A method and system for determining the phase sequence of a three-phase alternating voltage

Abstract

The application discloses a three-phase alternating voltage phase sequence judgment method and system, and belongs to the technical field of power electronic converter control. The method first samples three-phase power grid voltage and calculates the effective value, and then calculates the negative sequence proportion reflecting the power grid unbalance degree; a full-pass filter is used to phase-shift and normalize the A-phase voltage; three-phase voltage is subjected to coordinate transformation to obtain dq-axis components; and finally, a self-adaptive threshold is used to realize fast phase sequence judgment. The application discloses a three-phase alternating voltage phase sequence judgment method and system, and belongs to the technical field of power electronic converter control. The method first samples three-phase power grid voltage and calculates the effective value, and then calculates the negative sequence proportion reflecting the power grid unbalance degree; a full-pass filter is used to phase-shift and normalize the A-phase voltage; three-phase voltage is subjected to coordinate transformation to obtain dq-axis components; and finally, a self-adaptive threshold is used to realize fast phase sequence judgment. The application discards hardware zero-crossing detection and phase-locked loop, improves the anti-harmonic interference capability through the full-pass filter, adaptively adjusts the judgment threshold by using the negative sequence proportion, and can complete the judgment in only one sampling period, and has the advantages of accurate judgment, fast response, strong adaptability and low hardware cost, effectively solves the problems of phase sequence misjudgment and response lag of the energy storage converter during the on-grid and off-grid switching under the complex power grid condition, and guarantees the safe operation of the off-grid motor load.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converter control technology, specifically relating to a three-phase AC voltage phase sequence determination method and system. This determination method is applied to the grid-connected / off-grid switching control of energy storage converters. In grid-connected mode, it determines the grid phase sequence in real time and uses the determination result for phase sequence matching control of motor loads in off-grid mode. It is suitable for application scenarios that require pre-determining the load phase sequence in grid-connected mode to ensure the safe operation of off-grid motor loads. Background Technology

[0002] Energy storage converters (PCS) play a crucial role in the bidirectional flow of energy in distributed energy systems, operating in both grid-connected and off-grid modes. During grid-connection / off-grid switching scenarios, especially in off-grid mode where rotating loads such as motors need to be connected, it is essential to ensure that the phase sequence of the converter output corresponds accurately to the load. Incorrect phase sequence can lead to motor reversal, starting current surges, or even equipment damage.

[0003] Existing phase sequence detection methods mainly fall into the following two categories: 1. Hardware zero-crossing detection method The phase sequence is determined by detecting the zero-crossing points of the three-phase voltage waveform or by judging the rising edge sequence after converting it into a square wave. This method has a significant drawback: Extremely sensitive to power grid harmonics, which can cause zero-crossing drift or jitter on the edges of square waves; Additional hardware comparator circuitry is required, increasing system cost and complexity; The misjudgment rate is high in situations with severe voltage distortion (such as industrial power grids).

[0004] 2. Phase-locked loop (PLL) synchronization method

[0005] Phase-locked loops (PLLs) are used to track the grid voltage phase, and the phase sequence is determined by the direction of phase rotation. This method has the following problems: A standard phase-locked loop may lock onto a positive or negative sequence component when the phase sequence is unknown, leading to misjudgment of the phase sequence. The dynamic response of the phase-locked loop is coupled with the phase sequence determination, making it difficult to operate stably when the grid voltage is unbalanced. It requires a long lock-in time and cannot meet the needs of rapid offline handover.

[0006] Therefore, there is an urgent need for a phase sequence determination scheme that does not require hardware zero-crossing detection, has strong anti-harmonic interference capability, and does not rely on phase-locked loops, in order to improve the reliability of energy storage converters in grid-connected and off-grid switching under complex grid conditions. Summary of the Invention

[0007] The technical problem to be solved by this invention is the problem existing in the prior art. Specifically, this invention provides a three-phase AC voltage phase sequence determination method based on an all-pass filter and an adaptive threshold for negative sequence proportion, aiming to solve the following technical problems: eliminating the sensitivity of hardware zero-crossing detection to harmonics and improving the anti-interference capability of phase sequence determination; avoiding the use of phase-locked loops and eliminating the risk of phase sequence misjudgment caused by the uncertainty of the phase-locked loop locking direction; adaptively adjusting the judgment threshold according to the real-time imbalance of the power grid to improve the judgment accuracy under different power grid quality conditions; and achieving rapid phase sequence determination to meet the real-time requirements of on-grid and off-grid switching of energy storage converters.

[0008] The technical solution of the present invention is as follows: A method for determining the phase sequence of three-phase AC voltage includes the following steps: Step 1: Sample the three-phase grid voltage in real time to obtain the instantaneous three-phase grid voltage U. A U B U C According to the three-phase instantaneous grid voltage U A U B U C The effective value of the three-phase voltage U is calculated. A _ RMS U B _ RMS U C _ RMS ; Step 2, based on the grid rated voltage U r and the effective value of three-phase voltage U A _ RMS U B _ RMS U C _ RMS The proportion of negative order dx is calculated. Step 3: Use an all-pass filter to filter the instantaneous grid voltage U of phase A. A Perform 0-degree and 90-degree phase shifts to obtain the reference signal U after the 0-degree phase shift. A_D0’ and the reference signal U after a 90-degree phase shift A_D90’ Then, the two phase-shifted reference signals are normalized to obtain the normalized 0-degree reference signal U. A_D0 and 90-degree reference signal U A_D90 ; Step 4, calculate the three-phase instantaneous grid voltage U A U B U C The instantaneous grid voltage αβ component U is obtained by performing Clark transform. α U β Then, using the standardized 0-degree reference signal U A_D0 and 90-degree reference signal UA_D90 As a rotating coordinate axis, for the instantaneous grid voltage αβ component U α U β Perform Park transform to obtain the dq-axis component U of the instantaneous grid voltage. d and U q ; Step 5: Given an adaptive threshold E, perform the following judgment: If |U q If |≤E, then the phase sequence is determined to be positive; If |U q If |> is greater than E, then the phase sequence is determined to be negative.

[0009] Preferably, the effective value U of the three-phase voltage in step 1 A _ RMS U B _ RMS U C _ RMS The sliding window method is used for calculation, and its expression is:

[0010]

[0011]

[0012] Where N is the number of sampling points in one sampling period.

[0013] Preferably, the formula for calculating the negative order proportion dx in step 2 is: .

[0014] Preferably, the all-pass filter in step 3 includes an all-pass filter GPS0(S) and an all-pass filter GPS90(S), both of which are digital all-pass filters with unity gain and precise phase shift at the fundamental frequency. The all-pass filter GPS0(S) generates a 0-degree phase shift, and the all-pass filter GPS90(S) generates a 90-degree phase shift.

[0015] The standardized 0-degree reference signal U A_D0 and 90-degree reference signal U A_D90 The formula for calculation is: .

[0016] Preferably, the adaptive threshold E in step 5 is E = (K × dx + 0.05) × U r Where K is the threshold coefficient, K=1.0-3.0, which is adaptively adjusted according to the power grid harmonic level and sampling accuracy.

[0017] This invention also provides a three-phase AC voltage phase sequence determination system, applicable to the aforementioned three-phase AC voltage phase sequence determination method, comprising: The sampling module is used to sample the three-phase power grid voltage; The RMS value calculation module is used to calculate the RMS value U of the three-phase voltage. A _ RMS U B _ RMS U C _ RMS ; The negative sequence percentage calculation module is used to calculate the percentage based on the grid rated voltage U. r and the effective value of three-phase voltage U A _ RMS U B _ RMS U C _ RMS Calculate the proportion of negative order dx; The all-pass filter module, including all-pass filter GPS0(S) and all-pass filter GPS90(S), is used to filter the instantaneous grid voltage U of phase A. A Perform phase shifting treatment; The per-unitization module is used to standardize the phase-shifted reference signal. The coordinate transformation module, including the Clark transformation unit and the Park transformation unit, is used to transform the three-phase instantaneous grid voltage U A U B U C Converted to instantaneous grid voltage dq-axis component U d U q ; The phase sequence determination module is used to determine the q-axis component U of the instantaneous grid voltage. q The phase sequence is compared with the adaptive threshold E and the phase sequence is determined.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Strong resistance to harmonic interference Using an all-pass filter for phase shifting instead of hardware zero-crossing detection effectively avoids the zero-crossing drift problem caused by harmonics; at the same time, using the DQ component after coordinate transformation for judgment is equivalent to performing integral averaging on the signal, further suppressing the influence of high-frequency harmonics.

[0019] 2. No phase-locked loop required, avoiding misjudgments.

[0020] Park transformation is performed directly using a preset rotating coordinate system (0-degree and 90-degree reference axes generated based on phase A voltage), eliminating the need for phase-locked loop (PLL) to track the phase and completely eliminating the risk of the PLL locking the wrong direction due to unknown initial phase sequence.

[0021] 3. Adaptive threshold, highly adaptable

[0022] The negative order proportion dx is used as the threshold benchmark, enabling the judgment threshold to be adaptively adjusted according to the power grid imbalance. When the power grid quality is good, dx is small, the threshold is strict, and the judgment is accurate; when the power grid is unbalanced, dx is large, and the threshold is relaxed accordingly to avoid misjudgment.

[0023] 4. Fast judgment speed

[0024] There is no need to wait for the phase-locked loop to converge; coordinate transformation and comparison can be completed in just one sampling cycle, meeting the requirements of energy storage converters for rapid off-grid switching (typically required <100ms).

[0025] 5. Low hardware cost

[0026] No additional hardware zero-crossing comparator circuit is required; only software algorithm implementation is needed, which reduces system cost and hardware complexity. Attached Figure Description

[0027] Figure 1 This is a control diagram of the method of the present invention.

[0028] Figure 2 This is a flowchart of the method of the present invention.

[0029] Figure 3 The simulation results of this invention are shown in the figure. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0031] Figure 1 This is a control chart for the method of the present invention. Figure 2 This is a flowchart of the method of the present invention. Figure 1 and Figure 2 As can be seen, this invention provides a three-phase AC voltage phase sequence determination method, which is used in phase sequence detection scenarios for energy storage converters switching between grid and off-grid operation, and includes the following steps: Step 1: Sample the three-phase grid voltage in real time to obtain the instantaneous three-phase grid voltage U. A U B U C According to the three-phase instantaneous grid voltage U A U B U C The effective value of the three-phase voltage U is calculated. A _ RMS U B _ RMS U C _ RMS .

[0032] In this embodiment, the effective value U of the three-phase voltage A _ RMS U B _ RMS U C _ RMS The sliding window method is used for calculation, and its expression is:

[0033]

[0034]

[0035] Where N is the number of sampling points in one sampling period.

[0036] Step 2, based on the grid rated voltage U r and the effective value of three-phase voltage U A _ RMS U B _ RMS U C _ RMS The proportion of negative order dx is calculated.

[0037] In this embodiment, the formula for calculating the negative order proportion dx is: .

[0038] The dx value reflects the three-phase imbalance. Theoretically, in an ideal positive-sequence balanced power grid, dx≈0, while in a real power grid, dx is usually 0.01-0.05.

[0039] Step 3: Use an all-pass filter to filter the instantaneous grid voltage U of phase A. A Perform 0-degree and 90-degree phase shifts to obtain the reference signal U after the 0-degree phase shift. A_D0’ and the reference signal U after a 90-degree phase shift A_D90’ Then, the two phase-shifted reference signals are normalized to obtain the normalized 0-degree reference signal U. A_D0 and 90-degree reference signal U A_D90 .

[0040] In this embodiment, the all-pass filter includes an all-pass filter GPS0(S) and an all-pass filter GPS90(S), both of which are digital all-pass filters with unity gain and precise phase shift at the fundamental frequency. The all-pass filter GPS0(S) generates a 0-degree phase shift, and the all-pass filter GPS90(S) generates a 90-degree phase shift.

[0041] The standardized 0-degree reference signal U A_D0 and 90-degree reference signal U A_D90 The formula for calculation is: .

[0042] Step 4, calculate the three-phase instantaneous grid voltage U A U B U C The instantaneous grid voltage αβ component U is obtained by performing Clark transform. α U β Then, using the standardized 0-degree reference signal U A_D0 and 90-degree reference signal U A_D90 As a rotating coordinate axis, for the instantaneous grid voltage αβ component U α U β Perform Park transform to obtain the dq-axis component U of the instantaneous grid voltage. d and U q .

[0043] Step 5: Given an adaptive threshold E, perform the following judgment: If |U q If |≤E, then the phase sequence is determined to be positive; If |U q If |> is greater than E, then the phase sequence is determined to be negative.

[0044] In this embodiment, the adaptive threshold E = (K × dx + 0.05) × U r Where K is the threshold coefficient, K=1.0-3.0, which is adaptively adjusted according to the power grid harmonic level and sampling accuracy.

[0045] In this embodiment, the power of the energy storage converter is 50kW, the sampling frequency is 16kHz, N is 320 points, and U... r =230V, threshold coefficient K=2.0.

[0046] In this embodiment, a threshold value of K=2.0 is used. Through simulation and experimental verification, when the coefficient K is 2.0, under the power grid conditions of 5% harmonic distortion and 3% voltage imbalance, E=25.3 can be obtained. Figure 3 Simulation of a three-phase power grid with 5% voltage distortion and 3% voltage imbalance, using U calculated according to the patented scheme. q All values ​​are below E, and the phase sequence determination accuracy can reach 100%. Figure 3 As shown.

[0047] This invention also provides a three-phase AC voltage phase sequence determination system, applicable to the aforementioned three-phase AC voltage phase sequence determination method, comprising: The sampling module is used to sample the three-phase power grid voltage; The RMS value calculation module is used to calculate the RMS value U of the three-phase voltage. A _ RMSU B _ RMS U C _ RMS ; The negative sequence percentage calculation module is used to calculate the percentage based on the grid rated voltage U. r and the effective value of three-phase voltage U A _RMS,U B _RMS,U C _RMS calculates the proportion of negative order dx; The all-pass filter module, including all-pass filter GPS0(S) and all-pass filter GPS90(S), is used to filter the instantaneous grid voltage U of phase A. A Perform phase shifting treatment; The per-unitization module is used to standardize the phase-shifted reference signal. The coordinate transformation module, including the Clark transformation unit and the Park transformation unit, is used to transform the three-phase instantaneous grid voltage U A U B U C Converted to instantaneous grid voltage dq-axis component U d U q ; The phase sequence determination module is used to determine the q-axis component of the instantaneous grid voltage. U q The phase sequence is compared with the adaptive threshold E and the phase sequence is determined.

Claims

1. A method for determining the phase sequence of three-phase AC voltage, characterized in that, Includes the following steps: Step 1: Sample the three-phase grid voltage in real time to obtain the instantaneous three-phase grid voltage U. A U B U C According to the three-phase instantaneous grid voltage U A U B U C The effective value of the three-phase voltage U is calculated. A _ RMS U B _ RMS U C _ RMS ; Step 2, based on the grid rated voltage U r and the effective value of three-phase voltage U A _ RMS U B _ RMS U C _ RMS The proportion of negative order dx is calculated. Step 3: Use an all-pass filter to filter the instantaneous grid voltage U of phase A. A Perform 0-degree and 90-degree phase shifts to obtain the reference signal U after the 0-degree phase shift. A_D0’ and the reference signal U after a 90-degree phase shift A_D90’ Then, the two phase-shifted reference signals are normalized to obtain the normalized 0-degree reference signal U. A_D0 and 90-degree reference signal U A_D90 ; Step 4, calculate the three-phase instantaneous grid voltage U A U B U C The instantaneous grid voltage αβ component U is obtained by performing Clark transform. α U β Then, using the standardized 0-degree reference signal U A_D0 and 90-degree reference signal U A_D90 As a rotating coordinate axis, for the instantaneous grid voltage αβ component U α U β Perform Park transform to obtain the dq-axis component U of the instantaneous grid voltage. d and U q ; Step 5: Given an adaptive threshold E, perform the following judgment: If |U q If |≤E, then the phase sequence is determined to be positive; If |U q If |> is greater than E, then the phase sequence is determined to be negative.

2. The method for determining the phase sequence of three-phase AC voltage according to claim 1, characterized in that, The effective value of the three-phase voltage U mentioned in step 1 A _ RMS U B _ RMS U C _ RMS The sliding window method is used for calculation, and its expression is: Where N is the number of sampling points in one sampling period.

3. The method for determining the phase sequence of three-phase AC voltage according to claim 1, characterized in that, The formula for calculating the negative order proportion dx in step 2 is: 。 4. The method for determining the phase sequence of three-phase AC voltage according to claim 1, characterized in that, The all-pass filter described in step 3 includes an all-pass filter GPS0(S) and an all-pass filter GPS90(S), both of which are digital all-pass filters with unity gain and precise phase shift at the fundamental frequency. The all-pass filter GPS0(S) generates a 0-degree phase shift, and the all-pass filter GPS90(S) generates a 90-degree phase shift.

5. The per-unit 0-degree reference signal U A_D0 and 90-degree reference signal U A_D90 The formula for calculation is: 。 6. The method for determining the phase sequence of three-phase AC voltage according to claim 1, characterized in that, The adaptive threshold E in step 5 is E = (K × dx + 0.05) × U r Where K is the threshold coefficient, K=1.0-3.0, which is adaptively adjusted according to the power grid harmonic level and sampling accuracy.

7. A three-phase AC voltage phase sequence determination system, characterized in that, A three-phase AC voltage phase sequence determination method applicable to any one of claims 1-5, comprising: The sampling module is used to sample the voltage of the three-phase power grid; The RMS value calculation module is used to calculate the RMS value U of the three-phase voltage. A _ RMS U B _ RMS U C _ RMS ; The negative sequence percentage calculation module is used to calculate the percentage based on the grid rated voltage U. r and the effective value of three-phase voltage U A _ RMS U B _ RMS U C _ RMS Calculate the proportion of negative order dx; The all-pass filter module, including all-pass filter GPS0(S) and all-pass filter GPS90(S), is used to filter the instantaneous grid voltage U of phase A. A Perform phase shifting treatment; The per-unitization module is used to standardize the phase-shifted reference signal. The coordinate transformation module, including the Clark transformation unit and the Park transformation unit, is used to transform the three-phase instantaneous grid voltage U A U B U C Converted to instantaneous grid voltage dq-axis component U d U q ; The phase sequence determination module is used to determine the q-axis component U of the instantaneous grid voltage. q The phase sequence is compared with the adaptive threshold E and the phase sequence is determined.

Images