Switching abnormality detection method and device, photovoltaic direct-drive power system and photovoltaic air conditioner

Abstract

This invention discloses a method, device, photovoltaic direct-drive power system, and photovoltaic air conditioner for detecting switch anomalies. The method is applied to a photovoltaic direct-drive power system with photovoltaic cells and a DC / AC converter. A first switch is located between the negative terminal of the photovoltaic cell and the negative terminal of the DC / AC converter, and a second switch is located between the positive terminal of the photovoltaic cell and the positive terminal of the DC / AC converter. The method includes: after detecting no abnormality in the insulation impedance of the photovoltaic cell, determining whether there is an anomaly in the first switch based on the insulation impedance of the negative terminal of the DC / AC converter; after detecting no abnormality in the first switch, determining whether there is an anomaly in the second switch based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage. This invention enables automatic and accurate detection of switch anomalies in photovoltaic direct-drive power systems, preventing such anomalies from causing abnormal operation of the photovoltaic direct-drive power system.

Description

Technical Field

[0001] This invention relates to the field of electronic power technology, and more specifically, to a method and device for detecting switch malfunctions, a photovoltaic direct-drive power system, and a photovoltaic air conditioner. Background Technology

[0002] With the rapid development of modern society, energy consumption is enormous and environmental pollution is becoming increasingly serious. Clean and pollution-free solar energy has become a key focus of new energy development, and photovoltaic power generation technology has received much attention.

[0003] Photovoltaic power generation technology utilizes the photovoltaic effect at the semiconductor interface of solar photovoltaic panels to convert clean, pollution-free solar energy into electrical energy. The generated direct current (DC) is then converted into alternating current (AC) by a DC / AC converter for consumption. Switches (such as contactors and relays) act as the medium connecting the photovoltaic cells and the DC / AC converter, switching the photovoltaic cells in and out of the converter. Currently, most inverters on the market use mechanical DC disconnect switches, which are prone to failure. If a switch failure prevents the photovoltaic cells from being disconnected from the power system in time, the photovoltaic cells will continue to charge the bus capacitor when the equipment is off, causing damage. However, current photovoltaic direct-drive power systems generally rely on manual detection for switch faults, a cumbersome process that fails to achieve automatic and accurate fault detection, resulting in the inability to detect switch faults in a timely manner.

[0004] There is currently no effective solution to the problem that the existing technology for detecting switch faults in photovoltaic direct-drive power systems is cumbersome and cannot achieve automatic and accurate fault detection, resulting in the inability to detect switch faults in a timely manner. Summary of the Invention

[0005] This invention provides a switch fault detection method, device, photovoltaic direct-drive power system, and photovoltaic air conditioner to solve the problem that the switch fault detection process in the existing photovoltaic direct-drive power system is cumbersome, cannot achieve automatic and accurate fault detection, and thus cannot detect switch faults in a timely manner.

[0006] To address the aforementioned technical problems, this invention provides a switch anomaly detection method applied to a photovoltaic direct-drive power system with photovoltaic cells and a DC / AC converter. A first switch is disposed between the negative terminal of the photovoltaic cell and the negative terminal of the DC / AC converter, and a second switch is disposed between the positive terminal of the photovoltaic cell and the positive terminal of the DC / AC converter. The method includes:

[0007] The presence of an abnormality in the first switch is determined based on the insulation resistance of the negative terminal of the DC / AC converter.

[0008] After determining that the first switch has no abnormality, the second switch is judged to have an abnormality based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage.

[0009] Further, determining whether the first switch is faulty based on the insulation resistance of the negative terminal of the DC / AC converter includes:

[0010] The second switch is controlled to open, and then the insulation resistance of the negative terminal of the DC / AC converter is detected when the first switch is open and closed, respectively.

[0011] The insulation resistance of the negative terminal of the DC / AC converter is used to determine whether the first switch is malfunctioning.

[0012] Further, determining whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter includes:

[0013] After the first switch is turned off, it is determined whether the deviation between the insulation impedance of the negative terminal of the DC / AC converter and the insulation impedance of the negative terminal of the photovoltaic cell is within a first preset range.

[0014] If so, then the first switch is determined to be abnormally disconnected;

[0015] If not, then the first switch is determined to be open normally.

[0016] Furthermore, determining whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter also includes:

[0017] After the first switch is closed, it is determined whether the deviation between the insulation impedance of the negative terminal of the DC / AC converter and the insulation impedance of the negative terminal of the photovoltaic cell is within a first preset range.

[0018] If so, then the first switch is determined to be closed normally;

[0019] If not, then the first switch is determined to be abnormally closed.

[0020] Furthermore, after determining that the first switch detection is normal, the system determines whether the second switch is abnormal based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage, including:

[0021] The first switch is controlled to open, and then the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage are obtained when the second switch is open and closed, respectively.

[0022] The second switch is judged to determine whether it is malfunctioning based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage.

[0023] Furthermore, determining whether the second switch is malfunctioning based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage includes:

[0024] After the second switch is closed, it is determined whether the voltage difference between the positive and negative terminals of the photovoltaic cell and the deviation of the DC bus voltage are within a second preset range.

[0025] If so, then the second switch is determined to be closed normally;

[0026] If not, then the second switch is determined to be malfunctioning.

[0027] Furthermore, determining whether the second switch is malfunctioning based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage also includes:

[0028] After the second switch is turned off, it is determined whether the voltage difference between the positive and negative terminals of the photovoltaic cell and the deviation of the DC bus voltage are within a second preset range.

[0029] If so, then the second switch is determined to be abnormally disconnected;

[0030] If not, then the second switch is considered to be open normally.

[0031] Furthermore, before determining whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter, the method further includes:

[0032] Determine whether the insulation resistance of the photovoltaic cell is within the normal range;

[0033] If so, the system will trigger a determination of whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter.

[0034] Furthermore, after determining whether the second switch is malfunctioning based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage, the method further includes:

[0035] If the second switch is not faulty, then the photovoltaic cell is controlled to switch into the photovoltaic direct drive power system.

[0036] The present invention also provides a switch malfunction detection device for implementing the above-described switch malfunction detection method, the device comprising:

[0037] The first detection module is used to determine whether the first switch is abnormal based on the insulation resistance of the negative terminal of the DC / AC converter.

[0038] The second detection module is used to determine whether the second switch is abnormal after determining that the first switch is not abnormal, based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage.

[0039] The present invention also provides a photovoltaic direct-drive power system, including the above-mentioned switch anomaly detection device.

[0040] The present invention also provides a photovoltaic air conditioner, including the above-mentioned photovoltaic direct-drive power system.

[0041] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the program, when executed by a processor, implements the above-described switch anomaly detection method.

[0042] By applying the technical solution of this invention, the presence of an abnormality in the first switch between the negative terminal of the photovoltaic cell and the negative terminal of the DC / AC converter is determined based on the insulation resistance of the negative terminal of the DC / AC converter. After determining that the first switch is free of abnormality, the presence of an abnormality in the second switch between the positive terminal of the photovoltaic cell and the positive terminal of the DC / AC converter is determined based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage. Through the above solution, the abnormality of the switch in the photovoltaic direct-drive power system can be automatically and accurately detected, thus avoiding abnormal operation of the photovoltaic direct-drive power system caused by the aforementioned switch abnormalities. Attached Figure Description

[0043] Figure 1 This is a structural diagram of a photovoltaic direct-drive power system according to an embodiment of the present invention;

[0044] Figure 2 This is a flowchart of a switch anomaly detection method according to an embodiment of the present invention;

[0045] Figure 3 This is a schematic diagram of insulation impedance detection according to an embodiment of the present invention;

[0046] Figure 4 This is a connection structure diagram of a switch malfunction detection device according to an embodiment of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0048] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0049] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0050] It should be understood that although the terms "first," "second," etc., may be used to describe switches in the embodiments of the present invention, these switches should not be limited to these terms. These terms are only used to distinguish different switches. For example, without departing from the scope of the embodiments of the present invention, a first switch may also be referred to as a second switch, and similarly, a second switch may also be referred to as a first switch.

[0051] Depending on the context, the words “if” or “suppose” as used here can be interpreted as “when” or “in response to determination” or “in response to detection.” Similarly, depending on the context, the phrases “if determination” or “if detection (of the stated condition or event)” can be interpreted as “when determination” or “in response to determination” or “when detection (of the stated condition or event)” or “in response to detection (of the stated condition or event).”

[0052] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0053] The optional embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0054] Example 1

[0055] This embodiment provides a method for detecting switch malfunctions, applicable to photovoltaic direct-drive power systems with photovoltaic cells and DC / AC converters. Figure 1 A structural diagram of a photovoltaic direct-drive power system according to an embodiment of the present invention is shown below. Figure 1 As shown, the first switch KM1 is located between the negative terminal PV- of the photovoltaic cell and the negative terminal DC- of the DC / AC converter, and the second switch KM2 is located between the positive terminal PV+ of the photovoltaic cell and the positive terminal DC+ of the DC / AC converter. The first switch can be a contactor or a relay, etc.

[0056] Figure 2 The flowchart below shows a switch anomaly detection method according to an embodiment of the present invention. Figure 2 As shown, the method includes:

[0057] S101, determine whether the first switch KM1 is abnormal based on the insulation resistance of the negative terminal DC- of the DC / AC converter.

[0058] In this embodiment, the insulation impedance of the negative terminal DC- of the DC / AC converter can be calculated based on the ground voltage and leakage current of the negative terminal DC- of the DC / AC converter. The change in the insulation impedance of the negative terminal DC- of the DC / AC converter before and after the first switch KM1 is switched on and off can be used to determine whether the first switch KM1 is faulty. The insulation impedance of the negative terminal of the photovoltaic cell needs to be used as a reference. Therefore, the insulation impedance of the positive terminal PV+ and the insulation impedance of the negative terminal PV- of the photovoltaic cell are obtained first. Specifically, the ground voltage of the positive terminal PV+ of the photovoltaic cell (i.e., the ground voltage at detection point 1 in the figure) and the leakage current can be detected first. The insulation impedance of the positive terminal PV+ of the photovoltaic cell can be calculated based on the ratio of the ground voltage to the leakage current at detection point 1. Similarly, the ground voltage of the negative terminal PV- of the photovoltaic cell (i.e., the ground voltage at detection point 2 in the figure) and the leakage current can be detected. The insulation impedance of the negative terminal PV- of the photovoltaic cell can be calculated based on the ratio of the ground voltage to the leakage current at detection point 2.

[0059] In other embodiments of the present invention, the insulation resistance of the positive and negative terminals of a photovoltaic cell or the insulation resistance of the negative terminal DC- of a DC / AC converter can also be detected by the following methods:

[0060] Figure 3 This is a schematic diagram of insulation impedance detection according to an embodiment of the present invention, as shown below. Figure 3As shown: A DSP is used to control the third switch KM3 and the fourth switch KM4, which are connected to the positive terminals of two photovoltaic cells respectively. The DSP controls the opening and closing of switch K1 on the auxiliary branch to construct different circuit structures. The branch voltage Viso under different circuit structures is collected by an AD sampling module to derive two equations. The DSP then calculates the insulation resistance R of the positive terminal PV1+ of the first photovoltaic cell. x1 The insulation resistance R of the positive terminal PV2+ of the second photovoltaic cell x2 And the insulation resistance R of the negative terminal PV- shared by the two photovoltaic cells. yn If the insulation resistance exceeds the specified limit, a fault must be indicated and the equipment must be prevented from starting.

[0061] The insulation resistance detection principle of the positive terminal PV1+ of the first photovoltaic cell and the positive terminal PV2+ of the second photovoltaic cell is the same. Taking the insulation resistance detection of the positive terminal PV1 of the first photovoltaic cell as an example, with switch K1 open, the detected voltage is V. iso_off At this point, according to circuit principles, we have the following equation:

[0062]

[0063] Where Vpv1 is the voltage between the positive terminal PV1+ and the negative terminal PV- of the first photovoltaic cell.

[0064] With K1 closed, the detected voltage is given. Based on circuit principles, the following equation applies:

[0065]

[0066] By combining equations (1) and (2), the insulation impedance of PV1+ and PV- to ground can be calculated respectively.

[0067] In simple terms, the resistances of PV1+ and PV- to ground are the two unknowns. By setting up two equations with the resistance R1 input and output, the solution can be obtained.

[0068] Similarly, by setting up two equations for the input and output resistors R3, the insulation impedance of PV2+ and PV- to ground can be solved.

[0069] Similarly, the insulation resistance of the negative terminal DC- of the DC / AC converter can also be obtained using the above method, as long as... Figure 3 This can be achieved by connecting the PV- terminal of the DC / AC converter to the negative terminal DC-.

[0070] If the insulation resistance of both the positive terminal PV+ and the negative terminal PV- of the photovoltaic cell is less than the grid connection allowable resistance value, then the insulation resistance detection of the photovoltaic cell is determined to be normal. After determining that the insulation resistance detection of the photovoltaic cell is normal, the insulation resistance of the negative terminal DC- of the DC / AC converter is used to determine whether the first switch KM1 is abnormal.

[0071] S102, after the first switch KM1 is detected to be normal, the second switch KM2 is judged to be abnormal based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage.

[0072] The aforementioned DC bus voltage is the voltage between the positive terminal DC+ and the negative terminal DC- of the DC / AC converter.

[0073] The switch anomaly detection method of this embodiment determines whether the first switch KM1 is abnormal based on the insulation resistance of the negative terminal DC- of the DC / AC converter. After the first switch KM1 is found to be normal, the method determines whether the second switch KM2 is abnormal based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage. Through the above scheme, it is possible to automatically and accurately detect whether the first switch between the negative terminal PV- of the photovoltaic cell and the negative terminal DC- of the DC / AC converter, and the second switch between the positive terminal PV+ of the photovoltaic cell and the positive terminal DC+ of the DC / AC converter are abnormal, thus avoiding abnormal operation of the photovoltaic direct-drive power system caused by the above switch anomalies.

[0074] If the first switch KM1 closes normally, then after the first switch KM1 closes, the negative terminal PV- of the photovoltaic cell and the negative terminal DC- of the DC / AC converter are essentially connected through a wire. Therefore, the insulation resistance of the negative terminal DC- of the DC / AC converter should be equal to or close to the insulation resistance of the negative terminal PV- of the photovoltaic cell. If the first switch KM1 opens normally, then after the first switch KM2 opens, the negative terminal PV- of the photovoltaic cell and the negative terminal DC- of the DC / AC converter are essentially open-circuited. Therefore, the insulation resistance of the negative terminal DC- of the DC / AC converter and the insulation resistance of the negative terminal PV- of the photovoltaic cell are equal. The insulation resistance of the negative terminal PV- of the photovoltaic cell should differ significantly. Based on the above principle, after the insulation resistance test of the photovoltaic cell shows no abnormalities, the insulation resistance of the negative terminal DC- of the DC / AC converter is used to determine whether the first switch KM1 is abnormal. This includes: controlling the second switch KM2 to open, and then calculating the insulation resistance of the negative terminal DC- of the DC / AC converter based on its insulation resistance, both with the first switch KM1 open and closed; and determining whether the first switch KM1 is abnormal based on its insulation resistance. The insulation resistance of the negative terminal of the DC / AC converter is calculated based on its voltage to ground. Specifically, the insulation resistance of the negative terminal of the DC / AC converter is obtained by calculating the ratio of its voltage to ground to its leakage current.

[0075] Specifically, determining whether the first switch KM1 is malfunctioning based on the insulation resistance of the negative terminal DC- of the DC / AC converter includes: after the first switch KM1 is open, determining whether the deviation between the insulation resistance of the negative terminal DC- of the DC / AC converter and the insulation resistance of the negative terminal PV- of the photovoltaic cell is within a first preset range; if yes, the first switch KM1 is determined to be malfunctioning when it is open; if no, the first switch KM1 is determined to be malfunctioning when it is open; after the first switch KM1 is closed, determining whether the deviation between the insulation resistance of the negative terminal DC- of the DC / AC converter and the insulation resistance of the negative terminal PV- of the photovoltaic cell is within a first preset range; if yes, the first switch KM1 is determined to be malfunctioning when it is closed; if no, the first switch KM1 is determined to be malfunctioning when it is closed.

[0076] In practical implementation, if the insulation impedance test of the photovoltaic cell shows no abnormalities, the ground voltage and leakage current at sampling point 1 and sampling point 3 can be obtained respectively. Based on the ground voltage and leakage current at sampling point 3, the insulation impedance of the negative terminal DC- of the DC / AC converter is calculated. If the insulation impedance of the negative terminal DC- of the DC / AC converter is the same as or within the first preset error range of the photovoltaic cell's negative terminal PV-, then the first switch KM1 is determined to be abnormally open, and a fault is reported for the first switch KM1. If the deviation between the two insulation impedances is not within the first preset error range, then the first switch KM1 is determined to be normally open. If the first switch KM1 is determined to be normally open, the first switch KM1 is controlled to close, and the ground voltage at sampling point 1 and sampling point 2 is used to calculate the insulation impedance of the negative terminal DC- of the DC / AC converter. The insulation impedance of the positive terminal PV+ and the negative terminal PV- of the photovoltaic cell is calculated using voltage and leakage current. Then, the insulation impedance of the positive terminal PV+ of the photovoltaic cell and the negative terminal DC- of the DC / AC converter are calculated using the voltage to ground and leakage current at sampling points 1 and 3, respectively. If the insulation impedance of the negative terminal DC- of the DC / AC converter obtained above is the same as or the error is within a first preset range, then the first switch KM1 is determined to be closed normally. If the error between the two insulation impedances is outside the first preset range, then the first switch KM1 is determined to be closed abnormally, and a fault is reported for the first switch KM1.

[0077] If the second switch KM2 closes normally, then after the second switch KM2 closes, the positive terminal PV+ of the photovoltaic cell and the positive terminal DC+ of the converter are essentially connected through a wire. Therefore, the voltage Vov between the positive terminal PV+ and the negative terminal PV- of the photovoltaic cell should be equal to or close to the DC bus voltage. If the second switch KM2 opens normally, then after the first switch opens, the positive terminal PV+ of the photovoltaic cell and the positive terminal DC+ of the converter are essentially open-circuited. Therefore, the voltage Vov between the positive terminal PV+ and the negative terminal PV- of the photovoltaic cell is equal to or close to the DC bus voltage. The line voltages should differ significantly. Based on the above principle, after the first switch KM1 detects no abnormality, the second switch KM2 is judged to be abnormal based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage. This includes: controlling the first switch KM1 to open, and then obtaining the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage when the second switch KM2 is open and closed, respectively; and judging whether the second switch KM2 is abnormal based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage.

[0078] Specifically, the system determines whether the second switch KM2 is malfunctioning based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage. This includes: after the second switch KM2 is closed, determining whether the deviation of the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage is within a second preset range; if yes, the second switch KM2 is considered to be closed normally; if no, the second switch KM2 is considered to be closed abnormally; after the second switch KM2 is opened, determining whether the deviation of the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage is within a second preset range; if yes, the second switch KM2 is considered to be opened abnormally; if no, the second switch KM2 is considered to be opened normally.

[0079] In practical implementation, if the first switch KM1 is determined to be normal, it is opened while the second switch KM2 is closed. At this time, the voltage between sampling point 1 and sampling point 2, i.e., the output voltage Vpv of the photovoltaic cell, is detected. According to the electrical characteristics of the photovoltaic panel, if the second switch KM2 is closed normally, the output voltage Vpv of the photovoltaic cell will drop from the open-circuit voltage Vov before the second switch KM2 is closed to the DC bus voltage Vdc, i.e., Vov is close to Vdc. Therefore, if Vpv and the bus voltage Vdc are the same or fluctuate within a second preset range, it indicates that the second switch KM2 is closed normally; otherwise, the second switch KM2 is considered to be working. An abnormality is detected, and a fault is reported for the second switch KM2. Then, the second switch KM2 is opened. At this time, the voltage Vpv between sampling point 1 and sampling point 2 is detected. Assuming that the open-circuit voltage Vov of the photovoltaic cell is 1000V, Vpv = Vov = 1000V. Generally, when the photovoltaic cell is not switched on, the DC bus voltage is 600V. Therefore, if the difference between the photovoltaic side voltage Vpv and the bus voltage Vdc exceeds the second preset range (the voltage difference is about 400V), it means that the second switch KM2 is open normally. At this time, it can be determined that the second switch KM2 is working normally; otherwise, it is determined that the second switch KM2 is abnormal and a fault is reported for the second switch KM2.

[0080] To prevent photovoltaic cells from switching into the photovoltaic direct-drive power system when insulation impedance is abnormal, and to ensure the reliability of the power system, before determining whether the first switch is abnormal based on the insulation impedance of the negative terminal of the DC / AC converter, the method further includes: determining whether the insulation impedance of the photovoltaic cell is within the normal range; if so, triggering the determination of whether the first switch is abnormal based on the insulation impedance of the negative terminal of the DC / AC converter.

[0081] To ensure the reliability of the power system, the photovoltaic cells can only be connected after ensuring that the insulation impedance of the photovoltaic cells is normal and that the first switch KM1 and the second switch KM2 of the photovoltaic direct-drive power system are normal. Therefore, after judging whether the second switch KM2 is abnormal based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cells and the DC bus voltage, the method also includes: if the second switch KM2 is not abnormal, then control the photovoltaic cells to switch into the photovoltaic direct-drive power system.

[0082] To fully ensure the safety of the photovoltaic cell during insertion and removal, the above-mentioned switch detection process can be performed once before the photovoltaic electromagnetic cell is inserted and once after the photovoltaic cell is removed.

[0083] For photovoltaic direct-drive power systems, the installed capacity of photovoltaic cells is determined by the capacity of the electrical equipment in the system, generally in a 1:1 ratio. In other words, once the capacity of the electrical equipment is determined, the maximum capacity of the photovoltaic cells is also determined, and consequently, the maximum open-circuit voltage (Vov) of the photovoltaic cells is also determined.

[0084] After the DC bus voltage Vdc is established on the DC / AC converter side, the insulation impedance of the photovoltaic cells is tested before switching on the photovoltaic system. If the insulation impedance of the photovoltaic cells is normal, the switching test is performed. The photovoltaic system is switched on only after all tests are normal.

[0085] Example 2

[0086] This embodiment provides a switch malfunction detection device for implementing the switch malfunction detection method described in the above embodiment. Figure 4 The connection structure diagram of the switch malfunction detection device according to an embodiment of the present invention is as follows: Figure 4 As shown, the device includes: a first detection module 10, used to determine whether the first switch KM1 is abnormal based on the insulation resistance of the negative terminal DC- of the DC / AC converter.

[0087] In this embodiment, the specific method for detecting the insulation impedance of a photovoltaic cell can be to first detect the voltage to ground of the positive terminal PV+ of the photovoltaic cell, i.e., the voltage to ground at detection point 1 in the figure, and the leakage current. The insulation impedance of the positive terminal PV+ of the photovoltaic cell can be calculated based on the ratio of the voltage to ground at detection point 1 to the leakage current. Similarly, the voltage to ground of the negative terminal PV- of the photovoltaic cell, i.e., the voltage to ground at detection point 2 in the figure, and the leakage current can be detected. The insulation impedance of the negative terminal PV- of the photovoltaic cell can be calculated based on the ratio of the voltage to ground at detection point 2 to the leakage current.

[0088] The second detection module 20 is used to determine whether the second switch KM2 is abnormal after the first switch KM1 detects no abnormality, based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage.

[0089] The switch anomaly detection device in this embodiment uses a first detection module 10 to determine whether the first switch KM1 is abnormal based on the insulation resistance of the negative terminal DC- of the DC / AC converter. After the first switch KM1 is found to be normal, the second detection module 20 determines whether the second switch KM2 is abnormal based on the voltage difference between the positive terminal PV+ and the negative terminal of the photovoltaic cell and the DC bus voltage. This scheme can automatically and accurately detect anomalies in the first switch between the negative terminal PV- of the photovoltaic cell and the negative terminal DC- of the DC / AC converter, and in the second switch between the positive terminal PV+ of the photovoltaic cell and the positive terminal DC+ of the DC / AC converter, thus preventing abnormal operation of the photovoltaic direct-drive power system caused by such switch anomalies.

[0090] The first detection module 10 is specifically used to: control the second switch to open, and then calculate the insulation resistance of the negative terminal of the DC / AC converter based on the ground voltage of the negative terminal of the DC / AC converter when the first switch is open and closed respectively; and determine whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter.

[0091] When the first detection module 10 determines whether the first switch is malfunctioning based on the insulation impedance of the negative terminal of the DC / AC converter, the specific operations performed are as follows: After the first switch is opened, it determines whether the deviation between the insulation impedance of the negative terminal of the DC / AC converter and the insulation impedance of the negative terminal of the photovoltaic cell is within a first preset range; if yes, it determines that the first switch opening is malfunctioning; if no, it determines that the first switch opening is normal. After the first switch is closed, it determines whether the deviation between the insulation impedance of the negative terminal of the DC / AC converter and the insulation impedance of the negative terminal of the photovoltaic cell is within a first preset range; if yes, it determines that the first switch closing is normal; if no, it determines that the first switch closing is malfunctioning.

[0092] The second detection module 20 is specifically used to: control the first switch to open, and then, when the second switch is open and closed respectively, acquire the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage; and determine whether the second switch is malfunctioning based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage.

[0093] When the second detection module 20 determines whether the second switch is malfunctioning based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage, the specific operations performed are as follows: After the second switch is closed, it determines whether the deviation of the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage is within a second preset range; if yes, the second switch is determined to be closed normally; if no, the second switch is determined to be closed abnormally; after the second switch is opened, it determines whether the deviation of the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage is within a second preset range; if yes, the second switch is determined to be opened abnormally; if no, the second switch is determined to be opened normally.

[0094] To prevent photovoltaic cells from switching into the photovoltaic direct-drive power system when the insulation impedance is abnormal, and to ensure the reliability of the power system, the first detection module is also used to: determine whether the insulation impedance of the photovoltaic cells is within the normal range before determining whether the first switch is abnormal based on the insulation impedance of the negative terminal of the DC / AC converter; if so, trigger the determination of whether the first switch is abnormal based on the insulation impedance of the negative terminal of the DC / AC converter.

[0095] In other embodiments of the present invention, when there are no abnormalities in the insulation impedance of the photovoltaic cell, the first switch, and the second switch, the main control chip controls the photovoltaic cell to switch into the photovoltaic direct drive power system.

[0096] Example 3

[0097] This embodiment provides a photovoltaic direct-drive power system, including the aforementioned switch anomaly detection device, used to automatically and accurately detect whether there are any abnormalities in the first switch between the negative terminal PV- of the photovoltaic cell and the negative terminal DC- of the DC / AC converter, and the second switch between the positive terminal PV+ of the photovoltaic cell and the positive terminal DC+ of the DC / AC converter, thereby preventing abnormal operation of the power system caused by the aforementioned switch anomalies.

[0098] Example 4

[0099] This embodiment provides a photovoltaic air conditioner, including the aforementioned photovoltaic direct-drive power system, used to automatically and accurately detect whether there are any abnormalities in the first switch between the negative terminal PV- of the photovoltaic cell and the negative terminal DC- of the DC / AC converter, and the second switch between the positive terminal PV+ of the photovoltaic cell and the positive terminal DC+ of the DC / AC converter, thereby preventing abnormal operation of the power system caused by the abnormality of the aforementioned switches and improving the operational reliability of the photovoltaic air conditioner.

[0100] Example 5

[0101] This embodiment provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method.

[0102] The device embodiments described above are merely illustrative. The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0103] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting switch malfunctions, applied to a photovoltaic direct-drive power system with photovoltaic cells and a DC / AC converter, wherein a first switch is disposed between the negative terminal of the photovoltaic cell and the negative terminal of the DC / AC converter, and a second switch is disposed between the positive terminal of the photovoltaic cell and the positive terminal of the DC / AC converter, characterized in that, The method includes: The presence of an abnormality in the first switch is determined based on the insulation resistance of the negative terminal of the DC / AC converter. After determining that the first switch detection is normal, the system determines whether the second switch is abnormal based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage. This includes: controlling the first switch to open, and then acquiring the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage when the second switch is open and closed, respectively. The system then determines whether the second switch is abnormal based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage. This includes: after the second switch is closed, determining whether the deviation of the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage is within a second preset range; if yes, the second switch is considered to be closed normally; if no, the second switch is considered to be closed abnormally; after the second switch is open, determining whether the deviation of the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage is within a second preset range; if yes, the second switch is considered to be open abnormally; if no, the second switch is considered to be open normally.

2. The method according to claim 1, characterized in that, Determining whether the first switch is faulty based on the insulation resistance of the negative terminal of the DC / AC converter includes: The second switch is controlled to open, and then the insulation resistance of the negative terminal of the DC / AC converter is detected when the first switch is open and closed, respectively. The insulation resistance of the negative terminal of the DC / AC converter is used to determine whether the first switch is malfunctioning.

3. The method according to claim 2, characterized in that, Determining whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter includes: After the first switch is turned off, it is determined whether the deviation between the insulation impedance of the negative terminal of the DC / AC converter and the insulation impedance of the negative terminal of the photovoltaic cell is within a first preset range. If so, then the first switch is determined to be abnormally disconnected; If not, then the first switch is determined to be open normally.

4. The method according to claim 2, characterized in that, Determining whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter also includes: After the first switch is closed, it is determined whether the deviation between the insulation impedance of the negative terminal of the DC / AC converter and the insulation impedance of the negative terminal of the photovoltaic cell is within a first preset range. If so, then the first switch is determined to be closed normally; If not, then the first switch is determined to be abnormally closed.

5. The method according to claim 1, characterized in that, Before determining whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter, the method further includes: Determine whether the insulation resistance of the photovoltaic cell is within the normal range; If so, the system will trigger a determination of whether the first switch is malfunctioning based on the insulation resistance of the negative terminal of the DC / AC converter.

6. The method according to claim 1, characterized in that, After determining whether the second switch is malfunctioning based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage, the method further includes: If the second switch is not faulty, then the photovoltaic cell is controlled to switch into the photovoltaic direct drive power system.

7. A switch anomaly detection device, used to implement the switch anomaly detection method according to any one of claims 1 to 6, characterized in that, The device includes: The first detection module is used to determine whether the first switch is abnormal based on the insulation resistance of the negative terminal of the DC / AC converter. The second detection module is used to determine whether the second switch is abnormal after determining that the first switch is not abnormal, based on the voltage difference between the positive and negative terminals of the photovoltaic cell and the DC bus voltage.

8. A photovoltaic direct-drive power system, characterized in that, Includes the switch malfunction detection device as described in claim 7.

9. A photovoltaic air conditioner, characterized in that, Including the photovoltaic direct-drive power system as described in claim 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 6.

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