Power grid positive and negative sequence phase locking method based on all-pass filter and orthogonal characteristic

Abstract

The invention discloses a power grid positive and negative sequence phase locking method based on an all-pass filter and orthogonal characteristics, and the method comprises the steps: firstly converting a three-phase power grid voltage into alpha and beta coordinate system components through Clark transformation, carrying out the 90-degree phase delay processing of the alpha and beta components through an all-pass filter, and separating the positive and negative sequence alpha and beta components of a power grid; then, an orthogonal discrete reference signal is generated, a multiplication integral result of the positive and negative sequence alpha components and the reference signal is updated through sliding window integration, amplitudes and phase correlation trigonometric function values of the positive and negative sequence alpha components are calculated based on the integral result, and finally, real-time phase angles of the positive and negative sequence components are determined through an arcsine function. And independent locking of positive and negative sequence phases is realized. A PI regulator and a loop filter in a traditional phase-locked loop are omitted, the phase is extracted through a direct calculation method, and the method has the advantages of being simple in structure, rapid in dynamic response, high in harmonic interference resistance and high in calculation efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system control and power quality, and specifically relates to a positive and negative sequence phase-locked method for a power grid based on an all-pass filter and orthogonal characteristics. BACKGROUND

[0002] In a power system, the stable operation of a grid-connected converter (such as a photovoltaic inverter, a wind power converter, an energy storage converter, etc.) depends on the accurate synchronization of parameters such as the phase and frequency of the grid voltage. A phase-locked loop (PLL) is the core technology for achieving this synchronization function, and its performance directly affects the operational stability and power quality of the grid-connected device.

[0003] However, actual power grids often have non-ideal conditions such as voltage imbalance, harmonic distortion, frequency fluctuation, and deep drop, which pose strict requirements on the dynamic response speed, anti-interference ability, and robustness of the phase-locked loop. The widely used decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL) in the industry separates unbalanced components by constructing positive and negative sequence synchronous rotating coordinate systems and introducing a decoupling link, but this technology relies on multiple PI regulators and loop filters. Due to the inherent design contradiction between the proportional coefficient and the integral coefficient of the PI regulator - increasing the proportional coefficient can improve the dynamic response speed, but will reduce the system's anti-interference ability; increasing the integral coefficient can enhance the steady-state accuracy, but will cause dynamic response lag and overshoot, so the DDSRF-PLL cannot simultaneously consider dynamic performance and anti-interference. When a deep voltage drop (such as a drop amplitude ≥ 50%) or a phase mutation (such as a mutation angle ≥ 30°) occurs in the power grid, the traditional DDSRF-PLL is prone to dynamic performance deterioration, large phase tracking overshoot, and even loss of lock, which in turn leads to grid disconnection of the grid-connected device or system oscillation.

[0004] To improve the phase-locked performance, there are phase-locked schemes based on multi-stage generalized integrators (MSOGI), Kalman filtering, or adaptive filtering in the prior art. For example, MSOGI separates and suppresses positive and negative sequence components by cascading generalized integrators, but the multi-stage integration structure significantly increases the algorithm complexity, requiring more computing power of the digital processor (DSP / FPGA), which not only increases the hardware implementation cost but also prolongs the calculation delay; although the Kalman filtering type phase-locked method can optimize the noise suppression effect, it needs to establish a complex system state equation and perform iterative calculations, which also has the problems of large calculation amount and poor real-time performance, making it difficult to be widely promoted for low-cost grid-connected devices.

[0005] In summary, the existing phase-locked loop technology generally has the technical dilemma of "difficulty in balancing dynamic response speed, anti-interference ability, and calculation complexity", and there is an urgent need for a power grid positive and negative sequence phase-locked method that is simple in structure, fast in response, strong in anti-interference, and low in calculation amount, to meet the synchronization control needs of grid-connected converters under non-ideal power grid conditions. SUMMARY

[0006] In view of the defects of the existing phase-locked loop technology, such as the contradiction between dynamic response and anti-interference design, high algorithm complexity and large calculation amount, the present application aims to provide a power positive and negative sequence phase-locked method based on all-pass filter and orthogonal characteristics.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical means:

[0008] A power positive and negative sequence phase-locked method based on all-pass filter and orthogonal characteristics, comprising the following steps:

[0009] Step 1: presetting the power fundamental angular frequency , the fundamental frequency , the sampling frequency , defining the discrete time point , generating the discrete reference signal and , wherein N is the number of sampling points in a fundamental period;

[0010] Step 2: initializing the positive sequence and negative sequence component and the discrete quantity of the multiplication product integral result of the reference signal:

[0011] (1)

[0012] (2)

[0013] (3)

[0014] (4)

[0015] wherein, is the value of the positive sequence component at time n; is the value of the negative sequence component at time n;

[0016] Step 3: the obtained ABC three-phase voltage signal is converted into , voltage components in the , coordinate system through Clark transformation, and the transformation formula is:

[0017] (5)

[0018] (6)

[0019] wherein, , , These are the instantaneous sampled values ​​of the three-phase voltage;

[0020] Step 4: Use an all-pass filter to... , Perform 90° phase delay processing on each component to obtain the delayed components. , The calculation formula is:

[0021] (7)

[0022] (8)

[0023] in, and When it is the previous calculation cycle , The value; and When it is the previous calculation cycle , The value;

[0024] Step 5: Based on the results obtained in Step 4 , Combined with the results obtained in step 3 , Calculate and separate the grid voltage at , Positive sequence components in coordinate system , and negative order components , The calculation formula is:

[0025] (9);

[0026] Step 6: Based on the results obtained in Step 5 , Update the multiplication integral result in step 2 to obtain the latest result. , , , The calculation formula is:

[0027] (10)

[0028] (11)

[0029] (12)

[0030] (13)

[0031] wherein, in the formula, A is the amplitude of the positive sequence component, B is the amplitude of the negative sequence component, and φ is the phase angle of the positive sequence component. is the discrete time corresponding to the current sampling moment;

[0032] Step 7: Based on the integral result of Step 6, the amplitude of the positive sequence component A and the amplitude of the negative sequence component B are calculated, and the calculation formula is:

[0033] (14)

[0034] (15);

[0035] Step 8: Based on the integral result of Step 6 and the amplitude of Step 7, the sine value and cosine value of the fundamental phase angle of the positive sequence component and the sine value and cosine value of the fundamental phase angle of the negative sequence component are calculated, and the calculation formula is:

[0036] (16)

[0037] (17)

[0038] (18)

[0039] (19);

[0040] Step 9: Based on the trigonometric function values of Step 8, the real-time phase angle of the positive sequence component and the negative sequence component is determined:

[0041] If < 0, the real-time phase angle value of the positive sequence component is:

[0042] ;

[0043] Otherwise, it is:

[0044] ;

[0045] If < 0, the real-time phase angle value of the negative sequence component is:

[0046] ;

[0047] Otherwise, it is: ​​​​​​​​​​​​​

[0048] ;

[0049] The phase angles of the positive-sequence and negative-sequence components of the three-phase grid voltage are respectively related to the positive-sequence... Components, Negative Order The phase angles of the components are consistent, thus completing the positive and negative sequence phase locking of the power grid.

[0050] Preferably, in step 1, the fundamental frequency... The sampling frequency is 50Hz or 60Hz. ≥10kHz.

[0051] Preferably, in step 4, the parameters of the all-pass filter... Satisfy parameters .

[0052] Preferably, the length of the sliding window in step 6 is one fundamental period, that is, the window contains N consecutive sampling points, so as to realize real-time dynamic updating of the integration result.

[0053] Preferably, the phase angle calculation accuracy in step 9 is ≤0.1°, and the dynamic response time is ≤5ms.

[0054] The present invention has the following beneficial effects:

[0055] 1. Fast dynamic response speed and no overshoot: It eliminates the PI regulator and loop filter of traditional phase-locked loops, and achieves millisecond-level phase tracking through sliding window integration and direct phase calculation, without overshoot, and can adapt to extreme conditions such as deep voltage drops and phase changes in the power grid.

[0056] 2. Strong anti-interference capability: The phase delay characteristics of the all-pass filter and the correlation integral of the orthogonal reference signal together constitute a harmonic suppression mechanism, which can effectively suppress the influence of characteristic harmonics such as the 3rd, 5th, and 7th harmonics on the phase-locked loop accuracy. In a distorted power grid with a total harmonic distortion rate ≤20%, the phase-locked loop accuracy is still ≤0.1°.

[0057] 3. Low computational complexity: The algorithm only includes linear transformation, simple multiplication / addition and square root and inverse cosine operations, without iterative calculation or complex filtering links. The computational load is reduced by more than 40% compared with DDSRF-PLL and more than 60% compared with MSOGI-PLL. It can run stably on low-cost DSPs.

[0058] 4. Simple structure and high robustness: No need to adjust the PI regulator parameters, only the fundamental frequency and sampling frequency need to be preset. It has low parameter sensitivity, strong adaptability to different power grid conditions, and is easy to apply in engineering and promote on a large scale. Detailed Implementation

[0059] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] This invention provides a positive and negative sequence phase-locked loop (PLL) method for power grids based on an all-pass filter and orthogonal characteristics, comprising the following steps:

[0061] Step 1: Parameter preset and orthogonal reference signal generation

[0062] Preset power grid fundamental angular frequency Fundamental frequency (50Hz or 60Hz), sampling frequency (≥10kHz), define discrete time points N is the number of sampling points within one fundamental frequency period, generating a discrete reference signal. and This signal provides an orthogonal reference for subsequent phase calculations.

[0063] Step 2: Initialize the integration results

[0064] Initialize positive and negative order The discrete quantity of the integral result of multiplying a component with a reference signal:

[0065] (1)

[0066] (2)

[0067] (3)

[0068] (4)

[0069] in, Forward order The value of time n corresponding to the component; negative order The value of time n corresponding to the component;

[0070] The above integral results are used to reflect the positive and negative order. The correlation between the components and the orthogonal reference signal provides data support for phase calculation.

[0071] Step 3: Clark Transformation (Three-phase → , Coordinate system transformation

[0072] The sampled ABC three-phase voltage signals are converted into Clark transform. , Voltage components in coordinate system , The transformation formula is:

[0073] (5)

[0074] (6)

[0075] in, , , These are the instantaneous sampled values ​​of the three-phase voltage;

[0076] Convert the voltage in the three-phase stationary coordinate system to a two-phase stationary coordinate system. , Components in coordinate system , This eliminates the coupling relationship of the three-phase voltage, making it easier to separate the positive and negative sequence components later.

[0077] Step 4: Phase delay processing of the all-pass filter

[0078] Using an all-pass filter , Perform 90° phase delay processing on each component to obtain the delayed components. , The calculation formula is:

[0079] (7)

[0080] (8)

[0081] in, and When it is the previous calculation cycle , The value; and When it is the previous calculation cycle , The value of the parameter; ;

[0082] Its core advantage lies in the fact that it only changes the phase of the signal without affecting the amplitude, and its structure is simple (it can be calculated using only historical data from the previous cycle and current data), with extremely low computational load.

[0083] Step 5: Separation of positive and negative order components

[0084] Based on the results obtained in step 4 , Combined with the results obtained in step 3 , Calculate and separate the grid voltage at , Positive sequence components in coordinate system , and negative order components , The calculation formula is:

[0085] (9)

[0086] pass , and , A linear combination of these components can directly achieve distortion-free separation of positive and negative order components.

[0087] Step 6: Update points via sliding window

[0088] Based on the results obtained in step 5 , Update the multiplication integral result in step 2 to obtain the latest result. , , , The calculation formula is:

[0089] (10)

[0090] (11)

[0091] (12)

[0092] (13)

[0093] Wherein, in the formula The discrete time corresponding to the current sampling moment;

[0094] The length of the sliding window is one fundamental frequency period (N sampling points): when sampling time When < N, the integral result is the first The sum of the products of the sampling points; when When ≥N, the integral result is subtracted from the product of the earliest sampling points within the window. (at time -N), and add the product of the current sampling point to ensure that the integral result always reflects the signal characteristics within the latest fundamental period, avoiding phase lag caused by integration accumulation.

[0095] Step 7: Calculation of positive and negative sequence component amplitudes

[0096] Based on the integration results from step 6, the positive order is calculated. Component amplitude and negative order Component amplitude The calculation formula is:

[0097] (14)

[0098] (15)

[0099] The essence of this formula is to extract the effective amplitude of the fundamental component by integrating the correlation between the orthogonal reference signal and the target component, thereby suppressing the harmonic components.

[0100] Step 8: Calculation of phase-related trigonometric function values

[0101] Based on the integration result from step 6 and the amplitude from step 7, the positive sequence is calculated. The sine value of the fundamental phase angle of the component cosine value and negative order The sine value of the fundamental phase angle of the component cosine value The calculation formula is:

[0102] (16)

[0103] (17)

[0104] (18)

[0105] (19)

[0106] The calculation process does not require iteration and is achieved directly through linear operations, avoiding the dynamic lag of the PI regulator and ensuring the real-time performance of phase extraction.

[0107] Step 9: Determine the real-time phase angle

[0108] Based on the trigonometric function values ​​from step 8, determine the positive and negative order. Real-time phase angle of the component:

[0109] like < 0, then ascending order The real-time phase angle value of the component is:

[0110] ;

[0111] Otherwise, it is:

[0112] ;

[0113] like < 0, then negative order The real-time phase angle value of the component is:

[0114] ;

[0115] Otherwise, it is:

[0116] ;

[0117] By following the above 9 steps, the positive and negative order can be calculated. , In the coordinate system, the forward sequence Phase angle of the component and negative order Phase angle of the component The phase angles of the positive-sequence and negative-sequence components of the three-phase grid voltage are respectively related to the positive-sequence... Components, Negative Order The components are the same, thus completing the phase-locked loop operation of the positive and negative phases of the grid voltage.

[0118] The examples provided in this invention are not intended to limit the implementation. Those skilled in the art will recognize that various variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of this invention.

Claims

1. A positive-negative sequence phase-locked loop method for power grids based on an all-pass filter and orthogonal characteristics, characterized in that, Includes the following steps: Step 1: Preset the fundamental angular frequency of the power grid Fundamental frequency sampling frequency Define discrete time points Generate discrete reference signal and Where N is the number of sampling points within one fundamental frequency period; Step 2: Initialize the positive and negative order The discrete quantity of the integral result of multiplying a component with a reference signal: （1） （2） （3） （4） in, Forward order The value of time n corresponding to the component; negative order The value of time n corresponding to the component; Step 3: The sampled ABC three-phase voltage signals are converted into Clark transform. , Voltage components in coordinate system , The transformation formula is: （5） （6） in, , , These are the instantaneous sampled values ​​of the three-phase voltage; Step 4: Use an all-pass filter to... , Perform 90° phase delay processing on each component to obtain the delayed components. , The calculation formula is: （7） （8） in, and When it is the previous calculation cycle , The value; and When it is the previous calculation cycle , The value; Step 5: Based on the results obtained in Step 4 , Combined with the results obtained in step 3 , Calculate and separate the grid voltage at , Positive sequence components in coordinate system , and negative order components , The calculation formula is: （9）； Step 6: Based on the results obtained in Step 5 , Update the multiplication integral result in step 2 to obtain the latest result. , , , The calculation formula is: (10) (11) (12) (13) Wherein, in the formula The discrete time corresponding to the current sampling moment; Step 7: Based on the integration results from Step 6, calculate the positive order. Component amplitude and negative order Component amplitude The calculation formula is: (14) (15)； Step 8: Based on the integration result from Step 6 and the amplitude from Step 7, calculate the positive sequence. The sine value of the fundamental phase angle of the component cosine value and negative order The sine value of the fundamental phase angle of the component cosine value The calculation formula is: (16) (17) (18) (19)； Step 9: Based on the trigonometric function values ​​from Step 8, determine the positive and negative order. Real-time phase angle of the component: like < 0, then ascending order The real-time phase angle value of the component is: ； Otherwise, it is: ； like < 0, then negative order The real-time phase angle value of the component is: ； Otherwise, it is: ； The phase angles of the positive-sequence and negative-sequence components of the three-phase grid voltage are respectively with the positive-sequence... Components, Negative Order The phase angles of the components are consistent, thus completing the positive and negative sequence phase locking of the power grid.

2. The power grid positive and negative sequence phase-locked loop method based on an all-pass filter and orthogonal characteristics according to claim 1, characterized in that, In step 1, the fundamental frequency The sampling frequency is 50Hz or 60Hz. ≥10kHz.

3. The power grid positive and negative sequence phase-locked loop method based on an all-pass filter and orthogonal characteristics according to claim 1, characterized in that, In step 4, the parameters of the all-pass filter Satisfy parameters .

4. The power grid positive and negative sequence phase-locked loop method based on an all-pass filter and orthogonal characteristics according to claim 1, characterized in that, The length of the sliding window in step 6 is one fundamental period, meaning that the window contains N consecutive sampling points, enabling real-time dynamic updates of the integration results.

5. The power grid positive and negative sequence phase-locked loop method based on an all-pass filter and orthogonal characteristics according to claim 1, characterized in that, The phase angle calculation accuracy in step 9 is ≤0.1°, and the dynamic response time is ≤5ms.

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