Neutral line fault detection method and optical storage inverter
By calculating the line voltage and phase difference of each phase line in the three-phase line, we determine whether there is a fault in the neutral line, and solve the problem of relying on additional hardware to detect neutral line faults in the prior art, and achieve efficient and reliable fault detection.
Patent Information
- Application Number
- CN202411757934.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-02
- Publication Date
- 2025-03-18
AI Technical Summary
In three-phase and four-wire power supply systems, neutral wire disconnection will lead to unbalanced load voltage, affecting the power generation and loading of the optical storage all-in-one machine. The existing detection methods mostly rely on additional hardware circuits or instruments.
By calculating the line voltage and phase difference between each phase line in the three phase lines, the phase voltage of each phase line when there is no offset in the neutral line, and it is compared with the sampled phase voltage effective value to determine whether the neutral line has a fault.
It realizes the detection of faults such as disconnection or failure of neutral wires in the power grid without adding hardware circuits or instruments, reducing overall cost and loss and improving detection reliability.
Smart Images
Figure CN119644200A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of photovoltaic storage technology, and in particular to a neutral line fault detection method and a photovoltaic storage inverter. Background Art
[0002] In a three-phase four-wire power supply system, a broken neutral line will cause an unbalanced load voltage, causing the voltage of the line with a large load to decrease and the voltage of the line with a small load to increase. For a photovoltaic and storage system operating under a three-phase four-wire system, a broken neutral line seriously affects the power generation and load of the photovoltaic and storage system, so it needs to be quickly identified and the user needs to be alerted. Currently, there are few neutral line break detections based on photovoltaic and storage systems, and most existing detection methods are based on additional hardware circuits or instruments to detect whether the neutral point is offset. Summary of the invention
[0003] The present application aims to provide a neutral line fault detection method and a photovoltaic storage inverter, so as to detect faults such as disconnection or disconnection of the neutral line of the power grid without adding additional hardware circuits or instruments and equipment.
[0004] On one hand, the present application provides a neutral line fault detection method, which is applied to an inverter, and the method includes:
[0005] According to the line voltages between the three phase lines and the phase differences between the line voltages, the phase voltages of the phase lines when there is no offset in the neutral line are calculated;
[0006] According to the phase voltage of each phase line when there is no offset in the neutral line, the corresponding phase voltage effective value is calculated;
[0007] The calculated phase voltage effective value is compared with the sampled phase voltage effective value to determine whether a fault occurs in the neutral line.
[0008] In one example, the calculating, based on the line voltages between the three phase lines and the phase differences between the line voltages, of the phase voltages of the phase lines when there is no offset in the neutral line includes:
[0009] The phase voltage of each phase line when there is no offset in the neutral line is calculated based on the instantaneous value of the line voltage between each phase line and the phase difference between the instantaneous values of the line voltage.
[0010] In one example, the instantaneous value of the line voltage between each phase line is calculated by:
[0011] Sampling the instantaneous value of the phase voltage of each phase line;
[0012] The instantaneous value of the line voltage between the phase lines is calculated based on the instantaneous value of the phase voltage of each phase line obtained by sampling.
[0013] In one example, the phase difference between the instantaneous values of the line voltages is calculated as follows:
[0014] A phase-locked loop is used to lock the phase of the instantaneous value of the line voltage between each phase line, and then the phase difference between the instantaneous values of the line voltage is calculated.
[0015] In one example, the calculating, based on the instantaneous value of the line voltage between the phase lines and the phase difference between the instantaneous values of the line voltage, the phase voltage of each phase line when there is no offset in the neutral line includes:
[0016] According to the instantaneous value of the line voltage between each phase line, the effective value of the line voltage between each phase line is calculated;
[0017] A triangle ABC is constructed based on the effective value of the line voltage between each phase line and the phase difference between the instantaneous values of each line voltage. The first equilateral triangle ABF, the second equilateral triangle ACE and the third equilateral triangle BCD are constructed outward based on the three sides of the triangle ABC. The connecting point O of the diagonals AD, BE and CF is then determined. Finally, the sizes of the line segments AO, BO and CO are calculated to obtain the phase voltages of each phase line when there is no offset in the neutral line.
[0018] In one example, comparing the calculated phase voltage effective value with the sampled phase voltage effective value to determine whether the neutral line is faulty includes:
[0019] A difference between the calculated phase voltage effective value and the sampled phase voltage effective value is determined, and whether a fault occurs in the neutral line is determined based on the difference.
[0020] In one example, determining whether the neutral line fails according to the difference includes:
[0021] If the difference is greater than a preset threshold, it is determined that the neutral line fails; otherwise, the neutral line does not fail.
[0022] In one example, the fault of the neutral line includes a neutral line break or a neutral line disconnection.
[0023] On the other hand, the present application provides a photovoltaic storage inverter, wherein the DC end of the photovoltaic storage inverter is connected to a photovoltaic array and / or an energy storage battery, and the three-phase AC end and the neutral line end of the photovoltaic storage inverter are connected to the power grid one by one through three phase lines and a neutral line;
[0024] The photovoltaic power storage inverter also includes a control unit, which is configured to execute the neutral line fault detection method.
[0025] In one example, the photovoltaic energy storage inverter further includes an electric meter for sampling and obtaining an effective value of a phase voltage.
[0026] The neutral line fault detection method and photovoltaic storage inverter provided in the present application can realize the detection of neutral line disconnection or disconnection faults without adding additional hardware circuits or instruments and equipment, thereby reducing the coupling with the hardware circuit, reducing the overall cost and overall loss, and improving the reliability of detection. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 A schematic diagram of a photovoltaic storage system provided for an embodiment of the present application;
[0028] Figure 2 is a schematic diagram of a neutral line fault detection method provided in an embodiment of the present application;
[0029] Figure 3 It is a schematic diagram of the process of calculating the effective value of the line voltage between each phase line provided in the implementation mode of the present application.
[0030] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION
[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.
[0032] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "front", "back", "left", "right", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.
[0033] Figure 1 It is a schematic diagram of a photovoltaic storage system provided in an embodiment of the present application.
[0034] like Figure 1 As shown, the photovoltaic storage system includes a photovoltaic array, an energy storage battery, a photovoltaic storage inverter and an electric meter (i.e., the three-phase electric meter shown in the figure).
[0035] The DC end of the photovoltaic storage inverter is connected to the photovoltaic array and / or the energy storage battery, and the three-phase AC end (as shown in A, B, and C in the figure) and the neutral line end (as shown in N in the figure) of the photovoltaic storage inverter are connected to the power grid one by one through three phase lines and a neutral line; the voltage sampling port of the electric meter is used to sample the three-phase voltage (refer to the sampling voltage connection line in the figure), that is, to obtain the effective value of the voltage of each phase in the three phases.
[0036] The inverter integrates a voltage sampling unit, through which the three-phase voltage can be sampled, that is, the instantaneous value of the phase voltage of each phase line can be obtained.
[0037] The photovoltaic storage inverter also integrates a control unit, which can be implemented as an array of multiple logic gates, or can be implemented as a combination of a general microcontroller and a memory, in which a program executable in the microcontroller is stored, such as the neutral line fault detection program described below, so that the microcontroller can execute the neutral line fault detection method. It will be understood by those skilled in the art that the control unit can also be implemented in other forms of hardware.
[0038] Based on the above-mentioned photovoltaic storage system, the embodiment of the present application also provides a neutral line fault detection method, such as Figure 2 As shown, the method comprises the steps of:
[0039] S11, calculating the phase voltage of each phase line when there is no offset in the neutral line according to the line voltage between each phase line and the phase difference between each line voltage among the three phase lines;
[0040] S12, calculating the corresponding phase voltage effective value according to the phase voltage of each phase line when there is no offset in the neutral line;
[0041] S13: Compare the calculated phase voltage effective value with the sampled phase voltage effective value to determine whether the neutral line is faulty.
[0042] In one example, the calculating, based on the line voltages between the three phase lines and the phase differences between the line voltages, of the phase voltages of the phase lines when there is no offset in the neutral line includes:
[0043] The phase voltage of each phase line when there is no offset in the neutral line is calculated based on the instantaneous value of the line voltage between each phase line and the phase difference between the instantaneous values of the line voltage.
[0044] In one example, the instantaneous value of the line voltage between each phase line is calculated by:
[0045] Sampling the instantaneous value of the phase voltage of each phase line;
[0046] The instantaneous value of the line voltage between the phase lines is calculated based on the instantaneous value of the phase voltage of each phase line obtained by sampling.
[0047] In one example, the phase difference between the instantaneous values of the line voltages is calculated as follows:
[0048] A phase-locked loop is used to lock the phase of the instantaneous value of the line voltage between each phase line, and then the phase difference between the instantaneous values of the line voltage is calculated.
[0049] In one example, the calculating, based on the instantaneous value of the line voltage between the phase lines and the phase difference between the instantaneous values of the line voltage, the phase voltage of each phase line when there is no offset in the neutral line includes:
[0050] According to the instantaneous value of the line voltage between each phase line, the effective value of the line voltage between each phase line is calculated;
[0051] A triangle ABC is constructed based on the effective value of the line voltage between each phase line and the phase difference between the instantaneous values of each line voltage. The first equilateral triangle ABF, the second equilateral triangle ACE and the third equilateral triangle BCD are constructed outward based on the three sides of the triangle ABC. The connecting point O of the diagonals AD, BE and CF is then determined. Finally, the sizes of the line segments AO, BO and CO are calculated to obtain the phase voltages of each phase line when there is no offset in the neutral line.
[0052] The following combination Figure 3 To explain:
[0053] Assume that the instantaneous values of the phase voltages of each phase line obtained by sampling are U AN , U BN , U CN According to the instantaneous value of the phase voltage of each phase line obtained by sampling, the instantaneous value of the line voltage between each phase line is calculated to be U AB , U BC , U CA Among them, U AB =U AN -U BN , U BC =U BN -U CN , U CA =U CN -U AN .
[0054] The instantaneous value of line voltage U AB , U BC , U CA Use the phase-locked loop to lock the angle and calculate U AB with U BC , U BC with U CA , UCA with U AB The phase difference between them is Φ1, Φ2, Φ3, and the instantaneous value of the line voltage U AB , U BC , U CA Calculate the effective value U AB_rms , U BC_rms , U CA_rms .
[0055] The effective value of the line voltage between each phase line is U AB_rms , U BC_rms , U CA_rms The phase differences Φ1, Φ2, and Φ3 between the instantaneous values of the line voltages are used as the basis to construct triangle ABC, and then the three sides of triangle ABC are used as the basis to construct the first equilateral triangle ABF, the second equilateral triangle ACE, and the third equilateral triangle BCD. Then the connection point O of the diagonal lines AD, BE, and CF is determined, and finally the size of the line segments AO, BO, and CO is calculated to obtain the phase voltage of each phase line when there is no offset in the neutral line. Specifically, the calculation is performed through mathematical means including the proof of triangle congruence, the sine theorem, the properties of triangles, the properties of angles, etc. For example:
[0056] 1) Since AF=AB, ∠FAC=∠BAE, AC=AE; therefore triangle AFC≌triangle ABE, CF=BE.
[0057] 2) The same principle as 1) can be used to prove that triangle BCF≌triangle ABD, so CF=AD, so CF=AD=BE.
[0058] 3) Since triangle AFC≌triangle ABE, ∠ABE=∠AFC, so ∠BFC+∠FEB=120°, ∠BOF=60°; so ∠FOE=120°, according to the principle of vertical angles, ∠BOC=120°.
[0059] 4) Same as 3), ∠AOC=120°, ∠AOB=120°, that is, θ1, θ2, θ3 are all 120°. If AB, BC, CA represent the line voltage, then AO, BO, CO can represent the phase voltage of each phase line when the neutral point is not offset.
[0060] 5) Based on the known conditions, the lengths of AB, AF, and BF; the lengths of AC, AE, and CE; the lengths of BC, BD, and CD; the sizes of ∠ABC, ∠BCA, and ∠CAB;
[0061] Since ∠FAC=∠FAB+∠BAC, ∠FAB=60°, ∠BAC has been calculated in the formula, so ∠AFC=180°-∠FAB-∠BAC-∠ACF
[0062] Therefore, according to the sine theorem a / sinA=b / sinB, the formula for triangle AFC is: AF / sin∠ACF=AC / sin∠AFC, that is, AF / sin∠ACF=AC / (sin180°-∠FAB-∠BAC-∠ACF), in which only ∠ACF is an unknown variable and can be solved.
[0063] 6) Since ∠ACF has been calculated, we can use the sine theorem to express triangle AOC as AO / sin∠ACF=AC / sin∠AOC, where only AO is an unknown variable and can be solved.
[0064] 7) The same solution method as AO can be used to solve the size of BO and CO.
[0065] In one example, comparing the calculated phase voltage effective value with the sampled phase voltage effective value to determine whether the neutral line is faulty includes:
[0066] A difference between the calculated phase voltage effective value and the sampled phase voltage effective value is determined, and whether a fault occurs in the neutral line is determined based on the difference.
[0067] In one example, determining whether the neutral line fails according to the difference includes:
[0068] If the difference is greater than a preset threshold, it is determined that the neutral line fails; otherwise, the neutral line does not fail.
[0069] In one example, the fault of the neutral line includes a neutral line break or a neutral line disconnection.
[0070] by Figure 1 Take the following as an example, the specific neutral line fault detection conditions are as follows:
[0071] 1) When the PV-storage inverter is connected to the grid normally and the user load is not connected, if the neutral line is broken, the bus midpoint potential will jitter three times the grid frequency due to the characteristics of the inverter circuit. At this time, the bus midpoint is connected to the neutral line of the machine port, so there will also be a three-fold frequency jitter at the grid phase voltage sampling point. At this time, the neutral line break detection of the distribution network can be performed based on the above solution;
[0072] 2) When the photovoltaic storage inverter operates normally, is connected to the load and the neutral line of the distribution network is broken, the neutral line potential of the inverter will be clamped by the neutral point of the three-phase user load. At this time, the neutral point potential is determined by the balance of the load. If the load is unbalanced, the neutral line potential of the photovoltaic storage inverter will be offset. The neutral line break detection of the distribution network can be performed based on the above scheme.
[0073] It should be noted that the above neutral line fault detection method is also applicable to other three-phase four-wire application systems.
[0074] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but the scope of the present application is not limited thereby. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present application shall be within the scope of the present application.
Claims
1. A neutral line fault detection method, applied to an inverter, characterized in that: The method comprises: According to the line voltages between the three phase lines and the phase differences between the line voltages, the phase voltages of the phase lines when there is no offset in the neutral line are calculated; According to the phase voltage of each phase line when there is no offset in the neutral line, the corresponding phase voltage effective value is calculated; The calculated phase voltage effective value is compared with the sampled phase voltage effective value to determine whether a fault occurs in the neutral line.
2. The neutral line fault detection method according to claim 1, characterized in that: The method of calculating the phase voltage of each phase line when there is no offset in the neutral line according to the line voltage between each phase line in the three phase lines and the phase difference between each line voltage includes: The phase voltage of each phase line when there is no offset in the neutral line is calculated based on the instantaneous value of the line voltage between each phase line and the phase difference between the instantaneous values of the line voltage.
3. The neutral line fault detection method according to claim 2, characterized in that: The instantaneous value of the line voltage between each phase line is calculated by the following method: Sampling the instantaneous value of the phase voltage of each phase line; The instantaneous value of the line voltage between the phase lines is calculated based on the instantaneous value of the phase voltage of each phase line obtained by sampling.
4. The neutral line fault detection method according to claim 2, characterized in that: The phase difference between the instantaneous values of each line voltage is calculated in the following way: A phase-locked loop is used to lock the phase of the instantaneous value of the line voltage between each phase line, and then the phase difference between the instantaneous values of the line voltage is calculated.
5. The neutral line fault detection method according to claim 2, characterized in that: The method of calculating the phase voltage of each phase line when there is no offset in the neutral line according to the instantaneous value of the line voltage between each phase line and the phase difference between the instantaneous values of the line voltage, comprises: According to the instantaneous value of the line voltage between each phase line, the effective value of the line voltage between each phase line is calculated; A triangle ABC is constructed based on the effective value of the line voltage between each phase line and the phase difference between the instantaneous values of each line voltage. The first equilateral triangle ABF, the second equilateral triangle ACE and the third equilateral triangle BCD are constructed outward based on the three sides of the triangle ABC. The connecting point O of the diagonals AD, BE and CF is then determined. Finally, the sizes of the line segments AO, BO and CO are calculated to obtain the phase voltages of each phase line when there is no offset in the neutral line.
6. The neutral line fault detection method according to claim 1, characterized in that: The step of comparing the calculated phase voltage effective value with the sampled phase voltage effective value to determine whether the neutral line is faulty includes: A difference between the calculated phase voltage effective value and the sampled phase voltage effective value is determined, and whether a fault occurs in the neutral line is determined based on the difference.
7. The neutral line fault detection method according to claim 6, characterized in that: The determining whether the neutral line fails according to the difference includes: If the difference is greater than a preset threshold, it is determined that the neutral line fails; otherwise, the neutral line does not fail.
8. The neutral line fault detection method according to claim 1, characterized in that: The neutral line fault includes a neutral line break or a neutral line disconnection.
9. A solar-storage inverter, characterized in that: The DC end of the photovoltaic storage inverter is connected to the photovoltaic array and / or the energy storage battery, and the three-phase AC end and the neutral line end of the photovoltaic storage inverter are connected to the power grid one by one through three phase lines and the neutral line; The photovoltaic power storage inverter further includes a control unit, which is configured to execute the neutral line fault detection method according to any one of claims 1 to 8.
10. The photovoltaic energy storage inverter according to claim 9, characterized in that: The photovoltaic power storage inverter also includes an electric meter for sampling and obtaining the effective value of the phase voltage.