Impedance correction method of insulation detection resistor, photovoltaic inverter and dielectric

Abstract

The present application discloses an impedance correction method for an insulation detection resistor, a photovoltaic inverter, and a medium, relating to the technical field of photovoltaic inverters. The impedance correction method determines relatively accurate first and second insulation impedances by respectively obtaining a first leakage current, a first positive-pole-to-ground voltage at the positive input terminal, and a first negative-pole-to-ground voltage at the negative input terminal of the photovoltaic inverter when the MPPT module is under different input voltages. Based on the first and second insulation impedances, the second positive-pole-to-ground voltage at the positive input terminal, and the second negative-pole-to-ground voltage at the negative input terminal are detected to obtain a corrected impedance value of the insulation detection resistor, and the pre-stored impedance value is updated to achieve the purpose of correcting the impedance value of the insulation detection resistor. This solves the problem of inaccurate insulation impedance detection results before the photovoltaic inverter is connected to the grid due to changes in the impedance of the insulation detection resistor.

Description

Technical Field

[0001] The present application belongs to the technical field of inverters, and in particular relates to an impedance correction method for an insulation detection resistor of a photovoltaic inverter, a photovoltaic inverter, and a medium. Background Art

[0002] Photovoltaic inverters can convert direct current (DC) output from PV (Photovoltaics) cells into alternating current (AC), which can be fed into the power grid for grid connection or used to supply power to loads.

[0003] like Figure 1 As shown, before grid connection, it is necessary to test the first insulation resistance R1 of the PV inverter's positive input terminal PV+ to ground, and the second insulation resistance R2 of the PV inverter's negative input terminal PV- to ground. If both the first insulation resistance R1 and the second insulation resistance R2 are greater than or equal to a preset impedance threshold, the PV inverter is allowed to connect to the grid and operate normally after grid connection. If either the first insulation resistance R1 or the second insulation resistance R2 is less than the preset impedance threshold, the PV inverter is not allowed to connect to the grid.

[0004] like Figure 1 As shown in the figure, in the relevant insulation impedance detection scheme, an insulation detection resistor R3 is provided on the photovoltaic input side of the photovoltaic inverter to cooperate with the implementation of the photovoltaic inverter's insulation impedance detection to ground. The insulation detection resistor R3 is connected in series with the switch K between the ground wire (Protecting Earth, PE) and the negative input terminal PV- of the photovoltaic inverter. By switching the switch K to control the branch to which the insulation detection resistor R3 belongs to conduct or disconnect, the first insulation impedance R1 and the second insulation impedance R2 can be measured based on the different voltage and current relationships when conducting and disconnecting.

[0005] However, as the insulation resistance of the insulation test resistor R3 changes over time, it may cause inaccurate insulation resistance test results. Therefore, it is necessary to provide an insulation resistance correction method to ensure the accuracy of insulation resistance test results before the photovoltaic inverter is connected to the grid. Summary of the Invention

[0006] The present application provides an insulation detection resistor impedance correction method, a photovoltaic inverter, and a medium for correcting the impedance of the insulation detection resistor of the photovoltaic inverter, thereby solving the problem of inaccurate insulation impedance detection results before the photovoltaic inverter is connected to the grid due to changes in the impedance of the insulation detection resistor.

[0007] A first aspect of an embodiment of the present application provides an impedance correction method for an insulation detection resistor of a photovoltaic inverter. The photovoltaic inverter includes a photovoltaic input terminal, an MPPT module, a DC / AC module, and an insulation impedance detection branch. The photovoltaic input terminal, the MPPT module, and the DC / AC module are connected in sequence. The photovoltaic input terminal includes a positive input terminal and a negative input terminal. The insulation impedance detection branch is connected between the positive input terminal and a ground wire or between the negative input terminal and the ground wire. The insulation impedance detection branch includes an insulation detection resistor and a switch connected in series. The impedance correction method includes:

[0008] When the PV inverter is connected to the grid, the DC / AC module operates in bipolar SPWM modulation mode, and the insulation impedance detection branch is disconnected, change the input voltage of the MPPT module;

[0009] Acquire detection parameters under different input voltages; the detection parameters include a first leakage current, a first positive-pole-to-ground voltage of the positive input terminal, and a first negative-pole-to-ground voltage of the negative input terminal;

[0010] Determining a first insulation impedance between the positive input terminal and the ground and a second insulation impedance between the negative input terminal and the ground based on detection parameters at different input voltages;

[0011] When the photovoltaic inverter is off-grid, the insulation impedance detection branch is turned on, and the MPPT module stops working, obtaining a second positive-pole-to-ground voltage of the positive input terminal and a second negative-pole-to-ground voltage of the negative input terminal;

[0012] The impedance value of the insulation detection resistor is updated based on the first insulation impedance, the second insulation impedance, the second positive electrode-to-ground voltage, and the second negative electrode-to-ground voltage.

[0013] As an optional implementation of the first aspect, changing the input voltage of the MPPT module includes:

[0014] When the photovoltaic inverter is in a stable operating condition, obtaining a first input voltage of the MPPT module;

[0015] The duty cycle of the switch drive signal of the MPPT module is changed to change the input voltage of the MPPT module to a second input voltage; the second input voltage is different from the first input voltage.

[0016] As an optional implementation manner of the first aspect, a method for determining whether a photovoltaic inverter is in a stable operating condition includes:

[0017] Detect the output power of photovoltaic inverter;

[0018] When the output power of the photovoltaic inverter is greater than or equal to a preset power value, it is determined that the photovoltaic inverter is in a stable operating condition.

[0019] As an optional implementation manner of the first aspect, after determining the first insulation impedance of the positive input terminal to ground and the second insulation impedance of the negative input terminal to ground based on detection parameters at different input voltages, the impedance correction method further includes:

[0020] Detect the output voltage of the photovoltaic inverter;

[0021] At the moment corresponding to the zero-crossing point of the output voltage, the MPPT module is controlled to operate in the maximum power tracking mode and the DC / AC module is controlled to operate in the unipolar SPWM modulation mode.

[0022] As an optional implementation manner of the first aspect, after updating the impedance value of the insulation detection resistor based on the first insulation impedance, the second insulation impedance, the second positive electrode-to-ground voltage, and the second negative electrode-to-ground voltage, the impedance correction method further includes:

[0023] Before controlling the photovoltaic inverter to be grid-connected, obtaining a corrected first insulation impedance and a second insulation impedance based on the updated impedance value of the insulation detection resistor;

[0024] When the corrected first insulation impedance and the corrected second insulation impedance are both greater than or equal to a preset impedance threshold, the photovoltaic inverter is controlled to be connected to the grid.

[0025] As an optional implementation manner of the first aspect, when the photovoltaic inverter is grid-connected, the DC / AC module operates in a bipolar SPWM modulation mode, and the insulation impedance detection branch is disconnected, before changing the input voltage of the MPPT module, the impedance correction method further includes:

[0026] Before the PV inverter is connected to the grid, the modulation mode of the DC / AC module is configured as bipolar SPWM modulation.

[0027] As an optional implementation manner of the first aspect, after determining the first insulation impedance of the positive input terminal to ground and the second insulation impedance of the negative input terminal to ground based on detection parameters at different input voltages, the impedance correction method further includes:

[0028] Control photovoltaic inverter off-grid;

[0029] Stop sending the switch tube driving signal to the MPPT module to stop the MPPT module from working;

[0030] Control the insulation impedance detection branch circuit to be conductive.

[0031] As an optional implementation manner of the first aspect, the impedance correction method further includes:

[0032] Determine the preset duration based on the working environment of the photovoltaic inverter;

[0033] The impedance value of the insulation detection resistor is updated at every preset time interval.

[0034] A second aspect of an embodiment of the present application provides a photovoltaic inverter, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the impedance correction method provided in the first aspect are implemented.

[0035] A third aspect of the embodiments of the present application provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the steps of the impedance correction method provided in the first aspect are implemented.

[0036] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0037] When the DC / AC module operates in bipolar SPWM (Sinusoidal Pulse Width Modulation) mode, the common-mode leakage current of the photovoltaic inverter is zero. At this time, the leakage current of the photovoltaic inverter is equal to the residual current at the photovoltaic input terminal. Therefore, when the branch to which the insulation detection resistor belongs is disconnected, by respectively obtaining the first leakage current of the photovoltaic inverter, the first positive-pole-to-ground voltage of the positive input terminal, and the first negative-pole-to-ground voltage of the negative input terminal when the MPPT module is at different input voltages, multiple equations for the first insulation impedance and the second insulation impedance can be obtained, thereby determining relatively accurate first insulation impedance and second insulation impedance. In this way, when the photovoltaic inverter is off-grid, the branch to which the insulation detection resistor belongs is turned on, and the MPPT module stops working, the insulation impedance is re-detected to obtain the second positive pole-to-ground voltage of the positive input terminal and the second negative pole-to-ground voltage of the negative input terminal. At this time, based on the first insulation impedance and the second insulation impedance, the corrected impedance of the insulation detection resistor can be reversely deduced and the pre-stored impedance value can be updated to achieve the purpose of correcting the impedance value of the insulation detection resistor. This solves the problem of inaccurate insulation impedance detection results before the photovoltaic inverter is connected to the grid due to changes in the impedance of the insulation detection resistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The following is a schematic diagram of the structure of a photovoltaic inverter provided by the related art;

[0039] Figure 2 A first structural diagram of a photovoltaic inverter provided in an embodiment of the present application is shown;

[0040] Figure 3 A schematic diagram illustrating a flow chart of an impedance correction method for an insulation detection resistor provided in one embodiment of the present application is shown;

[0041] Figure 4 A second structural schematic diagram of a photovoltaic inverter provided in an embodiment of the present application is shown;

[0042] Figure 5 A third structural schematic diagram of a photovoltaic inverter provided in an embodiment of the present application is shown;

[0043] Figure 6 A fourth structural schematic diagram of a photovoltaic inverter provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0045] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0047] Photovoltaic inverters can convert the direct current output by photovoltaic cells into alternating current, which can be connected to the power grid or supply power to loads.

[0048] like Figure 1 As shown, current inverter grid-connection requirements require testing the first insulation resistance R1 of the PV inverter's positive input terminal PV+ to ground, and the second insulation resistance R2 of the PV inverter's negative input terminal PV- to ground, before grid connection. If both the first insulation resistance R1 and the second insulation resistance R2 are greater than or equal to a preset impedance threshold, the PV inverter is allowed to connect to the grid and operate normally after grid connection. If either the first insulation resistance R1 or the second insulation resistance R2 is less than the preset impedance threshold, the PV inverter is not allowed to connect to the grid to reduce safety issues.

[0049] like Figure 1As shown, in the relevant insulation impedance detection scheme, an insulation detection resistor R3 is installed on the photovoltaic input side of the photovoltaic inverter to facilitate the detection of the insulation impedance of the photovoltaic inverter to ground. The insulation detection resistor R3 is connected in series with a switch K, connected between the ground wire and the negative input terminal PV- of the photovoltaic inverter. By switching the branch to which the insulation detection resistor R3 belongs, the first insulation impedance R1 and the second insulation impedance R2 can be measured based on the different voltage and current relationships during the on and off conditions.

[0050] However, over time, the impedance of insulation test resistor R3 may change due to corrosion, aging, and other factors, resulting in inaccurate insulation resistance test results. Therefore, it is necessary to provide an insulation test resistor impedance correction method to ensure the accuracy of insulation resistance test results before the photovoltaic inverter is connected to the grid.

[0051] The embodiments of the present application provide an insulation detection resistor impedance correction method, a photovoltaic inverter, and a medium for correcting the impedance value of the insulation detection resistor R3 of the photovoltaic inverter, thereby solving the problem of inaccurate insulation impedance detection results before the photovoltaic inverter is connected to the grid due to changes in the impedance of the insulation detection resistor R3.

[0052] The impedance correction method proposed in the embodiments of this application is designed as follows: when the photovoltaic inverter is grid-connected, its leakage current is detected and relatively accurate first insulation resistance R1 and second insulation resistance R2 are calculated based on the leakage current. When the photovoltaic inverter is off-grid, the impedance value of the insulation detection resistor R3 is corrected using the calculated first insulation resistance R1 and second insulation resistance R2 based on the principle of resistor voltage division.

[0053] In order to illustrate the technical solution described in this application, specific embodiments are provided below.

[0054] Figure 2 A schematic structural diagram of a photovoltaic inverter 100 to which the impedance correction method for an insulation detection resistor provided in an embodiment of the present application is applicable is shown. For ease of description, only portions related to this embodiment are shown.

[0055] like Figure 2 As shown, the photovoltaic inverter 100 in this embodiment includes a photovoltaic input terminal, an MPPT (Maximum Power Point Tracking) module 10, a DC / AC (Direct Current to Alternating Current) module 20, and an insulation impedance detection branch 30. The photovoltaic input terminal includes a positive input terminal PV+ and a negative input terminal PV-.

[0056] The photovoltaic input terminal, MPPT module 10, and DC / AC module 20 are connected in sequence, and the insulation impedance detection branch 30 is connected between the positive input terminal PV+ and the ground line, or between the negative input terminal PV- and the ground line. This embodiment uses the insulation impedance detection branch 30 connected between the negative input terminal PV- and the ground line as an example. The insulation impedance detection branch 30 includes an insulation detection resistor R3 and a switch K connected in series. Optionally, one end of the switch K is connected to the ground line, and the other end is connected to one end of the insulation detection resistor R3. The other end of the insulation detection resistor R3 is connected to the negative input terminal PV-.

[0057] As an example, the photovoltaic input terminal is used to connect to the photovoltaic cell 200. For example, the positive output terminal of the photovoltaic cell 200 is connected to the positive input terminal PV+, and the negative output terminal of the photovoltaic cell 200 is connected to the negative input terminal PV-. Therefore, the photovoltaic cell 200 can provide power to the photovoltaic inverter 100 through the photovoltaic input terminal.

[0058] As an example, the MPPT module 10 is configured to track the maximum power point of the photovoltaic cell 200 when the photovoltaic inverter 100 is operating normally, ensuring that the photovoltaic cell 200 outputs at maximum power and converting the first direct current outputted by the photovoltaic cell 200 into a second direct current. This embodiment does not specifically limit the structure of the MPPT module 10; skilled artisans can implement it based on relevant technologies. For example, the output power of the photovoltaic cell 200 can be varied by changing the duty cycle of the switch drive signal of the MPPT module 10.

[0059] As an example, the DC / AC module 20 is used to convert the second DC power output by the MPPT module 10 into AC power. This AC power can be used to power a load or fed into the grid when the photovoltaic inverter 100 is connected to the grid. For example, when the output of the DC / AC module 20 is fed into the grid, one output terminal of the DC / AC module 20 serves as the live terminal L, and the other output terminal serves as the neutral terminal N. This embodiment does not specifically limit the structure of the DC / AC module 20, and those skilled in the art can implement it based on relevant technologies.

[0060] As an example, the insulation impedance detection branch 30 is used to assist the photovoltaic inverter 100 in detecting the first insulation impedance R1 between the positive input terminal PV+ and the ground, and the second insulation impedance R2 between the negative input terminal PV- and the ground, before the photovoltaic inverter 100 is connected to the grid. For example, when it is necessary to detect the first insulation impedance R1 and the second insulation impedance R2, the insulation impedance detection branch 30 can be controlled to be turned on. For another example, when the photovoltaic inverter is operating normally, the insulation impedance detection branch 30 can be controlled to be turned off. In this embodiment, the insulation impedance detection branch 30 can be controlled to be turned on by controlling the switch K to be closed, and the insulation impedance detection branch 30 can be controlled to be turned off by controlling the switch K to be closed. This embodiment does not specifically limit the structure of the switch K. For example, the switch K can be implemented using a relay switch, a semiconductor switch, a push button switch, etc.

[0061] Figure 3 A flow chart of an impedance correction method for the insulation detection resistor R3 of the photovoltaic inverter 100 provided in an embodiment of the present application is shown. For ease of description, only the portion related to this embodiment is shown.

[0062] like Figure 3 As shown, the impedance correction method provided in this embodiment includes the following steps:

[0063] S101 , when the photovoltaic inverter is connected to the grid, the DC / AC module operates in a bipolar SPWM modulation mode, and the insulation impedance detection branch is disconnected, changing the input voltage of the MPPT module.

[0064] In order to detect the leakage current of the photovoltaic inverter 100 and eliminate the influence of the insulation impedance itself in subsequent steps, the execution conditions of step S101 include that the photovoltaic inverter 100 is in the grid-connected state and the insulation impedance detection branch 30 is in the disconnected state.

[0065] Due to the structure of photovoltaic inverter 100, the leakage current of photovoltaic inverter 100 is equal to the sum of residual current and common-mode leakage current. However, when DC / AC module 20 operates in bipolar SPWM modulation mode, the common-mode leakage current can be suppressed to zero. In this case, the leakage current of photovoltaic inverter 100 is equal to the residual current. The residual current is equal to the sum of the current flowing through first insulation resistor R1 and the current flowing through second insulation resistor R2.

[0066] Due to the characteristics of the photovoltaic effect, the photovoltaic cell 200 can be considered a current source. Therefore, by changing the duty cycle of the switch drive signal in the MPPT module 10, the input voltage of the MPPT module 10 can be changed, that is, the voltage between the positive input terminal PV+ and the negative input terminal PV- can be changed.

[0067] S102: Acquire detection parameters under different input voltages, including a first leakage current, a first positive-to-ground voltage of the positive input terminal, and a first negative-to-ground voltage of the negative input terminal.

[0068] This embodiment does not specifically limit how to obtain the first leakage current, the first positive electrode-to-ground voltage, and the first negative electrode-to-ground voltage, and those skilled in the art can implement it according to relevant technologies.

[0069] As an example, since the common-mode leakage current is zero, the first leakage current can be obtained by detecting the leakage current of the live terminal L and the neutral terminal N. For example, the live terminal L and the neutral terminal N are simultaneously connected to a current transformer, and the current measured by the current transformer is the first leakage current.

[0070] As an example, the first positive electrode-to-ground voltage and the first negative electrode-to-ground voltage may be acquired through a voltage acquisition module.

[0071] Optionally, in this embodiment, detection parameters under at least two different input voltages are acquired to obtain at least two groups of related detection parameters.

[0072] For example, when the input voltage of the MPPT module 10 is equal to the first input voltage, the first leakage current is i1, the first positive voltage to ground of the positive input terminal PV+ is V11, and the first negative voltage to ground of the negative input terminal PV- is V12.

[0073] For another example, when the input voltage of the MPPT module 10 is equal to the second input voltage, the first leakage current is i2, the first positive voltage to ground of the positive input terminal PV+ is V21, and the first negative voltage to ground of the negative input terminal PV- is V22.

[0074] For another example, when the input voltage of the MPPT module 10 is equal to the third input voltage, the first leakage current is i3, the first positive voltage to ground of the positive input terminal PV+ is V31, and the first negative voltage to ground of the negative input terminal PV- is V32.

[0075] S103 : Determine a first insulation impedance between the positive input terminal and the ground and a second insulation impedance between the negative input terminal and the ground based on detection parameters at different input voltages.

[0076] Since in the bipolar SPWM modulation mode, the leakage current of the photovoltaic inverter 100 is equal to the sum of the current flowing through the first insulation resistor R1 and the current flowing through the second insulation resistor R2, the first insulation resistor R1 and the second insulation resistor R2 at this time can be determined by two sets of related detection parameters.

[0077] As an example, this embodiment is described by taking the acquisition of detection parameters at two different input voltages as an example. Therefore, the photovoltaic inverter 100 in this embodiment can acquire two sets of related detection parameters and determine the first insulation resistance R1 and the second insulation resistance R2 at this time based on the two sets of related detection parameters.

[0078] For example, the two sets of relevant detection parameters obtained include the first leakage current i1, the first positive electrode-to-ground voltage V11, the first negative electrode-to-ground voltage V12, and the first leakage current i2, the first positive electrode-to-ground voltage V21, and the first negative electrode-to-ground voltage V22. Based on the relationships V11 / R1+V12 / R2=i1 and V21 / R1+V22 / R2=i2, the first insulation resistance R1 and the second insulation resistance R2 can be determined.

[0079] For another example, the two sets of relevant detection parameters obtained include the first leakage current i1, the first positive electrode-to-ground voltage V11, the first negative electrode-to-ground voltage V12, and the first leakage current i3, the first positive electrode-to-ground voltage V31, and the first negative electrode-to-ground voltage V32. The first insulation resistance R1 and the second insulation resistance R2 can be determined based on the relationships V11 / R1+V12 / R2=i1 and V31 / R1+V32 / R2=i3.

[0080] S104 , when the photovoltaic inverter is off-grid, the insulation impedance detection branch is turned on, and the MPPT module stops working, obtaining a second positive-pole-to-ground voltage of the positive input terminal and a second negative-pole-to-ground voltage of the negative input terminal.

[0081] Since the first insulation resistance R1 and the second insulation resistance R2 have been determined in S103, in order to determine the actual impedance value of the insulation detection resistor R3 and thereby correct the impedance value of the insulation detection resistor R3, it is necessary to obtain the second positive-pole-to-ground voltage of the positive input terminal PV+ and the second negative-pole-to-ground voltage of the negative input terminal PV- when the photovoltaic inverter 100 is off-grid, the insulation resistance detection branch 30 is on, and the MPPT module 10 is stopped. It should be understood that obtaining the second positive-pole-to-ground voltage of the positive input terminal PV+ and the second negative-pole-to-ground voltage of the negative input terminal PV- when the photovoltaic inverter 100 is off-grid and the MPPT module 10 is stopped can avoid current shunting in these modules, thereby accurately determining the impedance value of the insulation resistance detection branch 30 based on Ohm's law and Kirchhoff's current law.

[0082] Optionally, the execution condition of step S104 also includes that the DC / AC module 20 also stops operating. That is, when the photovoltaic inverter 100 is off-grid, the insulation impedance detection branch 30 is turned on, the DC / AC module 20 stops operating, and the MPPT module 10 stops operating, the second positive-pole-to-ground voltage of the positive input terminal PV+ and the second negative-pole-to-ground voltage of the negative input terminal PV- are obtained.

[0083] S105 : Update the impedance value of the insulation detection resistor based on the first insulation impedance, the second insulation impedance, the second positive electrode-to-ground voltage, and the second negative electrode-to-ground voltage.

[0084] For example, the second positive electrode-to-ground voltage determined in S104 is U1, the second negative electrode-to-ground voltage is U2, and the first insulation resistance R1 and the second insulation resistance R2 are determined in S103. Then, according to the relationship U1 / R1=U2*(R2+R3) / (R2*R3), the true impedance value of the insulation detection resistor R3 can be determined, so as to update the impedance value of the insulation detection resistor R3.

[0085] Optionally, after the impedance value of the insulation detection resistor R3 is updated, the updated impedance value of the insulation detection resistor R3 may be further stored.

[0086] In summary, the impedance correction method of the insulation detection resistor R3 of the photovoltaic inverter 100 provided in this embodiment can determine the current first insulation impedance R1 and second insulation impedance R2 by measuring the leakage current and based on Ohm's law and Kirchhoff's current law, and thereby determine the true impedance value of the insulation detection resistor R3, thereby updating the impedance value of the insulation detection resistor R3 and achieving the purpose of correcting the impedance of the insulation detection resistor R3, thereby solving the problem of inaccurate insulation impedance detection results before the photovoltaic inverter 100 is connected to the grid due to changes in the impedance of the insulation detection resistor R3.

[0087] As an optional implementation of this embodiment, the impedance value of the insulation detection resistor R3 can be pre-stored in a memory of the photovoltaic inverter 100, or in a memory of another device that is coupled to the photovoltaic inverter 100. Therefore, in some embodiments, updating the impedance value of the insulation detection resistor R3 refers to updating the impedance value of the insulation detection resistor R3 stored in the memory of the photovoltaic inverter 100. With this configuration, before the photovoltaic inverter 100 is connected to the grid, the first insulation resistance R1 and the second insulation resistance R2 can be calculated based on the impedance value of the insulation detection resistor R3 stored in the memory. If both the first insulation resistance R1 and the second insulation resistance R2 are greater than or equal to a preset impedance threshold, the photovoltaic inverter 100 is allowed to connect to the grid; if either the first insulation resistance R1 or the second insulation resistance R2 is less than the preset impedance threshold, the photovoltaic inverter 100 is not allowed to connect to the grid.

[0088] In one embodiment of the present application, changing the input voltage of the MPPT module 10 in step S101 includes the following steps:

[0089] Obtaining a first input voltage of the MPPT module;

[0090] The duty cycle of the switch drive signal of the MPPT module is changed to change the input voltage of the MPPT module to a second input voltage; the second input voltage is different from the first input voltage.

[0091] As an example, as described above, the photovoltaic cell 200 can be considered a current source, and when the input voltage of the MPPT module 10 is changed, the input voltage fluctuates. However, when the photovoltaic inverter 100 is in a stable operating state, its output power is relatively stable, and the input voltage of the MPPT module 10 is also relatively stable. Therefore, in another embodiment of the present application, changing the input voltage of the MPPT module 10 in step S101 may further include the following steps:

[0092] S1011. When the photovoltaic inverter is in a stable operating condition, obtain a first input voltage of the MPPT module.

[0093] This embodiment does not specifically limit how to determine whether the photovoltaic inverter 100 is in a stable operating state. For example, it can be determined by parameters such as the output power, output voltage, or output current of the photovoltaic inverter 100.

[0094] S1012. Change the duty cycle of the switch drive signal of the MPPT module to change the input voltage of the MPPT module to a second input voltage; the second input voltage is different from the first input voltage.

[0095] In this embodiment, the input voltage of the MPPT module 10 is modified by changing the duty cycle of the switch driving signal of the MPPT module 10 .

[0096] It should be understood that the input voltage of the MPPT module 10 can be increased or decreased by changing the duty cycle, and this embodiment does not specifically limit this.

[0097] Based on the above S1011 and S1012, the second input voltage should also be the input voltage of the MPPT module 10 when the photovoltaic inverter 100 is in a stable working condition.

[0098] The impedance correction method for the insulation detection resistor R3 of the photovoltaic inverter 100 provided in this embodiment can improve the accuracy of the acquired detection parameters by obtaining detection parameters under different input voltages when the photovoltaic inverter 100 is in a stable operating condition, thereby improving the accuracy of the impedance correction of the insulation detection resistor R3.

[0099] In one embodiment of the present application, a method for determining whether the photovoltaic inverter 100 is in a stable operating state includes:

[0100] S201: Detect the output power of the photovoltaic inverter.

[0101] Optionally, the output power of the photovoltaic inverter 100 is determined by detecting the output voltage and output current of the photovoltaic inverter 100. For example, the output voltage between the live terminal L and the neutral terminal N, and the output current on the live terminal L are detected.

[0102] S202: When the output power of the photovoltaic inverter is greater than or equal to a preset power value, determine that the photovoltaic inverter is in a stable operating condition.

[0103] Optionally, when the output power of the photovoltaic inverter 100 is less than a preset power value, it is determined that the photovoltaic inverter 100 is not in a stable operating state.

[0104] For example, the preset power value is equal to half of the maximum output power of the photovoltaic inverter 100 .

[0105] The impedance correction method of the insulation detection resistor R3 of the photovoltaic inverter 100 provided in this embodiment detects the output power of the photovoltaic inverter 100 to determine whether the photovoltaic inverter 100 is in a stable operating condition, and has the advantage of being simple to implement.

[0106] In one embodiment of the present application, after step S103, the impedance correction method further includes:

[0107] S1031. Detect the output voltage of the photovoltaic inverter.

[0108] S1032 . At a moment corresponding to the zero-crossing point of the output voltage, control the MPPT module to operate in a maximum power point tracking mode and control the DC / AC module to operate in a unipolar SPWM modulation mode.

[0109] It is understood that when the photovoltaic inverter 100 is operating normally and connected to the grid, the MPPT module 10 operates in maximum power point tracking mode to ensure maximum utilization of the power of the photovoltaic cell 200, while the DC / AC module 20 typically operates in a unipolar SPWM modulation mode. Compared to the bipolar SPWM modulation mode, this modulation mode can reduce switching losses and thus improve power conversion efficiency. In this embodiment, after step S103, the first insulation resistance R1 and the second insulation resistance R2 at this time are determined, and the photovoltaic inverter 100 can be controlled to operate normally. Specifically, according to steps S1031 and S1032, the MPPT module 10 is controlled to operate in maximum power point tracking mode and the DC / AC module 20 is controlled to operate in a unipolar SPWM modulation mode. Steps S104 and S105 need to be executed after the photovoltaic inverter 100 is disconnected from the grid.

[0110] In other words, in one example, after step S103, the photovoltaic inverter 100 is immediately controlled to go off-grid so that steps S104 and S105 can be executed to promptly update the impedance value of the insulation detection resistor R3. In another example, after step S103, steps S1031 and S1032 are immediately executed to ensure that the photovoltaic inverter 100 operates normally. Then, at some point in the future, after the photovoltaic inverter 100 goes off-grid, steps S104 and S105 are executed again.

[0111] Therefore, the impedance correction method for the insulation detection resistor R3 of the photovoltaic inverter 100 provided in this embodiment allows for selecting the timing of impedance correction. For example, after obtaining the first insulation resistance R1 and the second insulation resistance R2 in step S103, the photovoltaic inverter 100 can be immediately controlled to be off-grid to enable timely impedance correction, or the photovoltaic inverter 100 can be controlled to operate normally to enable impedance correction to be performed at a future time.

[0112] In one embodiment of the present application, after step S105, the impedance correction method further includes:

[0113] S106 : Before controlling the photovoltaic inverter to be grid-connected, detect and obtain the corrected first insulation impedance and second insulation impedance based on the updated impedance value of the insulation detection resistor.

[0114] This embodiment does not specifically limit how to detect and obtain the corrected first insulation resistance R1 and the corrected second insulation resistance R2 based on the updated impedance value of the insulation detection resistor R3 , and those skilled in the art can implement it according to relevant technologies.

[0115] For example, when switch K is open, the voltage U11 of the positive input terminal PV+ to ground and the voltage U12 of the negative input terminal PV- to ground are obtained, yielding the relationship U11 / R1=U12 / R2. When switch K is closed, the voltage U21 of the positive input terminal PV+ to ground and the voltage U22 of the negative input terminal PV- to ground are obtained, yielding the relationship U21 / R1=U22(R2+R3) / (R2*R3). Based on these two relationships, the corrected first insulation resistance R1 and the corrected second insulation resistance R2 can be determined.

[0116] S107 : When the corrected first insulation impedance and the corrected second insulation impedance are both greater than or equal to a preset impedance threshold, control the photovoltaic inverter to be connected to the grid.

[0117] Optionally, when any one of the modified first insulation resistance R1 and the modified second insulation resistance R2 is less than a preset impedance threshold, a warning message is issued and the photovoltaic inverter 100 is not allowed to be connected to the grid.

[0118] In this embodiment, the updated impedance value of the insulation detection resistor R3 is used to detect the corrected first insulation impedance R1 and second insulation impedance R2, which can improve the accuracy of the insulation impedance detection result before the photovoltaic inverter 100 is connected to the grid and reduce the safety risk of the photovoltaic inverter 100 being connected to the grid.

[0119] In one embodiment of the present application, before step S101, the impedance correction method further includes the following steps:

[0120] S100: Before the photovoltaic inverter is connected to the grid, the modulation mode of the DC / AC module is configured to be bipolar SPWM modulation.

[0121] As an example, the impedance correction method provided in this embodiment can perform step S100 when the photovoltaic inverter 100 is grid-connected and operating normally, so that the modulation mode of the DC / AC module 20 becomes bipolar SPWM modulation, so as to perform step S101.

[0122] For example, when the photovoltaic inverter 100 is grid-connected and operating normally, the modulation mode of the DC / AC module 20 is unipolar SPWM modulation. After executing step S100, the modulation mode of the DC / AC module 20 changes to bipolar SPWM modulation. At this time, if the insulation impedance detection branch 30 is disconnected, or after the insulation impedance detection branch 30 is controlled to be disconnected, steps S101 to S105 can be executed to perform impedance correction on the insulation detection resistor R3 of the photovoltaic inverter 100.

[0123] In one embodiment of the present application, after step S103, the impedance correction method further includes the following steps:

[0124] S1033. Control the photovoltaic inverter to go off-grid.

[0125] S1034: Stop sending the switch tube driving signal to the MPPT module to stop the MPPT module from working.

[0126] S1035. Control the insulation impedance detection branch to be conductive.

[0127] The impedance correction method provided in this embodiment provides a method for timely updating the impedance value of the insulation detection resistor R3. Specifically, after determining the first insulation resistance R1 and the second insulation resistance R2 in step S103, the photovoltaic inverter 100 is disconnected from the grid, the switching transistor drive signal to the MPPT module 10 is stopped, and the insulation resistance detection branch 30 is turned on to meet the conditions for executing step S104.

[0128] In one embodiment of the present application, the impedance correction method further includes: updating the impedance value of the insulation detection resistor R3 at intervals of a preset time length.

[0129] Since the execution condition of step S101 includes that the photovoltaic inverter 100 is in a grid-connected state, and the execution condition of step S104 includes that the photovoltaic inverter 100 is in an off-grid state, that is, the process of completing the impedance correction of the insulation detection resistor R3 includes switching the photovoltaic inverter 100 between the grid-connected (or off-grid) state, which may have a certain impact on the operation of the photovoltaic inverter 100. For example, it may affect the efficiency of the photovoltaic inverter 100 in utilizing the photovoltaic cells 200.

[0130] Therefore, in order to reduce the number of times the photovoltaic inverter 100 switches between grid-connected (or off-grid) states and reduce adverse effects on the photovoltaic inverter 100, the impedance value of the insulation detection resistor R3 is updated at every preset time interval. That is, steps S101 to S105 are executed once at every preset time interval.

[0131] As an example, the method provided in the embodiment of the present application may further include: determining a preset duration based on the working environment of the photovoltaic inverter 100 .

[0132] It should be understood that different operating environments have different effects on the impedance of the insulation test resistor R3. For example, the aging rate of the insulation test resistor R3 varies under different operating environments. Therefore, under different operating environments, the change in the impedance of the insulation test resistor R3 due to aging and other factors over the same period of time will vary.

[0133] For example, in a normal working environment, the impedance value of the insulation detection resistor R3 is updated every 3 to 5 years. For another example, in a working environment with severe salt spray corrosion, the impedance value of the insulation detection resistor R3 is updated every six months.

[0134] As another example, the preset duration may also be set according to needs or manually set in the photovoltaic inverter 100 based on experience.

[0135] like Figure 4 As shown, in another embodiment of the present application, a photovoltaic inverter 100 is further provided. The photovoltaic inverter 100 is used to implement the above-mentioned impedance correction method of the insulation detection resistor R3.

[0136] As an example, the photovoltaic inverter 100 discloses a specific structure of the MPPT module 10 and the DC / AC module 20 .

[0137] As an example, the MPPT module 10 includes an inductor L0, a switch Q1, a diode D1, and a capacitor C2. As an example, the DC / AC module 20 includes switches Q2, Q3, Q4, and Q5, as well as inductors L1 and L2. It should be understood that the switches Q2, Q3, Q4, and Q5, as well as the inductors L1 and L2, form an H4 bridge topology.

[0138] Optionally, the input end of the MPPT module 10 is further provided with a capacitor C1 , and the output end of the DC / AC module 20 is further provided with a capacitor C3 .

[0139] One end of inductor L0 is connected to the positive input terminal PV+ and one end of capacitor C1. The other end is connected to the anode of diode D1 and the drain of switch Q1. The cathode of diode D1 is connected to one end of capacitor C2, the drain of switch Q2, and the drain of switch Q4. The other end of capacitor C2, the source of switch Q1, the source of switch Q3, the source of switch Q5, the negative input terminal PV-, and the other end of capacitor C1 are connected.

[0140] The source of the switch Q2 and the drain of the switch Q3 are connected to one end of the inductor L2. The other end of the inductor L2 is connected to the second end of the capacitor C3 and serves as the neutral terminal N of the photovoltaic inverter 100. The source of the switch Q4 and the drain of the switch Q5 are connected to one end of the inductor L1. The other end of the inductor L1 is connected to the first end of the capacitor C3 and serves as the live terminal L of the photovoltaic inverter 100.

[0141] The switch K and the insulation detection resistor R3 connected in series are connected between the ground and the negative input terminal PV-.

[0142] In this embodiment, the photovoltaic inverter 100 can change the input voltage of the MPPT module 10 by changing the duty cycle of the driving signal of the switch tube Q1, or can control the MPPT module 10 to stop working by controlling the switch tube Q1 to be in the off state.

[0143] In this embodiment, the photovoltaic inverter 100 can convert the second direct current output by the MPPT module 10 into alternating current by changing the duty cycle of the driving signals of the switch tubes Q2, Q3, Q4 and Q5, or can control the DC / AC module 20 to stop working by controlling the switch tubes Q2, Q3, Q4 and Q5 to be in the off state at all times.

[0144] like Figure 5 As shown, in another embodiment of the present application, a photovoltaic inverter 100 is further provided. The photovoltaic inverter 100 is used to implement the above-mentioned impedance correction method of the insulation detection resistor R3.

[0145] As an example, this embodiment discloses a photovoltaic inverter 100 and a power grid ( Figure 5 A connection structure of the Grid) and the photovoltaic inverter 100 and the load ( Figure 5 A connection structure of LOAD) shown in FIG.

[0146] For example, the first end of capacitor C3 serves as the live terminal L of the photovoltaic inverter 100 and is connected to the live terminal L of the power grid Grid (not shown) via switch S1. The second end of capacitor C3 serves as the neutral terminal N of the photovoltaic inverter 100 and is connected to the neutral line N of the power grid Grid (not shown). Therefore, the photovoltaic inverter 100 can be disconnected from the grid by controlling switch S1 to be opened, and connected to the grid by controlling switch S1 to be closed.

[0147] For another example, the live terminal L of the photovoltaic inverter 100 is also connected to the load LOAD (e.g., connected to the live terminal of an AC load) via a switch S2, and the neutral terminal N of the photovoltaic inverter 100 is also connected to the load LOAD (e.g., connected to the neutral terminal of an AC load). Therefore, the photovoltaic inverter 100 can be controlled to supply power to the load LOAD by closing the switch S2, and the photovoltaic inverter 100 can be controlled to stop supplying power to the load LOAD by opening the switch S2.

[0148] For another example, the grid is also connected to the load LOAD via the bypass switch S3. Therefore, the bypass switch S3 can be controlled to be closed to control the grid to supply power to the load LOAD, and the bypass switch S3 can be controlled to be open to stop the grid from supplying power to the load LOAD.

[0149] In another embodiment of the present application, the photovoltaic inverter 100 further includes an energy storage module.

[0150] As an example, the energy storage module is connected to the MPPT module 10 to utilize the electric energy output by the photovoltaic cell 200 to charge the energy storage module through the MPPT module 10 .

[0151] As an example, the energy storage module is connected to the DC / AC module 20 to utilize the electric energy output by the photovoltaic cell 200 to charge the energy storage module through the MPPT module 10 and the DC / AC module 20 .

[0152] The impedance correction method of the insulation detection resistor R3 provided in the above embodiment can be applied to Figure 2 、 Figure 4 or Figure 5 In the photovoltaic inverter 100 shown, the embodiment of the present application does not impose any limitation on the specific type of the photovoltaic inverter 100 .

[0153] Figure 61 is a schematic diagram of the structure of a photovoltaic inverter 100 provided in one embodiment of the present application. Figure 6 As shown, the photovoltaic inverter 100 includes: at least one processor 60 ( Figure 6 Only one is shown), a memory 61, wherein the memory 61 stores a computer program 62 that can be run on the processor 60. When the processor 60 executes the computer program 62, the steps of the above-mentioned impedance correction method of the insulation detection resistor R3 are implemented, for example Figure 3 Steps S101 to S105 are shown.

[0154] The photovoltaic inverter 100 may include, but is not limited to, a processor 60 and a memory 61. Those skilled in the art will understand that Figure 6 The photovoltaic inverter 100 is merely an example and does not limit the photovoltaic inverter 100 . The photovoltaic inverter 100 may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the photovoltaic inverter 100 may also include an input transmission device, a network access device, a bus, etc.

[0155] The processor 60 may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor.

[0156] In some embodiments, the memory 61 may be an internal storage unit of the photovoltaic inverter 100, such as a hard drive or memory of the photovoltaic inverter 100. The memory 61 may also be an external storage device of the photovoltaic inverter 100, such as a plug-in hard drive, a smart media card (SMC), a secure digital (SD) card, a flash memory card, etc. equipped on the photovoltaic inverter 100. Furthermore, the memory 61 may include both an internal storage unit of the photovoltaic inverter 100 and an external storage device. The memory 61 is used to store an operating system, application programs, a boot loader, data, and other programs, such as the program code of the computer program. The memory 61 may also be used to temporarily store data that has been sent or is about to be sent.

[0157] An embodiment of the present application further provides a photovoltaic inverter, comprising at least one memory, at least one processor, and a computer program stored in the at least one memory and executable on the at least one processor. When the processor executes the computer program, the photovoltaic inverter implements the steps of any of the above-mentioned method embodiments.

[0158] An embodiment of the present application further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps in the above-mentioned various method embodiments can be implemented.

[0159] It should be understood that the size of the serial numbers of the steps in the above method embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0160] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0161] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0162] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0163] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0164] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. The impedance correction method of the insulation detection resistor of the photovoltaic inverter is characterized in that: The photovoltaic inverter includes a photovoltaic input terminal, an MPPT module, a DC / AC module, and an insulation impedance detection branch, wherein the photovoltaic input terminal, the MPPT module, and the DC / AC module are connected in sequence, the photovoltaic input terminal includes a positive input terminal and a negative input terminal, the insulation impedance detection branch is connected between the positive input terminal and the ground wire or between the negative input terminal and the ground wire, and the insulation impedance detection branch includes an insulation detection resistor and a switch connected in series; The impedance correction method comprises: When the photovoltaic inverter is connected to the grid, the DC / AC module operates in a bipolar SPWM modulation mode, and the insulation impedance detection branch is disconnected, changing the input voltage of the MPPT module; Acquire detection parameters under different input voltages; the detection parameters include a first leakage current, a first positive-to-ground voltage of the positive input terminal, and a first negative-to-ground voltage of the negative input terminal; Determining a first insulation impedance of the positive input terminal to ground and a second insulation impedance of the negative input terminal to ground based on the detection parameters under different input voltages; When the photovoltaic inverter is off-grid, the insulation impedance detection branch is turned on, and the MPPT module stops working, obtaining a second positive-pole-to-ground voltage of the positive input terminal and a second negative-pole-to-ground voltage of the negative input terminal; The impedance value of the insulation detection resistor is updated based on the first insulation impedance, the second insulation impedance, the second positive electrode-to-ground voltage, and the second negative electrode-to-ground voltage.

2. The impedance correction method according to claim 1, wherein: Changing the input voltage of the MPPT module includes: When the photovoltaic inverter is in a stable operating state, obtaining a first input voltage of the MPPT module; The duty cycle of the switch drive signal of the MPPT module is changed to change the input voltage of the MPPT module to a second input voltage; the second input voltage is different from the first input voltage.

3. The impedance correction method according to claim 2, wherein: The method for determining that the photovoltaic inverter is in the stable operating condition includes: detecting the output power of the photovoltaic inverter; When the output power of the photovoltaic inverter is greater than or equal to a preset power value, it is determined that the photovoltaic inverter is in a stable operating state.

4. The impedance correction method according to claim 1, wherein: After determining the first insulation impedance of the positive input terminal to ground and the second insulation impedance of the negative input terminal to ground based on the detection parameters at different input voltages, the impedance correction method further includes: detecting an output voltage of the photovoltaic inverter; At a moment corresponding to a zero-crossing point of the output voltage, the MPPT module is controlled to operate in a maximum power point tracking mode and the DC / AC module is controlled to operate in a unipolar SPWM modulation mode.

5. The impedance correction method according to claim 1, wherein: After updating the impedance value of the insulation detection resistor based on the first insulation impedance, the second insulation impedance, the second positive electrode-to-ground voltage, and the second negative electrode-to-ground voltage, the impedance correction method further includes: Before controlling the photovoltaic inverter to be grid-connected, obtaining the first insulation impedance and the second insulation impedance after correction based on the updated impedance value of the insulation detection resistor; When the corrected first insulation impedance and the corrected second insulation impedance are both greater than or equal to a preset impedance threshold, the photovoltaic inverter is controlled to be connected to the grid.

6. The impedance correction method according to claim 1, wherein: When the photovoltaic inverter is grid-connected, the DC / AC module operates in a bipolar SPWM modulation mode, and the insulation impedance detection branch is disconnected, before changing the input voltage of the MPPT module, the impedance correction method further includes: Before the photovoltaic inverter is connected to the grid, the modulation mode of the DC / AC module is configured as bipolar SPWM modulation.

7. The impedance correction method according to claim 1, wherein: After determining the first insulation impedance of the positive input terminal to ground and the second insulation impedance of the negative input terminal to ground based on the detection parameters at different input voltages, the impedance correction method further includes: Controlling the photovoltaic inverter to be off-grid; Stop sending the switch tube driving signal to the MPPT module to stop the MPPT module from working; The insulation impedance detection branch is controlled to be conductive.

8. The impedance correction method according to any one of claims 1 to 7, characterized in that: The impedance correction method further includes: Determining a preset duration based on the working environment of the photovoltaic inverter; The impedance value of the insulation detection resistor is updated at intervals of the preset time length.

9. A photovoltaic inverter comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the impedance correction method according to any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the impedance correction method according to any one of claims 1 to 8 are implemented.

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