Photovoltaic insulation failure localization method, photovoltaic system, inverter and controller thereof

Abstract

The application discloses a photovoltaic insulation failure positioning method, a photovoltaic system, an inverter and a controller thereof. The photovoltaic insulation failure positioning method comprises the following steps: acquiring the current of each photovoltaic array; and when the current of any one photovoltaic array meets a preset current flow direction, determining that the photovoltaic array meeting the preset current flow direction is ground insulation failure. Therefore, the photovoltaic array or photovoltaic string with ground insulation failure can be positioned, so that the maintenance personnel only need to check the photovoltaic array or photovoltaic string with ground insulation failure when performing maintenance, thereby greatly reducing the maintenance workload and maintenance time.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a method for locating photovoltaic insulation failure, a photovoltaic system, an inverter and its controller. Background Technology

[0002] A photovoltaic system generally includes a photovoltaic array and an inverter. The inverter consists of multiple maximum power point tracking (MPPT) branches and an inverter circuit. The MPPT branches collect the output current from all the photovoltaic arrays and output it to the inverter circuit through a DC bus.

[0003] With the increasing application of photovoltaics, construction quality and aging can easily lead to insulation damage in the cables connecting the photovoltaic strings to the inverter in photovoltaic arrays, resulting in insulation failure between the photovoltaic strings and ground. When the insulation of the photovoltaic strings to ground fails, maintenance personnel need to repair and troubleshoot the insulation damage points. However, inverters in practical applications have multiple maximum power point tracking (MPPT) branches, each connecting to a photovoltaic array consisting of multiple photovoltaic strings, each with positive and negative cables. This results in a large number of photovoltaic string cables that maintenance personnel need to inspect, leading to a heavy workload and long maintenance time. Taking a high-power string inverter as an example, it includes 12 MPPT branches, each connecting to a photovoltaic array consisting of two photovoltaic strings, each with positive and negative cables. Therefore, maintenance personnel need to inspect at least 48 cables, resulting in a large workload. Summary of the Invention

[0004] The main objective of this invention is to provide a method for locating photovoltaic insulation failures. This method aims to detect the current flow direction of a photovoltaic array and locate photovoltaic arrays with ground insulation failures, or photovoltaic strings within photovoltaic arrays with ground insulation failures, based on the current flow direction. This reduces the workload of maintenance personnel and shortens the maintenance time.

[0005] To achieve the above objectives, this invention proposes a photovoltaic insulation failure location method, applied to a photovoltaic system comprising multiple photovoltaic arrays. The photovoltaic insulation failure location method includes the following steps:

[0006] S100, Obtain the current of each of the photovoltaic arrays;

[0007] S200. When the current of any one of the photovoltaic arrays meets the first preset current flow direction, it is determined that the photovoltaic array that meets the first preset current flow direction has failed to achieve ground insulation.

[0008] In one embodiment, each of the photovoltaic arrays includes multiple photovoltaic strings, which are connected in parallel with each other.

[0009] Step S100 includes: obtaining the output current of the first electrode and / or the second electrode of each photovoltaic string in each photovoltaic array;

[0010] Step S200 includes: when the output current of the first electrode and / or the second electrode of any photovoltaic string satisfies the second preset current flow direction, confirming that the first electrode and / or the second electrode of the photovoltaic string that satisfies the second preset current flow direction has failed to be insulated from the ground.

[0011] The polarity of the first electrode is opposite to that of the second electrode.

[0012] In one embodiment, the first preset current flow direction is the opposite direction of the current flow direction when the photovoltaic array is operating normally; and / or,

[0013] The second preset current flow direction is the opposite direction of the output current flow of the first electrode and / or the second electrode when the photovoltaic string is working normally.

[0014] In one embodiment, the first preset current flow direction is the opposite direction of the current flow direction of the photovoltaic array at a previous preset time interval; and / or,

[0015] The second preset current direction is the opposite direction of the output current flow at the moment of the previous preset time interval of the first electrode and / or the second electrode of the photovoltaic string.

[0016] In one embodiment, the following step is further included after step S200:

[0017] The control display device displays information about the photovoltaic string that has failed to achieve ground insulation.

[0018] In one embodiment, the following step is further included after step S200:

[0019] The information about the photovoltaic string that has failed to maintain its ground insulation is transmitted to a smart terminal device.

[0020] The present invention also proposes a controller for an inverter, the controller comprising a processor, a memory, and a photovoltaic insulation failure location program stored in the memory and executable on the processor, wherein the photovoltaic insulation failure location program, when executed by the processor, implements the steps of the photovoltaic insulation failure location method described above.

[0021] The present invention also proposes an inverter for use in a photovoltaic system, the photovoltaic system comprising multiple photovoltaic arrays, wherein the inverter comprises:

[0022] The controller of the aforementioned inverter, and

[0023] The current sampling circuit has its detection terminal connected to the first and second electrodes of each photovoltaic string in the photovoltaic array, and its output terminal connected to the controller of the inverter. The current sampling circuit is used to sample the output current of the first and / or second electrodes of each photovoltaic string in the photovoltaic array.

[0024] In one embodiment, the inverter further includes:

[0025] A voltage conversion circuit, with its input terminal connected to the photovoltaic array, is used to convert the DC power output from the photovoltaic array into voltage.

[0026] The inverter circuit has its input terminal connected to the output terminal of the voltage conversion circuit, and its controlled terminal connected to the controller of the inverter. The inverter circuit is used to convert the DC power output by the voltage conversion circuit into AC power under the control of the controller of the inverter.

[0027] In one embodiment, the voltage conversion circuit is a three-level voltage conversion circuit;

[0028] The input terminal of the three-level voltage conversion circuit is connected to the photovoltaic array, the first level output terminal of the three-level voltage conversion circuit is connected to the positive terminal of the DC bus, the second level output terminal of the three-level voltage conversion circuit is connected to the midpoint of the DC bus, and the third level output terminal of the three-level voltage conversion circuit is connected to the negative terminal of the DC bus.

[0029] In one embodiment, the three-level voltage conversion circuit includes a first inductor, a second inductor, a first switching transistor, a second switching transistor, a first diode, and a second diode;

[0030] One end of the first inductor is connected to the first electrode of the photovoltaic array, and one end of the second inductor is connected to the second electrode of the photovoltaic array; the other end of the first inductor, the first lead of the first switch, and the anode of the first diode are interconnected, and the cathode of the first diode is the first level output terminal of the three-level voltage conversion circuit; the second lead of the first switch is connected to the first lead of the second switch, and their common terminal is the second level output terminal of the three-level voltage conversion circuit; the other end of the second inductor, the second lead of the second switch, and the cathode of the second diode are interconnected, and the anode of the second diode is the third level output terminal of the three-level voltage conversion circuit.

[0031] The present invention also proposes a photovoltaic system, characterized in that the photovoltaic system includes multiple photovoltaic arrays and the inverter described above.

[0032] This invention detects the output current of each photovoltaic array or the output current of each photovoltaic string within each photovoltaic array. When the output current of the photovoltaic array flows in the opposite direction to its normal operating current, it confirms that the photovoltaic array has failed to maintain its insulation to ground. Alternatively, when the output current of a photovoltaic string flows in the opposite direction to its normal operating current, it confirms that the photovoltaic string has failed to maintain its insulation to ground. Upon determining that a photovoltaic string or array has failed to maintain its insulation to ground, its location can be easily and quickly determined based on its serial number or other available information. This allows maintenance personnel to perform repairs based on the location information, significantly reducing the workload and time required for maintenance. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0034] Figure 1 This is a circuit diagram of an embodiment of the inverter of the present invention;

[0035] Figure 2 This is a flowchart illustrating an embodiment of the photovoltaic failure location method of the present invention;

[0036] Figure 3 This is a schematic diagram of the current flow direction in an embodiment of the inverter of the present invention;

[0037] Figure 4 This is a flowchart illustrating another embodiment of the photovoltaic failure location method of the present invention;

[0038] Figure 5 This is a schematic diagram of the current flow direction of another embodiment of the inverter of the present invention;

[0039] Figure 6 This is a circuit diagram of another embodiment of the inverter of the present invention.

[0040] Explanation of icon numbers:

[0041]

[0042]

[0043] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0046] This invention proposes a photovoltaic insulation failure location method, which locates the photovoltaic string with ground insulation failure, thereby reducing the workload and time required for maintenance after insulation failure.

[0047] In one embodiment, this photovoltaic insulation failure location method is applied to a photovoltaic system to locate photovoltaic strings with ground insulation failure. (See also...) Figure 1 The photovoltaic system includes multiple photovoltaic arrays 11-12 and multiple level conversion circuits 21-22. Figure 1 In the first photovoltaic array 11, the positive output currents Istr1p and Istr2p of the first photovoltaic string 111 and the second photovoltaic string 112 converge at the junction point A through their corresponding positive cables to form the positive output current Imppt1p of the first photovoltaic array 11. The negative output currents Istr1n and Istr2n of the first photovoltaic string 111 and the second photovoltaic string 112 converge at the junction point B through their corresponding positive cables to form the negative output current Imppt1n of the first photovoltaic array 11, and are then output to the first level conversion circuit 21. The positive output currents Istr3p and Istr4p and the negative output currents Istr3n and Istr4n of the third photovoltaic string 121 and the fourth photovoltaic string 122 of the second photovoltaic array 12 converge at the junction points C and D respectively to form the positive output current Imppt2p and the negative output current Imppt2n of the second photovoltaic array 12, and are then output to the second level conversion circuit 22.

[0048] Reference Figure 2 The photovoltaic insulation failure location method includes the following steps:

[0049] S100, Obtain the current of each of the photovoltaic arrays;

[0050] In this embodiment, the executing entity can be the controller of a photovoltaic system or the controller of an inverter. Current can be acquired using a Hall effect sensor and then output to the executing entity.

[0051] It should be noted that when the positive cable of a photovoltaic string in one photovoltaic array fails to be insulated from the ground, and the negative cable of a photovoltaic string in another photovoltaic array fails to be insulated from the ground, the output current of the positive and negative cables of the two strings will be detected. For example, Istr3p and Istr2n are both reverse currents, that is, the current flows in the opposite direction under normal operating conditions of the photovoltaic strings, which will also be reflected as the output current of the photovoltaic array being a reverse current.

[0052] Specifically Figure 3 Let's take an example. Figure 3 In the circuit shown, the current of each of the four photovoltaic strings is 10 amps. When the insulation of the negative cable of the second photovoltaic string 112 and the positive cable of the third photovoltaic string 121 to ground fails, that is, when there is a grounding point, taking the point of failure of the negative cable of the second photovoltaic string 112 and the positive cable of the third photovoltaic string 121 as nodes, according to Kirchhoff's current law, the current Istr2n from the two points of failure to the junction point B or C is -10 amps, and Istr3p is -10 amps. (The calculation of -10 amps is based on the fact that the current of the strings is positive under normal operation). That is, the output currents Istr2n and Istr3p of the negative cable of the second photovoltaic string 112 and the positive cable of the third photovoltaic string 121 are both reverse currents.

[0053] Step S100 of this embodiment, obtaining the current of each photovoltaic array, can be interpreted as: obtaining the output current of the positive cable and the output current of the negative cable of each photovoltaic string in each photovoltaic array, for example... Figure 1 The Istr1p, Istr2p, Istr3p, Istr4p, Istr1n, Istr2n, Istr3n, and Istr4n are shown. This can be obtained by additionally setting up Hall effect sensors. Alternatively, it can be interpreted as obtaining the positive and negative output currents of each photovoltaic array, for example... Figure 1 The Imppt1p, Imppt1n, Imppt2p, and Imppt2n are shown. At this point, data can be directly read / polled from the maximum power point tracking (MPPT) control circuit. This means reusing the output current of the photovoltaic array sampled by the MPPT control circuit during operation. In this way, no circuit modifications are needed; only the internal program of the execution unit needs to be adjusted, or simply adding a Hall sensor to supplement the sampling of current not collected by the MPPT control circuit.

[0054] S200. When the current of any one of the photovoltaic arrays meets the preset current flow direction, it is determined that the photovoltaic array that meets the preset current flow direction has failed to achieve ground insulation.

[0055] The preset current flow direction refers to the opposite direction of the current flow when the photovoltaic array or photovoltaic string is operating normally. In this embodiment, the photovoltaic system can pre-store the current flow direction when the photovoltaic array or photovoltaic string is operating normally. When the current flow direction of the photovoltaic array is opposite to the pre-stored direction, it is determined that the photovoltaic array or the photovoltaic string within the photovoltaic array has failed to maintain its insulation to ground. Alternatively, the current of the photovoltaic array or photovoltaic string is sampled twice consecutively at preset time intervals, and if the current directions of the two samples are inconsistent, it is determined that the photovoltaic array or photovoltaic string has failed to maintain its insulation to ground.

[0056] It should be noted that due to the uneven output current of different photovoltaic arrays, the output current of each photovoltaic string within a photovoltaic array is also uneven, and the output current of the same photovoltaic string varies with the light intensity at different times. In other words, the output current of a photovoltaic array or photovoltaic string is time-varying. Therefore, relying on the magnitude of the output current of a photovoltaic array or photovoltaic string for insulation failure location cannot determine whether the change in current magnitude is due to insulation failure to ground of the photovoltaic string or due to the inherent characteristics of the photovoltaic system. The solution adopted in this embodiment is: when the flow direction of the output current of the photovoltaic array or photovoltaic string meets a preset current flow direction, the insulation failure to ground of that photovoltaic array or photovoltaic string is determined. This eliminates the influence of light intensity on the detection of insulation failure to ground, effectively improving the detection accuracy.

[0057] This invention detects the output current of each photovoltaic array or the output current of each photovoltaic string within each photovoltaic array. When the output current of the photovoltaic array flows in the opposite direction to its normal operating current, it confirms that the photovoltaic array has failed to maintain its insulation to ground. Alternatively, when the output current of a photovoltaic string flows in the opposite direction to its normal operating current, it confirms that the photovoltaic string has failed to maintain its insulation to ground. Upon determining that a photovoltaic string or array has failed to maintain its insulation to ground, its location can be easily and quickly determined based on its serial number or other available information. This allows maintenance personnel to perform repairs based on the location information, significantly reducing the workload and time required for maintenance.

[0058] Reference Figure 4 In one embodiment, each of the photovoltaic arrays includes multiple photovoltaic strings, which are connected in parallel with each other.

[0059] Step S100 includes: obtaining the output current of the first electrode and / or the second electrode of each photovoltaic string in each photovoltaic array;

[0060] Step S200 includes: when the output current of the first electrode and / or the second electrode of any photovoltaic string meets the second preset current flow direction, confirming that the first electrode and / or the second electrode of the photovoltaic string that meets the second preset current flow direction has failed to be insulated from the ground; wherein, the polarity of the first electrode is opposite to that of the second electrode.

[0061] The second preset current flow direction can refer to the opposite direction of the current flow when the photovoltaic string fails to achieve ground insulation. One of the first and second electrodes is the positive terminal of the photovoltaic string, and the other is the negative terminal.

[0062] It should be noted that in practical applications, an optical array consists of multiple photovoltaic strings connected in parallel. Therefore, even if the photovoltaic array with ground insulation failure is located, maintenance personnel still need to check and repair the cables of multiple photovoltaic strings inside the photovoltaic array one by one, which will still result in a large workload and maintenance time.

[0063] This embodiment obtains the output current of the first and / or second electrodes of each photovoltaic string in each photovoltaic array, and confirms that the first and / or second electrodes of the photovoltaic string satisfying the second preset current flow direction have failed to maintain their insulation to ground. This allows for precise location of which photovoltaic string's positive or negative cable has failed to maintain its insulation to ground. In other words, this embodiment can directly locate the cable with failed insulation to ground, allowing maintenance personnel to directly repair the located cable, reducing maintenance workload and time.

[0064] Reference Figure 3 and Figure 5 The current between photovoltaic strings may be balanced or unbalanced, but regardless of the operating condition, tracking the current direction for insulation failure location can achieve a higher accuracy rate. Specifically:

[0065] Taking the ground insulation failure of the negative cable of the second photovoltaic string 112 and the positive cable of the third photovoltaic string 121 as an example,

[0066] Figure 3 The diagram illustrates the current flow under balanced current conditions among the photovoltaic strings. Taking the output current of the first to fourth photovoltaic strings 122 as an example, which is 10A, according to Kirchhoff's current law, the output current Istr2n of the negative cable of the second photovoltaic string 112 is -10A, and the output current Istr3p of the positive cable of the third photovoltaic string 121 is -10A.

[0067] Figure 5The diagram illustrates the current flow under conditions of current imbalance between photovoltaic arrays. Taking the output currents of the first to fourth photovoltaic strings 122 as examples (10A, 5A, 8A, and 2A respectively), according to Kirchhoff's current law, the current Istr2n of the negative cable of the second photovoltaic string 112 is -10A, and the current Istr3p of the positive cable of the third photovoltaic string 121 is -7A.

[0068] Under certain interference, currents such as -10A or -7A can be easily detected as reverse currents instead of forward currents, thus effectively improving detection accuracy.

[0069] Reference Figure 1 In one embodiment, the first preset current flow direction is the opposite direction of the current flow direction when the photovoltaic array is working normally; and / or, the second preset current flow direction is the opposite direction of the output current flow direction of the first electrode and / or the second electrode when the photovoltaic string is working normally.

[0070] In this embodiment, the current flow direction of the photovoltaic array or photovoltaic string during normal operation, or its opposite direction, is stored in a memory. Then, the output current direction of the photovoltaic array or photovoltaic string at the current moment is compared with the pre-stored direction. When the output current direction of the photovoltaic array or photovoltaic string at the current moment is opposite to the current flow direction during normal operation, it can be determined that the photovoltaic array or photovoltaic string has failed to maintain its insulation to ground. Since the current direction in the memory can be checked and confirmed by professionals before being saved, the correctness of the pre-stored current direction can be ensured, thereby improving the reliability of insulation failure location.

[0071] Reference Figure 1 In one embodiment, the first preset current direction is the opposite direction of the current flow of the photovoltaic array at a previous preset time interval; and / or, the second preset current direction is the opposite direction of the output current flow of the first electrode and / or the second electrode of the photovoltaic string at a previous preset time interval.

[0072] The preset time interval can be set according to actual needs; in this embodiment, it can be selected as 10 to 50 seconds. That is, the output current of the photovoltaic array or photovoltaic string is continuously collected twice at time intervals of 10 to 50 seconds, and when the directions of the two output currents are inconsistent, it is determined that the photovoltaic array or photovoltaic string has failed to maintain its insulation to ground. This eliminates the need to store the current direction in advance, reducing the design difficulty of the control program.

[0073] In other embodiments, the current direction within a preset time period can be taken. That is, when the current direction is consistent within the preset time period, the current direction is stored in the memory / register and then compared with the current direction at the current moment. This can improve the accuracy of the current direction data.

[0074] In one embodiment, the photovoltaic insulation failure location method further includes the following steps: displaying information about the photovoltaic string with ground insulation failure; and / or transmitting the information about the photovoltaic string with ground insulation failure to a smart terminal device.

[0075] In practical applications, the positive and negative cables of all photovoltaic strings can be numbered, and a mapping table containing the numbers and the locations of the positive and negative cables of the photovoltaic strings can be stored.

[0076] The control display shows the location of the positive and negative cables of the photovoltaic string with ground insulation failure. Maintenance personnel can use the display to pinpoint the location of the cable to be repaired, improving maintenance efficiency.

[0077] Alternatively, the location of the positive and negative cables of the photovoltaic string with ground insulation failure can be transmitted to a smart terminal device. Maintenance personnel can then use the smart terminal device to identify cables with ground insulation failure anytime, anywhere, improving maintenance efficiency.

[0078] This invention also proposes a controller for an inverter, comprising a processor, a memory, and a photovoltaic insulation failure location program stored in the memory and executable on the processor. When executed by the processor, the photovoltaic insulation failure location program implements the steps of the aforementioned photovoltaic insulation failure location method. Since the controller of this inverter employs all the technical solutions of the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated upon further here.

[0079] The present invention also proposes an inverter for use in a photovoltaic system, the photovoltaic system comprising multiple photovoltaic arrays, the inverter comprising: the controller of the inverter described above, and a current sampling circuit, the detection terminal being connected to the first electrode and the second electrode of each photovoltaic string in the photovoltaic array, the output terminal of the current sampling circuit being connected to the controller of the inverter, the current sampling circuit being used to sample the output current of the first electrode and / or the second electrode of each photovoltaic string in each photovoltaic array.

[0080] Since this inverter adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0081] Reference Figure 1In one embodiment, the inverter further includes: a voltage conversion circuit, with its input terminal connected to the photovoltaic array, for converting the DC power output from the photovoltaic array into voltage; and an inverter circuit, with its input terminal connected to the output terminal of the voltage conversion circuit, and its controlled terminal connected to the inverter's controller, for converting the DC power output from the voltage conversion circuit into AC power under the control of the inverter's controller. The voltage conversion circuit can be a two-level or a three-level type, and is not limited here, for example, a symmetrical boost circuit.

[0082] The inverter may further include a maximum power point tracking (MPPT) control circuit connected to the voltage conversion circuit. The MPPT control circuit acquires the internal resistance of the photovoltaic array connected to the voltage conversion circuit and adjusts the equivalent resistance of the voltage conversion circuit to match the internal resistance of the photovoltaic array. This ensures the photovoltaic array operates at its maximum power point. By configuring the MPPT control circuit, the photovoltaic array operates at its maximum power point, thus controlling its output power.

[0083] Reference Figure 5 In one embodiment, the voltage conversion circuit is a three-level voltage conversion circuit;

[0084] The input terminal of the three-level voltage conversion circuit is connected to the photovoltaic array, the first level output terminal of the three-level voltage conversion circuit is connected to the positive terminal VBUS+ of the DC bus, the second level output terminal of the three-level voltage conversion circuit is connected to the midpoint M of the DC bus, and the third level output terminal of the three-level voltage conversion circuit is connected to the negative terminal VBUS- of the DC bus.

[0085] It should be noted that under certain operating conditions, such as when the output currents of the photovoltaic strings are uneven, if the output current of the photovoltaic string with ground insulation failure in one photovoltaic array is greater than the sum of the output currents of all photovoltaic strings in another photovoltaic array, the two-level voltage conversion circuit may cause the ground insulation failure to be missed. The three-level voltage conversion circuit set in this embodiment can solve this problem, as detailed below:

[0086] The industrial control is as follows: When the output current of each photovoltaic string is uneven, when the output current of the photovoltaic string with ground insulation failure in one photovoltaic array is greater than the sum of the output currents of all photovoltaic strings in another photovoltaic array, for example, the output current of the first photovoltaic string 111 is 8A, the output current of the second photovoltaic string is 13A, and the output currents of the third photovoltaic string 121 and the fourth photovoltaic string 122 are all 5A, then the output current of the second photovoltaic string 112 is greater than the sum of the output currents of the third photovoltaic string 121 and the fourth photovoltaic string 122.

[0087] Figure 5 and Figure 6 The diagrams illustrate the current flow when the insulation of the negative cable of the second photovoltaic string 112 and the positive cable of the third photovoltaic string 121 fails to ground under the aforementioned operating conditions, specifically when the voltage conversion circuit is a three-level voltage conversion circuit and a two-level voltage conversion circuit. (Refer to...) Figure 6 When a two-level voltage conversion circuit is used, the positive output currents Istr3p and Istr4p of the third photovoltaic string 121 and the fourth photovoltaic string 122 converge into the negative terminal of the second photovoltaic string 112. The positive output current Imppt1p of the first photovoltaic array 11 is 21A, and the negative output current Imppt2n of the second photovoltaic array 12 is 10A. Therefore, the negative output current Imppt1n of the first photovoltaic array 11 is 11A. Analyzing the junction point B using Kirchhoff's laws, the actual current Istr2n from junction point B to the failure point is positive 3A. This indicates that the negative cable of the second photovoltaic string 112 has failed to maintain its insulation to ground. However, the current Istr2n in the negative cable is positive, causing the method of detecting insulation failure by current direction to miss the detection.

[0088] Reference Figure 5 Since the voltage conversion circuit is a three-level voltage conversion circuit, the bus capacitors include a first bus capacitor C1 and a second bus capacitor C2. One end of the first bus capacitor C1 is connected to the positive DC bus VBUS+, and the other end of the first bus capacitor C1 is connected to one end of the second bus capacitor C2. The other end of the second bus capacitor C2 is connected to the negative DC bus VBUS-. The common terminal of the first bus capacitor C1 and the second bus capacitor C2 is the bus midpoint M. At this time, when the insulation of the positive cable of the third photovoltaic string 121 to ground fails, a path is formed between the bus midpoint M, the first switch T1 of the second level conversion circuit 22, and the first inductor L1, so that the bus current will not flow to the bus junction point B. Therefore, the output current Imppt1n of the negative terminal of the first photovoltaic array 11 is 0A instead of 11A. At this time, by analyzing the bus junction point B using Kirchhoff's law, it can be determined that the actual current Istr2n from the bus junction point B to the failure point is opposite to the negative current Istr1n of the first photovoltaic string 111, that is, it is a reverse current. In other words, as long as the insulation of the negative cable of the second photovoltaic string 112 and the positive cable of the third photovoltaic string 121 to ground fails, the current Istr2n of the negative cable of the second photovoltaic string 112 must be a reverse current. Therefore, the three-level voltage conversion circuit proposed in this embodiment can effectively solve the problem of missed detection under this condition.

[0089] In practical applications, the three-level voltage conversion circuit includes a first inductor L1, a second inductor L2, a first switch T1, a second switch T2, a first diode D1, and a second diode D2. One end of the first inductor L1 is connected to the first electrode of the photovoltaic array, and one end of the second inductor L2 is connected to the second electrode of the photovoltaic array. The other end of the first inductor L1, the first lead of the first switch T1, and the anode of the first diode D1 are interconnected, and the cathode of the first diode D1 is the first-level output terminal. The second lead of the first switch T1 is connected to the first lead of the second switch T2, and their common terminal is the second-level output terminal. The other end of the second inductor L2, the second lead of the second switch T2, and the cathode of the second diode D2 are interconnected, and the anode of the second diode D2 is the third-level output terminal. The first switch T1 and the second switch T2 can be one or more of transistors, MOSFETs, or IGBTs. The specific working principle of the symmetrical three-level boost circuit is not detailed here.

[0090] In this embodiment, when the output current of a photovoltaic string in one photovoltaic array that has failed to achieve ground insulation is greater than the sum of the output currents of all photovoltaic strings in another photovoltaic array, and when the positive cable of the second photovoltaic array 12 fails to achieve ground insulation, a path is formed between the midpoint M of the DC bus, the first switch of the second level conversion circuit 22, and the first inductor. This ensures that the output current Imppt1n of the negative terminal of the first photovoltaic array 11 is 0A, and further ensures that when the negative cable of the second photovoltaic string 112 fails to achieve ground insulation, its output current Istr2n is a reverse current. Furthermore, a diode can be connected in parallel between the input and output terminals of the first and second switches to ensure that a path is formed between the midpoint M of the bus, the first switch (sixth diode) of the second level conversion circuit 22, and the first inductor.

[0091] The present invention also proposes a photovoltaic system, characterized in that the photovoltaic system includes multiple photovoltaic arrays and the inverter described above. The specific structure of the inverter is as described in the above embodiments. Since the photovoltaic system adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0092] In one embodiment, each photovoltaic array includes multiple photovoltaic strings connected in parallel. These multiple photovoltaic strings share a single level conversion circuit and maximum power point tracking control circuit, effectively reducing costs.

[0093] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for locating photovoltaic insulation failures, applied to photovoltaic systems, characterized in that, The photovoltaic system includes multiple photovoltaic arrays and an inverter. The inverter includes a three-level voltage conversion circuit. The input terminal of the three-level voltage conversion circuit is connected to the photovoltaic arrays. The first level output terminal of the three-level voltage conversion circuit is connected to the positive terminal of the DC bus. The second level output terminal of the three-level voltage conversion circuit is connected to the midpoint of the DC bus. The third level output terminal of the three-level voltage conversion circuit is connected to the negative terminal of the DC bus. The photovoltaic insulation failure location method includes the following steps: S100, Obtain the current of each of the photovoltaic arrays; S200. When the current of any one of the photovoltaic arrays meets the first preset current flow direction, it is determined that the photovoltaic array that meets the first preset current flow direction has failed to achieve ground insulation. Each of the photovoltaic arrays includes multiple photovoltaic strings, which are connected in parallel with each other. S100 includes: acquiring the output current of the first electrode and / or the second electrode of each photovoltaic string in each photovoltaic array; S200 includes: when the output current of each photovoltaic string is not equal, based on the three-level voltage conversion circuit, when the output current of the first electrode and / or the second electrode of any photovoltaic string satisfies the second preset current flow direction, confirming that the first electrode and / or the second electrode of the photovoltaic string that satisfies the second preset current flow direction has failed to be insulated from the ground. Wherein, the polarity of the first electrode is opposite to that of the second electrode; One of the first electrode and the second electrode is the positive electrode of the photovoltaic string, and the other is the negative electrode of the photovoltaic string; The first preset current direction is the opposite direction of the current flow when the photovoltaic array is working normally, and the second preset current direction is the opposite direction of the output current flow of the first electrode and / or the second electrode when the photovoltaic string is working normally.

2. The photovoltaic insulation failure location method as described in claim 1, characterized in that, The first preset current flow direction is the opposite direction of the current flow direction of the photovoltaic array at a previous preset time interval; and / or, The second preset current flow direction is the opposite direction of the output current flow at the moment of the previous preset time interval between the first electrode and / or the second electrode of the photovoltaic string.

3. The photovoltaic insulation failure location method according to any one of claims 1-2, characterized in that, The following steps are included after step S200: The control display device displays information about the photovoltaic string that has failed to achieve ground insulation.

4. The photovoltaic insulation failure location method according to any one of claims 1-2, characterized in that, The following steps are included after step S200: The information about the photovoltaic string that has failed to maintain its ground insulation is transmitted to a smart terminal device.

5. A controller for an inverter, characterized in that, The inverter controller includes a processor, a memory, and a photovoltaic insulation failure location program stored in the memory and executable on the processor. When the photovoltaic insulation failure location program is executed by the processor, it implements the steps of the photovoltaic insulation failure location method as described in any one of claims 1 to 4.

6. An inverter used in a photovoltaic system, characterized in that, The photovoltaic system includes multiple photovoltaic arrays, and the inverter includes: The controller for the inverter as described in claim 5, and The current sampling circuit has its detection terminal connected to the first and second electrodes of each photovoltaic string in the photovoltaic array, and its output terminal connected to the controller of the inverter. The current sampling circuit is used to sample the output current of the first and / or second electrodes of each photovoltaic string in the photovoltaic array.

7. The inverter as described in claim 6, characterized in that, The inverter also includes: A voltage conversion circuit, with its input terminal connected to the photovoltaic array, is used to convert the DC power output from the photovoltaic array into voltage. The inverter circuit has its input terminal connected to the output terminal of the voltage conversion circuit, and its controlled terminal connected to the controller of the inverter. The inverter circuit is used to convert the DC power output by the voltage conversion circuit into AC power under the control of the controller of the inverter.

8. The inverter as described in claim 7, characterized in that, The voltage conversion circuit is a three-level voltage conversion circuit; The input terminal of the three-level voltage conversion circuit is connected to the photovoltaic array, the first level output terminal of the three-level voltage conversion circuit is connected to the positive terminal of the DC bus, the second level output terminal of the three-level voltage conversion circuit is connected to the midpoint of the DC bus, and the third level output terminal of the three-level voltage conversion circuit is connected to the negative terminal of the DC bus.

9. The inverter as described in claim 8, characterized in that, The three-level voltage conversion circuit includes a first inductor, a second inductor, a first switching transistor, a second switching transistor, a first diode, and a second diode; One end of the first inductor is connected to the first electrode of the photovoltaic array, and one end of the second inductor is connected to the second electrode of the photovoltaic array; the other end of the first inductor, the first lead of the first switch, and the anode of the first diode are interconnected, and the cathode of the first diode is the first level output terminal of the three-level voltage conversion circuit; the second lead of the first switch is connected to the first lead of the second switch, and their common terminal is the second level output terminal of the three-level voltage conversion circuit; the other end of the second inductor, the second lead of the second switch, and the cathode of the second diode are interconnected, and the anode of the second diode is the third level output terminal of the three-level voltage conversion circuit.

10. A photovoltaic system, characterized in that, The photovoltaic system includes multiple photovoltaic arrays and an inverter as described in any one of claims 6 to 9.

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