CN115453195A - Insulation resistance detection method and detection circuit of a photovoltaic inverter system - Google Patents

Abstract

The application relates to an insulation resistance detection method and a detection circuit of a photovoltaic inverter system, including: the photovoltaic inverter system includes a photovoltaic output circuit and a BOOST switch circuit, and the insulation resistance detection circuit includes a detection sub-circuit and a discharge circuit, controlled by a control unit BOOST switch circuit, detection sub-circuit, and discharge circuit. The first controllable switch in the detection sub-circuit is controlled to be turned on or off, and it is judged whether the insulation resistance of the photovoltaic array of the photovoltaic output circuit is normal. In the case of abnormal insulation resistance, control the second controllable switch of the BOOST switch circuit to turn on or off, and determine that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit. When the second controllable switch is controlled to be turned off, the third controllable switch of the discharge circuit is controlled to be turned on to discharge the electric energy output by the photovoltaic output circuit. Using this method can accurately locate the photovoltaic sub-array with low impedance, make the inverter stand by under weak light conditions, reduce the failure rate of the power relay, and eliminate the risk of bus overvoltage caused by the short circuit of the solar array.

Description

Insulation resistance detection method and detection circuit of a photovoltaic inverter system

technical field

The present application relates to the field of photovoltaic technology, in particular to an insulation resistance detection method and detection circuit of a photovoltaic inverter system.

Background technique

In the photovoltaic power generation system, the solar panel is a device that converts sunlight energy into electrical energy based on the photovoltaic effect principle of the semiconductor interface. However, photovoltaic modules, cables, and photovoltaic input terminals of inverters are placed in the open air for a long time, and are subjected to various external forces, resulting in changes in the impedance of the entire photovoltaic system to ground, which in turn affects the safety of the photovoltaic power generation system. Therefore, the insulation resistance must be tested before grid connection.

With the development of photovoltaic grid-connected technology, the current detection of photovoltaic inverter insulation resistance is to detect whether there is an abnormal impedance by detecting the overall input impedance. If there is abnormal impedance, the switch tube can be used to detect the branch with abnormal impedance.

However, when the switching tube in the BOOST switching circuit is turned on to off, the energy stored in the inductance in the photovoltaic inverter system will be transferred to the bus, which will exceed the overvoltage value of the bus and cause device damage.

Contents of the invention

Based on this, it is necessary to provide an insulation resistance detection method and a detection circuit of a photovoltaic inverter system capable of protecting the components on the bus from being damaged in view of the above technical problems.

In a first aspect, the present application provides a method for detecting insulation resistance of a photovoltaic inverter system. Applied to an insulation resistance detection circuit, the photovoltaic inverter system includes a photovoltaic output circuit and a BOOST switch circuit connected to the photovoltaic output circuit, and the insulation resistance detection circuit includes a detection sub-circuit connected to the photovoltaic output circuit, and The discharge circuit connected to the photovoltaic output circuit, and the control unit connected to the BOOST switch circuit, the detection sub-circuit and the discharge circuit, the method includes:

Controlling the conduction or disconnection of the first controllable switch in the detection sub-circuit, and judging whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit is normal;

In the case of abnormal insulation resistance, control the conduction or disconnection of the second controllable switch in the BOOST switch circuit, and determine that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit;

When the second controllable switch is controlled to be turned off, the third controllable switch in the discharge circuit is controlled to be turned on, so as to discharge the electric energy output by the photovoltaic output circuit.

In one of the embodiments, controlling the on or off of the first controllable switch in the detection sub-circuit, and judging whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit is normal includes:

Controlling the on or off of the first controllable switch in the detection sub-circuit to obtain the first parallel impedance between the output positive pole of the photovoltaic output circuit and the common ground and the output negative pole of the photovoltaic output circuit and the common ground a second parallel impedance between ground;

acquiring a parallel value of the first parallel impedance and the second parallel impedance;

Based on the parallel connection value, it is judged whether the insulation resistance of the photovoltaic square array in the photovoltaic output circuit is normal.

In one embodiment, if the parallel connection value is less than a set threshold, the insulation resistance is abnormal; otherwise, the insulation resistance is normal.

In one of the embodiments, controlling the turn-on or disconnection of the second controllable switch in the BOOST switch circuit, and determining that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit includes:

Controlling the second controllable switch corresponding to the photovoltaic sub-array to turn on sequentially, and judging whether the corresponding photovoltaic sub-array has abnormal insulation resistance according to the voltage of the common ground to the negative output pole of the photovoltaic output circuit.

In one of the embodiments, if the voltage of the common ground to the negative output pole of the photovoltaic output circuit remains unchanged, it is not the component whose input of the photovoltaic sub-array has abnormal insulation resistance to ground; otherwise, the photovoltaic sub-array The array input impedance is abnormal.

In one of the embodiments, after discharging the electric energy output by the photovoltaic output circuit, it further includes,

When the output positive pole of the photovoltaic output circuit and the output negative pole of the photovoltaic output circuit return to the original voltage, the third controllable switch of the discharge circuit is turned off to stop energy consumption.

In one embodiment, the maximum power point power of each photovoltaic sub-array is obtained, and based on the maximum power point power of each photovoltaic sub-array, it is judged whether the requirement for grid-connected output is met.

In a second aspect, the present application also provides an insulation resistance detection circuit of a photovoltaic inverter system. The circuit includes: the photovoltaic inverter system includes a photovoltaic output circuit and a BOOST switch circuit connected to the photovoltaic output circuit, wherein the insulation resistance detection circuit includes a detection sub-circuit connected to the photovoltaic output circuit , a discharge circuit connected to the photovoltaic output circuit, and a control unit connected to the BOOST switch circuit, the detection sub-circuit and the discharge circuit; wherein the control unit is used for:

Controlling the conduction or disconnection of the first controllable switch in the detection sub-circuit, and judging whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit is normal;

In the case of abnormal insulation resistance, control the conduction or disconnection of the second controllable switch in the BOOST switch circuit, and determine that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit;

When the second controllable switch is controlled to be turned off, the third controllable switch in the discharge circuit is controlled to be turned on, so as to discharge the electric energy output by the photovoltaic output circuit.

In one of the embodiments, the detection sub-circuit includes test resistors R1, R2, R3, R4 and first controllable switches S1, S2;

After the test resistor R3 is connected in parallel with the first controllable switch S1, it is connected in series with the test resistor R2, after the circuit is connected in series, the input terminal of the circuit is connected to the positive output pole of the photovoltaic output circuit, and the output terminal is connected to the common ground;

After the test resistor R4 is connected in parallel with the first controllable switch S2, it is connected in series with the test resistor R1. After the circuit is connected in series, the input terminal of the circuit is connected to the common ground, and the output terminal is connected to the output cathode of the photovoltaic output circuit.

In one of the embodiments, the bleeder circuit includes a bleeder resistor Rd and the third controllable switch Qd;

The bleeder resistor Rd is connected in series with the third controllable switch Qd, the series connected circuit is connected in parallel to the positive output pole of the photovoltaic output circuit and the negative output pole of the photovoltaic output circuit, and the input terminal is connected to the photovoltaic output circuit The output positive pole of the photovoltaic output circuit is connected to the output negative pole of the photovoltaic output circuit.

The insulation resistance detection method and circuit of the above-mentioned photovoltaic inverter system firstly control the detection sub-circuit through the control unit to judge whether the insulation resistance of the photovoltaic output circuit is normal; if the insulation resistance is abnormal, then control the BOOST switch circuit to determine whether there is insulation resistance in the photovoltaic output circuit The photovoltaic sub-circuit with abnormal impedance; while controlling the BOOST switch circuit, it also controls the discharge circuit, which is used to discharge the electric energy output by the photovoltaic output circuit during the conduction or disconnection of the BOOST switch circuit, ensuring that during the insulation resistance detection process, Devices on the photovoltaic output circuit will not be damaged due to overvoltage.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Figure 1 is a schematic structural diagram of a photovoltaic inverter system;

Fig. 2 is a structural schematic diagram of an insulation resistance detection circuit;

Fig. 3 is the flowchart of the insulation resistance detection method of photovoltaic inverter system;

Fig. 4 is the flowchart of calculating the insulation resistance of the photovoltaic array of the photovoltaic inverter system;

Fig. 5 is a low-light detection flowchart for detecting whether the photovoltaic output power meets grid-connected output in an embodiment;

6 is a circuit diagram of an insulation resistance detection circuit in an exemplary embodiment;

Fig. 7 is a circuit diagram for detecting PV1 branch insulation resistance in an embodiment;

Fig. 8 is a circuit diagram for detecting PV2 branch insulation resistance in an embodiment;

Fig. 9 is a circuit diagram of detecting PV3 branch insulation resistance in an embodiment.

detailed description

In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application. In addition, it can also be understood that although such development efforts may be complex and lengthy, for those of ordinary skill in the art relevant to the content disclosed in this application, the technology disclosed in this application Some design, manufacturing or production changes based on the content are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

Reference in this application to an "embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The occurrences of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is understood explicitly and implicitly by those of ordinary skill in the art that the embodiments described in this application can be combined with other embodiments without conflict.

Unless otherwise defined, the technical terms or scientific terms involved in the application shall have the usual meanings understood by those with ordinary skill in the technical field to which the application belongs. Words such as "a", "an", "an" and "the" involved in this application do not indicate a limitation on quantity, and may indicate singular or plural numbers. The terms "comprising", "comprising", "having" and any variations thereof involved in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product or process that includes a series of steps or modules (units). The apparatus is not limited to the listed steps or units, but may further include steps or units not listed, or may further include other steps or units inherent to the process, method, product or apparatus. The words "connected", "connected", "coupled" and similar words mentioned in this application are not limited to physical or mechanical connection, but may include electrical connection, no matter it is direct or indirect. "Multiple" referred to in the present application means greater than or equal to two. "And/or" describes the association relationship of associated objects, indicating that there may be three types of relationships. For example, "A and/or B" may indicate: A exists alone, A and B exist simultaneously, and B exists independently. The terms "first", "second", "third" and the like involved in this application are only used to distinguish similar objects, and do not represent a specific ordering of objects.

Figure 1 is a schematic structural diagram of a photovoltaic inverter system. As shown in FIG. 1 , the photovoltaic inverter system includes a photovoltaic output circuit 101 and a BOOST switch circuit 102 connected to the photovoltaic output circuit. 2 is a schematic structural diagram of an insulation resistance detection circuit, wherein the insulation resistance detection circuit includes a detection sub-circuit 103 connected to the photovoltaic output circuit, and a discharge circuit 104 connected to the photovoltaic output circuit. The insulation resistance detection method of the photovoltaic inverter system provided in the embodiment of the present application can be applied in the circuit environment as shown in FIG. 2 .

The control unit connected to the BOOST switch circuit 102 , the detection sub-circuit 103 and the discharge circuit 104 is used to perform the following insulation resistance detection method. As shown in Figure 3, the insulation resistance detection method of the photovoltaic inverter system includes:

S101. Control the on or off of the first controllable switch in the detection sub-circuit, and judge whether the insulation resistance of the photovoltaic square array in the photovoltaic output circuit is normal.

Control the conduction or disconnection of the first controllable switch on the detection sub-circuit 103, so that the resistance value of the test resistor on the circuit changes, and obtain the formula of the loop current when the resistance value of the test resistor changes according to Kirchhoff's current law Group, through the calculation of the formula group, the parallel value of the insulation resistance of the photovoltaic output circuit is obtained. Judging whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit is normal or not according to the parallel connection value.

S102. In the case of abnormal insulation resistance, control the second controllable switch in the BOOST switch circuit to turn on or off, and determine that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit.

Control the on or off of the second controllable switch in each BOOST switch circuit 102 one by one, when detecting a certain photovoltaic sub-array, turn on the corresponding second controllable switch, and turn off the other second controllable switches On, to determine whether the voltage of the common ground terminal to the output negative electrode of the photovoltaic output circuit 101 remains unchanged, and to locate which photovoltaic sub-array has abnormal insulation resistance.

S103. When controlling the second controllable switch to be turned off, control the third controllable switch in the discharge circuit to be turned on, so as to discharge the electric energy output by the photovoltaic output circuit.

When the second controllable switch is from the closed state to the open state, the energy stored in the inductance is released, and the current will flow from the diode to the busbar of the photovoltaic output circuit. The three controllable switches are turned on, which divides all the current flowing into the bus bar into two, and part of the current flows into the discharge circuit, and the excess energy is released through the discharge circuit.

In the above method, due to the disconnection of the second controllable switch tube, the energy released by the inductance will be converted into current, which will all flow into the busbar of the photovoltaic output circuit, causing damage to the devices on the busbar due to overvoltage. The circuit divides the leakage to release the excess voltage, so that the voltage on the bus is maintained in a normal state, and the devices on the photovoltaic output circuit are not damaged.

In some embodiments, as shown in FIG. 4 , controlling whether the first controllable switch in the detection sub-circuit is turned on or off, and judging whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit is normal includes:

S201. Control the on or off of the first controllable switch in the detection sub-circuit to obtain the first parallel impedance between the output positive pole of the photovoltaic output circuit and the common ground and the first parallel impedance between the output negative pole of the photovoltaic output circuit and the common ground. second parallel impedance.

When the first controllable switch is turned on or off, the resistance value of the test resistor incorporated into the circuit is different, and the current formula under different resistance values is obtained. According to the current formulas under different resistance conditions, a formula group is formed, and the first parallel impedance and the second parallel impedance are obtained through the calculation inside the formula group.

S202. Obtain a parallel connection value of the first parallel impedance and the second parallel impedance.

Perform parallel impedance calculation on the first parallel impedance and the second parallel impedance to obtain a parallel value.

S203. Determine whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit is normal based on the parallel connection value.

If the parallel connection value is less than the set threshold, the insulation resistance is abnormal; otherwise, the insulation resistance is normal.

Among them, if the obtained parallel value is less than the maximum input voltage of the photovoltaic output circuit than 30mA (the basic requirement of the photovoltaic grid-connected inverter), the insulation resistance is abnormal.

From step S201 to step S203, by turning on or off the first controllable switch, the parallel connection value of the first parallel impedance and the second parallel impedance is obtained, and according to the parallel value, it is judged whether the insulation resistance of the photovoltaic array is abnormal, realizing It detects whether there is abnormal insulation resistance in the photovoltaic array before the photovoltaic grid is connected, and avoids the abnormal insulation resistance from affecting the safety of the photovoltaic system.

In some embodiments, controlling the disconnection or conduction of the second controllable switch in the BOOST switch circuit 102, and determining that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit includes:

Sequentially control the second controllable switch corresponding to the photovoltaic sub-array to be turned on, and judge whether the corresponding photovoltaic sub-array has abnormal insulation resistance according to the voltage of the common ground to the output negative pole of the photovoltaic output circuit.

In the above embodiment, the accuracy of insulation resistance detection is improved by sequentially performing insulation resistance abnormality judgment on all photovoltaic sub-arrays of the photovoltaic array.

In some embodiments, if the voltage of the common ground to the output cathode of the photovoltaic output circuit remains unchanged, it is not the component whose input of the photovoltaic sub-array has an abnormal insulation resistance to the ground; otherwise, the photovoltaic sub-array has an abnormal insulation resistance to the ground .

In some embodiments, after discharging the electric energy output by the photovoltaic output circuit, it also includes:

When the output positive pole of the photovoltaic output circuit and the output negative pole of the photovoltaic output circuit return to the original voltage, the third controllable switch of the discharge circuit is turned off to stop energy consumption.

In the above embodiment, after the positive and negative pole voltages of the photovoltaic output circuit return to the original voltage, the third controllable switch is turned off to stop energy consumption, so that the energy generated by the photovoltaic inverter system is not wasted and leaked. The redundant energy generated by the second controllable switch is discharged, and the circuit connected between the positive and negative poles of the photovoltaic output circuit of the photovoltaic inverter system and the circuit components are protected from damage.

In one embodiment, as shown in Figure 5, a weak light detection method for detecting whether the photovoltaic output power meets the grid-connected output is provided, and the application of the method to the structure in Figure 2 is used as an example for illustration, including the following steps:

Calculate the maximum power point power of each photovoltaic sub-array, and judge whether it meets the requirements of grid-connected output based on the maximum power point power of each photovoltaic sub-array.

In performing step S101, the first controllable switch of the control detection sub-circuit is turned on or off, and it is judged whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit is normal, and in step S102, when the insulation resistance is abnormal, control the first control of the BOOST switch circuit. Step S301 is performed after the controllable switch is turned on or off, and after the photovoltaic sub-arrays with abnormal insulation resistance in the photovoltaic output circuit are determined.

S301. Calculate the maximum power point power of the branch where each photovoltaic sub-array is located.

Specifically, when the second controllable switch corresponding to a photovoltaic sub-array is turned on, and the other second controllable switches are turned off, the output of the battery panel of the photovoltaic sub-array is short-circuited at this time, the voltage is 0, and the current is the largest. The ammeter reads the short-circuit current at this time, and then according to the open-circuit voltage, the maximum power point power of the photovoltaic sub-array can be calculated.

S302 , summing the maximum power point powers of all photovoltaic branches to obtain the maximum total power of the photovoltaic output circuit 101 .

S303. Determine whether the maximum total power satisfies the requirement for grid-connected output.

Among them, the demand for grid-connected output is a fixed value determined by the number of photovoltaic sub-arrays in the photovoltaic square array.

Specifically, when the maximum total power is greater than the demand for grid-connected output, photovoltaic grid-connected output can be performed; when the maximum total power is less than the demand for grid-connected output, photovoltaic grid-connected output will not be performed, and it can be judged that for low light conditions.

In the above weak light detection method for detecting whether the photovoltaic output power meets the grid-connected output, the maximum total power of the photovoltaic output circuit is obtained by calculating the maximum power point power of each photovoltaic branch, and it is judged whether the maximum total power meets the requirements of the grid-connected output. If it is not satisfied, it can be known that it is under low-light conditions at this time. Because photovoltaic modules are greatly affected by lighting conditions, especially when the sun is weak in the morning and evening, if the output voltage of photovoltaic modules is high, it can meet the grid-connection requirements; if the energy is very weak, it will cause inverter The relay inside the device will be cut off back and forth, which will affect the service life of the relay. Therefore, performing low-light detection before grid connection can make the inverter stand by under low-light conditions, reducing the failure rate of power relays.

In an exemplary embodiment, as shown in FIG. 6 , the photovoltaic output circuit 101 includes photovoltaic sub-arrays PV1, PV2, and PV3, and inductors L1, L2, L3 and diodes D1, L3, and diodes D1, D2 , D3 , the input ends of the second controllable switches Q1 , Q2 , Q3 are connected to the corresponding photovoltaic sub-arrays PV1 , PV2 , PV3 , and the output ends are connected to the output negative electrode BUS− of the photovoltaic output circuit 101 . The insulation resistance circuit includes a detection sub-circuit 103 and a discharge circuit 104, the detection sub-circuit 103 includes a test resistor and a first controllable switch, and the discharge circuit 104 includes a discharge resistor and a third controllable switch.

Assume that the insulation resistance of photovoltaic sub-array PV1 to ground is Riso1, the insulation resistance of photovoltaic sub-array PV2 to ground is Riso2, the insulation resistance of photovoltaic sub-array PV3 to ground is Riso3, and the insulation resistance of photovoltaic output circuit negative to ground is Riso2. For Risoy.

According to Kirchhoff's current law, both the first controllable switches S1 and S2 are turned off. At this time, the voltage of the common ground terminal to the output negative pole of the photovoltaic output circuit 101 is V _E1 , and the insulation resistance Riso1, Riso2, and Riso3 flow through the circuit. And the sum of the currents of the test resistors R2, R3 is equal to the sum of the currents flowing through the insulation resistance Risoy and the test resistors R1, R4, and the following formula (1) is obtained:

According to Kirchhoff's current law, the first controllable switch S1 is closed, and the first controllable switch S2 is opened. At this time, the voltage of the common ground terminal to the output negative pole of the photovoltaic output circuit 101 is V _E2 , and the loop flows through The sum of the currents of the insulation resistance Riso1, Riso2, Riso3 and the test resistor R2 is equal to the sum of the currents flowing through the insulation resistance Risoy and the test resistors R1 and R4, and the following formula (2) is obtained:

According to Kirchhoff's current law, both the first controllable switches S1 and S2 are closed. At this time, the voltage of the common ground terminal to the output negative electrode of the photovoltaic output circuit 101 is V _E3 , and the insulation resistance Riso1, Riso2, Riso3 and The sum of the currents of the test resistor R2 is equal to the sum of the currents flowing through the insulation resistance Risoy and the test resistor R1, and the following formula (3) is obtained:

According to Kirchhoff's current law, the first controllable switch S1 is opened and S2 is closed. At this time, the voltage of the common ground terminal to the output negative pole of the photovoltaic output circuit 101 is V _E4 , and the insulation resistance Riso1, Riso2, and Riso3 flow through the circuit. And the sum of the currents of the test resistors R2 and R3 is equal to the sum of the currents flowing through the insulation resistance Risoy and the test resistor R1, and the following formula (4) is obtained:

According to the formula obtained above, the parallel connection value of the parallel connection insulation resistance of the photovoltaic output circuit 101 is calculated as follows:

Subtract formula (2) from formula (1) to get result (5):

Subtract formula (4) from formula (3) to get result (6):

If the obtained parallel value is less than the maximum input voltage ratio of the photovoltaic output circuit by 30mA (the standard requirement of the photovoltaic grid-connected inverter), the insulation resistance is abnormal. At this time, the judgment result is negative, and step S102 is executed.

Step S102 , in the case of abnormal insulation resistance, turn on or off the second controllable switch in the BOOST switch circuit 102 , and determine that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit.

As shown in Figure 7, the second controllable switch Q1 of the BOOST switch circuit 102 is closed, and Q2 and Q3 are opened. If the output negative voltage of the common ground terminal to the photovoltaic output circuit 101 remains unchanged at this time, it is not a photovoltaic sub-array PV1 has an abnormal ground insulation resistance, otherwise, PV sub-array PV1 has abnormal ground insulation resistance.

At this time, the photovoltaic sub-array PV1 panel output is short-circuited, the voltage is 0, and the current is the maximum. The short-circuit current I1 at this time is obtained through the ammeter A1, and the maximum power point power of the photovoltaic sub-array PV1 is calculated according to the open-circuit voltage V _PV1 .

As shown in Figure 8, the second controllable switch Q2 of the BOOST switch circuit 102 is closed, and Q1 and Q3 are opened. If the output negative voltage of the common ground terminal to the photovoltaic output circuit 101 remains unchanged at this time, it is not a photovoltaic sub-array There is an abnormal insulation resistance to the ground of the PV2 circuit, otherwise, the PV2 circuit of the photovoltaic sub-array has an abnormal insulation resistance to the ground.

At this time, the output of the photovoltaic sub-array PV2 panel is short-circuited, the voltage is 0, and the current is the maximum. The short-circuit current I2 at this time is obtained through the ammeter A2, and the maximum power point power of the photovoltaic sub-array PV2 is calculated according to the open-circuit voltage V _PV2 .

As shown in Figure 9, the second controllable switch Q3 of the BOOST switch circuit 102 is closed, and Q1 and Q2 are opened. If the output negative voltage of the common ground terminal to the photovoltaic output circuit 101 remains unchanged at this time, it is not a photovoltaic sub-array There is an abnormal insulation resistance to the ground of the PV3 circuit, otherwise, the PV3 circuit of the photovoltaic sub-array has an abnormal insulation resistance to the ground.

At this time, the photovoltaic sub-array PV3 panel output is short-circuited, the voltage is 0, and the current is the maximum. The short-circuit current I3 at this time is obtained through the ammeter A3, and the maximum power point power of the photovoltaic sub-array PV3 is calculated according to the open-circuit voltage V _PV3 .

When the judgment of whether the insulation resistance of the photovoltaic sub-array of a certain path is abnormal is completed, the corresponding second controllable switch needs to be adjusted from the closed state to the open state, and step S103 is executed at this time.

Step S103 , when the second controllable switch is controlled to be turned off, the third controllable switch in the discharge circuit 104 is controlled to be turned on, so as to discharge the electric energy output by the photovoltaic output circuit.

As shown in Figure 7, when the second controllable switch Q1 changes from the closed state to the open state, the current flowing through Q1 will flow from the diode D1 into the busbar of the photovoltaic output circuit, and at this time, the leakage current on the busbar will be connected in parallel. The third controllable switch in the discharge circuit 104 is turned on, and the current originally flowing through the bus will partially flow into the discharge circuit, allowing the discharge resistor Rd to carry the excess voltage. When the voltage on the bus returns to a normal state, the first Three controllable switches are disconnected.

As shown in Figure 8, when the second controllable switch Q2 is from the closed state to the open state, the current flowing through Q2 will flow from the diode D2 into the busbar of the photovoltaic output circuit, and at this time the leakage current on the busbar will be connected in parallel. The third controllable switch in the discharge circuit 104 is turned on, and the current originally flowing through the bus will partially flow into the discharge circuit, allowing the discharge resistor Rd to carry the excess voltage. When the voltage on the bus returns to a normal state, the first Three controllable switches are disconnected.

As shown in Figure 9, when the second controllable switch Q3 is from the closed state to the open state, the current flowing through Q3 will flow from the diode D3 into the busbar of the photovoltaic output circuit, and at this time the leakage current on the busbar will be connected in parallel. The third controllable switch in the discharge circuit 104 is turned on, and the current originally flowing through the bus will partially flow into the discharge circuit, allowing the discharge resistor Rd to carry the excess voltage. When the voltage on the bus returns to a normal state, the first Three controllable switches are disconnected.

Step S302 , summing the maximum power point power of all photovoltaic branches to obtain the maximum total power of the photovoltaic output circuit 101 .

Step S303, judging whether the maximum total power meets the requirement of grid-connected output.

Among them, the demand for grid-connected output is a fixed value determined by the number of photovoltaic sub-arrays in the photovoltaic square array.

Specifically, when the maximum total power is greater than the demand for grid-connected output, photovoltaic grid-connected output can be performed; when the maximum total power is less than the demand for grid-connected output, photovoltaic grid-connected output will not be performed, and it can be judged that for low light conditions.

It should be understood that although the steps in the flow charts involved in the above embodiments are shown sequentially according to the arrows, these steps are not necessarily executed sequentially in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least some of the steps in the flow charts involved in the above-mentioned embodiments may include multiple steps or stages, and these steps or stages are not necessarily executed at the same time, but may be performed at different times For execution, the execution order of these steps or stages is not necessarily performed sequentially, but may be executed in turn or alternately with other steps or at least a part of steps or stages in other steps.

Based on the same inventive concept, the embodiment of this application also provides an insulation resistance detection circuit for a photovoltaic inverter system. The solution to the problem provided by the circuit is similar to the solution described in the above method, so the following For the specific limitations of the provided one or more embodiments of the insulation resistance detection circuit of the photovoltaic inverter system, please refer to the above definition for the insulation resistance detection method of the photovoltaic inverter system, which will not be repeated here.

In one embodiment, as shown in Figure 2, it specifically includes: the insulation resistance detection circuit includes a detection sub-circuit 103 connected to the photovoltaic output circuit, a discharge circuit 104 connected to the photovoltaic output circuit, and a BOOST switch circuit 102, a detection sub-circuit A control unit connected to the sub-circuit 103 and the discharge circuit 104, wherein the control unit is used for:

Control the conduction or disconnection of the first controllable switch in the detection sub-circuit 103, and judge whether the insulation resistance of the photovoltaic array in the photovoltaic output circuit 101 is normal;

In the case of abnormal insulation resistance, control the conduction or disconnection of the second controllable switch in the BOOST switch circuit 102, and determine that there is a photovoltaic sub-array with abnormal insulation resistance in the photovoltaic output circuit;

While the second controllable switch is controlled to be turned off, the third controllable switch in the discharge circuit 104 is controlled to be turned on, so as to discharge the electric energy output by the photovoltaic output circuit.

Among them, the detection sub-circuit 103 includes a part connected in series between the output positive pole BUS+ of the photovoltaic output circuit 101 and the common ground terminal PE, connected in series with the test resistance R2 after the test resistor R3 is connected in parallel with the first control switch S1, and connected in the photovoltaic output circuit 101. The part between the negative output pole BUS- of the output terminal PE and the common ground terminal PE is connected in series with the test resistor R1 after the test resistor R4 is connected in parallel with the first control switch S2. The discharge circuit 104 includes a discharge resistor Rd and a third controllable switch Qd, the discharge resistor Rd is connected in series with the third controllable switch Qd, and the circuit connected in series is connected in parallel between the output positive pole of the photovoltaic output circuit 101 and the photovoltaic output On the output negative pole of the circuit 101 , the input terminal is connected to the output positive pole of the photovoltaic output circuit 101 , and the output terminal is connected to the output negative pole of the photovoltaic output circuit 101 .

The technical features of the above embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be It is considered to be within the range described in this specification.

The above-mentioned embodiments only express several implementation modes of the present application, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be determined by the appended claims.

Claims (10)

1. An insulation impedance detection method of a photovoltaic inverter system, applied to an insulation impedance detection circuit, the photovoltaic inverter system including a photovoltaic output circuit and a BOOST switch circuit connected to the photovoltaic output circuit, the insulation impedance detection circuit including a detection sub-circuit connected to the photovoltaic output circuit, a bleeder circuit connected to the photovoltaic output circuit, and a control unit connected to the BOOST switch circuit, the detection sub-circuit, and the bleeder circuit, the method comprising:

controlling the connection or disconnection of a first controllable switch in the detection sub-circuit, and judging whether the insulation impedance of a photovoltaic square matrix in the photovoltaic output circuit is normal or not;

under the condition of abnormal insulation impedance, controlling the conduction or the disconnection of a second controllable switch in the BOOST switch circuit, and determining that a photovoltaic sub-array with abnormal insulation impedance exists in the photovoltaic output circuit;

and when the second controllable switch is controlled to be switched off, the third controllable switch in the discharge circuit is controlled to be switched on so as to discharge the electric energy output by the photovoltaic output circuit.

2. The insulation impedance detection method of a photovoltaic inverter system according to claim 1, wherein controlling on or off of a first controllable switch in the detection sub-circuit and determining whether insulation impedance of a photovoltaic square matrix in the photovoltaic output circuit is normal comprises:

controlling the on or off of a first controllable switch in the detection sub-circuit to obtain a first parallel impedance between an output anode of the photovoltaic output circuit and a common ground and a second parallel impedance between an output cathode of the photovoltaic output circuit and the common ground;

acquiring a parallel value of the first parallel impedance and the second parallel impedance;

and judging whether the insulation impedance of the photovoltaic square matrix in the photovoltaic output circuit is normal or not based on the parallel connection value.

3. The insulation impedance detecting method of a photovoltaic inverter system according to claim 2,

if the parallel value is smaller than a set threshold value, the insulation impedance is abnormal; otherwise, the insulation resistance is normal.

4. The insulation impedance detection method of a photovoltaic inverter system according to claim 1, wherein the step of controlling the on or off of a second controllable switch in the BOOST switch circuit and determining that a photovoltaic subarray with abnormal insulation impedance exists in the photovoltaic output circuit comprises:

and sequentially controlling the second controllable switches corresponding to the photovoltaic sub-arrays to be conducted, and judging whether the corresponding photovoltaic sub-arrays have abnormal insulation impedance or not according to the voltage of the output cathode of the photovoltaic output circuit on the common ground.

5. The insulation impedance detection method of a photovoltaic inverter system according to claim 4,

if the voltage of the common ground to the output cathode of the photovoltaic output circuit is kept unchanged, the component is not the component with abnormal ground insulation impedance at the input of the photovoltaic sub-array; otherwise, the input impedance of the photovoltaic sub-array is abnormal.

6. The insulation impedance detection method of a photovoltaic inverter system according to claim 1, further comprising, after discharging the electric power output from the photovoltaic output circuit,

and when the output positive electrode of the photovoltaic output circuit and the output negative electrode of the photovoltaic output circuit recover to the original voltage, the third controllable switch of the bleeder circuit is switched off, and the energy consumption is stopped.

7. The insulation impedance detecting method of a photovoltaic inverter system according to claim 1,

and acquiring the maximum power point power of each photovoltaic sub-array, and judging whether the requirement of grid-connected output is met or not based on the maximum power point power of each photovoltaic sub-array.

8. An insulation resistance detection circuit of a photovoltaic inverter system, the photovoltaic inverter system comprising a photovoltaic output circuit and a BOOST switch circuit connected with the photovoltaic output circuit, characterized in that the insulation resistance detection circuit comprises a detection sub-circuit connected with the photovoltaic output circuit, a bleeder circuit connected with the photovoltaic output circuit, and a control unit connected with the BOOST switch circuit, the detection sub-circuit and the bleeder circuit; wherein the control unit is configured to:

controlling the connection or disconnection of a first controllable switch in the detection sub-circuit, and judging whether the insulation impedance of a photovoltaic square matrix in the photovoltaic output circuit is normal or not;

under the condition of abnormal insulation impedance, controlling the second controllable switch in the BOOST switch circuit to be switched on or switched off, and determining that a photovoltaic sub-array with abnormal insulation impedance exists in the photovoltaic output circuit;

and controlling the second controllable switch to be switched off and controlling the third controllable switch in the bleeder circuit to be switched on at the same time so as to bleed off the electric energy output by the photovoltaic output circuit.

9. The insulation impedance detection circuit of a photovoltaic inverter system according to claim 8,

the detection sub-circuit comprises test resistors R1, R2, R3 and R4 and first controllable switches S1 and S2;

the test resistor R3 is connected in parallel with the first controllable switch S1 and then connected in series with the test resistor R2, the input end of the series circuit is connected with the output anode of the photovoltaic output circuit, and the output end of the series circuit is connected with the common ground;

the test resistor R4 is connected with the first controllable switch S2 in parallel and then connected with the test resistor R1 in series, the input end of the circuit after series connection is connected with the common ground, and the output end of the circuit is connected with the output cathode of the photovoltaic output circuit.

10. The insulation impedance detection circuit of a photovoltaic inverter system according to claim 8, wherein:

the bleeder circuit comprises a bleeder resistor Rd and a third controllable switch Qd;

the leakage resistor Rd is connected in series with the third controllable switch Qd, the series circuit is connected in parallel with the output anode of the photovoltaic output circuit and the output cathode of the photovoltaic output circuit, the input end is connected with the output anode of the photovoltaic output circuit, and the output end is connected with the output cathode of the photovoltaic output circuit.

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