Photovoltaic grid-connected inverter system and insulation resistance online detection method and device thereof

Abstract

The invention discloses a photovoltaic grid-connected inverter system and an insulation resistance online detection method and device thereof, the photovoltaic grid-connected inverter system comprises a plurality of photovoltaic arrays and an inverter, the plurality of photovoltaic arrays are connected in parallel with a direct current bus of the inverter, each photovoltaic array comprises a photovoltaic power station, a direct current leakage current sensor and a direct current relay, and the direct current leakage current sensor is connected with the direct current relay. A photovoltaic branch where each photovoltaic array is located is connected in series with a photovoltaic power station, a direct-current relay and a direct-current leakage current sensor; wherein the positive electrode insulation impedance and the negative electrode insulation impedance of each photovoltaic branch are respectively connected in parallel with a pair of unbalanced resistors controlled by the first auxiliary fling-cut switch; and the positive and negative insulation resistors of the DC bus of the inverter are respectively connected in parallel with the other pair of unbalanced resistors controlled by the second auxiliary fling-cut switch. According to the method, the insulation resistance detection can be conveniently carried out, and the photovoltaic array with the insulation resistance fault can be accurately positioned, so that the photovoltaic array with the fault can be conveniently and automatically cut off to keep the continuous operation of the normal photovoltaic array.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to a photovoltaic grid-connected inverter system and an online insulation impedance detection method and device thereof. Background Art

[0002] Detecting the insulation impedance of the photovoltaic array is a mandatory standard and requirement that the inverter needs to meet. Centralized photovoltaic power stations mostly use non-isolated inverters. According to the technical safety requirements of grid-connected inverters: before the inverter system is started, the insulation impedance of the photovoltaic array input will be measured. If the insulation impedance is less than Umax, pv / 30mA (Umax, pv is the maximum output voltage of the photovoltaic array), the inverter will display a fault and cannot start; when the inverter is already connected to the grid, the photovoltaic array residual current detection will continue. When the continuous residual current or the sudden residual current exceeds the threshold, the inverter will disconnect and issue a fault. When the insulation impedance of some photovoltaic array inputs is low, the inverter will immediately report a fault and cause all connected normal arrays to shut down, resulting in a waste of resources.

[0003] Therefore, when the inverter is connected to the grid, the relevant DC insulation online monitoring method cannot perform insulation impedance detection, and will only continue to detect the residual current of the photovoltaic array. At this time, when an insulation fault occurs in the array input, the inverter will immediately disconnect and issue a system insulation impedance low fault message. It is impossible to determine which specific arrays have reduced input insulation impedance and automatically cut off the faulty array to maintain continuous operation. Summary of the invention

[0004] The present invention aims to solve the technical problems in the related art at least to a certain extent. To this end, the first object of the present invention is to provide a photovoltaic grid-connected inverter system, which can facilitate insulation impedance detection and accurately locate the photovoltaic array with insulation impedance fault, so as to facilitate automatic removal of the faulty array to maintain the continuous operation of the normal photovoltaic array.

[0005] A second object of the present invention is to provide an online detection method for insulation impedance.

[0006] The third object of the present invention is to provide an online detection device for insulation impedance.

[0007] To achieve the above object, the present invention is implemented through the following technical solutions:

[0008] A photovoltaic grid-connected inverter system comprises a plurality of photovoltaic arrays and an inverter, wherein the plurality of photovoltaic arrays are connected in parallel with a DC bus of the inverter, each photovoltaic array comprises a photovoltaic power station, a DC leakage current sensor and a DC relay, and a photovoltaic branch where each photovoltaic array is located is connected in series with the photovoltaic power station, the DC relay and the DC leakage current sensor; wherein the positive and negative insulation impedances of each photovoltaic branch are respectively connected in parallel with a pair of unbalanced resistors controlled by a first auxiliary switching switch; and the positive and negative insulation impedances of the DC bus of the inverter are respectively connected in parallel with another pair of unbalanced resistors controlled by a second auxiliary switching switch.

[0009] Preferably, the positive and negative insulation impedances of the inverter DC bus are also respectively connected in parallel with another pair of unbalanced resistors controlled by the third auxiliary switching switch.

[0010] To achieve the above object, the second aspect of the present invention provides an insulation impedance online detection method, which is applied to the photovoltaic grid-connected inverter system as claimed in claim 1 or 2, and the method comprises:

[0011] When the inverter is connected to the grid, the DC bus voltage to ground is sampled in real time, and the residual current or residual current mutation of each photovoltaic array input is sampled by the DC leakage current sensor;

[0012] For each photovoltaic array, determining whether the residual current and / or the residual current mutation amount is greater than a corresponding current threshold;

[0013] When the residual current and / or the residual current mutation amount is greater than a corresponding current threshold, calibrating the corresponding photovoltaic array as a target photovoltaic array;

[0014] Calculating the real-time insulation impedance of the target photovoltaic array input according to the DC bus-to-ground voltage, and determining that the target photovoltaic array has an insulation fault when the real-time insulation impedance is greater than a preset impedance threshold;

[0015] The DC relay of the target photovoltaic array is controlled to be disconnected to isolate the photovoltaic array circuit with insulation impedance fault, and an alarm is sent to the background.

[0016] Preferably, the residual current is the sum of the positive and negative currents input by the corresponding photovoltaic array.

[0017] Preferably, the method further comprises:

[0018] Before the inverter is started, the initial insulation impedance of the inverter DC bus and the initial insulation impedance and initial residual current of each photovoltaic array input are calculated, and when the initial insulation impedance and the initial residual current are both lower than the corresponding thresholds, the first to third auxiliary switching switches are controlled to be disconnected, and the inverter is controlled to start.

[0019] Preferably, when the residual current and / or the residual current mutation amount is greater than the corresponding current threshold, the DC relay of the corresponding photovoltaic array is controlled to be disconnected to isolate the photovoltaic array circuit with insulation impedance fault, and an alarm is issued to the background.

[0020] Preferably, before the inverter is started, the first to third auxiliary switching switches are switched on and off so as to calculate the initial insulation impedance of the inverter DC bus and the initial insulation impedance of each photovoltaic array input.

[0021] Preferably, the unbalanced resistance of the target photovoltaic array is switched on and off to achieve real-time insulation impedance calculation of the target photovoltaic array input.

[0022] To achieve the above object, the present invention provides an insulation impedance online detection device in a third aspect, comprising:

[0023] The detection module is used to detect the voltage between the DC bus and the ground, the residual current or the residual current mutation amount input by each photovoltaic array when the inverter is connected to the grid;

[0024] A first calculation module, used for calculating and judging whether the residual current and / or the residual current mutation amount is greater than a corresponding current threshold, and when the residual current and / or the residual current mutation amount is greater than the corresponding current threshold, marking the corresponding photovoltaic array as a target photovoltaic array, and controlling the first action module or the second action module to act;

[0025] A first action module, configured to control the unbalanced resistance of the target photovoltaic array when the residual current and / or the residual current mutation amount is greater than a corresponding current threshold;

[0026] A second calculation module is used to calculate the real-time insulation impedance of the target photovoltaic array input according to the DC bus-to-ground voltage after the first action module is actuated, and control the second action module to act when the real-time insulation impedance is greater than a preset impedance threshold;

[0027] The second action module is used to control the DC relay of the target photovoltaic array to disconnect after receiving the control instruction output by the first calculation module or the second calculation module that the target photovoltaic array has an insulation fault, so as to isolate the photovoltaic array circuit with insulation impedance fault and issue an alarm to the background.

[0028] Preferably, the residual current detected by the detection module is the sum of the positive and negative currents input by the corresponding photovoltaic array.

[0029] The present invention has at least the following technical effects:

[0030] When the inverter is connected to the grid, the present invention can sample and obtain the DC bus voltage to the ground, the residual current or the residual current mutation amount of each photovoltaic array input in real time, and then for each photovoltaic array, determine whether the residual current and / or the residual current mutation amount is greater than the corresponding current threshold. If so, the corresponding photovoltaic array is calibrated as the target photovoltaic array, and then the real-time insulation impedance of the target photovoltaic array input is calculated according to the DC bus voltage to the ground, and when the real-time insulation impedance is greater than the preset impedance threshold, it is determined that the target photovoltaic array has an insulation fault, and then the DC relay of the target photovoltaic array is controlled to be disconnected, so that the photovoltaic array circuit with insulation impedance fault can be isolated. Therefore, the present invention can calculate the real-time insulation impedance of the photovoltaic array input, and combined with the residual current of the photovoltaic array input, it can be determined whether the insulation impedance of the photovoltaic array is abnormal, and the abnormal array can be timely cut off through the DC relay, thereby ensuring the safety of the grid-connected inverter system and improving the system operation efficiency.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The schematic diagram is a structural diagram of a photovoltaic grid-connected inverter system according to an embodiment of the present invention.

[0033] Figure 2 It is a structural schematic diagram of an insulation impedance online detection device according to an embodiment of the present invention.

[0034] Figure 3 It is a flow chart of an insulation impedance online detection method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The present embodiment is described in detail below, and examples of the embodiment are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0036] In accordance with the technical safety requirements for grid-connected inverters, currently centralized photovoltaic power stations all use non-isolated inverters with multiple photovoltaic array inputs, and the insulation impedance is only tested before the inverter system is started and connected to the grid; when the inverter is connected to the grid, insulation impedance detection cannot be performed, and only photovoltaic array residual current detection will continue. At this time, when an insulation impedance fault occurs in the photovoltaic array input, the inverter will immediately disconnect and issue a system low insulation impedance fault. It is impossible to determine which specific photovoltaic array input insulation impedance is reduced, and automatically cut off the faulty photovoltaic array to maintain continuous operation.

[0037] The present embodiment provides a photovoltaic grid-connected inverter system based on a DC system and an online detection method and device for its insulation impedance. The solution can measure the residual current of each photovoltaic array input of the inverter and the DC bus-to-ground voltage in real time. When it is monitored that the residual current of some photovoltaic arrays or its sudden change exceeds the set threshold, the unbalanced resistance is controlled in real time. By measuring the positive and negative bus-to-ground voltages and residual currents under different states, the insulation impedance of the abnormal photovoltaic array is calculated, and the real-time insulation impedance of the abnormal photovoltaic array can be obtained, so as to determine whether the abnormal photovoltaic array has an insulation impedance fault, and further isolation measures can be taken.

[0038] This embodiment calculates the real-time insulation impedance of the photovoltaic array and combines it with the residual current to determine whether the insulation impedance of the photovoltaic array is abnormal. The abnormal photovoltaic array is promptly cut off through the DC relay, which can ensure the safety of the grid-connected inverter system and improve the system operation efficiency.

[0039] The photovoltaic grid-connected inverter system and its insulation impedance online detection method and device of this embodiment are described below with reference to the accompanying drawings.

[0040] Figure 1 FIG. 1 is a schematic diagram of the structure of a photovoltaic grid-connected inverter system according to an embodiment of the present invention. Figure 1 As shown, the photovoltaic grid-connected inverter system includes a plurality of photovoltaic arrays and an inverter, wherein the plurality of photovoltaic arrays are connected in parallel with the inverter DC bus, each photovoltaic array includes a photovoltaic power station, namely PV1, ..., PVn, a DC leakage current sensor, namely T1, ..., Tn, and a DC relay, namely Km1, ..., Kmn, and each photovoltaic branch where the photovoltaic array is located is connected in series with the photovoltaic power station, the DC relay, and the DC leakage current sensor; wherein the positive and negative insulation impedances of each photovoltaic branch are respectively connected to a pair of unequal polarity electrodes controlled by the first auxiliary switching switch. The positive and negative insulation impedances Rn± of the nth photovoltaic branch are respectively connected in parallel with a pair of unbalanced resistors Rn1 and Rn2 controlled by the first auxiliary switching switch Kn on the nth photovoltaic branch; the positive and negative insulation impedances of the inverter DC bus are respectively connected in parallel with another pair of unbalanced resistors controlled by the second auxiliary switching switch, for example, the positive and negative insulation impedances R± of the inverter DC bus are respectively connected in parallel with the unbalanced resistors RA1 and RA2 switched by the second auxiliary switching switch KA, and the inverter side of the inverter is connected to the grid. It should be noted that the positive and negative insulation impedances R± of the inverter DC bus are also respectively connected in parallel with the unbalanced resistors RB1 and RB2 switched by the third auxiliary switching switch KB. In this embodiment, the resistance values ​​of the unbalanced resistors R11 to Rn1 are all 100K, the resistance values ​​of the unbalanced resistors R12 to Rn2 are all 110K, the resistance values ​​of the unbalanced resistors Rm1 and Rm2 are 224K and 226K respectively, the resistance values ​​of the unbalanced resistors RA1 and RB2 are respectively 300K, and the resistance values ​​of the unbalanced resistors RA2 and RB1 are respectively 400K.

[0041] It should be noted that the DC leakage current sensor of this embodiment is installed on the positive and negative poles of each photovoltaic array input, and is mainly used to accurately monitor the residual current of each photovoltaic array. In this embodiment, a group of unbalanced resistors installed between the positive and negative poles of each photovoltaic array and the grounding pole, which are controlled by the first auxiliary switching switch, are used for residual current calibration and insulation impedance calculation of each photovoltaic array. In this embodiment, between the photovoltaic array interface and its circuit breaker, the DC relay connected in series on each photovoltaic array is used to accurately, quickly and controllably execute the action module command, and the segmented insulation impedance fault input photovoltaic array is used to ensure that the inverter does not carry the residual current of the faulty photovoltaic array. Among them, the DC relay adopts a normally open contact and is energized after the inverter starts the self-test normally. After calculating and detecting the insulation impedance fault, the DC relay of the corresponding photovoltaic array is disconnected. At the same time, the DC relay will automatically disconnect the DC relay when the system fails and loses power to ensure the safety of the inverter.

[0042] In view of the technical problem that the insulation impedance of the DC side cannot be detected in real time when the grid-connected inverter is in the grid-connected working state, and the insulation fault input branch cannot be isolated, the insulation impedance online detection method of this embodiment relies on the attached Figure 2 The device shown, Figure 2 Schematic diagram of the structure of the insulation impedance online detection device according to the embodiment of the present invention. Figure 2 As shown, the insulation impedance online detection device includes a detection module, a first calculation module, a first action module, a second calculation module and a second action module.

[0043] This embodiment provides an insulation impedance online detection method. Figure 3 FIG. 1 is a flow chart of an insulation impedance online detection method according to an embodiment of the present invention. Figure 3 As shown, the method includes:

[0044] Step S101: When the inverter is connected to the grid, the DC bus voltage to the ground is sampled in real time, and the residual current or residual current mutation amount input to each photovoltaic array is sampled by a DC leakage current sensor.

[0045] Among them, the residual current is the sum of the positive and negative currents input by the corresponding photovoltaic array.

[0046] Step S102: for each photovoltaic array, determine whether the residual current and / or the residual current mutation amount is greater than a corresponding current threshold.

[0047] Step S103: when the residual current and / or the residual current mutation amount is greater than the corresponding current threshold, the corresponding photovoltaic array is calibrated as a target photovoltaic array.

[0048] It should be noted that when the residual current and / or the residual current mutation amount is significantly greater than the corresponding current threshold, the DC relay of the corresponding photovoltaic array can also be directly controlled to disconnect to isolate the photovoltaic array circuit with insulation impedance fault and send an alarm to the background.

[0049] The residual current and / or the residual current mutation amount may also be compared with the corresponding initial residual current measured before the inverter is started to determine whether the corresponding photovoltaic array has an insulation impedance fault.

[0050] Step S104: Calculate the real-time insulation impedance of the target photovoltaic array input according to the DC bus-to-ground voltage, and determine that the target photovoltaic array has an insulation fault when the real-time insulation impedance is greater than a preset impedance threshold.

[0051] In this embodiment, the unbalanced resistance of the target photovoltaic array can be switched on, that is, the first auxiliary switching switch is switched on, so as to realize the real-time insulation impedance calculation of the target photovoltaic array input.

[0052] The real-time insulation impedance may also be compared with the corresponding initial insulation impedance measured before the inverter is started. When the insulation impedance deviates from the initial insulation impedance, it is determined that an insulation impedance fault exists in the target photovoltaic array.

[0053] Step S105: Control the DC relay of the target photovoltaic array to be disconnected to isolate the photovoltaic array circuit with insulation impedance fault, and send an alarm to the background.

[0054] In one embodiment of the present invention, the method further includes calculating the initial insulation impedance of the inverter DC bus and the initial insulation impedance and initial residual current of each photovoltaic array input before the inverter is started, and when the initial insulation impedance and the initial residual current are both lower than the corresponding threshold value, controlling the first to third auxiliary switching switches to be disconnected, and controlling the inverter to start. Before the inverter is started, the first to third auxiliary switching switches are switched on and off to calculate the initial insulation impedance of the inverter DC bus and the initial insulation impedance of each photovoltaic array input.

[0055] Specifically, the insulation impedance online detection method is divided into the following steps:

[0056] Step 1: After the inverter meets the startup conditions, the residual current and DC bus voltage to ground of each photovoltaic array input of the inverter are obtained in real time and filtered.

[0057] In this embodiment, the detection module can be used to obtain the residual current and DC bus voltage to ground of each photovoltaic array input of the inverter in real time. The process of extracting the residual current and DC bus voltage to ground is as follows:

[0058] (1) The sampling of the DC bus voltage to ground is to sample the PV positive voltage to ground and the PV negative voltage to ground of the photovoltaic power station.

[0059] (2) The residual current is generally sampled by a DC leakage current sensor, which samples the sum of the positive and negative currents of each photovoltaic array input. For example, the DC leakage current sensor Tn samples the sum of the positive and negative currents of the photovoltaic array input of the nth photovoltaic branch, △In.

[0060] Step 2: When it is detected that the input residual current of the photovoltaic array and its mutation amount exceed the corresponding current threshold, it is inferred that the insulation of the photovoltaic array is abnormal.

[0061] In this embodiment, the first calculation module can be used to calculate and compare in real time whether the residual current and the mutation amount input by each photovoltaic array exceed the corresponding current threshold. If exceeded, the photovoltaic array is calibrated, that is, calibrated as a target photovoltaic array.

[0062] Optionally, in the embodiment of the present invention, each current threshold may be modified by comparing the recommended value (300mA / 30mA) and the historical measurement value in combination with the actual on-site operating environment.

[0063] It should be noted that when the first calculation module compares and calculates the residual current and its mutation amount and obviously determines that the insulation of the relevant photovoltaic array is abnormal, the second action module can be directly used to automatically control the DC relay of the photovoltaic array to disconnect, so as to isolate the photovoltaic array circuit with insulation impedance fault and send an alarm to the background.

[0064] When the first calculation module infers that the photovoltaic array has insulation abnormality and is marked as the target photovoltaic array, the real-time insulation impedance of the target photovoltaic array can be calculated. Specifically, the first action module can be used to control the unbalanced resistance controlled by the first auxiliary switching switch so that the measured positive and negative bus voltages and residual currents are different, and then the second calculation module is used to calculate the real-time insulation impedance of the target photovoltaic array at this time.

[0065] For example, when the first calculation module calibrates the photovoltaic array of the first photovoltaic branch as the target photovoltaic array, the first action module can be used to control the action of the first auxiliary switching switch K1 on the first photovoltaic branch to switch the corresponding unbalanced resistors R11 and R12 into the photovoltaic array circuit, and then the second calculation module is used to calculate the real-time insulation impedance of the first photovoltaic array.

[0066] When the real-time insulation impedance calculated by the target photovoltaic array exceeds the preset impedance threshold, it can be determined that the target photovoltaic array has an insulation fault. Then the second action module is used to automatically control the DC relay of the target photovoltaic array to disconnect, so as to isolate the photovoltaic array circuit with insulation impedance fault and send an alarm to the background.

[0067] Optionally, this embodiment can directly calculate the initial insulation impedance of the inverter bus DC and each photovoltaic array input to determine whether to start the inverter. R+ and R- are the insulation impedance of the positive and negative DC bus to the ground, that is, the initial insulation impedance. The resistors Rm1 and Rm2 are the unbalanced resistances of the positive and negative bus to the ground, respectively. These two resistors play a role in balancing the voltage of the DC bus to the ground under normal circumstances, so as not to cause the DC bus to be unstable due to excessive insulation resistance to the ground. The two sets of resistors switched by the second auxiliary switching switch KA and the third auxiliary switching switch KB make the measured positive and negative DC bus voltages different under different circumstances, so as to calculate the initial insulation impedance of the DC bus to the ground.

[0068] When all switches are disconnected, measure the positive and negative DC bus voltages U+ and U- to ground respectively, and obtain the following equations about R+ and R-:

[0069]

[0070] Among them, the 224k resistor is Rm1 and the 226k resistor is Rm2.

[0071] Close the second auxiliary switch KA and measure the ground voltage U' of the positive and negative DC busbars respectively. + and U' - , we get the following equations about R+ and R-:

[0072]

[0073] Among them, the 300k resistor is RA1 and the 400k resistor is RA2.

[0074] Optionally, equations 1 and 2 are a set of two-dimensional equations about R+ and R-, and the values ​​of the initial insulation impedances R+ and R- of the DC bus to ground can be calculated by solving them. In practical applications, considering factors such as the decrease in the insulation impedances of the positive and negative buses, a third auxiliary switching switch KB is set to calculate the insulation impedance of the DC bus to ground under different working conditions.

[0075] It can be understood that by closing the first auxiliary switching switch Kn on the nth photovoltaic branch, the initial insulation impedances Rn+ and Rn- of each photovoltaic array input can be calculated using the above principle.

[0076] The initial insulation impedance calculation is completed before the inverter starts the self-test. When the calculated initial residual current and initial insulation impedance are within the corresponding thresholds, the auxiliary switching switch is controlled to be disconnected and the inverter is started.

[0077] Furthermore, the present invention also provides an insulation impedance online detection device, comprising a detection module, a first calculation module, a first action module, a second calculation module and a second action module connected in sequence, wherein the first calculation module is also connected to the second action module.

[0078] In this embodiment, the detection module is used to detect the DC bus voltage to ground, the residual current or the residual current mutation amount input to each photovoltaic array when the inverter is connected to the grid; the first calculation module is used to calculate and determine whether the residual current and / or the residual current mutation amount is greater than the corresponding current threshold, and when the residual current and / or the residual current mutation amount is greater than the corresponding current threshold, the corresponding photovoltaic array is calibrated as the target photovoltaic array, and the first action module or the second action module is controlled to operate; the first action module is used to control the unbalanced resistance of the target photovoltaic array when the residual current and / or the residual current mutation amount is greater than the corresponding current threshold; the second calculation module is used to calculate the real-time insulation impedance input to the target photovoltaic array according to the DC bus voltage to ground after the first action module is operated, and control the second action module to operate when the real-time insulation impedance is greater than the preset impedance threshold; the second action module is used to control the DC relay of the target photovoltaic array to disconnect after receiving the control instruction output by the first calculation module or the second calculation module that the target photovoltaic array has an insulation fault, so as to isolate the photovoltaic array circuit with insulation impedance fault, and send an alarm to the background.

[0079] The residual current detected by the detection module is the sum of the positive and negative currents input by the corresponding photovoltaic array.

[0080] It should be noted that the specific implementation of the insulation impedance online detection device of this embodiment can refer to the specific implementation of the insulation impedance online detection method mentioned above, and will not be repeated here to avoid redundancy.

[0081] In summary, the present invention can perform online insulation monitoring of all photovoltaic arrays of the inverter in real time, locate the faulty photovoltaic array and accurately isolate it through a DC relay, thereby ensuring that the remaining photovoltaic arrays with normal insulation impedance continue to generate electricity and ensuring that the inverter operates without stopping.

[0082] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0083] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A photovoltaic grid-connected inverter system, characterized in that: It includes multiple photovoltaic arrays and inverters, and the multiple photovoltaic arrays are connected in parallel with the inverter DC bus. Each photovoltaic array includes a photovoltaic power station, a DC leakage current sensor and a DC relay. The photovoltaic branch where each photovoltaic array is located is connected in series with the photovoltaic power station, the DC relay and the DC leakage current sensor; wherein the positive and negative insulation impedances of each photovoltaic branch are respectively connected in parallel with a pair of unbalanced resistors controlled by a first auxiliary switching switch; and the positive and negative insulation impedances of the inverter DC bus are respectively connected in parallel with another pair of unbalanced resistors controlled by a second auxiliary switching switch.

2. The photovoltaic grid-connected inverter system according to claim 1, characterized in that: The positive and negative insulation impedances of the inverter DC bus are also respectively connected in parallel with another pair of unbalanced resistors controlled by the third auxiliary switching switch.

3. An insulation impedance online detection method, characterized in that: Applied to the photovoltaic grid-connected inverter system according to claim 1 or 2, the method comprises: When the inverter is connected to the grid, the DC bus voltage to ground is sampled in real time, and the residual current or residual current mutation of each photovoltaic array input is sampled by the DC leakage current sensor; For each photovoltaic array, determining whether the residual current and / or the residual current mutation amount is greater than a corresponding current threshold; When the residual current and / or the residual current mutation amount is greater than a corresponding current threshold, calibrating the corresponding photovoltaic array as a target photovoltaic array; Calculating the real-time insulation impedance of the target photovoltaic array input according to the DC bus-to-ground voltage, and determining that the target photovoltaic array has an insulation fault when the real-time insulation impedance is greater than a preset impedance threshold; The DC relay of the target photovoltaic array is controlled to be disconnected to isolate the photovoltaic array circuit with insulation impedance fault, and an alarm is sent to the background.

4. The insulation impedance online detection method according to claim 3, characterized in that: The residual current is the sum of the positive and negative currents input by the corresponding photovoltaic array.

5. The insulation impedance online detection method according to claim 3, characterized in that: The method further comprises: Before the inverter is started, the initial insulation impedance of the inverter DC bus and the initial insulation impedance and initial residual current of each photovoltaic array input are calculated, and when the initial insulation impedance and the initial residual current are both lower than the corresponding thresholds, the first to third auxiliary switching switches are controlled to be disconnected, and the inverter is controlled to start.

6. The insulation impedance online detection method according to claim 3, characterized in that: When the residual current and / or the residual current mutation amount is greater than the corresponding current threshold, the DC relay of the corresponding photovoltaic array is controlled to be disconnected to isolate the photovoltaic array circuit with insulation impedance fault, and an alarm is issued to the background.

7. The insulation impedance online detection method according to claim 5, characterized in that: Before starting the inverter, the first to third auxiliary switching switches are switched on and off to calculate the initial insulation impedance of the inverter DC bus and the initial insulation impedance of each photovoltaic array input.

8. The insulation impedance online detection method according to claim 3, characterized in that: By switching on and off the unbalanced resistance of the target photovoltaic array, the real-time insulation impedance calculation of the target photovoltaic array input is realized.

9. An insulation impedance online detection device, characterized in that: include: The detection module is used to detect the voltage between the DC bus and the ground, the residual current or the residual current mutation amount input by each photovoltaic array when the inverter is connected to the grid; A first calculation module, used for calculating and judging whether the residual current and / or the residual current mutation amount is greater than a corresponding current threshold, and when the residual current and / or the residual current mutation amount is greater than the corresponding current threshold, marking the corresponding photovoltaic array as a target photovoltaic array, and controlling the first action module or the second action module to act; A first action module, configured to control the unbalanced resistance of the target photovoltaic array when the residual current and / or the residual current mutation amount is greater than a corresponding current threshold; A second calculation module is used to calculate the real-time insulation impedance of the target photovoltaic array input according to the DC bus-to-ground voltage after the first action module is actuated, and control the second action module to act when the real-time insulation impedance is greater than a preset impedance threshold; The second action module is used to control the DC relay of the target photovoltaic array to disconnect after receiving the control instruction output by the first calculation module or the second calculation module that the target photovoltaic array has an insulation fault, so as to isolate the photovoltaic array circuit with insulation impedance fault and issue an alarm to the background.

10. The insulation impedance online detection device according to claim 9, characterized in that: The residual current detected by the detection module is the sum of the positive and negative currents input by the corresponding photovoltaic array.

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