A photovoltaic storage system and a method for detecting insulation impedance to ground

Abstract

The present application provides a photovoltaic storage system and a method for detecting insulation impedance to ground, which are used to improve the detection accuracy of insulation impedance to ground after one or more conversion circuits are connected in parallel. The photovoltaic storage system includes: one or more conversion circuits and a detection circuit; the detection circuit includes an AC signal source and a sampling resistor connected in series, a first sampling circuit and a control circuit; the control circuit is used to control the AC signal source to output harmonic signals of the first frequency and the second frequency respectively; the first sampling circuit is used to collect the voltage across the sampling resistor to obtain the first voltage when the AC signal source outputs a harmonic signal of the first frequency, and to collect the second voltage when the AC signal source outputs a harmonic signal of the second frequency, and send the first voltage and the second voltage to the control circuit; the control circuit is also used to determine the insulation impedance to ground after one or more conversion circuits are connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage.

Description

Technical Field

[0001] The present application relates to the field of energy technology, and in particular to a photovoltaic storage system and a method for detecting insulation impedance to ground. Background Art

[0002] With the rapid development of new energy technologies, photovoltaic storage systems have been increasingly widely used. Photovoltaic storage systems, also known as solar photovoltaic (PV) energy storage power generation systems, can be composed of a photovoltaic power generation circuit, an energy storage circuit and an inverter circuit in parallel. Among them, the photovoltaic power generation circuit can convert clean and pollution-free solar energy into electrical energy, which can not only be supplied to residents' equipment after the inverter circuit to meet the daily power supply needs of residents, but also be sent to the energy storage circuit for storage, thereby effectively improving the reliability of residents' electricity use. Among them, each circuit included in the photovoltaic storage system generally includes a converter, for example, the photovoltaic power generation circuit usually includes a maximum power point tracking (MPPT) converter, the energy storage circuit usually includes a direct current-direct current (DC-DC) converter, and the inverter circuit usually includes an inverter, so the photovoltaic power generation circuit, the energy storage circuit and the inverter circuit are all conversion circuits.

[0003] However, since each conversion circuit in the photovoltaic storage system may have a very high voltage level, the insulation performance directly affects the safe operation of the system. In order to ensure the safety of operators, the normal operation of electrical equipment and the safe operation of the system, it is a basic condition for the safe operation of the photovoltaic storage system to quickly and accurately detect the insulation condition of the photovoltaic storage system to the ground and handle the fault in time.

[0004] Therefore, how to accurately detect the insulation impedance to ground after one or more conversion circuits are connected in parallel is a problem worth studying and solving. Summary of the invention

[0005] The present application provides a photovoltaic storage system and a method for detecting insulation impedance to ground, which are used to improve the accuracy of insulation impedance detection to ground without increasing system costs.

[0006] In a first aspect, an embodiment of the present application provides a photovoltaic storage system, comprising one or more conversion circuits and a detection circuit, wherein the one or more conversion circuits are connected in parallel between a positive bus and a negative bus; the detection circuit comprises a signal source excitation branch, a first sampling circuit and a control circuit; one end of the signal source excitation branch is connected to a ground line, and the other end is connected to the positive bus or the negative bus; the signal source excitation branch comprises an AC signal source and a sampling resistor connected in series; the first sampling circuit is connected in parallel to the sampling resistor, and the control circuit is respectively connected to an input end of the AC signal source and an output end of the first sampling circuit; the control circuit is used to control the AC signal source to separate The first sampling circuit is used to collect the voltage across the sampling resistor to obtain a first voltage when the AC signal source outputs the harmonic signal of the first frequency, and to collect the voltage across the sampling resistor to obtain a second voltage when the AC signal source outputs the harmonic signal of the second frequency, and to send the first voltage and the second voltage to the control circuit; the control circuit is also used to determine the insulation impedance to ground of the one or more conversion circuits after being connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage.

[0007] In the above scheme, the present application connects the detection circuit in parallel with one or more conversion circuits on the bus, and adopts the harmonic injection method, which can take into account the influence of parasitic capacitance existing in one or more conversion circuits due to wiring. The insulation impedance to ground determined by the present application does not include parasitic capacitance. Compared with the scheme adopted in the prior art, which does not consider the influence of parasitic capacitance, resulting in the inclusion of parasitic capacitance in the determined insulation impedance to ground, thereby causing the disadvantage of low detection accuracy, the photovoltaic storage system provided by the present application can improve the accuracy of detecting the insulation impedance to ground, thereby improving the accuracy of insulation condition detection, and thus ensuring the safety of the photovoltaic storage system.

[0008] In a possible design, the detection circuit may also include a DC blocking capacitor, and the other end of the signal source excitation branch is connected to the positive bus or the negative bus through the DC blocking capacitor, which is used to isolate the DC signal of the one or more conversion circuits for the detection circuit. In this design, the DC blocking capacitor can be used to isolate the DC high-voltage signal of one or more conversion circuits for the detection circuit, thereby eliminating the influence of the DC signal in the detection circuit and improving the accuracy of the insulation impedance detection to the ground.

[0009] In a specific design, the first sampling circuit is also used to collect the first phase corresponding to the first voltage when the first voltage is collected, and to collect the second phase corresponding to the second voltage when the second voltage is collected, and send the first phase and the second phase to the control circuit; the control circuit is specifically used to determine the insulation impedance to ground after the one or more conversion circuits are connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage, the first phase and the second phase. In this design, on the basis of including a DC blocking capacitor in the detection circuit, in order to avoid the influence of the DC blocking capacitor on the insulation impedance to ground after detecting one or more conversion circuits in parallel, the insulation impedance to ground can be further calculated in combination with the voltage signal phase collected on the sampling resistor after harmonic injection, thereby improving the accuracy of detecting the insulation condition.

[0010] After the control circuit determines the insulation impedance to ground of the one or more conversion circuits connected in parallel, the following scenarios may be included:

[0011] Scenario 1: The control circuit is also used to determine that the insulation condition of the one or more conversion circuits is normal when the insulation impedance to ground is greater than or equal to the first impedance threshold. In this design, it can be understood that if the insulation impedance to ground of one or more conversion circuits is large enough after being connected in parallel, it means that the insulation condition of the photovoltaic storage system is normal, that is, there is no insulation impedance fault to ground.

[0012] Scenario 2, the detection circuit also includes a leakage current sampling circuit connected to the one or more conversion circuits in a one-to-one correspondence; the input end of each leakage current sampling circuit is respectively connected to the input end and the output end of the connected conversion circuit, and the output end of each leakage current sampling circuit is connected to the control circuit; each leakage current sampling circuit is used to sample the first leakage current between the connected conversion circuit and the positive bus and the second leakage current between the connected conversion circuit and the negative bus to obtain the total leakage current of the connected conversion circuit, and send the total leakage current to the control circuit; the control circuit is also used to determine that the insulation condition of the conversion circuit corresponding to the total leakage current with the largest median value of the total leakage current sent by each leakage current sampling circuit is abnormal when the insulation impedance to ground is less than a second impedance threshold; wherein the second impedance threshold is half of the first impedance threshold.

[0013] In this design, it can be understood that if the insulation impedance to ground after one or more conversion circuits are connected in parallel is small, it can indicate that the insulation condition of the photovoltaic storage system is abnormal, that is, there is an insulation impedance fault to ground. Furthermore, each conversion circuit can be detected by the value of the total leakage current of each conversion circuit, wherein the conversion circuit with a larger leakage current value indicates a smaller insulation impedance to ground, thereby locating the faulty circuit in the conversion circuit.

[0014] Scenario 3, the detection circuit also includes a second sampling circuit and a third sampling circuit; the second sampling circuit is connected to the positive bus at one end and the ground at the other end, and is connected to the control circuit, and is used to sample the voltage between the positive bus and the ground to obtain a first bus voltage, and send the first bus voltage to the control circuit; the third sampling circuit is connected to the negative bus at one end and the ground at the other end, and is connected to the control circuit, and is used to sample the voltage between the negative bus and the ground to obtain a second bus voltage, and send the second bus voltage to the control circuit; the control circuit is also used to: when the insulation impedance to ground is less than the first impedance threshold and greater than or equal to the second impedance threshold, based on each The first leakage current and the second leakage current, the first bus voltage, the second bus voltage and the insulation impedance to ground of the conversion circuit are used to determine the positive insulation impedance to ground of the one or more conversion circuits after being connected in parallel between the positive bus and the ground, and the negative insulation impedance to ground of the one or more conversion circuits after being connected in parallel between the negative bus and the ground; when the positive insulation impedance to ground is greater than or equal to the first impedance threshold, it is determined that the insulation condition between the positive bus and the ground of the one or more conversion circuits is normal, otherwise it is abnormal; and when the negative insulation impedance to ground is greater than or equal to the first impedance threshold, it is determined that the insulation condition between the negative bus and the ground in the one or more conversion circuits is normal, otherwise it is abnormal.

[0015] In this design, it can be understood that if it is impossible to determine whether one or more conversion circuits are abnormal based on the insulation impedance to ground after one or more conversion circuits are connected in parallel, it can be determined whether there is an abnormality by first calculating the positive pole insulation impedance to ground and the negative pole insulation impedance to ground respectively, because the parallel impedance (the insulation impedance to ground after parallel connection) is smaller than any branch impedance. If each branch impedance (that is, the positive pole insulation impedance to ground and the negative pole insulation impedance to ground introduced in the aforementioned design) is normal, it can also be determined that the insulation condition of the one or more conversion circuits is normal.

[0016] In the design of obtaining the total leakage current by collecting the first leakage current and the second leakage current of the connected conversion circuit by using the leakage current sampling circuit as described above, since there is an AC signal source in the detection circuit, the total leakage current collected by the leakage current sampling circuit contains not only a DC signal but also an AC signal. In order to further improve the detection accuracy of the control circuit, before the control circuit performs the insulation impedance detection to the ground based on the total leakage current, the total leakage current collected by the leakage current sampling circuit can also be filtered. The filtering can include at least the following two methods:

[0017] Filtering method 1, the detection circuit also includes an AC signal filter connected to each leakage current sampling circuit in a one-to-one correspondence; the input end of each AC signal filter is connected to the corresponding leakage current sampling circuit, and the output end is connected to the control circuit; the AC signal filter is used to filter out the AC signal contained in the total leakage current of the conversion circuit sampled by the leakage current sampling circuit. In this design, in order to improve the accuracy of the insulation impedance detection to the ground, before the control circuit processes based on the leakage current, the AC signal contained in the leakage current can also be filtered out by analog filtering, thereby ensuring the accuracy of the calculation of the positive electrode to ground insulation impedance and the negative electrode to ground insulation impedance.

[0018] Filtering method 2, the control circuit is also used to: receive the total leakage current of the conversion circuit connected to the target leakage current sampling circuit sampled by the target leakage current sampling circuit; the target leakage current sampling circuit is any leakage current sampling circuit in each of the leakage current sampling circuits; after performing analog-to-digital conversion on the total leakage current of the conversion circuit connected to the target leakage current sampling circuit, filter out the AC signal contained in the total leakage current after the analog-to-digital conversion. In this design, in order to improve the accuracy of the insulation impedance detection to the ground, before the control circuit performs processing based on the leakage current, the AC signal contained in the leakage current can also be filtered out by digital filtering, thereby ensuring the accuracy of the calculation of the positive electrode insulation impedance to the ground and the negative electrode insulation impedance to the ground.

[0019] In a possible design, the insulation impedance to ground complies with the following formula:

[0020]

[0021]

[0022] Among them, the represents the first voltage, the represents the second voltage; the ω 1 represents the harmonic signal of the first frequency, the ω 2 represents the harmonic signal of the second frequency; the R r represents the impedance of the sampling resistor, the Rx represents the insulation resistance to ground, the C x represents the capacitance value of the parasitic capacitance of the optical storage system; represents the maximum voltage of the harmonic signal of the first frequency, the Represents the maximum voltage of the harmonic signal of the second frequency.

[0023] In this design, through the above two formulas, since the unknown number in the formula is R x and C x , so the insulation resistance to ground can be solved, and since this application calculates R x When the parasitic capacitance C x By calculating it as a known quantity, the accuracy of ground insulation impedance detection can be improved, thereby ensuring the safety of the photovoltaic storage system.

[0024] In another possible design, the insulation resistance to ground complies with the following formula:

[0025]

[0026] Among them, the represents the first voltage, the represents the second voltage; the ω 1 represents the harmonic signal of the first frequency, the ω 2 represents the harmonic signal of the second frequency; the R r represents the impedance of the sampling resistor, the C r represents the capacitance value of the DC blocking capacitor; the R x represents the insulation resistance to ground, the C x represents the capacitance value of the parasitic capacitance of the optical storage system; represents the maximum voltage of the harmonic signal of the first frequency, the represents the maximum voltage of the harmonic signal of the second frequency; represents the first phase, the represents the second phase.

[0027] In this design, through any three of the above formulas, since the unknown number in the formula is C r , R x and C x , so the insulation resistance to ground can be solved, and since this application calculates R x When the parasitic capacitance C r and C x By calculating it as a known quantity, the accuracy of ground insulation impedance detection can be improved, thereby ensuring the safety of the photovoltaic storage system.

[0028] In yet another possible design, the insulation impedance to ground complies with the following formula:

[0029] or

[0030] Among them, the C x R x It complies with the following formula:

[0031]

[0032] Among them, the represents the first voltage, the represents the second voltage; the ω 1 represents the harmonic signal of the first frequency, the ω 2 represents the harmonic signal of the second frequency; the R r represents the impedance of the sampling resistor; the R x represents the insulation resistance to ground, the C x represents the capacitance value of the parasitic capacitance of the optical storage system; represents the maximum voltage of the harmonic signal of the first frequency, the represents the maximum voltage of the harmonic signal of the second frequency; represents the first phase, the represents the second phase.

[0033] In this design, the insulation resistance R to ground is obtained by solving the above x The formula for calculating R in this application can be obtained x When the parasitic capacitance C r and C x By calculating it as a known quantity, the accuracy of ground insulation impedance detection can be improved, thereby ensuring the safety of the photovoltaic storage system.

[0034] In a second aspect, an embodiment of the present application further provides a method for detecting insulation impedance to ground, which is applied to the photovoltaic storage system as introduced in the first aspect, and the method includes: the control circuit controls the AC signal source to output harmonic signals of a first frequency and a second frequency respectively, and the first frequency is different from the second frequency; the control circuit receives a first voltage and a second voltage sent by the first sampling circuit; wherein the first voltage is obtained by the first sampling circuit collecting the voltage across the sampling resistor when the AC signal source outputs the harmonic signal of the first frequency, and the second voltage is obtained by the first sampling circuit collecting the voltage across the sampling resistor when the AC signal source outputs the harmonic signal of the second frequency; the control circuit determines the insulation impedance to ground of the one or more conversion circuits after being connected in parallel based on the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage.

[0035] In a specific design, the method further includes: the control circuit receives the first phase and the second phase sent by the first sampling circuit; wherein the first phase is obtained by sampling the first phase corresponding to the first voltage when the first sampling circuit samples the first voltage, and the second phase is obtained by sampling the second phase corresponding to the second voltage when the first sampling circuit samples the second voltage. The control circuit determines the insulation impedance to ground after the one or more conversion circuits are connected in parallel based on the harmonic signals of the first and second frequencies, the first voltage and the second voltage, which can be specifically implemented as follows: the control circuit determines the insulation impedance to ground after the one or more conversion circuits are connected in parallel based on the harmonic signals of the first and second frequencies, the first voltage and the second voltage, the first phase and the second phase.

[0036] After the control circuit determines the insulation impedance to ground of the one or more conversion circuits after being connected in parallel, the method may further include the following scenarios:

[0037] Scenario 1: When the insulation impedance to ground is greater than or equal to a first impedance threshold, the control circuit determines that the insulation condition of the one or more conversion circuits is normal.

[0038] Scenario 2, the detection circuit also includes a leakage current sampling circuit connected to one or more conversion circuits in a one-to-one correspondence; the input end of each leakage current sampling circuit is respectively connected to the input end and the output end of the connected conversion circuit, and the output end of each leakage current sampling circuit is connected to the control circuit. The method also includes: the control circuit receives the total leakage current of the connected conversion circuit sent by each leakage current sampling circuit; wherein the total leakage current of the conversion circuit is obtained by sampling the first leakage current between the connected conversion circuit and the positive bus and the second leakage current between the connected conversion circuit and the negative bus by each leakage current sampling circuit; when the insulation impedance to ground is less than the second impedance threshold, the control circuit determines that the insulation condition of the conversion circuit corresponding to the leakage current with the largest median leakage current sent by each leakage current sampling circuit is abnormal; wherein the second impedance threshold is half of the first impedance threshold.

[0039] Scenario 3, the detection circuit also includes a second sampling circuit and a third sampling circuit; the second sampling circuit has one end connected to the positive bus and the other end connected to the ground, and is connected to the control circuit, for sampling the voltage between the positive bus and the ground to obtain a first bus voltage, and sending the first bus voltage to the control circuit; the third sampling circuit has one end connected to the negative bus and the other end connected to the ground, and is connected to the control circuit, for sampling the voltage between the negative bus and the ground to obtain a second bus voltage, and sending the second bus voltage to the control circuit. The method also includes: when the insulation impedance to ground is less than the first impedance threshold and greater than or equal to the second impedance threshold, the control circuit determines the positive insulation impedance to ground of the one or more conversion circuits after being connected in parallel between the positive bus and the ground, and the negative insulation impedance to ground of the one or more conversion circuits after being connected in parallel between the negative bus and the ground based on the first bus voltage, the second bus voltage and the insulation impedance to ground. When the positive electrode-to-ground insulation impedance is greater than or equal to the first impedance threshold, the control circuit determines that the insulation condition between the positive electrode bus and the ground wire of the one or more conversion circuits is normal, otherwise it is abnormal. And when the negative electrode-to-ground insulation impedance is greater than or equal to the first impedance threshold, the control circuit determines that the insulation condition between the negative electrode bus and the ground wire in the one or more conversion circuits is normal, otherwise it is abnormal.

[0040] In a third aspect, the present application provides a chip, which may be a chip in an inverter, and is used to execute the method described in any one of the designs in the second aspect above.

[0041] For the beneficial effects of the second to third aspects, please refer to the beneficial effects corresponding to the various designs in the first aspect, and they will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1a It is a structural schematic diagram of a photoelectric storage system;

[0043] Figure 1b is a schematic diagram of the structure of another photovoltaic storage system;

[0044] Figure 2a One of the structural schematic diagrams of a photovoltaic storage system provided in an embodiment of the present application;

[0045] Figure 2b A schematic diagram of the structure of a signal source excitation branch provided in an embodiment of the present application;

[0046] Figure 2c A second structural diagram of a photovoltaic storage system provided in an embodiment of the present application;

[0047] Figure 2d One of the equivalent circuit diagrams of a photovoltaic storage system provided in an embodiment of the present application;

[0048] Figure 3 A third structural diagram of a photovoltaic storage system provided in an embodiment of the present application;

[0049] Figure 4 The second equivalent circuit diagram of a photovoltaic storage system provided in an embodiment of the present application;

[0050] Figure 5a The third equivalent circuit diagram of a photovoltaic storage system provided in an embodiment of the present application;

[0051] Figure 5b A vector diagram of a photovoltaic storage system provided in an embodiment of the present application;

[0052] Figure 6a A fourth structural diagram of a photovoltaic storage system provided in an embodiment of the present application;

[0053] Figure 6b This is a fourth schematic diagram of an equivalent circuit of a photovoltaic storage system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0054] The present application will be described in further detail below in conjunction with the accompanying drawings.

[0055] With the rapid development of new energy technologies, photovoltaic storage systems are increasingly widely used. Photovoltaic storage systems, also known as solar photovoltaic energy storage power generation systems, can be composed of a photovoltaic power generation circuit, an energy storage circuit and an inverter circuit in parallel. Among them, the photovoltaic power generation circuit can convert clean and pollution-free solar energy into electrical energy, which can not only be supplied to residents' equipment after passing through the inverter circuit to meet the residents' daily power supply needs, but can also be sent to the energy storage circuit for storage, thereby effectively improving the reliability of residents' electricity use.

[0056] like Figure 1a As shown, the photovoltaic storage system 10 may include an energy storage circuit 11, a photovoltaic power generation circuit 12, and an inverter circuit 13. The energy storage circuit 11, the photovoltaic power generation circuit 12, and the inverter circuit 13 may be connected in parallel to the positive bus (BUS+) and the negative bus (BUS-).

[0057] The photovoltaic power generation circuit 12 may generally include photovoltaic components (such as photovoltaic panels), so that light energy (solar energy) can be used to generate electricity, that is, the absorbed light energy (solar energy) is converted into photovoltaic power through the photovoltaic panel, wherein the "photovoltaic power generation circuit" may also be referred to as a "photovoltaic system", etc. If the output power of the photovoltaic power generation circuit 12 is large, part of the photovoltaic power output by the photovoltaic power generation circuit 12 can be output to the AC power grid 14 after passing through the inverter circuit 13, and used to supply residents' equipment to meet the residents' daily power supply needs. Another part of the photovoltaic power can be sent to the energy storage circuit 11 for storage.

[0058] The energy storage circuit 11 may generally include an energy storage component, or an energy storage battery cluster, etc., which can be charged and discharged through the energy storage component to improve the reliability of power supply in the photovoltaic storage system 10, wherein the "energy storage circuit" may also be referred to as an "energy storage system", etc. When the output power of the photovoltaic power generation circuit 12 is relatively large, the energy storage circuit 11 may store the photovoltaic power in the photovoltaic power generation circuit 12 except for the output to the AC power grid 14, that is, "charging" or "storing power". Moreover, when the output power of the photovoltaic power generation circuit 12 is relatively small, the energy storage circuit 11 may output the stored electric energy to output it to the AC power grid 14 after passing through the inverter circuit 13.

[0059] The inverter circuit 13 can perform DC-AC conversion on the DC power received from the photovoltaic power generation circuit 12 and / or the energy storage circuit 11, and output the obtained AC power to the AC power grid 14. Alternatively, the inverter circuit 13 can also perform AC-DC conversion on the AC power received from the AC power grid 14, and output the obtained DC power to the energy storage circuit 11 for storage. Among them, the "inverter circuit" can also be called "inverter", "photovoltaic inverter", "bidirectional inverter (powerconversion system, PCS)", etc. In addition, the inverter circuit 13 can also serve as a charge and discharge control device for the energy storage circuit 11, and control the energy storage circuit 11 to charge or discharge according to the power demand of the AC power grid 14, thereby improving the reliability and effectiveness of the power supply of the photovoltaic storage system.

[0060] It can be understood that in the daytime, especially in sunny days and other scenes with strong light energy, the photovoltaic power generation circuit 12 has output power, and it is considered that the photovoltaic power generation circuit 12 can supply power to the AC power grid 14 through the inverter circuit 13. In scenes with stronger light energy, the greater the output power of the photovoltaic power generation circuit 12, when the output power is greater than the target power required by the AC power grid 14, it can be considered that only the photovoltaic power generation circuit 12 supplies power to the AC power grid 14 through the inverter circuit 13; and part of the electric energy in the output power of the photovoltaic power generation circuit 12 that exceeds the target power can also be stored in the energy storage circuit 11. In scenes with weak light energy, the output power of the photovoltaic power generation circuit 12 is small, and when the output power cannot meet the target power required by the AC power grid 14, the photovoltaic power generation circuit 12 and the energy storage circuit 11 jointly supply power to the AC power grid 14 through the inverter circuit 13. In scenes such as cloudy days or nights, the output power of the photovoltaic power generation circuit 12 may approach 0W, and it can be considered that only the energy storage circuit 11 supplies power to the AC power grid 14 through the inverter circuit 13. That is to say, the DC power received by the inverter circuit 13 may come only from the photovoltaic power generation circuit 12 , only from the energy storage circuit 11 , or may be a mixed power including battery power output by the energy storage circuit 11 and photovoltaic power output by the photovoltaic power generation circuit 12 .

[0061] For example, the target power required by the AC power grid 14 is 60W, and the power of the photovoltaic power output by the photovoltaic power generation circuit 12 is 80W. The inverter circuit 13 can provide 60W of the photovoltaic power to the AC power grid 14, and the remaining 20W of the photovoltaic power can be stored in the energy storage circuit 11 as charging power. Furthermore, when the power of the photovoltaic power output by the photovoltaic power generation circuit 12 is 30W, the inverter circuit 13 can control the energy storage circuit 11 to provide the remaining 30W of DC power. When the power of the photovoltaic power output by the photovoltaic power generation circuit 12 is 0W, the inverter circuit 13 can control the energy storage circuit 11 to provide all the 60W of power required by the AC power grid 14.

[0062] In general scenarios, such as Figure 1b As shown, the energy storage circuit 11 may include multiple conversion circuits consisting of energy storage battery clusters and direct current-direct current (DC-DC) converters connected in parallel on the bus. The photovoltaic power generation circuit 12 may include multiple conversion circuits consisting of photovoltaic (PV) panels and maximum power point tracking (MPPT) converters connected in parallel on the bus. Therefore, the photovoltaic power generation circuit, energy storage circuit and inverter circuit can all be called conversion circuits. Among them,

[0063] The energy storage battery cluster included in the energy storage circuit 11 is used for storing and outputting electric energy. The DC-DC converter included in the energy storage circuit 11 is used for voltage conversion between the battery cluster and the inverter circuit 13, so that the voltage of the DC electric energy can be adapted to the voltage of the battery cluster and the inverter circuit 13 respectively; or for voltage conversion between the battery cluster and the photovoltaic power generation circuit 12, so that the voltage of the DC electric energy can be adapted to the voltage of the battery cluster and the photovoltaic power generation circuit 13 respectively. For example, assuming that the working voltage of the battery cluster is 100V and the working voltage of the inverter circuit 13 is 1000V, when the battery cluster outputs electric energy, that is, when supplying power, the DC-DC converter is used to convert the electric energy provided by the battery cluster from 100V to 1000V, so that the electric energy after the voltage conversion can be adapted to the working voltage of the inverter circuit 13. Similarly, assuming that the operating voltage of the battery cluster is 100V and the operating voltage of the photovoltaic power generation circuit 12 is 200V, when the battery cluster stores electrical energy, that is, when charging, the DC-DC converter is used to convert the electrical energy provided by the photovoltaic power generation circuit 12 from 200V to 100V, so that the electrical energy after the voltage conversion can be adapted to the operating voltage of the battery cluster.

[0064] The PV panel included in the photovoltaic power generation circuit 12 is used to convert light energy (such as solar energy) into electrical energy. The MPPT converter included in the photovoltaic power generation circuit 12 is used to perform voltage conversion, which can realize that the PV panel can work at the voltage value corresponding to the maximum output power point, and then the output power of the photovoltaic power generation circuit 12 can reach the maximum value. Among them, the determining factors of the maximum output power point of the PV panel are mainly the working temperature and light intensity of the PV panel. For example, at a first temperature, the voltage corresponding to the maximum output power point of the PV panel is 100V, and at a second temperature, the voltage corresponding to the maximum output power point of the PV panel is 110V. Therefore, in the scenario where the working temperature of the PV panel changes from the first temperature to the second temperature, in order to obtain the maximum output power, the working voltage of the PV panel is converted from 100V to 110V through the MPPT converter.

[0065] In such Figure 1b In the photovoltaic storage system shown, since each conversion circuit connected in parallel to the busbar (the conversion circuit can be a storage circuit, photovoltaic power generation circuit or inverter circuit as described above) has a very high voltage level, it is important to quickly and accurately identify abnormal insulation conditions of the photovoltaic storage system 10 to the ground, which is important for operator safety, normal operation of electrical equipment and safe operation of the photovoltaic storage system. However, most of the insulation impedance detection schemes currently available in the prior art do not consider the influence of parasitic capacitance in the photovoltaic storage system, and for photovoltaic storage systems with multiple conversion circuits connected in parallel, the influence of parasitic capacitance is more significant, so the detection accuracy is not high. It should be noted that the parasitic capacitance in the photovoltaic storage system 10 is not an actual capacitance, but may be due to the mutual capacitance between the wiring included in the system, which is like parasitic between the wiring, or the parasitic capacitance may also be due to the capacitance contained in the PV panel in the photovoltaic storage system 10, or other non-real capacitance in the photovoltaic storage system 10.

[0066] In view of this, in order to accurately detect the insulation impedance to ground after one or more conversion circuits are connected in parallel, the present application provides a photovoltaic storage system and a ground insulation impedance detection scheme. By adding a detection circuit and a control circuit to the photovoltaic storage system, and using harmonic injection to determine the insulation impedance to ground after one or more conversion circuits are connected in parallel, it is possible to first determine whether the insulation condition of the photovoltaic storage system meets the safe operating conditions based on the insulation impedance to ground.

[0067] It should be noted that in the description of the present application, "at least one" refers to "one or more". Among them, "multiple" refers to two or more. In view of this, in the embodiments of the present application, "multiple" can also be understood as "at least two". "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, it should be understood that in the description of the present application, words such as "first" and "second" are only used for the purpose of distinguishing the description, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order.

[0068] Figure 2a The schematic diagram of the structure of a photovoltaic storage system provided by the present application is shown. The photovoltaic storage system includes: one or more conversion circuits (such as Figure 2a The conversion circuit 1 ... conversion circuit n) and the detection circuit 15 are included. Wherein, the one or more conversion circuits are connected in parallel between the positive bus and the negative bus. Based on the above Figure 1a and Figure 1b In the introduction of the photovoltaic storage system 10, the conversion circuit can be the aforementioned energy storage circuit 11, or the photovoltaic power generation circuit 12, or the inverter circuit 13. The detection circuit 15 includes a signal source excitation branch 151, a first sampling circuit 152 and a control circuit 153.

[0069] One end of the signal source excitation branch 151 is connected to the ground wire, and the other end is connected to the positive bus or the negative bus ( Figure 2a The positive busbar is used as an example in the example, and the negative busbar is not connected in the example. Figure 2a As shown in FIG. 1 , the signal source excitation branch 151 may specifically include an AC signal source 151a and a sampling resistor 151b connected in series. Based on this, four connection modes of the signal source excitation branch 151 can be obtained, such as Figure 2b As shown, connection mode 1 and connection mode 3 indicate that the signal source excitation branch 151 is connected between the positive bus and the ground; and connection mode 1 indicates that one end of the AC signal source 151a is connected to the ground, and the other end is connected to the sampling resistor 151b, and the other end of the sampling resistor 151b is connected to the positive bus; connection mode 3 indicates that one end of the AC signal source 151a is connected to the positive bus, and the other end is connected to the sampling resistor 151b, and the other end of the sampling resistor 151b is connected to the ground. Similarly, connection mode 2 and connection mode 4 indicate that the signal source excitation branch 151 is connected between the negative bus and the ground, and the details are not repeated here. It should be noted that Figure 2a In the subsequent embodiments, the signal source excitation branch 151 adopts Figure 2b The connection method 1 shown in FIG. 1 is described as an example.

[0070] The first sampling circuit 152 is connected in parallel to the sampling resistor 151 b , and the control circuit 153 is connected to the input end of the AC signal source and the output end of the first sampling circuit respectively.

[0071] The control circuit 153 is used to control the AC signal source 151a to output harmonic signals of a first frequency and a second frequency respectively, wherein the first frequency is different from the second frequency. The first sampling circuit 152 is used to collect the voltage across the sampling resistor 151b to obtain a first voltage when the AC signal source 151a outputs the harmonic signal of the first frequency, and to collect the voltage across the sampling resistor 151b to obtain a second voltage when the AC signal source 151a outputs the harmonic signal of the second frequency, and to send the first voltage and the second voltage to the control circuit 153. The control circuit 153 is also used to determine the insulation impedance to ground of the one or more conversion circuits after being connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage.

[0072] In order to better understand the embodiments of the present application, one or more conversion circuits are used as Figure 1b The photovoltaic storage system shown in FIG. 1 is used as an example for specific introduction. Figure 2c As shown, Figure 2c In the figure, a represents the structural diagram of the photovoltaic storage system, and b represents the system equivalent circuit diagram after the photovoltaic storage system is equivalent. It can be understood that by analyzing the system equivalent circuit, the working principle of the photovoltaic storage system provided by the present application can be more clearly understood.

[0073] First of all Figure 2c The system equivalent circuit shown in b is introduced. The conversion circuits included in the photovoltaic storage system can generally be connected in parallel on the busbar in a common cathode or common anode manner. When implementing this application, the conversion circuits included in the photovoltaic storage system using a common cathode manner is used as an example. The system equivalent circuit is as follows Figure 2c If the conversion circuits included in the photovoltaic storage system are connected in parallel on the busbar in a common anode manner, the same principle can be used for circuit analysis, and this application will not repeat it in detail.

[0074] For example, the DC-DC converter included in the photovoltaic storage system can be equivalent to the insulation impedance of the positive electrode of the battery cluster assembly to the ground (for example Figure 2c The R shown in b p1 ,……,R pn ) and the insulation resistance of the negative electrode of the battery cluster assembly to ground (e.g. Figure 2c The R shown in b n1 ,……,R nnThe MPPT converter included in the solar storage system can be equivalent to the insulation impedance of the positive pole of the PV panel to the ground (for example Figure 2c The R shown in b pvp1 ,……,R pvpn ) and the insulation resistance of the negative pole of the PV panel to ground (e.g. Figure 2c The R shown in b pvn1 ,……,R pvnn The inverter circuit 13 included in the photovoltaic storage system can be equivalent to the insulation impedance of the positive pole of the inverter component to the ground (for example Figure 2c The R shown in b vp ) and the insulation resistance of the negative pole of the inverter assembly to ground (e.g. Figure 2c The R shown in b vn ).

[0075] Exemplarily, each conversion circuit included in the photovoltaic storage system is connected in parallel on the busbar, combined with Figure 2c The system equivalent circuit shown in b can be obtained by the following formula 1a:

[0076] R p =R p1 / / R p2 / / … / / R pn / / R pvp1 / / … / / R pvpn / / R vp Formula 1a

[0077] Similarly, the insulation impedance of the negative electrode to ground after one or more conversion circuits are connected in parallel can be obtained by the following formula 1b:

[0078] R n =R n1 / / R n2 / / … / / R nn / / R pvn1 / / … / / R pvnn / / R vn Formula 1b

[0079] Based on the above formulas 1a and 1b, Figure 2c The system equivalent circuit in is simplified to obtain Figure 2d The simplified equivalent circuit is shown. Figure 2d The simplified equivalent circuit shown in a includes: the R p , the R n , the positive parasitic capacitance C after one or more conversion circuits are connected in parallel p , the negative parasitic capacitance C after one or more conversion circuits are connected in parallel nAnd the detection circuit 15. Considering the influence of parasitic capacitance in the photovoltaic storage system 10, the positive electrode parasitic capacitance C p And the negative parasitic capacitance C after parallel connection n .

[0080] Furthermore, for Figure 2d The simplified equivalent circuit shown in a in FIG. 1 can also be used to calculate the insulation impedance R to ground after one or more conversion circuits are connected in parallel based on the parallel impedance formula. x That is, the insulation impedance to ground is the parallel impedance of the positive electrode insulation impedance to ground and the negative electrode insulation impedance to ground after one or more conversion circuits are connected in parallel. The insulation impedance to ground R after the one or more conversion circuits are connected in parallel x It can be obtained by the following formula 1c:

[0081]

[0082] Similarly, according to the calculation rules for multiple capacitors in parallel, the total parasitic capacitance C after one or more conversion circuits are connected in parallel can be obtained by the following formula 1d: x :

[0083] C x =C p +C n Formula 1d

[0084] Based on the above formulas 1c and 1d, Figure 2d The simplified equivalent circuit shown in a is further simplified to obtain Figure 2d The simplified equivalent circuit shown in b.

[0085] In addition, in Figure 2d In the simplified equivalent circuit shown in , based on the superposition theorem (in order to determine the effect of each independent signal source, all other voltage sources in the circuit must be set to zero, which can also be understood as replacing all other independent voltage sources with short circuits), it can be obtained that when the AC signal source 151a included in the detection circuit 15 is working, the ideal DC voltage source can be considered to be short-circuited, that is, it can be understood that the battery cluster, PV panel, and positive bus and negative bus included in the photovoltaic storage system can be considered to have a voltage of 0, that is, they can be considered as wires, so in Figure 2d Not shown.

[0086] In introducing the system structure diagram of the optical storage system provided by this application (such as Figure 2c As shown in a), the system equivalent circuit (as shown in Figure 2c b) and the simplified equivalent circuit (as shown in Figure 2d After that, the optical storage system 10 provided by the present application is introduced through an embodiment as follows.

[0087] The control circuit 153 controls the AC signal source to output harmonic signals of a first frequency and a second frequency respectively, wherein the first frequency is different from the second frequency. Exemplarily, the control circuit 153 sends a drive signal to the AC signal source 151a, and the drive signal is used to drive the AC signal source 151a to output a harmonic signal of a specified frequency.

[0088] The first sampling circuit 152 is used to collect the voltage across the sampling resistor 151b to obtain a first voltage when the AC signal source 151a outputs the harmonic signal of the first frequency, and to collect the voltage across the sampling resistor 151b to obtain a second voltage when the AC signal source 151a outputs the harmonic signal of the second frequency, and to send the first voltage and the second voltage to the control circuit.

[0089] The control circuit 153 determines the insulation impedance R to ground after the one or more conversion circuits are connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage. x .

[0090] When implemented, through Figure 2d The simplified equivalent circuit shown in b can be obtained as follows: s An example that can be expressed as Formula 2 is as follows:

[0091]

[0092] Wherein, ω in Formula 2 represents the frequency of the harmonic signal injected by the AC signal source 151a, which is a known number; R r is the impedance value of the sampling resistor 151b, which is a known number; C x , R x As an unknown number when this application is implemented.

[0093] exist Figure 2d In the simplified equivalent circuit shown in FIG. 1 b, the maximum voltage of the harmonic signal output by the AC signal source 151a can be determined based on the harmonic signal of the known frequency (such as the first frequency or the second frequency introduced above) output by the AC signal source 151a. The resistance voltage across the sampling resistor 151b can be collected by the first sampling circuit 152 According to the principle that the current in a series circuit is equal everywhere, the following formula 3 can be obtained:

[0094]

[0095] Based on the principle shown in the above formula 3, when the AC signal source 151a outputs the first frequency (assuming ω1 When , we can get the following formula 4a:

[0096]

[0097] in, It is used to indicate the sampling resistance R detected by the first sampling circuit when the first frequency is injected into the AC signal source 151a. r The first voltage across the two ends, the Represents the maximum voltage of the harmonic signal of the first frequency.

[0098] Similarly, when the AC signal source 151a outputs the second frequency (assuming ω 2 When , we can get the following formula 4b:

[0099]

[0100] in, It is used to indicate the sampling resistance R detected by the first sampling circuit when the second frequency is injected into the AC signal source 151a. r The second voltage across the terminals, Represents the maximum voltage of the harmonic signal of the second frequency.

[0101] For example, the above formula 4a and formula 4b are combined, where the unknown number is R x and C x , the other numbers are known, so the insulation resistance R to ground after one or more conversion circuits are connected in parallel can be calculated x It should be noted that the above formula 4a and formula 4b are only one form of expression, and the formula expression forms obtained after deformation, shifting, etc. belong to the present application.

[0102] Through the above calculation method, it can be obtained that when implementing the present application, the influence of parasitic capacitance existing in one or more conversion circuits is taken into consideration, and the parasitic capacitance C x The insulation resistance to ground after parallel connection is R x As unknowns, the harmonic injection method is used to output two harmonic signals of different frequencies through the AC signal source 151a, and then the insulation impedance R to ground after one or more conversion circuits are connected in parallel can be solved by formula 4a and formula 4b. x Through this solar storage system, due to the solved R x Does not include parasitic capacitance C x Therefore, compared with the technical solution in the prior art that does not consider the influence of parasitic capacitance, the present application can improve the detection accuracy of the insulation condition of the photovoltaic storage system, thereby improving the safety of the photovoltaic storage system.

[0103] In addition, in another possible design, based on the harmonic injection implementation method adopted in the present application, in order to avoid the influence of the DC signal in one or more conversion circuits on the signal source excitation branch 151, when the present application is implemented, the detection circuit 15 may also include a DC blocking capacitor 154, and the other end of the signal source excitation branch 151 is connected to the positive bus or the negative bus through the DC blocking capacitor 154, which is used to isolate the DC signal of the one or more conversion circuits for the detection circuit 15. Figure 3 As shown, the DC blocking capacitor can be used to isolate the high-voltage DC signal input from the positive bus, thereby eliminating the influence of the DC signal in the detection circuit 15, thereby ensuring the safe operation of the detection circuit 15. Figure 2d The same principle as the simplified equivalent circuit, the evolved equivalent circuit after the detection circuit 15 includes the DC blocking capacitor 154 is as follows Figure 4 However, the DC blocking capacitor 154 will also affect the insulation impedance R to ground after the detection circuit 15 detects one or more conversion circuits connected in parallel. x The detection accuracy is affected, so when calculating R x The DC blocking capacitors also need to be considered.

[0104] At this time, if Figure 4 The total circuit impedance Z in the simplified equivalent circuit shown is s1 An example that can be expressed as Formula 5 is as follows:

[0105]

[0106] In an optional implementation, based on the same principle as the aforementioned formula 3, formula 4a and formula 4b, the following formula 6a and formula 6b can be obtained:

[0107]

[0108] The parameters in the above formulas 6a and 6b have the same meanings as those in the above formulas 4a and 4b, and are not repeated here. However, in the above formulas 6a and 6b, if the calculation of R x At the same time, consider the parasitic capacitance C x and the DC blocking capacitor C r Because there are three unknowns, at least three formulas need to be combined to obtain the effect. Based on this, when the present application is implemented, the first sampling circuit 152 is also used to collect the first phase corresponding to the first voltage when the first voltage is collected, and to collect the second phase corresponding to the second voltage when the second voltage is collected, and send the first phase and the second phase to the control circuit.

[0109] According to the calculation formula of the phase in the AC circuit in the prior art, the following first phase can be obtained respectively: and the second phase The expressions of formulas 6c and 6d are:

[0110]

[0111] In this example, by combining formulas 6a to 6d, any three of them can be used to calculate the unknown number C. r , C x and R x The parameters included in the above formulas 6c and 6d have the same meanings as the formulas introduced above, and will not be repeated here. It should be noted that the above formulas 6a to 6d are only one form of expression, and the formula expression forms obtained after deformation, shifting, etc. belong to the present application.

[0112] Therefore, when the present application is implemented, the control circuit 153 can be specifically used to determine the insulation impedance R to ground after the one or more conversion circuits are connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage, the first phase and the second phase. x .

[0113] In another optional implementation manner, when implementing the present application, R can also be obtained based on the vector diagram. x The calculation formula is as follows. Figure 5a and 5b Based on the implementation method of the harmonic injection method used in this application, Figure 5a The voltage and current signals in the simplified equivalent circuit are vector values ​​(or vector values), that is, the voltage and current signals have directions. For example, Figure 5a The sampling resistor R r The current i r is the main circuit current in the simplified equivalent circuit, which is equal to the parasitic capacitance C x The branch current i cx And insulation resistance to ground R x The branch current i Rx The sum, for example, can be expressed as It should be noted that the branch current i cx and branch current i Rx The directions are perpendicular to each other, such as Figure 5b Assume that i cx and i Rx The direction angle is α, then we can get Figure 5b The a in FIG. 1 shows the expression of tanα.

[0114] Furthermore, after the sampling resistor 151b receives the harmonic signal output by the AC signal source 151a, it will have a certain phase difference relative to the phase when the AC signal source 151a outputs, that is, the first phase corresponding to the first voltage at both ends of the sampling resistor 151b and the second phase corresponding to the second voltage are collected by the aforementioned first sampling circuit 152. For the convenience of analysis, the direction of the collected voltage and current at the sampling resistor 151b is used as the initial phase direction, and the following can be obtained: Figure 5b The vector diagram is shown in b. represents the phase difference of the sampling resistor 151b relative to the AC signal 151a (where The first phase may include and the second phase ). The voltage across the DC blocking capacitor 154 and the voltage across the sampling resistor 151b are perpendicular to each other, and the maximum voltage of the harmonic signal output by the AC signal source 151a is |V s | is a known number. Figure 5a The simplified equivalent circuit shown can be obtained Therefore, we can get the following equation: Figure 5b The vector diagram shown in b is Represents C x or R x The voltage across the two ends. Figure 5b The vector diagram shown in b in FIG. 1 shows |V cr | two expressions, by |V cr |The two expressions can be combined to obtain the following equation relationship between Formula 7a and Formula 7b:

[0115]

[0116] The unknown in Formula 7a and Formula 7b is C x , R x and C r , by combining the above formulas 7a and 7b, we can get C x R x The expression of is shown in Formula 7c below:

[0117]

[0118] according to Figure 5b From the expression of tanα shown in a, we can get that α can be expressed in the form of the following formula 7d:

[0119] α=arctan(ωC x R x ) Formula 7d

[0120] In addition, according to Figure 5b The vector diagram shown in b in Figure 1 also gives The relationship between x The expression can be shown as in the following formula 7e1 or 7e2:

[0121]

[0122] And, we can get C from formula 7c x R x Substituting the expression into Formula 7e1 or 7e2, we can get R x The calculation formula does not include the unknown number C x and C r , from which we can get the application to determine R x It will not be affected by parasitic capacitance and DC blocking capacitance, thus improving the accuracy of detecting insulation impedance to ground.

[0123] When the present application is implemented, the control circuit 153 can determine the insulation resistance R to ground. x Afterwards, based on the determined R x Further performing abnormal analysis on the insulation condition of the one or more conversion circuits may specifically include the following scenarios:

[0124] Scenario 1: Insulation resistance to ground R x Greater than or equal to the first impedance threshold (assuming R th to represent), that is, R x ≥R th , the control circuit 153 can determine that the insulation condition of the one or more conversion circuits is normal. It can be understood that if the insulation impedance to the ground of one or more conversion circuits connected in parallel is large enough, it means that the insulation condition of the photovoltaic storage system is normal, that is, there is no insulation impedance fault to the ground.

[0125] For example, assuming R th It is expressed as the minimum acceptable insulation resistance to ground. Based on the principle that "parallel impedance is less than any branch impedance", the insulation resistance to ground R x ≥R th Based on this, we can further infer that R p and R n Both are greater than R th Similarly, due to R p and R n It is also calculated by connecting multiple conversion circuits in parallel to the insulation impedance to ground. It can be further inferred that R pi (i ranges from 1 to n, vp1 to vpn), R vp and R ni(i ranges from 1 to n, vp1 to vpn), R vn They are also greater than R th It can be concluded that, in the scenario of detecting the insulation impedance to ground of each conversion circuit in the photovoltaic storage system, it can be determined that the insulation impedance to ground of one or more conversion circuits connected in parallel satisfies R th , from which it can be inferred that the insulation condition of each conversion circuit is normal.

[0126] Scenario 2: On the contrary, the control circuit 153 can be in the insulation resistance R x When the impedance is less than the first impedance threshold, the one or more conversion circuits cannot determine that the insulation condition is normal, so further abnormality detection is required.

[0127] In this scenario 2, the control circuit 153 can also be based on R th / 2 is used as the boundary to further divide into two possible detection situations:

[0128] Detection situation 1: when the insulation impedance to ground Rx is less than a second impedance threshold (wherein the second impedance threshold is half of the first impedance threshold), that is, R x <R th / 2, the control circuit 153 can determine that there is an abnormality in the one or more conversion circuits, and determine the conversion circuit with abnormal insulation condition.

[0129] For example, assuming R p is the minimum insulation resistance to ground R th , at this time, if the insulation resistance to ground R is determined x Less than R th / 2, then determine at least R n Less than R th . It can be determined that in R x <R th / 2, it can be determined that at R p and R n At least one impedance value is smaller than R th Therefore, it can be determined that the insulation impedance to ground in one or more conversion circuits included in the photovoltaic storage system is abnormal, so fault location needs to be performed.

[0130] Specifically, when the present application is implemented, fault location can be performed by using a leakage current detection method. For example, Figure 6aAs shown, the detection circuit 15 also includes leakage current sampling circuits 156i (i is 1...n) connected to one or more conversion circuits in a one-to-one correspondence; the input end of each leakage current sampling circuit 156i is respectively connected to the input end and output end of the connected conversion circuit, and the output end of each leakage current sampling circuit 156i is connected to the control circuit 153; each leakage current sampling circuit 156i is used to sample the first leakage current (assuming I pi ) and the second leakage current between the connected conversion circuit and the negative bus (assuming that I ni To express it), we can get the total leakage current of the connected conversion circuit (assuming that I i =I pi +I ni ), and sends the total leakage current to the control circuit 153.

[0131] After the control circuit 153 receives the total leakage current of each conversion circuit, it determines that the insulation condition of the conversion circuit corresponding to the leakage current with the largest value is abnormal. It can also be understood that the insulation impedance to ground of the conversion circuit corresponding to the total leakage current with the largest value is the smallest, so there is an abnormality. For example, if the total leakage current I corresponding to the conversion circuit 1 is 1 The value of I i (the i is 1...n) is the maximum value, indicating that the insulation impedance to ground in the conversion circuit 1 is the smallest, that is, the insulation condition of the conversion circuit 1 is abnormal.

[0132] In addition, in order to avoid safety problems caused by abnormalities in multiple conversion circuits, when the present application is implemented, after the first abnormal conversion circuit is determined, the abnormal conversion circuit can be switched out, and the remaining one or more conversion circuits can continue to be tested using the ground insulation impedance detection method provided by the present application until the insulation impedance of the remaining one or more conversion circuits is normal. For example, continuing to use the example in the aforementioned embodiment, the conversion circuit 1 determined to have an abnormal insulation condition is removed from the photovoltaic storage system, and the remaining conversion circuits 2, ..., n are also tested for ground insulation impedance using the method provided by the present application to determine whether the remaining conversion circuits 2, ..., n still contain abnormal conversion circuits.

[0133] Detection situation 2: when the insulation impedance to ground Rx is less than the first impedance threshold R th , and is greater than or equal to the second impedance threshold R th / 2, that is, R th / 2≤R x <R th , it is impossible to determine whether there is an abnormality in the solar energy storage system, and the positive electrode to ground insulation resistance R can be further calculated. pAnd the negative pole to ground insulation resistance R n For example, based on the analysis of the detection situation 1 in the above scenario 1 and scenario 2, it can be determined that in R th / 2≤R x <R th When the insulation condition of the photovoltaic storage system is normal, it may also be abnormal, so it needs to be further determined.

[0134] Specifically, R can also be calculated by the leakage current detection method. p and R n Continue as Figure 6a As shown, the detection circuit 15 may also include a second sampling circuit 155a and a third sampling circuit 155b; the second sampling circuit 155a is connected to the positive bus at one end and to the ground at the other end, and is connected to the control circuit 153, and is used to sample the voltage between the positive bus and the ground to obtain the first bus voltage V bus+ , and sends the first bus voltage to the control circuit 153; the third sampling circuit 155b is connected to the negative bus at one end and the ground at the other end, and is connected to the control circuit 153, and is used to sample the voltage between the negative bus and the ground to obtain the second bus voltage V bus- and sends the second bus voltage to the control circuit 153.

[0135] Exemplarily, a leakage current detection method is used to detect abnormalities in the photovoltaic storage system. Figure 6a The leakage current sampling circuit 156i shown can collect and obtain the first leakage current I of each conversion circuit. pi and the second leakage current I ni , during implementation, the total first leakage current I of the one or more conversion circuits may be further calculated. psum and the total second leakage current I nsum , as shown in the following formulas 8a and 8b:

[0136]

[0137] It should be noted that after sampling the leakage current, the leakage current sampling circuit can also convert the leakage current into a voltage according to the characteristics of the photovoltaic storage system, and achieve this through a conversion coefficient k, wherein the conversion coefficient k can be determined in advance according to the characteristics of the photovoltaic storage system, thereby obtaining V E The expression is shown in Formula 8c below:

[0138] V E = k(I psum +I nsum ) Formula 8c

[0139] In addition, the total first leakage current flow I of the one or more conversion circuits psum The first bus voltage V can also be obtained by sampling bus+ And the positive electrode to ground insulation resistance R p To express, similarly, I nsum You can also use V bus- And the positive electrode to ground insulation resistance R n To express it, we can get the following formula 8d:

[0140]

[0141] By combining the above formula 8d and formula 1c, we can calculate the unknown number R p and R n The value of .

[0142] In the calculation of the unknown number R p and R n After the value of R p and R n Respectively and R th It can be understood that in the R p Greater than or equal to the R th When the insulation condition between the positive bus and the ground line of the one or more conversion circuits is determined to be normal, otherwise it is abnormal; and, in the R n Greater than or equal to the R th When the insulation condition between the negative bus and the ground wire in the one or more conversion circuits is determined to be normal, otherwise it is abnormal. In addition, for example, if it is determined that there is an abnormality between the positive bus and the ground wire, the circuit components (such as DC-DC converter, MPPT converter, etc.) connected to the positive bus can be further located for fault location.

[0143] It should be noted that after locating the abnormal conversion circuit, the control circuit 153 can send an alarm message to the main dispatching unit of the photovoltaic storage system, thereby reminding maintenance personnel to repair the photovoltaic storage system and eliminate safety hazards.

[0144] When the above-mentioned detection is performed using the leakage current detection method, since the leakage current collected from the conversion circuit contains the AC signal output by the AC signal source 151a and the DC signal of the conversion circuit itself, in order to ensure the accuracy of the ground insulation impedance detection, the AC signal contained in the leakage current needs to be filtered before the control circuit 153 determines the ground insulation impedance based on the leakage current.

[0145] An optional implementation method is an analog filtering method. Specifically, continue as follows Figure 6aAs shown, the detection circuit 15 also includes an AC signal filter 157i (i is 1...n) connected to each leakage current sampling circuit 156i in a one-to-one correspondence; the input end of each AC signal filter 157i is connected to the corresponding leakage current sampling circuit 156i, and the output end is connected to the control circuit 153; the AC signal filter 157i is used to filter out the AC signal contained in the total leakage current of the conversion circuit sampled by the leakage current sampling circuit 156i. The AC signal filter 157i can be implemented by a low-pass filter and a notch filter.

[0146] An optional implementation is a digital filtering method. Specifically, the control circuit 153 is also used to: receive the total leakage current of the conversion circuit connected to the target leakage current sampling circuit sampled by the target leakage current sampling circuit 156i; the target leakage current sampling circuit is any leakage current sampling circuit among the leakage current sampling circuits; after performing analog-to-digital conversion on the total leakage current of the conversion circuit connected to the target leakage current sampling circuit, filter out the AC signal contained in the total leakage current after the analog-to-digital conversion.

[0147] It should be noted that the insulation impedance method to ground provided in the present application can also be applied to the detection of insulation impedance to ground of any high voltage DC system, such as electric vehicles, power batteries, etc.

[0148] According to the method provided in the embodiment of the present application, the present application also provides a chip, such as a chip in an inverter, which is used to execute Figures 1a to 6b A method according to any one of the embodiments shown.

[0149] It should be understood that the above-mentioned embodiments or implementation methods in each embodiment can be used in combination.

[0150] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0151] The present application is described with reference to the flowchart and / or block diagram of the method, device (system), and computer program product according to the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the process and / or box in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for implementing the function specified in one process or multiple processes in the flowchart and / or one box or multiple boxes in the block diagram.

[0152] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including an instruction device that implements the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0153] These computer program instructions may also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0154] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A solar energy storage system, characterized in that: include: One or more conversion circuits and detection circuits, wherein the one or more conversion circuits are connected in parallel between the positive bus and the negative bus; The detection circuit includes a signal source excitation branch, a first sampling circuit, a control circuit and a DC blocking capacitor; one end of the signal source excitation branch is connected to the ground wire, and the other end is connected to the positive bus or the negative bus through the DC blocking capacitor; the signal source excitation branch includes an AC signal source and a sampling resistor connected in series; the first sampling circuit is connected in parallel to the sampling resistor, and the control circuit is respectively connected to the input end of the AC signal source and the output end of the first sampling circuit; The control circuit is used to control the AC signal source to output harmonic signals of a first frequency and a second frequency respectively, wherein the first frequency is different from the second frequency; The first sampling circuit is used to collect the voltage across the sampling resistor to obtain a first voltage when the AC signal source outputs the harmonic signal of the first frequency, and to collect the voltage across the sampling resistor to obtain a second voltage when the AC signal source outputs the harmonic signal of the second frequency, and to send the first voltage and the second voltage to the control circuit; The DC blocking capacitor is used to isolate the DC signal of the one or more conversion circuits for the detection circuit; The first sampling circuit is further configured to collect a first phase corresponding to the first voltage when the first voltage is collected, and collect a second phase corresponding to the second voltage when the second voltage is collected, and send the first phase and the second phase to the control circuit; The control circuit is further used to obtain the insulation impedance to ground of the one or more conversion circuits after being connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage, and the first phase and the second phase; wherein the first voltage does not include the voltage of the DC blocking capacitor, and the second voltage does not include the voltage of the DC blocking capacitor; Among them, the equivalent circuit after the one or more variable circuits are connected in parallel includes: the insulation impedance to ground and parasitic capacitance in parallel; one end of the insulation impedance to ground and parasitic capacitance in parallel is connected to the ground wire, and the other end is connected to the connection node between the DC blocking capacitor and the positive bus or the negative bus; when calculating the insulation impedance to ground, the capacitance value of the DC blocking capacitor, the capacitance value of the parasitic capacitor and the insulation impedance to ground are used as unknowns.

2. The photovoltaic storage system according to claim 1, characterized in that: The control circuit is further configured to determine that the insulation status of the one or more conversion circuits is normal when the insulation impedance to ground is greater than or equal to a first impedance threshold.

3. The photovoltaic storage system according to claim 2, characterized in that: The detection circuit also includes leakage current sampling circuits connected to the one or more conversion circuits in a one-to-one correspondence; the input end of each leakage current sampling circuit is connected to the input end and the output end of the connected conversion circuit respectively, and the output end of each leakage current sampling circuit is connected to the control circuit; Each of the leakage current sampling circuits is used to sample a first leakage current between the connected conversion circuit and the positive bus and a second leakage current between the connected conversion circuit and the negative bus, obtain a total leakage current of the connected conversion circuit, and send the total leakage current to the control circuit; The control circuit is also used to determine that the insulation condition of the conversion circuit corresponding to the total leakage current with the largest median value of the total leakage current sent by each of the leakage current sampling circuits is abnormal when the insulation impedance to ground is less than a second impedance threshold; wherein the second impedance threshold is half of the first impedance threshold.

4. The solar storage system according to claim 3, characterized in that: The detection circuit also includes a second sampling circuit and a third sampling circuit; The second sampling circuit has one end connected to the positive bus and the other end connected to the ground line, and is connected to the control circuit, and is used to sample the voltage between the positive bus and the ground line to obtain a first bus voltage, and send the first bus voltage to the control circuit; The third sampling circuit has one end connected to the negative bus and the other end connected to the ground line, and is connected to the control circuit, and is used to sample the voltage between the negative bus and the ground line to obtain a second bus voltage, and send the second bus voltage to the control circuit; The control circuit is also used for: When the insulation impedance to ground is less than the first impedance threshold and greater than or equal to the second impedance threshold, based on the first leakage current and the second leakage current of each of the conversion circuits, the first bus voltage, the second bus voltage, and the insulation impedance to ground, determine the positive insulation impedance to ground of the one or more conversion circuits after being connected in parallel between the positive bus and the ground, and the negative insulation impedance to ground of the one or more conversion circuits after being connected in parallel between the negative bus and the ground; When the insulation impedance of the positive electrode to the ground is greater than or equal to the first impedance threshold, determining that the insulation condition of the one or more conversion circuits between the positive electrode bus and the ground line is normal, otherwise it is abnormal; and When the insulation impedance of the negative electrode to the ground is greater than or equal to the first impedance threshold, it is determined that the insulation condition between the negative electrode bus and the ground wire in the one or more conversion circuits is normal, otherwise it is abnormal.

5. The photovoltaic storage system according to claim 4, characterized in that: The detection circuit also includes an AC signal filter connected to each of the leakage current sampling circuits in a one-to-one correspondence; the input end of each AC signal filter is connected to the corresponding leakage current sampling circuit, and the output end is connected to the control circuit; The AC signal filter is used to filter out the AC signal contained in the total leakage current of the conversion circuit sampled by the leakage current sampling circuit.

6. The photovoltaic storage system according to claim 4, characterized in that: The control circuit is also used for: Receive the total leakage current of the conversion circuit connected to the target leakage current sampling circuit sampled by the target leakage current sampling circuit; the target leakage current sampling circuit is any leakage current sampling circuit among the leakage current sampling circuits; After performing analog-to-digital conversion on the total leakage current of the conversion circuit connected to the target leakage current sampling circuit, an AC signal included in the total leakage current after the analog-to-digital conversion is filtered out.

7. The photovoltaic storage system according to any one of claims 1 to 6, characterized in that: The insulation resistance to ground complies with the following formula: Among them, the represents the first voltage, the represents the second voltage; ω1 represents the harmonic signal of the first frequency, and ω2 represents the harmonic signal of the second frequency; R r represents the impedance of the sampling resistor, the R x represents the insulation resistance to ground, the C x represents the capacitance value of the parasitic capacitance of the optical storage system; represents the maximum voltage of the harmonic signal of the first frequency, the Represents the maximum voltage of the harmonic signal of the second frequency.

8. The photovoltaic storage system according to claim 1, characterized in that: The insulation resistance to ground complies with the following formula: Among them, the represents the first voltage, the represents the second voltage; ω1 represents the harmonic signal of the first frequency, and ω2 represents the harmonic signal of the second frequency; R r represents the impedance of the sampling resistor, the C r represents the capacitance value of the DC blocking capacitor; the R x represents the insulation resistance to ground, the C x represents the capacitance value of the parasitic capacitance of the optical storage system; represents the maximum voltage of the harmonic signal of the first frequency, the represents the maximum voltage of the harmonic signal of the second frequency; represents the first phase, the represents the second phase.

9. The photovoltaic storage system according to claim 1, characterized in that: The insulation resistance to ground complies with the following formula: or Among them, the C x R x It complies with the following formula: Among them, the represents the first voltage, the represents the second voltage; ω1 represents the harmonic signal of the first frequency, and ω2 represents the harmonic signal of the second frequency; R r represents the impedance of the sampling resistor; the R x represents the insulation resistance to ground, the C x represents the capacitance value of the parasitic capacitance of the optical storage system; represents the maximum voltage of the harmonic signal of the first frequency, the represents the maximum voltage of the harmonic signal of the second frequency; represents the first phase, the represents the second phase.

10. A method for detecting insulation impedance to ground, characterized in that: Applied to a photovoltaic storage system, the photovoltaic storage system comprises one or more conversion circuits and a detection circuit, the one or more conversion circuits are connected in parallel between a positive bus and a negative bus; The detection circuit includes a signal source excitation branch, a first sampling circuit, a control circuit and a DC blocking capacitor; one end of the signal source excitation branch is connected to the ground wire, and the other end is connected to the positive bus or the negative bus through the DC blocking capacitor; the signal source excitation branch includes an AC signal source and a sampling resistor connected in series; the first sampling circuit is connected in parallel to the sampling resistor, and the control circuit is respectively connected to the input end of the AC signal source and the output end of the first sampling circuit; The method comprises: The control circuit controls the AC signal source to output harmonic signals of a first frequency and a second frequency respectively, wherein the first frequency is different from the second frequency; The control circuit receives a first voltage, a second voltage, a first phase, and a second phase sent by the first sampling circuit; wherein the first voltage is obtained by the first sampling circuit collecting the voltage across the sampling resistor when the AC signal source outputs a harmonic signal of the first frequency, and the second voltage is obtained by the first sampling circuit collecting the voltage across the sampling resistor when the AC signal source outputs a harmonic signal of the second frequency; wherein the first phase is obtained by collecting a first phase corresponding to the first voltage when the first sampling circuit collects the first voltage, and the second phase is obtained by collecting a second phase corresponding to the second voltage when the first sampling circuit collects the second voltage; The control circuit determines the insulation impedance to ground of the one or more conversion circuits after being connected in parallel according to the harmonic signals of the first frequency and the second frequency, the first voltage and the second voltage, and the first phase and the second phase; wherein the first voltage does not include the voltage of the DC blocking capacitor, and the second voltage does not include the voltage of the DC blocking capacitor; Among them, the equivalent circuit after the one or more variable circuits are connected in parallel includes: the insulation impedance to ground and parasitic capacitance in parallel; one end of the insulation impedance to ground and parasitic capacitance in parallel is connected to the ground wire, and the other end is connected to the connection node between the DC blocking capacitor and the positive bus or the negative bus; when calculating the insulation impedance to ground, the capacitance value of the parasitic capacitance, the capacitance value of the DC blocking capacitor and the insulation impedance to ground are used as unknowns.

11. The method according to claim 10, characterized in that The method further comprises: When the insulation impedance to ground is greater than or equal to a first impedance threshold, the control circuit determines that the insulation condition of the one or more conversion circuits is normal.

12. The method according to claim 11, characterized in that The detection circuit also includes leakage current sampling circuits connected to the one or more conversion circuits in a one-to-one correspondence; the input end of each leakage current sampling circuit is connected to the input end and the output end of the connected conversion circuit respectively, and the output end of each leakage current sampling circuit is connected to the control circuit; The method further comprises: The control circuit receives the total leakage current of the connected conversion circuit sent by each leakage current sampling circuit; wherein the total leakage current of the conversion circuit is obtained by each leakage current sampling circuit sampling a first leakage current between the connected conversion circuit and the positive bus and a second leakage current between the connected conversion circuit and the negative bus; When the insulation impedance to ground is less than a second impedance threshold, the control circuit determines that the insulation condition of the conversion circuit corresponding to the total leakage current with the largest median value of the total leakage current sent by each of the leakage current sampling circuits is abnormal; wherein the second impedance threshold is half of the first impedance threshold.

13. The method according to claim 12, characterized in that The detection circuit also includes a second sampling circuit and a third sampling circuit; The second sampling circuit has one end connected to the positive bus and the other end connected to the ground line, and is connected to the control circuit, and is used to sample the voltage between the positive bus and the ground line to obtain a first bus voltage, and send the first bus voltage to the control circuit; The third sampling circuit has one end connected to the negative bus and the other end connected to the ground line, and is connected to the control circuit, and is used to sample the voltage between the negative bus and the ground line to obtain a second bus voltage, and send the second bus voltage to the control circuit; The method further comprises: When the insulation impedance to ground is less than the first impedance threshold and greater than or equal to the second impedance threshold, the control circuit determines the insulation impedance to ground of the positive electrode of the one or more conversion circuits after being connected in parallel between the positive bus and the ground, and the insulation impedance to ground of the negative electrode of the one or more conversion circuits after being connected in parallel between the negative bus and the ground based on the first bus voltage, the second bus voltage and the insulation impedance to ground; When the insulation impedance of the positive electrode to the ground is greater than or equal to the first impedance threshold, the control circuit determines that the insulation condition of the one or more conversion circuits between the positive electrode bus and the ground line is normal, otherwise it is abnormal; and When the insulation impedance of the negative electrode to the ground is greater than or equal to the first impedance threshold, the control circuit determines that the insulation condition between the negative electrode bus and the ground wire in the one or more conversion circuits is normal, otherwise it is abnormal.

Images