Grounding impedance measurement apparatus and method, inverter, and photovoltaic system

Abstract

A grounding impedance measurement apparatus and method, an inverter, and a photovoltaic system. The grounding impedance measurement apparatus comprises: a first impedance network connected between a direct-current (DC) line of an input end of an inverter and a first AC line of an output end of the inverter; a second impedance network connected between the DC line and a second AC line of the output end of the inverter; and a control module for determining, on the basis of a first sampled voltage on the first impedance network and / or a second sampled voltage on the second impedance network, whether grounding impedance of a DC side of the inverter is abnormal or not.

Description

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

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 202310830710.6, filed on July 6, 2023, entitled “A ground impedance detection device, detection method, inverter and photovoltaic system,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the field of detection circuits, and in particular to a ground impedance detection device, a detection method, an inverter, and a photovoltaic system. Background Art

[0004] In a grid-connected photovoltaic system, if the DC resistance to ground at the output of the photovoltaic DC power supply is too low, there is a risk of a short circuit between the DC and AC sides. Therefore, all grid-connected photovoltaic systems require DC-side ground impedance testing.

[0005] Because most current inverters have metal casings and are grounded, the ground impedance detection method used utilizes the casing ground potential point. This detection method involves alternating fixed-value resistors between the ground potential point and the positive and negative terminals of the PV DC power supply through the switching of relays or semiconductor switches. The voltage values ​​at the ground potential points are then measured to calculate the ground impedance from both ends of the PV DC power supply to ground. These detection methods all utilize the casing ground point or the ground potential point directly connected to the AC side of the power supply. Therefore, they are not suitable for PV inverters with non-metal casings and no ground connection, and therefore have certain limitations.

[0006] Summary of the Invention

[0007] According to various embodiments of the present application, a ground impedance detection device, a detection method, an inverter, and a photovoltaic system are provided.

[0008] In a first aspect, the present application provides a ground impedance detection device, comprising a first impedance network, a second impedance network, and a control module;

[0009] The first impedance network is connected between a DC line at the input end and a first AC line at the output end of the inverter;

[0010] The second impedance network is connected between the DC line and a second AC line at the output of the inverter;

[0011] The control module is used to determine whether the grounding impedance on the DC side of the inverter is abnormal according to the first sampled voltage on the first impedance network and / or the second sampled voltage on the second impedance network.

[0012] In one embodiment, the ground impedance detection device further includes a third impedance network connected between the first AC line or the second AC line and the DC line.

[0013] In one embodiment, the control module is used to calculate the grounding impedance based on the first sampling voltage and / or the second sampling voltage, and the impedance values ​​of the first impedance network and the second impedance network, and determine whether the grounding impedance is abnormal based on the grounding impedance and a safety threshold.

[0014] In one embodiment, the control module is used to calculate the ground impedance based on the first sampled voltage and / or the second sampled 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, and determine whether the ground impedance is abnormal based on the ground impedance and a safety threshold.

[0015] In one embodiment, the control module is configured to determine whether the ground impedance is abnormal based on the first sampled voltage and / or the second sampled voltage and a corresponding voltage threshold.

[0016] In one embodiment, the control module is configured to determine whether the ground impedance is abnormal based on a difference or ratio between the second sampling voltage and the first sampling voltage and a corresponding voltage threshold.

[0017] In one embodiment, the first sampled voltage and the second sampled voltage are amplitudes or effective values ​​of grid frequency components of voltages on the first impedance network and the second impedance network, respectively.

[0018] In one embodiment, the control module is configured to calculate the ground impedance based on the first sampled voltage and / or the second sampled voltage, and the impedance values ​​of the first impedance network, the second impedance network, and the third impedance network, and determine whether the ground impedance is abnormal based on the ground impedance and a safety threshold;

[0019] Or the control module is used to calculate the ground impedance based on the first sampled voltage and / or the second sampled 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, the second impedance network, and the third impedance network, and determine whether the ground impedance is abnormal based on the ground impedance and a safety threshold.

[0020] In one embodiment, the first sampled voltage and the second sampled voltage are phasors.

[0021] In one embodiment, the ground impedance detection device further includes: a switch connected in series with the third impedance network, and the switch is used to control whether to connect to the third impedance network.

[0022] In one embodiment, the control module is configured to determine whether the ground impedance is abnormal based on the second sampling voltage and the first sampling voltage respectively obtained before and after the switch is closed, and corresponding voltage thresholds.

[0023] In one embodiment, the control module is used to calculate the ground impedance based on the second sampled voltage and the first sampled voltage obtained before and after the switching switch is closed, 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 determine whether the ground impedance is abnormal based on the ground impedance and a safety threshold.

[0024] In one embodiment, the impedance value of the first impedance network is equal to the impedance value of the second impedance network.

[0025] In one embodiment, the impedance value of the third impedance network at the grid frequency is much greater than the safety threshold of the ground impedance.

[0026] In one embodiment, the first impedance network includes capacitors and / or resistors; the second impedance network includes capacitors and / or resistors.

[0027] In one embodiment, the first AC line is one of a live line and a 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.

[0028] In a second aspect, the present application also provides a ground impedance detection method. The method comprises:

[0029] Acquire a first sampled voltage between a DC line at an input end of the inverter and a first AC line at an output end and / or a second sampled voltage between the DC line and a second AC line at an output end of the inverter;

[0030] Whether the grounding impedance on the DC side of the inverter is abnormal is determined according to the first sampling voltage and / or the second sampling voltage.

[0031] In a third aspect, the present application further provides an inverter, comprising:

[0032] DC / AC conversion circuit for power conversion;

[0033] And the ground impedance detection device as described in the first aspect.

[0034] In a fourth aspect, the present application further provides a photovoltaic system, comprising:

[0035] DC power supply;

[0036] The inverter is connected between the DC power supply and the power grid, and includes the ground impedance detection device as described in the first aspect.

[0037] The details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without any creative work.

[0039] FIG1 is a schematic structural diagram of a photovoltaic system according to some embodiments.

[0040] FIG2 is a schematic diagram of an equivalent circuit of the embodiment shown in FIG1 .

[0041] FIG3 is a schematic diagram of the circuit structure of a ground impedance detection device in some embodiments.

[0042] FIG4 is a schematic structural diagram of an insulation impedance detection device in a split-phase power grid in some embodiments.

[0043] FIG5 is a schematic structural diagram of an insulation impedance detection device in a three-phase power grid in some embodiments.

[0044] FIG6 is a schematic structural diagram of a ground impedance detection device in a split-phase power grid according to some other embodiments.

[0045] FIG. 7 is a schematic diagram of an equivalent circuit of the embodiment shown in FIG. 6 .

[0046] FIG8 is a schematic structural diagram of an insulation resistance detection device according to some other embodiments.

[0047] FIG9 is a schematic diagram of an equivalent circuit of the embodiment shown in FIG8 .

[0048] FIG10 is a schematic structural diagram of an insulation impedance detection device according to yet other embodiments.

[0049] FIG11 is a schematic diagram of an equivalent state of the embodiment shown in FIG10 when the switch is disconnected.

[0050] FIG12 is a schematic diagram of an equivalent state of the embodiment shown in FIG10 when the switch is closed.

[0051] FIG13 is a flow chart of a ground impedance detection method in some embodiments. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0053] As used in this application and the claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not intended to refer to the singular but may include the plural. Generally speaking, the terms "comprises" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements.

[0054] Although the present application makes various references to certain modules in the system according to embodiments of the present application, any number of different modules can be used and run on a computing device and / or processor. The modules are illustrative only, and different aspects of the system and method can use different modules.

[0055] It should be understood that when a unit or module is described as being "connected" or "coupled" to other units, modules, or blocks, it can refer to being directly connected or coupled, or communicating with other units, modules, or blocks, or there can be intervening units, modules, or blocks, unless the context clearly indicates otherwise. As used herein, the term "and / or" may include any and all combinations of one or more of the associated listed items.

[0056] FIG1 is a schematic structural diagram of a photovoltaic system according to some embodiments. As shown in FIG1 , the photovoltaic system includes a DC power supply 100 and an inverter 300;

[0057] The DC power supply 100 is used to provide DC power;

[0058] The inverter 300 is connected between the DC power source 100 and the grid 200 , and is configured to invert DC power into AC power and provide the AC power to the grid 200 .

[0059] Specifically, the input end of the inverter 300 is electrically connected to the DC power supply 100 via a DC (Direct Current) line, and the output end of the inverter 300 is electrically connected to the grid 200 via an AC (Alternating Current) line. The grid 200 is an AC grid.

[0060] Furthermore, the inverter 300 includes a DC / AC conversion circuit 310 and a ground impedance detection device 320 connected between the DC line at the input end and the AC line at the output end of the inverter. The DC / AC conversion circuit 310 is used to perform power conversion, and the ground impedance detection device 320 is used to detect the ground impedance at the input end of the inverter 300.

[0061] As shown in FIG1 , RE1 is the ground impedance of the positive electrode of the DC power supply 100 , and RE2 is the ground impedance of the negative electrode of the DC power supply 100 , where “+” and “−” represent the positive and negative polarities of the DC power supply, respectively.

[0062] The ground impedance detection device 320 includes a first impedance network 321, a second impedance network 322 and a control module 324;

[0063] The first impedance network 321 is connected between a DC line at the input end and a first AC line at the output end of the inverter 300;

[0064] A second impedance network 322 is connected between the DC line and a second AC line at the output of the inverter 300;

[0065] The control module 324 is configured to determine whether the ground impedance of the DC side of the inverter 300 is abnormal based on the first sampled voltage on the first impedance network 321 and / or the second sampled voltage on the second impedance network 322 .

[0066] This embodiment utilizes a first impedance network and a second impedance network, located between a DC line at the inverter input and an AC line at the inverter output, to obtain the voltage between the corresponding DC line and the AC line. Based on this voltage, the system determines whether the ground impedance is abnormal. Because voltage sampling at the chassis ground potential point is unnecessary, the system is suitable for inverters without a grounded chassis. This eliminates the need for a grounding wire, further reducing manufacturing costs. The detection device also features a simple structure, reduced hardware components, and low cost. Furthermore, the system is computationally simple and easy to implement.

[0067] Specifically, the DC line at the input end of inverter 300 includes a positive DC line and a negative DC line, which are respectively connected to the positive and negative poles of the DC power supply. Ground impedance detection device 320 can be connected to either DC line. Control module 324 includes a processor, such as an MCU (Micro Controller Unit) or a DSP (Digital Signal Processor).

[0068] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal can be connected to a corresponding DC power supply through a corresponding DC line, and the DC line connected to the ground impedance detection device 320 is the negative DC line of any input terminal.

[0069] 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 remotely grounded. The grounding point can be the positive end of the power grid 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 position of the grounding point does not affect the grounding impedance detection of this embodiment.

[0070] When the power grid 200 is a single-phase power grid, the first AC line is a live line and the second AC line is a neutral line, or the first AC line is a neutral line and the second AC line is a live line.

[0071] When the power grid 200 is a split-phase power grid or a three-phase power grid, the output end of the inverter 300 is connected to the neutral line, the first AC line is any live line, and the second AC line is a neutral line or a live line different from the first AC line; or the second AC line is any live line, the first AC line is a neutral line or a live line different from the second AC line, and other AC lines in the split-phase power grid or the three-phase power grid are not shown in the figure.

[0072] In some embodiments, the ground impedance detection device 320 further includes a sampling module 323, which samples the voltage on the first impedance network 321 to obtain a first sampled voltage and / or samples the voltage on the second impedance network 322 to obtain a second sampled voltage.

[0073] Specifically, the sampling module 323 includes a sampling circuit, for example, an ADC (analog-to-digital converter).

[0074] In some embodiments, the DC power supply 100 can be a photovoltaic component, specifically a single photovoltaic component, or a photovoltaic string or array formed by multiple photovoltaic components connected in series and / or in parallel. The DC power supply 100 can also be an energy storage battery or other types of renewable energy.

[0075] In some embodiments, the DC / AC conversion circuit 310 may be of an isolated type or a non-isolated type, or may be a multi-stage conversion circuit including a first-stage DC / DC boost circuit and a first-stage DC / AC inverter circuit.

[0076] In some embodiments, the chassis of the inverter 300 is not grounded.

[0077] In some embodiments, the inverter 300 further includes a controller (not shown in FIG. 1 ) configured to control the DC / AC conversion circuit to perform inversion.

[0078] In some embodiments, the control module 324 may be integrated into a controller (not shown in FIG. 1 ).

[0079] In some embodiments, the ground impedance detection device 320 may be separately provided outside the inverter 300 .

[0080] Specifically, the control module 324 determines whether the grounding impedance on the DC side of the inverter 300 is abnormal based on the first sampled voltage on the first impedance network 321 and / or the second sampled voltage on the second impedance network 322 and a preset threshold value, where the threshold value includes a safety threshold value of the grounding impedance and a voltage threshold value corresponding to the safety threshold value of the grounding impedance.

[0081] In some specific embodiments, the control module 324 calculates the ground impedance based on the first sampling voltage and / or the second sampling voltage, and the impedance values ​​of the first impedance network 321 and the second impedance network 322, and determines whether the ground impedance is abnormal based on the comparison result of the ground impedance and the safety threshold.

[0082] In some specific embodiments, the control module 324 calculates the ground impedance based on the first sampled voltage and / or the second sampled 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 ground impedance is abnormal based on a comparison result between the ground impedance and the safety threshold.

[0083] In some specific embodiments, the control module 324 determines whether the ground impedance is abnormal based on the first sampled voltage and / or the second sampled voltage and a corresponding voltage threshold.

[0084] The control module 324 may determine the corresponding voltage threshold value according to the grid voltage, the impedance values ​​of the first impedance network 321 and the second impedance network 322 , and the safety threshold value of the ground impedance.

[0085] In some specific embodiments, the first sampled voltage and the second sampled voltage are phasors.

[0086] In one specific embodiment, only the AC component in the circuit is considered. Taking the power grid as a single-phase power grid as an example, FIG2 is a schematic diagram of an equivalent circuit of the embodiment shown in FIG1 . 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 at both ends of the first impedance network 321 is sam1 It can be expressed by the following formula (1):

[0087] Among them, V gis the grid voltage, Z1 is the impedance value of the first impedance network 321, Z2 is the impedance value of the second impedance network 322, R E1 / / R E2 is the grounding impedance R E1 and R E2 The parallel value of the first sampling voltage V sam1 is a phasor.

[0088] From the above analysis, it can be seen that the control module 324 can sam1 , grid voltage V g The ground impedance value R is calculated by calculating the impedance values ​​of the first impedance network 321 and the second impedance network 322. E1 / / R E2 , based on the grounding impedance value and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered to be abnormal, otherwise, it is normal.

[0089] In this embodiment, the grid voltage V g = equal to the voltage between the first AC line and the second AC line, which can be obtained by the first sampling voltage V sam1 and the second sampling voltage V sam2 Calculated, that is, the grid voltage V g It can be expressed as the first sampling voltage V sam1 and the second sampling voltage V sam2 It can also be obtained by direct sampling through the sampling module 323.

[0090] It should be noted that, according to the same principle, the second sampling voltage V sam2 It can be expressed by the following formula (2):

[0091] Among them, the second sampling voltage V sam2 is a phasor.

[0092] Therefore, the control module 324 can also be based on the second sampling voltage V sam2 , grid voltage V g The ground impedance R is calculated by calculating the impedance values ​​of the first impedance network 321 and the second impedance network 322. E1 / / R E2 , based on the grounding impedance and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered that the grounding impedance is abnormal, otherwise, it is normal.

[0093] In some other specific embodiments, the first sampling voltage V sam1 and the second sampling voltage V sam2are the amplitudes or effective values ​​of the grid frequency components of the voltages across the first impedance network 321 and the second impedance network 322 , respectively.

[0094] In one embodiment, the impedance values ​​of the first impedance network 321 and the second impedance network 322 are equal, but are not limited thereto. When the grounding impedance R E1 or R E2 The impedance value of one side is too small or too small at the same time (that is, when it is less than the safety threshold, it is considered that the DC side grounding impedance is abnormal), making it much smaller than the impedance value of the first impedance network 321 or the second impedance network 322. The grid voltage V g It will be mainly distributed on the second impedance network 322. The voltage amplitude on the second impedance network 322 is equal to V g , that is, V sam2 Equal to V g , when the grounding impedance R E1 and R E2 The impedance value is greater than the safety threshold, for example, when the grounding impedance R E1 and R E2 When the impedance value of the first impedance network 321 or the second impedance network 322 is much greater than the impedance value 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, that is, V sam2 Equal to V g / 2. According to the circuit characteristics, the smaller the ground impedance value is, the higher the second sampling voltage V sam2 The larger the voltage, the greater the control module 324 is. sam2 and the corresponding voltage threshold to determine whether the ground impedance is abnormal. When the second sampling voltage V sam2 When the voltage is greater than the corresponding threshold, the ground impedance is considered abnormal, otherwise the ground impedance is normal. sam2 is the magnitude of the grid frequency component of the voltage across the second impedance network 322 .

[0095] It should be noted that, according to the same principle, the first sampling voltage V sam1 The corresponding voltage threshold is used to determine whether the ground impedance is abnormal, wherein the first sampling voltage V sam1 is the amplitude of the grid frequency component of the voltage on the first impedance network 321 .

[0096] In this embodiment, there is no need to calculate the ground impedance. Whether the ground impedance is abnormal can be detected directly based on the sampled voltage and the voltage threshold. This solution does not require calculation, is relatively simple to implement, and saves controller resources.

[0097] In some specific embodiments, the control module 324 controls the second sampling voltage V sam2 and the first sampling voltage V sam1The difference or ratio between the values ​​and the corresponding voltage threshold is used to determine whether the ground impedance is abnormal.

[0098] In one embodiment, the control module 324 generates a voltage signal according to the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the ground impedance and the corresponding first voltage threshold is used to determine whether the ground impedance is abnormal.

[0099] When the grounding impedance R E1 or R E2 The impedance value of one side is too small or too small at the same time (that is, when it is less than the safety threshold, it is considered that the DC side grounding impedance is abnormal), making it much smaller than the impedance value of the first impedance network 321 or the second impedance network 322. The grid voltage V g The voltage of the first impedance network 321 is mainly distributed on the second impedance network 322. E1 and / or R E2 The voltage amplitude of the second impedance network 322 will be much greater than the voltage amplitude of the first impedance network 321. E1 and R E2 The impedance value is greater than the safety threshold, such as the grounding impedance R E1 and R E2 When the impedance value of the second impedance network 322 is much greater than that 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. According to 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.

[0100] From the above analysis, we can see that by comparing the first sampling voltage V sam1 and the second sampling voltage V sam2 It can be determined whether the DC side grounding impedance is abnormal. The first sampling voltage V sam1 and the second sampling voltage V sam2 are the amplitudes of the grid frequency components of the voltages across the first impedance network 321 and the second impedance network 322 , respectively.

[0101] Specifically, the control module 324 converts the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between them 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.

[0102] In some other specific embodiments, according to the above analysis, the second sampling voltage V sam2 and the first sampling voltage V sam1 The comparison result of the ratio of the voltage and the corresponding voltage threshold is used to determine whether the DC side grounding impedance is abnormal, but the present invention is not limited thereto.

[0103] FIG3 shows a schematic diagram of the circuit structure of a ground impedance detection device in some embodiments. As shown in the figure, the first impedance network 321 includes a resistor R1 and a capacitor C eq1 The second impedance network 322 includes a resistor R2 and a capacitor C eq2 , capacitor C eq1 and capacitor C eq2 The EMC (Electro Magnetic Compatibility) filter capacitor provided in the inverter 300 may be reused or provided separately. Optionally, the first impedance network 321 may also not include the capacitor C eq1 The second impedance network 322 may also not include the capacitor C eq2 .

[0104] The resistance of resistor R1 is much larger than that of capacitor C eq1 At the grid frequency, the capacitive reactance value of resistor R2 is much larger than that of capacitor C. eq2 Capacitive reactance value at the grid frequency, capacitance C eq1 and capacitor C eq2 The capacitive reactance value at the grid frequency is much larger than the safety threshold of the ground impedance.

[0105] It should be noted that by setting the capacitor C eq1 and capacitor C eq2 , can improve the measurement accuracy of the first sampling voltage and the first sampling voltage, further improve the detection accuracy of the ground impedance, and the capacitor C eq1 and capacitor C eq2 The larger the capacitance value, the higher the measurement accuracy.

[0106] In some specific embodiments, the resistor R1 can be replaced by a voltage divider circuit including a voltage divider resistor, and the first sampling voltage can be obtained by sampling the voltage on any voltage divider resistor, and / or the resistor R2 can be replaced by a voltage divider circuit including a voltage divider resistor, and the second sampling voltage can be obtained by sampling the voltage on any voltage divider resistor.

[0107] By adopting a resistor voltage divider circuit, high-resistance isolation is achieved between the DC side and the AC side while obtaining the sampling value. By selecting a reasonable resistance value, the insulation strength requirements of the DC side and the AC side can be met.

[0108] In some specific embodiments, the resistor R1 and / or the resistor R2 may also be replaced by a capacitor or a capacitor voltage divider circuit.

[0109] Figure 4 is a structural diagram of a ground impedance detection device of an example embodiment when used in a split-phase power grid. Specifically, as shown in Figure 4, 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, and the second AC line is the live line. The working principle of the insulation detection impedance device is similar to the aforementioned scheme and will not be repeated here.

[0110] FIG5 is a schematic structural diagram of a ground impedance detection device according to another exemplary embodiment when used in a three-phase power grid. As shown in FIG5 , 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, and the second AC line is the live line. The working principle of the insulation detection impedance device is similar to that of the aforementioned solution and will not be described in detail here.

[0111] In another exemplary embodiment, when the power grid 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 N, and the first AC line and the second AC line are both live lines, as shown in FIG6 , the control module 324 generates a voltage signal according to the first sampled voltage V sam1 and / or the second sampling voltage V sam2 , 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 are used to calculate the ground impedance, and determine whether the ground impedance is abnormal based on the ground impedance and a safety threshold.

[0112] Considering only the AC component, FIG7 shows an equivalent circuit diagram of this exemplary embodiment. The first sampling voltage V sam1 and the second sampling voltage V sam2 can be expressed by the following formulas (3) and (4):

[0113] Among them, V g1 is the first phase voltage of the split-phase grid, V g2 is the second phase voltage of the split-phase grid,

[0114] From the above, it can be seen that the control module 324 can sam1 Or the second sampling voltage V sam2 , grid voltage V g1 , grid voltage V g2 The ground impedance value R is calculated by calculating the impedance values ​​of the first impedance network 321 and the second impedance network 322. E1 / / R E2 , based on the grounding impedance value and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered to be abnormal, otherwise, it is normal.

[0115] When the voltage of the split-phase grid is balanced, the grid voltage V g1 and grid voltage V g2 The first sampling voltage V sam1 and the second sampling voltage V sam2 Calculation shows that the grid voltage V g1 and grid voltage V g2 Both are the first sampling voltage V sam1 and the second sampling voltage V sam2 The grid voltage V can also be obtained by sampling the voltage between the first AC line and the second AC line. g1 and grid voltage V g2 Both are half the voltage between the first AC line and the second AC line.

[0116] When the voltage of the split-phase grid is unbalanced, the grid voltage V g1 and grid voltage V g2 The 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 the sampling module 323 respectively.

[0117] 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 the first AC line and the second AC line are both live lines, as shown in FIG8 , the ground impedance detection device 320 further includes a third impedance network 325 connected between the DC line and the first AC line or the second AC line, and the control module 324 can be configured to generate a voltage signal according to 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 ground impedance is abnormal. The first AC line is any live line, and the second AC line is another live line different from the first AC line.

[0118] The voltage threshold used here can be determined based on the phase voltage of each phase of the power grid (ie, the power 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.

[0119] In a specific embodiment, the impedance value of the third impedance network 325 at the grid frequency is much greater than the safety threshold of the ground impedance. The third impedance network 325 is, for example, a capacitor, but is not limited thereto.

[0120] Considering only the AC component, taking the split-phase power grid as an example, FIG9 shows a schematic diagram of an equivalent circuit of the embodiment shown in FIG8 , wherein Z3 is an equivalent circuit of the third impedance network 325 , and the first sampling voltage V sam1 and the second sampling voltage Vsam2 They can be expressed as the following formulas (5) and (6):

[0121] Among them, V g1 is the first phase voltage of the split-phase grid, V g2 is the second phase voltage of the split-phase power grid, and Z3 is the impedance value of the third impedance network 325.

[0122] When the grounding impedance R E1 or R E2 If one of the impedance values ​​is too small or both are too small (i.e., less than the safety threshold, it is considered that the DC side grounding impedance is abnormal), until it is much smaller than the impedance value of the third impedance network 325, the grid voltage V g1 The main effect is on the first impedance network 321, the grid voltage V g2 The main effect is on the second impedance network 322. It is easy to know that when the grid voltage V g1 and V g2 Under the joint action of , and when the voltage amplitudes of the two are consistent, the amplitude of the voltage on the first impedance network 321 and the amplitude of the voltage on the second impedance network 322 are nearly equal. E1 and R E2 Greater than the safety threshold, that is, when the grounding impedance R E1 and R E2 When the impedance value of the first impedance network 321 or the second impedance network 322 is much greater than the impedance value of the first impedance network 321, the impedance value of the first impedance network 321 is greater than the parallel impedance value of the second impedance network 322 and the third impedance network 325. The amplitude of the voltage on the second impedance network 322 will be smaller than the amplitude of the voltage on the first impedance network 321. It is easy to know that when the grounding impedance R E1 and R E2 When the ground impedance changes, the difference between the amplitudes of the voltages on the second impedance network 322 and the first impedance network 321 will also change. According to the circuit characteristics, the smaller the ground impedance, the smaller the difference between the two.

[0123] From the above analysis, we can see that by comparing the first sampling voltage V sam1 and the second sampling voltage V sam2 It can be determined whether the DC side grounding impedance is abnormal.

[0124] Specifically, the control module 324 converts the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between them 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 ground impedance detection scheme of this embodiment can be applied to split-phase power grids and three-phase power grids where the output end of the inverter 300 is not connected to the neutral line, thereby expanding the scope of application.

[0126] It should be noted that the control module 324 can also be configured according to the first sampling voltage V sam1 Or the second sampling voltage V sam2 , grid voltage V g1 , grid voltage V g2 , and the impedance values ​​of the first to third impedance networks are calculated to obtain the ground impedance value R E1 / / R E2 , based on the grounding impedance value and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered to be abnormal, otherwise, it is normal.

[0127] When the phase voltages of the split-phase grid are balanced, the grid voltage V g1 and grid voltage V g2 The first sampling voltage V sam1 and the second sampling voltage V sam2 Calculation shows that the grid voltage V g1 and grid voltage V g2 Both are the first sampling voltage V sam1 and the second sampling voltage V sam2 Half of the sum.

[0128] It can also be calculated by sampling the voltage between the first AC line and the second AC line through the sampling module. In this case, 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.

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

[0130] In some embodiments, as shown in FIG10 , the ground impedance detection device 320 further includes a switch 326 connected in series with the third impedance network 325. According to the above analysis, by controlling the switch 326 to be opened and closed, the ground impedance detection device 320 can be applied to different scenarios. For example, when the power grid is a single-phase power grid, the switch 326 is controlled to be opened; when the power grid is a split-phase power grid or a three-phase power grid and the output end of the inverter 300 is not connected to the neutral line, if the second sampling voltage V sam2 and the first sampling voltage V sam1The difference between the two and the preset second voltage threshold is used to determine whether the grounding impedance is abnormal, and the switching switch 326 is controlled to be closed; when the power grid is a split-phase power grid or a three-phase power grid and the output end 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 be disconnected.

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

[0132] In a specific embodiment, the control module 324 obtains the grid type according to a grid type signal provided by the host computer.

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

[0134] In some embodiments, as shown in FIG10 , the control module 324 obtains the second sampled voltage V before and after the switch 326 is closed. sam2 and the first sampling voltage V sam1 and a comparison result of the corresponding voltage threshold to determine whether the ground impedance is abnormal.

[0135] When the voltages of each phase of a split-phase grid or a three-phase grid are unbalanced, taking a split-phase grid as an example, for example, 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 and the second sampling voltage V sam2 The difference between them affects the value of the first sampling voltage V sam1 and the second sampling voltage V sam2 The difference between the ground impedance R E1 / / R E2 size.

[0136] In this case, the grid voltage V can be eliminated by controlling the switching state of the switch 326 and switching the switch 326 to open or close. g1 and V g2 The amplitude is not equal to the ground impedance R E1 / / R E2 The impact of size judgment.

[0137] The grid voltage V g1 and V g2 In the form of common mode and differential mode, respectively, as shown in formula (7) and formula (8):

[0138] In an exemplary embodiment, as shown in FIG11 , when the switch 326 is disconnected, the circuit state at this time is a superposition of the state m1 and the state m2 , as shown in FIG12 , R E is the grounding impedance R E1 and R E2 In parallel form, therefore, under this condition, the second sampling voltage V sam2 and the first sampling voltage V sam1 The first difference between V diff1 It can be expressed as the second sampling voltage V in state m1 sam2_m1 and the first sampling voltage V sam1_m1 The difference between V diff_m1 and the second sampling voltage V in state m2 sam2_m2 and the first sampling voltage V sam1_m2 The difference between V diff_m2 The superposition of is shown in formula (9): diff1 =V diff_m1 +V diff_m2 (9);

[0139] In circuit state m1, the grid voltage V g1 and V g2 The amplitudes are consistent, and Z1=Z2, so V diff_m1 =0, thus we get the expression shown in formula (10): V diff1 =V diff_m2 (10);

[0140] When the switch 326 is closed, the circuit state is the superposition of state m3 and state m4. In circuit state m3, the grid voltage V g1 and V g2 The amplitude of the second sampling voltage V sam2 and the first sampling voltage V sam1 The second difference between V diff2 It can be expressed as the second sampling voltage V in state m3 sam2_m3 and the first sampling voltage V sam1_m3 The difference between V diff_m3 and the second sampling voltage V in state m4 sam2_m4 and the first sampling voltage V sam1_m4 The difference between V diff_m4 The superposition of is as shown in formula (11): V diff2 =V diff_m3 +V diff_m4 (11);

[0141] Since the ground 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, V diff_m2 ≈V diff_m4 .

[0142] Therefore, we can get V diff2 -V diff1 =V diff_m3 .

[0143] It can be seen from the circuit characteristics that the smaller the ground impedance is, the more likely the second sampling voltage V is obtained when the switch 326 is disconnected. sam2 and the first sampling voltage V sam1 The first difference between V diff1 The second sampling voltage V obtained in the closed state sam2 and the first sampling voltage V sam1 The second difference between V diff2 The smaller the difference between the two.

[0144] From the above analysis, it can be seen that the second sampling voltage V is obtained by comparing the second sampling voltage V before and after the switch 326 is closed. sam2 and the first sampling voltage V sam1 The difference between them can be used to determine whether the DC side grounding impedance is abnormal.

[0145] Specifically, when the switch 326 is open, the control module 324 obtains a first difference between the second sampled voltage and the first sampled voltage. When the switch 326 is closed, the control module 324 obtains a second difference between the second sampled voltage and the first sampled voltage, and determines whether the ground impedance is abnormal based on a comparison result between the difference between the second difference and the first difference and a third voltage threshold. When the difference between the second difference and the first difference is less than the third voltage threshold, it indicates that the ground impedance is abnormal; otherwise, the ground impedance is normal.

[0146] In this embodiment, by opening and closing the switch 326, the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the two can be used to determine the ground impedance of the DC side, which can eliminate the difference between the voltage amplitudes of the phases in the power grid and the ground impedance R. E1 / / R E2 The impact of size judgment can further improve the detection accuracy.

[0147] In addition, according to the above analysis, we can get formula (12): V diff2 -V diff1 =V sam2_m3 -V sam1_m3 (12);

[0148] Combining formulas (5) and (6), it can be seen that the control module 324 obtains the second sampling voltage V according to the switching switch 326 before and after closing. sam2 and the first sampling voltage V sam1 The ground impedance is calculated based on the voltage 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 .

[0149] Specifically, when the switch 326 is disconnected, the control module 324 obtains the second sampling voltage V sam2 and the first sampling voltage V sam1 The first difference between V diff1 When the switch is closed, the control module obtains the second difference V between the second sampling voltage and the first sampling voltage diff2 , and according to the second difference V diff2 and the first difference V diff1 The ground impedance value R is calculated by 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. E1 / / R E2 , based on the grounding impedance value and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered to be abnormal, otherwise, it is normal.

[0150] When the power grid is a three-phase power grid, the principle is the same as that of the split-phase power grid and will not be described in detail here.

[0151] In summary, the ground impedance detection device provided by the present 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 input end of the inverter and an AC line at the output end, and determines whether the ground 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 grounding potential point of the casing, it is suitable for inverters without a grounded casing, and the use of a grounding wire is eliminated. The detection device has a simple structure, reduces the number of hardware components, and further reduces the manufacturing cost of the equipment. At the same time, the calculation is simple and easy to implement. It is widely applicable to single-phase, split-phase, and three-phase power grids. It can further eliminate the influence of inconsistent grid voltage amplitude on ground impedance detection in split-phase and three-phase power grids, thereby improving detection accuracy.

[0152] As shown in FIG13 , the present application also provides a method for detecting ground impedance, comprising the following steps:

[0153] Step S30, obtaining a first sampled voltage between a DC line at an input end of the inverter and a first AC line at an output end and / or a second sampled voltage between the DC line and a second AC line at an output end of the inverter;

[0154] Step S32 : determining whether the ground impedance on the DC side of the inverter is abnormal based on the first sampled voltage and / or the second sampled voltage and a threshold.

[0155] Specifically, a first impedance network 321 connected between a DC line at the input end of the inverter and a first AC line at the output end and a second impedance network 322 connected between the DC line and a second AC line at the output end of the inverter can be provided, and a voltage on the first impedance network 321 is sampled to obtain a first sampled voltage V sam1 And / or sampling the voltage on the second impedance network 322 to obtain a second sampled voltage V sam2 .

[0156] In some embodiments, the DC line at the input end of the inverter 300 includes a positive DC line and a negative DC line, which are respectively used to connect to the positive and negative poles of the DC power supply. The first impedance network 321 and the second impedance network 322 can be connected to any DC line.

[0157] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal is connected to a corresponding DC power source through a corresponding DC line, and the DC line connected to the first impedance network 321 and the second impedance network 322 is the negative DC line of any input terminal.

[0158] 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 remotely grounded. The grounding point can be the positive end of the power grid 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 position of the grounding point does not affect the grounding impedance detection of this embodiment.

[0159] When the power grid 200 is a single-phase power grid, the first AC line is a live line and the second AC line is a neutral line, or the first AC line is a neutral line and the second AC line is a live line.

[0160] When the power grid 200 is a split-phase power grid or a three-phase power grid, the output end of the inverter 300 is connected to the neutral line, the first AC line is any live line, and the second AC line is a 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 a neutral line or a live line different from the second AC line.

[0161] In some embodiments, the first sampling voltage V sam1 and the second sampling voltage V sam2 is a phasor.

[0162] In some specific embodiments, the ground impedance is calculated based on the first sampling voltage and / or the second sampling voltage, and the impedance values ​​of the first impedance network and the second impedance network, and whether the ground impedance is abnormal is determined based on a comparison result between the ground impedance and a safety threshold.

[0163] When the grounding impedance is less than the safety threshold, it is considered abnormal; otherwise, it is normal.

[0164] In some specific embodiments, the ground impedance is calculated based on the first sampled voltage and / or the second sampled 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, and whether the ground impedance is abnormal is determined based on a comparison result between the ground impedance and a safety threshold.

[0165] When the grounding impedance is less than the safety threshold, it is considered abnormal; otherwise, it is normal.

[0166] Grid voltage V g The first sampling voltage V sam1 and the second sampling voltage V sam2 It can be obtained by calculation or by direct sampling.

[0167] In some other embodiments, the first sampling voltage V sam1 and the second sampling voltage V sam2 are the amplitudes or effective values ​​of the grid frequency components of the voltages across the first impedance network 321 and the second impedance network 322 , respectively.

[0168] In some specific embodiments, according to the first sampling voltage V sam1 And / or the second sampling voltage Vsam2 and the corresponding voltage threshold to determine whether the ground impedance is abnormal.

[0169] The corresponding voltage threshold value may be determined according to the grid voltage, the impedance values ​​of the first impedance network and the second impedance network, and the safety threshold value of the ground impedance.

[0170] Specifically, the second sampling voltage V sam2 and the corresponding voltage threshold to determine whether the ground impedance is abnormal. When the second sampling voltage V sam2 When it is greater than the voltage threshold, the ground impedance is considered abnormal, otherwise the ground impedance is normal.

[0171] It should be noted that, according to the same principle, the first sampling voltage V sam1 The corresponding voltage threshold is used to determine whether the ground impedance is abnormal, wherein the first sampling voltage V sam1 is the amplitude or effective value of the grid frequency component of the voltage on the second impedance network 321.

[0172] In some specific embodiments, according to 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 ground impedance is abnormal.

[0173] In one embodiment, according to the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the ground impedance and the corresponding first voltage threshold is used to determine whether the ground impedance is abnormal.

[0174] When the difference is greater than a first voltage threshold, it indicates that the grounding impedance is abnormal; otherwise, the grounding impedance is normal. The first voltage threshold corresponds to a safety threshold of the DC side grounding impedance.

[0175] In other specific embodiments, the second sampling voltage V sam2 and the first sampling voltage V sam1 The comparison result of the ratio of the voltage and the corresponding voltage threshold is used to determine whether the DC side grounding impedance is abnormal, but the present invention is not limited thereto.

[0176] In this embodiment, there is no need to calculate the ground impedance. Whether the ground impedance is abnormal can be detected directly based on the sampled voltage and the voltage threshold. This solution does not require calculation, is relatively simple to implement, and saves controller resources.

[0177] In some embodiments, the first impedance network 321 includes a resistor R1 and a capacitor C eq1 The second impedance network 322 includes a resistor R2 and a capacitor C eq2 , capacitor C eq1 and capacitor C eq2 The EMC filter capacitor provided in the inverter 300 can be reused or provided separately. Optionally, the first impedance network 321 may not include the capacitor C eq1 The second impedance network 322 may also not include the capacitor C eq2 .

[0178] The resistance of resistor R1 is much larger than that of capacitor C eq1 At the grid frequency, the capacitive reactance value of resistor R2 is much larger than that of capacitor C. eq2 Capacitive reactance value at the grid frequency, capacitance C eq1 and capacitor C eq2 The capacitive reactance value at the grid frequency is much larger than the safety threshold of the ground impedance.

[0179] It should be noted that by setting the capacitor C eq1 and capacitor C eq2, can improve the measurement accuracy of the first sampling voltage and the first sampling voltage, further improve the detection accuracy of the ground impedance, and the capacitor C eq1 and capacitor C eq2 The larger the capacitance value, the higher the measurement accuracy.

[0180] In some specific embodiments, the resistor R1 can be replaced by a voltage divider circuit including a voltage divider resistor, and the first sampling voltage can be obtained by sampling the voltage on any voltage divider resistor, and / or the resistor R2 can be replaced by a voltage divider circuit including a voltage divider resistor, and the second sampling voltage can be obtained by sampling the voltage on any voltage divider resistor.

[0181] By adopting a resistor voltage divider circuit, high-resistance isolation is achieved between the DC side and the AC side while obtaining the sampling value. By selecting a reasonable resistance value, the insulation strength requirements of the DC side and the AC side can be met.

[0182] In some specific embodiments, the resistor R1 and / or the resistor R2 may also be replaced by a capacitor or a capacitor voltage divider circuit.

[0183] 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.

[0184] When the power grid is a split-phase power grid or a three-phase power grid, the output end of the inverter 300 is not connected to the neutral line N, and the first AC line and the second AC line are both live lines, 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 compared to determine whether the ground impedance is abnormal.

[0185] The voltage threshold may be determined according to 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 a safety threshold of the ground impedance.

[0186] In a specific embodiment, the impedance value of the third impedance network 325 at the grid frequency is much greater than the safety threshold of the ground impedance. The third impedance network 325 is, for example, a capacitor, but is not limited thereto.

[0187] In a specific embodiment, the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between them 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.

[0188] It should be noted that the first sampling voltage V sam1 Or the second sampling voltage Vsam2 , grid voltage, and the impedance values ​​of the first to third impedance networks to calculate the ground impedance value R E1 / / R E2 , based on the grounding impedance value and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered to be abnormal, otherwise, it is normal.

[0189] In this embodiment, by adding a third impedance network, the ground impedance detection scheme of this embodiment can be applied to split-phase power grids and three-phase power grids where the output end of the inverter 300 is not connected to the neutral line, thereby expanding the scope of application.

[0190] In some embodiments, the method further includes: providing a switching switch connected in series with the third impedance network, and controlling whether the switching switch is closed according to actual application requirements.

[0191] Specifically, for example, when the power grid is a single-phase power grid, the switch 326 is controlled to be disconnected; when the power grid is a split-phase power grid or a three-phase power grid and the output end of the inverter 300 is not connected to the neutral line, if the second sampling voltage V sam2 and the first sampling voltage V sam1 The difference between the two and the preset second voltage threshold is used to determine whether the grounding impedance is abnormal, and the switching switch 326 is controlled to be closed; when the power grid is a split-phase power grid or a three-phase power grid and the output end 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 be disconnected.

[0192] In a specific embodiment, the grid type is obtained according to a grid type signal provided by a host computer.

[0193] In this embodiment, by adding a switching switch, the ground impedance detection solution of this embodiment can be applied to single-phase, split-phase power grids and three-phase power grids, etc., and therefore has a wide range of applications.

[0194] In some specific embodiments, the second sampling voltage V is obtained before and after the switch 326 is closed. sam2 and the first sampling voltage V sam1 and a comparison result of the corresponding voltage threshold to determine whether the ground impedance is abnormal.

[0195] Specifically, when the switch 326 is disconnected, the second sampling voltage V sam2 and the first sampling voltage V sam1 The first difference between V diff1 When the switch is closed, the second difference V between the second sampling voltage and the first sampling voltage is obtained diff2 , and according to the second difference V diff2 and the first difference Vdiff1 The ground impedance value R is calculated by the difference between the ground impedance value and the grid 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. E1 / / R E2 , based on the grounding impedance value and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered to be abnormal, otherwise, it is normal.

[0196] In this embodiment, by opening and closing the switch, the DC side grounding impedance is determined based on the difference between the two second sampling voltages and the first sampling voltage, which can eliminate the grounding impedance R caused by the unequal voltage amplitudes of the phases in the power grid. E1 / / R E2 The impact of size judgment can further improve the detection accuracy.

[0197] In some other specific embodiments, the second sampling voltage V is obtained before and after the switch 326 is closed. sam2 and the first sampling voltage V sam1 , the grid voltage, and 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 are used to calculate the ground impedance.

[0198] Specifically, when the switch 326 is disconnected, the control module 324 obtains the second sampling voltage V sam2 and the first sampling voltage V sam1 The first difference between V diff1 When the switch is closed, the control module obtains the second difference V between the second sampling voltage and the first sampling voltage diff2 , and according to the second difference V diff2 and the first difference V diff1 The ground impedance value R is calculated by the difference between the ground impedance value and the grid 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. E1 / / R E2 , based on the grounding impedance value and the safety threshold, it is determined whether the grounding impedance is abnormal. When the grounding impedance is less than the safety threshold, it is considered to be abnormal, otherwise, it is normal.

[0199] In summary, the ground impedance detection device provided herein utilizes a first impedance network and a second impedance network, arranged between a DC line at the inverter input and an AC line at the inverter output, to obtain the voltage between a DC line and the corresponding AC line. Based on this voltage, the device determines whether the ground impedance is abnormal. Because voltage sampling at the chassis ground potential point is unnecessary, the device is suitable for inverters without a grounded chassis, eliminating the need for a grounding wire. Furthermore, the detection device features a simple structure, reduces the number of hardware components, and further reduces manufacturing costs. Furthermore, the device is computationally simple and easy to implement, and is widely applicable to single-phase, split-phase, and three-phase power grids. Furthermore, the device can eliminate the impact of inconsistent grid voltage amplitudes on ground impedance detection in split-phase and three-phase power grids, thereby improving detection accuracy.

[0200] The present application also provides an inverter, comprising:

[0201] DC / AC conversion circuit for power conversion;

[0202] And a ground impedance detection device as in any of the above embodiments.

[0203] Furthermore, the DC / AC conversion circuit can convert direct current into any one of single-phase alternating current, two-phase alternating current and three-phase alternating current, and provide the converted power to the power grid.

[0204] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal is connected to a corresponding DC power source through a corresponding DC line, and the DC line connected to the ground impedance detection device 320 is the negative DC line of any input terminal.

[0205] The inverter proposed in this embodiment utilizes a first impedance network and a second impedance network, located between a DC line at the inverter input and an AC line at the inverter output, to obtain the voltage between the corresponding DC line and the AC line. This voltage is then used to determine whether the ground impedance is abnormal. Because voltage sampling at the ground potential point of the chassis is unnecessary, the system is suitable for inverters without a grounded chassis, eliminating the need for a grounding wire and further reducing manufacturing costs. The detection device also features a simple structure, reduced hardware components, and low cost. Furthermore, the calculations are simple and easy to implement.

[0206] The present application also provides a photovoltaic system, comprising:

[0207] DC power supply;

[0208] The inverter is connected between the DC power supply and the power grid, and includes the ground impedance detection device as described in any of the above embodiments.

[0209] In some embodiments, when the inverter 300 includes multiple input terminals, each input terminal is connected to a corresponding DC power source through a corresponding DC line.

[0210] It should be understood that, although the various steps in the flowcharts involved in the various embodiments described above are displayed in sequence according to the instructions of the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the flowcharts involved in the various embodiments described above can include multiple steps or multiple stages, and these steps or stages are not necessarily executed and completed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of steps or stages in other steps.

[0211] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, 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.

[0212] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A ground impedance detection device, characterized in that: It includes a first impedance network, a second impedance network and a control module; The first impedance network is connected between a DC line at the input end of the inverter and a first AC line at the output end; The second impedance network is connected between the DC line and a second AC line at the output of the inverter; The control module is used to determine whether the grounding impedance on the DC side of the inverter is abnormal according to the first sampled voltage on the first impedance network and / or the second sampled voltage on the second impedance network.

2. The ground impedance detection device according to claim 1, wherein: The ground impedance detection device further includes a third impedance network connected between the first AC line or the second AC line and the DC line.

3. The ground impedance detection device according to claim 1, wherein: The control module is used to calculate the ground impedance according to the first sampled voltage and / or the second sampled voltage and the impedance values ​​of the first impedance network and the second impedance network, and determine whether the ground impedance is abnormal according to the ground impedance and a safety threshold.

4. The ground impedance detection device according to claim 1, wherein: The control module is used to calculate the ground impedance according to the first sampled voltage and / or the second sampled 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, and determine whether the ground impedance is abnormal according to the ground impedance and a safety threshold.

5. The ground impedance detection device according to claim 1 or 2, wherein: The control module is used to determine whether the ground impedance is abnormal according to the first sampling voltage and / or the second sampling voltage and a corresponding voltage threshold.

6. The ground impedance detection device according to claim 5, wherein: The control module is used to determine whether the ground impedance is abnormal according to a difference or a ratio between the second sampling voltage and the first sampling voltage and a corresponding voltage threshold.

7. The ground impedance detection device according to claim 5, wherein: The first sampled voltage and the second sampled voltage are respectively the amplitudes or effective values ​​of the grid frequency components of the voltages on the first impedance network and the second impedance network.

8. The ground impedance detection device according to claim 2, wherein: The control module is used to calculate the ground impedance according to the first sampled voltage and / or the second sampled voltage, and the impedance values ​​of the first impedance network, the second impedance network, and the third impedance network, and determine whether the ground impedance is abnormal according to the ground impedance and a safety threshold; Or the control module is used to calculate the grounding impedance based on the first sampled voltage and / or the second sampled 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, the second impedance network, and the third impedance network, and determine whether the grounding impedance is abnormal based on the grounding impedance and the safety threshold.

9. The ground impedance detection device according to claim 3, 4 or 8, wherein: The first sampled voltage and the second sampled voltage are phasors.

10. The ground impedance detection device according to claim 2, wherein: The ground impedance detection device further includes: a switching switch connected in series with the third impedance network, and the switching switch is used to control whether to connect to the third impedance network.

11. The ground impedance detection device according to claim 10, wherein: The control module is used to determine whether the ground impedance is abnormal according to the second sampling voltage and the first sampling voltage respectively obtained before and after the switching switch is closed, and the corresponding voltage threshold.

12. The ground impedance detection device according to claim 10, wherein: The control module is used to calculate the ground impedance according to the second sampled voltage and the first sampled voltage respectively obtained before and after the switching switch is closed, 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 determine whether the ground impedance is abnormal according to the ground impedance and a safety threshold.

13. The ground impedance detection device according to claim 1, wherein: The impedance value of the first impedance network is equal to the impedance value of the second impedance network.

14. The ground impedance detection device according to claim 2, wherein: The impedance value of the third impedance network at the grid frequency is much larger than the safety threshold of the ground impedance.

15. The ground impedance detection device according to claim 1, wherein: The first impedance network includes a capacitor and / or a resistor; The second impedance network includes a capacitor and / or a resistor.

16. The ground impedance detection device according to claim 1, wherein: 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 the live line.

17. A method for detecting ground impedance, characterized in that: include: Acquire a first sampled voltage between a DC line at an input end of the inverter and a first AC line at an output end and / or a second sampled voltage between the DC line and a second AC line at an output end of the inverter; Whether the ground impedance on the DC side of the inverter is abnormal is determined according to the first sampled voltage and / or the second sampled voltage.

18. An inverter, characterized in that: include: DC / AC conversion circuit for power conversion; And a ground impedance detection device as described in any one of claims 1 to 16.

19. A photovoltaic system comprising: DC power supply; An inverter is connected between the DC power supply and the power grid, and comprises a ground impedance detection device as claimed in any one of claims 1 to 16.

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