Power supply system and insulation resistance detection equipment thereof

Abstract

The invention provides a power supply system and an insulation resistance detection device thereof. The insulation resistance detection device comprises a control unit, an impedance circuit and a first controllable switch. According to the insulation resistance detection equipment, when the current flowing through the control unit is smaller than the rated current, the first controllable switch connected with the impedance circuit in parallel is switched on, so that the bypassed impedance circuit does not generate the heat dissipation problem any more, a heat dissipation component is not additionally arranged, and the heat dissipation problem can be solved. When the current flowing through the control unit is greater than the rated current, the first controllable switch is switched off, and the impedance circuit is merged into a current loop, so that the current loop is formed among the alternating-current cable or the direct-current source, the control unit, the impedance circuit and the grounding circuit to charge the capacitor, and the total load connected with the control unit is ensured to reach the minimum load resistance of the control unit; and the stability of ground insulation impedance detection is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a power supply system and insulation impedance detection equipment thereof. Background Art

[0002] In recent years, new energy power supply systems such as photovoltaic power generation systems have been increasingly widely used in the field of electronic power. Photovoltaic power generation systems can convert clean and pollution-free solar energy into electrical energy, which can not only supply residential equipment to meet the daily power supply needs of residents, but also be incorporated into the power grid for storage. The application of photovoltaic power generation systems in the field of electronic power can effectively improve the reliability of residents' electricity use.

[0003] In the photovoltaic power generation system, the converted electric energy will be input to the residents' equipment or connected to the power grid through the AC cable, and the AC cable will have an AC insulation impedance to the ground. When the AC insulation impedance to the ground is small, it means that the insulation between the AC cable and the ground is poor, and the AC cable is at risk of leakage or short circuit grounding. In the photovoltaic power generation system, the photovoltaic module will have a DC insulation impedance to the ground. When the DC insulation impedance to the ground is small, it means that the insulation between the photovoltaic module and the ground is poor, and the photovoltaic module is at risk of leakage or short circuit grounding. The DC insulation impedance to the ground and the AC insulation impedance to the ground together constitute the insulation impedance to the ground in the photovoltaic power generation system. When the insulation impedance to the ground is small, it means that there is a risk of leakage or short circuit grounding in the photovoltaic power generation system. This will not only affect the safety of residents' electricity use, but also make the power supply stability of the photovoltaic power generation system itself worse, reducing the reliability of the photovoltaic power generation system. Therefore, in order to maintain the reliability of the photovoltaic power generation system, it is necessary to detect the insulation impedance to the ground in the photovoltaic power generation system, and promptly discover the abnormal insulation impedance to the ground in the photovoltaic power generation system, so that users can repair the abnormality in time and restore the reliability of the photovoltaic power generation system. How to ensure the stability of insulation impedance detection has become a problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a power supply system and an insulation impedance detection device thereof, which are used to achieve stability in insulation impedance detection to the ground.

[0005] In the first aspect, the present application provides a power supply system, including: multiple power converters and insulation impedance detection equipment. The input end of the power converter is used to connect a DC source, which can be a photovoltaic module or an energy storage battery. The output ends of the multiple power converters are connected in parallel, and the output ends are used to connect to a power grid or a load through an AC cable. There is usually an AC insulation impedance to the ground between the AC cables between the multiple power converters and the power grid or the load and the ground, that is, the grounding circuit. There is usually a DC insulation impedance to the ground between the DC source such as the photovoltaic module and the ground, that is, the grounding circuit. The AC insulation impedance to the ground and the DC insulation impedance to the ground constitute the insulation impedance to the ground of the power supply system. The insulation impedance to the ground is not a real impedance element, but a virtual impedance element used to characterize the degree of insulation between the conductor and the ground in the power supply system. The smaller the insulation impedance to the ground, the greater the possibility of leakage or ground short circuit, and the worse the stability and reliability of the power supply system. In order to identify the phenomenon of leakage or ground short circuit in the power supply system, it is usually necessary to use an insulation detection device to detect the impedance value of the insulation impedance to the ground in the power supply system.

[0006] In the present application, the insulation impedance detection device includes: a control unit, an impedance circuit and a first controllable switch. The impedance circuit includes a resistor and a capacitor connected in series, the first controllable switch is arranged in parallel with the impedance circuit, and the control unit and the impedance circuit are connected in series with the ground, i.e., the grounding circuit. The control unit can be used to output a common-mode voltage signal to the AC side of the power converter, i.e., the control unit and the impedance circuit are connected in series between the AC cable and the grounding circuit. Alternatively, the control unit can also be used to output a common-mode voltage signal to the DC side of the power converter, i.e., the control unit and the impedance circuit are connected in series between the input end of the power converter and the grounding circuit.

[0007] Due to the AC insulation impedance to ground between the AC cable and the grounding circuit, and the DC insulation impedance to ground between the DC source and the grounding circuit, a loop can be formed between the AC cable or the DC source, the grounding circuit and the control unit. Ignoring the impedance of the conductor inside the grounding circuit and the control unit, if the control unit turns on the first controllable switch, the common-mode voltage signal is only applied to the insulation impedance to ground. When the common-mode voltage signal is a constant value, the larger the insulation impedance to ground, the smaller the current flowing through the control unit. By detecting the relationship between the current flowing through the control unit and the rated current, it can be determined whether the insulation impedance to ground is greater than the minimum load resistance that the insulation impedance detection device can operate. When it is determined that the current flowing through the control unit is less than the rated current, it is considered that the insulation impedance detection device can work normally, and the control unit turns on the first controllable switch in parallel with the impedance circuit, so that the bypassed impedance circuit will not generate heat dissipation problems and additional heat dissipation components are configured, which can solve the heat dissipation problem. In addition, when the first controllable switch is turned on, the resistance value of the insulation impedance to ground can be calculated by the common-mode voltage signal output by the control unit and the current flowing through the control unit.

[0008] During the operation of the insulation impedance detection device, if it is determined that the current flowing through the control unit is greater than the rated current, it means that the current flowing through the control unit becomes larger due to the decrease in the insulation impedance to the ground. At this time, the resistance value of the insulation impedance to the ground exceeds the minimum load resistance of the control unit, that is, when it exceeds the load capacity of the control unit, it will cause the control unit to be unable to output the common-mode voltage signal of the set voltage. The load capacity refers to the ability of the control unit to drive the load (here refers to the insulation impedance to the ground) without affecting its output voltage when outputting the common-mode voltage signal. Specifically, the load capacity is mainly reflected in whether the output voltage of the control unit can remain unchanged when the control unit is in the current insulation impedance to the ground. Based on this, in the present application, when the current flowing through the control unit is greater than the rated current, it is necessary to disconnect the first controllable switch so that the impedance circuit is incorporated into the current loop to form a current loop between the AC cable or DC source, the control unit, the impedance circuit and the grounding circuit. The access of the impedance circuit makes the total load (the sum of the insulation impedance to the ground and the impedance circuit) of the access control unit reach the minimum load resistance of the control unit, so that the control unit can normally output the common-mode voltage signal to ensure the stability of the insulation impedance detection to the ground. After the first controllable switch is disconnected, the control unit can charge the capacitor in the impedance circuit, and the insulation impedance to ground can be calculated by detecting the charging time when the capacitor in the impedance circuit is charged to a set voltage value.

[0009] In some embodiments of the present application, after the capacitor in the impedance circuit is charged, in order to facilitate the subsequent ground insulation impedance detection, the first controllable switch can be turned on after the first controllable switch is turned off for a set time to discharge the capacitor. Exemplarily, the set time needs to be greater than or equal to the charging time of the capacitor.

[0010] In some embodiments of the present application, the insulation impedance detection device may further include a second controllable switch, which is arranged in series with the control unit and the impedance circuit. The control unit is also used to: when discharging the capacitor in the impedance circuit, disconnect the second controllable switch and discharge the capacitor through the resistor in the impedance circuit.

[0011] In the present application, the R value can be calculated according to the zero-state response formula of the impedance circuit: Ut = Upid*[1-exp(-t / RC)], where Ut is the voltage value across the capacitor, t is the charging time of the capacitor, C is the capacitance of the capacitor and is a known quantity, Upid is the voltage value of the common-mode voltage signal output by the control unit, and R is the total resistance value connected to the control unit. The R value can be calculated by detecting the charging time t used when the capacitor is charged to a set voltage value, that is, the voltage value across the capacitor rises to the set voltage value. Specifically, in order to facilitate the detection of the voltage value Ut and the charging time t across the capacitor, the voltage value Ut across the capacitor can be set to a specific multiple of the common-mode voltage Upid, so that the charging time is an integer multiple of the RC time constant. For example, when Ut = 0.95*Upid, the charging time t is three times the RC time constant. After calculating the R value through the above formula, since R = Rpid + Rx, Rpid is the resistance value of the resistor in the impedance circuit and is a known quantity, and Rx is the insulation impedance to ground, which includes: the DC insulation impedance to ground between the DC source and the ground circuit, and the AC insulation impedance to ground between the AC cable and the ground circuit. The impedance value of the insulation impedance to ground can be finally calculated through the calculated R value, completing the detection of the insulation impedance to ground.

[0012] In some embodiments of the present application, the power supply system may further include a data collector. The data collector is used to: when it is determined that the current flowing through the control unit is greater than the rated current, restart multiple power converters in sequence, wherein the power converter with a DC to ground insulation impedance less than the short-circuit threshold cannot be restarted to automatically cut off the fault point. For example, 30 photovoltaic modules are set in the power supply system, and the data collector restarts the 30 power converters in sequence when it is determined that the current flowing through the control unit is greater than the rated current, that is, when the insulation impedance to ground becomes smaller in the power supply system. Each power converter will perform ISO detection when it is restarted, that is, detect the DC to ground insulation impedance of the connected photovoltaic module. If the DC to ground insulation impedance is less than the short-circuit threshold, it means that the power converter is abnormal and cannot be started. After the data collector polls all power converters, the power converter connected to the photovoltaic module with abnormal DC to ground insulation impedance cannot be started, and the faulty photovoltaic module is automatically cut off in the power supply system, and the power converters connected to other photovoltaic modules with normal DC to ground insulation impedance are normally started and connected to the power supply system. By polling and restarting the power converter through the data collector, the equipment with abnormal DC-to-ground insulation impedance can be automatically cut off, which can reduce the cost of power supply system operation and maintenance.

[0013] In some embodiments of the present application, if the data collector determines that the current flowing through the control unit is less than the rated current after restarting multiple power converters in sequence, it means that the insulation impedance to ground in the power supply system has returned to normal, which means that the previous abnormal insulation impedance to ground was caused by abnormal DC insulation impedance to ground, and the abnormal fault has been isolated by polling and restarting the power converter.

[0014] In some embodiments of the present application, if the data collector determines that the current flowing through the control unit is still greater than or equal to the rated current after restarting all power converters in sequence, it means that there is still an abnormality in the insulation impedance to ground in the power supply system, and the abnormality in the insulation impedance to ground is caused by the abnormal AC insulation impedance to ground. At this time, the data collector can issue an abnormal AC insulation impedance to ground alarm, or the data collector disconnects the AC cable from the power grid or load to isolate the fault. The data collector can specifically send a trip signal to a substation connected between the power grid and the power converter to disconnect the AC cable from the power grid and isolate the short circuit fault.

[0015] In some embodiments of the present application, the insulation impedance detection device may be specifically integrated into the power converter, or the insulation impedance detection device may also be provided independently of the power converter.

[0016] In some embodiments of the present application, the insulation impedance detection device can be integrated into an anti-potential induced attenuation (PID) device, that is, the insulation impedance detection device provided by the present application can be a PID device.

[0017] In the second aspect, the present application provides an insulation impedance detection device for a power supply system, which is applied to a power supply system, wherein the power supply system includes a plurality of power converters, and the input end of the power converter is used to connect a DC source, and the DC source includes a photovoltaic module or an energy storage battery. The output ends of the plurality of power converters are connected in parallel, and the output ends are used to connect a power grid or a load through an AC cable. There is usually an AC insulation impedance to ground between the AC cable between the plurality of power converters and the power grid or the load and the ground, i.e., the grounding circuit, and there is usually a DC insulation impedance to ground between the DC source such as the photovoltaic module and the ground, i.e., the grounding circuit. The AC insulation impedance to ground and the DC insulation impedance to ground constitute the insulation impedance to ground in the power supply system. The insulation impedance detection device includes: a control unit, an impedance circuit, and a first controllable switch. The impedance circuit includes a resistor and a capacitor connected in series, the first controllable switch is arranged in parallel with the impedance circuit, and the control unit and the impedance circuit are connected in series to the ground, i.e., the grounding circuit. The control unit can be used to output a common mode voltage signal to the AC side of the power converter, that is, the control unit and the impedance circuit are connected in series between the AC cable and the grounding circuit. Alternatively, the control unit can also be used to output a common-mode voltage signal to the DC side of the power converter, that is, the control unit and the impedance circuit are connected in series between the input end of the power converter and the ground circuit. Due to the AC insulation impedance to ground between the AC cable and the ground circuit, and the DC insulation impedance to ground between the DC source and the ground circuit, a loop can be formed between the AC cable or the DC source, the ground circuit and the control unit. Ignoring the impedance of the conductor inside the ground circuit and the control unit, if the control unit turns on the first controllable switch, the common-mode voltage signal is only applied to the insulation impedance to ground. When the common-mode voltage signal is a constant value, the greater the insulation impedance to ground, the smaller the current flowing through the control unit. By detecting the relationship between the current flowing through the control unit and the rated current, it can be determined whether the insulation impedance to ground is greater than the minimum load resistance that the insulation impedance detection device can operate. When it is determined that the current flowing through the control unit is less than the rated current, it is considered that the insulation impedance detection device can work normally, and the control unit can turn on the first controllable switch in parallel with the impedance circuit, so that the bypassed impedance circuit will not cause heat dissipation problems and additional heat dissipation components are configured, which can solve the heat dissipation problem. Moreover, when the first controllable switch is turned on, the resistance value of the insulation impedance to ground can be calculated by the common-mode voltage signal output by the control unit and the current flowing through the control unit. During the operation of the insulation impedance detection device, if it is determined that the current flowing through the control unit is greater than the rated current, it means that the current flowing through the control unit increases due to the decrease in the insulation impedance to ground. At this time, the resistance value of the insulation impedance to ground exceeds the minimum load resistance of the control unit, that is, exceeds the load capacity of the control unit, which will cause the control unit to be unable to output a common-mode voltage signal of the set voltage. Load capacity refers to the ability of the control unit to drive the load (here refers to the insulation impedance to ground) without affecting its output voltage when outputting a common-mode voltage signal.Specifically, the load capacity is mainly reflected in the current insulation impedance to ground of the control unit, and whether its output voltage can remain unchanged. Based on this, in the present application, when the current flowing through the control unit is greater than the rated current, it is necessary to disconnect the first controllable switch so that the impedance circuit is incorporated into the current loop, that is, a current loop is formed between the AC cable or DC source, the control unit, the impedance circuit and the ground circuit, and the access of the impedance circuit makes the total load (the sum of the insulation impedance to ground and the impedance circuit) of the access control unit reach the minimum load resistance of the control unit, so that the control unit can output the common mode voltage signal normally, and ensure the stability of the insulation impedance detection to ground. After the first controllable switch is disconnected, the control unit can charge the capacitor in the impedance circuit, and the insulation impedance to ground can be calculated by detecting the charging time when the capacitor in the impedance circuit is charged to the set voltage value.

[0018] In some embodiments of the present application, after completing the charging time detection of the capacitor in the impedance circuit, in order to facilitate the subsequent insulation impedance detection to the ground, the first controllable switch can be turned on after the first controllable switch is turned off for a set time to discharge the capacitor. Exemplarily, the set time needs to be greater than or equal to the above charging time.

[0019] In some embodiments of the present application, the insulation impedance detection device may further include a second controllable switch, which is arranged in series with the control unit and the impedance circuit. The control unit is also used to: when discharging the capacitor in the impedance circuit, disconnect the second controllable switch and discharge the capacitor through the resistor in the impedance circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the power supply system architecture;

[0021] Figure 2 A structural schematic diagram of a power supply system in the prior art;

[0022] Figure 3 A schematic diagram of a structure of a power supply system provided in an embodiment of the present application;

[0023] Figure 4 A schematic diagram of a process for detecting insulation impedance to ground of a power supply system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be understood as being limited to the embodiments described herein; on the contrary, these embodiments are provided to make the present application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0025] Reference Figure 1 , the photovoltaic storage system 100 (solar photovoltaic energy storage power generation system) as a power supply system includes a photovoltaic system and an energy storage system. In the photovoltaic system, the photovoltaic module 10 directly converts solar energy into electrical energy using the photovoltaic effect, wherein the photovoltaic module 10 generally includes a plurality of cells connected in series or in parallel to achieve a certain output power. The photovoltaic inverter 201 is used to convert the direct current from the photovoltaic module 10 into alternating current. The output ends of the plurality of photovoltaic inverters 201 are connected in parallel and sent to the box-type substation 30 corresponding to the photovoltaic inverter 201 through an AC cable for voltage transformation. The box-type substation 30 corresponding to each photovoltaic inverter 201 can convert the low-voltage alternating current output by the photovoltaic inverter 201 into medium-voltage alternating current, and then transmit the alternating current to the booster station 40 and transmit it to the power grid 50 or other loads. In the energy storage system, the energy storage battery 60 can store unstable electric energy, and convert direct current into alternating current through the energy storage converter 202 (Power Conversion System, PCS), and then deliver stable electric energy to the power grid 50 or other loads after passing through the box-type substation 30 corresponding to the energy storage battery 60. In addition, the energy storage converter 202 can also convert the alternating current of the power grid 50 into direct current to charge the energy storage battery 60, and then store the electric energy in the energy storage battery 60.

[0026] In the above power supply system, there will be an AC insulation impedance to the ground between the AC cable and the ground. When the AC insulation impedance to the ground is small, it means that the insulation between the AC cable and the ground is poor, and the AC cable is at risk of leakage or short circuit grounding. In the power supply system, there will be a DC insulation impedance to the ground between the photovoltaic module and the ground. When the DC insulation impedance to the ground is small, it means that the insulation between the photovoltaic module and the ground is poor, and the photovoltaic module is at risk of leakage or short circuit grounding. The DC insulation impedance to the ground and the AC insulation impedance to the ground together constitute the insulation impedance to the ground in the power supply system. When the insulation impedance to the ground is small, it means that there is a risk of leakage or short circuit grounding in the power supply system. This will not only affect the safety of residents' electricity use, but also make the power supply stability of the power supply system itself worse, reducing the reliability of the power supply system. Therefore, in order to maintain the reliability of the power supply system, it is necessary to detect the insulation impedance to the ground in the power supply system, and promptly discover the abnormal phenomenon of the insulation impedance to the ground in the power supply system, so that users can repair the abnormality in time and restore the reliability of the photovoltaic power generation system.

[0027] At present, in order to ensure that the insulation impedance detection equipment can be started and ensure stability when the insulation impedance to ground is small, refer to Figure 2, a current limiting resistor Ry will be connected in series between the insulation impedance detection device and the AC cable, and the common mode voltage signal output by the insulation impedance detection device will be divided between the current limiting resistor Ry and the insulation impedance of the photovoltaic power generation system to the ground. The voltage sensor can detect the voltage division value Urx of the insulation impedance to the ground. Since the voltage Upid of the common mode voltage signal is controlled by the insulation impedance detection device as a known quantity, the current limiting resistor Ry is also a known quantity. Therefore, according to the voltage division formula: Urx / Upid=Rx / (Rx+Ry), the insulation impedance to the ground Rx can be solved. The insulation impedance to the ground Rx includes the DC insulation impedance to the ground Rdc and the AC insulation impedance to the ground Rz.

[0028] In order to ensure the stability of insulation impedance detection, the current limiting resistor Ry used in the above insulation impedance detection device will have heat dissipation problems, and additional heat dissipation components need to be configured. Moreover, this solution cannot be used when the system heat dissipation conditions are limited.

[0029] In view of this, the embodiment of the present application provides a power supply system and an insulation impedance detection device thereof, in order to achieve the stability of the insulation impedance detection to the ground. The insulation impedance detection device provided by the present application adds a controllable switch and an impedance circuit in parallel inside. When the insulation impedance to the ground becomes smaller and causes the current flowing through the control unit to be greater than the rated current, the controllable switch is disconnected, so that the impedance circuit is incorporated into the current loop, so as to form a current loop between the AC cable or DC source, the control unit, the impedance circuit and the grounding circuit to charge the capacitor, and ensure that the total load connected to the control unit reaches the minimum load resistance of the control unit, so that the control unit can normally output a common-mode voltage signal, and ensure the stability of the insulation impedance detection to the ground. When the insulation impedance to the ground is large and the current flowing through the control unit is less than the rated current, the controllable switch in parallel with the impedance circuit is turned on, so that the bypassed impedance circuit will not cause heat dissipation problems and additional heat dissipation components are configured, which can solve the heat dissipation problem.

[0030] Reference Figure 3 , a power supply system provided in the present application includes: multiple power converters and insulation impedance detection equipment. The input end of the power converter is used to connect a DC source, and the DC source can specifically be a photovoltaic module or an energy storage battery. The photovoltaic module is used to receive the radiant energy of sunlight and convert the received radiant energy into electrical energy in the form of direct current. The photovoltaic module can be obtained by connecting multiple solar cells in series and / or in parallel. The output ends of multiple power converters are connected in parallel, and the output ends are used to connect to a power grid or a load through an AC cable. When the DC source is a photovoltaic module, the power converter can specifically be a photovoltaic inverter, and when the DC source is an energy storage battery, the power converter is a PCS, Figure 3In the figure, a DC source is a photovoltaic module 10 and a power converter is a photovoltaic inverter 201 as an example. The power converter is used to receive electric energy in the form of DC from the DC source, and after converting the electric energy in the form of DC into electric energy in the form of AC, the electric energy in the form of AC is output to the power grid 50 or the load through an AC cable. Considering that the power grid may affect the power generation process of the power converter and the DC source when the voltage is unstable, a box-type substation 30 can also be set between the power grid 50 and the power converter, and the output end of the power converter is connected to the input end of the box-type substation 30 through an AC cable, and the output end of the box-type substation 30 is connected to the power grid 50. There is usually an AC insulation impedance Rz between the AC cables between the multiple power converters and the power grid 50 or the load and the ground, i.e., the grounding circuit. There is usually a DC insulation impedance Rdc between the DC source such as the photovoltaic module 10 and the ground, i.e., the grounding circuit. The AC insulation impedance Rz and the DC insulation impedance Rdc constitute the insulation impedance Rx in the power supply system. The insulation impedance to the ground is not a real impedance element, but a virtual impedance element used to characterize the insulation degree between the conductor in the power supply system and the ground, that is, the insulation impedance to the ground can be considered as a virtual impedance element connected to the ground circuit. The impedance value of the virtual impedance element is related to the conductivity, thickness, temperature, and humidity of the insulating medium covering the internal conductor of the AC cable or DC source. When the conductivity of the insulating medium is better, the thickness is thinner, the temperature is higher, or the humidity is greater, the impedance value of the insulation impedance Rx to the ground is smaller, which means that the insulation between the internal conductor of the AC cable or DC source and the ground is worse, the possibility of leakage or short circuit grounding of the AC cable or DC source is greater, and the stability and reliability of the power supply system are also worse. In order to identify leakage or ground short circuit in the power supply system, it is usually necessary to use insulation detection equipment to detect the impedance value of the insulation impedance to ground in the power supply system. Once the impedance value detected is found to be small to a certain extent, a dedicated person can be immediately commissioned to inspect the AC cable and DC source to promptly discover and repair the abnormal insulation impedance to ground in the power supply system to maintain the stability and reliability of the power supply system.

[0031] In some embodiments of the present application, the insulation impedance detection device may be specifically integrated into the power converter, or the insulation impedance detection device may also be provided independently of the power converter.

[0032] In some embodiments of the present application, the insulation impedance detection device can be integrated into an anti-potential induced attenuation (PID) device, that is, the insulation impedance detection device provided by the present application can be a PID device.

[0033] Reference Figure 3The insulation impedance detection device provided in the embodiment of the present application includes: a control unit, an impedance circuit and a first controllable switch K1. The impedance circuit includes a resistor Rpid and a capacitor C connected in series. The first controllable switch K1 is arranged in parallel with the impedance circuit. The control unit and the impedance circuit are connected in series and connected to the ground, i.e., the grounding circuit. The positions of the control unit and the impedance circuit can be interchanged. Figure 3 In the circuit topology shown, the impedance circuit is connected between the control unit and the ground circuit. Figure 3 , the control unit can be used to output a common-mode voltage signal to the AC side of the power converter, that is, the control unit and the impedance circuit are connected in series between the AC cable and the grounding circuit. Alternatively, the control unit can also be used to output a common-mode voltage signal to the DC side of the power converter, that is, the control unit and the impedance circuit are connected in series between the input end of the power converter and the grounding circuit. Specifically, the control unit can adjust the common-mode voltage signal output by the internal output voltage source according to the common-mode voltage of the DC source to the ground collected by the power converter. The common-mode voltage signal can limit the floating voltage of the DC source to the ground, and minimize the damage to the DC source caused by the bias potential difference to the ground generated during the power generation process of the DC source.

[0034] Due to the AC insulation impedance to ground between the AC cable and the grounding circuit, and the DC insulation impedance to ground between the DC source and the grounding circuit, a loop can be formed between the AC cable or the DC source, the grounding circuit and the control unit. Ignoring the impedance of the conductor inside the grounding circuit and the control unit, if the control unit turns on the first controllable switch K1, the common-mode voltage signal is only applied to the insulation impedance to ground. When the common-mode voltage signal is a constant value, the larger the insulation impedance to ground, the smaller the current flowing through the control unit. By detecting the relationship between the current flowing through the control unit and the rated current, it can be determined whether the insulation impedance to ground is greater than the minimum load resistance that the insulation impedance detection device can operate. When it is determined that the current flowing through the control unit is less than the rated current, it is considered that the insulation impedance detection device can work normally. The control unit can turn on the first controllable switch K1 in parallel with the impedance circuit, so that the bypassed impedance circuit will not generate heat dissipation problems and additional heat dissipation components are configured, which can solve the heat dissipation problem. In addition, when the first controllable switch K1 is turned on, the resistance value of the insulation impedance to ground can be calculated by the common-mode voltage signal output by the control unit and the current flowing through the control unit.

[0035] During the operation of the insulation impedance detection device, if it is determined that the current flowing through the control unit is greater than the rated current, it means that the current flowing through the control unit becomes larger due to the decrease in the insulation impedance to the ground. At this time, the resistance value of the insulation impedance to the ground exceeds the minimum load resistance of the control unit, that is, when it exceeds the load capacity of the control unit, it will cause the control unit to be unable to output the common-mode voltage signal of the set voltage. The load capacity refers to the ability of the control unit to drive the load (here refers to the insulation impedance to the ground) without affecting its output voltage when outputting a common-mode voltage signal. Specifically, the load capacity is mainly reflected in whether the output voltage of the control unit can remain unchanged when the control unit is in the current insulation impedance to the ground. Based on this, in the present application, when the current flowing through the control unit is greater than the rated current, it is necessary to disconnect the first controllable switch K1 so that the impedance circuit is incorporated into the current loop to form a current loop between the AC cable or DC source, the control unit, the impedance circuit and the grounding circuit. The access of the impedance circuit makes the total load (the sum of the insulation impedance to the ground and the impedance circuit) of the access control unit reach the minimum load resistance of the control unit, ensuring that the control unit can output the common-mode voltage signal normally. After the first controllable switch K1 is disconnected, the control unit can charge the capacitor C in the impedance circuit. By detecting the charging time when the capacitor C in the impedance circuit is charged to a set voltage value, the insulation impedance to ground can be calculated.

[0036] In the present application, the R value can be calculated according to the zero-state response formula of the impedance circuit: Ut = Upid*[1-exp(-t / RC)], where Ut is the voltage value across the capacitor, t is the charging time of the capacitor, C is the capacitance of the capacitor and is a known quantity, Upid is the voltage value of the common-mode voltage signal output by the control unit, and R is the total resistance value connected to the control unit. The R value can be calculated by detecting the charging time t used when the capacitor C is charged to the set voltage value, that is, the voltage value across the capacitor C rises to the set voltage value. Specifically, in order to facilitate the detection of the voltage value Ut and the charging time t across the capacitor C, the voltage value Ut across the capacitor C can be set to a specific multiple of the common-mode voltage Upid, so that the charging time t is an integer multiple of the RC time constant. For example, when Ut = 0.95*Upid, the charging time t is three times the RC time constant. After calculating the R value through the above formula, since R = Rpid + Rx, Rpid is the resistance value of the resistor in the impedance circuit and is a known quantity, and Rx is the insulation impedance to ground, which includes: the DC insulation impedance to ground Rdc between the DC source and the ground circuit, and the AC insulation impedance to ground Rz between the AC cable and the ground circuit. The impedance value of the insulation impedance to ground Rx can be calculated through the calculated R value, and the detection of the insulation impedance to ground is completed.

[0037] In some embodiments of the present application, after completing the charging time detection of the capacitor C in the impedance circuit, in order to facilitate the subsequent re-detection of the insulation impedance Rx to the ground and ensure the continuity of the insulation impedance detection to the ground, the first controllable switch K1 may be turned on after being turned off for a set time to discharge the capacitor C. Exemplarily, the set time needs to be greater than or equal to the above-mentioned charging time.

[0038] Reference Figure 3 In some other embodiments of the present application, the insulation impedance detection device may further include a second controllable switch K2, which is arranged in series with the control unit and the impedance circuit. The positions of the second controllable switch K2, the control unit, and the impedance circuit may be interchangeable. Figure 3 In the circuit topology shown, the second controllable switch K2 is connected between the impedance circuit and the ground circuit. When the control unit discharges the capacitor C in the impedance circuit, that is, when the first controllable switch K1 is turned on, the second controllable switch K2 can also be turned off to discharge the capacitor C through the resistor Rpid in the impedance circuit.

[0039] Reference Figure 3 , the power supply system provided by the present application may also include a data collector. The data collector is used to: when it is determined that the current flowing through the control unit is greater than the rated current, restart multiple power converters in sequence, wherein the power converter with a DC-to-ground insulation impedance less than the short-circuit threshold cannot be restarted to automatically cut off the fault point. For example, 30 photovoltaic modules are set in the power supply system, and the data collector restarts the 30 power converters in sequence when it is determined that the current flowing through the control unit is greater than the rated current, that is, when the insulation impedance to the ground becomes smaller in the power supply system. Each power converter will perform ISO detection when it is restarted, that is, detect the DC-to-ground insulation impedance of the connected photovoltaic module. If the DC-to-ground insulation impedance is less than the short-circuit threshold, it means that the power converter is abnormal and cannot be started. After the data collector polls all power converters, the power converter connected to the photovoltaic module with abnormal DC-to-ground insulation impedance cannot be started, and the faulty photovoltaic module is automatically cut off in the power supply system, and the power converters connected to other photovoltaic modules with normal DC-to-ground insulation impedance are normally started and connected to the power supply system. By polling and restarting the power converter through the data collector, the equipment with abnormal DC-to-ground insulation impedance can be automatically cut off, which can reduce the cost of power supply system operation and maintenance.

[0040] In some embodiments of the present application, if the data collector determines that the current flowing through the control unit is less than the rated current after restarting multiple power converters in sequence, it means that the insulation impedance to ground in the power supply system has returned to normal, which means that the previous abnormal insulation impedance to ground was caused by abnormal DC insulation impedance to ground, and the abnormal fault has been isolated by polling and restarting the power converter.

[0041] In some embodiments of the present application, if the data collector determines that the current flowing through the control unit is still greater than or equal to the rated current after restarting all power converters in sequence, it means that there is still an abnormality in the insulation impedance to ground in the power supply system, and the abnormality in the insulation impedance to ground is caused by the abnormal AC insulation impedance to ground. At this time, the data collector can issue an abnormal AC insulation impedance to ground alarm, or the data collector disconnects the AC cable from the power grid or load to isolate the fault. The data collector can specifically send a trip signal to a substation connected between the power grid and the power converter to disconnect the AC cable from the power grid and isolate the short circuit fault.

[0042] The complete process of ground insulation impedance detection of the power supply system provided by the present application is described below through a specific embodiment.

[0043] Reference Figure 4 , after the insulation impedance test equipment starts running, the steps performed include:

[0044] S1, the control unit outputs a common mode voltage signal. At this time, the first controllable switch arranged in parallel with the impedance circuit is in a conducting state.

[0045] S2. The control unit determines whether the current flowing through the control unit is less than the rated current. If yes, execute step S1; if no, execute step S3.

[0046] S3. When the current flowing through the control unit is greater than the rated current, the control unit disconnects the first controllable switch and calculates the insulation resistance to ground according to the detected charging time when the capacitor is charged to the set voltage value.

[0047] S4: Determine whether the insulation impedance to ground is less than the alarm threshold. If so, proceed to step S5.

[0048] S5. When the insulation impedance to ground is less than the alarm threshold, an abnormal insulation impedance alarm to ground is sent to the data collector.

[0049] S6. When the data collector receives an abnormal insulation impedance alarm, it restarts multiple power converters in sequence, so that the power converters with DC insulation impedance to ground less than the short-circuit threshold cannot be restarted, and the faulty DC source is automatically isolated.

[0050] Exemplarily, after calculating the insulation impedance to ground in the above step S3, the method may further include: S7, turning on the first controllable switch to discharge the capacitor in the impedance circuit, and then executing step S1, S2 or S3.

[0051] In some embodiments of the present application, when discharging the capacitor in the impedance circuit in the above step S7, the control unit may also disconnect the second controllable switch arranged in series with the impedance circuit to discharge the capacitor through the resistor in the impedance circuit.

[0052] The above-mentioned power supply system and its insulation impedance detection device provided by the present application, the insulation impedance detection device includes: a control unit, an impedance circuit and a first controllable switch, the impedance circuit includes a resistor and a capacitor connected in series, the first controllable switch is arranged in parallel with the impedance circuit, the control unit and the impedance circuit are connected in series between the AC cable and the grounding circuit, or, the control unit and the impedance circuit are connected in series between the input end of the power converter and the grounding circuit. When the current flowing through the control unit is less than the rated current, the insulation impedance detection device turns on the first controllable switch so that the bypassed impedance circuit will not cause heat dissipation problems and additional heat dissipation components are configured, which can solve the heat dissipation problem. When the current flowing through the control unit is greater than the rated current, the first controllable switch is disconnected, so that the impedance circuit is incorporated into the current loop, so as to form a current loop between the AC cable or DC source, the control unit, the impedance circuit and the grounding circuit to charge the capacitor, ensure that the total load connected to the control unit reaches the minimum load resistance of the control unit, and ensure the stability of the insulation impedance detection to the ground.

[0053] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A power supply system, characterized in that: include: Multiple power converters and insulation impedance testing equipment; The input end of the power converter is used to connect to a DC source, the output ends of the multiple power converters are connected in parallel, and the output end is used to connect to a power grid or a load through an AC cable, wherein the DC source includes a photovoltaic module or an energy storage battery; The insulation impedance detection device comprises: a control unit, an impedance circuit and a first controllable switch, the impedance circuit comprises a resistor and a capacitor connected in series, and the first controllable switch is arranged in parallel with the impedance circuit; the control unit and the impedance circuit are connected in series between the AC cable and the grounding circuit, or the control unit and the impedance circuit are connected in series between the input end of the power converter and the grounding circuit; The control unit is used to: turn on the first controllable switch when the current flowing through the control unit is less than the rated current; and turn off the first controllable switch when the current flowing through the control unit is greater than or equal to the rated current, so as to form a current between the AC cable or the DC source, the control unit, the impedance circuit and the grounding circuit to charge the capacitor.

2. The power supply system according to claim 1, characterized in that: The control unit is further configured to: after turning off the first controllable switch for a set time period, turn on the first controllable switch to discharge the capacitor.

3. The power supply system according to claim 2, characterized in that: The insulation impedance detection device further comprises a second controllable switch, which is arranged in series with the control unit and the impedance circuit; The control unit is further configured to disconnect the second controllable switch when discharging the capacitor.

4. The power supply system according to any one of claims 1 to 3, characterized in that: When charging the capacitor, the capacitance value of the capacitor conforms to the following formula: Ut=Upid*[1-exp(-t / RC)], R=Rpid+Rx, wherein Ut is the voltage value across the capacitor, t is the charging time of the capacitor, C is the capacitance value of the capacitor, Upid is the voltage value of the common mode voltage signal output by the control unit, Rpid is the resistance value of the resistor, and Rx is the insulation impedance to ground, and the insulation impedance to ground includes: the DC insulation impedance to ground between the DC source and the grounding circuit, and the AC insulation impedance to ground between the AC cable and the grounding circuit.

5. The power supply system according to any one of claims 1 to 4, characterized in that: The power supply system also includes a data collector; The data collector is used to restart the multiple power converters in sequence when the current flowing through the control unit is greater than the rated current, wherein the power converter with a DC-to-ground insulation impedance less than a short-circuit threshold cannot be restarted.

6. The power supply system according to claim 5, characterized in that: The data collector is also used for: After restarting the multiple power converters in sequence, if the current flowing through the control unit is greater than the rated current, an abnormal AC insulation impedance alarm to ground is issued, or the AC cable is disconnected from the power grid or the load.

7. The power supply system according to any one of claims 1 to 6, characterized in that: The insulation impedance detection device is integrated into the power converter, or is independent of the power converter.

8. An insulation impedance detection device, characterized in that: Applied to a power supply system, the power supply system comprises a plurality of power converters; the input end of the power converter is used to connect to a DC source, the output ends of the plurality of power converters are connected in parallel, and the output end is used to connect to a power grid or a load through an AC cable, wherein the DC source comprises a photovoltaic module or an energy storage battery; The insulation impedance detection device comprises: a control unit, an impedance circuit and a first controllable switch, the impedance circuit comprises a resistor and a capacitor connected in series, and the first controllable switch is arranged in parallel with the impedance circuit; the control unit and the impedance circuit are connected in series between the AC cable and the grounding circuit, or the control unit and the impedance circuit are connected in series between the input end of the power converter and the grounding circuit; The control unit is used to: turn on the first controllable switch when the current flowing through the control unit is less than the rated current; and turn off the first controllable switch when the current flowing through the control unit is greater than or equal to the rated current, so as to form a current between the AC cable or the DC source, the control unit, the impedance circuit and the grounding circuit to charge the capacitor.

9. The insulation impedance detection device according to claim 8, characterized in that: The control unit is further configured to: after turning off the first controllable switch for a set time period, turn on the first controllable switch to discharge the capacitor.

10. The insulation impedance detection device according to claim 9, characterized in that: The insulation impedance detection device further comprises a second controllable switch, which is arranged in series with the control unit and the impedance circuit; The control unit is further configured to disconnect the second controllable switch when discharging the capacitor.

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