Improved three-phase synchronous phase-locked loop control system and control method

Abstract

The invention relates to the technical field of electric power, in particular to an improved three-phase synchronous phase-locked loop control system and control method. Wherein the control system comprises a coordinate transformation unit, an SG filter, a proportional-integral controller, an integral link unit and a modulator, the input end of the coordinate transformation unit is connected with three-phase power grid voltage, the output end of the coordinate transformation unit is connected with the input end of the SG filter, the output end of the SG filter is connected with the input end of the proportional-integral controller, and the output end of the integral link unit is connected with the modulator. The output end of the proportional integral controller is connected with the input end of the integral link unit, the output end of the integral link unit is connected with the input end of the modulator, and the output end of the modulator is connected with the input end of the coordinate transformation unit. According to the invention, the SG filter is introduced into the traditional SRF-PLL to eliminate frequency doubling components on d and q axes when the three-phase voltage of the SRF-PLL is unbalanced, so that the operation efficiency of the whole system is greatly improved, a phase locking result does not contain harmonic components, and the phase locking accuracy is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to an improved three-phase synchronous phase-locked loop control system and a control method. Background Art

[0002] In many power electronics applications, such as dynamic voltage restorer, static VAR compensator (SVG), active power filter (APF), uninterruptible power supply (UPS), photovoltaic power generation system and wind power generation system, it is necessary to use a phase-locked loop to obtain the precise phase of the grid voltage. The performance of the phase-locked loop directly affects the overall effect of the system. Therefore, the phase-locked loop technology is very important.

[0003] The three-phase synchronous phase-locked loop (SRF-PLL) is widely used in three-phase systems due to its simplicity and convenience. As a complex and dynamic system, the operation of the power grid may be disturbed by various factors, such as grid faults and nonlinear loads, which will cause instability, imbalance or harmonic pollution of the voltage vector. In this case, if the phase-locked loop cannot accurately capture the voltage phase, the control system will not be able to effectively manage the power signal, which may cause malfunction of the protection system and even serious damage to the power device. Therefore, the three-phase phase-locked loop must have strong anti-interference ability to ensure that the phase information can be reliably detected even under harsh conditions to ensure the stable operation of the system and the safety of the protection equipment.

[0004] The traditional single synchronous rotating coordinate system phase-locked loop SRF-PLL is very effective for phase locking of three-phase balanced voltage, but it cannot be effectively phase-locked when the three-phase voltage is unbalanced or distorted. When the grid voltage is distorted, appropriately reducing the SRF-PLL bandwidth can obtain more accurate phase information, but its dynamic response speed will be significantly reduced. At present, in order to solve the problem of abnormal phase locking of SRF-PLL when the three phases are unbalanced, a dual synchronous reference coordinate system decoupling phase-locked loop (DDSRF-PLL) or a dual generalized second-order integrator phase-locked loop (DSOGI-PLL) is generally used, or a low-pass filter and a band-stop filter are added to the SRF-PLL. DDSRF-PLL eliminates the double frequency components in the d and q axis components by introducing positive and negative sequence voltage feedforward control. This method requires the calculation of positive and negative components separately, and the control method is complex and computationally intensive. DSOGI-PLL is an advanced frequency automatic control technology. It uses automatic phase adjustment to obtain the instantaneous phase of a sine wave that changes with time, and uses the frequency selection characteristics of SOGI itself to filter out the double frequency fluctuation component. This method requires the introduction of two SOGI filters and needs to be processed in a two-phase stationary coordinate system. The overall calculation is complex and computationally intensive. The method of adding a low-pass filter or a band-stop filter to the SRF-PLL is simple and convenient, but it can easily cause phase and amplitude offsets and reduce the response speed of the system. Summary of the invention

[0005] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description and other drawings of the description.

[0006] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide an improved three-phase synchronous phase-locked loop control system and control method. In a three-phase unbalanced system, if SRF-PLL is used for phase locking, d , q A double frequency fluctuation component is introduced into the axis, which causes phase locking failure and system instability. In order to solve the above problems, DDSRF-PLL and DSOGI-PLL are usually used for phase locking, or low-pass filters and band-stop filters are added to SRF-PLL to remove d , q The double frequency component on the axis, but these methods have complex control algorithms and require real-time update operations, which are computationally intensive. d , q In order to solve the problem of the double frequency fluctuation component introduced by the axis, an improved SRF-PLL based on the Savitzky Golay Filter (SG) algorithm is proposed. Under the premise of ensuring that the signal is not distorted, the calculation amount of the phase-locked loop is greatly reduced and the SG filter is effectively filtered out. d , q The axis introduces a double frequency fluctuation component.

[0007] The present invention provides an improved three-phase synchronous phase-locked loop control system, comprising a coordinate transformation unit, an SG filter, a proportional-integral controller, an integral link unit and a modulator; the input end of the coordinate transformation unit is connected to the three-phase power grid voltage, the output end of the coordinate transformation unit is connected to the input end of the SG filter, the output end of the SG filter is connected to the input end of the proportional-integral controller, the output end of the proportional-integral controller is connected to the input end of the integral link unit, the output end of the integral link unit is connected to the input end of the modulator, and the output end of the modulator is connected to the input end of the coordinate transformation unit; the SG filter comprises an original data input unit, a sliding window, a fitting data unit and a fitting data output unit.

[0008] The present invention introduces SG filter into the traditional three-phase synchronous phase-locked loop (SRF-PLL), constructs an improved three-phase synchronous phase-locked loop (SRF-PLL) based on Savitzky Golay algorithm, so as to eliminate the three-phase synchronous phase-locked loop (SRF-PLL) when the three-phase voltage is unbalanced.d , q The double frequency component on the axis greatly improves the operating efficiency of the entire system, and the improved three-phase synchronous phase-locked loop (SRF-PLL) ensures that the phase-locked result does not contain harmonic components, greatly improving the accuracy of the phase-locked.

[0009] In some embodiments, the SG filter is calculated by an SG filtering algorithm to obtain a filtering result.

[0010] In some embodiments, the SG filtering algorithm is specifically: Get the original data in the sliding window of the SG filter; The original data are fitted using a polynomial to obtain fitted data; Calculate the residual sum of squares between the fitted data and the original data; Solve for the partial derivative of the residual sum of squares; Solve for the fitting coefficients; Get the polynomial of the fitting result.

[0011] In some embodiments, if a set of time series signals , using a window width of 2 M +1 sliding window for signal filtering, then the original data in the sliding window is .

[0012] In some embodiments, the polynomial is an N-order polynomial, specifically: ; In the formula, is the fitting result; is the fitting coefficient.

[0013] In some embodiments, the expression for the residual sum of squares is: .

[0014] In some embodiments, solving the partial derivative of the residual sum of squares is specifically: ; In the formula, Indicates The fitting coefficients; Simplifying the above formula, we get: .

[0015] In some embodiments, the fitting coefficients are solved by introducing the first matrix and the second matrix, specifically: Will Using the first matrix, the first matrix is ​​a matrix with (2M+1) rows and (N+1) columns, and its expression is: , Then we have: , In the formula, , , ; If the second matrix is: , Then we have: , In the formula, , ; Will Using the matrix It means that its expression is: ; Will Using the matrix It means that its expression is: ; According to the partial derivatives, the first matrix, the second matrix, the matrix And the matrix , we can get: ; According to the above formula, the fitting coefficient matrix can be obtained as follows: .

[0016] In some embodiments, the polynomial of the fitting result is represented by a matrix: .

[0017] In some embodiments, .

[0018] In some embodiments, an output terminal of the SG filter and an input terminal of the proportional-integral controller are provided with a given voltage.

[0019] In some embodiments, a reference angular frequency is provided between the output end of the proportional-integral controller and the input end of the integral link unit.

[0020] The present invention also provides an improved three-phase synchronous phase-locked loop control method, comprising: Collect three-phase grid voltage signals; The three-phase grid voltage signal is converted into a two-phase grid voltage signal by using coordinate transformation; The SG filtering algorithm is used to filter the two-phase grid voltage signal to obtain the filtering result; The filtering result is subjected to proportional-integral control to realize a phase-locked loop.

[0021] The present invention introduces the SG filtering algorithm into the traditional three-phase synchronous phase-locked loop (SRF-PLL) and constructs the open-loop transfer function of the three-phase synchronous phase-locked loop (SRF-PLL) to eliminate the three-phase synchronous phase-locked loop (SRF-PLL) when the three-phase voltage is unbalanced. d , q The double frequency component on the axis greatly improves the operating efficiency of the entire system, and the improved three-phase synchronous phase-locked loop (SRF-PLL) ensures that the phase-locked result does not contain harmonic components, greatly improving the accuracy of the phase-locked.

[0022] In some embodiments, the open-loop transfer function of the phase-locked loop is: , In the formula, is the transfer function of the SG filter, is the Laplace operator; is the proportional coefficient of the PI controller; is the integral coefficient of the PI controller, is the three-phase composite voltage vector.

[0023] In some embodiments, the SG filtering algorithm is specifically: Get the original data in the sliding window of the SG filter; The original data are fitted using a polynomial to obtain fitted data; Calculate the residual sum of squares between the fitted data and the original data; Solve for the partial derivative of the residual sum of squares; Solve for the fitting coefficients; Get the polynomial of the fitting result.

[0024] By adopting the above technical solution, the beneficial effects of the present invention are: The present invention introduces SG filter into the traditional three-phase synchronous phase-locked loop (SRF-PLL), constructs an improved three-phase synchronous phase-locked loop (SRF-PLL) based on Savitzky Golay algorithm, so as to eliminate the three-phase synchronous phase-locked loop (SRF-PLL) when the three-phase voltage is unbalanced. d , q The double frequency component on the axis greatly improves the operating efficiency of the entire system, and the improved three-phase synchronous phase-locked loop (SRF-PLL) ensures that the phase-locked result does not contain harmonic components, greatly improving the accuracy of the phase-locked.

[0025] The present invention introduces the SG filtering algorithm into the traditional three-phase synchronous phase-locked loop (SRF-PLL), and establishes an improved three-phase synchronous phase-locked loop (SRF-PLL) based on the Savitzky Golay algorithm, so as to change the open-loop transfer function of the phase-locked loop. Compared with other phase-locked loop methods such as DSOGI-PLL and DDSRF-PLL, the present invention is simpler and has a smaller overall calculation amount.

[0026] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure.

[0027] Undoubtedly, these and other objects of the present invention will become more apparent after the following detailed description of the preferred embodiment described with reference to various figures and drawings.

[0028] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, one or several preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation of the present invention.

[0030] In the drawings, the same reference numerals are used for the same components and the drawings are schematic and not necessarily drawn to scale.

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only one or several embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on such drawings without paying creative work.

[0032] Figure 1 It is a three-phase grid-connected inverter model; Figure 2 It is the control block diagram of SRF-PLL; Figure 3 It is a schematic diagram of the three-phase voltage synthesis vector; Figure 4 It is the equivalent block diagram of the transfer function of PLL; Figure 5 This is the equivalent block diagram of the simplified PLL transfer function; Figure 6 It is a control block diagram of an improved three-phase synchronous phase-locked loop of the present invention; Figure 7 It is the waveform of the three-phase voltage amplitude unbalanced power grid; Figure 8 It is the overall waveform of the SRF-PLL startup process; Fig. 9 This is the local amplified waveform after the SRF-PLL is stabilized; Fig.10 It is the waveform of the dq axis voltage component of SRF-PLL after being processed by the SG algorithm; Fig.11 It is the dq axis voltage waveform of the improved SRF-PLL based on Savitzky Golay algorithm. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but are not used to limit the present invention.

[0034] In addition, in the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0035] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral body; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. However, if it is indicated as a direct connection, it means that the two connected bodies are not connected through a transition structure, but are connected to form a whole through a connecting structure. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0036] In the present invention, unless otherwise clearly specified and limited, the first feature "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction 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 refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples. SUMMARY OF THE INVENTION In many power electronics applications, dynamic voltage restorers, static VAR compensators, active power filters, uninterruptible power supplies, photovoltaic power generation systems, and wind power generation systems all require the use of phase-locked loops to obtain the precise phase of the grid voltage. The performance of the phase-locked loop directly affects the overall effect of the system. Therefore, phase-locked loop technology is crucial.

[0038] The three-phase synchronous phase-locked loop (SRF-PLL) is widely used in three-phase systems due to its simplicity and convenience. As a complex and dynamic system, the operation of the power grid may be disturbed by various factors, such as grid faults and nonlinear loads, which will cause instability, imbalance or harmonic pollution of the voltage vector. In this case, if the phase-locked loop cannot accurately capture the voltage phase, the control system will not be able to effectively manage the power signal, which may cause malfunction of the protection system and even serious damage to the power device. Therefore, the three-phase phase-locked loop must have strong anti-interference capabilities to ensure that the phase information can be reliably detected even under harsh conditions to ensure the stable operation of the system and the safety of the protection equipment.

[0039] The traditional single synchronous rotating coordinate system phase-locked loop SRF-PLL is very effective in phase locking of three-phase balanced voltage, but it cannot effectively phase lock when the three-phase voltage is unbalanced or distorted. When the grid voltage is distorted, appropriately reducing the SRF-PLL bandwidth can obtain more accurate phase information, but its dynamic response speed will be significantly reduced.

[0040] At present, in order to solve the problem of abnormal SRF-PLL phase locking when the three phases are unbalanced, dual synchronous reference frame decoupling phase-locked loop (DDSRF-PLL), dual generalized second-order integrator phase-locked loop (DSOGI-PLL) or adding low-pass filter and band-stop filter to SRF-PLL are generally used. Among them, DDSRF-PLL eliminates the double frequency components in the d and q axis components by introducing positive and negative sequence voltage feedforward control. This method needs to calculate the positive and negative components separately, and the control method is complex and the calculation is large; DSOGI-PLL is an advanced frequency automatic control technology, which uses the automatic adjustment of the phase to obtain the instantaneous phase of the sine wave that changes with time, and uses the frequency selection characteristics of SOGI itself to filter out the double frequency fluctuation component. This method needs to introduce two SOGI filters and needs to be processed in a two-phase stationary coordinate system. The overall calculation is complex and the calculation is large; the method of adding a low-pass filter or a band-stop filter to the SRF-PLL is simple and convenient, but it is easy to cause phase and amplitude deviations, reducing the response speed of the system.

[0041] In view of the above technical problems, the basic concept of the present invention is to provide an improved SRF-PLL based on the Savitzky Golay Filter (SG) algorithm, which greatly reduces the calculation amount of the phase-locked loop and effectively filters out the double frequency fluctuation components introduced by the d and q axes while ensuring that the signal is not distorted.

[0042] Exemplary Systems Reference Figure 6 , Figure 6 This is an improved three-phase synchronous phase-locked loop control block diagram of the present invention. The exemplary system includes a coordinate transformation unit, an SG filter, a proportional-integral controller, an integral link unit and a modulator. The input end of the coordinate transformation unit is connected to the three-phase grid voltage, the output end of the coordinate transformation unit is connected to the input end of the SG filter, the output end of the SG filter is connected to the input end of the proportional-integral controller, the output end of the proportional-integral controller is connected to the input end of the integral link unit, the output end of the integral link unit is connected to the input end of the modulator, and the output end of the modulator is connected to the input end of the coordinate transformation unit. The SG filter includes an original data input unit, a sliding window, a fitting data unit and a fitting data output unit. The size of the sliding window is 2 M +1, the fitting data unit includes the weight coefficient corresponding to the N-order fitting polynomial and the window data.

[0043] In an implementation manner of the embodiment of the present invention, the SG filter is calculated by an SG filtering algorithm to obtain a filtering result.

[0044] In one implementation of the embodiment of the present invention, the SG filtering algorithm is specifically: Get the original data in the sliding window of the SG filter; The original data are fitted using a polynomial to obtain fitted data; Calculate the residual sum of squares between the fitted data and the original data; Solve for the partial derivative of the residual sum of squares; Solve for the fitting coefficients; Get the polynomial of the fitting result.

[0045] In one implementation of the present invention, the core idea of ​​the SG filter algorithm is to use a polynomial to locally fit the data, and then use this polynomial to estimate the filtered value. That is, the SG filter uses a sliding window, fits a polynomial in the window, and then uses the value of this polynomial to replace the original data value at the center of the window. Assume that there is a set of time series signals , using a window width of 2 M +1 sliding window for signal filtering, then the original data in the sliding window is .

[0046] In an implementation manner of the embodiment of the present invention, the polynomial is an N-order polynomial, specifically: ; In the formula, is the fitting result; is the fitting coefficient.

[0047] In one implementation of the embodiment of the present invention, the residual sum of squares is expressed as: .

[0048] In one implementation of the embodiment of the present invention, the partial derivative of the residual sum of squares is solved as follows: ; In the formula, Indicates The fitting coefficients; Simplifying the above formula, we get: .

[0049] In one implementation of the embodiment of the present invention, the fitting coefficient is solved by introducing the first matrix and the second matrix, specifically: Will Using the first matrix, the first matrix is ​​a matrix with (2M+1) rows and (N+1) columns, and its expression is: , Then we have: , In the formula, , , ; If the second matrix is: , Then we have: , In the formula, , ; Will Using the matrix It means that its expression is: ; Will Using the matrix It means that its expression is: ; According to the partial derivatives, the first matrix, the second matrix, the matrix And the matrix , we can get: ; According to the above formula, the fitting coefficient matrix can be obtained as follows: .

[0050] In one implementation of the embodiment of the present invention, the polynomial of the fitting result is represented by a matrix as follows: .

[0051] Selection Window The central value of As a result of filtering. So far, the SG filtering algorithm has been built. From the polynomial of the fitting result, it can be seen that the fitting coefficients are independent of the data to be filtered. The fitting coefficient matrix is ​​given by M , N Therefore, the fitting coefficient of the SG filtering algorithm is determined. When the SG filtering algorithm is introduced in the SRF-PLL, there is no need to update the fitting coefficient in real time, which greatly reduces the amount of calculation and improves the operating efficiency of the entire control algorithm.

[0052] In one implementation of the embodiment of the present invention, .

[0053] In an implementation manner of the embodiment of the present invention, a given voltage is provided at the output end of the SG filter and the input end of the proportional-integral controller.

[0054] In an implementation manner of the embodiment of the present invention, a reference angular frequency is arranged between the output end of the proportional-integral controller and the input end of the integral link unit.

[0055] Exemplary Methods The exemplary method comprises the following steps: Step 1: Collect three-phase grid voltage signals; Step 2: Convert the three-phase grid voltage signal into a two-phase grid voltage signal by using coordinate transformation; Step 3: Use the SG filtering algorithm to filter the two-phase grid voltage signal to obtain a filtering result; Step 4: Perform proportional-integral control on the filtered result to realize a phase-locked loop.

[0056] The specific construction process of this exemplary method is as follows: Reference Figure 1 , Figure 1 is a three-phase grid-connected inverter model. Figure 1 middle, , They are DC bus voltage, DC bus capacitance, inverter side inductance 、Filter capacitor , Grid-side inductance To form an LCL filter, is the parasitic inductance on the grid side, is the coupling point voltage, The phase angle of the power grid is obtained by using a phase-locked loop (PLL) to obtain the voltage at the common coupling point. The phase angle.

[0057] Reference Figure 2-Figure 5 , Figure 2 This is the control block diagram of SRF-PLL. Figure 3 It is a schematic diagram of the three-phase voltage synthesis vector. Figure 4 The equivalent block diagram of the transfer function of the PLL is: Figure 5 This is the equivalent block diagram of the simplified PLL transfer function. Figure 2 It can be seen that the voltage at the common coupling point is Three-phase voltage at , , After park rotation transformation, the grid voltage is obtained d axis, q Shaft voltage component. Figure 3 As shown, the d-axis is used in the two-phase stationary coordinate system Axis Angle express dq The current position of the axis coordinate system. Figure 3 It is known that because dq Coordinate system and three-phase composite voltage vector by The speed of rotation is synchronous, so as long as d Axis and three-phase composite voltage vector If overlap, dq The rotation angle of the shaft is the resultant voltage vector When the three-phase composite voltage vector and d When the shafts coincide, the three-phase composite voltage vector exist q The component on the axis is 0. Figure 2 middle, q Axis voltage setting Set to 0. However, in actual process, the phase obtained by the phase-locked loop Phase with actual grid voltage It is impossible to completely overlap, the result is just very close. Figure 2 , Figure 3 The equivalent block diagram of the transfer function of the PLL can be derived, such as Figure 4 As shown. When the phase locked loop obtains the phase Phase with actual grid voltage The difference is very small, satisfying the Taylor expansion formula, , so Figure 4 Simplified Figure 5 .

[0058] The open-loop transfer function of the PLL is: , In the formula, is the Laplace operator; is the proportional coefficient of the PI controller; is the integral coefficient of the PI controller.

[0059] The closed loop function of the PLL is: , In the formula, is the damping factor; is the cut-off angular frequency.

[0060] The SG filtering algorithm is introduced into the SRF-PLL, and the results are as follows Figure 6 As shown, the open-loop transfer function is: , In the formula, is the transfer function of the SG filter.

[0061] At this point, the improved three-phase synchronous phase-locked loop control method based on Savitzky Golay algorithm has been completed.

[0062] The present invention introduces an SG filter into a traditional three-phase synchronous phase-locked loop (SRF-PLL), that is, introduces an SG filtering algorithm, and constructs an improved three-phase synchronous phase-locked loop (SRF-PLL) based on the Savitzky Golay algorithm to eliminate the three-phase synchronous phase-locked loop (SRF-PLL) when the three-phase voltage is unbalanced. d , q The double frequency component on the axis greatly improves the operating efficiency of the entire system, and the improved three-phase synchronous phase-locked loop (SRF-PLL) ensures that the phase-locked result does not contain harmonic components, greatly improving the accuracy of the phase-locked. The details are as follows: Table 1 Parameters of the improved three-phase synchronous phase-locked loop based on Savitzky Golay algorithm

[0063] Table 1 gives all the parameters involved in the three-phase unbalanced power grid and the improved three-phase synchronous phase-locked loop based on the Savitzky Golay algorithm in the experiment.

[0064] Figure 7 This is a three-phase voltage amplitude unbalanced grid waveform. The voltage frequencies of phases A, B, and C are all 50Hz, and the voltage amplitude of phase A is 80% of that of phases B and C.

[0065] In a three-phase voltage amplitude unbalanced system, the traditional SRF-PLL is used for phase locking. d axis, q The shaft voltage waveform is as follows Figure 8 and Fig. 9 . Figure 8 This is the overall waveform of the SRF-PLL startup process. Fig. 9 This is the local amplified waveform after the SRF-PLL is stabilized. Figure 8-Figure 9 It can be seen that when the SRF-PLL starts working, it takes 400ms for the phase-locked loop to enter a stable state. q Shaft voltage component is 0. However, since the three-phase voltage amplitudes are not equal, d axis, q Voltage component of the shaft , There is a disturbance with a frequency of 100 Hz.

[0066] Fig.10 For SRF-PLL dq The waveform of the shaft voltage component after being processed by the SG algorithm. M =5, N =5 SG algorithm for traditional SRF-PLL dq The shaft voltage component is filtered and obtained , . It can be found d axis, q Voltage component of the shaft , The 100Hz disturbance superimposed on the SG filter is completely filtered out. Since the processing frequency of the SG filter is 200Hz, although it can ensure that the signal is not distorted, it will cause a significant step change in the signal before entering the steady state, making dq The shaft electric component is discontinuous, which will cause the phase-locked loop to oscillate and even cause the entire phase-locked loop to fail to enter a steady state. Therefore, the SG filtering algorithm is not applicable to the stage before entering a steady state.

[0067] Fig.11 The improved SRF-PLL based on Savitzky Golay algorithm dq Shaft voltage waveform. Fig.11 As shown, in At this moment, SRF-PLL starts to lock the phase. After 400ms of adjustment time, dq The axis component voltage enters a steady state. d axis, q Voltage component of the shaft , There is a double frequency disturbance. 1 second after the SRF-PLL is started, the SG filter algorithm is enabled. Since the adjustment time is 400ms, the entire adjustment time has been avoided when the SG filter algorithm is running. d axis, q Voltage component of the shaft , has entered a steady state. At this moment, the SG filtering algorithm is introduced into the SRF-PLL. d axis, q Shaft voltage component , The double frequency interference on the signal is successfully filtered out and the entire signal is not distorted.

[0068] It should be understood that the embodiments disclosed in the present invention are not limited to the specific processing steps or materials disclosed herein, but should be extended to equivalent substitutions of such features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0069] The "embodiment" mentioned in the specification means that the specific features or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, phrases or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0070] In addition, the described features or characteristics may be combined in one or more embodiments in any other suitable manner. In the above description, some specific details, such as thickness, quantity, etc., are provided to provide a comprehensive understanding of the embodiments of the present invention. However, those skilled in the relevant art will understand that the present invention can be implemented without one or more of the above specific details or can also be implemented using other methods, components, materials, etc.

Claims

1. An improved three-phase synchronous phase-locked loop control system, characterized in that: It includes a coordinate transformation unit, an SG filter, a proportional integral controller, an integral link unit and a modulator. The input end of the coordinate transformation unit is connected to the three-phase grid voltage, the output end of the coordinate transformation unit is connected to the input end of the SG filter, the output end of the SG filter is connected to the input end of the proportional-integral controller, the output end of the proportional-integral controller is connected to the input end of the integral link unit, the output end of the integral link unit is connected to the input end of the modulator, and the output end of the modulator is connected to the input end of the coordinate transformation unit. The SG filter includes an original data input unit, a sliding window, a fitting data unit and a fitting data output unit.

2. The improved three-phase synchronous phase-locked loop control system according to claim 1 is characterized in that: The SG filter is calculated by an SG filtering algorithm to obtain a filtering result.

3. The improved three-phase synchronous phase-locked loop control system according to claim 2 is characterized in that: The SG filtering algorithm is specifically: Get the original data in the sliding window of the SG filter; The original data are fitted using a polynomial to obtain fitted data; Calculate the residual sum of squares between the fitted data and the original data; Solve for the partial derivative of the residual sum of squares; Solve for the fitting coefficients; Get the polynomial of the fitting result.

4. The improved three-phase synchronous phase-locked loop control system according to claim 3 is characterized in that: If a set of time series signals , using a window width of 2 M +1 sliding window for signal filtering, then the original data in the sliding window is .

5. The improved three-phase synchronous phase-locked loop control system according to claim 4 is characterized in that: The polynomial is an N-order polynomial, specifically: ； In the formula, is the fitting result; is the fitting coefficient.

6. The improved three-phase synchronous phase-locked loop control system according to claim 5, characterized in that: The expression of the residual sum of squares is: 。 7. The improved three-phase synchronous phase-locked loop control system according to claim 6, characterized in that: The partial derivative of the residual sum of squares is solved as follows: ； In the formula, Indicates The fitting coefficients; Simplifying the above formula, we get: 。 8. The improved three-phase synchronous phase-locked loop control system according to claim 7, characterized in that: The fitting coefficients are solved by introducing the first matrix and the second matrix, specifically: Will Using the first matrix, the first matrix is ​​a matrix with (2M+1) rows and (N+1) columns, and its expression is: ， Then we have: ， In the formula, , , ; If the second matrix is: ， Then we have: ， In the formula, , ; Will Using the matrix It means that its expression is: ； Will Using the matrix It means that its expression is: ； According to the partial derivatives, the first matrix, the second matrix, the matrix And the matrix , we can get: ； According to the above formula, the fitting coefficient matrix can be obtained as follows: 。 9. The improved three-phase synchronous phase-locked loop control system according to claim 8, characterized in that: The polynomial of the fitting result is expressed in matrix as: 。 10. The improved three-phase synchronous phase-locked loop control system according to claim 4, characterized in that: 。 11. The improved three-phase synchronous phase-locked loop control system according to claim 1, characterized in that: The output end of the SG filter and the input end of the proportional-integral controller are provided with a given voltage.

12. The improved three-phase synchronous phase-locked loop control system according to claim 1, characterized in that: A reference angular frequency is arranged between the output end of the proportional-integral controller and the input end of the integral link unit.

13. An improved three-phase synchronous phase-locked loop control method, characterized in that: include: Collect three-phase grid voltage signals; The three-phase grid voltage signal is converted into a two-phase grid voltage signal by using coordinate transformation; The SG filtering algorithm is used to filter the two-phase grid voltage signal to obtain the filtering result; The filtering result is subjected to proportional-integral control to realize a phase-locked loop.

14. The improved three-phase synchronous phase-locked loop control method according to claim 13, characterized in that: The open-loop transfer function of the phase-locked loop is: ， In the formula, is the transfer function of the SG filter, is the Laplace operator; is the proportional coefficient of the PI controller; is the integral coefficient of the PI controller, is the three-phase composite voltage vector.

15. The improved three-phase synchronous phase-locked loop control method according to claim 13, characterized in that: The SG filtering algorithm is specifically: Get the original data in the sliding window of the SG filter; The original data are fitted using a polynomial to obtain fitted data; Calculate the residual sum of squares between the fitted data and the original data; Solve for the partial derivative of the residual sum of squares; Solve for the fitting coefficients; Get the polynomial of the fitting result.

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