Ground impedance detection device, detection method, inverter and photovoltaic system

Abstract

The application relates to a grounding impedance detection device, a detection method, an inverter and a photovoltaic system, which comprises a first impedance network connected between a DC line at an input end of an inverter and a first AC line at an output end of the inverter; a second impedance network connected between the DC line and a second AC line at an output end of the inverter; and a control module for judging whether the grounding impedance of the DC side of the inverter is abnormal according to a first sampling voltage on the first impedance network and / or a second sampling voltage on the second impedance network. The DC line at the input end of the inverter and the first impedance network and the second impedance network at the output end of the inverter are arranged, the sampling voltage between the DC line and the corresponding AC line is obtained, and whether the grounding impedance is abnormal is judged according to the sampling voltage. The voltage sampling on the casing grounding potential point is not needed, the number of hardware components is reduced, and the equipment manufacturing cost is lowered. Furthermore, the influence of the inconsistent grid voltage amplitude in split-phase and three-phase power grids on the grounding impedance detection can be eliminated, and the detection precision is improved.

Description

Technical Field

[0001] This application relates to the field of detection circuits, and in particular to a grounding impedance detection device, detection method, inverter, and photovoltaic system. Background Technology

[0002] In a grid-connected photovoltaic (PV) system, if the DC resistance to ground at the output of the PV DC power supply is too low, it can cause a short circuit risk on both the DC and AC sides. Therefore, all grid-connected PV systems require DC-side grounding impedance testing.

[0003] Since most inverters currently have metal casings that are grounded, the grounding impedance detection methods utilize the casing's grounding potential point. The detection method involves connecting fixed-value resistors between the grounding potential point and the positive and negative terminals of the photovoltaic DC power supply by switching a relay or semiconductor switch, and then sequentially collecting the voltage values ​​at the grounding potential point to calculate the grounding impedance from the photovoltaic DC power supply terminals to ground. These detection methods all utilize the casing grounding point or the grounding potential point directly connected to the AC side, therefore they are not suitable for photovoltaic inverters with non-metallic casings and no grounding wire connection, and thus have certain limitations. Summary of the Invention

[0004] Therefore, it is necessary to provide a grounding impedance detection device, detection method, inverter, and photovoltaic system to address the aforementioned technical problems.

[0005] In a first aspect, this application provides a grounding impedance detection device, comprising:

[0006] A first impedance network is connected between a DC line at the input of the inverter and a first AC line at the output.

[0007] A second impedance network is connected between the DC line and the second AC line at the inverter output.

[0008] The control module determines whether the grounding impedance of the DC side of the inverter is abnormal based on the first sampled voltage on the first impedance network and / or the second sampled voltage on the second impedance network.

[0009] In one embodiment, the grounding impedance detection device further includes a third impedance network connected between the first AC line or the second AC line and the DC line.

[0010] In one embodiment, the control module calculates the grounding impedance based on the first sampling voltage and / or the second sampling voltage, as well as the impedance values ​​of the first impedance network and the second impedance network, and determines whether the grounding impedance is abnormal based on the grounding impedance and the corresponding safety threshold.

[0011] In one embodiment, the control module calculates the grounding impedance based on the first sampling voltage and / or the second sampling voltage, the voltage between the first AC line and the second AC line or the mains voltage, and the impedance values ​​of the first impedance network and the second impedance network, and determines whether the grounding impedance is abnormal based on the grounding impedance and the corresponding safety threshold.

[0012] In one embodiment, the control module determines whether the grounding impedance is abnormal based on the first sampling voltage and / or the second sampling voltage and the corresponding voltage threshold.

[0013] In one embodiment, the control module determines whether the grounding impedance is abnormal based on the difference or ratio between the second sampling voltage and the first sampling voltage and a corresponding voltage threshold.

[0014] In one embodiment, the first sampling voltage and the second sampling voltage are respectively the magnitude or effective value of the grid frequency component of the voltage on the first impedance network and the second impedance network.

[0015] In one embodiment, the control module calculates the grounding impedance based on the first sampling voltage and / or the second sampling voltage, as well as the impedance values ​​of the first impedance network, the second impedance network, and the third impedance network, and determines whether the grounding impedance is abnormal based on the grounding impedance and the corresponding safety threshold.

[0016] Alternatively, the control module may calculate the grounding impedance based on the first sampling voltage and / or the second sampling voltage, the voltage between the first AC line and the second AC line or the mains voltage, and the impedance values ​​of the first impedance network, the second impedance network, and the third impedance network, and determine whether the grounding impedance is abnormal based on the grounding impedance and the corresponding safety threshold.

[0017] In one embodiment, the first sampling voltage and the second sampling voltage are phasors.

[0018] In one embodiment, the grounding impedance detection device further includes a switching switch connected in series with the third impedance network, the switching switch being used to control whether to connect to the third impedance network.

[0019] In one embodiment, the control module determines whether the grounding impedance is abnormal by acquiring the second sampling voltage and the first sampling voltage before and after the switching switch is closed, as well as the corresponding voltage threshold.

[0020] In one embodiment, the control module calculates the grounding impedance based on the second sampling voltage and the first sampling voltage, the voltage between the first AC line and the second AC line obtained before and after the switching switch is closed, as well as the impedance values ​​of the first impedance network, the second impedance network, and the third impedance network. The control module then determines whether the grounding impedance is abnormal based on the grounding impedance and the safety threshold among the threshold values.

[0021] In one embodiment, the impedance value of the first impedance network is equal to the impedance value of the second impedance network.

[0022] In one embodiment, the impedance value of the third impedance network at the grid frequency is much greater than the safety threshold of the grounding impedance.

[0023] In one embodiment, the first impedance network and / or the second impedance network include capacitors and / or resistors.

[0024] In one embodiment, the first AC line is one of the live wire and the neutral wire, and the second AC line is the other of the live wire and the neutral wire; or the first AC line and the second AC line are both live wires.

[0025] Secondly, this application also provides a method for detecting grounding impedance. The method includes:

[0026] Obtain the first sampled voltage between the DC line at the input terminal of the inverter and the first AC line at the output terminal, and / or the second sampled voltage between the DC line and the second AC line at the output terminal of the inverter;

[0027] Determine whether the grounding impedance of the DC side of the inverter is abnormal based on the first sampling voltage and / or the second sampling voltage.

[0028] Thirdly, this application also provides an inverter, comprising:

[0029] DC / AC conversion circuits are used for power conversion.

[0030] And the grounding impedance detection device as described in the first aspect.

[0031] Fourthly, this application also provides a photovoltaic system, comprising:

[0032] DC power supply;

[0033] An inverter, connected between the DC power supply and the grid, includes a grounding impedance detection device as described in the first aspect.

[0034] The grounding impedance detection device provided in this application obtains the voltage between a DC line and the corresponding AC line by setting a first impedance network and a second impedance network between the DC line at the input end and the AC line at the output end of the inverter. The device then determines whether the grounding impedance is abnormal based on the voltage between the DC line and the corresponding AC line. Since there is no need to sample the voltage at the chassis grounding potential point, it is suitable for inverters without a grounding casing, eliminating the need for a grounding wire. Furthermore, the detection device has a simple structure, reduces the number of hardware components, and further lowers the equipment manufacturing cost. The calculation is simple and easy to implement; it is widely applicable to single-phase, split-phase, and three-phase power grids; and it can further eliminate the influence of inconsistent grid voltage amplitudes on grounding impedance detection in split-phase and three-phase power grids, improving detection accuracy. Attached Figure Description

[0035] Figure 1 These are schematic diagrams of the structure of photovoltaic systems according to some embodiments;

[0036] Figure 2 for Figure 1 The equivalent circuit diagram of the embodiment shown is illustrated.

[0037] Figure 3 This is a schematic diagram of the circuit structure of the grounding impedance detection device in some embodiments;

[0038] Figure 4 This is a schematic diagram of the insulation impedance detection device in a split-phase power grid according to one embodiment;

[0039] Figure 5 This is a schematic diagram of the insulation impedance detection device in a three-phase power grid according to one embodiment;

[0040] Figure 6 This is a schematic diagram of the grounding impedance detection device in a split-phase power grid according to another embodiment;

[0041] Figure 7 for Figure 6 The equivalent circuit diagram of the embodiment shown is illustrated.

[0042] Figure 8 This is a schematic diagram of the insulation resistance detection device in some other embodiments;

[0043] Figure 9 for Figure 8 The equivalent circuit diagram of the embodiment shown is illustrated.

[0044] Figure 10 This is a schematic diagram of the insulation resistance detection device according to some other embodiments;

[0045] Figure 11 for Figure 10 The diagram shows the equivalent state of the embodiment when the switch is off;

[0046] Figure 12 for Figure 10 The diagram shows the equivalent state of the embodiment when the switch is closed;

[0047] Figure 13 This is a flowchart illustrating the grounding impedance detection method in some embodiments. Detailed Implementation

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of the present invention. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0049] As indicated in this invention and the claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0050] While this invention makes various references to certain modules in systems according to embodiments of the invention, any number of different modules can be used and run on computing devices and / or processors. Modules are merely illustrative, and different aspects of the system and method may use different modules.

[0051] It should be understood that when a unit or module is described as "connected" or "coupled" to other units, modules, or blocks, it may refer to a direct connection or coupling, or communication with other units, modules, or blocks, or the presence of intermediate units, modules, or blocks, unless the context explicitly indicates otherwise. The term "and / or" as used herein may include any and all combinations of one or more of the related listed items.

[0052] Figure 1 These are schematic diagrams of the structure of photovoltaic systems in some embodiments, such as... Figure 1 As shown, the photovoltaic system includes:

[0053] DC power supply 100 is used to provide DC power;

[0054] Inverter 300 is connected between DC power supply 100 and grid 200 to invert DC power into AC power and supply it to grid 200.

[0055] Specifically, the input terminal of inverter 300 is electrically connected to DC power supply 100 via DC line, and the output terminal of inverter 300 is electrically connected to grid 200 via AC line.

[0056] Furthermore, the inverter 300 includes a DC / AC conversion circuit 310 connected between the DC line at the inverter input terminal and the AC line at the output terminal, and a grounding impedance detection device 320. The DC / AC conversion circuit 310 is used to perform power conversion, and the grounding impedance detection device 320 is used to detect the grounding impedance at the input terminal of the inverter 300.

[0057] like Figure 1 As shown, RE1 is the grounding impedance of the positive terminal of DC power supply 100, and RE2 is the grounding impedance of the negative terminal of DC power supply 100. "+" and "-" represent the positive and negative polarities of the DC power supply, respectively.

[0058] The grounding impedance detection device 320 includes: a first impedance network 321 connected between a DC line at the input end of the inverter 300 and a first AC line at the output end;

[0059] A second impedance network 322 is connected between the DC line and the second AC line at the output of the inverter 300;

[0060] The control module 324 determines whether the grounding impedance of the DC side of the inverter 300 is abnormal based on the first sampling voltage on the first impedance network 321 and / or the second sampling voltage on the second impedance network 322.

[0061] This embodiment uses a first impedance network and a second impedance network set between a DC line at the inverter input and an AC line at the output to obtain the voltage between the corresponding DC line and the AC line. The voltage between the DC line and the corresponding AC line is then used to determine whether the grounding impedance is abnormal. Since there is no need to sample the voltage at the chassis grounding potential point, it is suitable for inverters without a grounding casing. It also eliminates the need for a grounding wire, further reducing equipment manufacturing costs. Furthermore, the detection device has a simple structure, reduces the number of hardware components, and is low-cost; the calculations are also simple and easy to implement.

[0062] Specifically, the DC lines at the input of the inverter 300 include a positive DC line and a negative DC line, which are connected to the positive and negative terminals of the DC power supply, respectively. The grounding impedance detection device 320 can be connected to either DC line.

[0063] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal is connected to a corresponding DC line and a corresponding DC power supply, and the DC line connected to the grounding impedance detection device 320 is the negative DC line of any input terminal.

[0064] The power grid 200 can be a single-phase power grid, a split-phase power grid, or a three-phase power grid. The power grid 200 is grounded at a remote end. This grounding point can be the positive end or the negative end of the power grid. If it is a split-phase power grid, it can also be at the midpoint of the power grid. The location of this grounding point does not affect the grounding impedance detection in this embodiment.

[0065] When the power grid 200 is a single-phase power grid, the first AC line is the live wire and the second AC line is the neutral wire, or the first AC line is the neutral wire and the second AC line is the live wire.

[0066] When the power grid 200 is a split-phase power grid or a three-phase power grid, the output terminal of the inverter 300 is connected to the neutral line. The first AC line is any live line, and the second AC line is the neutral line or a live line different from the first AC line; or the second AC line is any live line, and the first AC line is the neutral line or a live line different from the second AC line. Other AC lines in the split-phase power grid or three-phase power grid are not shown in the diagram.

[0067] In some embodiments, the grounding impedance detection device 320 further includes a sampling module 323, which samples the voltage 321 on the first impedance network to obtain a first sampling voltage and / or samples the voltage on the second impedance network 322 to obtain a second sampling voltage.

[0068] In some embodiments, the DC power supply 100 may be a photovoltaic module. The DC power supply 100 may be a photovoltaic string or array formed by multiple photovoltaic modules connected in series and / or in parallel, or it may be an energy storage battery or other types of renewable energy.

[0069] In some embodiments, the DC / AC conversion circuit 310 may be isolated or non-isolated, or it may be a multi-stage conversion form that includes a first-stage DC / DC boost circuit and a first-stage DC / AC inverter circuit.

[0070] In some embodiments, the chassis of inverter 300 is not grounded.

[0071] In some embodiments, the inverter 300 further includes a controller ( Figure 1 (Not shown in the image), used to control the DC / AC conversion circuit to perform inversion.

[0072] In some embodiments, the control module 324 may be integrated inside the controller. Figure 1 (Not shown in the image).

[0073] In some embodiments, the grounding impedance detection device 320 may be separately installed outside the inverter 300.

[0074] Specifically, the control module 324 determines whether the grounding impedance of the DC side of the inverter 300 is abnormal based on the first sampling voltage on the first impedance network 321 and / or the second sampling voltage on the second impedance network 322 and a preset threshold. The threshold includes a safety threshold for the grounding impedance and a voltage threshold corresponding to the safety threshold for the grounding impedance.

[0075] In some specific embodiments, the control module 324 calculates the grounding impedance based on the first sampling voltage and / or the second sampling voltage, as well as the impedance values ​​of the first impedance network 321 and the second impedance network 322, and determines whether the grounding impedance is abnormal based on the comparison result between the grounding impedance and the safety threshold.

[0076] In some specific embodiments, the control module 324 calculates the grounding impedance based on the first sampling voltage and / or the second sampling voltage, the voltage between the first AC line and the second AC line or the grid voltage, and the impedance values ​​of the first impedance network 321 and the second impedance network 322, and determines whether the grounding impedance is abnormal based on the comparison result between the grounding impedance and the safety threshold.

[0077] In some specific embodiments, the control module 324 determines whether the grounding impedance is abnormal based on the first sampling voltage and / or the second sampling voltage and the corresponding voltage threshold.

[0078] The control module 324 can determine the size of the corresponding voltage threshold based on the grid voltage, the impedance values ​​of the first impedance network 321 and the second impedance network 322, and the safety threshold of the grounding impedance.

[0079] In some specific embodiments, the first sampling voltage and the second sampling voltage are phasors.

[0080] In one specific embodiment, only the AC component in the circuit is considered, taking a single-phase power grid as an example. Figure 2 for Figure 1 The equivalent circuit diagram of the embodiment shown shows that the equivalent circuit of the first impedance network 321 is Z1, and the equivalent circuit of the second impedance network 322 is Z2. At this time, the first sampling voltage V across the first impedance network 321 is... sam1 It can be expressed by the following formula (1):

[0081]

[0082] Among them, V g Z1 is the mains voltage, Z2 is the impedance value of the first impedance network 321, Z2 is the impedance value of the second impedance network 322, RE1 / / RE2 is the parallel value of the grounding impedances RE1 and RE2, and the first sampling voltage V is the mains voltage. sam1 It is a phasor.

[0083] From the above analysis, it can be seen that the control module 324 can determine the first sampling voltage V based on the first sampling voltage V. sam1 Grid voltage V g The grounding impedance value RE1 / / RE2 is calculated from the impedance values ​​of the first impedance network 321 and the second impedance network 322. The grounding impedance is judged to be abnormal based on the grounding impedance value and the safety threshold. When the grounding impedance is less than the safety threshold, the grounding impedance is considered abnormal; otherwise, it is normal.

[0084] In this embodiment, the grid voltage V g The voltage between the first AC line and the second AC line is equal to the voltage across the first sampling voltage V. sam1 Second sampling voltage V sam2 Calculated, i.e., grid voltage V g This can be expressed as the first sampling voltage V. sam1 Second sampling voltage V sam2 The sum; or it can be obtained directly by sampling module 323.

[0085] It should be noted that, following the same principle, the second sampling voltage V across the first impedance network 321... sam2 It can be expressed by the following formula (2):

[0086]

[0087] Among them, the second sampling voltage V sam2 It is a phasor.

[0088] Therefore, the control module 324 can also adjust the second sampling voltage V based on the second sampling voltage V. sam2 Grid voltage V g The grounding impedance RE1 / / RE2 is calculated from the impedance values ​​of the first impedance network 321 and the second impedance network 322. The grounding impedance is then used to determine whether it is abnormal. If the grounding impedance is less than the safety threshold, it is considered abnormal; otherwise, it is considered normal.

[0089] In other specific embodiments, the first sampling voltage V sam1 Second sampling voltage V sam2 These are the magnitudes or effective values ​​of the grid frequency components of the voltages on the first impedance network 321 and the second impedance network 322, respectively.

[0090] In one specific embodiment, the impedance values ​​of the first impedance network 321 and the second impedance network 322 are equal, but this is not limited to this. When the impedance value of either the grounding impedance RE1 or RE2 is too small or both are too small (i.e., less than the safety threshold, the DC side grounding impedance is considered abnormal), causing it to be much smaller than the impedance value of the first impedance network 321 or the second impedance network 322, the grid voltage V on the grid side... gThe voltage will be mainly distributed across the second impedance network 322, and the magnitude of the voltage across the second impedance network 322 is equal to V. g V sam2 equals V g When the impedance values ​​of grounding impedances RE1 and RE2 are greater than the safety threshold, for example, when the grounding impedances RE1 and RE2 are much greater than the impedance values ​​of the first impedance network 321 or the second impedance network 322, the amplitude of the voltage on the second impedance network 322 is equal to V. g / 2, i.e., V sam2 equals V g / 2. As can be seen from the circuit characteristics, the smaller the grounding impedance, the lower the second sampling voltage V. sam2 The larger the voltage, the more the control module 324 can adjust the voltage based on the second sampling voltage V. sam2 The grounding impedance is judged to be abnormal based on the corresponding voltage threshold. When the second sampling voltage V sam2 When the voltage exceeds the threshold, the grounding impedance is considered abnormal; otherwise, the grounding impedance is normal. The second sampling voltage V... sam2 The magnitude of the grid frequency component of the voltage on the second impedance network 322.

[0091] It should be noted that, following the same principle, the first sampling voltage V can also be used. sam1 The grounding impedance is determined by the corresponding voltage threshold, where the first sampling voltage V sam1 The magnitude of the grid frequency component of the voltage on the second impedance network 321.

[0092] In this embodiment, there is no need to calculate the grounding impedance. The grounding impedance can be detected directly based on the sampled voltage and voltage threshold. This scheme does not require calculation, is relatively simple to implement, and saves controller resources.

[0093] In some specific embodiments, the control module 324 determines the second sampling voltage V based on the second sampling voltage V. sam2 and the first sampling voltage V sam1 The difference or ratio between the values ​​and the corresponding voltage threshold is used to determine whether the grounding impedance is abnormal.

[0094] In one specific embodiment, the control module 324 determines the second sampling voltage V based on the second sampling voltage V. sam2 and the first sampling voltage V sam1 The difference between the values ​​and the corresponding first voltage threshold are used to determine whether the grounding impedance is abnormal.

[0095] When either the grounding impedance RE1 or RE2 is too small, or both are too small (i.e., less than the safety threshold), the DC-side grounding impedance is considered abnormal, causing it to be much smaller than the impedance value of the first impedance network 321 or the second impedance network 322. The grid voltage V on the grid side... gThe voltage will be mainly distributed across the second impedance network 322. The voltage of the first impedance network 321 is pulled down by the grounding impedances RE1 and / or RE2. The amplitude of the voltage on the second impedance network 322 will be much greater than the amplitude of the voltage on the first impedance network 321. When the impedance values ​​of the grounding impedances RE1 and RE2 are greater than the safety threshold, for example, when the grounding impedances RE1 and RE2 are much greater than the impedance values ​​of the first impedance network 321 or the second impedance network 322, the amplitude of the voltage on the second impedance network 322 will be close to or even equal to the amplitude of the voltage on the first impedance network 321. As can be seen from the circuit characteristics, the smaller the grounding impedance, the greater the difference between the amplitude of the voltage on the second impedance network 322 and the amplitude of the voltage on the first impedance network 321.

[0096] From the above analysis, it can be seen that by comparing the first sampling voltage V sam1 Second sampling voltage V sam2 This allows us to determine whether the DC-side grounding impedance is abnormal. The first sampling voltage V sam1 Second sampling voltage V sam2 These are the magnitudes of the grid frequency components of the voltages on the first impedance network 321 and the second impedance network 322, respectively.

[0097] Specifically, the control module 324 will input the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the two values ​​is compared with a preset first voltage threshold to determine whether the grounding impedance is abnormal. When the difference is greater than the first voltage threshold, it indicates that the grounding impedance is abnormal; otherwise, the grounding impedance is normal. The first voltage threshold corresponds to the safety threshold of the DC side grounding impedance.

[0098] In some other specific embodiments, based on the above analysis, the second sampling voltage V can also be used as a reference. sam2 and the first sampling voltage V sam1 The comparison between the ratio and the corresponding voltage threshold can be used to determine whether the DC side grounding impedance is abnormal, but it is not limited to this.

[0099] Figure 3 A circuit structure diagram of a grounding impedance detection device according to some embodiments is shown. The first impedance network 321 includes a resistor R1 and a capacitor Ceq1, and the second impedance network 322 includes a resistor R2 and a capacitor Ceq2. The capacitors Ceq1 and Ceq2 can reuse the EMC filter capacitors provided in the inverter 300, or they can be set separately. Optionally, the first impedance network 321 may not include the capacitor Ceq1, and the second impedance network 322 may not include the capacitor Ceq2.

[0100] The resistance of resistor R1 is much greater than the capacitive reactance of capacitor Ceq1 at the power grid frequency, the resistance of resistor R2 is much greater than the capacitive reactance of capacitor Ceq2 at the power grid frequency, and the capacitive reactance of capacitors Ceq1 and Ceq2 at the power grid frequency is much greater than the safety threshold of the grounding impedance.

[0101] It should be noted that by setting capacitors Ceq1 and Ceq2, the measurement accuracy of the first sampling voltage and the first sampling voltage can be improved, and the detection accuracy of the grounding impedance can be further improved. Moreover, the larger the capacitance values ​​of capacitors Ceq1 and Ceq2, the higher the measurement accuracy.

[0102] In some specific embodiments, resistor R1 can be replaced with a voltage divider circuit including voltage divider resistors, and the first sampling voltage can be obtained by sampling the voltage across any voltage divider resistor; and / or resistor R2 can be replaced with a voltage divider circuit including voltage divider resistors, and the second sampling voltage can be obtained by sampling the voltage across any voltage divider resistor.

[0103] By employing a resistor voltage divider circuit, high-impedance isolation is achieved between the DC and AC sides while acquiring the sampled values. By selecting appropriate resistance values, the insulation strength requirements between the DC and AC sides can be met.

[0104] In some specific embodiments, resistors R1 and / or R2 can also be replaced by capacitors or capacitor voltage divider circuits.

[0105] Figure 4 This is a schematic diagram of the structure of a grounding impedance detection device used in a split-phase power grid, as shown in the example embodiment. Figure 4 As shown, the inverter 300 is connected to the neutral line N, the power grid is a split-phase power grid, the first AC line is the neutral line N, the second AC line is the live line, and the working principle of the insulation detection impedance device is similar to the aforementioned scheme, so it will not be described again here.

[0106] Figure 5 This is a schematic diagram of the grounding impedance detection device used in a three-phase power grid, as another example embodiment. Figure 5 As shown, the inverter 300 is connected to the neutral line N, the power grid is a three-phase power grid, the first AC line is the neutral line N, the second AC line is the live line, and the working principle of the insulation detection impedance device is similar to the aforementioned scheme, so it will not be described again here.

[0107] In another example embodiment, when the power grid is a split-phase or three-phase power grid, and the output terminal of the inverter 300 is connected to the neutral line N, and both the first AC line and the second AC line are live wires, such as Figure 6 As shown, the control module 324 determines the voltage based on the first sampling voltage V. sam1 and / or the second sampling voltage V sam2The grounding impedance is calculated based on the voltage between the first AC line and the second AC line or the mains voltage, and the impedance values ​​of the first impedance network and the second impedance network. The grounding impedance is then used to determine whether the grounding impedance is abnormal based on the grounding impedance and the safety threshold.

[0108] Considering only the communication component, Figure 7 The equivalent circuit diagram of this example embodiment is shown, with the first sampling voltage V. sam1 Second sampling voltage V sam2 The terms can be expressed by the following formulas (3) and (4):

[0109]

[0110]

[0111] Among them, V g1 V is the first phase voltage of the split-phase power grid. g2 This refers to the second phase voltage of the split-phase power grid.

[0112] As can be seen from the above, the control module 324 can adjust the first sampled voltage V. sam1 Or the second sampling voltage V sam2 Grid voltage V g1 Grid voltage V g2 The grounding impedance value RE1 / / RE2 is calculated from the impedance values ​​of the first impedance network 321 and the second impedance network 322. The grounding impedance is judged to be abnormal based on the grounding impedance value and the safety threshold. When the grounding impedance is less than the safety threshold, the grounding impedance is considered abnormal; otherwise, it is normal.

[0113] When the voltage of the split-phase power grid is balanced, the grid voltage V g1 and grid voltage V g2 The first sampling voltage V can be used sam1 Second sampling voltage V sam2 The calculated value is V. g1 and grid voltage V g2 Both are the first sampling voltage V sam1 Second sampling voltage V sam2 Half of the sum; or it can be calculated by sampling the voltage between the first AC line and the second AC line, the grid voltage V. g1 and grid voltage V g2 Both are half the voltage between the first AC line and the second AC line.

[0114] When the voltage of a split-phase power grid is unbalanced, the grid voltage V g1 and grid voltage V g2The voltage between the live wire L1 and the neutral wire N and the voltage between the live wire L2 and the neutral wire N can be obtained by sampling module 323.

[0115] In some embodiments, when the power grid is a split-phase power grid or a three-phase power grid, the output terminal of the inverter 300 is not connected to the neutral line N, and both the first AC line and the second AC line are live wires, such as Figure 8 As shown, the grounding impedance detection device 320 also includes a third impedance network 325 connected between the DC line and the first AC line or the second AC line. The control module 324 can detect the grounding impedance based on the second sampling voltage V. sam2 and the first sampling voltage V sam1 The difference or ratio between the two values ​​is compared with the corresponding voltage threshold to determine whether the grounding impedance is abnormal. The first AC line is any live wire, and the second AC line is another live wire different from the first AC line.

[0116] The voltage threshold used here can be determined based on the phase voltage of each phase of the power grid (i.e., the grid voltage), the impedance value of the first impedance network 321, the impedance value of the second impedance network 322, the impedance value of the third impedance network 325, and the safety threshold of the grounding impedance.

[0117] In one specific embodiment, the impedance value of the third impedance network 325 at the power grid frequency is much greater than the safety threshold of the grounding impedance. The third impedance network 325 is, for example, a capacitor, but is not limited thereto.

[0118] Considering only the AC component, taking a split-phase power grid as an example, Figure 9 It shows Figure 8 The equivalent circuit diagram of the embodiment shown is illustrated, where Z3 is the equivalent circuit of the third impedance network 325, and the first sampling voltage V... sam1 Second sampling voltage V sam2 These can be expressed as equations (5) and (6) respectively:

[0119]

[0120]

[0121] Among them, V g1 V is the first phase voltage of the split-phase power grid. g2 Z1 is the second phase voltage of the split-phase power grid, and Z2 is the impedance value of the third impedance network 325.

[0122] When either the grounding impedance RE1 or RE2 is too small, or both are too small (i.e., less than the safety threshold), the DC-side grounding impedance is considered abnormal. If the impedance is significantly smaller than the impedance value of the third impedance network 325, the grid voltage V... g1 Its main function is on the first impedance network 321, and the mains voltage Vg2 Its main function is on the second impedance network 322, and it is easy to see that when the mains voltage V... g1 and V g2 Under the combined effect of the two impedance networks, and when their voltage amplitudes are consistent, the voltage amplitudes on the first impedance network 321 and the second impedance network 322 are approximately equal. When the grounding impedances RE1 and RE2 are greater than the safety threshold, that is, when the grounding impedances RE1 and RE2 are much greater than the impedance values ​​of the first impedance network 321 or the second impedance network 322, the impedance value of the first impedance network 321 is less than the parallel impedance value of the second impedance network 322 and the third impedance network 325. The voltage amplitude on the second impedance network 322 will be less than the voltage amplitude on the first impedance network 321. It is easy to see that when the grounding impedances RE1 and RE2 change, the difference between the voltage amplitudes on the second impedance network 322 and the first impedance network 321 will also change. According to the circuit characteristics, the smaller the grounding impedance, the smaller the difference between the two.

[0123] From the above analysis, it can be seen that by comparing the first sampling voltage V sam1 Second sampling voltage V sam2 This allows you to determine whether the DC side grounding impedance is abnormal.

[0124] Specifically, the control module 324 will input the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the two values ​​is compared with a preset second voltage threshold to determine whether the grounding impedance is abnormal. When the difference is less than the second voltage threshold, it indicates that the grounding impedance is abnormal; otherwise, the grounding impedance is normal.

[0125] In this embodiment, by adding a third impedance network, the grounding impedance detection scheme of this embodiment can be applied to the condition that the output terminal of the inverter 300 is not connected to the neutral line in split-phase power grids and three-phase power grids, thus expanding the application range.

[0126] It should be noted that the control module 324 can adjust the voltage based on the first sampled voltage V. sam1 Or the second sampling voltage V sam2 Grid voltage V g1 Grid voltage V g2 The grounding impedance values ​​RE1 / / RE2 are calculated from the impedance values ​​of the first to third impedance networks. The grounding impedance is then used to determine whether it is abnormal based on the grounding impedance value and the safety threshold. If the grounding impedance is less than the safety threshold, it is considered abnormal; otherwise, it is considered normal.

[0127] When the phase voltages of a split-phase power grid are in balance, the grid voltage V g1 and grid voltage V g2 It can be obtained through the first sampling voltage V sam1 Second sampling voltage V sam2The calculated grid voltage V is at this time. g1 and grid voltage V g2 Both are the first sampling voltage V sam1 Second sampling voltage V sam2 Half of the sum.

[0128] Alternatively, the voltage between the first AC line and the second AC line can be sampled and calculated using a sampling module. In this case, the grid voltage V is... g1 and grid voltage V g2 Both are half the voltage between the first AC line and the second AC line.

[0129] When the power grid is a three-phase power grid, the principle is the same as that of a split-phase power grid, and will not be repeated here.

[0130] In some embodiments, such as Figure 10 As shown, the grounding impedance detection device 320 also includes a switching switch 326 connected in series with the third impedance network 325. Based on the above analysis, by controlling the switching switch 326 to open and close, the grounding impedance detection device 320 can be applied to different scenarios. For example, when the power grid is a single-phase grid, the switching switch 326 can be opened; when the power grid is a split-phase grid or a three-phase grid and the output of the inverter 300 is connected to the neutral line, if the second sampling voltage V is used... sam2 and the first sampling voltage V sam1 The difference between the two voltage values ​​and the preset second voltage threshold are used to determine whether the grounding impedance is abnormal, and the switching switch 326 is controlled to close. When the power grid is a split-phase power grid or a three-phase power grid and the output terminal of the inverter 300 is connected to the neutral line, the first AC line is the live line and the second AC line is the neutral line, the switching switch 326 is controlled to open.

[0131] The switching switch 326 can be a semiconductor switch or a relay.

[0132] In one specific embodiment, the control module 324 obtains the power grid type based on the power grid type signal provided by the host computer.

[0133] In this embodiment, by adding a switching switch, the grounding impedance detection scheme can be applied to single-phase, split-phase power grids and three-phase power grids simultaneously, and different grounding impedance detection schemes can be adopted as needed, thus having a wide range of applications.

[0134] In some embodiments, such as Figure 10 As shown, the control module 324 acquires the second sampling voltage V before and after the switch 326 is closed. sam2 and the first sampling voltage V sam1 The comparison results of the corresponding voltage thresholds are used to determine whether the grounding impedance is abnormal.

[0135] When the phase voltages of a split-phase power grid or a three-phase power grid are unbalanced, taking a split-phase power grid as an example, for instance, there is a grid voltage V... g1 and V g2 When the amplitudes are not equal, the grid voltage V g1 and V g2 The deviation will affect the first sampling voltage V sam1 Second sampling voltage V sam2 The difference between them has an impact, making it impossible to directly judge the first sampled voltage V. sam1 Second sampling voltage V sam2 The difference between RE1 and RE2 is used to determine the magnitude of the grounding impedance.

[0136] In this situation, the mains voltage V can be eliminated by opening and closing the two circuit states of the switch 326. g1 and V g2 The impact of unequal amplitudes on the determination of the magnitude of grounding impedance RE1 / / RE2.

[0137] The grid voltage V can be g1 and V g2 The common mode and differential mode are respectively shown in equations (7) and (8):

[0138]

[0139]

[0140] In one example embodiment, such as Figure 11 As shown, when the switch 326 is open, the circuit state is a superposition of state m1 and state m2, as follows: Figure 12 As shown, RE is the parallel connection of grounding impedances RE1 and RE2. Therefore, under this operating condition, the second sampling voltage V sam2 and the first sampling voltage V sam1 The first difference V between them diff1 This can be represented as the second sampling voltage V under state m1. sam2_m1 and the first sampling voltage V sam1_m1 The difference V between diff_m1 The second sampling voltage V under state m2 sam2_m2 and the first sampling voltage V sam1_m2 The difference V between diff_m2 The superposition is shown in equation (9):

[0141] V diff1 =V diff_m1 +V diff_m2 (9);

[0142] In circuit state m1, the mains voltage V g1 and Vg2 The amplitudes are consistent, and Z1 = Z2, therefore V diff_m1 =0, thus obtaining the expression shown in equation (10):

[0143] V diff1 =V diff_m2 (10);

[0144] When switch 326 is closed, the circuit state is a superposition of state m3 and state m4. In circuit state m3, the mains voltage V g1 and V g2 The amplitudes are consistent, and the second sampling voltage V sam2 and the first sampling voltage V sam1 The second difference V between them diff2 This can be represented as the second sampling voltage V under state m3. sam2_m3 and the first sampling voltage V sam1_m3 The difference V between diff_m3 The second sampling voltage V under state m4 sam2_m4 and the first sampling voltage V sam1_m4 The difference V between diff_m4 The superposition of these is as shown in equation (11):

[0145] V diff2 =V diff_m3 +V diff_m4 (11);

[0146] Since the grounding impedance is much smaller than the parallel impedance value of the second impedance network 322 and the third impedance network 325 when it is near the safety threshold, therefore V diff_m2 ≈V diff_m4 .

[0147] Therefore, we can obtain V diff2 -V diff1 =V diff_m3 .

[0148] As can be seen from the circuit characteristics, the smaller the grounding impedance, the better the second sampling voltage V can be obtained when the switch 326 is open. sam2 and the first sampling voltage V sam1 The first difference V between them diff1 The second sampling voltage V obtained in the closed state smn2 and the first sampling voltage V sam1 The second difference V between them diff2 The smaller the difference between the two.

[0149] The above analysis shows that the second sampling voltage V is obtained by comparing the switching switch 326 before and after it is closed. sam2 and the first sampling voltage V sam1The difference between the two values ​​can be used to determine whether the DC side grounding impedance is abnormal.

[0150] Specifically, when the switch 326 is open, the control module 324 acquires a first difference between the second sampled voltage and the first sampled voltage. When the switch 326 is closed, the control module 324 acquires a second difference between the second sampled voltage and the first sampled voltage. Based on a comparison between the difference between the second and first differences and a third voltage threshold, the control module 324 determines whether the grounding impedance is abnormal. If the difference between the second and first differences is less than the third voltage threshold, the grounding impedance is abnormal; otherwise, the grounding impedance is normal.

[0151] In this embodiment, by opening and closing the switching switch 326, the second sampling voltage V is obtained twice. sam2 and the first sampling voltage V sam1 The difference between the two values ​​is used to determine the DC-side grounding impedance, which can eliminate the influence of unequal voltage amplitudes in each phase of the power grid on the determination of the magnitude of the grounding impedance RE1 / / RE2, and further improve the detection accuracy.

[0152] Furthermore, based on the above analysis, equation (12) is obtained:

[0153] V diff2 -V diff1 =V sam2_m3 -V sam1_m3 (12);

[0154] Combining formulas (5) and (6), it can be seen that the control module 324 obtains the second sampling voltage V before and after the switching switch 326 is closed. sam2 and the first sampling voltage V sam1 The grounding impedance is calculated based on the voltage between the first AC line and the second AC line, as well as the impedance values ​​of the first impedance network 321, the second impedance network 322, and the third impedance network 325.

[0155] Specifically, when the switching switch 326 is turned off, the control module 324 acquires the second sampling voltage V. sam2 and the first sampling voltage V sam1 The first difference V between them diff1 When the switching switch is closed, the control module obtains a second difference V between the second sampled voltage and the first sampled voltage. diff2 And based on the second difference V diff2 The first difference V difflThe grounding impedance value RE1 / / RE2 is calculated based on the difference between the first AC line and the second AC line, the impedance value of the first impedance network 321, the impedance value of the second impedance network 322, and the impedance value of the third impedance network 325. The grounding impedance is then compared with the safety threshold to determine whether the grounding impedance is abnormal. If the grounding impedance is less than the safety threshold, the grounding impedance is considered abnormal; otherwise, it is normal.

[0156] When the power grid is a three-phase power grid, the principle is the same as that of a split-phase power grid, and will not be repeated here.

[0157] In summary, the grounding impedance detection device provided in this application obtains the voltage between a DC line and the corresponding AC line by setting a first impedance network and a second impedance network between a DC line at the inverter input and an AC line at the output. The device then determines whether the grounding impedance is abnormal based on this voltage. Since there is no need to sample the voltage at the chassis grounding potential point, it is suitable for inverters without a grounding casing, eliminating the need for a grounding wire. Furthermore, the detection device has a simple structure, reducing the number of hardware components and further lowering manufacturing costs. The calculations are simple and easy to implement; it is widely applicable to single-phase, split-phase, and three-phase power grids; and it can further eliminate the influence of inconsistent grid voltage amplitudes on grounding impedance detection in split-phase and three-phase power grids, improving detection accuracy.

[0158] like Figure 13 As shown, this application also provides a method for detecting grounding impedance, including the following steps:

[0159] Step S30: Obtain the first sampled voltage between a DC line at the input terminal of the inverter and the first AC line at the output terminal, and / or the second sampled voltage between the DC line and the second AC line at the output terminal of the inverter.

[0160] Step S32: Determine whether the grounding impedance of the DC side of the inverter is abnormal based on the first sampling voltage and / or the second sampling voltage and the threshold.

[0161] Specifically, a first impedance network 321 can be set up between a DC line at the input of the inverter and a first AC line at the output, and a second impedance network 322 can be set up between the DC line and a second AC line at the output of the inverter. The voltage on the first impedance network 321 is sampled to obtain a first sampling voltage V. sam1 And / or sample the voltage on the second impedance network 322 to obtain the second sampled voltage V. sam2 .

[0162] In some embodiments, the DC lines at the input of the inverter 300 include a positive DC line and a negative DC line, which are connected to the positive and negative terminals of the DC power supply, respectively, and the grounding impedance detection device 320 can be connected to either DC line.

[0163] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal is connected to a corresponding DC line and a corresponding DC power supply, and the DC line connected to the grounding impedance detection device 320 is the negative DC line of any input terminal.

[0164] The power grid 200 can be a single-phase power grid, a split-phase power grid, or a three-phase power grid. The power grid 200 is grounded at a remote end. This grounding point can be the positive end or the negative end of the power grid. If it is a split-phase power grid, it can also be at the midpoint of the power grid. The location of this grounding point does not affect the grounding impedance detection in this embodiment.

[0165] When the power grid 200 is a single-phase power grid, the first AC line is the live wire and the second AC line is the neutral wire, or the first AC line is the neutral wire and the second AC line is the live wire.

[0166] When the power grid 200 is a split-phase power grid or a three-phase power grid, the output terminal of the inverter 300 is connected to the neutral line. The first AC line is any live line, and the second AC line is the neutral line or a live line different from the first AC line; or the second AC line is any live line, and the first AC line is the neutral line or a live line different from the second AC line.

[0167] In some embodiments, the first sampling voltage V sam1 Second sampling voltage V sam2 It is a phasor.

[0168] In some specific embodiments, the grounding impedance is calculated based on the first sampling voltage and / or the second sampling voltage, as well as the impedance values ​​of the first impedance network and the second impedance network, and the grounding impedance is judged to be abnormal based on the comparison result between the grounding impedance and the safety threshold.

[0169] When the grounding impedance is less than the safety threshold, the grounding impedance is considered abnormal; otherwise, it is normal.

[0170] In some specific embodiments, the grounding impedance is calculated based on the first sampling voltage and / or the second sampling voltage, the voltage between the first AC line and the second AC line or the grid voltage, and the impedance values ​​of the first impedance network and the second impedance network. The grounding impedance is then compared with a safety threshold to determine whether the grounding impedance is abnormal.

[0171] When the grounding impedance is less than the safety threshold, the grounding impedance is considered abnormal; otherwise, it is normal.

[0172] Grid voltage V g It can be obtained through the first sampling voltage V sam1 Second sampling voltage V sam2 It can be obtained through calculation or by direct sampling.

[0173] In other embodiments, the first sampling voltage V sam1 Second sampling voltage V sam2 These are the magnitudes or effective values ​​of the grid frequency components of the voltages on the first impedance network 321 and the second impedance network 322, respectively.

[0174] In some specific embodiments, based on the first sampling voltage V sam1 and / or the second sampling voltage V sam2 Use the corresponding voltage threshold to determine whether the grounding impedance is abnormal.

[0175] The voltage threshold can be determined based on the grid voltage, the impedance values ​​of the first and second impedance networks, and the safety threshold of the grounding impedance.

[0176] Specifically, it can be based on the second sampling voltage V sam2 The grounding impedance is judged to be abnormal based on the corresponding voltage threshold. When the second sampling voltage V sam2 If the voltage exceeds the threshold, the grounding impedance is considered abnormal; otherwise, the grounding impedance is normal.

[0177] It should be noted that, following the same principle, the first sampling voltage V can also be used. sam1 The grounding impedance is determined by the corresponding voltage threshold, where the first sampling voltage V sam1 The magnitude or effective value of the grid frequency component of the voltage on the second impedance network 321.

[0178] In some specific embodiments, based on the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference or ratio between the values ​​and the corresponding voltage threshold is used to determine whether the grounding impedance is abnormal.

[0179] In one specific embodiment, based on the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the values ​​and the corresponding first voltage threshold are used to determine whether the grounding impedance is abnormal.

[0180] When the difference is greater than the first voltage threshold, it indicates that the grounding impedance is abnormal; otherwise, the grounding impedance is normal. The first voltage threshold corresponds to the safety threshold of the DC side grounding impedance.

[0181] In other specific embodiments, the second sampling voltage V can also be used as a reference. sam2 and the first sampling voltage V sam1 The comparison between the ratio and the corresponding voltage threshold can be used to determine whether the DC side grounding impedance is abnormal, but it is not limited to this.

[0182] In this embodiment, there is no need to calculate the grounding impedance. The grounding impedance can be detected directly based on the sampled voltage and voltage threshold. This scheme does not require calculation, is relatively simple to implement, and saves controller resources.

[0183] In some embodiments, the first impedance network 321 includes a resistor R1 and a capacitor Ceq1, and the second impedance network 322 includes a resistor R2 and a capacitor Ceq2. The capacitors Ceq1 and Ceq2 can reuse the EMC filter capacitors provided in the inverter 300, or they can be set separately. Optionally, the first impedance network 321 may not include the capacitor Ceq1, and the second impedance network 322 may not include the capacitor Ceq2.

[0184] The resistance of resistor R1 is much greater than the capacitive reactance of capacitor Ceq1 at the power grid frequency, the resistance of resistor R2 is much greater than the capacitive reactance of capacitor Ceq2 at the power grid frequency, and the capacitive reactance of capacitors Ceq1 and Ceq2 at the power grid frequency is much greater than the safety threshold of the grounding impedance.

[0185] It should be noted that by setting capacitors Ceq1 and Ceq2, the measurement accuracy of the first sampling voltage and the first sampling voltage can be improved, and the detection accuracy of the grounding impedance can be further improved. Moreover, the larger the capacitance values ​​of capacitors Ceq1 and Ceq2, the higher the measurement accuracy.

[0186] In some specific embodiments, resistor R1 can be replaced with a voltage divider circuit including voltage divider resistors, and the first sampling voltage can be obtained by sampling the voltage across any voltage divider resistor; and / or resistor R2 can be replaced with a voltage divider circuit including voltage divider resistors, and the second sampling voltage can be obtained by sampling the voltage across any voltage divider resistor.

[0187] By employing a resistor voltage divider circuit, high-impedance isolation is achieved between the DC and AC sides while acquiring the sampled values. By selecting appropriate resistance values, the insulation strength requirements between the DC and AC sides can be met.

[0188] In some specific embodiments, resistors R1 and / or R2 can also be replaced by capacitors or capacitor voltage divider circuits.

[0189] In some embodiments, the method further includes: providing a third impedance network connected between the DC line and the first AC line or the second AC line.

[0190] When the power grid is a split-phase or three-phase power grid, the output terminal of inverter 300 is not connected to the neutral line N, and both the first AC line and the second AC line are live wires, the second sampling voltage V can be used as a reference. sam2 and the first sampling voltage V sam1 The difference or ratio between the values ​​is compared with the corresponding voltage threshold to determine whether the grounding impedance is abnormal.

[0191] The voltage threshold can be determined based on the grid voltage, the impedance value of the first impedance network, the impedance value of the second impedance network, the impedance value of the third impedance network, and the safety threshold of the grounding impedance.

[0192] In one specific embodiment, the impedance value of the third impedance network 325 at the power grid frequency is much greater than the safety threshold of the grounding impedance. The third impedance network 325 is, for example, a capacitor, but is not limited thereto.

[0193] In one specific embodiment, the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the two values ​​is compared with a preset second voltage threshold to determine whether the grounding impedance is abnormal. When the difference is less than the second voltage threshold, it indicates that the grounding impedance is abnormal; otherwise, the grounding impedance is normal.

[0194] It should be noted that it can also be based on the first sampling voltage V sam1 Or the second sampling voltage V sam2 The grounding impedance value RE1 / / RE2 is calculated from the grid voltage and the impedance values ​​of the first to third impedance networks. The grounding impedance is then used to determine whether it is abnormal. If the grounding impedance is less than the safety threshold, it is considered abnormal; otherwise, it is considered normal.

[0195] In this embodiment, by adding a third impedance network, the grounding impedance detection scheme of this embodiment can be applied to the condition that the output terminal of the inverter 300 is not connected to the neutral line in split-phase power grids and three-phase power grids, thus expanding the application range.

[0196] In some embodiments, the system further includes: a switching switch connected in series with the third impedance network, which can control whether the switching switch is closed according to actual application requirements.

[0197] Specifically, for example, when the power grid is a single-phase power grid, the switching switch 326 is opened; when the power grid is a split-phase power grid or a three-phase power grid and the output terminal of the inverter 300 is connected to the neutral line, if the second sampling voltage V is used... sam2 and the first sampling voltage V sam1 The difference between the two voltage values ​​and the preset second voltage threshold are used to determine whether the grounding impedance is abnormal, and the switching switch 326 is controlled to close. When the power grid is a split-phase power grid or a three-phase power grid and the output terminal of the inverter 300 is connected to the neutral line, the first AC line is the live line and the second AC line is the neutral line, the switching switch 326 is controlled to open.

[0198] In one specific embodiment, the power grid type is obtained based on the power grid type signal provided by the host computer.

[0199] In this embodiment, by adding a switching switch, the grounding impedance detection scheme can be applied to single-phase, split-phase power grids, and three-phase power grids, thus having a wide range of applications.

[0200] In some specific embodiments, the second sampling voltage V is obtained before and after the switching switch 326 is closed. sam2 and the first sampling voltage V sam1 The comparison results of the corresponding voltage thresholds are used to determine whether the grounding impedance is abnormal.

[0201] Specifically, when the switching switch 326 is open, the second sampling voltage V is acquired. sam2 and the first sampling voltage V sam1 The first difference V between them diff1 When the switching switch is closed, the second difference V between the second sampling voltage and the first sampling voltage is obtained. diff2 And based on the second difference V diff2 The first difference V diff1 The grounding impedance value RE1 / / RE2 is calculated based on the difference between the grounding impedance and the mains voltage, the impedance value of the first impedance network 321, the impedance value of the second impedance network 322, and the impedance value of the third impedance network 325. The grounding impedance is then compared with the safety threshold to determine whether the grounding impedance is abnormal. If the grounding impedance is less than the safety threshold, the grounding impedance is considered abnormal; otherwise, it is normal.

[0202] In this embodiment, by opening and closing the switching switch, the DC side grounding impedance is determined based on the difference between the two obtained second sampling voltages and the first sampling voltage. This can eliminate the influence of unequal voltage amplitudes in each phase of the power grid on the determination of the magnitude of the grounding impedance RE1 / / RE2, and further improve the detection accuracy.

[0203] In other specific embodiments, the second sampling voltage V is obtained before and after the switching switch 326 is closed. sam2 and the first sampling voltage V sam1 The grounding impedance is calculated based on the grid voltage, the impedance values ​​of the first impedance network 321, the second impedance network 322, and the third impedance network 325.

[0204] Specifically, when the switching switch 326 is turned off, the control module 324 acquires the second sampling voltage V. sam2 and the first sampling voltage V sam1 The first difference V between them diff1 When the switching switch is closed, the control module obtains a second difference V between the second sampled voltage and the first sampled voltage. diff2 And based on the second difference V diff2 The first difference V diff1The grounding impedance value RE1 / / RE2 is calculated based on the difference between the grounding impedance and the mains voltage, the impedance value of the first impedance network 321, the impedance value of the second impedance network 322, and the impedance value of the third impedance network 325. The grounding impedance is then compared with the safety threshold to determine whether the grounding impedance is abnormal. If the grounding impedance is less than the safety threshold, the grounding impedance is considered abnormal; otherwise, it is normal.

[0205] In summary, the grounding impedance detection device provided in this application obtains the voltage between a DC line and the corresponding AC line by setting a first impedance network and a second impedance network between a DC line at the inverter input and an AC line at the output. The device then determines whether the grounding impedance is abnormal based on this voltage. Since there is no need to sample the voltage at the chassis grounding potential point, it is suitable for inverters without a grounding casing, eliminating the need for a grounding wire. Furthermore, the detection device has a simple structure, reducing the number of hardware components and further lowering manufacturing costs. The calculations are simple and easy to implement; it is widely applicable to single-phase, split-phase, and three-phase power grids; and it can further eliminate the influence of inconsistent grid voltage amplitudes on grounding impedance detection in split-phase and three-phase power grids, improving detection accuracy.

[0206] This application also provides an inverter, including:

[0207] DC / AC conversion circuits are used for power conversion.

[0208] And a grounding impedance detection device as described in any of the above embodiments.

[0209] Furthermore, the DC / AC conversion circuit can convert direct current into any one of single-phase alternating current, two-phase alternating current, or three-phase alternating current, and supply it to the power grid.

[0210] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal is connected to a corresponding DC line and a corresponding DC power supply, and the DC line connected to the grounding impedance detection device 320 is the negative DC line of any input terminal.

[0211] The inverter proposed in this embodiment obtains the voltage between a DC line and a corresponding AC line by setting a first impedance network and a second impedance network between the DC line at the inverter input and the AC line at the output. The voltage between the DC line and the corresponding AC line is then used to determine whether the grounding impedance is abnormal. Since there is no need to sample the voltage at the chassis grounding potential point, it is suitable for inverters without a grounding casing. It also eliminates the need for a grounding wire, further reducing equipment manufacturing costs. Furthermore, the detection device has a simple structure, reduces the number of hardware components, and is low in cost; the calculation is also simple and easy to implement.

[0212] This application also provides a photovoltaic system, including:

[0213] DC power supply;

[0214] An inverter, connected between the DC power supply and the grid, includes a grounding impedance detection device as described in any of the above embodiments.

[0215] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal is connected to a corresponding DC power supply via a corresponding DC line.

[0216] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0217] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0218] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A grounding impedance detection device, characterized in that, The grounding impedance detection device includes: A first impedance network is connected between a DC line at the input of the inverter and a first AC line at the output. A second impedance network is connected between the DC line and the second AC line at the inverter output. A third impedance network connected between the first or second AC line and the DC line; A switching switch connected in series with the third impedance network, the switching switch being used to control whether to connect to the third impedance network; The sampling module is connected to the first impedance network and the second impedance network respectively, and is used to sample the first sampling voltage of the first impedance network and the second sampling voltage of the second impedance network. The control module is used to acquire the first difference between the first sampled voltage and the second sampled voltage when the switching switch is open, and the second difference between the first sampled voltage and the second sampled voltage when the switching switch is closed, and to determine whether the grounding impedance is abnormal based on the difference between the first difference and the second difference.

2. The grounding impedance detection device according to claim 1, characterized in that, The first sampling voltage and the second sampling voltage are the amplitude or effective value of the grid frequency component of the voltage on the first impedance network and the second impedance network, respectively.

3. The grounding impedance detection device according to claim 1, characterized in that, The first sampling voltage and the second sampling voltage are phasors.

4. The grounding impedance detection device according to claim 1, characterized in that, The control module calculates the grounding impedance based on the first difference, the second difference, the voltage between the first AC line and the second AC line, and the impedance values ​​of the first impedance network, the second impedance network, and the third impedance network, and determines whether the grounding impedance is abnormal based on the grounding impedance and the safety threshold among the thresholds.

5. The grounding impedance detection device according to claim 1, characterized in that, The impedance value of the first impedance network is equal to the impedance value of the second impedance network.

6. The grounding impedance detection device according to claim 1, characterized in that, The impedance value of the third impedance network at the power grid frequency is much greater than the safety threshold of the grounding impedance.

7. The grounding impedance detection device according to claim 1, characterized in that, The first impedance network and / or the second impedance network include capacitors and / or resistors.

8. The grounding impedance detection device according to claim 1, characterized in that, The first AC line is one of the live line and the neutral line, and the second AC line is the other of the live line and the neutral line; or the first AC line and the second AC line are both live lines.

9. A method for detecting grounding impedance, characterized in that, The method, applied to the grounding impedance detection device as described in claim 1, comprises: Disconnect the switching switch and obtain the first sampled voltage between a DC line at the inverter input terminal and a first AC line at the output terminal and the second sampled voltage between the DC line and the second AC line at the inverter output terminal; Close the switching switch to obtain the second difference between the first sampled voltage and the second sampled voltage; The grounding impedance is determined to be abnormal based on the difference between the first difference and the second difference.

10. An inverter, characterized in that, include: DC / AC conversion circuits are used for power conversion. And the grounding impedance detection device as described in any one of claims 1-8.

11. A photovoltaic system, characterized in that, include: DC power supply; An inverter, connected between the DC power supply and the grid, includes a grounding impedance detection device as described in any one of claims 1-8.

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