal P and the ground terminal E will be collectively referred to as the insulation resistance RP. The explanation will mainly focus on measuring the insulation resistance RN as an example. When measuring the insulation resistance RP, the same measurement method as for the insulation resistance RN can be used.

[0013] 2 is a block diagram of the insulation resistance measuring device according to the first embodiment. The insulation resistance measuring device 100 includes a voltage application circuit 11, a voltage measurement unit 12, a discharge circuit 13, a switch 14, a current measurement unit 15, a control circuit 16, and terminals T1 and T2.

[0014] In FIG. 2, terminal T1 (first terminal) is connected to a ground terminal E, and terminal T2 (second terminal) is connected to a negative terminal N or a positive terminal P (see FIG. 1). A voltage application circuit 11 applies an application voltage Va between terminals T1 and T2. The voltage of terminal T2 is, for example, positive relative to terminal T1. A voltage measurement unit 12 measures the voltage value between terminals T1 and T2. For example, the voltage measurement unit 12 has a resistor Rm. The voltage value measured by resistive division of the resistor Rm is output to the control circuit 16. The resistance value of the resistor Rm is, for example, 10 MΩ to 500 MΩ, and is 10 MΩ as an example.

[0015] The discharge circuit 13 is electrically connected between terminals T1 and T2. The discharge circuit 13 has a resistor Rd, one end of which is connected to terminal T1 via a current measuring unit 15 and the other end of which is connected to terminal T2. The resistance value of the resistor Rd is, for example, 100 kΩ to 1 MΩ, and is, for example, 500 kΩ. The resistance value of the resistor Rd is lower than the resistance value of the resistor Rm. The switch 14 electrically connects the discharge circuit 13 between terminals T1 and T2 or electrically disconnects the discharge circuit 13 from terminal T2 based on a control signal from the control circuit 16. The switch 14 may be provided between the discharge circuit 13 and terminal T1.

[0016] In FIG. 2, current measurement unit 15 measures the current flowing between terminal T1 and terminal T2. For example, when a voltage generated by voltage application circuit 11 is applied to the object to be measured, current measurement unit 15 measures the value of the current flowing from terminal T2 to the object to be measured (insulation resistance) to terminal T1. When the charge remaining in the capacitance component of the object to be measured is discharged by discharge circuit 13, current measurement unit 15 measures the value of the current flowing from the object to be measured to terminal T1 to current measurement unit 15 to discharge circuit 13 to terminal T2. Depending on the polarity of the charge accumulated in the object to be measured, the current may flow in the opposite direction. Current measurement unit 15 outputs the measured current value to control circuit 16. Control circuit 16 acquires the voltage value measured by voltage measurement unit 12 and the current value measured by current measurement unit 15. For example, the outputs of voltage measurement unit 12 and current measurement unit 15 are analog signals. The control circuit 16 converts the analog signals output by the voltage measurement unit 12 and the current measurement unit 15 into digital signals and acquires the converted signals as voltage and current values, respectively. The control circuit 16 controls the voltage application circuit 11 and the switch 14 based on the acquired voltage and current values. The control circuit 16 calculates the insulation resistance based on the voltage and current values. At least some of the functions of the control circuit 16 may be executed by a processor such as a CPU (Central Processing Unit) in cooperation with software. At least some of the functions of the control circuit 16 may be executed by a dedicated hardware circuit.

[0017] 3(a) and 3(b) are equivalent circuit diagrams of the first and second states in the first embodiment. An example will be described in which the insulation resistance RN is measured. As shown in FIG. 3(a), the first state is a state in which the voltage application circuit 11 does not apply the application voltage Va and the discharge circuit 13 is electrically connected between terminals T1 and T2. The measurements of the voltage measurement unit 12 and the current measurement unit 15 are taken as the voltage value V1 and the current value I1, respectively. An insulation resistance Rp and a capacitance to earth Cp are connected in parallel between terminals T1 and T2, and a solar cell string 40 is connected in series to the insulation resistance Rp and the capacitance to earth Cp. The electromotive force of the solar cell string 40 is Vc. An insulation resistance Rn and a capacitance to earth Cn are connected in parallel to the electromotive force Vc, the insulation resistance Rp, and the capacitance to earth Cp between terminals T1 and T2.

[0018] The insulation resistance measured at this time is RN. The voltage applied across the insulation resistance RN is V1 + Vc, so we obtain Equation 1. Note that the resistance value of the insulation resistance RN is RN. V1+Vc=RN×I1 Formula 1

[0019] As shown in Fig. 3(b), the second state is a state in which the discharge circuit 13 is electrically disconnected from at least one of the terminals T1 and T2 and an applied voltage Va is applied to the voltage application circuit 11. The applied voltage Va is, for example, 200V to 2000V, and is 1500V as an example. The measured values ​​of the voltage measurement unit 12 and the current measurement unit 15 are a voltage value V2 and a current value I2, respectively. The voltage applied across the insulation resistance RN is V2 + Vc, and thus Equation 2 is obtained. V2+Vc=RN×I2 Formula 2

[0020] From equations 1 and 2, the insulation resistance RN can be calculated using equation 3. RN=(V2-V1) / (I2-I1) Equation 3) In this way, the insulation resistance RN can be calculated based on the voltage values ​​V1 and V2 and the current values ​​I1 and I2.

[0021] FIG. 4 is a diagram showing voltage values ​​versus time in the first state. The horizontal axis of FIG. 4 indicates the time when switch 14 is turned on, with 0 as the time. The vertical axis indicates voltage value V measured by voltage measurement unit 12. Electric charge is accumulated in earth capacitance Cn. Therefore, when discharge circuit 13 is connected between terminals T1 and T2, the charge in earth capacitance Cn is discharged via discharge circuit 13. As a result, voltage value V exponentially decays over time and reaches a constant voltage value V0. If voltage value V1 and current value I1 are measured before voltage value V reaches voltage value V0, the measurement error of insulation resistance RN will increase.

[0022] In the comparative example, the voltage value V1 and the current value I1 are measured after a certain waiting time (e.g., several seconds) has elapsed since the discharge circuit 13 was connected between terminals T1 and T2. However, the discharge time depends on the earth capacitance CN (the capacitance connected between terminals T1 and T2 in FIG. 3(a)), the insulation resistance RN, the magnitude of the resistance Rd of the discharge circuit 13, and the amount of charge stored in the earth capacitance CN. If the waiting time is too long compared to the discharge time, a long waiting time will occur after the discharge from the earth capacitance CN has finished, and the waiting time will be wasted. On the other hand, if the waiting time is too short compared to the discharge time, the voltage value V1 and the current value I1 will be measured while the charge stored in the earth capacitance CN is still in the middle of discharging, and the accuracy of the insulation resistance RN will deteriorate.

[0023] As shown in FIG. 4, in the first embodiment, measurement of the voltage value V1 and the current value I1 is started based on the rate of change ΔV / Δt of the voltage value V with respect to time. For example, when ΔV / Δt is equal to or greater than a threshold value Th, such as ΔVa / Δt, the discharge of the charge in the earth capacitance CN is insufficient. Therefore, the first state is maintained. When ΔV / Δt is smaller than the threshold value Th, such as ΔVb / Δt, it is determined that the discharge of the charge in the earth capacitance CN is sufficient, and measurement of the voltage value V1 and the current value I1 is started. This makes it possible to start measurement of the voltage value V1 and the current value I1 when the discharge is almost complete, regardless of the length of the discharge time.

[0024] Depending on the charge stored in the earth capacitance CN, the voltage value may increase over time and reach a constant voltage value V0. For this reason, the absolute value of the rate of change |ΔV / Δt| is used for the determination. The specific control flow of the control circuit 16 is explained below.

[0025] 5 is a flowchart showing the operation of the control circuit in the first embodiment. As shown in FIG. 5, the control circuit 16 starts measurement (step S10). For example, the user connects terminal T1 to the ground terminal E and terminal T2 to the N terminal. Then, the user turns on the measurement start switch. When the PV measurement start switch is turned on, the control circuit 16 starts measurement.

[0026] As shown in FIG. 5, the control circuit 16 is set to the first state (step S11). Specifically, the control circuit 16 does not generate the applied voltage Va to the voltage application circuit 11, and sets the voltage application circuit 11 to a high impedance. The control circuit 16 turns on the switch 14 to electrically connect the discharge circuit 13 between the terminals T1 and T2. Next, the control circuit 16 acquires a voltage value V from the voltage measurement unit 12 (step S12). Next, the control circuit 16 calculates a rate of change ΔV / Δt of the voltage value based on the acquired voltage value V (step S13). For example, the control circuit 16 converts the analog output signal of the voltage measurement unit 12 into a digital voltage value V at a constant sampling period Δt. Therefore, the control circuit 16 divides the difference ΔV between the previously sampled voltage value and the currently sampled voltage value by Δt to calculate the rate of change ΔV / Δt. In step S13, the control circuit 16 may calculate the difference ΔV based on the acquired voltage value V. The difference ΔV corresponds to the amount of voltage change during the predetermined period Δt.

[0027] Next, the control circuit 16 determines whether the absolute value of the rate of change |ΔV / Δt| is equal to or greater than the threshold value Th (step S14). In step S14, the control circuit 16 may determine whether the absolute value |ΔV| of the difference ΔV is equal to or greater than the threshold value Th. If the determination is Yes, the process returns to step S12. If the determination is No, the control circuit 16 acquires the voltage value V1 and the current value I1 from the voltage measurement unit 12 and the current measurement unit 15, respectively (step S15).

[0028] Next, the control circuit 16 changes the first state to the second state (step S16). Specifically, the control circuit 16 turns off the switch 14 to electrically disconnect the discharge circuit 13 from the terminal T2. The control circuit 16 causes the voltage application circuit 11 to generate the application voltage Va. Next, the control circuit 16 acquires the voltage value V2 and the current value I2 from the voltage measurement unit 12 and the current measurement unit 15, respectively (step S17).

[0029] Next, the control circuit 16 calculates the insulation resistance RN (step S18). Specifically, the control circuit 16 measures the insulation resistance RN using Equation 3. Equation 3 is an example, and the insulation resistance RN may be calculated using another method. Thereafter, the control circuit 16 ends the measurement (step S19). Specifically, it causes the voltage application circuit 11 to stop applying the applied voltage Va. Next, the control circuit 16 outputs the calculated resistance value of the insulation resistance RN (step S20). Specifically, the control circuit 16 may cause the display unit to display the measured value of the insulation resistance RN. The control circuit 16 may also output the measured value of the insulation resistance RN to an external device. Then, the process ends.

[0030] 5 , in the insulation resistance measuring device 100 of the first embodiment, when the absolute value |ΔV| of the voltage change amount of the voltage value V or the absolute value |ΔV / Δt| of the rate of change of the voltage value V with respect to time acquired from the voltage measuring unit 12 is equal to or greater than the threshold value Th, the control circuit 16 returns to step S12 and maintains the first state. When |ΔV| or |ΔV / Δt| is smaller than the threshold value Th in the first state, the control circuit 16 proceeds to step S15, and acquires the voltage value V1 (first voltage value) and the current value I2 (first current value) from the voltage measuring unit 12 and the current measuring unit 15, respectively, while maintaining the first state. Thereafter, as in step S16, the control circuit 16 enters the second state and acquires the voltage value V2 (second voltage value) and the current value I2 (second current value) from the voltage measuring unit 12 and the current measuring unit 15, respectively, as in step S17. As in step S18, the control circuit 16 calculates the insulation resistance RN or RP between the terminals T1 and T2 based on the voltage values ​​V1, V2 and the current values ​​I1 and I2.

[0031] As a result, in FIG. 4, the voltage value V1 and the current value I1 can be measured at the point when the voltage value V approaches the voltage value V0. This allows for an appropriate waiting time before measurement begins and improves measurement accuracy. The threshold value Th may be determined in advance and stored in a memory or the like. The threshold value Th may be changed for each measurement. The threshold value Th may be set based on the voltage value V when the time t is 0. For example, when the output voltage of the photovoltaic string 40 is several kV, the voltage of the earth capacitance CN may be several hundred volts. In such a case, the threshold value Th may be set to 10 V / sec to 1 V / sec.

[0032] As described above, in the first state, control circuit 16 may proceed to step S15 when the first value calculated based on the difference ΔV corresponding to the amount of voltage change in the voltage value V acquired from voltage measurement unit 12 over a predetermined period Δt satisfies a predetermined condition. The first value is, for example, the absolute value of the amount of voltage change |ΔV| or the absolute value of the voltage change rate |ΔV / Δt|. The predetermined condition may be, for example, that the absolute value of the amount of voltage change or the absolute value of the voltage change rate is smaller than threshold value Th.

[0033] (Modification 1 of the first embodiment) FIG. 6 is a flowchart showing the operation of the control circuit in Modification 1 of the first embodiment. As shown in FIG. 6, the operations of steps S10 and S11 are the same as those in FIG. 5. Next, the control circuit 16 acquires the current value I from the current measurement unit 15 (step S12A). Next, the control circuit 16 calculates the rate of change ΔI / Δt of the current value based on the acquired current value I (step S13A). For example, the control circuit 16 calculates the rate of change ΔI / Δt by dividing the difference ΔI between the previously sampled current value and the currently sampled current value by Δt. In step S13A, the control circuit 16 may calculate the difference ΔI based on the acquired current value I. The difference ΔI corresponds to the amount of current change during a predetermined period Δt.

[0034] Next, the control circuit 16 determines whether the absolute value of the rate of change |ΔI / Δt| is equal to or greater than a threshold value Th (step S14A). In step S14A, the control circuit 16 may determine whether the absolute value |I| of the current value I is equal to or greater than a threshold value Th. Alternatively, the control circuit 16 may determine whether the absolute value |ΔI| of the difference ΔI is equal to or greater than a threshold value Th. If the result is Yes, the process returns to step S12A. If the result is No, the process proceeds to step S15. The operations from step S15 onwards are the same as those in FIG. 5.

[0035] When the discharge circuit 13 is connected between the terminals T1 and T2, the charge of the earth capacitance Cn is discharged via the discharge circuit 13. As a result, similar to Fig. 4, the current value I exponentially decays over time and becomes 0. Therefore, as in steps S12A to S14A, when |I|, |ΔI|, or |I / Δt| is equal to the threshold value Th, the process may proceed to step S15.

[0036] As in the first modification of the first embodiment, in the first state, the control circuit 16 may proceed to step S15 when the current value I acquired from the current measurement unit 15 or a second value calculated based on a difference ΔI corresponding to the amount of current change in the current value I during a predetermined period Δt satisfies a predetermined condition. The second value is, for example, the absolute value of the amount of current change |ΔI| or the absolute value of the rate of current change |ΔI / Δt|. The predetermined condition may be, for example, that the absolute value of the current value |I|, the absolute value of the amount of current change, or the absolute value of the rate of current change is smaller than a threshold value Th.

[0037] 3(a), in the first state, current measurement unit 15 is connected in series with discharge circuit 13 between terminals T1 and T2, and voltage measurement unit 12 is connected in parallel to discharge circuit 13 and in series with current measurement unit 15. As shown in FIG. 3(b), in the second state, current measurement unit 15 is connected in series with voltage application circuit 11 between terminals T1 and T2, and voltage measurement unit 12 is connected in parallel to voltage application circuit 11 and in series with current measurement unit 15. With these connections, the resistance value of insulation resistance RN can be calculated using the voltage value V1 and current value I1 measured in the first state and the voltage value V2 and current value I1 measured in the second state, as shown in Equation 3.

[0038] 2, the discharge circuit 13 has a resistor Rd (first resistor) connected between the terminals T1 and T2, which allows the charge of the earth capacitance CN to be discharged via the discharge circuit 13.

[0039] As shown in FIG. 1 , terminal T1 is connected to the positive terminal P or negative terminal N of the solar cell 41, and terminal T2 is connected to the positive terminal P or negative terminal N of the solar cell 41. When exposed to light, the solar cell 41 generates an electromotive force. Therefore, the insulation resistances RN and RP can be measured using the voltage value V1 and current value I1 in the first state and the voltage value V2 and current value I2 in the second state. In the solar cell string 40, the solar cells 41 are cascade-connected to increase the voltage. As the number of cascade-connected solar cells increases, the earth capacitances Cn and Cp increase. This increases the discharge time in FIG. 4 . Therefore, if the standby time is extended to match the solar cell string 40 with large earth capacitances Cn and Cp, as in the comparative example, the standby time will be long when measuring the insulation resistance of the solar cell string 40 with small earth capacitances Cn and Cp. Therefore, by using the insulation resistance measuring device 100 of the first embodiment to measure the insulation resistance RN of the solar cell 41, the insulation resistance can be measured appropriately.

[0040] The insulation resistance measuring device 100 may measure insulation resistance other than that of the solar cell 41. For example, the insulation resistance measuring device 100 can measure the insulation resistance of a system in which an electromotive force is generated between terminals.

[0041] (Second embodiment) Fig. 7 is a block diagram of an insulation resistance measuring apparatus according to the second embodiment. As shown in Fig. 7, an insulation resistance measuring apparatus 102 according to the second embodiment includes a discharge circuit 13A, a switch 14A, a resistor R10, a switch 17, an input unit 18, and a protection circuit 19 in addition to the components of the insulation resistance measuring apparatus 100 according to the first embodiment.

[0042] The discharge circuit 13A and the switch 14A are connected in parallel to the discharge circuit 13 and the switch 14 between the terminals T1 and T2. The discharge circuit 13A has a resistor RdA, one end of which is connected to the terminal T1 via the current measuring unit 15 and the other end of which is connected to the terminal T2. The resistance value of the resistor RdA is different from the resistance value of the resistor Rd. For example, the resistance value of the resistor RdA is lower than the resistance value of the resistor Rd. The switch 14A electrically connects the discharge circuit 13A between the terminals T1 and T2 or electrically disconnects the discharge circuit 13A from the terminal T2 based on a control signal from the control circuit 16. The switch 14A may be provided between the discharge circuit 13 and the terminal T1.

[0043] Resistor R10 is connected between voltage application circuit 11 and voltage measurement unit 12. Resistor R10 has resistors R11 and R12 connected in series. Switch 17 is connected in parallel with resistor R12 and in series with resistor R11. Information used by the user to operate insulation resistance measuring device 102 is input to input unit 18. Input unit 18 is, for example, an operation button or an operation switch.

[0044] Protection circuit 19 includes switch 19A connected in parallel to current measurement unit 15. Switch 19A is turned off when there is no overcurrent during discharge. This allows current measurement unit 15 to measure the current flowing through discharge circuit 13 or 13A. If an overcurrent flows during discharge, current measurement unit 15 detects the overcurrent and turns on switch 19A. This allows the current flowing through current measurement unit 15 to be bypassed to protection circuit 19, thereby protecting current measurement unit 15.

[0045] 8 is a flowchart showing the operation of the control circuit in the second embodiment. In FIG. 8, in step S11, control circuit 16 turns on switch 14 and turns off switch 14A. This connects discharge circuit 13 between terminals T1 and T2. Next, in step S12, control circuit 16 acquires voltage value V from voltage measurement unit 12. Next, control circuit 16 determines whether the absolute value |V| of voltage value V is equal to or greater than threshold voltage Th2 (step S21). If No, the process proceeds to step S13.

[0046] If the answer is Yes in step S21, the control circuit 16 switches the discharge circuit 13 to the discharge circuit 13A (step S22). Specifically, the control circuit 16 turns off the switch 14 and turns on the switch 14A. As a result, the discharge circuit 13A is connected between the terminals T1 and T2 instead of the discharge circuit 13. Then, the process proceeds to step S12. The rest of the flow is the same as in FIG. 5 of the first embodiment, and a description thereof will be omitted.

[0047] As shown in FIG. 8, when the absolute value |V| of the voltage value V acquired from the voltage measurement unit 12 in the first state is equal to or greater than the threshold voltage Th2, the discharge circuit 13 is switched to the discharge circuit 13A. This changes the resistance value of the resistor RdA of the discharge circuit 13A to a lower value. When the absolute value |V| of the voltage value V is high, a large amount of charge is stored in the earth capacitance CN. Therefore, by lowering the resistor RdA of the discharge circuit 13A, the discharge time can be shortened. For example, the resistance value of the resistor RdA is equal to or less than 1 / 2 or 1 / 5 of the resistance value of the resistor Rd.

[0048] In step S21, when the control circuit 16 acquires the voltage value V for the first time after entering the first state, it determines whether the absolute value |V| of the voltage value V is greater than or equal to the threshold voltage Th2, and when the control circuit 16 acquires the voltage value V for the second time or later, it may proceed to step S13 without determining whether the absolute value |V| of the voltage value V is greater than or equal to the threshold voltage Th2.

[0049] After step S14, the control circuit 16 may change the resistance value of the resistor Rd of the discharge circuit 13 based on |ΔV / Δt|. For example, when the rate of decrease of |ΔV / Δt| is smaller than a predetermined value, the control circuit 16 reduces the resistance value of the resistor Rd. This shortens the discharge time.

[0050] In this way, in the first state, the control circuit 16 changes the resistance value of the resistor Rd based on the voltage value V or the rate of change ΔV / Δt (first value) obtained from the voltage measurement unit 12. This makes it possible to adjust the discharge time.

[0051] As a method for changing the resistance value of the resistor in the discharge circuit, an example has been described in which resistors Rd and RdA are prepared and switches 14 and 14A are used to switch between resistors Rd and RdA, but the resistance value of the resistor in the discharge circuit may also be switched by combining one or more switches and multiple resistors.

[0052] Returning to Fig. 7, a resistor R10 (second resistor) is connected in series with the voltage application circuit 11 between terminals T1 and T2. The resistor R10 has resistors R11 and R12 connected in series, and a switch 17 connected in parallel with the resistor R12. The switch 17 is turned on or off in response to a command from the control circuit 16. The resistor R10 has the function of limiting overcurrent.

[0053] 9 is a flowchart showing the operation of the control circuit in the second embodiment. As shown in FIG. 9, the control circuit 16 acquires mode information from the input unit 18 (step S30). The modes include a first mode and a second mode. The first mode is a mode in which the insulation resistance RN (first insulation resistance) is measured according to the flow of FIG. 5 or FIG. 8. The second mode is a mode in which the insulation resistance of an object to be measured that does not generate an electromotive force is measured, for example.

[0054] Next, the control circuit 16 determines whether the acquired information is the first mode or the second mode (step S31). If the information is the first mode in step S31, the control circuit 16 turns off the switch 17 (step S38), and then the control circuit 16 measures the insulation resistance in the first mode (step S39). Specifically, the control circuit 16 measures the insulation resistance RN according to the flow of FIG. 5 or FIG. 8, and then the process ends.

[0055] In step S31, when the second mode is selected, the control circuit 16 performs steps S32 to S37 for second-mode measurement. First, the control circuit 16 turns on the switch 17 (step S32). Next, the control circuit 16 sets the switch 17 to the second state (step S33), similar to step S16 in FIGS. 5 and 8. Next, the control circuit 16 acquires a voltage value V3 (third voltage value) and a current value I3 (third current value) from the voltage measurement unit 12 and the current measurement unit 15, respectively, similar to step S17 in FIGS. 5 and 8 (step S34). Next, the control circuit 16 calculates an insulation resistance R2 (second insulation resistance) between terminals T1 and T2 based on the acquired voltage value V3 and current value I3 (step S35). Specifically, the control circuit 16 sets the insulation resistance R2 to, for example, V3 / I3. Next, the control circuit 16 ends the measurement (step S36), similar to step S19 in FIGS. 5 and 8. Next, the control circuit 16 outputs information about the insulation resistance R2 (step S37), similar to step S20 in Figures 5 and 8. Then, the process ends.

[0056] Depending on the type of insulation resistance to be measured, the resistance value of the resistor connected in series to voltage application circuit 11 may be changed. For example, when insulation resistance measuring device 102 is used to measure the insulation resistance of a solar cell, there is a possibility that a high voltage will be applied to terminal T2, so switch 17 is turned off and the resistance value of resistor R10 connected in series to voltage application circuit 11 is increased. On the other hand, when insulation resistance measuring device 102 is used to measure the insulation resistance of an object that does not generate an electromotive force, a high voltage will not be applied to terminal T2. Therefore, switch 17 is turned on and the resistance value of the resistor connected in series to voltage application circuit 11 is decreased.

[0057] As described above, in step S30 of Figure 9, control circuit 16 acquires information on whether to select the first mode or the second mode. In steps S31, S32, and S33, control circuit 16 changes the resistance value of resistor R10 based on the acquired information. This enables insulation resistance measuring device 102 to measure both insulation resistance RN or RP and insulation resistance R2, which is a measurement target that does not generate electromotive force.

[0058] The control circuit 16 sets the resistance value of the resistor R10 when the acquired information indicates the first mode to be higher than the resistance value of the resistor R10 when the acquired information indicates the second mode, thereby making it possible to increase the resistance value of the resistor R10 in the first mode, in which a high voltage may be applied to the terminal T2.

[0059] Although an example has been described in which resistors R11 and R12 and switch 17 are used as a method for changing the resistance value of resistor R10, the resistance value of resistor R10 may be switched by combining one or more switches with multiple resistors.

[0060] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims. [Explanation of symbols]

[0061] 11: Voltage application circuit 12: Voltage measurement section 13, 13A: Discharge circuit 14, 14A, 17: Switch 15: Current measurement section 16: Control circuit 18: Input section 19: Protection circuit 40: Solar cell string 41: Solar cell 42: Diode

Claims

1. A first terminal; A second terminal; a discharge circuit connected between the first terminal and the second terminal; a voltage measurement unit that measures a voltage between the first terminal and the second terminal; a current measuring unit that measures a current flowing between the first terminal and the second terminal; a voltage application circuit that applies a voltage between the first terminal and the second terminal; In a first state in which the voltage application circuit does not apply the applied voltage and the discharge circuit is connected between the first terminal and the second terminal, when a first value calculated based on a voltage change amount in a predetermined period of a voltage value acquired from the voltage measurement unit, a current value acquired from the current measurement unit, or a second value calculated based on a current change amount in the current value in a predetermined period of time satisfies a predetermined condition, a first voltage value and a first current value are acquired from the voltage measurement unit and the current measurement unit, respectively; after acquiring the first voltage value and the first current value, in a second state in which the discharge circuit is disconnected from at least one of the first terminal and the second terminal and the voltage application circuit is caused to apply the application voltage, acquiring a second voltage value and a second current value from the voltage measurement unit and the current measurement unit, respectively; a control circuit that calculates a first insulation resistance between the first terminal and the second terminal based on the first voltage value, the first current value, the second voltage value, and the second current value; An insulation resistance measuring device comprising:

2. In the first state, the current measurement unit is connected in series with the discharge circuit between the first terminal and the second terminal, and the voltage measurement unit is connected in parallel with the discharge circuit and in series with the current measurement unit; 2. The insulation resistance measuring device according to claim 1, wherein in the second state, the current measuring unit is connected in series with the voltage application circuit between the first terminal and the second terminal, and the voltage measuring unit is connected in parallel with the voltage application circuit and in series with the current measuring unit.

3. 3. The insulation resistance measuring device according to claim 1, wherein the first terminal is connected to a ground terminal of a solar cell, and the second terminal is connected to a positive terminal or a negative terminal of the solar cell.

4. 3. The insulation resistance measuring device according to claim 1, wherein the discharge circuit includes a first resistor connected between the first terminal and the second terminal.

5. 5. The insulation resistance measuring device according to claim 4, wherein the control circuit, in the first state, changes the resistance value of the first resistor based on the voltage value acquired from the voltage measuring unit or the first value.

6. a second resistor connected in series with the voltage application circuit between the first terminal and the second terminal; 3. The insulation resistance measuring device according to claim 1, wherein the control circuit acquires information on whether to select a first mode in which the first insulation resistance is measured or a second mode in which the first state is not implemented and a third voltage value and a third current value are acquired from the voltage measuring unit and the current measuring unit, respectively, in the second state, and a second insulation resistance between the first terminal and the second terminal is calculated based on the third voltage value and the third current value, and changes the resistance value of the second resistor based on the acquired information.

7. 7. The insulation resistance measuring device according to claim 6, wherein the control circuit sets the resistance value of the second resistor when the information indicates the first mode higher than the resistance value of the second resistor when the information indicates the second mode.

8. 3. The insulation resistance measuring device according to claim 1, wherein the predetermined condition is that the absolute value of the voltage change amount or the absolute value of the voltage change rate with respect to time of the voltage value acquired from the voltage measuring unit is smaller than a threshold value.

9. 3. The insulation resistance measuring device according to claim 1, wherein the predetermined condition is a condition in which an absolute value of the amount of current change, an absolute value of the current value acquired from the current measuring unit, or an absolute value of a current change rate with respect to time of the current value is smaller than a threshold value.

10. In a first state in which no voltage is applied between a first terminal and a second terminal and a discharge circuit is connected between the first terminal and the second terminal, when a first value calculated based on a voltage change amount in a predetermined period of time in a voltage value acquired from a voltage measurement unit that measures the voltage between the first terminal and the second terminal, a current value acquired from a current measurement unit that measures the current flowing between the first terminal and the second terminal, or a second value calculated based on a current change amount in the current value in a predetermined period of time satisfies a predetermined condition, a first voltage value and a first current value are acquired from the voltage measurement unit and the current measurement unit, respectively; after acquiring the first voltage value and the first current value, in a second state in which the discharge circuit is disconnected from at least one of the first terminal and the second terminal and the applied voltage is applied between the first terminal and the second terminal, a second voltage value and a second current value are acquired from the voltage measurement unit and the current measurement unit, respectively; an insulation resistance between the first terminal and the second terminal calculated based on the first voltage value, the first current value, the second voltage value, and the second current value;

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