A frequency adaptive sliding mode observer phase-locked loop for grid synchronization

Abstract

The application belongs to the technical field of power electronics and power grid synchronization, and discloses a frequency adaptive sliding mode observer phase-locked loop for power grid synchronization, which comprises a quadrature signal generator based on a sliding mode observer, a phase detector, a loop filter, a voltage-controlled oscillator and a frequency feedforward branch, and the loop filter is a PI controller; the proportional coefficient of the PI controller is Kp; the integral coefficient of the PI controller is Ki; and the frequency estimation value of the phase-locked loop is ω0; the frequency feedforward branch is used for returning the frequency reference of the quadrature signal generator to the quadrature signal generator; and the phase-locked loop can adapt to frequency changes and ensure high-precision power grid synchronization technology, so as to meet the strict demand of MEA power grid on real-time state estimation.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and power grid synchronization technology, and specifically relates to a frequency-adaptive sliding mode observer phase-locked loop for power grid synchronization. Background Technology

[0002] More Electric Aircraft (MEA) represents a crucial direction in the evolution of modern aviation propulsion systems. Its core lies in the large-scale replacement of traditional hydraulic, pneumatic, and mechanical actuation systems widely used in aircraft with high-performance electric systems. This electrification revolution significantly reduces the overall weight and size of aircraft, improves energy efficiency and system maintenance convenience, and lays a solid foundation for a more environmentally friendly and economical next-generation aircraft. However, this profound systemic transformation also places unprecedentedly high demands on the stability, reliability, and power quality of the onboard power grid. MEA power grids typically employ a variable frequency AC power supply system, with an operating frequency range of 360Hz to 800Hz, rather than the traditional constant frequency of 50Hz. This wide-range variable frequency operation is a necessary consequence of adapting to significant variations in aircraft engine speed, but it also makes real-time and accurate measurement of fundamental power grid parameters, particularly the frequency and phase of voltage, extremely difficult.

[0003] Grid synchronization technology is the cornerstone for ensuring the coordinated operation of all airborne power electronic equipment with the power grid, achieving efficient energy management and high-quality power supply. As a key technology for grid synchronization, phase-locked loops (PLLs) have long performed excellently in power frequency or constant frequency AC power grids, reliably tracking voltage phase. However, when PLLs are directly applied to complex scenarios such as multi-electric aircraft with wideband and variable frequency operation, traditional PLL structures face severe challenges in terms of dynamic response speed, phase tracking accuracy, and anti-interference robustness: significant phase lag and estimation errors exist when the frequency changes drastically, making it difficult to meet the stringent synchronization requirements of the high-dynamic, high-reliability power systems of multi-electric aircraft. For example, the Time-Delay Phase-Locked Loop (TD-PLL) technology generates orthogonal signals through a T / 4 delay, offering a simple structure and fast dynamic response, but it generates steady-state errors when the grid frequency deviates from the nominal value; the Inverse Park Transform Phase-Locked Loop (IPT-PLL) technology utilizes filtered... Axial voltages construct orthogonal signals, but the phase delay introduced by the low-pass filter degrades performance; although the second-order generalized integrator phase-locked loop (SOGI-PLL) has good harmonic suppression capabilities, its accuracy decreases significantly under DC bias and harmonic interference.

[0004] Therefore, a phase-locked loop (PLL) technology that can adapt to changes in grid frequency while ensuring high accuracy is needed to meet the stringent requirements of MEA grids for real-time state estimation. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a frequency-adaptive sliding mode observer phase-locked loop for power grid synchronization.

[0006] The technical problem to be solved by this invention is achieved through the following technical solution:

[0007] A frequency-adaptive sliding mode observer phase-locked loop (PLL) for power grid synchronization includes: an orthogonal signal generator, a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). The PLL receives the grid voltage as input to the orthogonal signal generator, which outputs a fundamental signal of the grid voltage and an orthogonal signal thereof based on a frequency reference. The fundamental signal and the orthogonal signal are input to the phase detector, causing it to output a phase error signal based on a phase reference. The phase error signal is input to the loop filter, causing it to output a frequency correction. The VCO generates a frequency estimate based on the frequency correction and integrates the frequency estimate to obtain a phase estimate. The phase reference is the phase estimate. The orthogonal signal generator is an orthogonal signal generator based on a sliding mode observer. The loop filter is a PI controller. The proportional gain of the PI controller is... , The integral coefficient of the PI controller , , The frequency estimate is given; the sliding mode observer phase-locked loop further includes: a frequency feedforward branch, used to... The frequency reference is returned to the orthogonal signal generator. .

[0008] Optionally, the sliding mode observer phase-locked loop is designed in the following manner:

[0009] Construct an orthogonal signal generator based on a sliding mode observer;

[0010] The orthogonal signal generator is combined with a phase-locked loop to obtain an initial sliding mode observer phase-locked loop, which is then simplified into a linear time-invariant system.

[0011] By deriving the transfer function of the linear time-invariant system, a fourth-order system is obtained;

[0012] By performing pole distribution analysis on the fourth-order system, three dominant poles are determined, and the fourth-order system is reduced to a third-order system based on the three dominant poles.

[0013] The closed-loop characteristic polynomial of the third-order system is combined with a damping coefficient. Natural frequency and key coefficient The coefficients of the characteristic polynomial of the determined standard third-order system are matched to obtain the coefficient matching relation; wherein, the key coefficients For use based on Determine the location of the real poles in the standard third-order system;

[0014] Based on the coefficient matching formula, a key coefficient is obtained. The equation;

[0015] ;

[0016] in, The frequency of the grid voltage;

[0017] According to the aforementioned key coefficients The equation is used to determine the optimal system that makes the real poles of the standard third-order system closest to the origin. value;

[0018] make , will the current Value and the optimal Substitute the values ​​into the coefficient matching formula and the formula about The equation is derived. , , and The relationship is as follows:

[0019] ,

[0020] ,

[0021] ;

[0022] according to , and Based on the relationship, the proportional coefficient and integral coefficient of the PI controller are set, and according to... and The relationship is introduced into the frequency feedforward branch to obtain the designed sliding mode observer phase-locked loop.

[0023] Optionally, .

[0024] Optionally, .

[0025] Optionally, .

[0026] This invention also provides a phase-locked loop method for grid voltage, implemented using the aforementioned sliding mode observer phase-locked loop, the method comprising:

[0027] The grid voltage is input to an orthogonal signal generator based on a sliding mode observer, and the orthogonal signal generator outputs the fundamental signal of the grid voltage and the orthogonal signal of the fundamental signal based on a frequency reference.

[0028] The fundamental signal and the quadrature signal are input into the phase detector so that the phase detector outputs a phase error signal based on the phase reference.

[0029] The phase error signal is input to the PI controller so that the PI controller outputs a frequency correction value; wherein, the proportional coefficient of the PI controller... , The integral coefficient of the PI controller , ;

[0030] The frequency correction value is input to the voltage-controlled oscillator (VCO), which then adds the frequency correction value to the frequency of the mains voltage to obtain a frequency estimate. For the frequency estimate Integrate to obtain the phase estimate;

[0031] Based on the frequency estimate The frequency reference is adjusted, and the phase estimate is fed back to the phase detector as the phase reference to achieve phase tracking and locking of the grid voltage.

[0032] Optionally, based on the frequency estimate Adjusting the frequency reference includes: The frequency reference is returned to the orthogonal signal generator. .

[0033] Optionally, .

[0034] Optionally, .

[0035] Optionally, .

[0036] The frequency-adaptive sliding mode observer phase-locked loop for power grid synchronization provided by this invention utilizes an orthogonal signal generator constructed from sliding mode observers to robustly extract pure fundamental signals from distorted power grid voltages such as harmonics, laying the foundation for high-precision phase synchronization estimation; secondly, this invention adjusts the parameters of the PI controller ( , Based on real-time frequency estimation and adaptive adjustment, the dynamic performance of the phase-locked loop (PLL) is automatically optimized and maintained consistently across the entire frequency range. Furthermore, this invention introduces a frequency feedforward branch into the PLL, significantly improving its ability to quickly track changes in grid frequency. These features work synergistically to enable the PLL provided by this invention to possess excellent anti-interference capabilities, rapid response, and steady-state error-free tracking capability under conditions of strong interference and frequency fluctuations, making it suitable for demanding grid synchronization scenarios such as new energy grid integration and power quality control.

[0037] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0038] Figure 1 A schematic diagram of the linearized structure of an orthogonal signal generator based on a sliding mode observer is shown.

[0039] Figure 2 The power grid voltage estimation error of the SMO-QSG (Slide Mode Observer Quadrature Signal Generator) under different conditions is shown. The curve of change;

[0040] Figure 3 This is a schematic diagram of the phase-locked loop structure of a sliding mode observer proposed in this invention;

[0041] Figure 4 A schematic diagram of a PLL (phase-locked loop) structure with an ideal quadrature PD (phase angle detector) is shown.

[0042] Figure 5 This is a linearized block diagram of an SMO-PLL (Slide Mode Observer Phase-Locked Loop) proposed in this invention;

[0043] Figure 6 This is a schematic diagram of the structure of an adaptive sliding mode observer based phase-locked loop (ASMO-PLL) proposed in this invention.

[0044] Figure 7 A comparison diagram of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL during grid voltage drops is shown.

[0045] Figure 8 The figure shows a comparison of the amplitude of the ASMO-PLL provided by the present invention and the existing SOGI-PLL during grid voltage drops.

[0046] Figure 9 The diagram shows a comparison of the frequency errors between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there are harmonic disturbances in the grid voltage.

[0047] Figure 10 The figure shows a comparison of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there are harmonic disturbances in the grid voltage.

[0048] Figure 11 The diagram shows a comparison of the frequency errors between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a DC bias in the grid voltage.

[0049] Figure 12 A comparison diagram of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL is shown when there is a DC bias in the grid voltage.

[0050] Figure 13 A comparison diagram of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL is shown when there is a phase jump in the grid voltage.

[0051] Figure 14 A comparison diagram of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL is shown when there is a phase jump in the grid voltage.

[0052] Figure 15 The diagram shows a frequency comparison between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a small jump in the grid voltage frequency.

[0053] Figure 16 The diagram shows a comparison of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a small jump in the grid voltage frequency.

[0054] Figure 17 The diagram shows a comparison of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a small frequency jump in the grid voltage.

[0055] Figure 18The diagram shows a frequency comparison between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency jumps sharply from 450Hz to 750Hz.

[0056] Figure 19 The diagram shows a comparison of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency jumps significantly from 450Hz to 750Hz.

[0057] Figure 20 The diagram shows a comparison of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency jumps sharply from 450Hz to 750Hz.

[0058] Figure 21 The diagram shows a frequency comparison between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency is gradually increased from 450Hz to 460Hz.

[0059] Figure 22 The diagram shows a comparison of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency is gradually increased from 450Hz to 460Hz.

[0060] Figure 23 The diagram shows a comparison of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency gradually increases from 450Hz to 460Hz. Detailed Implementation

[0061] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0062] To achieve a power grid synchronization technology that can adapt to changes in power grid frequency while ensuring high precision, this invention provides a frequency-adaptive sliding mode observer phase-locked loop for power grid synchronization. The sliding mode observer phase-locked loop includes: an orthogonal signal generator, a phase detector, a loop filter, a voltage-controlled oscillator, and a frequency feedforward branch.

[0063] The grid voltage is input to an orthogonal signal generator, which outputs the fundamental signal of the grid voltage and its orthogonal signal based on a frequency reference. The frequency reference of the orthogonal signal generator varies with the frequency estimate of the phase-locked loop (PLL) of the sliding mode observer. Adaptive adjustments, such as frequency references. , Preferably, The fundamental and quadrature signals output from the quadrature signal generator are input into the phase detector, which outputs a phase error signal based on a phase reference. This phase reference is the phase estimate output by the phase-locked loop of the sliding mode observer. The aforementioned loop filter is a PI (Proportional-Integral) controller; the phase error signal output from the phase detector is input to this PI controller, and the PI controller outputs a frequency correction value; in this invention, the proportional coefficient of the PI controller... , Preferably, Integral coefficient of PI controller , Preferably, It is worth noting that, in this invention, the proportional and integral coefficients of the PI controller are also estimated to change with the frequency of the sliding mode observer's phase-locked loop. It adapts to changes. Then, the frequency correction is input to the voltage-controlled oscillator (VCO), which contains a frequency synthesizer and an integrator. The frequency synthesizer adds the frequency correction to the frequency of the mains voltage to obtain a frequency estimate. Then, the integrator estimates the frequency. Integrate to obtain and output the phase estimate of the sliding mode observer phase-locked loop. .

[0064] The frequency-adaptive sliding mode observer phase-locked loop for power grid synchronization provided by this invention utilizes an orthogonal signal generator constructed from sliding mode observers to robustly extract pure fundamental signals from distorted power grid voltages such as harmonics, laying the foundation for high-precision phase synchronization estimation; secondly, this invention adjusts the parameters of the PI controller ( , Based on real-time frequency estimation and adaptive adjustment, the dynamic performance of the phase-locked loop (PLL) is automatically optimized and maintained consistently across the entire frequency range. Furthermore, this invention introduces a frequency feedforward branch into the PLL, significantly improving its ability to quickly track frequency changes. These features work synergistically to enable the sliding mode observer PLL provided by this invention to possess excellent anti-interference capabilities, fast response, and steady-state error-free tracking capability under conditions of strong interference and frequency fluctuations. It is suitable for demanding power grid synchronization scenarios such as multi-electric aircraft, new energy grid integration, and power quality control.

[0065] The sliding mode observer phase-locked loop provided by this invention is constructed in the following manner:

[0066] Step 1: Construct an orthogonal signal generator (SMO-QSG) based on a sliding mode observer.

[0067] Specifically, firstly, considering the potential distortion in a single-phase system, the grid voltage requiring phase locking may be affected by harmonics, DC bias, and other interferences. Taking these interferences into account, the grid voltage can be expressed as:

[0068] (1);

[0069] in, Indicates the amplitude of the grid voltage, It is its maximum amplitude. The frequency representing the mains voltage, This represents the initial phase angle of the grid voltage. This indicates a disturbance in the grid voltage, since there is no information about the disturbance. Therefore, equation (1) can be applied to any disturbance, such as harmonics and DC bias, because it provides accurate information. Indicates time.

[0070] Then, define the system (here referring to SMO-QSG) state. ,in, It is the fundamental frequency voltage. Its orthogonal signal is represented as follows:

[0071] (2);

[0072] (3);

[0073] Define system state The derivative is , represented as:

[0074] (4);

[0075] To construct a sliding mode observer, based on , and The relationship between them can be defined by the following mathematical model:

[0076] (5);

[0077] in, C =[0,0,1], , , It is its derivative. , This represents the output variables of the system (in this case, SMO-QSG).

[0078] Then, the sliding mode observer is designed as follows:

[0079] (6);

[0080] (7);

[0081] (8)

[0082] (9);

[0083] in, Indicates estimation , It is its derivative; Indicates estimation , Indicates estimation , Symbolic function, superscript This represents the transpose of a vector. This indicates the sliding mode control item. This represents the estimated fundamental voltage. This represents the orthogonal signal representing the estimated fundamental voltage. and These are the observer parameters. The linear gain matrix is ​​designed as follows: , This is the gain coefficient of the nonlinear part of the sliding mode observer. In practice, the observer parameters can be selected by configuring the system poles of the sliding mode observer. Specifically, to obtain satisfactory dynamic performance and appropriate overshoot, the specified eigenvalues ​​are placed on the real axis and within ±120 degrees of the complex plane. Furthermore, it is also necessary to ensure that... Satisfying the Hurwitz matrix, therefore design L 1 = -5 ω ², L 2= ω ² and L 3=-3 ω .

[0084] Then, based on the above sliding mode observer, an orthogonal signal generator (SMO-QSG) based on the sliding mode observer is constructed. This SMO-QSG contains a nonlinear module (sign function), which is applied to the variable... There are discontinuities at certain points. To address this issue, a mathematical expression based on a smooth approximation is used. By replacing the sign function, we obtain an orthogonal signal generator based on a sliding mode observer, the structure of which is as follows: Figure 1 As shown, where , , They represent the estimates respectively. , , . This represents the integrator. In this SMO-QSG, an integrator is introduced by... , will originally be in A sign function that is discontinuous at a given point is transformed into a globally continuous and differentiable smooth function, where, It is a small regularization parameter, and its value range is .

[0085] Figure 2 The grid voltage estimation error of SMO-QSG under different conditions is shown. The curve showing the change. Figure 2 The data shows that, with As the value increases, the grid voltage estimation error (whose unit is the same as the grid voltage unit) gradually decreases and tends to stabilize, but the improvement effect on the steady-state error is not significant. Therefore, taking... →∞ can simplify the block diagram of SMO-QSG; the simplified SMO-QSG only needs to be deleted. Figure 1 The part within the dashed box, such as Figure 3 As shown in the left-hand side.

[0086] The simplified transfer function of SMO-QSG is as follows:

[0087] (10);

[0088] (11);

[0089] in, Complex frequency domain variables, yes The complex frequency domain representation, yes The complex frequency domain representation, yes The complex frequency domain representation of .

[0090] Step 2: Combine the quadrature signal generator with the phase-locked loop to obtain the initial sliding mode observer phase-locked loop, and simplify the initial sliding mode observer phase-locked loop into a linear time-invariant system.

[0091] Here, the quadrature signal generator is combined with a phase-locked loop (PLL). Specifically, the signal output from the quadrature signal generator is input into a PLL to obtain the initial sliding mode observer-PLL (SMO-PLL), the structure of which is shown below. Figure 3 ,in, This represents the stationary coordinate system used in the Park transform module of the phase-locked loop to process orthogonal AC signals. This represents the synchronous rotating coordinate system used for phase-locked loop error detection and control in the Park transformation module of the phase-locked loop. It is the voltage vector that is rotating. coordinate system The components on the axis, under ideal phase-locked state, It equals the magnitude of the voltage vector. It is the cross-axis component reflecting the phase error generated by the phase detector inside the phase-locked loop. It is the nominal frequency of the grid voltage, which is a constant.

[0092] Then, the dynamic performance of SMO-PLL is analyzed by establishing a small-signal linearization model, the construction of which is derived from the linearization process near the operating point. Figure 4 The diagram shows the structure of a PLL with an ideal quadrature PD (phase detector), which includes a phase detector (PD), a loop filter (LF), and a voltage-controlled oscillator (VCO). Therefore, the phase signal error of the PD output is:

[0093] (12);

[0094] (13);

[0095] in, Indicates the phase angle signal error. This represents the phase angle of the grid voltage. That is its estimated value.

[0096] Formula (12) derives the dynamic error value of the phase angle detection loop. Then, formula (13) approximates the nonlinear trigonometric function terms by assuming the estimated value deviates very little from the actual value, thus simplifying the SMO-PLL system model into a linear time-invariant system, such as... Figure 5 As shown, where This indicates the preset grid voltage phase angle.

[0097] Step 3: By deriving the transfer function of the above linear time-invariant system, a fourth-order system is obtained.

[0098] Specifically, the transfer function of SMO-PLL is as follows:

[0099] (14);

[0100] in, yes The complex frequency domain representation, It is a phase estimate. The complex frequency domain representation, It is the proportional gain of the PI controller. It is the integral coefficient of the PI controller. In SMO-PLL, .

[0101] As can be seen from the transfer function above, the current SMO-PLL is a fourth-order system.

[0102] Step 4: Determine the three dominant poles by performing pole distribution analysis on the fourth-order system, and reduce the fourth-order system to a third-order system based on these three dominant poles.

[0103] Specifically, in the design and analysis of control systems, to simplify calculations and highlight dominant dynamic characteristics, the dominant pole method is often used to reduce the order of high-order models. In this invention, for the original fourth-order system, pole distribution analysis is first used to identify the three poles closest to the imaginary axis among the four poles. These poles constitute the dominant mode of the system response. By accurately retaining these three dominant poles while discarding the minor pole with the weakest impact on the overall system dynamics, the fourth-order system can be reduced to a third-order system, as shown in the following model:

[0104] (15);

[0105] Step 5: Combine the closed-loop characteristic polynomial of the above third-order system with a polynomial determined by the damping coefficient. Natural frequency and key coefficient The coefficients of the characteristic polynomial of a given standard third-order system are matched to obtain the coefficient matching relation; among which, the key coefficients... For use based on Determine the location of the real poles in a standard third-order system.

[0106] Specifically, the closed-loop characteristic polynomial of the above third-order system is:

[0107] (16);

[0108] The above is based on the damping coefficient Natural frequency and key coefficient The characteristic polynomial of a standard third-order system is:

[0109] (17);

[0110] By matching the coefficients of equation (16) and equation (17), the coefficient matching relationship is obtained as follows:

[0111] (18);

[0112] (19);

[0113] (20);

[0114] Step 6: Based on the above matching formula, obtain a key coefficient. The equation.

[0115] Specifically, by combining the previous equations (18) and (19) to eliminate ,get:

[0116] (twenty one);

[0117] When equation (21) When a solution exists, the discriminant of the quadratic function can be obtained using the discriminant property:

[0118] (twenty two);

[0119] Thus, we obtain a key coefficient. The equation:

[0120] (twenty three);

[0121] Step 7: Based on the above information regarding key coefficients The equations determine the optimal system that makes the real poles of the standard third-order system closest to the origin. value.

[0122] Specifically, It is a key coefficient, and its function is based on Determine the location of the real poles in a standard third-order system. The location of the real poles has a decisive impact on the dynamic performance and filtering capability of the system: to maintain high modulus filtering capability, i.e., to achieve excellent noise suppression and fast response characteristics, the real poles should be as close as possible to the origin of the complex plane. This is because poles close to the origin can reduce the phase lag of the system, enhance the attenuation of high-frequency interference, and thus improve steady-state accuracy and robustness. Therefore, determine the optimal location of the real poles in the standard third-order system that makes them as close as possible to the origin. The value is its minimum value .

[0123] Step 8, let , will the current Value and Optimal Substituting the values ​​into the coefficient matching relation and about The equation is derived. , , and The relationship.

[0124] Specifically, the selection of the damping coefficient is crucial when optimizing the dynamic performance of a control system. For a typical second-order system, to achieve a fast response speed while ensuring an appropriate stability margin, the damping coefficient is often set to... This value allows the system to achieve a smaller overshoot and shorter settling time in a step response, thus achieving a better balance between speed and stability. Therefore, Substituting into equation (19), we can obtain:

[0125] ,

[0126] (twenty four);

[0127] Based on this, then Substituting (18)-(20), we can derive... , , and The relationship is as follows:

[0128] (25);

[0129] (26);

[0130] (27);

[0131] Then, through equation (25) Substituting the solution into (27), and and The relation (24) ultimately yields , , and The relationship is as follows:

[0132] (28);

[0133] (29);

[0134] (30);

[0135] Step 9, according to , and Based on the relationship, set the proportional and integral coefficients of the PI controller, and according to... and By introducing a frequency feedforward branch into the phase-locked loop (PLL), a well-designed sliding mode observer PLL is obtained.

[0136] Specifically, according to equations (28)-(30), the proportional and integral coefficients of the PI controller are optimally set as shown in equations (29) and (30). However, in practical engineering applications, equations (29) and (30) can be appropriately extended. , and The relationship is represented as:

[0137] (31),

[0138] (32);

[0139] Similarly, according to and The relationship (28) introduces a frequency feedforward branch into the phase-locked loop, and its function is expressed as follows:

[0140] (33);

[0141] Preferably, , , .

[0142] Therefore, by combining equations (31)-(33) with the phase-locked loop, the frequency-adaptive sliding mode observer phase-locked loop (ASMO-PLL) provided in this invention can be obtained.

[0143] The ASMO-PLL provided by this invention uses frequency estimation values Feedback to the PI controller and To adjust the model parameters and the frequency estimates The signal is then fed back to the signal generator to adjust the frequency reference. Since the mains frequency can be considered constant at any given time, it can be adjusted via... and The adaptive adjustment modifies the control bandwidth of the phase-locked loop in real time, while the dynamically adjusted control bandwidth can better adapt to the frequency changes of the power grid and accurately estimate the power grid state under a wide range of signal changes.

[0144] It is worth mentioning that, in existing technologies that use phase-locked loops to achieve grid voltage phase tracking, in order to ensure stable operation under frequency disturbances, the input frequency variation needs to be controlled. Limited to a certain range, that is, satisfying ,in, This is the cutoff frequency of the phase-locked loop. This represents the maximum allowed frequency offset.

[0145] In this invention, to improve the adaptability of the phase-locked loop to changes in the power grid environment, the proportional coefficient of the PI controller is... , It is deeply integrated with the real-time grid frequency feedback mechanism in the phase-locked loop (PLL). Through this integration, the parameters of the PI controller can be dynamically adjusted according to changes in the grid frequency, thereby achieving adaptive updates of model parameters when the grid frequency fluctuates, without having to consider the aforementioned limitations, thus enhancing the robustness and tracking accuracy of the PLL.

[0146] Furthermore, it is worth mentioning that there is a class of existing technologies that achieve grid synchronization based on the observer itself (without involving a phase-locked loop). However, these technologies often have a high computational burden in MEA grids, and their steady-state accuracy and dynamic response are still insufficient. For example, while PLLs based on linear Kalman filters enhance anti-interference capabilities through repeated observers, their implementation is complex; adaptive observers improve dynamic performance, but struggle to balance speed and accuracy over a wide frequency range. This invention, by deeply integrating a sliding mode observer with a phase-locked loop, inherits the robustness of the observer while utilizing the simple closed-loop feedback structure of the phase-locked loop, thus outperforming single-observer schemes in terms of computational complexity, wide frequency adaptability, and dynamic response speed.

[0147] The ASMO-PLL provided by this invention can be implemented through a digital hardware platform. Specifically, the various modules included in the ASMO-PLL are mapped onto a Field Programmable Gate Array (FPGA) or a Digital Signal Processor (DSP). For example, in an FPGA implementation, the quadrature signal generator, phase detector, loop filter, and voltage-controlled oscillator can be implemented as independent logic function units written in a hardware description language (such as Verilog HDL or VHDL). The connection relationships between the modules correspond to the physical paths for signal transmission within the FPGA via registers or data buses. In a DSP implementation, each module corresponds to a software function or task called sequentially in an interrupt service routine. The connection relationships between modules are reflected in the data interface and calling order between functions, i.e., the output variable of the previous function serves as the input variable of the next function. For example, Figure 6 The diagram shows a block diagram of a frequency adaptive sliding mode observer phase-locked loop, including: SMO-QSG, phase detector, PI controller, voltage-controlled oscillator (VCO) and frequency feedforward path (FFP). Figure 6 The SMO-QSG, phase detector, VCO, and FFP are already labeled; the remaining components constitute the PI controller. Furthermore... Figure 6 In This indicates calculating the square. It is understandable that, according to... Figure 6 The signal flow and data dependencies shown can be implemented on a selected digital hardware platform (FPGA or DSP) to realize the ASMO-PLL provided by this invention.

[0148] It should be noted that, Figure 6The structure shown is merely an example and does not constitute a limitation on the structure of the ASMO-PLL provided by this invention. Specifically, the innovation of the ASMO-PLL provided by this invention compared to the prior art lies in: the quadrature signal generator uses a sliding mode observer-based quadrature signal generator, and the proportional gain of the PI controller... Integral coefficient Furthermore, a frequency feedforward branch is introduced. Those skilled in the art can incorporate the innovations proposed in this invention into existing phase-locked loops, thereby obtaining sliding mode observer phase-locked loops with different specific structures based on the technical concept of this invention. The actual ASMO-PLLs that can be designed are not limited to... Figure 6 The structure shown.

[0149] Figure 7 The figure shows a comparison of the frequency errors of the ASMO-PLL provided by the present invention and the existing SOGI-PLL when the grid voltage drops. Figure 8 A comparison graph showing the amplitude of the ASMO-PLL provided by this invention with that of the existing SOGI-PLL during grid voltage dips is presented. Figures 7-8 As can be seen, when the grid voltage drops, the initial grid voltage is 1 p.u. and the frequency is 450 Hz. Then, the amplitude change of the grid voltage is 0.5 p.u. The ASMO-PLL of the present invention has a dynamic response time of less than 10 ms, similar to SOGI-PLL, but the ASMO-PLL of the present invention has a smaller frequency error (SOGI-PLL has an error of 2.568 Hz, while ASMO-PLL has a frequency error of 0.2 Hz) and more accurate amplitude estimation (SOGI-PLL has a static error of 0.17 p.u. in amplitude estimation, while ASMO-PLL does not).

[0150] Figure 9 The diagram shows a comparison of the frequency errors between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there are harmonic disturbances in the grid voltage. Figure 10 A comparison diagram of the phase errors of the ASMO-PLL provided by this invention and the existing SOGI-PLL is shown when harmonic disturbances exist in the grid voltage. From Figures 9-10As can be seen, under the condition of harmonic disturbances in the grid voltage, the initial grid voltage is 1 p.u. and the frequency is 450 Hz. A 5th harmonic of 0.03 p.u. and a 7th harmonic of 0.01 p.u. are added to the grid voltage. Due to the presence of harmonics, all signals are affected by the steady-state error of the estimated signal. Compared with the traditional SOGI-PLL, the ASMO-PLL of this invention has a smaller difference in dynamic performance, a smaller frequency error (SOGI-PLL is 2.6 Hz, ASMO-PLL is 1.2 Hz), and more accurate phase estimation (SOGI-PLL has a static error of 0.065 rad, while the phase estimation error of ASMO-PLL is almost zero).

[0151] Figure 11 The diagram shows a comparison of the frequency errors between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a DC bias in the grid voltage. Figure 12 A comparison diagram of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL is shown when there is a DC bias in the grid voltage. From Figures 11-12 As can be seen, with a DC bias in the grid voltage, the initial grid voltage is 1 p.u. and the frequency is 450 Hz. Then, a DC bias of 0.01 p.u. is added to the grid voltage. Both the ASMO-PLL proposed in this invention and the traditional SOGI-PLL have short dynamic response times. However, the SMO-PLL has a smaller frequency error (SOGI-PLL's frequency error is 2.92 Hz, while ASMO-PLL's is 1.12 Hz) and more accurate phase estimation (SOGI-PLL's static error is 0.065 rad, while ASMO-PLL's phase error is only 0.01 rad).

[0152] Figure 13 A comparison diagram of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL is shown when there is a phase jump in the grid voltage. Figure 14 This diagram shows a comparison of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a phase jump in the grid voltage; from Figures 13-14 As can be seen, when there is a phase jump in the grid voltage, the initial grid voltage is 1 p.u., the frequency is 450 Hz, and then the phase jumps to π / 6. From Figure 13It can be concluded that the ASMO-PLL proposed in this invention has a shorter dynamic response time, within 10ms, while the dynamic response time of the traditional SOGI-PLL is three times that of the former. Furthermore, the ASMO-PLL has a smaller frequency error (SOGI-PLL has a frequency error of 2.68Hz, while ASMO-PLL has 0.3Hz), and its phase estimation is also more accurate (SOGI-PLL always has a static error of 0.065rad in phase estimation, while ASMO-PLL has almost no phase estimation error).

[0153] Figure 15 The diagram shows a frequency comparison between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a small jump in the grid voltage frequency. Figure 16 The diagram shows a comparison of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a small jump in the grid voltage frequency. Figure 17 This paper presents a comparison diagram of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when there is a small frequency jump in the grid voltage; from Figures 15-17 As can be seen, when there is a small jump in the grid voltage frequency, the initial grid voltage is 1 p.u. and the frequency is 450 Hz, then the frequency changes from 450 Hz to 460 Hz. The ASMO-PLL proposed in this invention can accurately estimate the grid frequency within 2 milliseconds. In contrast, a typical SOGI-PLL can track the grid frequency, but its frequency estimation error is larger (SOGI-PLL's frequency error is 2.64 Hz, while ASMO-PLL's is 0.22 Hz). Furthermore, SOGI-PLL has a static error in phase estimation, while ASMO-PLL achieves accurate estimation.

[0154] Figure 18 The diagram shows a frequency comparison between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency jumps sharply from 450Hz to 750Hz. Figure 19 The diagram shows a comparison of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency jumps significantly from 450Hz to 750Hz. Figure 20 A comparison diagram of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL is shown when the grid voltage frequency jumps sharply from 450Hz to 750Hz. According to... Figures 18-20 As can be seen, when the grid voltage frequency jumps sharply from 450Hz to 750Hz, the ASMO-PLL proposed in this invention can quickly and accurately lock onto the 750Hz frequency, while the SOGI-PLL exhibits significant tracking lag during transient processes. Furthermore, regarding phase tracking, from... Figure 20It can be seen that the phase error of ASMO-PLL is almost zero, while the phase error of SOGI-PLL fluctuates significantly. Experimental results show that the ASMO-PLL proposed in this invention can effectively cope with extreme frequency differences, and its dynamic response speed and estimation accuracy are superior to SOGI-PLL, verifying its application potential in power grid environments with strong nonlinearity and large frequency differences.

[0155] Figure 21 The diagram shows a frequency comparison between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency is gradually increased from 450Hz to 460Hz. Figure 22 The diagram shows a comparison of the frequency error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency is gradually increased from 450Hz to 460Hz. Figure 23 This paper presents a comparison of the phase error between the ASMO-PLL provided by this invention and the existing SOGI-PLL when the grid voltage frequency gradually increases from 450Hz to 460Hz. Figures 21-23 As can be seen, both ASMO-PLL and SOGI-PLL can track frequency changes in terms of dynamic performance, but the ASMO-PLL curve proposed in this invention is smoother and less volatile, and its estimation error remains within a very small range. In contrast, the SOGI-PLL estimation curve exhibits significant fluctuations, a relatively slower tracking speed, and a larger steady-state error (SOGI-PLL's frequency error is 2.7 Hz, while ASMO-PLL's is 0.28 Hz). Regarding phase estimation, SOGI-PLL's static error remains consistently at 0.085 rad, while ASMO-PLL's phase error is almost zero. Experimental results clearly demonstrate that under conditions of slowly changing frequency disturbances, ASMO-PLL outperforms SOGI-PLL in both dynamic response speed and steady-state accuracy.

[0156] In summary, compared with existing phase-locked loops, the sliding mode observer phase-locked loop provided by this invention utilizes a quadrature signal generator constructed from sliding mode observers, which can robustly extract pure fundamental signals from distorted grid voltages such as harmonics, laying the foundation for high-precision phase synchronization estimation; secondly, this invention enables the PI controller parameters ( , Based on real-time frequency estimation and adaptive adjustment, the dynamic performance of the phase-locked loop (PLL) is automatically optimized and maintained consistently across the entire frequency range. Furthermore, this invention introduces a frequency feedforward branch into the PLL, significantly improving its ability to quickly track frequency changes. These features work synergistically to enable the PLL provided by this invention to possess excellent anti-interference capabilities, rapid response, and steady-state error-free tracking capability under conditions of strong interference and frequency fluctuations, making it suitable for demanding grid synchronization scenarios such as new energy grid integration and power quality control.

[0157] Based on the same inventive concept, embodiments of the present invention also provide a phase-locked method for grid voltage, implemented through the aforementioned sliding mode observer phase-locked loop (ASMO-PLL), the method comprising:

[0158] Step 1: Input the grid voltage into the quadrature signal generator based on the sliding mode observer, so that the quadrature signal generator outputs the fundamental signal of the grid voltage and the quadrature signal of the fundamental signal based on the frequency reference;

[0159] Step 2: Input the fundamental signal and the quadrature signal into the phase detector so that the phase detector outputs a phase error signal based on the phase reference;

[0160] Step 3: Input the phase error signal into the PI controller so that the PI controller outputs the frequency correction amount; wherein, the proportional coefficient of the PI controller... , Integral coefficient of PI controller , ;

[0161] Step 4: Input the frequency correction value into the voltage-controlled oscillator (VCO) so that the VCO adds the frequency correction value to the frequency of the mains voltage to obtain the frequency estimate. For frequency estimates Integrate to obtain the phase estimate;

[0162] Step 5: Based on the frequency estimate The frequency reference is adjusted, and the phase estimate is fed back to the phase detector as the phase reference to achieve phase tracking and locking of the grid voltage.

[0163] It should be noted that, for the various modules involved in the method embodiments, since they have already been described in detail in the sliding mode observer phase-locked loop embodiment, the description here is relatively simple. For relevant parts, please refer to the description in the phase-locked loop embodiment.

[0164] It should be noted that the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention.

[0165] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0166] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings and the disclosure in carrying out the claimed invention. In the description of the invention, the word "comprising" does not exclude other components or steps, "a" or "an" does not exclude a plurality, and "a plurality" means two or more, unless otherwise explicitly specified. Furthermore, while different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce good results.

[0167] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A frequency-adaptive sliding mode observer phase-locked loop for power grid synchronization, comprising: The system comprises an orthogonal signal generator, a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). The orthogonal signal generator receives grid voltage as input and outputs a fundamental signal of the grid voltage and an orthogonal signal thereof based on a frequency reference. The fundamental signal and the orthogonal signal are input to the phase detector, causing it to output a phase error signal based on a phase reference. The phase error signal is input to the loop filter, causing it to output a frequency correction value. The VCO generates a frequency estimate based on the frequency correction value and integrates the frequency estimate to obtain a phase estimate. The phase reference is the phase estimate. The orthogonal signal generator is characterized by being a sliding mode observer-based orthogonal signal generator; the loop filter is a PI controller; and the proportional gain of the PI controller is specified. , The integral coefficient of the PI controller , , The frequency estimate is given; the sliding mode observer phase-locked loop further includes: a frequency feedforward branch, used to... The frequency reference is returned to the orthogonal signal generator. ; The sliding mode observer phase-locked loop is designed in the following manner: Construct an orthogonal signal generator based on a sliding mode observer; The orthogonal signal generator is combined with a phase-locked loop to obtain an initial sliding mode observer phase-locked loop, which is then simplified into a linear time-invariant system. By deriving the transfer function of the linear time-invariant system, a fourth-order system is obtained; By performing pole distribution analysis on the fourth-order system, three dominant poles are determined, and the fourth-order system is reduced to a third-order system based on the three dominant poles. The closed-loop characteristic polynomial of the third-order system is combined with a damping coefficient. Natural frequency and key coefficient The coefficients of the characteristic polynomial of the determined standard third-order system are matched to obtain the coefficient matching relation; wherein, the key coefficients For use based on Determine the location of the real poles in the standard third-order system; Based on the coefficient matching formula, a key coefficient is obtained. The equation; ； in, The frequency of the grid voltage; According to the aforementioned key coefficients The equation is used to determine the optimal system that makes the real poles of the standard third-order system closest to the origin. value; make , will the current Value and the optimal Substitute the values ​​into the coefficient matching formula and the key coefficients The equation is derived. , , and The relationship is as follows: ， ， ； according to , and Based on the relationship, the proportional coefficient and integral coefficient of the PI controller are set, and according to... and The relationship is introduced into the frequency feedforward branch to obtain the designed sliding mode observer phase-locked loop.

2. The frequency-adaptive sliding mode observer phase-locked loop according to claim 1, characterized in that, 。 3. The frequency-adaptive sliding mode observer phase-locked loop according to claim 1, characterized in that, 。 4. The frequency-adaptive sliding mode observer phase-locked loop according to claim 1, characterized in that, 。 5. A phase-locking method for grid voltage, characterized in that, This is achieved using the sliding mode observer phase-locked loop according to any one of claims 1-4, the method comprising: The grid voltage is input to an orthogonal signal generator based on a sliding mode observer, and the orthogonal signal generator outputs the fundamental signal of the grid voltage and the orthogonal signal of the fundamental signal based on a frequency reference. The fundamental signal and the quadrature signal are input into the phase detector so that the phase detector outputs a phase error signal based on the phase reference. The phase error signal is input to the PI controller so that the PI controller outputs a frequency correction value; wherein, the proportional coefficient of the PI controller... , The integral coefficient of the PI controller , ; The frequency correction value is input to the voltage-controlled oscillator (VCO), which then adds the frequency correction value to the frequency of the mains voltage to obtain a frequency estimate. For the frequency estimate Integrate to obtain the phase estimate; Based on the frequency estimate The frequency reference is adjusted, and the phase estimate is fed back to the phase detector as the phase reference to achieve phase tracking and locking of the grid voltage.

6. The phase-locking method according to claim 5, characterized in that, Based on the frequency estimate Adjusting the frequency reference includes: The frequency reference is returned to the orthogonal signal generator. .

7. The phase-locking method according to claim 5, characterized in that, 。 8. The phase-locking method according to claim 5, characterized in that, 。 9. The phase-locking method according to claim 6, characterized in that, 。

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