Photovoltaic power generation system and its insulation impedance detection method

Abstract

The present application discloses a photovoltaic power generation system and an insulation impedance detection method thereof. The insulation impedance detection method comprises: obtaining the input voltage of each MPPT unit and the voltage to ground of the DC bus, and calculating the voltage to ground of the input terminal of each MPPT unit; after adjusting the impedance to ground of the DC bus, again obtaining the input voltage of each MPPT unit and the voltage to ground of the DC bus, and calculating the voltage to ground of the input terminal of each MPPT unit; and determining the insulation impedance to ground of each MPPT unit input terminal based on the voltage to ground of each MPPT unit input terminal obtained from the two calculations. By determining the insulation impedance to ground of each MPPT unit input terminal, the present application can accurately locate faulty photovoltaic cell modules, reduce the workload of subsequent troubleshooting, and avoid the problem of false fault alarms caused by low insulation impedance in high temperature and high humidity environments.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic power generation system and an insulation impedance detection method thereof. Background Art

[0002] Photovoltaic power generation is now increasingly widely used in both domestic and international power generation markets. Grid-connected photovoltaic inverters are key components of photovoltaic power generation systems, converting the DC power from photovoltaic cell modules into AC power for grid-connected power generation. For safety reasons, grid-connected photovoltaic inverters must monitor the insulation resistance of their inputs to ground. If the insulation resistance falls below the specified value, an alarm will be issued, preventing grid-connected power generation.

[0003] Current photovoltaic power generation systems typically have multiple MPPTs (Maximum Power Point Tracking) channels. Existing insulation impedance detection methods typically measure the insulation impedance of the positive and negative DC busbars to ground. However, these methods cannot precisely pinpoint the specific MPPT channel with insulation anomalies, making subsequent troubleshooting difficult. Furthermore, the insulation impedance of the positive and negative DC busbars to ground is the parallel value of the insulation impedance of each MPPT channel to ground. The greater the number of parallel connections, the lower the impedance. This deteriorates insulation in high temperature and humidity conditions, potentially causing false triggering of the insulation impedance of the positive and negative DC busbars, leading to system shutdown. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a photovoltaic power generation system and its insulation impedance detection method, so as to accurately locate the faulty photovoltaic cell components, reduce the workload of subsequent troubleshooting, and at the same time avoid the problem of false fault alarms caused by low insulation impedance in high temperature and high humidity environments.

[0005] The technical solutions adopted by this application to solve the above technical problems are as follows:

[0006] According to one aspect of the present application, a method for detecting insulation impedance of a photovoltaic power generation system is provided. The photovoltaic power generation system includes a DC bus, multiple MPPT units, and an inverter. The input end of each MPPT unit is connected to its corresponding photovoltaic cell assembly, and the output ends of the multiple MPPT units are connected in parallel and then connected to the input end of the inverter via the DC bus. The insulation impedance detection method includes:

[0007] Obtaining the input voltage of each MPPT unit and the voltage of the DC bus to ground, and calculating the voltage of the input end of each MPPT unit to ground;

[0008] After adjusting the ground impedance of the DC bus, the input voltage of each MPPT unit and the ground voltage of the DC bus are obtained again, and the ground voltage of the input end of each MPPT unit is calculated;

[0009] The insulation resistance of each MPPT unit input terminal to ground is determined based on the voltage to ground of each MPPT unit input terminal obtained from the two previous calculations.

[0010] According to another aspect of the present application, there is provided a photovoltaic power generation system including a DC bus, a plurality of MPPT units, an inverter, and a controller;

[0011] The input end of each MPPT unit is connected to its corresponding photovoltaic cell assembly, and the output ends of multiple MPPT units are connected in parallel and then connected to the input end of the inverter through the DC bus;

[0012] The controller is configured to obtain the input voltage of each MPPT unit and the voltage to ground of the DC bus, and calculate the voltage to ground of the input end of each MPPT unit; after adjusting the impedance to ground of the DC bus, obtain the input voltage of each MPPT unit and the voltage to ground of the DC bus again, and calculate the voltage to ground of the input end of each MPPT unit; and determine the insulation impedance to ground of each MPPT unit input end based on the voltage to ground of each MPPT unit input end obtained by the two calculations.

[0013] The photovoltaic power generation system and insulation impedance detection method thereof of the embodiment of the present application can accurately locate the faulty photovoltaic cell assembly by determining the insulation impedance to ground of the input end of each MPPT unit, thereby reducing the workload of subsequent troubleshooting and avoiding the problem of false fault alarms caused by low insulation impedance in high temperature and high humidity environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of a photovoltaic power generation system provided in an embodiment of the present application;

[0015] Figure 2 Schematic diagram of the insulation impedance detection method of the photovoltaic power generation system provided in an embodiment of the present application.

[0016] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer and more understandable, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0018] In the description of this application, it should be understood that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "front," "back," "left," and "right" are based on the directions or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific direction, be constructed, or operate in a specific direction. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0019] An embodiment of the present application provides a photovoltaic power generation system, including a DC bus, a plurality of MPPT units, an inverter, and a controller;

[0020] The input end of each MPPT unit is connected to its corresponding photovoltaic cell assembly, and the output ends of multiple MPPT units are connected in parallel and then connected to the input end of the inverter through the DC bus;

[0021] The controller is configured to obtain the input voltage of each MPPT unit and the voltage to ground of the DC bus, and calculate the voltage to ground of the input end of each MPPT unit; after adjusting the impedance to ground of the DC bus, obtain the input voltage of each MPPT unit and the voltage to ground of the DC bus again, and calculate the voltage to ground of the input end of each MPPT unit; and determine the insulation impedance to ground of each MPPT unit input end based on the voltage to ground of each MPPT unit input end obtained by the two calculations.

[0022] In one example, the photovoltaic power generation system further includes an alarm module;

[0023] The controller is configured to compare the insulation resistance to ground of any one of the multiple MPPT units with a preset threshold; if the insulation resistance to ground of any one of the MPPT units is less than the preset threshold, generate an alarm and / or control the photovoltaic power generation system to shut down;

[0024] The alarm module is configured to obtain the alarm information to generate an alarm.

[0025] Specifically, the alarm module may use various methods to give an alarm, such as sound, light, text prompt, etc. Controlling the photovoltaic power generation system to shut down includes controlling the inverter to shut down.

[0026] In one example, the controller is independent of the inverter or any one of the multiple MPPT units; or, the controller is integrated into the inverter; or, the controller is integrated into any one of the multiple MPPT units.

[0027] In one example, the photovoltaic power generation system further includes a detector for detecting the input voltage of each MPPT unit and the voltage of the DC bus to ground.

[0028] Specifically, when detecting the DC bus voltage to ground, for a photovoltaic power generation system with a common negative input and output pole, only the negative DC bus voltage to ground can be detected; for a photovoltaic power generation system with a common positive input and output pole, only the positive DC bus voltage to ground can be detected. It is understood that it is also feasible to detect both the positive and negative DC bus voltages to ground.

[0029] In one example, the photovoltaic power generation system further includes a first ground impedance adjustment unit connected to the positive DC bus and / or a second ground impedance adjustment unit connected to the negative DC bus.

[0030] Specifically, the first ground impedance adjustment unit (or the second ground impedance adjustment unit) may be composed of a plurality of resistors connected in series and parallel, and the ground impedance may be adjusted by controlling the corresponding relay bypass.

[0031] For ease of understanding, the following Figure 1 , explained with two MPPT units:

[0032] like Figure 1 As shown, the input of MPPT1 unit is connected to its corresponding photovoltaic cell assembly PV1, the input of MPPT2 unit is connected to its corresponding photovoltaic cell assembly PV2, and the output of MPPT1 unit and MPPT2 unit are connected in parallel and then connected to the input of the inverter through the positive and negative DC bus. R1 is connected between the positive DC bus and ground, and R2 is connected between the negative DC bus and ground. The resistance values of R1 and R2 are both known and variable.

[0033] In the figure, Ubusp represents the voltage of the positive DC bus to ground, Ubusn represents the voltage of the negative DC bus to ground, and Ubus represents the voltage between the positive and negative DC buses; Upv1 represents the input voltage of the MPPT1 unit, Up1 represents the positive voltage to ground at the input end of the MPPT1 unit, Un1 represents the negative voltage to ground at the input end of the MPPT1 unit, Rx1 represents the positive insulation resistance to ground at the input end of the MPPT1 unit, and Ry1 represents the negative insulation resistance to ground at the input end of the MPPT1 unit; Upv2 represents the input voltage of the MPPT2 unit, Up2 represents the positive voltage to ground at the input end of the MPPT2 unit, Un2 represents the negative voltage to ground at the input end of the MPPT2 unit, Rx2 represents the positive insulation resistance to ground at the input end of the MPPT2 unit, and Ry2 represents the negative insulation resistance to ground at the input end of the MPPT2 unit.

[0034] Initially, adjust the resistance values of R1 and R2 (or use their default values), denoted as R11 and R21 respectively; detect the input voltage of MPPT1 unit (denoted as Upv11), the input voltage of MPPT2 unit (denoted as Upv21), the voltage between the positive and negative DC bus (denoted as Ubus1), and the voltage of the negative DC bus to ground (denoted as Ubusn1);

[0035] Then, calculate the voltage to ground at the input of MPPT1 and MPPT2 units as follows:

[0036] The negative pole voltage to ground of the MPPT1 unit input terminal: Un11 = Ubusn1;

[0037] The positive voltage to ground of the MPPT1 unit input terminal is: Up11 = Upv11 - Ubusn1;

[0038] The negative pole voltage to ground of the MPPT2 unit input terminal: Un21 = Ubusn1;

[0039] The positive pole voltage to ground of the MPPT2 unit input terminal is: Up21 = Ubusn-Ubusn1.

[0040] Next, adjust the resistance values of R1 and R2 again, recording them as R12 and R22 respectively; and again test the input voltage of MPPT1 unit (recorded as Upv12), the input voltage of MPPT2 unit (recorded as Upv22), the voltage between the positive and negative DC bus bars (recorded as Ubus2), and the voltage of the negative DC bus bar to ground (recorded as Ubusn2);

[0041] Next, calculate the voltage to ground at the input of MPPT1 and MPPT2 units as follows:

[0042] The negative pole voltage to ground of the MPPT1 unit input terminal: Un12 = Ubusn2;

[0043] The positive voltage to ground of the MPPT1 unit input terminal is: Up12 = Upv12 - Ubusn2;

[0044] The negative pole voltage to ground of the MPPT2 unit input terminal: Un22 = Ubusn2;

[0045] The positive pole voltage to ground of the MPPT2 unit input terminal is: Up22 = Ubusn-Ubusn2.

[0046] Finally, the insulation resistance of the positive and negative electrodes of the input terminals of MPPT1 and MPPT2 to ground is calculated using the front and rear bridge principle. The calculation method is:

[0047] Insulation resistance of the positive pole of the MPPT1 unit input terminal to ground:

[0048] Insulation resistance of the negative pole of the MPPT1 unit input terminal to ground:

[0049] Insulation resistance of the positive pole of the MPPT2 unit input to ground:

[0050] Insulation resistance of the negative pole of the MPPT2 unit input terminal to ground:

[0051] in:

[0052] Furthermore, it is possible to determine whether the calculated insulation resistances of the positive and negative poles to ground of the input ends of the MPPT1 unit and the MPPT2 unit are less than a preset threshold value, for example: whether the insulation resistance of the positive pole to ground of the MPPT1 unit input end is less than a preset threshold value 1, whether the insulation resistance of the negative pole to ground of the MPPT1 unit input end is less than a preset threshold value 2, whether the insulation resistance of the positive pole to ground of the MPPT2 unit input end is less than a preset threshold value 3, whether the insulation resistance of the negative pole to ground of the MPPT2 unit input end is less than a preset threshold value 4. If they are less than the preset threshold value, an alarm is issued or the inverter is controlled to shut down.

[0053] like Figure 2 As shown, another embodiment of the present application provides an insulation impedance detection method for a photovoltaic power generation system. The photovoltaic power generation system can refer to the above content and will not be described in detail here.

[0054] The insulation impedance detection method comprises:

[0055] Step S11, obtaining the input voltage of each MPPT unit and the voltage of the DC bus to ground, and calculating the voltage of the input end of each MPPT unit to ground;

[0056] Step S12: After adjusting the impedance of the DC bus to ground, the input voltage of each MPPT unit and the voltage of the DC bus to ground are obtained again, and the voltage of the input end of each MPPT unit to ground is calculated;

[0057] Step S13: Determine the insulation resistance of each MPPT unit input terminal to ground based on the voltage to ground of each MPPT unit input terminal obtained from the two previous calculations.

[0058] In one example, determining the insulation resistance of each MPPT unit input terminal to ground further includes:

[0059] comparing the insulation resistance to ground of an input terminal of any one of the multiple MPPT units with a preset threshold;

[0060] If the insulation impedance to ground of any MPPT unit input terminal is less than a preset threshold, an alarm message is generated and / or the photovoltaic power generation system is controlled to shut down.

[0061] In one example, the voltage of the DC bus to ground includes the voltage of the positive DC bus to ground and / or the voltage of the negative DC bus to ground.

[0062] In one example, the impedance of the DC bus to ground includes the impedance of the positive DC bus to ground and / or the impedance of the negative DC bus to ground.

[0063] In one example, the voltage of the MPPT unit input terminal to ground includes a voltage of the negative pole of the MPPT unit input terminal to ground and a voltage of the positive pole of the MPPT unit input terminal to ground.

[0064] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but are not intended to limit the scope of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and essence of the present application shall fall within the scope of the present application.

Claims

1. A method for detecting insulation impedance of a photovoltaic power generation system, the photovoltaic power generation system comprising a DC bus, a plurality of MPPT units, and an inverter; the input end of each MPPT unit is connected to its corresponding photovoltaic cell assembly, and the output ends of the plurality of MPPT units are connected in parallel and then connected to the input end of the inverter via the DC bus; characterized in that: The insulation impedance detection method comprises: Obtaining the input voltage of each MPPT unit and the voltage of the DC bus to ground, and calculating the voltage of the input end of each MPPT unit to ground; After adjusting the ground impedance of the DC bus, the input voltage of each MPPT unit and the ground voltage of the DC bus are obtained again, and the ground voltage of the input end of each MPPT unit is calculated; Determine the insulation resistance of each MPPT unit input terminal to ground based on the voltage to ground of each MPPT unit input terminal obtained from the two previous calculations. The step of determining the insulation resistance of each MPPT unit input terminal to ground further includes: comparing the insulation resistance to ground of an input terminal of any one of the multiple MPPT units with a preset threshold; If the insulation impedance to ground of any MPPT unit input terminal is less than a preset threshold, an alarm message is generated and / or the photovoltaic power generation system is controlled to shut down.

2. The insulation resistance detection method according to claim 1, wherein: The voltage of the DC bus to ground includes the voltage of the positive DC bus to ground and / or the voltage of the negative DC bus to ground.

3. The insulation resistance detection method according to claim 1, wherein: The ground impedance of the DC bus includes the ground impedance of the positive DC bus and / or the ground impedance of the negative DC bus.

4. The insulation resistance detection method according to claim 1, wherein: The voltage to ground of the MPPT unit input terminal includes the voltage to ground of the negative pole of the MPPT unit input terminal and the voltage to ground of the positive pole of the MPPT unit input terminal.

5. A photovoltaic power generation system, characterized in that: Includes DC bus, multiple MPPT units, inverter and controller; The input end of each MPPT unit is connected to its corresponding photovoltaic cell assembly, and the output ends of multiple MPPT units are connected in parallel and then connected to the input end of the inverter through the DC bus; The controller is configured to obtain the input voltage of each MPPT unit and the voltage to ground of the DC bus, and calculate the voltage to ground of the input end of each MPPT unit; after adjusting the impedance to ground of the DC bus, obtain the input voltage of each MPPT unit and the voltage to ground of the DC bus again, and calculate the voltage to ground of the input end of each MPPT unit; determine the insulation impedance to ground of each MPPT unit input end based on the voltage to ground of each MPPT unit input end obtained by the two calculations; The photovoltaic power generation system further includes an alarm module; The controller is configured to compare the insulation resistance to ground of any one of the multiple MPPT units with a preset threshold; if the insulation resistance to ground of any one of the MPPT units is less than the preset threshold, generate an alarm and / or control the photovoltaic power generation system to shut down; The alarm module is configured to obtain the alarm information to generate an alarm.

6. The photovoltaic power generation system according to claim 5, characterized in that: The photovoltaic power generation system further includes a detector for detecting the input voltage of each MPPT unit and the voltage of the DC bus to ground.

7. The photovoltaic power generation system according to claim 5, characterized in that: The photovoltaic power generation system further includes a first ground impedance adjustment unit connected to the positive DC bus and / or a second ground impedance adjustment unit connected to the negative DC bus.

8. The photovoltaic power generation system according to claim 5, characterized in that: The controller is independent of the inverter or any one of the multiple MPPT units; or, the controller is integrated into the inverter; or, the controller is integrated into any one of the multiple MPPT units.

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