Insulation resistance measuring device and insulation resistance measuring method

Abstract

The insulation resistance measuring device of the present application includes a first terminal, a second terminal, a discharge circuit connected between the first terminal and the second terminal, a voltage measuring unit that measures the voltage between the first terminal and the second terminal, a current measuring unit that measures the 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 control circuit that, 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, acquires a first voltage value and a first current value from the voltage measuring unit and the current measuring unit when a first value calculated based on the voltage variation amount within a prescribed period of the voltage value acquired from the voltage measuring unit, the current value acquired from the current measuring unit, or a second value calculated based on the current variation amount within a prescribed period of the current value satisfies a prescribed condition, acquires a second voltage value and a second current value from the voltage measuring unit and the current measuring unit 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 applies the application voltage after the first voltage value and the first current value are acquired, 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.

Description

Technical Field

[0001] This disclosure relates to an insulation resistance measuring device and a method for measuring insulation resistance. Background Technology

[0002] For example, when measuring the insulation resistance to ground in a solar cell, there is a known method that involves connecting a discharge circuit between the grounding terminal and the positive or negative terminal of the solar cell, and measuring the voltage and current between the terminals without applying a voltage between them. Then, the discharge circuit is electrically disconnected from the terminals, a voltage is applied between the terminals, and the voltage and current between the terminals are measured (e.g., Patent Document 1).

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2016-99223 Summary of the Invention The problem that the invention aims to solve A capacitance to ground exists between the grounding terminal and either the positive or negative terminal of a solar cell. To determine high-precision insulation resistance, the insulation resistance is measured after the charge accumulated in the capacitance to ground has been discharged. Therefore, after connecting a discharge resistor between the grounding terminal and either the positive or negative terminal of the solar cell, the insulation resistance measurement begins after a fixed waiting time. However, if the charge accumulated in the capacitance to ground is small, the measurement may not begin until after the capacitance has completely discharged, thus increasing the invalid time. If the charge accumulated in the capacitance to ground is large, the insulation resistance measurement begins before the capacitance has completely discharged, resulting in reduced measurement accuracy.

[0004] The purpose of this disclosure is to provide an insulation resistance measuring device and a method for appropriately measuring insulation resistance.

[0005] Solution for solving the problem According to an embodiment of this 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 measuring unit for measuring the voltage between the first terminal and the second terminal; a current measuring unit for measuring the current flowing between the first terminal and the second terminal; a voltage applying circuit for applying an applied voltage between the first terminal and the second terminal; and a control circuit, in a first state where the voltage applying 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 the voltage change over a predetermined period based on the voltage value obtained from the voltage measuring unit, and the voltage obtained from the current measuring unit... When the current value obtained, or the second value calculated based on the current change within a specified period of the current value, meets the specified conditions, a first voltage value and a first current value are obtained from the voltage measuring unit and the current measuring unit, respectively. After obtaining the first voltage value and the first current value, in a second state where the discharge circuit is disconnected from at least one of the first terminal and the second terminal and the voltage applying circuit is applied to the applied voltage, a second voltage value and a second current value are obtained from the voltage measuring unit and the current measuring unit, respectively. Based on the first voltage value, the first current value, the second voltage value, and the second current value, a first insulation resistance between the first terminal and the second terminal is calculated.

[0006] According to an embodiment of this disclosure, in a first state where no voltage is applied between the first terminal and the second terminal and a discharge circuit is connected between the first terminal and the second terminal, when a first value calculated based on the voltage change over a predetermined period from a voltage measuring unit that measures the voltage between the first terminal and the second terminal, a current value obtained from a current measuring unit that measures the current flowing between the first terminal and the second terminal, or a second value calculated based on the current change over a predetermined period from the current value, satisfies a predetermined condition, a first voltage value and a first current value are obtained from the voltage measuring unit and the current measuring unit, respectively. After obtaining the first voltage value and the first current value, in a second state where 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 obtained from the voltage measuring unit and the current measuring unit, respectively. Based on the first voltage value, the first current value, the second voltage value, and the second current value, the insulation resistance between the first terminal and the second terminal is calculated.

[0007] Invention Effects According to this disclosure, insulation resistance can be properly measured. Attached Figure Description

[0008] Figure 1 This is a block diagram of the measuring device using the first embodiment.

[0009] Figure 2 This is a block diagram of the insulation resistance measuring device according to the first embodiment.

[0010] Figure 3A This is the equivalent circuit diagram of the first state in the first embodiment.

[0011] Figure 3B This is the equivalent circuit diagram of the second state in the first embodiment.

[0012] Figure 4 It is a graph showing the voltage value in the first state relative to time.

[0013] Figure 5 This is a flowchart illustrating the operation of the control circuit in the first embodiment.

[0014] Figure 6 This is a flowchart illustrating the operation of the control circuit in a variation of the first embodiment, Example 1.

[0015] Figure 7 This is a block diagram of the insulation resistance measuring device according to the second embodiment.

[0016] Figure 8 This is a flowchart illustrating the operation of the control circuit in the second embodiment.

[0017] Figure 9 This is a flowchart illustrating the operation of the control circuit in the second embodiment. Detailed Implementation

[0018] Hereinafter, the embodiments for carrying out this disclosure will be described in detail with reference to the accompanying drawings. The embodiments described below are examples for embodying the technical concept of the invention and do not limit this disclosure to the described configurations or values. Furthermore, in the accompanying drawings, the same reference numerals are used to label the same components, and sometimes repeated descriptions are appropriately omitted.

[0019] (First Implementation) Figure 1 This is a block diagram of a solar cell system employing the first embodiment. (Example) Figure 1As shown, the solar cell system 110 includes a solar cell string 40, a junction box 44, and a load 46. The solar cell string 40 has multiple units connected in series between the positive terminal P and the negative terminal N, each consisting of a solar cell 41 (PV: Photovoltaic) and a diode 42 connected in parallel. The junction box 44 includes switches 45p and 45n. Switch 45p electrically connects or disconnects the positive terminal P from the load 46. Switch 45n electrically connects or disconnects the negative terminal N from the load 46. The load 46 is, for example, a downstream power supply system. There is an insulation resistance Rn and a capacitance to ground Cn between the negative terminal N and the ground terminal. There is an insulation resistance Rp and a capacitance to ground Cp between the positive terminal P and the ground terminal. If the solar cell string 40 is subjected to a higher voltage, the capacitances to ground Cn and Cp increase. The capacitances to ground Cn and Cp are, for example, 0.1μF to 10μF. The insulation resistances Rn and Rp are, for example, 1MΩ to 1000MΩ.

[0020] like Figure 1 As shown, when measuring the insulation resistance Rn using the insulation resistance measuring device 100, firstly, switches 45p and 45n of the junction box 44 are set to non-connected. Terminal T1 of the insulation resistance measuring device 100 is connected to the grounding terminal E inside the junction box 44. Then, terminal T2 is connected to the negative terminal N inside the junction box 44. The insulation resistance measuring device 100 measures the insulation resistance Rn. Then, when measuring the insulation resistance Rp, with switches 45p and 45n set to non-connected, terminal T2 of the insulation resistance measuring device 100 is connected to the positive terminal P inside the junction box 44. The insulation resistance measuring device 100 measures the insulation resistance Rp. Furthermore, the insulation resistances Rn and Rp are connected in parallel between the grounding terminal E and the negative terminal N. Therefore, it is possible to measure only at least one of the insulation resistances Rn and Rp. In the following explanation, the insulation resistances Rn and Rp connected in parallel when measuring between the negative terminal N and the grounding terminal E will be collectively referred to as insulation resistance RN. Similarly, the insulation resistances Rp and Rn connected in parallel when measuring between the positive terminal P and the grounding terminal E will be collectively referred to as insulation resistance RP. The explanation will primarily focus on measuring insulation resistance RN. When measuring insulation resistance RP, the same measurement method as for insulation resistance RN can be used.

[0021] Figure 2 This 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 measuring unit 12, a discharge circuit 13, a switch 14, a current measuring unit 15, a control circuit 16, and terminals T1 and T2.

[0022] exist Figure 2In the middle, terminal T1 (first terminal) is connected to ground terminal E, and terminal T2 (second terminal) is connected to negative terminal N or positive terminal P (refer to...). Figure 1 The voltage application circuit 11 applies an applied voltage Va between terminals T1 and T2. The voltage at terminal T2 is positive, for example, relative to terminal T1. The voltage measuring unit 12 measures the voltage value between terminals T1 and T2. For example, the voltage measuring unit 12 has a resistor Rm. The voltage value measured by dividing the resistance of resistor Rm is output to the control circuit 16. The resistance value of resistor Rm is, for example, 10 MΩ to 500 MΩ, and is 10 MΩ as an example.

[0023] 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 resistor Rd is, for example, 100kΩ to 1MΩ, and 500kΩ is an example. The resistance value of resistor Rd is lower than that of resistor Rm. The switch 14, based on a control signal from the control circuit 16, electrically connects the discharge circuit 13 between terminals T1 and T2, or electrically disconnects the discharge circuit 13 from terminal T2. The switch 14 may also be located between the discharge circuit 13 and terminal T1.

[0024] exist Figure 2In this circuit, the current measuring unit 15 measures the current flowing between terminals T1 and T2. For example, when an applied voltage generated by the voltage application circuit 11 is applied to the test object, the current measuring unit 15 measures the current value flowing along the path from terminal T2 to the test object (insulation resistance) to terminal T1. Additionally, when the discharge circuit 13 discharges the charge remaining in the capacitance component of the test object, the current measuring unit 15 measures the current value flowing along the path from the test object to terminal T1 to the current measuring unit 15 to the discharge circuit 13 to terminal T2. Depending on the polarity of the charge accumulated in the test object, the current may sometimes flow in the opposite direction. The current measuring unit 15 outputs the measured current value to the control circuit 16. The control circuit 16 acquires the voltage value measured by the voltage measuring unit 12 and the current value measured by the current measuring unit 15. For example, the outputs of the voltage measuring unit 12 and the current measuring unit 15 are analog signals. The control circuit 16 converts the analog signals output from the voltage measuring unit 12 and the current measuring unit 15 into digital signals, and acquires the converted signals as voltage and current values, respectively. Based on the acquired voltage and current values, the control circuit 16 controls the voltage application circuit 11 and the switch 14. The control circuit 16 calculates the insulation resistance based on the voltage and current values. At least a portion of the functions of the control circuit 16 can be executed collaboratively by a processor such as a CPU (Central Processing Unit) and software. At least a portion of the functions of the control circuit 16 can also be executed by dedicated hardware circuitry.

[0025] Figure 3A and Figure 3B This is an equivalent circuit diagram of the first and second states in the first embodiment. The explanation will take the measurement of insulation resistance RN as an example. Figure 3A As shown, the first state is when the voltage application circuit 11 does not apply the applied voltage Va and the discharge circuit 13 is electrically connected between terminals T1 and T2. The measured values ​​of the voltage measuring unit 12 and the current measuring unit 15 are set as the voltage value V1 and the current value I1, respectively. An insulation resistor Rp and a capacitance to ground Cp are connected in parallel between terminals T1 and T2, and the solar cell string 40 is connected in series with the insulation resistor Rp and the capacitance to ground Cp. The electromotive force of the solar cell string 40 is Vc. Between terminals T1 and T2, the insulation resistor Rn and the capacitance to ground Cn are connected in parallel with the electromotive force Vc, the insulation resistor Rp, and the capacitance to ground Cp.

[0026] At this point, the measured insulation resistance is RN. Since the voltage applied across the insulation resistance RN is V1 + Vc, it becomes Equation 1. Furthermore, the resistance value of the insulation resistance RN is set as RN.

[0027] V1+Vc=RN×I1 Equation 1 like Figure 3BAs shown, the second state is a state in which the discharge circuit 13 is electrically disconnected from at least one of terminals T1 and T2, and the voltage application circuit 11 applies an applied voltage Va. The applied voltage Va is, for example, 200V to 2000V, and 1500V is used as an example. The measured values ​​of the voltage measuring unit 12 and the current measuring unit 15 are set as voltage value V2 and current value I2, respectively. Since the voltage applied across the insulation resistance RN is V2 + Vc, it becomes Equation 2.

[0028] V² + Vc = RN × I² (Equation 2) Based on Equations 1 and 2, the insulation resistance RN is calculated using Equation 3.

[0029] RN = (V2 - V1) / (I2 - I1) (Equation 3) Thus, the insulation resistance RN can be calculated based on the voltage values ​​V1, V2, and the current values ​​I1 and I2.

[0030] Figure 4 This is a graph representing the voltage values ​​relative to time in the first state. Figure 4 The horizontal axis represents the time when switch 14 is turned on as 0. The vertical axis represents the voltage value V measured by voltage measuring unit 12. Charge accumulates in the ground capacitor Cn. Therefore, if a discharge circuit 13 is connected between terminals T1 and T2, the charge in the ground capacitor Cn is discharged through the discharge circuit 13. As a result, the voltage value V decays exponentially over time, becoming a fixed voltage value V0. If the voltage value V1 and current value I1 are measured before the voltage value V reaches the voltage value V0, the measurement error of the insulation resistance RN increases.

[0031] In the comparative example, after connecting the discharge circuit 13 between terminals T1 and T2, the voltage value V1 and the current value I1 are measured after a fixed waiting time (e.g., several seconds). However, the discharge time of the charge depends on the capacitance CN to ground (in Figure 3A The parameters include the capacitance connected between terminals T1 and T2, the insulation resistance RN, the resistance Rd of the discharge circuit 13, and the amount of charge stored in the ground capacitor CN. If the waiting time is too long relative to the discharge time, a long waiting period will still be required after the discharge from the ground capacitor CN is completed, resulting in wasted waiting time. On the other hand, if the waiting time is too short relative to the discharge time, the accuracy of the insulation resistance RN will deteriorate in terms of voltage value V1 and current value I1 because the charge stored in the ground capacitor CN is still in the discharge process.

[0032] like Figure 4As shown, in the first embodiment, the measurement of voltage value V1 and current value I1 begins based on the rate of change of voltage value V with respect to time ΔV / Δt. For example, if ΔV / Δt is above the threshold Th, the discharge of charge on the ground capacitor CN is insufficient. Therefore, the first state is maintained. If ΔV / Δt is less than the threshold Th, it is determined that the discharge of charge on the ground capacitor CN is sufficient, and the measurement of voltage value V1 and current value I1 begins. Thus, regardless of the length of the discharge time, the measurement of voltage value V1 and current value I1 can begin at the point when the discharge is approximately complete.

[0033] Based on the charge accumulated in the capacitance CN to ground, the voltage value sometimes increases over time, becoming a fixed voltage value V0. Therefore, the determination is made based on the absolute value of the rate of change, |ΔV / Δt|. The specific control flow of control circuit 16 is explained below.

[0034] Figure 5 This is a flowchart illustrating the operation of the control circuit in the first embodiment. For example... Figure 5 As shown, control circuit 16 begins measurement (step S10). For example, the user connects terminal T1 to ground terminal E and terminal T2 to N terminal. Then, the user turns on the measurement start switch. Control circuit 16 begins measurement when the PV measurement start switch is turned on.

[0035] like Figure 5 As shown, the control circuit 16 is set to the first state (step S11). Specifically, the control circuit 16 prevents the voltage application circuit 11 from generating an applied voltage Va, making the voltage application circuit 11 a high impedance. The control circuit 16 turns on the switch 14, electrically connecting the discharge circuit 13 between terminals T1 and T2. Next, the control circuit 16 acquires the voltage value V from the voltage measuring unit 12 (step S12). Next, the control circuit 16 calculates the rate of change of the voltage value ΔV / Δt based on the acquired voltage value V (step S13). For example, the control circuit 16 converts the analog output signal of the voltage measuring unit 12 into a digital signal voltage value V within a fixed sampling period Δt. Therefore, the rate of change ΔV / Δt is calculated by dividing the difference ΔV between the previously sampled voltage value and the current sampled voltage value by Δt. In step S13, the control circuit 16 may also calculate the difference ΔV based on the acquired voltage value V. The difference ΔV corresponds to the amount of voltage change during the specified period Δt.

[0036] Next, the control circuit 16 determines whether the absolute value of the rate of change |ΔV / Δt| is greater than or equal to the threshold Th (step S14). In step S14, the control circuit 16 may also determine whether the absolute value of the difference ΔV |ΔV| is greater than or equal to the threshold Th. If it is "yes", the circuit returns to step S12. If it is "no", the control circuit 16 acquires the voltage value V1 and the current value I1 from the voltage measuring unit 12 and the current measuring unit 15, respectively (step S15).

[0037] Next, the control circuit 16 sets the first state to the second state (step S16). Specifically, the control circuit 16 disconnects the switch 14, electrically cutting off the discharge circuit 13 from terminal T2. The control circuit 16 causes the voltage application circuit 11 to generate an applied voltage Va. Then, the control circuit 16 acquires the voltage value V2 and the current value I2 from the voltage measuring unit 12 and the current measuring unit 15, respectively (step S17).

[0038] Next, the control circuit 16 calculates the insulation resistance RN (step S18). Specifically, the control circuit 16 uses Equation 3 to measure the insulation resistance RN. Equation 3 is an example, and other methods can also be used to calculate the insulation resistance RN. Then, the control circuit 16 ends the measurement (step S19). Specifically, the voltage application circuit 11 stops applying the applied voltage Va. Next, the control circuit 16 outputs the calculated insulation resistance RN value (step S20). Specifically, the control circuit 16 can also display the measured value of the insulation resistance RN on the display unit. Alternatively, the control circuit 16 can output the measured value of the insulation resistance RN to an external device. Then, the process ends.

[0039] According to the insulation resistance measuring device 100 of the first embodiment, such as Figure 5 As shown in step S14, in the first state, when the absolute value of the voltage change |ΔV| or the absolute value of the rate of change of voltage V relative to time |ΔV / Δt| obtained from the voltage measuring unit 12 is above the threshold Th, the control circuit 16 returns to step S12 and maintains the first state. In the first state, when |ΔV| or |ΔV / Δt| is less than the threshold Th, the control circuit 16 enters step S15, and while maintaining the first state, obtains voltage value V1 (first voltage value) and current value I2 (first current value) from the voltage measuring unit 12 and the current measuring unit 15, respectively. Then, as shown in step S16, the control circuit 16 is set to the second state, and as shown in step S17, obtains voltage value V2 (second voltage value) and current value I2 (second current value) from the voltage measuring unit 12 and the current measuring unit 15, respectively. As shown in step S18, the control circuit 16 calculates the insulation resistance RN or RP between terminals T1 and T2 based on the voltage values ​​V1, V2, and current values ​​I1 and I2.

[0040] Therefore, in Figure 4In this method, at a time point when the voltage value V is close to the voltage value V0, the voltage value V1 and the current value I1 can be measured. Therefore, the waiting time until the start of the measurement can be optimized, and the measurement accuracy can be improved. A threshold Th can also be predetermined and stored in memory. The threshold Th can also be changed for each measurement. The threshold Th can also be set based on the voltage value V at time t = 0. For example, when the output voltage of the solar cell string 40 is several kV, the voltage of the ground capacitance CN is sometimes several hundred V. In the case described above, the threshold Th can be set to 10 V / s to 1 V / s.

[0041] As described above, in the first state, the control circuit 16 can proceed to step S15 when a first value calculated based on the difference ΔV, which corresponds to the voltage change within a predetermined period Δt corresponding to the voltage value V obtained from the voltage measuring unit 12, satisfies a predetermined condition. The first value is, for example, the absolute value of the 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 voltage change or the absolute value of the voltage change rate is less than a threshold Th.

[0042] (Modification 1 of the first embodiment) Figure 6 This is a flowchart illustrating the operation of the control circuit in Modification 1 of the first embodiment. For example... Figure 6 As shown, the actions of steps S10 and S11 are similar to... Figure 5 The same applies. Next, the control circuit 16 acquires the current value I from the current measuring unit 15 (step S12A). Then, based on the acquired current value I, the control circuit 16 calculates the rate of change of the current value ΔI / Δt (step S13A). For example, the control circuit 16 calculates the rate of change ΔI / Δt as the value obtained by dividing the difference ΔI between the previously sampled current value and the current sampled current value by Δt. In step S13A, the control circuit 16 may also calculate the difference ΔI based on the acquired current value I. The difference ΔI corresponds to the amount of current change within a specified period Δt.

[0043] Next, control circuit 16 determines whether the absolute value of the rate of change |ΔI / Δt| is greater than or equal to the threshold Th (step S14A). In step S14A, control circuit 16 can also determine whether the absolute value of the current value I |I| is greater than or equal to the threshold Th. Additionally, control circuit 16 can also determine whether the absolute value of the difference ΔI |ΔI| is greater than or equal to the threshold Th. If the result is "yes", return to step S12A. If the result is "no", proceed to step S15. The actions after step S15 are the same as... Figure 5 same.

[0044] When discharge circuit 13 is connected between terminals T1 and T2, the charge on the ground capacitor Cn is discharged through discharge circuit 13. Thus, with Figure 4Similarly, the current value I decays exponentially over time until it becomes 0. Therefore, as shown in steps S12A to S14A, when |I|, |ΔI|, or |ΔI / Δt| is the threshold Th, we can proceed to step S15.

[0045] As shown in Variation 1 of the first embodiment, the control circuit 16 can proceed to step S15 in the first state when the current value I obtained from the current measuring unit 15, or a second value calculated based on the difference ΔI of the current change within a predetermined period Δt corresponding to the current value I, meets a predetermined condition. The second value is, for example, the absolute value of the current change |ΔI| or the absolute value of the current change rate |ΔI / Δt|. The predetermined condition may be, for example, the condition that the absolute value of the current value |I|, the absolute value of the current change |ΔI|, or the absolute value of the current change rate |ΔI / Δt| is less than a threshold Th.

[0046] like Figure 3A As shown, in the first state, the current measuring unit 15 is connected in series with the discharge circuit 13 between terminals T1 and T2, and the voltage measuring unit 12 is connected in parallel to the discharge circuit 13 and in series with the current measuring unit 15. Figure 3B As shown, in the second state, the current measuring unit 15 is connected in series with the voltage application circuit 11 between terminals T1 and T2, and the voltage measuring unit 12 is connected in parallel to the voltage application circuit 11 and in series with the current measuring unit 15. With such a connection, as shown in Equation 3, the resistance value of the 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.

[0047] like Figure 2 As shown, the discharge circuit 13 has a resistor Rd (first resistor) connected between terminals T1 and T2. Thus, the charge on the ground capacitor CN can be discharged via the discharge circuit 13.

[0048] like Figure 1 As shown, terminal T1 is connected to either the positive terminal P or the negative terminal N of the solar cell, and terminal T2 is connected to either the positive terminal P or the negative terminal N of the solar cell 41. The solar cell 41 generates an electromotive force when illuminated. Therefore, by 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, the insulation resistance RN and RP can be measured. In the solar cell string 40, the voltage is increased by cascading the solar cells 41. If the number of cascaded solar cells increases, the capacitance to ground Cn and Cp increase. Therefore, Figure 4The discharge time becomes longer. Therefore, if the waiting time is extended to match the large ground capacitance Cn and Cp of the solar cell string 40, as shown in the comparative example, the waiting time becomes longer when measuring the insulation resistance of the small ground capacitance Cn and Cp of the solar cell string 40. 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.

[0049] The insulation resistance measuring device 100 can also 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 that generates an electromotive force between terminals.

[0050] (Second Implementation) Figure 7 This is a block diagram of the insulation resistance measuring device according to the second embodiment. Figure 7 As shown, the insulation resistance measuring device 102 according to the second embodiment, in addition to the insulation resistance measuring device 100 of the first embodiment, also includes a discharge circuit 13A, a switch 14A, a resistor R10, a switch 17, an input section 18, and a protection circuit 19.

[0051] Discharge circuit 13A and switch 14A are connected in parallel between terminals T1 and T2. Discharge circuit 13A has a resistor RdA, one end of which is connected to terminal T1 via current measuring unit 15, and the other end of which is connected to terminal T2. The resistance value of resistor RdA is different from that of resistor Rd. For example, the resistance value of resistor RdA is lower than that of resistor Rd. Switch 14A electrically connects discharge circuit 13A between terminals T1 and T2 or electrically disconnects discharge circuit 13A from terminal T2 based on a control signal from control circuit 16. Switch 14A may also be provided between discharge circuit 13A and terminal T1.

[0052] Resistor R10 is connected between voltage application circuit 11 and voltage measuring unit 12. Resistor R10 has resistors R11 and R12 connected in series. Switch 17 is connected in parallel to resistor R12 and in series with resistor R11. Information for the user to operate the insulation resistance measuring device 102 is input to input unit 18. Input unit 18 is, for example, an operation button or operation switch.

[0053] The protection circuit 19 includes a switch 19A connected in parallel to the current measuring unit 15. Switch 19A is open when there is no overcurrent during discharge. Therefore, the current measuring unit 15 can measure the current flowing through the discharge circuit 13 or 13A. If an overcurrent flows during discharge, the current measuring unit 15 detects the overcurrent and turns on switch 19A. As a result, the current flowing to the current measuring unit 15 is bypassed and diverted to the protection circuit 19, thereby protecting the current measuring unit 15.

[0054] Figure 8 This is a flowchart illustrating the operation of the control circuit in the second embodiment. Figure 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 the voltage value V from voltage measuring unit 12. Then, control circuit 16 determines whether the absolute value |V| of voltage value V is greater than or equal to the threshold voltage Th2 (step S21). If the result is "no", proceed to step S13.

[0055] When "Yes" is selected in step S21, the control circuit 16 switches the discharge circuit 13 to the discharge circuit 13A (step S22). Specifically, the control circuit 16 opens switch 14 and opens switch 14A. Thus, the discharge circuit 13A is connected between terminals T1 and T2 to replace the discharge circuit 13. Then, the process proceeds to step S12. The remaining procedures are the same as in the first embodiment. Figure 5 Same, explanation omitted.

[0056] like Figure 8 As shown, in the first state, when the absolute value |V| of the voltage value V obtained from the voltage measuring unit 12 is greater than or equal to the threshold voltage Th2, the discharge circuit 13 is switched to the discharge circuit 13A. Consequently, the resistance value RdA of the discharge circuit 13A is changed to a lower value. When the absolute value |V| of the voltage value V is high, more charge accumulates in the ground capacitance CN. Therefore, by reducing the resistance RdA of the discharge circuit 13A, the discharge time can be shortened. For example, the resistance value of RdA is less than or equal to 1 / 2 to 1 / 5 of the resistance value of Rd.

[0057] In step S21, the control circuit 16 may determine whether the absolute value |V| of the voltage value V is above the threshold voltage Th2 when it first acquires the voltage value V after becoming the first state. However, when acquiring the voltage value V for the second time or later, it may not determine whether the absolute value |V| of the voltage value V is above the threshold voltage Th2, and proceed to step S13.

[0058] After step S14, the control circuit 16 can also change the resistance value of the discharge circuit 13's resistor Rd based on |ΔV / Δt|. For example, when the rate of decrease of |ΔV / Δt| is less than a predetermined value, the resistance value of resistor Rd is reduced. This shortens the discharge time.

[0059] Thus, 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 measuring unit 12. This allows for adjustment of the discharge time.

[0060] As a method for changing the resistance value of the discharge circuit, an example is given of preparing resistors Rd and RdA and using switches 14 and 14A to switch resistors Rd and RdA. However, it is also possible to combine one or more switches with multiple resistors to switch the resistance value of the discharge circuit.

[0061] return Figure 7 A resistor R10 (the second resistor) is connected in series with the voltage application circuit 11 between terminals T1 and T2. Resistor R10 has R11 and R12 connected in series, and a switch 17 connected in parallel with resistor R12. Switch 17 is turned on or off according to the instruction of control circuit 16. Resistor R10 has the function of limiting overcurrent.

[0062] Figure 9 This is a flowchart illustrating the operation of the control circuit in the second embodiment. For example... Figure 9 As shown, the control circuit 16 obtains mode information from the input section 18 (step S30). The modes include a first mode and a second mode. The first mode is obtained through... Figure 5 or Figure 8 The procedure is used to determine the insulation resistance RN (first insulation resistance). The second mode is, for example, the mode for determining the insulation resistance of an object that does not generate an electromotive force.

[0063] Next, the control circuit 16 determines whether the acquired information is in the first mode or the second mode (step S31). In step S31, in the first mode, the control circuit 16 opens 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... Figure 5 or Figure 8 The procedure is used to determine the insulation resistance RN. Then the process ends.

[0064] In step S31, in the second mode, the control circuit 16 performs steps S32 to S37 as a determination of the second mode. First, the control circuit 16 turns on the switch 17 (step S32), then the control circuit 16 and... Figure 5 and Figure 8Step S16 is similarly set to the second state (step S33). Next, control circuit 16 and... Figure 5 and Figure 8 Similarly, in step S17, voltage value V3 (third voltage value) and current value I3 (third current value) are obtained from voltage measuring unit 12 and current measuring unit 15 respectively (step S34). Next, control circuit 16 calculates the insulation resistance R2 (second insulation resistance) between terminals T1 and T2 based on the obtained voltage value V3 and current value I3 (step S35). Specifically, control circuit 16 sets the insulation resistance R2 to, for example, V3 / I3. Then, control circuit 16 and... Figure 5 and Figure 8 Step S19 similarly concludes the measurement (step S36). Next, control circuit 16 and... Figure 5 and Figure 8 Similarly, step S20 outputs information about the insulation resistance R2 (step S37). Then the process ends.

[0065] Depending on the type of insulation resistance to be measured, the resistance value of the resistor connected in series with the voltage application circuit 11 may be changed. For example, when the insulation resistance measuring device 102 is used to measure the insulation resistance of a solar cell, since a high voltage may be applied to terminal T2, the switch 17 is turned off, increasing the resistance value of the resistor R10 connected in series with the voltage application circuit 11. On the other hand, when the insulation resistance measuring device 102 is used to measure the insulation resistance of an object that does not generate an electromotive force, no high voltage is applied to terminal T2. Therefore, the switch 17 is turned on, decreasing the resistance value of the resistor connected in series with the voltage application circuit 11.

[0066] As mentioned above, in Figure 9 In step S30, the control circuit 16 acquires information about which of the first and second modes to select. In steps S31, S32, and S33, the control circuit 16, based on the acquired information, changes the resistance value of resistor R10. Thus, the insulation resistance measuring device 102 can measure both the insulation resistance RN or RP and the insulation resistance R2 of the object being measured, which does not generate an electromotive force.

[0067] The control circuit 16 sets the resistance value of resistor R10 to be higher when the acquired information indicates the first mode than when it indicates the second mode. Therefore, in the first mode, where a high voltage can be applied to terminal T2, the resistance value of resistor R10 can be increased.

[0068] As a method for changing the resistance value of resistor R10, an example using resistors R11, R12, and switch 17 is given, but one or more switches can also be combined with multiple resistors to switch the resistance value of resistor R10.

[0069] As described above, the embodiments have been illustrated, but these embodiments are merely examples and the present invention is not limited to them. The embodiments described above can be implemented in various other ways, and various combinations, omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, and are also included within the scope of the invention as described in the claims and its equivalents.

[0070] This application claims priority to basic patent application No. 2024-071198 filed with the Japan Patent Office on April 25, 2024, and basic patent application No. 2025-007891 filed with the Japan Patent Office on January 20, 2025, the entire contents of which are incorporated herein by reference.

[0071] Explanation of reference numerals in the attached figures 11: Voltage application circuit 12: Voltage Measurement Section 13, 13A: Discharge circuit 14, 14A, 17: Switches 15: Current Measurement Section 16: Control Circuit 18: Input Section 19: Protection Circuit 40: Solar cell strings 41: Solar cells 42: Diode.

Claims

1. An insulation resistance measuring device, comprising: First terminal; Second terminal; A discharge circuit is connected between the first terminal and the second terminal; The voltage measuring unit measures the voltage between the first terminal and the second terminal; The current measuring unit measures the current flowing between the first terminal and the second terminal; A voltage application circuit applies an applied voltage between the first terminal and the second terminal; as well as In a first state where 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 the voltage change within a predetermined period of the voltage value obtained from the voltage measurement unit, a current value obtained from the current measurement unit, or a second value calculated based on the current change within a predetermined period of the current value meets a predetermined condition, the control circuit obtains a first voltage value and a first current value from the voltage measurement unit and the current measurement unit, respectively. After obtaining the first voltage value and the first current value, in a second state where the discharge circuit is disconnected from at least one of the first terminal and the second terminal, and the voltage application circuit applies the applied voltage, the second voltage value and the second current value are obtained from the voltage measuring unit and the current measuring unit, respectively. Based on the first voltage value, the first current value, the second voltage value, and the second current value, calculate the first insulation resistance between the first terminal and the second terminal.

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

3. The insulation resistance measuring device according to claim 1 or 2, wherein, The first terminal is connected to the ground terminal of the solar cell, and the second terminal is connected to either the positive or negative terminal of the solar cell.

4. The insulation resistance measuring device according to claim 1 or 2, wherein, The discharge circuit has a first resistor connected between the first terminal and the second terminal.

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

6. The insulation resistance measuring device according to claim 1 or 2, wherein, The insulation resistance measuring device includes a second resistor, which is connected in series with the voltage application circuit between the first terminal and the second terminal. The control circuit acquires information about which of the first and second modes to select, and changes the resistance value of the second resistor based on the acquired information. The first mode is the mode of measuring the first insulation resistance, and the second mode is the mode of acquiring a third voltage value and a third current value from the voltage measuring unit and the current measuring unit respectively in the second state without implementing the first state, and calculating the second insulation resistance between the first terminal and the second terminal based on the third voltage value and the third current value.

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 represents the first mode to be higher than the resistance value of the second resistor when the information represents the second mode.

8. The insulation resistance measuring device according to claim 1 or 2, wherein, The specified condition is that the absolute value of the voltage change or the absolute value of the rate of change of the voltage value obtained from the voltage measuring unit with respect to time is less than a threshold.

9. The insulation resistance measuring device according to claim 1 or 2, wherein, The specified condition is that the absolute value of the change in current, the absolute value of the current value obtained from the current measuring unit, or the absolute value of the rate of change of the current value relative to time is less than a threshold.

10. An insulation resistance measurement method, wherein in a first state where 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 the amount of voltage change within a predetermined period of a voltage value obtained from a voltage measuring unit that measures the voltage between the first terminal and the second terminal, a current value obtained from a current measuring unit that measures the current flowing between the first terminal and the second terminal, or a second value calculated based on the amount of current change within a predetermined period of the current value meets a predetermined condition, a first voltage value and a first current value are obtained from the voltage measuring unit and the current measuring unit, respectively. After obtaining the first voltage value and the first current value, in a second state where 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, the second voltage value and the second current value are obtained from the voltage measuring unit and the current measuring unit, respectively. Based on the first voltage value, the first current value, the second voltage value, and the second current value, calculate the insulation resistance between the first terminal and the second terminal.

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