Power conversion device

Abstract

An insulation resistance measurement device according to an embodiment of the present invention comprises: a variable resistance unit that is connected between a DC link terminal and a ground; and an insulation resistance calculation unit that calculates insulation resistance by using a first voltage of the DC link terminal and a second voltage measured from the variable resistance unit, wherein the insulation resistance calculation unit calculates the insulation resistance by using the second voltage in a first state and the second voltage in a second state in which the resistance from the first state is variable.

Description

power conversion device

[0001] The present invention relates to a power conversion device, and more specifically, to an insulation resistance measuring device capable of measuring insulation resistance using a simple circuit, and a power conversion device including the same.

[0002] Solar power generation is becoming widely adopted as an eco-friendly energy source, replacing conventional chemical and nuclear power generation. Solar power generation can be either standalone, with a battery connected to a converter, or grid-connected. Standalone systems typically consist of solar cells, storage batteries, and power conversion equipment, while grid-connected systems are connected to commercial power sources, enabling the exchange of power with load grid lines.

[0003] When generating solar power using multiple solar panels, maintaining insulation across the multiple channels connecting them is essential for stable system operation. Technology capable of accurately and quickly detecting whether insulation is maintained is essential.

[0004] The technical problem to be solved by the present invention is to provide an insulation resistance measuring device capable of measuring insulation resistance using a simple circuit and a power conversion device including the same.

[0005] In order to solve the above technical problem, an insulation resistance measuring device according to one embodiment of the present invention includes a variable resistance unit connected between a DC link terminal and a ground; and an insulation resistance calculating unit that calculates insulation resistance using a first voltage of the DC link terminal and a second voltage measured from the variable resistance unit, wherein the insulation resistance calculating unit calculates the insulation resistance using the second voltage in a first state and the second voltage in a second state in which the resistance is varied in the first state.

[0006] In addition, the variable resistor unit comprises: a first resistor connected in parallel with the DC link terminal; a second resistor connected in series with the first resistor; a first switch having one end connected to a first node between the first resistor and the second resistor and the other end connected to ground; a third resistor connected in parallel with the first resistor; a second switch connected in series with the third resistor;

[0007] A fourth resistor connected in parallel with the second resistor; and a third switch connected in series with the fourth resistor, wherein the second voltage may be a voltage across both terminals of the second resistor.

[0008] Additionally, it may include a voltage sensor unit that measures the first voltage and the second voltage.

[0009] In addition, the insulation resistance calculation unit can turn on the first switch, calculate a third voltage across both ends of the first resistor using the difference between the first voltage and the second voltage, and compare the magnitudes of the second voltage and the third voltage.

[0010] In addition, the insulation resistance calculation unit can turn on the third switch when the second voltage is greater than the third voltage, and can turn on the second switch when the third voltage is greater than the second voltage.

[0011] In addition, the insulation resistance calculation unit can measure the first voltage and the second voltage again after turning on the third switch, and calculate the insulation resistance using the difference between the re-measured second voltage and the previously measured second voltage.

[0012] In addition, the insulation resistance calculation unit can calculate the third voltage again by measuring the first voltage and the second voltage again after turning on the second switch, and calculate the insulation resistance using the difference between the recalculated third voltage and the previously calculated third voltage.

[0013] Additionally, the resistance values ​​of the third resistor and the fourth resistor may be the same.

[0014] In order to solve the above technical problem, a power conversion device according to an embodiment of the present invention includes: a plurality of first power conversion units that convert power of a PV module and are connected in parallel; a second power conversion unit that converts output of the plurality of first power conversion units and outputs the converted output to a grid; a DC link terminal connected between the plurality of first power conversion units and the second power conversion units; and an insulation resistance measuring unit that is connected in parallel with the DC link terminal and measures insulation resistance, wherein the insulation resistance measuring unit includes: a variable resistor unit connected between the DC link terminal and ground; and an insulation resistance calculating unit that calculates insulation resistance using a first voltage of the DC link terminal and a second voltage measured from the variable resistor unit, wherein the insulation resistance calculating unit calculates the insulation resistance using the second voltage in a first state and the second voltage in a second state in which the resistance is varied in the first state.

[0015] In addition, the variable resistor unit includes a first resistor connected in parallel with the DC link terminal; a second resistor connected in series with the first resistor; a first switch having one end connected to a first node between the first resistor and the second resistor and the other end connected to ground; a third resistor connected in parallel with the first resistor; a second switch connected in series with the third resistor; a fourth resistor connected in parallel with the second resistor; and a third switch connected in series with the fourth resistor, wherein the second voltage may be a voltage across both ends of the second resistor.

[0016] In addition, the insulation resistance calculation unit may turn on the first switch, calculate a third voltage at both ends of the first resistor using the difference between the first voltage and the second voltage, compare the magnitudes of the second voltage and the third voltage, and turn on the third switch if the second voltage is greater than the third voltage, and turn on the second switch if the third voltage is greater than the second voltage.

[0017] In addition, when the third switch is turned on, the insulation resistance calculation unit can measure the first voltage and the second voltage again, and calculate the insulation resistance using the difference between the re-measured second voltage and the previously measured second voltage.

[0018] In addition, when the second switch is turned on, the insulation resistance calculation unit can measure the first voltage and the second voltage again to calculate the third voltage again, and calculate the insulation resistance using the difference between the recalculated third voltage and the previously calculated third voltage.

[0019] According to embodiments of the present invention, insulation resistance can be measured using a simple circuit.

[0020] Figure 1 is a drawing explaining a solar power generation system to which an insulation resistance measuring device according to an embodiment of the present invention is applied.

[0021] Figure 2 is a block diagram of an insulation resistance measuring device according to one embodiment of the present invention.

[0022] Figures 3 to 6 are drawings for explaining an insulation resistance measuring device according to an embodiment of the present invention.

[0023] Figure 7 is a block diagram of a power conversion device according to an embodiment of the present invention.

[0024] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

[0025] However, the technical idea of ​​the present invention is not limited to some of the embodiments described, but can be implemented in various different forms, and within the scope of the technical idea of ​​the present invention, one or more of the components between the embodiments can be selectively combined or substituted for use.

[0026] In addition, terms (including technical and scientific terms) used in the embodiments of the present invention may be interpreted as having a meaning that can be generally understood by a person of ordinary skill in the technical field to which the present invention belongs, unless explicitly and specifically defined and described, and terms that are commonly used, such as terms defined in a dictionary, may be interpreted in consideration of the contextual meaning of the relevant technology.

[0027] Additionally, the terms used in the embodiments of the present invention are intended to describe the embodiments and are not intended to limit the present invention.

[0028] In this specification, the singular may also include the plural unless specifically stated otherwise in the phrase, and when it is described as “A and / or at least one (or more) of B, C”, it may include one or more of all combinations that can be combined with A, B, C.

[0029] Additionally, in describing components of embodiments of the present invention, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only intended to distinguish the components from other components, and are not intended to limit the nature, order, or sequence of the components.

[0030] And, when a component is described as being 'connected', 'coupled', or 'connected' to another component, it may include not only cases where the component is 'connected', 'coupled', or 'connected' directly to the other component, but also cases where the component is 'connected', 'coupled', or 'connected' by another component between the component and the other component.

[0031] Additionally, when described as being formed or arranged "above" or "below" each component, "above" or "below" includes not only cases where the two components are in direct contact with each other, but also cases where one or more other components are formed or arranged between the two components. Furthermore, when expressed as "above" or "below," the meaning may include not only the upward direction but also the downward direction based on one component.

[0032] Figure 1 is a drawing explaining a solar power generation system to which an insulation resistance measuring device according to an embodiment of the present invention is applied.

[0033] As illustrated in FIG. 1, a solar power generation system may include a solar power source (10), an inverter (20), a battery pack (30), and a load (LOAD, 50). However, those skilled in the art will understand that, in addition to the components illustrated in FIG. 1, other general components may be further included in the solar power generation system. For example, the solar power generation system may further include a grid (GRID, 40). Alternatively, those skilled in the art will understand that, according to another embodiment, some of the components illustrated in FIG. 1 may be omitted.

[0034] A solar power source (10) can be composed of a plurality of photovoltaic modules in which photovoltaic cells are assembled, and a photovoltaic cell that is made by joining a P-type semiconductor and an N-type semiconductor generates electricity with light. Specifically, when light is shone on a photovoltaic cell, electrons and holes are generated inside. The generated charges move to the P pole and the N pole, respectively, and a potential difference is generated between the P pole and the N pole due to this action, and when a load is connected to the photovoltaic cell, current flows. Here, a photovoltaic cell means the smallest unit that generates electricity, and photovoltaic cells are assembled to form a battery module, and the battery modules can again form an array connected in series / parallel to form a photovoltaic power source (10).

[0035] The inverter (20) can convert the DC (direct current) power generated from the solar power source (10) by the photovoltaic effect into AC (alternating current) power to supply power to the grid (40) or load (50). Here, the grid (40) may refer to a system (Grid) for transmitting and distributing power generated from the solar power generation system. Meanwhile, the amount of power generated from the solar power source (10) continuously changes due to temporal factors such as sunrise and sunset or external factors such as weather. Therefore, the inverter (20) controls the voltage generated from the solar power source (10) to find the maximum power and supplies it to the grid (40). At this time, if the power to operate the inverter is lower than the output power of the inverter, the inverter (20) may consume the power of the grid (40) in reverse. Of course, in this case, the inverter can block the power flowing into the grid (40) to prevent the power from being reversed. Accordingly, various optimization control methods are applied to the solar power generation system to extract maximum power from the solar power source (10) so that the operation of the above-described inverter (20) can be performed more efficiently. Representative maximum power point tracking (MPP) methods of the solar power source (10) include the PO (Perturbation and Observation) method, the IC (Incremental Conductance) control method, and the CV (Constant Voltage) control method. Here, the PO method is a method of periodically measuring the voltage and current of the solar power source (10), calculating the power, and then tracking the MPP using the power value. The IC control method is a method of measuring the voltage and current generated from the solar power source (10) and controlling it so that the rate of change in power with respect to the change in the terminal voltage operating point of the array becomes '0'. The CV control method is a method of controlling with a constant reference voltage (ref V) regardless of the operating voltage or power of the array that constitutes the solar power source (10).Depending on each optimizer control method, the power source input from the solar power source (10) to the inverter can operate as a voltage source or a current source.

[0036] The load (50) may refer to a product that utilizes an electrical form used in real life. For example, an inverter (20) can obtain AC power of a desired voltage and frequency through an appropriate conversion method, switching element, or control circuit, and supply electricity to home appliances or machinery in industrial facilities. In addition, in the case of solar power generation, there is bound to be a gap in power generation due to the absence of sunlight at night or changes in the weather, where sufficient power generation is not possible. Therefore, to compensate for this shortcoming, a battery is essential for solar power generation systems to ensure a stable power supply.

[0037] The battery pack (30) may include at least one of a DC-DC converter, a battery, a battery management system (BMS), and a battery control circuit. The battery may be composed of a lithium-ion battery or a nickel-metal hydride battery, but is not necessarily limited to such a configuration, and may refer to a battery that can be used semi-permanently through charging. The DC-DC converter is a device that converts DC power generated through a solar power source (10) into DC power suitable for the battery, or converts the power of the battery into power suitable for the grid, and can generally convert power by converting DC power into AC power and then back converting the AC power into DC power again. The battery management system (BMS) may provide a function to prevent misuse of cells constituting the battery, balancing between unit cells, measuring the remaining charge (SOC: State of Charge), temperature maintenance, or system monitoring. Therefore, based on a sensor that measures the status of a cell and a function that receives the measured values ​​of the sensor and transmits them to the control system of the application product, a circuit that generates an abnormal signal and blocks or opens the power circuit between cells when the temperature and charging status of the system exceed a set value can be constructed and controlled.

[0038] Fig. 2 is a block diagram of an insulation resistance measuring device (100) according to one embodiment of the present invention. Figs. 3 to 6 are drawings for explaining an insulation resistance measuring device according to an embodiment of the present invention.

[0039] An insulation resistance measuring device (100) according to an embodiment of the present invention detects insulation resistance for a plurality of channels. Here, the channels for which insulation resistance is to be detected may include a plurality of PV modules (320). Each of the plurality of PV modules (320) may be connected to a first power conversion unit (220). Alternatively, a plurality of battery packs may be connected. By detecting the insulation resistance, it is possible to determine whether insulation is maintained in the power output from the PV module (320). The PV module (320) determined to be safe by maintaining insulation may be connected to a device or circuit to which power output is to be supplied. That is, the insulation resistance measuring device (100) according to an embodiment of the present invention may be used to confirm whether the insulation resistance is maintained above a reference value before connecting to the PV module (320). The resistance measuring device according to an embodiment of the present invention may measure insulation resistance for a plurality of channels. The plurality of channels may be connected in parallel. When multiple channels are connected in parallel, the insulation resistance of the connected channels can be measured to determine safety. Even with a large number of parallel channels, insulation resistance can be measured quickly and accurately, providing high scalability. It goes without saying that the devices connected to the channels measuring insulation resistance can include not only solar power panels or battery packs, but also various other devices requiring insulation.

[0040] An insulation resistance measuring device (100) according to one embodiment of the present invention can measure insulation resistance by being connected to a DC link terminal (210).

[0041] A variable resistor unit (110) is connected between a DC link terminal (210) and ground (310). The variable resistor unit (110) includes a plurality of resistors and switching elements, so that the connection state of the resistors can be varied, and through this, the resistance connected between the DC link terminal (210) and ground (310) can be varied.

[0042] The insulation resistance calculation unit (120) calculates the insulation resistance using the first voltage of the DC link terminal (210) and the second voltage measured from the variable resistance unit (110). Here, the insulation resistance calculation unit (120) can calculate the insulation resistance using the second voltage in the first state and the second voltage in the second state in which the resistance is varied from the first state.

[0043] The variable resistor unit (110) may include a first resistor (111), a second resistor (112), a third resistor (114), a fourth resistor (116), a first switch (113), a second switch (115), and a third switch (117). The variable resistor unit (110) may have components connected as shown in Fig. 3. The first switch (113), the second switch (115), and the third switch (117) may include a relay, a semiconductor device MOSFET, etc.

[0044] The first resistor (111) is connected in parallel with the DC link terminal (210), and the first resistor (111) and the second resistor (112) can be connected in series. The node between the first resistor (111) and the second resistor (112) can be connected to the ground (310). The first resistor (111) and the second resistor (112) are connected to the ground (310) when the first switch (113) is turned on, thereby forming a path with the DC link terminal (210), and voltage can be applied. The insulation resistance calculation unit (120) can calculate the insulation resistance using the second voltage, which is the voltage at both ends of the second resistor (112). The voltage sensor unit (not shown) can measure the first voltage or the second voltage, which is the voltage of the DC link terminal.

[0045] A third resistor (114) may be connected in parallel with a first resistor (111), and the third resistor (114) and a second switch (115) may be connected in series. The third resistor (114) and the second switch (115) may be variable switching units that vary the first resistor (111). When the second switch (115) is turned on, the third resistor (114) may be connected in parallel with the first resistor (111), and when the second switch (115) is turned off, the third resistor (114) may be disconnected from the first resistor (111).

[0046] A fourth resistor (116) may be connected in parallel with the second resistor (112), and the fourth resistor (116) and the third switch (117) may be connected in series. The fourth resistor (116) and the third switch (117) may be variable switching units that vary the second resistor (112). When the third switch (117) is turned on, the fourth resistor (116) may be connected in parallel with the second resistor (112), and when the third switch (117) is turned off, the fourth resistor (116) may be disconnected from the second resistor (112). The resistance values ​​of the third resistor and the fourth resistor may be the same.

[0047] In the normal mode where insulation resistance is not calculated, the first switch (113), the second switch (115), and the third switch (117) can be kept in the off state. In order to calculate the insulation resistance, the first switch (113) is first turned on, and in order to calculate the insulation resistance using the values ​​measured at the first and second points in time, the second switch (115) or the third switch (117) can be turned off at the first point in time and turned on at the second point in time.

[0048] In order to calculate the insulation resistance, the insulation resistance calculation unit (120) first turns on the first switch (113), calculates the third voltage across the first resistor (111) using the difference between the first voltage and the second voltage, and compares the magnitudes of the second voltage and the third voltage. Thereafter, if the second voltage is greater than the third voltage, the third switch (117) can be turned on, and if the third voltage is greater than the second voltage, the second switch (115) can be turned on. By varying the resistance value of the resistor with the larger magnitude of the voltage across the two resistors, quick calculation is possible, and by making a large change in the magnitude of the voltage, the voltage difference can be increased, thereby reducing the error in calculating the insulation resistance.

[0049] After turning on the third switch (117), the first voltage and the second voltage are measured again, and the insulation resistance can be calculated using the difference between the re-measured second voltage and the previously measured second voltage.

[0050] Alternatively, after turning on the second switch (115), the first voltage and the second voltage are measured again to recalculate the third voltage, and the insulation resistance can be calculated using the difference between the recalculated third voltage and the previously calculated third voltage.

[0051] The sum of the insulation resistances visible on the side of the plurality of PV modules (320) at the DC link (210) is expressed as a difference in the second voltage or the third voltage that varies depending on the variation of the variable resistance unit (110), and the insulation resistance can be calculated from the difference between the second voltage or the voltage at a point in time before the variation and the second voltage or the third voltage at a point in time after the variation.

[0052] The insulation resistance for multiple PV module (320) channels is formed in a form of being connected in parallel, and it is possible to check whether the insulation is well maintained by calculating the total parallel insulation resistance. When multiple resistors are connected in parallel, the total parallel resistance becomes smaller than the smallest resistance value of each resistor connected in parallel. Using this point, the total parallel insulation resistance is calculated, and by determining whether the calculated total parallel insulation resistance is higher than the reference insulation resistance, it is possible to quickly determine whether the insulation is maintained without calculating the individual insulation resistance. If the total parallel insulation resistance is higher than the reference insulation resistance, it means that the individual insulation resistance is also higher than the reference insulation resistance, and it can be determined that the insulation is operating normally.

[0053] When the second switch (115) is turned on and the change in the third voltage is utilized, the insulation resistance can be calculated as follows.

[0054] The insulation resistance is equal to the total parallel resistance value of the first resistor (111), the second resistor (112), and the third resistor (114) multiplied by the third voltage of the first resistor (111) in the first state and the ratio of the voltage change, and the values ​​of the first resistor (111), the second resistor (112), and the third resistor (114). That is, the total parallel insulation resistance can be calculated using the voltage values ​​of the first state and the second state of the third voltage, which is the voltage of the first resistor (111), the second resistor (112), the third resistor (114), and the first resistor (111). This can be expressed as follows.

[0055] [Mathematical Formula 1]

[0056]

[0057] Here, R_iso ​​is the insulation resistance, R_T_EX is the sum of the insulation resistances of the entire PV module, V_p_0 is the third voltage at the first point in time, △V is the voltage difference between the first state and the second state, R_S is the third resistor (114), R_P is the first resistor (111), and R_N is the second resistor (112).

[0058] When the third switch is turned on and the change in the second voltage is utilized, the insulation resistance can be calculated as follows.

[0059] The insulation resistance is equal to the resistance value obtained by subtracting the total parallel resistance value of the first resistor (111), the second resistor (112), and the fourth resistor (116) from the fourth resistor obtained by multiplying the second voltage of the first resistor (111) in the first state by the ratio of the voltage change. That is, the total parallel insulation resistance can be calculated using the voltage values ​​of the first state and the second state of the second voltage, which is the voltage of the first resistor (111), the second resistor (112), the fourth resistor (116), and the second resistor (112). This can be expressed as follows.

[0060] [Equation 2]

[0061]

[0062] Here, V_N_0 is the second voltage at the first point in time.

[0063] As shown in Fig. 4, when configuring a circuit for measuring insulation resistance for each channel of a plurality of PV modules (320), as the number of channels increases, the number of detection circuits increases, which may lead to circuit complexity and increased cost.

[0064] The insulation resistance measuring device (100) according to an embodiment of the present invention can measure the entire insulation resistance by adding a simple insulation resistance measuring circuit to the DC link terminal (210), as shown in FIG. 5. The method for measuring the insulation resistance according to an embodiment of the present invention may include the steps of FIG. 6. First, the first switch S_PE is turned on (closed), the first voltage V_link, which is the voltage across the capacitor of the DC link terminal (210), and the second voltage V_N_0, which is the voltage of the second resistor, are measured, and the third voltage V_P_0, which is the voltage of the first resistor, can be calculated by subtracting the second voltage from the first voltage. (V_P_0 = V_link - V_N_0)

[0065] By comparing the second voltage and the third voltage, the resistance value corresponding to the voltage is varied using the larger voltage, and the insulation resistance is calculated accordingly, so that the insulation resistance can be calculated quickly and accurately. If the third voltage is larger than the second voltage (V_P_0 > V_N_0), the second switch S_P can be turned on (closed), and if the third voltage is not larger than the second voltage (V_P_0 <= V_N_0), the third switch S_N can be turned on (closed).

[0066] Afterwards, in the second state, the first voltage V_link, which is the voltage across the capacitor of the DC link terminal (210), and the second voltage V_N_1, which is the voltage of the second resistor, can be measured. By subtracting the second voltage from the first voltage, the third voltage V_P_0 in the second state, which is the voltage of the first resistor, can be calculated. (V_P_1 = V_link - V_N_1) The voltage difference △V is calculated, (△V = V_P_1 - V_P_0 = V_N_1- V_N_0), and the insulation resistance R_EX can be calculated using △V.

[0067] The following equation can be derived from the current relationship of the circuit of Fig. 5 in which the first switch (113) is turned on.

[0068] [Equation 3]

[0069]

[0070]

[0071] Here, V_in: PV input voltage, V_P: Voltage from Floating Ground (FG) to PV (+) terminal, V_N: Voltage from PV (-) terminal to FG, PE represents Protective Earth ground, I_Plk: PV (+) terminal leakage current, I_Nlk: PV (+) terminal leakage current, I_P: Current flowing from PV (+) terminal to FG, I_N: Current flowing from FG to PV (-) terminal, R_P_EX: PV (+) terminal insulation resistor, R_N_EX: PV (-) terminal insulation resistor, R_P: Resistance between PV (+) terminal and FG, R_N: Resistance between PV (-) terminal and FG, R_S: Sensing resistor, S: Switch.

[0072] In the first state, mathematical expression 3 can be expressed as follows.

[0073] [Equation 4]

[0074]

[0075] When the third voltage is greater than the second voltage, the second switch is turned on, and in the second state, it can be expressed as follows.

[0076] [Equation 5]

[0077]

[0078]

[0079]

[0080] If we subtract Equation 5 from Equation 4, we get the following, and through this, we can calculate the insulation resistance.

[0081] [Equation 6]

[0082]

[0083] If the third voltage is not greater than the second voltage, the third switch is turned on and in the second state, it can be expressed as follows.

[0084] [Equation 6]

[0085]

[0086]

[0087] As in mathematical expression 5, by subtracting mathematical expression 6 from mathematical expression 4, the insulation resistance can be calculated as in mathematical expression 2.

[0088] Fig. 7 is a block diagram of a power conversion device (200) according to an embodiment of the present invention. A detailed description of each component of the power conversion device (200) according to an embodiment of the present invention corresponds to the detailed description of the insulation resistance measuring device (100) of Figs. 1 to 6, and thus, any overlapping description will be kept brief.

[0089] A power conversion device (200) according to an embodiment of the present invention includes a second power conversion unit (230), a DC link terminal (210), and an insulation resistance measurement unit (100), and the insulation resistance measurement unit (100) may include a variable resistance unit (110) and an insulation resistance calculation unit (120).

[0090] The first power conversion unit (220) converts the power of the PV module (320) and is connected in parallel, and the second power conversion unit (230) can convert the output of a plurality of first power conversion units (220) and output it to the grid (330). The first power conversion unit (220) may be a DC-DC converter, and the second power conversion unit (230) may be an AC-DC inverter. The DC link terminal (210) is connected between the plurality of first power conversion units (220) and the second power conversion units (230), and may include an insulation resistance measurement unit (100) that is connected in parallel with the DC link terminal (210) and measures insulation resistance. The insulation resistance measuring unit (100) may include a variable resistance unit (110) connected between a DC link terminal (210) and a ground (310) and an insulation resistance calculating unit (120) that calculates insulation resistance using a first voltage of the DC link terminal (210) and a second voltage measured from the variable resistance unit (110). The insulation resistance calculating unit (120) may calculate the insulation resistance using the second voltage in a first state and the second voltage in a second state in which the resistance is varied in the first state.

[0091] The variable resistor unit (110) includes a first resistor connected in parallel with the DC link terminal (210), a second resistor connected in series with the first resistor, a first switch having one end connected to a first node between the first resistor and the second resistor and the other end connected to ground, a third resistor connected in parallel with the first resistor, a second switch connected in series with the third resistor, a fourth resistor connected in parallel with the second resistor, and a third switch connected in series with the fourth resistor, and the second voltage may be a voltage across both ends of the second resistor.

[0092] The insulation resistance calculation unit may turn on the first switch, calculate a third voltage at both ends of the first resistor using the difference between the first voltage and the second voltage, compare the magnitudes of the second voltage and the third voltage, and turn on the third switch if the second voltage is greater than the third voltage, and turn on the second switch if the third voltage is greater than the second voltage.

[0093] The insulation resistance calculation unit may, when the third switch is turned on, re-measure the first voltage and the second voltage, and calculate the insulation resistance using the difference between the re-measured second voltage and the previously measured second voltage, and, when the second switch is turned on, measure the first voltage and the second voltage again, re-calculate the third voltage, and calculate the insulation resistance using the difference between the re-calculated third voltage and the previously calculated third voltage.

[0094] As described above, the present invention has been described with specific details such as specific components and limited examples and drawings, but these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those with ordinary knowledge in the field to which the present invention pertains can make various modifications and variations from this description.

[0095] Therefore, the idea of ​​the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. Variable resistance part connected between the DC link terminal and ground; and It includes an insulation resistance calculation unit that calculates insulation resistance using the first voltage of the DC link terminal and the second voltage measured from the variable resistance unit, The above insulation resistance calculation unit is, An insulation resistance measuring device that calculates the insulation resistance by using the second voltage in the first state and the second voltage in the second state in which the resistance is varied in the first state.

2. In paragraph 1, The above variable resistor part, A first resistor connected in parallel with the above DC link terminal; A second resistor connected in series with the first resistor; A first switch having one end connected to a first node between the first resistor and the second resistor, and the other end connected to ground; A third resistor connected in parallel with the first resistor; A second switch connected in series with the third resistor; a fourth resistor connected in parallel with the second resistor; and Including a third switch connected in series with the fourth resistor, The above second voltage is an insulation resistance measuring device which is a voltage across both ends of the above second resistor.

3. In paragraph 2, An insulation resistance measuring device including a voltage sensor unit that measures the first voltage and the second voltage.

4. In paragraph 2, The above insulation resistance calculation unit is, Turn on the first switch above, An insulation resistance measuring device that calculates a third voltage across both ends of the first resistor by using the difference between the first voltage and the second voltage, and compares the magnitudes of the second voltage and the third voltage.

5. In paragraph 4, The above insulation resistance calculation unit is, If the second voltage is greater than the third voltage, the third switch is turned on, An insulation resistance measuring device that turns on the second switch when the third voltage is greater than the second voltage.

6. In paragraph 5, The above insulation resistance calculation unit is, After turning on the third switch, the first voltage and the second voltage are measured again, An insulation resistance measuring device that calculates insulation resistance by using the difference between the second voltage measured again and the second voltage measured previously.

7. In paragraph 5, The above insulation resistance calculation unit is, After turning on the second switch, the first voltage and the second voltage are measured again to calculate the third voltage again. An insulation resistance measuring device that calculates insulation resistance by using the difference between the third voltage calculated again and the third voltage calculated previously.

8. In paragraph 2, The resistance values ​​of the third resistor and the fourth resistor are the same insulation resistance measuring device.

9. A plurality of first power conversion units that convert power from the PV module and are connected in parallel; A second power conversion unit that converts the output of the plurality of first power conversion units and outputs it to the grid; A DC link terminal connected between the plurality of first power conversion units and the second power conversion units; and It includes an insulation resistance measuring unit that is connected in parallel with the above DC link terminal and measures the insulation resistance, The above insulation resistance measuring unit, A variable resistor connected between the DC link terminal and ground; and It includes an insulation resistance calculation unit that calculates insulation resistance using the first voltage of the DC link terminal and the second voltage measured from the variable resistance unit, The above insulation resistance calculation unit is, A power conversion device that calculates the insulation resistance by using the second voltage in the first state and the second voltage in the second state in which the resistance is varied in the first state.

10. In paragraph 9, The above variable resistor part, A first resistor connected in parallel with the above DC link terminal; A second resistor connected in series with the first resistor; A first switch having one end connected to a first node between the first resistor and the second resistor, and the other end connected to ground; A third resistor connected in parallel with the first resistor; A second switch connected in series with the third resistor; a fourth resistor connected in parallel with the second resistor; and Including a third switch connected in series with the fourth resistor, A power conversion device in which the second voltage is the voltage across both ends of the second resistor.

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