CN114039544A

CN114039544A - Photovoltaic inverter, insulation impedance detection method and photovoltaic power generation system

Info

Publication number: CN114039544A
Application number: CN202111306955.6A
Authority: CN
Inventors: 吴子恒; 陈长春; 田燃; 常文宇
Original assignee: Sungrow Power Supply Co Ltd
Current assignee: Sungrow Power Supply Co Ltd
Priority date: 2021-11-05
Filing date: 2021-11-05
Publication date: 2022-02-11
Anticipated expiration: 2041-11-05
Also published as: CN114039544B

Abstract

A photovoltaic inverter, a detection method of insulation impedance and a photovoltaic power generation system relate to the technical field of photovoltaic power generation. The photovoltaic inverter comprises a rectifying circuit, an insulation impedance detection circuit and a controller. The first end of the insulation impedance detection circuit is connected with the direct current bus, the second end of the insulation impedance detection circuit is grounded, and the controllable switch is used for adjusting the size of the resistor connected into the insulation impedance detection circuit. The input end of the rectification circuit is connected with an alternating current power grid, and the output end of the rectification circuit is connected with a direct current bus. When the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifying circuit, the controller determines that the stable time spent on the ground voltage of the direct-current bus is a first time interval after the working state of the controllable switch is switched; and determining the insulation resistance to the ground of the direct current bus by using the voltage to the ground of any direct current bus after the controllable switch is closed for the first time interval and the voltage to the ground after the controllable switch is opened for the first time interval. The scheme improves the accuracy of ground insulation impedance detection.

Description

Photovoltaic inverter, insulation impedance detection method and photovoltaic power generation system

Technical Field

The application relates to the technical field of photovoltaic power generation, in particular to a photovoltaic inverter, an insulation impedance detection method and a photovoltaic power generation system.

Background

Photovoltaic power generation is a technology for converting light energy into electric energy by utilizing the photovoltaic effect of a semiconductor interface, and has been rapidly developed. The photovoltaic power generation system generally includes a photovoltaic module and a photovoltaic inverter, the photovoltaic module is configured to convert light energy into direct current, and the photovoltaic inverter is configured to convert the direct current transmitted by the photovoltaic module into alternating current and output the alternating current.

The direct current input end of the photovoltaic inverter is connected with a direct current bus, and the direct current bus comprises a positive direct current bus and a negative direct current bus. And the ground insulation resistance of the positive and negative direct current buses, namely the direct current end to ground insulation resistance of the photovoltaic inverter. Because the photovoltaic module, the cable and the like are generally placed in the open air and are influenced by dust, rain, snow, external force friction and the like, the direct-current end-to-ground insulation impedance of the photovoltaic inverter can be changed, and the safe operation of the photovoltaic power generation system is influenced, so that before the photovoltaic inverter starts to work, the direct-current end-to-ground insulation impedance of the photovoltaic inverter needs to be detected so as to protect the photovoltaic power generation system.

At present, when detecting the dc-to-ground insulation impedance of a photovoltaic inverter, a bridge method is generally adopted, as shown in fig. 1, an insulation impedance detection circuit 201 is arranged between a positive dc bus and a negative dc bus and ground, the insulation impedance detection circuit 201 includes a resistor network and a controllable switch, a resistor connected in the resistor network is changed by switching the working state of the controllable switch, and the ground insulation impedance of the positive dc bus and the negative dc bus is determined according to the resistance value of the connected resistor and the ground voltage of the positive dc bus and the negative dc bus. However, the photovoltaic modules included in the photovoltaic array 01 have distributed capacitance to ground, as shown in C1 and C2 in fig. 1, as the power level of the photovoltaic inverter 20 increases, the number of the photovoltaic modules increases, and the distributed capacitance becomes larger and larger, at this time, when the controllable switch in the insulation resistance control detection circuit 201 is controlled to be turned on or turned off, the voltage to ground of the positive and negative dc buses is inaccurate, and therefore the insulation resistance to ground of the positive and negative dc buses cannot be accurately obtained, which easily causes the false protection or the non-protection of the photovoltaic inverter, and reduces the safety of the photovoltaic power generation system.

Disclosure of Invention

In order to solve the technical problem, the application provides a photovoltaic inverter, a detection method of insulation resistance and a photovoltaic power generation system, so that the accuracy of ground insulation resistance detection is improved, and the safety of the photovoltaic power generation system is further improved.

In a first aspect, the present application provides a photovoltaic inverter for converting direct current into alternating current, an input of the photovoltaic inverter is connected to a photovoltaic array through a direct current bus, the direct current bus includes a positive direct current bus and a negative direct current bus, an output of the photovoltaic inverter is connected to an alternating current grid, the photovoltaic inverter includes: rectifier circuit, insulation impedance detection circuitry and controller. The first end of the insulation impedance detection circuit is connected with the direct current bus, the second end of the insulation impedance detection circuit is grounded, the insulation impedance detection circuit can be a resistor network and comprises a controllable switch, and the controllable switch is used for adjusting the size of a resistor connected into the insulation impedance detection circuit. The input end of the rectifying circuit is used for connecting an alternating current power grid, and the output end of the rectifying circuit is used for connecting a direct current bus. When the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the controller determines that the time when the ground voltage of the direct-current bus reaches a stable state after the working state of the controllable switch is switched is a first time interval, and the region time interval represents the influence time of the distributed capacitance charge-discharge of the photovoltaic module on the voltage measurement. The controller then determines the insulation resistance to ground of the dc bus using the voltage to ground of either dc bus after the controllable switch is closed for the first time interval and the voltage to ground after the controllable switch is open for the first time interval.

In summary, according to the technical scheme of the application, when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifier circuit, no matter how the illumination changes in the detection process, the output voltage of the photovoltaic module is clamped to the output voltage of the rectifier circuit, and therefore the influence of the illumination change on the voltage detection accuracy is eliminated. On the other hand, after the working state of the controllable switch is switched, for example, the state is switched from open to closed, or the state is switched from closed to open, when the voltage of the direct current bus to the ground reaches stable use, that is, when the voltage of the direct current bus to the ground is charged and discharged, according to the scheme of the application, after the first time interval is detected, the charging and discharging of the distributed capacitor are completed, the detected voltage to the ground is a stable true value, then the impedance of the direct current bus to the ground is calculated by using the voltage of the direct current bus to the ground, so that the accuracy of the impedance detection of the ground insulation is improved, and further the safety of the photovoltaic power generation system is improved.

In one possible implementation manner, when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the controller determines that the time spent on the voltage to ground of the negative direct-current bus or the positive direct-current bus reaching the stable state is a first time interval after controlling the controllable switch to be switched from the open state to the closed state.

When the voltage to ground of one direct current bus reaches a stable state, the distributed capacitance of the photovoltaic array can be determined to finish charging and discharging.

In a possible implementation manner, the photovoltaic inverter further includes a transformer, an input end of the transformer is connected to the ac power grid, an output end of the transformer is connected to an input end of the rectification circuit, and the transformer is configured to boost an input voltage of the transformer.

Through setting up the transformer, can promote the alternating current that rectifier circuit's input is connected, and then promote the voltage of rectifier circuit output to with the voltage clamp of photovoltaic array to higher voltage.

In one possible implementation, the output voltage of the rectifying circuit is equal to the maximum open circuit voltage of the photovoltaic array.

No matter how the illumination intensity changes at this moment, photovoltaic array output end voltage clock is by the clamp to the maximum open circuit voltage, consequently can eliminate the illumination intensity and change the influence to voltage detection accuracy to after the voltage is by the clamp to the maximum open circuit voltage, can directly carry out the detection of first time interval, promoted the convenience.

In one possible implementation manner, the controller is configured to determine a voltage to ground of the first dc bus as a first voltage after controlling the controllable switch to be turned off for a first time interval; and after the controllable switch is controlled to be closed for a first time interval, determining that the voltage to ground of the first direct current bus is a second voltage, and determining the insulation impedance to ground of the direct current bus by using the output voltage of the rectifying circuit, the first voltage and the second voltage, wherein the first direct current bus is a positive direct current bus or a negative direct current bus.

It will be appreciated that the controller may also control the controllable switch to open for a first time interval before controlling the controllable switch to close for a first time interval.

In one possible implementation, the output voltage of the rectifier circuit is less than the maximum open circuit voltage of the photovoltaic array.

At this time, the power consumption of the rectifier circuit and the step-up transformer can be properly reduced to reduce the power consumption in the insulation resistance detection process.

In a possible implementation manner, the controller is specifically configured to determine that a voltage to ground of the first dc bus is a first voltage after the controllable switch is controlled to be turned off for a first time interval; after the controllable switch is controlled to be closed for a first time interval, the voltage to ground of the first direct current bus is determined to be a second voltage, when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, the voltage to ground of the direct current bus is determined by using the output voltage, the first voltage and the second voltage of the rectifying circuit, and the first direct current bus is a positive direct current bus or a negative direct current bus.

When the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, namely the direct current bus voltage is always clamped to the output voltage of the rectifying circuit, the influence of the illumination intensity change on the direct current bus voltage at the moment can be ignored.

In one possible implementation manner, when the current open-circuit voltage of the photovoltaic array is greater than the output voltage of the rectifying circuit, or when the voltage between the direct-current buses is greater than the output voltage of the rectifying circuit, the controller controls the controllable switch to be switched off for a first time interval, then the voltage to ground of the first direct-current bus is determined to be the third voltage, and the voltage between the direct-current buses is determined to be the fifth voltage. After the controller controls the controllable switch to be closed for a first time interval, the voltage to ground of the first direct current bus is determined to be a fourth voltage, and the voltage between the direct current buses is determined to be a sixth voltage. When the difference value of the fifth voltage and the sixth voltage is within a preset voltage range, the change of the characterization illumination intensity in the first time interval is small, the influence on the voltage of the direct current bus is small, and at the moment, the controller determines the insulation resistance of the direct current bus to the ground by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.

In one possible implementation, the rectifier circuit is a bridge rectifier circuit employing diodes.

The diode bridge rectifier circuit is adopted to avoid common-mode interference caused by high-frequency switching-on and switching-off of the power switch device, so that the accuracy of ground insulation impedance calculation can be improved.

In one possible implementation, the insulation resistance detection circuit includes a first branch, a second branch, and a third branch. The first end of the first branch circuit is connected with the positive direct current bus, the first end of the second branch circuit is connected with the negative direct current bus, and the second end of the first branch circuit and the second end of the second branch circuit are grounded through the third branch circuit. The third branch comprises a controllable switch for adjusting the resistance of the third branch.

In a second aspect, the present application provides an insulation resistance detection method applied to a photovoltaic inverter, the method including:

when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, determining that the stable time spent on the ground voltage of the direct-current bus after the working state of the controllable switch is switched is a first time interval;

and determining the insulation resistance to the ground of the direct current bus by using the voltage to the ground of any direct current bus after the controllable switch is closed for the first time interval and the voltage to the ground after the controllable switch is opened for the first time interval.

In summary, with the method provided by the present application, when the current open circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifier circuit, no matter how the illumination changes in the detection process, the output voltage of the photovoltaic module is clamped to the output voltage of the rectifier circuit, thereby eliminating the influence of the illumination change on the voltage detection accuracy. On the other hand, after the working state of the controllable switch is switched, for example, the state is switched from open to closed, or the state is switched from closed to open, when the voltage of the direct current bus to the ground reaches stable use, that is, when the voltage of the direct current bus to the ground is charged and discharged, according to the scheme of the application, after the first time interval is detected, the charging and discharging of the distributed capacitor are completed, the detected voltage to the ground is a stable true value, then the impedance of the direct current bus to the ground is calculated by using the voltage of the direct current bus to the ground, so that the accuracy of the impedance detection of the ground insulation is improved, and further the safety of the photovoltaic power generation system is improved.

In a possible implementation manner, when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifier circuit, it is determined that the time taken for the ground voltage of the dc bus to reach the steady state after the operating state of the controllable switch is switched is a first time interval, and specifically, the method includes:

when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, after the controllable switch is controlled to be switched from the off state to the on state, the time spent on the voltage to ground of the negative direct-current bus or the positive direct-current bus reaching the stable state is determined to be a first time interval.

In a possible implementation manner, determining the ground insulation resistance of the dc bus by using the ground voltage of any dc bus after the controllable switch is closed for the first time interval and the ground voltage of any dc bus after the controllable switch is opened for the first time interval specifically includes:

after the controllable switch is controlled to be switched off for a first time interval, determining that the voltage to ground of the first direct current bus is a first voltage, and the first direct current bus is a positive direct current bus or a negative direct current bus;

after the controllable switch is controlled to be closed for a first time interval, determining the voltage to ground of the first direct current bus as a second voltage;

and determining the insulation resistance of the direct current bus to the ground by using the output voltage of the rectifying circuit, the first voltage and the second voltage.

when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, the ground insulation impedance of the direct current buses is determined by the output voltage of the rectifying circuit, the first voltage and the second voltage.

In one possible implementation, the method further includes:

when the current open-circuit voltage of the photovoltaic array is greater than the output voltage of the rectifying circuit, or when the voltage between the direct-current buses is greater than the output voltage of the rectifying circuit, after the controllable switch is controlled to be switched off for a first time interval, determining the voltage to ground of the first direct-current bus as a third voltage, and determining the voltage between the direct-current buses as a fifth voltage;

after the controllable switch is controlled to be closed for a first time interval, determining that the voltage to ground of the first direct current bus is fourth voltage, and determining that the voltage between the direct current buses is sixth voltage;

and when the difference value of the fifth voltage and the sixth voltage is within a preset voltage range, determining the insulation resistance of the direct current bus to the ground by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.

In a third aspect, the present application further provides a photovoltaic power generation system, where the photovoltaic power generation system includes the photovoltaic inverter provided in the foregoing implementation manner, and further includes a plurality of photovoltaic modules. The photovoltaic modules are used for converting light energy into direct current and transmitting the direct current to the input end of the photovoltaic inverter. The output end of the photovoltaic inverter is the output end of the photovoltaic power generation system. The plurality of photovoltaic modules may be connected in series to form a photovoltaic array, or the plurality of photovoltaic modules may be connected in series to form a plurality of photovoltaic string, and the plurality of photovoltaic string are then connected in parallel to form the photovoltaic array, which is not specifically limited in this application.

This photovoltaic inverter of photovoltaic power generation system can detect and obtain the time that distributed capacitance charge-discharge accomplished to when distributed capacitance charge-discharge accomplished back, reuse the detected value of the voltage to ground confirm the insulation impedance to ground of direct current generating line, promoted the accuracy when the insulation impedance to ground detects, and then promoted photovoltaic power generation system self security.

Drawings

FIG. 1 is a schematic diagram of an insulation resistance detection circuit;

FIG. 2 is a schematic diagram of a photovoltaic power generation system;

FIG. 3 is a schematic view of another photovoltaic power generation system;

fig. 4 is a schematic diagram of a photovoltaic inverter provided in an embodiment of the present application;

fig. 5 is a schematic diagram of another photovoltaic inverter provided in an embodiment of the present application;

fig. 6 is a schematic diagram of an insulation resistance detection circuit according to an embodiment of the present application;

fig. 7 is a flowchart of a method for detecting insulation resistance according to an embodiment of the present application;

fig. 8 is a flowchart of another insulation resistance detection method according to an embodiment of the present application;

fig. 9 is a flowchart of another insulation resistance detection method provided in the embodiment of the present application;

fig. 10 is a schematic view of a photovoltaic power generation system according to an embodiment of the present application.

Detailed Description

In order to make the technical solution more clearly understood by those skilled in the art, an application scenario of the technical solution of the present application is first described below.

Referring to fig. 2, a schematic diagram of a photovoltaic power generation system is shown.

The illustrated photovoltaic power generation system includes a photovoltaic inverter 20 and a plurality of photovoltaic modules 10. The output end of the photovoltaic module 10 is connected with the input end of the photovoltaic inverter 20, and the output end of the photovoltaic inverter 20 is connected with the alternating current power grid 40.

The photovoltaic module 10 is a dc power supply formed by series and parallel packaging of solar cells.

A plurality of photovoltaic modules 10 can form a photovoltaic group string in a mode of connecting positive electrodes and negative electrodes in series end to form a photovoltaic array; the plurality of photovoltaic modules 10 may also be connected in series to form a plurality of photovoltaic strings, and then the plurality of photovoltaic strings are connected in parallel to form a photovoltaic array, which is not specifically limited in this application.

Referring to fig. 3, a schematic view of another photovoltaic power generation system is shown.

The illustrated photovoltaic power generation system includes: an ac combiner box 30, a plurality of photovoltaic modules 10, and a plurality of photovoltaic inverters 20.

The dc side of the pv inverter 20 is connected to one or more pv modules 10, and in practical applications, the dc side of the pv inverter 20 is generally connected to a plurality of pv modules 10.

The photovoltaic inverter 20 may include two power conversion circuits, a Direct Current (DC) -DC conversion circuit in the first stage, and a Direct Current (AC) conversion circuit, that is, an inverter circuit in the second stage.

The ac power output by the photovoltaic inverters 20 is collected by the ac combiner box 30 and then connected to the ac power grid 904.

For the photovoltaic inverter 20 in each photovoltaic power generation system, the dc input end of the photovoltaic inverter is connected to a dc bus, and the dc bus includes a positive dc bus and a negative dc bus. And the ground insulation resistance of the positive and negative direct current buses, namely the direct current end to ground insulation resistance of the photovoltaic inverter.

Because the photovoltaic module, the cable and the like are generally placed in the open air and are influenced by dust, rain, snow, external force friction and the like, the direct-current end ground insulation impedance of the photovoltaic inverter can be changed, and the safe operation of the photovoltaic power generation system is influenced, so that before the photovoltaic inverter starts to work, the direct-current end ground insulation impedance of the photovoltaic inverter needs to be detected so as to protect the photovoltaic power generation system and further ensure that the photovoltaic inverter can be safely connected to the grid.

At present, when the direct current terminal of the photovoltaic inverter is detected as the ground insulation impedance, a bridge method is generally adopted, but as the power level of the photovoltaic inverter 20 is increased, the number of the photovoltaic modules 10 is continuously increased, so that the distributed capacitance of the photovoltaic modules 10 is increased, and at the moment, when a controllable switch in the insulation impedance detection circuit 201 is controlled to be turned on or turned off, the influence of the discharge of the distributed capacitance is received, so that the collected ground voltages of the positive and negative direct current buses are inaccurate, further, the ground insulation impedances of the positive and negative direct current buses cannot be accurately obtained, the photovoltaic inverter is easily subjected to error protection or no protection, and the safety of a photovoltaic power generation system is reduced.

In order to solve the above problems, embodiments of the present application provide a photovoltaic inverter, a detection method of insulation resistance, and a photovoltaic power generation system. When the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the controller of the photovoltaic inverter determines that the earth voltage of the direct-current bus is the first time interval after the working state of the controllable switch is switched, namely, the charging and discharging time of the distributed capacitor is determined when the working state of the switch is switched, the earth voltage of any direct-current bus after the first time interval of the controllable switch is closed and the earth voltage after the first time interval of the controllable switch is disconnected are utilized to determine the earth insulation impedance of the direct-current bus, so the accuracy of the earth insulation impedance detection of the positive direct-current bus and the negative direct-current bus is improved, and the safety of a photovoltaic power generation system is further improved.

In order to make the technical solutions more clearly understood by those skilled in the art, the technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application.

The terms "first", "second", and the like in the description of the present application are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated

In the present application, unless expressly stated or limited otherwise, the term "coupled" is to be construed broadly, e.g., "coupled" may be a fixed connection, a removable connection, or an integral part; may be directly connected or indirectly connected through an intermediate.

The embodiment of the application provides a photovoltaic inverter, and the output of photovoltaic inverter can connect three-phase alternating current electric wire netting or two-phase alternating current electric wire netting, all uses the output of photovoltaic inverter to connect three-phase alternating current electric wire netting as the example in following drawings and explains, and the principle when connecting two-phase alternating current electric wire netting is similar, no longer gives details.

Referring to fig. 4, the drawing is a schematic diagram of a photovoltaic inverter provided in an embodiment of the present application.

The input of the illustrated photovoltaic inverter 20 is connected to the photovoltaic array 01 via a dc bus, and the output of the photovoltaic inverter 20 is connected to an ac power grid 40. The photovoltaic inverter 20 includes: an insulation resistance detection circuit 201, a rectifier circuit 202, a controller 203 and an inverter circuit 204.

The inverter circuit 204 may be a two-level inverter circuit or a multi-level inverter circuit, which is not specifically limited in this embodiment. The inverter circuit 204 is configured to convert a direct current into an alternating current, and the specific implementation manner and the working principle of the inverter circuit 204 are relatively mature technologies, which are not described herein again in this embodiment of the application.

The first point of the insulation resistance detection circuit 201 is connected to the dc line, that is, to the positive dc BUS (BUS +) and the negative dc BUS (BUS-). The second terminal of the insulation resistance detection circuit 201 is grounded. The insulation resistance detection circuit 201 includes a resistor network and a controllable switch S1. When the operating state of the controllable switch S1 changes, the size of the resistor connected to the insulation resistance detection circuit 201 can be adjusted, and the detection value of the dc bus to the ground voltage can be changed.

The controller 203 is capable of controlling the operating state of the controllable switch S1. When the current open-circuit voltage of the photovoltaic array 01 is smaller than or equal to the output voltage of the rectifying circuit 202, the voltage between the direct-current buses is clamped to be equal to the output voltage of the rectifying circuit 202, the controller 203 controls the controllable switch S1 to be switched from the off state to the on state at the moment, or controls the controllable switch S1 to be switched from the on state to the off state, namely controls the controllable switch S1 to be switched to the working state, and then the time when the voltage to ground of the direct-current buses reaches the stable voltage is determined as a first time interval. The first time interval is the time taken for charging or discharging the distributed capacitance of the photovoltaic array 01.

In practical applications, the controller 203 may switch the operation state of the controllable switch S1 for a plurality of times, so as to obtain a plurality of first time intervals, and reduce the measurement error by averaging.

After determining the first time interval, the controller 203 controls the controllable switch S1 to close the first time interval, so that the charging and discharging of the distributed capacitor of the photovoltaic array 01 are completed, and the voltage to ground of one dc bus is obtained; and then, the controllable switch S1 is controlled to be switched off for a first preset time interval, so that the voltage to ground of the direct current bus is obtained again after the distributed capacitor of the photovoltaic array 01 is charged and discharged. The obtained direct-current voltage is the real voltage of the direct-current bus to the ground, and the influence of the distributed capacitance of the photovoltaic array on the detection value of the direct-current bus to the ground voltage is reduced. The obtained voltage may be a voltage of the positive dc bus or a voltage of the negative dc bus, which is not limited in this embodiment of the application.

In other embodiments, the controller 203 may also control the controllable switch S1 to open for a first time interval before controlling the controllable switch S1 to close for a first time interval, which is not described herein again.

In summary, according to the technical scheme provided by the embodiment of the present application, when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifier circuit, no matter how the illumination changes in the detection process, the output voltage of the photovoltaic module is clamped to the output voltage of the rectifier circuit, and therefore the influence of the illumination change on the voltage detection accuracy is eliminated. On the other hand, after the working state of the controllable switch is switched, for example, the state is switched from open to closed, or the state is switched from closed to open, when the voltage of the direct current bus to the ground reaches stable use, that is, when the voltage of the direct current bus to the ground is charged and discharged, according to the scheme of the application, after the first time interval is detected, the charging and discharging of the distributed capacitor are completed, the detected voltage to the ground is a stable true value, then the impedance of the direct current bus to the ground is calculated by using the voltage of the direct current bus to the ground, so that the accuracy of the impedance detection of the ground insulation is improved, and further the safety of the photovoltaic power generation system is improved.

The type of controllable switch S1 may be any one or a combination of more than one of the following: a relay, an Insulated Gate Bipolar Transistor (IGBT), a Metal Oxide Semiconductor field Effect Transistor (MOSFET, hereinafter referred to as MOS Transistor), a Silicon Carbide field Effect Transistor (SiC MOSFET), and the like, and embodiments of the present invention are not particularly limited.

The controller 203 may be an Application Specific Integrated Circuit (ASIC), a Programmable Logic Device (PLD), a Digital Signal Processor (DSP), or a combination thereof. The PLD may be a Complex Programmable Logic Device (CPLD), a Field-Programmable Gate Array (FPGA), a General Array Logic (GAL), or any combination thereof, and the embodiments of the present invention are not limited in particular.

The following description is made with reference to specific implementations.

Referring to fig. 5, a schematic diagram of another photovoltaic inverter provided in the practice of the present application is shown.

The embodiment of the present application is different from the embodiment corresponding to fig. 4 in that the embodiment further includes: a transformer 205.

The input end of the transformer 205 is connected to the ac power grid, the output end of the transformer 205 is connected to the input end of the rectifier circuit 202, and the transformer 205 is configured to boost the voltage to boost the input voltage of the rectifier circuit 202, so as to boost the output voltage of the rectifier circuit.

In a possible implementation manner, the rectifier circuit 202 is a diode full-bridge rectifier circuit, that is, a diode bridge is used to rectify the alternating current, and a controllable switching device is not used in the rectifier circuit 202. The common-mode interference can be brought by the controllable switching device when the controllable switching device is switched on or switched off at high frequency, and further, the sampling result of the voltage of the direct-current bus to the ground can be influenced by the distributed capacitance loop, so that the detection error of the insulation resistance of the direct-current bus to the ground is improved.

The following describes a method for detecting the insulation resistance of the dc bus to ground.

First, an implementation when the output voltage of the rectifier circuit 202 is equal to the maximum open circuit voltage of the photovoltaic array 01 will be described.

At this time, regardless of the variation of the illumination intensity, the output voltage of the photovoltaic array 01 is always clamped to be equal to the output voltage of the rectifying circuit 202, so that the influence of the variation of the illumination intensity on the detection result is eliminated.

At this time, after the controller 203 controls the controllable switch S1 to switch from open to closed, it is determined that the time taken for the voltage to ground of the positive dc bus or the negative dc bus to reach the steady state is the first time interval.

The first time interval is stored when the distributed capacitance of the photovoltaic array 01 is charged or discharged, that is, the influence time caused by the distributed capacitance is determined.

After the controller 203 controls the controllable switch S1 to open for the first time interval, it determines the voltage to ground of the first dc bus as the first voltage. After the controller 203 controls the controllable switch S1 to close for a first time interval, the ground voltage of the first dc bus is determined to be a second voltage, and the ground insulation impedance of the dc bus is determined by using the output voltage of the rectifying circuit, the first voltage and the second voltage, where the first dc bus is a positive dc bus or the negative dc bus.

The following description is made with reference to a specific implementation of the insulation resistance detection circuit 201.

Referring to fig. 6, the diagram is a schematic diagram of an insulation resistance detection circuit according to an embodiment of the present application.

The insulation resistance detection circuit 201 includes a first branch, a second branch, and a third branch. The first end of the first branch circuit is connected with the positive direct current bus, the first end of the second branch circuit is connected with the negative direct current bus, and the second end of the first branch circuit and the second end of the second branch circuit are grounded through the third branch circuit. The third branch comprises a controllable switch for adjusting the resistance of the third branch.

For illustration, the present application only exemplifies that the first branch includes a resistor R1, the second branch includes a resistor R2, and the third branch includes a resistor R3, where the controllable switch S1 is connected in parallel with R2.

The earth insulation resistance of the positive direct current bus is R +, and the earth insulation resistance of the negative direct current bus is R-. After the controllable switch S1 is continuously disconnected for a first time interval, R1 is connected to the first branch, R2 is connected to the second branch, and R3 is connected to the third branch, at this time, the equivalent parallel resistance R4 of R + satisfies:

R4＝R1+R3+R1*R3/R2 (1)

the equivalent parallel resistance R5 of R-at this time satisfies:

R5＝R2+R3+R2*R3/R1 (2)

at this time, the voltage to ground of the positive dc bus is V1, the voltage to ground of the negative dc bus is V2, and the voltage between the dc buses is Vo, there is the following equation:

V1-V2＝Vo (3)

after the controllable switch S1 is continuously closed for a first time interval, R1 is connected to the first branch, R2 is short-circuited, R3 is connected to the third branch, the equivalent parallel resistance of R + is changed from R4 to infinity, and the equivalent parallel resistance of R-is changed from R5 to R3. At this time, the voltage to ground of the positive dc bus is V3, the voltage to ground of the negative dc bus is V4, and the voltage between the dc buses is Vo, there is the following equation:

V3-V4＝Vo (5)

the earth insulation resistance R + of the positive direct current bus and the earth insulation resistance R-of the negative direct current bus can be determined by solving the equation.

The voltage between the dc buses is Vo, that is, the output voltage of the rectifying circuit 202, and is a known quantity, and at this time, the voltage to ground of one dc bus is determined, that is, the voltage to ground of the other dc bus is determined. Namely, the first voltage is V1, and the second voltage is V3; alternatively, the first voltage is V2 and the second voltage is V4.

The above is only one possible implementation manner of the insulation resistance detection circuit 201, and when the insulation resistance detection circuit 201 adopts a similar calculation principle of other implementation manners, the details are not repeated herein.

It can be understood that, in practical applications, the output voltage of the rectifying circuit 202 may be set to be slightly smaller than the maximum open-circuit voltage of the photovoltaic array 01, so as to protect the photovoltaic array 01.

The following describes an implementation when the output voltage of the rectifier circuit 202 is less than the maximum open circuit voltage of the photovoltaic array 01.

When the current open-circuit voltage of the photovoltaic array 01 is smaller than or equal to the output voltage of the rectifying circuit 202, the voltage between the direct-current buses is clamped to be equal to the output voltage of the rectifying circuit 202, the controller 203 controls the controllable switch S1 to be switched from the off state to the on state at the moment, or controls the controllable switch S1 to be switched from the on state to the off state, namely controls the controllable switch S1 to be switched to the working state, and then the time when the voltage to ground of the direct-current buses reaches the stable voltage is determined as a first time interval. The first time interval is the time taken for charging or discharging the distributed capacitance of the photovoltaic array 01.

After the controller 203 stores the first time interval, after controlling the controllable switch S1 to turn off the first time interval, determining the voltage to ground of the first dc bus as a first voltage; after the controllable switch is controlled to be closed for a first time interval, the voltage to ground of the first direct current bus is determined to be a second voltage, and when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit 202, the ground insulation impedance of the direct current bus is determined by using the output voltage of the rectifying circuit, the first voltage and the second voltage, wherein the first direct current bus is a positive direct current bus or a negative direct current bus.

That is, at this time, the controller 203 needs to ensure that the voltage between the dc buses is always clamped to be equal to the output voltage of the rectifier circuit 202 during the detection process, so as to eliminate the influence of the sudden change of the illumination intensity on the voltage detection. When the voltage between the dc buses is equal to the output voltage of the rectifier circuit 202, representing that the illumination intensity is not suddenly increased at this time, that is, the output voltage of the photovoltaic array 01 is not suddenly increased to exceed the output voltage of the rectifier circuit 202, the controller 203 may determine the ground insulation resistance R + of the positive dc bus and the ground insulation resistance R-of the negative dc bus according to the processes of the above equations (1) to (6).

It can be understood that, after the first voltage is obtained, the operating state of the controllable switch is switched, and the second voltage value is obtained after the first time interval, that is, the above detection method generally requires that the illumination intensity is not suddenly and significantly increased within the time length of the first time interval.

In a possible implementation manner, when the controller 203 determines that the voltage between the dc buses is always greater than the output voltage of the rectifier circuit 202, the current voltage sampling result is discarded and the above detection process is restarted, so as to loop until the first voltage and the second voltage meeting the condition are obtained.

In another possible implementation manner, when it is determined that the current open-circuit voltage of the photovoltaic array is greater than the output voltage of the rectifier circuit, or when the voltage between the dc buses is greater than the output voltage of the rectifier circuit in the above detection process, it indicates that the voltage detection may be greatly affected by the sudden change of the illumination intensity at this time, after the controller 203 controls the controllable switch S1 to be turned off for the first time interval, it is determined that the voltage to ground of the first dc bus is the third voltage, and it is determined that the voltage between the dc buses is the fifth voltage; and after the controllable switch is controlled to be closed for a first time interval, determining that the voltage to ground of the first direct current bus is fourth voltage, and determining that the voltage between the direct current buses is sixth voltage.

When the difference value of the fifth voltage and the sixth voltage is within the preset voltage range, the controller 203 determines the insulation resistance of the direct current bus to the ground by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.

It can be understood that, the obtaining time interval of the fifth voltage and the sixth voltage is a first time interval, and when the difference value between the fifth voltage and the sixth voltage is within a preset voltage range, that is, the voltage change of the dc bus within the first time interval is within the preset voltage range, the representation that the illumination intensity is relatively stable in the detection process at this time and does not change suddenly is performed.

At this time, the voltage between the direct current buses is greater than the output voltage of the rectifying circuit 202, so that the voltage between the direct current buses and the voltage to ground of one direct current bus need to be acquired, and the voltage to ground of the other direct current bus is further determined; or the voltages to ground of the two dc buses are collected separately, and the following description will proceed with an example of the insulation resistance detection circuit shown in fig. 6.

When the controllable switch S1 is continuously turned off for the first time interval, the voltage to ground of the positive dc bus is V1, the voltage to ground of the negative dc bus is V2, and the voltage between the dc buses, i.e. the fifth voltage, is Vo1, there is the following formula:

V1-V2＝Vo1 (7)

after the controllable switch S1 is continuously closed for the first time interval, the voltage to ground of the positive dc bus is V3, the voltage to ground of the negative dc bus is V4, and the voltage between the dc buses, i.e. the sixth voltage is Vo2, then the following formula exists:

V3-V4＝Vo2 (8)

when the difference value between Vo1 and Vo2 is within the preset voltage range, the controller 203 determines that the detected value of the dc bus line-to-ground voltage at that time is valid, and further determines the ground insulation resistance R + of the positive dc bus and the ground insulation resistance R-of the negative dc bus.

When the first direct current bus is a positive direct current bus, the third voltage is V1, and the fourth voltage is V3; or when the first direct current bus is a negative direct current bus, the third voltage is V2, and the fourth voltage is V3.

In conclusion, by the technical scheme provided by the embodiment of the application, the influence of the distributed capacitance and illumination intensity change of the photovoltaic array on the detection of the insulation impedance of the direct current bus by adopting a bridge method can be obviously reduced, the accuracy of the detection of the insulation impedance of the ground is improved, and the safety of a photovoltaic power generation system is further improved.

Based on the photovoltaic inverter provided by the above embodiment, the embodiment of the present application further provides a method for detecting insulation of a dc line of the photovoltaic inverter, which is specifically described below with reference to the accompanying drawings.

Referring to fig. 7, the figure is a flowchart of an insulation detection method according to an embodiment of the present application.

For specific implementation of the photovoltaic inverter, reference may be made to the description of the above embodiments, which is not repeated herein, and the method includes the following steps:

s301: when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the stable time interval is determined after the ground voltage of the direct-current bus is switched in the working state of the controllable switch.

When the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, the voltage between the direct-current buses is clamped to be equal to the output voltage of the rectifying circuit, the controllable switch is controlled to be switched to be in a conducting state from a disconnecting state at the moment, or the controllable switch is controlled to be switched to be in a disconnecting state from a conducting state, namely the controllable switch is controlled to be switched to be in a working state, and then the first time interval is determined when the voltage to ground of the direct-current buses is stable.

The first time interval is the time taken for charging or discharging the distributed capacitance of the photovoltaic array.

S302: and determining the insulation resistance to the ground of the direct current bus by using the voltage to the ground of any direct current bus after the controllable switch is closed for the first time interval and the voltage to the ground after the controllable switch is opened for the first time interval.

Controlling the controllable switch to be closed for a first time interval so as to obtain the voltage to ground of one direct current bus after the distributed capacitor of the photovoltaic array is charged and discharged; and then, the controllable switch is controlled to be switched off for a first preset time interval, so that the voltage to ground of the direct current bus is obtained again after the distributed capacitor of the photovoltaic array is charged and discharged. The obtained direct-current voltage is the real voltage of the direct-current bus to the ground, and the influence of the distributed capacitance of the photovoltaic array on the detection value of the direct-current bus to the ground voltage is reduced. The obtained voltage may be a voltage of the positive dc bus or a voltage of the negative dc bus, which is not limited in this embodiment of the application.

In other embodiments, the controllable switch may be controlled to open for the first time interval first, and then the controllable switch is controlled to close for the first time interval, which is not described herein again.

The following description is made in conjunction with specific process steps.

Referring to fig. 8, the figure is a flowchart of another insulation resistance detection method provided in the embodiment of the present application.

The following first describes an implementation when the output voltage of the rectifier circuit is equal to the maximum open circuit voltage of the photovoltaic array, the method comprising the steps of:

s401: after the controllable switch is controlled to be switched off for a first time interval, the voltage to ground of the first direct current bus is determined to be a first voltage, and the first direct current bus is a positive direct current bus or a negative direct current bus.

S402: and after the controllable switch is controlled to be closed for a first time interval, determining the voltage to ground of the first direct current bus as a second voltage.

S403: and determining the insulation resistance of the direct current bus to the ground by using the output voltage of the rectifying circuit, the first voltage and the second voltage.

Referring to fig. 9, it is a flowchart of another insulation resistance detection method provided in the embodiments of the present application.

The following describes an implementation when the output voltage of the rectifier circuit is less than the maximum open circuit voltage of the photovoltaic array, and the method includes the following steps:

s501: and judging whether the current open-circuit voltage of the photovoltaic array is greater than the output voltage of the rectifying circuit.

If not, go to step S502, and if so, go to step S506.

S502: after the controllable switch is controlled to be switched off for a first time interval, the voltage to ground of the first direct current bus is determined to be a first voltage, and the first direct current bus is a positive direct current bus or a negative direct current bus.

S503: and after the controllable switch is controlled to be closed for a first time interval, determining the voltage to ground of the first direct current bus as a second voltage.

S504: and judging whether the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit.

If yes, go to S505; if not, go to step S506.

S505: and determining the insulation resistance of the direct current bus to the ground by using the output voltage of the rectifying circuit, the first voltage and the second voltage.

S506: and after the controllable switch is controlled to be switched off for a first time interval, determining the voltage to ground of the first direct current bus as a third voltage, and determining the voltage between the direct current buses as a fifth voltage.

S507: and after the controllable switch is controlled to be closed for a first time interval, determining that the voltage to ground of the first direct current bus is fourth voltage, and determining that the voltage between the direct current buses is sixth voltage.

S508: it is determined whether a difference between the fifth voltage and the sixth voltage is within a preset voltage range.

If yes, go to S509; if not, go to step S506.

S509: and determining the insulation resistance of the direct current bus to the ground by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.

The division of the above steps is only for convenience of description, and does not limit the technical scheme of the present application, and those skilled in the art can also make appropriate adjustments to the above steps when implementing the method. For example, the sequence of S401 and S402 may be switched, that is, the controllable switch is controlled to be closed first, and then the controllable switch is controlled to be opened.

In summary, with the method provided by the embodiment of the present application, when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifier circuit, no matter how the illumination changes in the detection process, the output voltage of the photovoltaic module is clamped to the output voltage of the rectifier circuit, thereby eliminating the influence of the illumination change on the voltage detection accuracy.

On the other hand, after the working state of the controllable switch is switched, for example, the state is switched from open to closed, or the state is switched from closed to open, when the voltage of the direct current bus to the ground reaches stable use, that is, when the voltage of the direct current bus to the ground is charged and discharged, according to the scheme of the application, after the first time interval is detected, the charging and discharging of the distributed capacitor are completed, the detected voltage to the ground is a stable true value, then the impedance of the direct current bus to the ground is calculated by using the voltage of the direct current bus to the ground, so that the accuracy of the impedance detection of the ground insulation is improved, and further the safety of the photovoltaic power generation system is improved.

Based on the photovoltaic inverter provided by the above embodiments, the embodiments of the present application further provide a photovoltaic power generation system, which is specifically described below with reference to the accompanying drawings.

Referring to fig. 10, the figure is a schematic view of a photovoltaic power generation system provided in an embodiment of the present application.

The illustrated photovoltaic power generation system 100 includes a photovoltaic array 01 and a photovoltaic inverter 20.

Wherein the photovoltaic array 01 comprises a plurality of photovoltaic modules 10, in some embodiments, a plurality of photovoltaic modules 10 may be connected in series to form a photovoltaic module 10; in other embodiments, a plurality of photovoltaic modules 10 may be connected in series to form a plurality of photovoltaic strings, which are then connected in parallel to form the photovoltaic array 01.

Photovoltaic inverter 20 may include a single stage power conversion circuit, i.e., only a DC-AC conversion circuit; the photovoltaic inverter 20 may further include a two-stage power conversion circuit, where the first stage is a DC-DC conversion circuit, and the second stage is a DC-AC conversion circuit, that is, an inverter circuit, which is not particularly limited in this embodiment of the present application.

For specific implementation and operation principle of the photovoltaic inverter 20, reference may be made to the relevant description in the above embodiments, and the embodiments of the present application are not described herein again.

To sum up, the controller of the photovoltaic inverter 20 provided in the embodiment of the present application can detect the time required for completing the charging and discharging of the distributed capacitor, and after the charging and discharging of the distributed capacitor are completed, determine the ground insulation impedance of the dc bus by using the detected value of the ground voltage, thereby improving the accuracy of the ground insulation impedance detection, and further improving the safety of the photovoltaic power generation system.

It should be understood that in the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" for describing an association relationship of associated objects, indicating that there may be three relationships, e.g., "a and/or B" may indicate: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b, c may be single or plural.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. The above-described apparatus embodiments are merely illustrative, and the units and modules described as separate components may or may not be physically separate. In addition, some or all of the units and modules may be selected according to actual needs to achieve the purpose of the solution of the embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

The foregoing is directed to embodiments of the present application and it is noted that numerous modifications and adaptations may be made by those skilled in the art without departing from the principles of the present application and are intended to be within the scope of the present application.

Claims

1. A photovoltaic inverter, wherein an input of the photovoltaic inverter is connected to a photovoltaic array through a DC bus, the DC bus comprises a positive DC bus and a negative DC bus, an output of the photovoltaic inverter is connected to an AC power grid, the photovoltaic inverter comprises: the device comprises a rectifying circuit, an insulation impedance detection circuit and a controller;

the first end of the insulation impedance detection circuit is connected with the direct current bus, the second end of the insulation impedance detection circuit is grounded, the insulation impedance detection circuit comprises a controllable switch, and the controllable switch is used for adjusting the size of a resistor connected into the insulation impedance detection circuit;

the input end of the rectifying circuit is used for connecting the alternating current power grid, and the output end of the rectifying circuit is used for connecting the direct current bus;

the controller is used for determining that the time spent on stabilizing the ground voltage of the direct current bus after the working state of the controllable switch is switched is a first time interval when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit; and determining the insulation resistance to the ground of the direct current bus by using the voltage to the ground of any direct current bus after the controllable switch is closed for a first time interval and the voltage to the ground after the controllable switch is opened for the first time interval.

2. The pv inverter of claim 1, wherein the controller is configured to determine the first time interval when the voltage to ground of the negative dc bus or the positive dc bus reaches a steady state after controlling the controllable switch to switch from open to closed when the present open circuit voltage of the pv array is less than or equal to the output voltage of the rectifier circuit.

3. The photovoltaic inverter of claim 1, further comprising a transformer;

the input end of the transformer is connected with the alternating current power grid, and the output end of the transformer is connected with the input end of the rectifying circuit;

the transformer is used for boosting voltage.

4. The photovoltaic inverter of claim 3, wherein the output voltage of the rectifying circuit is equal to the maximum open circuit voltage of the photovoltaic array.

5. The photovoltaic inverter of claim 4, wherein the controller is configured to determine the voltage to ground of the first dc bus as the first voltage after controlling the controllable switch to open the first time interval; after the controllable switch is controlled to be closed for the first time interval, the voltage to ground of the first direct current bus is determined to be a second voltage, the output voltage of the rectifying circuit, the first voltage and the second voltage are used for determining the insulation impedance to ground of the direct current bus, and the first direct current bus is the positive direct current bus or the negative direct current bus.

6. The photovoltaic inverter of any of claims 1-3, wherein the output voltage of the rectifying circuit is less than the maximum open circuit voltage of the photovoltaic array.

7. The photovoltaic inverter of claim 6, wherein the controller is configured to determine the voltage to ground of the first dc bus as the first voltage after controlling the controllable switch to open the first time interval; after the controllable switch is controlled to be closed for the first time interval, the voltage to ground of the first direct current bus is determined to be a second voltage, when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, the first voltage and the second voltage are used for determining the insulation impedance to ground of the direct current bus, and the first direct current bus is the positive direct current bus or the negative direct current bus.

8. The photovoltaic inverter of claim 7, wherein the controller is further configured to determine the voltage to ground of the first dc bus as a third voltage and determine the voltage between the dc buses as a fifth voltage after controlling the controllable switch to be turned off for the first time interval when a current open circuit voltage of the photovoltaic array is greater than an output voltage of the rectifying circuit or when a voltage between the dc buses is greater than an output voltage of the rectifying circuit; after the controllable switch is controlled to be closed for the first time interval, determining that the voltage to ground of the first direct current bus is fourth voltage, and determining that the voltage between the direct current buses is sixth voltage; when the difference value of the fifth voltage and the sixth voltage is within a preset voltage range, determining the insulation resistance to the ground of the direct current bus by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.

9. The photovoltaic inverter according to claim 1, wherein the rectifier circuit is a bridge rectifier circuit using a diode.

10. The photovoltaic inverter of claim 1, wherein the insulation resistance detection circuit comprises a first branch, a second branch, and a third branch;

the first end of the first branch circuit is connected with the positive direct-current bus, the first end of the second branch circuit is connected with the negative direct-current bus, and the second end of the first branch circuit and the second end of the second branch circuit are grounded through the third branch circuit;

the third branch comprises a controllable switch for adjusting the resistance of the third branch.

11. The method for detecting the insulation impedance is applied to a photovoltaic inverter, the input end of the photovoltaic inverter is connected with a photovoltaic array through a direct current bus, the direct current bus comprises a positive direct current bus and a negative direct current bus, the output end of the photovoltaic inverter is connected with an alternating current power grid, the photovoltaic inverter comprises a rectifying circuit and an insulation impedance detection circuit, the first end of the insulation impedance detection circuit is connected with the direct current bus, the second end of the insulation impedance detection circuit is grounded, the insulation impedance detection circuit comprises a controllable switch, the controllable switch is used for adjusting the size of a resistor connected into the insulation impedance detection circuit, the input end of the rectifying circuit is used for being connected with the alternating current power grid, and the output end of the rectifying circuit is used for being connected with the direct current bus, and the method comprises the following steps:

and determining the insulation resistance to the ground of the direct current bus by using the voltage to the ground of any direct current bus after the controllable switch is closed for a first time interval and the voltage to the ground after the controllable switch is opened for the first time interval.

12. The insulation resistance detection method according to claim 11, wherein when the current open-circuit voltage of the photovoltaic array is less than or equal to the output voltage of the rectifier circuit, determining that the time taken for the ground voltage of the dc bus to reach the steady state after the operating state of the controllable switch is switched is a first time interval, specifically comprising:

and when the current open-circuit voltage of the photovoltaic array is smaller than or equal to the output voltage of the rectifying circuit, after the controllable switch is controlled to be switched from the off state to the on state, determining that the time spent on the voltage to ground of the negative direct-current bus or the positive direct-current bus reaches a stable state is the first time interval.

13. The method according to claim 11 or 12, wherein the determining the insulation resistance to ground of the dc bus by using the voltage to ground of any one of the dc buses after the controllable switch is closed for the first time interval and after the controllable switch is opened for the first time interval specifically comprises:

after the controllable switch is controlled to be switched off for the first time interval, determining that the voltage to ground of a first direct current bus is a first voltage, wherein the first direct current bus is the positive direct current bus or the negative direct current bus;

after the controllable switch is controlled to be closed for the first time interval, determining that the voltage to ground of the first direct current bus is a second voltage;

14. The method according to claim 11 or 12, wherein the determining the insulation resistance to ground of the dc bus by using the voltage to ground of any one of the dc buses after the controllable switch is closed for the first time interval and after the controllable switch is opened for the first time interval specifically comprises:

when the voltage between the direct current buses is always equal to the output voltage of the rectifying circuit, the first voltage and the second voltage are used for determining the insulation impedance of the direct current buses to the ground.

15. The method of detecting insulation resistance according to claim 14, further comprising:

when the current open-circuit voltage of the photovoltaic array is greater than the output voltage of the rectifying circuit, or when the voltage between the direct current buses is greater than the output voltage of the rectifying circuit, after the controllable switch is controlled to be switched off for the first time interval, determining the voltage to ground of the first direct current bus as a third voltage, and determining the voltage between the direct current buses as a fifth voltage;

after the controllable switch is controlled to be closed for the first time interval, determining that the voltage to ground of the first direct current bus is fourth voltage, and determining that the voltage between the direct current buses is sixth voltage;

when the difference value of the fifth voltage and the sixth voltage is within a preset voltage range, determining the insulation resistance to the ground of the direct current bus by using the third voltage, the fourth voltage, the fifth voltage and the sixth voltage.

16. A photovoltaic power generation system, characterized in that it comprises a photovoltaic inverter according to any one of claims 1 to 10, and further comprises a plurality of photovoltaic modules;

the photovoltaic modules are used for converting light energy into direct current and transmitting the direct current to the input end of the photovoltaic inverter;

the output end of the photovoltaic inverter is the output end of the photovoltaic power generation system.