Double-live-wire inverter and power grid end detection method thereof

Abstract

The invention discloses a double-live-wire inverter and a power grid end detection method thereof. The power grid end detection method of the double-live-wire inverter comprises the following steps: S1, obtaining a first phase voltage instantaneous value and a second phase voltage instantaneous value of the inverter; s2, carrying out per-unit processing on the first phase voltage instantaneous value and the second phase voltage instantaneous value of the inverter to respectively obtain a first phase voltage per-unit value and a second phase voltage per-unit value; s3, multiplying the first phase voltage per unit value by the second phase voltage per unit value to obtain a per unit value product; and S4, judging whether the phase sequence of the inverter is normal or not according to the per unit value product. According to the method, the connection of the power grid end of the double-live-wire inverter can be rapidly detected without a complex phase-locked loop.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage systems, and in particular to a dual-live-wire inverter and a grid-end detection method thereof. Background Art

[0002] There are many grid standards around the world. For example, some countries / regions have two types of grids: 120V / 240V dual-phase grid and 120V / 208V three-phase grid. Dual-phase grid is also called split-phase grid, which is the grid specification used in many countries. Before connecting a dual-phase inverter to the grid, the output port voltage must be tested to ensure that: a. the grid specification is consistent with the inverter output specification; b. the wiring is correct, otherwise it will fail to connect to the grid.

[0003] like Figure 1a , the output port of the dual live wire inverter 10 is correctly connected to the grid 20, wherein the L1 terminal of the inverter 10 is connected to the L1 terminal of the grid 20, and the L2 terminal of the inverter 10 is connected to the L2 terminal of the grid 20. At this time, the output voltages VL1N (the voltage between the port L1 and the port N) and VL2N (the voltage between the port L2 and the port N) of the inverter 10 have normal amplitudes and a phase difference of 180°. In addition, since the dual live wire inverter has no positive and negative phase sequence, such as Figure 1b If the L1 terminal of the inverter 10 is connected to the L2 terminal of the grid 20, and the L2 terminal of the inverter 10 is connected to the L1 terminal of the grid 20, which is also correctly connected, then the amplitudes of the output voltages VL1N and VL2N of the inverter 10 are also normal and the phase difference is 180°.

[0004] like Figure 2 , the ports of the dual-live-wire inverter 10 and the grid 20 are incorrectly connected, wherein the L1 and L2 ports of the inverter 10 are both connected to the L2 port of the grid 20, the port voltages VL1N and VL2N of the inverter 10 have normal amplitudes and equal phases, and the output port voltage of the dual-live-wire inverter at this time does not meet the aforementioned condition b.

[0005] like Figure 3a , the dual live wire inverter is connected to the three-phase grid, the L1 and L2 ports of the inverter are connected to the L1 and L2 ports of the grid respectively, the amplitude of the inverter port voltage VL1N and VL2N is normal and the phase difference is 120°; Figure 3b , the dual live wire inverter is connected to the three-phase grid, the L1 and L2 ports of the inverter are connected to the L1 and L3 ports of the grid respectively, and the amplitudes of the inverter port voltages VL1N and VL2N are normal and the phase difference is 120°. Figure 3a and Figure 3b The output port voltages of the dual live wire inverters do not satisfy the aforementioned condition a.

[0006] Connection errors or grid specification errors can cause inverter grid connection failure. The above are just a few common wiring errors. Figure 1a and Figure 1b Any connection method other than the correct one shown in the figure can be considered as connection error, which will not be listed here one by one.

[0007] The inverter grid connection needs to ensure the synchronization of voltage amplitude, phase and frequency. When the grid voltage amplitude and frequency are normal, the grid phase detection must be performed before the inverter is grid connected. The conventional practice in the prior art is: after the inverter is connected to the grid end L1, L2, N one by one, the inverter uses two phase-locked loops to track the phases of its own port voltages VL1N and VL2N respectively, and determines whether the phase difference between VL1N and VL2N is 180°. Common software phase-locked loops usually require software filtering, coordinate transformation, low-pass filtering and integration, but this algorithm is relatively complex.

[0008] The disclosure of the above background technology content is only used to assist in understanding the concept and technical solution of the present invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above content has been disclosed on the filing date of this patent application, the above background technology should not be used to evaluate the novelty and creativity of the present application. Summary of the invention

[0009] In order to solve the above technical problems, the present invention proposes a dual-fireline inverter and a grid-end detection method thereof, which can quickly detect the connection of the grid end of the dual-fireline inverter without a complex phase-locked loop.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention discloses a grid-side detection method for a dual-live-wire inverter, comprising the following steps: S1: Obtain the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter; S2: normalizing the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter to obtain the first phase voltage normalized value and the second phase voltage normalized value respectively; S3: multiplying the first phase voltage per unit value and the second phase voltage per unit value to obtain a per unit value product; S4: judging whether the phase sequence of the inverter is normal according to the product of the per-unit values.

[0011] Preferably, step S4 specifically includes: judging whether the per-unit value product is greater than a preset threshold value, and if so, judging that the phase sequence of the inverter is abnormal; otherwise, judging that the phase sequence of the inverter is normal.

[0012] Preferably, the preset threshold value ranges from [-0.375 , -0.5].

[0013] Preferably, step S4 specifically includes: repeating steps S1 to S3 multiple times to calculate k per unit value product, and according to k The per-unit value products are calculated to obtain the filtered value of the per-unit value product; and whether the phase sequence of the inverter is normal is judged according to the filtered value of the per-unit value product, wherein: k is a positive integer greater than 2.

[0014] Preferably, k The sampling point number is greater than the sampling point number of the inverter power frequency cycle, the sampling point number of the inverter power frequency cycle = sampling frequency / inverter output voltage frequency, wherein the sampling frequency refers to the frequency of obtaining the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter in step S1.

[0015] Preferably, according to k The per-unit value product is used to calculate the filtered value of the per-unit value product, specifically using the following formula:

[0016] In the formula, VT AVE ( k ) represents the filtered value of the per-unit product, N Indicates the number of sampling points of the inverter power frequency cycle, V 2 ( i ) means that according to i The instantaneous value of the first phase voltage of the inverter obtained this time and the instantaneous value of the second phase voltage correspond to the calculated per unit value product.

[0017] Preferably, according to i The instantaneous value of the first phase voltage of the inverter obtained this time and the instantaneous value of the second phase voltage corresponding to the calculated per unit value product V 2 ( i )for:

[0018] In the formula, Indicates that according to i The first phase voltage per unit value is calculated from the instantaneous value of the first phase voltage of the inverter obtained the first time, and , V L1N ( i ) indicates the i The instantaneous value of the first phase voltage of the inverter obtained for the first time, V L1N_RMS is the effective value of the first phase voltage of the inverter; Indicates that according to i The second phase voltage per unit value is calculated from the instantaneous value of the second phase voltage of the inverter obtained the second time, and , V L2N ( i ) indicates the i The instantaneous value of the second phase voltage of the inverter obtained for the second time, V L2N_RMS is the effective value of the second phase voltage of the inverter.

[0019] Preferably, before executing step S1, the method further includes: detecting whether the frequency and voltage at the grid end are normal; if normal, starting to execute step S1.

[0020] In a second aspect, the present invention discloses a dual-live-wire inverter, wherein two phases of the inverter are respectively connected to a grid end, and the inverter is used to determine whether the phase sequence of the inverter is normal according to the grid end detection method of the dual-live-wire inverter described in the first aspect.

[0021] In a third aspect, the present invention discloses a computer-readable storage medium, in which a computer program is stored, wherein the computer program is configured to be executable by a processor to execute the grid-end detection method of the dual live wire inverter described in the first aspect.

[0022] Compared with the prior art, the beneficial effect of the present invention is that: the present invention proposes a dual-live-wire inverter and a grid-end detection method thereof, which normalizes the instantaneous values ​​of the phase voltages of the inverter and calculates the product of the normalized values ​​to determine whether the phase sequence of the inverter is normal, wherein no complex phase-locked loop is required, and problems such as grid wiring errors and grid specification errors can be quickly identified. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1a and Figure 1b They are the correct connection diagrams between the output ports of the dual-fire inverter and the power grid; Figure 2 This is a schematic diagram of the incorrect connection between the output port of the dual-fire inverter and the power grid; Figure 3a and Figure 3b They are the connection diagrams of dual-fire inverters connected to the three-phase grid; Figure 4 is a flow chart of a grid-side detection method of a dual-live-wire inverter according to Embodiment 1 of the present invention; Figure 5 It is a flow chart of a grid-side detection method of a dual-live-wire inverter according to a specific embodiment of the present invention; Figure 6 is a graph of the standard threshold value versus phase difference; Figure 7 is a schematic diagram of measurement results of Example 1 of the present invention; Figure 8is a schematic diagram of measurement results of Example 2 of the present invention; Fig. 9 is a schematic diagram of measurement results of Example 3 of the present invention; Fig.10 Schematic diagram of measurement results of Example 4 of the present invention. DETAILED DESCRIPTION

[0025] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope and application of the present invention.

[0026] It should be noted that when a component is referred to as being "fixed to" or "disposed on" another component, it can be directly on the other component or indirectly on the other component. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for both fixing and circuit / signal communication.

[0027] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply 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 a limitation on the present invention.

[0028] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0029] like Figure 4 As shown, the first embodiment of the present invention discloses a grid-side detection method for a dual-live-wire inverter, comprising the following steps: S1: Obtain the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter; S2: normalizing the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter to obtain a first phase voltage normalized value and a second phase voltage normalized value respectively; S3: multiplying the first phase voltage per unit value and the second phase voltage per unit value to obtain a per unit value product; S4: judging whether the phase sequence of the inverter is normal according to the product of the per-unit values.

[0030] Wherein, step S4 specifically includes: judging whether the per-unit product is greater than a preset threshold value, if so, judging that the phase sequence of the inverter is abnormal, otherwise, judging that the phase sequence of the inverter is normal. The preset threshold value has a value range of [-0.375, -0.5]. In a specific example, the preset threshold value is -0.375.

[0031] Further, step S4 specifically includes: repeating steps S1 to S3 multiple times to calculate k per unit value product, and according to k The per-unit value products are calculated to obtain the filtered value of the per-unit value product; and whether the phase sequence of the inverter is normal is judged according to the filtered value of the per-unit value product, wherein: k is a positive integer greater than 2. That is, it is determined whether the filtered value of the per-unit value product is greater than a preset threshold value, if so, it is determined that the phase sequence of the inverter is abnormal, otherwise, it is determined that the phase sequence of the inverter is normal.

[0032] in, k The sampling point number is greater than the sampling point number of the inverter power frequency cycle, the sampling point number of the inverter power frequency cycle = sampling frequency / inverter output voltage frequency, wherein the sampling frequency refers to the frequency of obtaining the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter in step S1.

[0033] according to k The per-unit value product is used to calculate the filtered value of the per-unit value product, specifically using the following formula: In the formula, VT AVE ( k ) represents the filtered value of the per-unit product, N Indicates the number of sampling points of the inverter power frequency cycle, V 2 ( i ) means that according to i The instantaneous value of the first phase voltage of the inverter obtained this time and the instantaneous value of the second phase voltage correspond to the calculated per unit value product.

[0034] According to i The instantaneous value of the first phase voltage of the inverter obtained this time and the instantaneous value of the second phase voltage corresponding to the calculated per unit value product V 2 ( i )for:

[0035] In the formula, Indicates that according to iThe first phase voltage per unit value is calculated from the instantaneous value of the first phase voltage of the inverter obtained the first time, and , V L1N ( i ) indicates the i The instantaneous value of the first phase voltage of the inverter obtained for the first time, V L1N_RMS is the effective value of the first phase voltage of the inverter; Indicates that according to i The second phase voltage per unit value is calculated from the instantaneous value of the second phase voltage of the inverter obtained the second time, and , V L2N ( i ) indicates the i The instantaneous value of the second phase voltage of the inverter obtained for the second time, V L2N_RMS is the effective value of the second phase voltage of the inverter.

[0036] Before executing step S1, the method further includes: detecting whether the frequency and voltage at the grid end are normal. If they are normal, step S1 is executed.

[0037] The following is a further detailed description of the grid-side detection method of the dual-live-wire inverter disclosed in the first embodiment of the present invention in combination with specific embodiments.

[0038] like Figure 5 As shown, the grid-side detection method of the dual live wire inverter according to a specific embodiment of the present invention comprises the following steps: A1: After determining that the grid frequency and grid voltage are normal, grid phase detection begins.

[0039] A2: CPU controller samples the instantaneous value of the inverter voltage V L1N ( i )and V L2N ( i ), V L1N ( i ) indicates the i The instantaneous value of the first phase voltage of the inverter at the sampling moment, V L2N ( i ) indicates the i The instantaneous value of the second phase voltage of the inverter at the sampling moment, i Indicates i The sampling time, i =1, 2, 3, ...; Respectively V L1N ( i)and V L2N ( i ) to obtain the per-unit value of the two-phase voltage and : (1) (2) In the formula, V L1N_RMS is the effective value of the first phase voltage of the inverter, V L2N_RMS is the effective value of the second phase voltage of the inverter.

[0040] A3: Multiply the per-unit values ​​of the two-phase voltages to get the per-unit product: (3) A4: Repeat steps A2 to A3 until the last sampling is k times and satisfied k When it is greater than N, the average value of the per-unit product obtained by the previous N samples is calculated to obtain the filtered value of the per-unit product: (4) Where N is the number of sampling points in the inverter power frequency cycle. For example, if the inverter output voltage frequency is 50Hz and the sampling frequency is 20KHz, then N = 20KHz / 50Hz = 400.

[0041] A5: Determine the filter value of the per-unit product VT AVE ( k ) is greater than the preset threshold VT TH ,if VT AVE ( k ) > VT TH , it is judged as abnormal phase sequence, otherwise it is judged as normal phase sequence.

[0042] The following derivation preset threshold VT TH The value of: First assume that the phase difference is θ , and obtain the theoretical standard threshold value under this phase difference VT ( θ ); Among them, the grid voltage can be approximated as a sine wave. is equivalent to: (5) Will is equivalent to: (6) but VT ( θ ) is: (7) Where N is the number of sampling points in the inverter power frequency cycle.

[0043] Combining the above formula (7) we can get the standard threshold VT ( θ )and θ The relationship is as Figure 6 As shown, the phase can be judged whether it is correct by comparing the relationship between the actual value and the theoretical value. When the grid is correctly connected, the voltage V L1 and V L2 The phase difference is 180°, correspondingly, VT (180°) = -0.5; the error range is usually ±30°, so it is considered that V L1 and V L2 The phase difference is between 150° and 210°, which is normal. VT (150°)= VT (210°) = -0.375.

[0044] Therefore, in this specific embodiment, the preset threshold VT TH Set to -0.375, when VT AVE ( k )> VT TH When the phase sequence is abnormal, it is judged as abnormal; otherwise, it is judged as normal.

[0045] Specific examples are as follows: Example 1: like Figure 1a As shown, L1N and L2N are connected to the dual hot grid, V L1N Lead 180°, the measurement result is as follows Figure 7 , where the horizontal axis represents time, the vertical axis in the upper figure represents the actual voltage value of each phase of the inverter collected, and the vertical axis in the lower figure represents the measured value VT AVE ( k ); after measuring 60ms VT AVE Stable at around -0.5, due to VT AVE ( k ) < VT TH , so it is determined that the grid connection is normal.

[0046] Example 2: like Figure 2 As shown, L1N and L2N are connected to the dual hot grid, V L1N With V L2N In phase, the measurement results are as follows Figure 8 , where the horizontal axis represents time, the vertical axis in the upper figure represents the actual voltage value of each phase of the inverter collected, and the vertical axis in the lower figure represents the measured value VT AVE ( k ); after measuring 60ms VT AVE Stable at around 0.5, due to VT AVE > VT TH , so it is determined that the grid connection is abnormal.

[0047] Example 3: like Figure 3a As shown, L1N and L2N are connected to the three-phase grid, V L1N Leading 120°, the measurement results are as follows Fig. 9 , where the horizontal axis represents time, the vertical axis in the upper figure represents the actual voltage value of each phase of the inverter collected, and the vertical axis in the lower figure represents the measured value VT AVE ( k ); after measuring 60ms VT AVE Stable at around -0.25, due to VT AVE > VT TH , so it is determined that the grid connection is abnormal.

[0048] Example 4: like Figure 3b As shown, L1N and L2N are connected to the three-phase grid, V L1N The hysteresis is 120°, and the measurement results are as follows Fig.10 , where the horizontal axis represents time, the vertical axis in the upper figure represents the actual voltage value of each phase of the inverter collected, and the vertical axis in the lower figure represents the measured value VT AVE ( k ); after measuring 60ms VT AVE Stable at around -0.25, due to VT AVE > VT TH , so it is determined that the grid connection is abnormal.

[0049] It can be seen from the test results of Examples 1 to 4 above that the method of the present invention can accurately detect the grid-side connection errors of the dual-fire inverter.

[0050] As in the above-mentioned examples, the grid-side detection method of the dual-live-wire inverter proposed in the present invention can quickly identify grid wiring errors and grid specification errors without the need for a complex phase-locked loop.

[0051] Embodiment 2 of the present invention discloses a dual-live-wire inverter, wherein two phases of the inverter are respectively connected to a grid end, and the inverter is used to determine whether the phase sequence of the inverter is normal according to the grid end detection method of the dual-live-wire inverter in embodiment 1.

[0052] Embodiment 3 of the present invention discloses a computer-readable storage medium, in which a computer program is stored, wherein the computer program is configured to be executable by a processor to execute the steps of the grid-end detection method of the dual live wire inverter in the above-mentioned embodiment 1.

[0053] Optionally, the computer-readable storage medium may include, but is not limited to, various media that can store computer programs, such as a USB flash drive, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk or an optical disk.

[0054] The background section of the present invention may contain background information about the problem or environment of the present invention, rather than describing the prior art by others. Therefore, the content contained in the background section is not an admission by the applicant that the prior art is available.

[0055] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, in the absence of mutual contradiction, the technical personnel in this field can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope defined by the attached claims.

Claims

1. A grid-side detection method for a dual-live-wire inverter, characterized in that: The following steps are involved: S1: Obtain the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter; S2: normalizing the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter to obtain the first phase voltage normalized value and the second phase voltage normalized value respectively; S3: multiplying the first phase voltage per unit value and the second phase voltage per unit value to obtain a per unit value product; S4: judging whether the phase sequence of the inverter is normal according to the product of the per-unit values.

2. The grid-side detection method of the dual live-wire inverter according to claim 1, characterized in that: Step S4 specifically includes: determining whether the per-unit value product is greater than a preset threshold value, if so, determining that the phase sequence of the inverter is abnormal, otherwise, determining that the phase sequence of the inverter is normal.

3. The grid-side detection method of the dual live-wire inverter according to claim 2, characterized in that: The preset threshold value ranges from [-0.375 , -0.5].

4. The grid-side detection method of the dual live-wire inverter according to claim 1, characterized in that: Step S4 specifically includes: repeating steps S1 to S3 multiple times to calculate k per unit value product, and according to k The per-unit value products are calculated to obtain the filtered value of the per-unit value product; and whether the phase sequence of the inverter is normal is judged according to the filtered value of the per-unit value product, wherein: k is a positive integer greater than 2.

5. The grid-side detection method of the dual live-wire inverter according to claim 4, characterized in that: k The sampling point number is greater than the sampling point number of the inverter power frequency cycle, the sampling point number of the inverter power frequency cycle = sampling frequency / inverter output voltage frequency, wherein the sampling frequency refers to the frequency of obtaining the instantaneous value of the first phase voltage and the instantaneous value of the second phase voltage of the inverter in step S1.

6. The grid-side detection method of the dual live-wire inverter according to claim 5, characterized in that: according to k The per-unit value product is used to calculate the filtered value of the per-unit value product, specifically using the following formula: ； In the formula, VT AVE ( k ) represents the filtered value of the per-unit product, N Indicates the number of sampling points of the inverter power frequency cycle, V 2 ( i ) means that according to i The instantaneous value of the first phase voltage of the inverter obtained this time and the instantaneous value of the second phase voltage correspond to the calculated per unit value product.

7. The grid-end detection method of the dual live-wire inverter according to claim 6, characterized in that: According to i The instantaneous value of the first phase voltage of the inverter obtained this time and the instantaneous value of the second phase voltage corresponding to the calculated per unit value product V 2 ( i )for: ； In the formula, Indicates that according to i The first phase voltage per unit value is calculated from the instantaneous value of the first phase voltage of the inverter obtained the first time, and , V L1N ( i ) indicates the i The instantaneous value of the first phase voltage of the inverter obtained for the first time, V L1N_RMS is the effective value of the first phase voltage of the inverter; Indicates that according to i The second phase voltage per unit value is calculated from the instantaneous value of the second phase voltage of the inverter obtained the second time, and , V L2N ( i ) indicates the i The instantaneous value of the second phase voltage of the inverter obtained for the second time, V L2N_RMS is the effective value of the second phase voltage of the inverter.

8. The grid-side detection method of a dual live-wire inverter according to claim 1, characterized in that: Before executing step S1, the process also includes: detecting whether the frequency and voltage at the grid end are normal; if they are normal, starting to execute step S1.

9. A dual live wire inverter, characterized in that: The two phases of the inverter are respectively connected to the grid end, and the inverter is used to determine whether the phase sequence of the inverter is normal according to the grid end detection method of the dual live wire inverter according to any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that: A computer program is stored in the computer-readable storage medium, wherein the computer program is configured to be executable by a processor to execute the grid-side detection method for the dual-live-wire inverter according to any one of claims 1 to 8.

Images