Non-linear compensation-based transient synchronization stabilization control method and device for grid-following type inverter

Abstract

The invention discloses a transient synchronization stabilization control method and device for a grid-following type inverter based on nonlinear compensation, and relates to the technical field of new energy grid-connected control, and the method comprises the steps: determining a stability margin judgment signal according to a power angle signal at a current moment when a power grid detection signal is a power grid fault signal; constructing a phase-locked loop nonlinear model based on the power angle signal, and determining expressions of first nonlinear compensation and second nonlinear compensation; and performing compensation control on a phase angle output by the phase-locked loop by adopting a PI regulator and a nonlinear compensation expression according to the amplitude of the q-axis power grid voltage at the current moment, a power angle signal and a stability margin judgment signal. According to the method, the nonlinear compensation expression of the output phase angle of the phase-locked loop is determined from the nonlinear model of the phase-locked loop, and then nonlinear compensation control is performed on the output phase angle of the phase-locked loop, so that the voltage phase of a power grid can be effectively tracked, and the synchronization stability with a grid-type inverter during a fault period is enhanced.

Description

Technical Field

[0001] The present application relates to the technical field of new energy grid-connected control, and in particular to a method and device for transient synchronous stabilization control of a grid-connected inverter based on nonlinear compensation. Background Art

[0002] Grid-following inverters, the core components of grid-connected wind and photovoltaic power generation systems, achieve phase synchronization with the grid through a three-phase synchronous coordinate system phase-locked loop (PLL). Their stability is directly related to the grid's ability to absorb renewable energy and its safe operation. Under normal grid operating conditions, traditional PLLs employ a PI control strategy, effectively tracking the grid voltage phase and maintaining the decoupling characteristics of the inverter's vector control. However, when a severe grid fault (such as a three-phase short circuit or voltage sag) occurs, the severe disturbance causes the PLL to deviate from its equilibrium point and operate in a nonlinear region. If the operating point cannot return to the attracting domain, transient synchronization instability occurs. During this period, the PLL output phase angle continuously oscillates and gradually diverges. This process disrupts the decoupling performance of the inverter's current inner loop control, causing the inverter's output voltage and current to continuously oscillate in frequency and amplitude. This in turn triggers overcurrent or overvoltage protection mechanisms, forcing the inverter to shut down and exit operation, limiting its ability to absorb renewable energy. Existing transient synchronization stabilization control strategies suffer from reliance on online estimation of grid information and an inability to adaptively adjust parameters. Summary of the Invention

[0003] The purpose of this application is to provide a transient synchronization stabilization control method for a grid-following inverter based on nonlinear compensation, which can enhance the synchronization stability of the grid-following inverter during a fault.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides a method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation, comprising:

[0006] Obtain the current grid voltage and power angle signals;

[0007] Performing coordinate conversion on the grid voltage at the current moment to obtain the d-axis grid voltage and the q-axis grid voltage at the current moment, and determining a grid detection signal based on the d-axis grid voltage; the grid detection signal includes a grid normal signal and a grid fault signal;

[0008] When the grid detection signal is a normal grid signal, the phase angle of the phase-locked loop output is controlled by a phase-locked loop PI regulator according to the amplitude of the q-axis grid voltage;

[0009] When the power grid detection signal is a power grid fault signal, a stability margin judgment signal is determined according to the power angle signal at the current moment;

[0010] Constructing a nonlinear model of a phase-locked loop based on a power angle signal, and deriving expressions of the first nonlinear compensation and the second nonlinear compensation according to the nonlinear model of the phase-locked loop;

[0011] According to the amplitude of the q-axis grid voltage, the power angle signal and the stability margin judgment signal at the current moment, the phase angle output by the phase-locked loop is compensated and controlled using a PI regulator and expressions of the first nonlinear compensation and the second nonlinear compensation.

[0012] In a second aspect, the present application provides a computer device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-mentioned transient synchronous stabilization control method of the grid-following inverter based on nonlinear compensation.

[0013] In a third aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned transient synchronous stabilization control method for a grid-following inverter based on nonlinear compensation.

[0014] In a fourth aspect, the present application provides a computer program product, including a computer program, which, when executed by a processor, implements the above-mentioned transient synchronous stabilization control method for a grid-following inverter based on nonlinear compensation.

[0015] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0016] The present application provides a transient synchronization stabilization control method for a grid-following inverter based on nonlinear compensation. The key starting point is to study an adaptive transient synchronization stabilization control scheme that does not rely on precise grid parameters and does not require adjustment of current instructions. Starting from the nonlinear model of the phase-locked loop, by analyzing the improved energy function with clear physical meaning, a transient synchronization stabilization strategy based on nonlinear compensation is proposed. The nonlinear compensation expression of the phase angle of the phase-locked loop output is determined based on the nonlinear model of the phase-locked loop, and then the phase angle of the phase-locked loop output is nonlinearly compensated and controlled. It can effectively track the grid voltage phase, make up for the shortcomings of the existing strategy, and enhance the synchronization stability of the grid-following inverter in transient state. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1This is a diagram of the application environment of a transient synchronization stabilization control method for a grid-following inverter based on nonlinear compensation in one embodiment of the present application;

[0019] Figure 2 A flowchart of a method for transient synchronization and stabilization control of a grid-following inverter based on nonlinear compensation provided in one embodiment of the present application;

[0020] Figure 3 A simplified model diagram of a grid-connected inverter system provided in one embodiment of the present application;

[0021] Figure 4 A typical PLL control structure diagram provided in an embodiment of the present application;

[0022] Figure 5 An improved energy function stability domain estimation diagram provided by an embodiment of the present application;

[0023] Figure 6 A damping function constraint diagram provided in an embodiment of the present application;

[0024] Figure 7 This is a diagram of an improved PLL control structure provided by an embodiment of the present application;

[0025] Figure 8 A constraint diagram of the damping function after compensation provided in an embodiment of the present application;

[0026] Figure 9 A post-compensation restoring force constraint diagram provided in an embodiment of the present application;

[0027] Figure 10 A stability comparison diagram of a conventional PLL and an improved PLL under a grid fault condition with a balance point provided in one embodiment of the present application;

[0028] Figure 11 A stability comparison diagram of a conventional PLL and an improved PLL under a grid fault condition with a balance point supplemented according to an embodiment of the present application;

[0029] Figure 12 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0031] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0032] The transient synchronization stabilization control method of the grid-following inverter based on nonlinear compensation provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown, the terminal communicates with the server via a network. The data storage system can store the data that the server needs to process. The data storage system can be set up separately, integrated with the server, or placed in the cloud or on other servers. The terminal can send the current grid voltage and power angle signal to the server. After the server receives the current grid voltage and power angle signal, the server obtains the current grid voltage and power angle signal; performs coordinate transformation on the current grid voltage to obtain the current d-axis grid voltage and q-axis grid voltage, and determines a grid detection signal based on the d-axis grid voltage; the grid detection signal includes a normal grid signal and a fault grid signal; when the grid detection signal is a normal grid signal, the grid detection signal including the normal grid signal and the fault grid signal is used according to the amplitude of the q-axis grid voltage; when the grid detection signal is a normal grid signal, a PI regulator controls the phase angle output by the phase-locked loop (PLL); when the grid detection signal is a fault grid signal, a stability margin judgment signal is determined based on the current power angle signal; a nonlinear model of the PLL based on the power angle signal is constructed, and expressions for first and second nonlinear compensations are derived based on the nonlinear model of the PLL; and based on the amplitude of the current q-axis grid voltage, the power angle signal, and the stability margin judgment signal, the PI regulator and expressions for the first and second nonlinear compensations are used to compensate and control the phase angle output by the PLL. The server can feed back the phase angle of the compensated phase-locked loop output to the terminal. In addition, in some embodiments, the transient synchronization and stabilization control method for a grid-following inverter based on nonlinear compensation can also be implemented independently by the server or the terminal. For example, the terminal can directly perform transient synchronization and stabilization control of the grid-following inverter based on nonlinear compensation for the current grid voltage and power angle signal. Alternatively, the server can obtain the current grid voltage and power angle signal from a data storage system and perform transient synchronization and stabilization control of the grid-following inverter based on nonlinear compensation.

[0033] The terminals may be, but are not limited to, various desktop computers, laptops, smart phones, tablet computers, IoT devices, and portable wearable devices. The server may be implemented as an independent server or a server cluster consisting of multiple servers, or as a cloud server.

[0034] In an exemplary embodiment, Figure 2As shown, a method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation is provided. The method is executed by a computer device, specifically a computer device such as a terminal or a server, or a terminal and a server. In the embodiment of the present application, the method is applied to Figure 1 The server in is used as an example to illustrate, including the following steps 101 to 106.

[0035] Step 101: Obtain the current grid voltage and power angle signals.

[0036] Step 102 , coordinate conversion is performed on the grid voltage at the current moment to obtain the d-axis grid voltage and the q-axis grid voltage at the current moment, and a grid detection signal is determined based on the d-axis grid voltage; the grid detection signal includes a grid normal signal and a grid fault signal.

[0037] Step 103 : When the grid detection signal is a normal grid signal, a phase-locked loop (PI) regulator is used to control the phase angle of the phase-locked loop output according to the amplitude of the q-axis grid voltage.

[0038] Specifically, the phase-locked loop PI regulator is a parallel structure, and its expression is:

[0039]

[0040] Among them, G p (s) is the transfer function of the PI regulator of the phase-locked loop (PLL); K p Represents the proportional gain of the PI regulator of the phase-locked loop; K i It represents the integral gain of the PI regulator of the phase-locked loop, and s is a complex variable.

[0041] Step 104 : When the power grid detection signal is a power grid fault signal, a stability margin judgment signal is determined according to the power angle signal at the current moment.

[0042] Step 105: construct a phase-locked loop nonlinear model based on the power angle signal, and derive expressions of the first nonlinear compensation and the second nonlinear compensation according to the phase-locked loop nonlinear model.

[0043] Step 106 , based on the amplitude of the q-axis grid voltage, the power angle signal, and the stability margin judgment signal at the current moment, the phase angle of the phase-locked loop output is controlled using a PI regulator and expressions of the first nonlinear compensation and the second nonlinear compensation.

[0044] Implementing steps 101 to 106 above, this application focuses on studying an adaptive transient synchronous stability control scheme that does not rely on precise grid parameters and does not require adjustment of current commands. Starting from the nonlinear model of the phase-locked loop, by analyzing an improved energy function with clear physical meaning, a transient synchronous stabilization strategy based on nonlinear compensation is proposed. This can effectively expand the attraction domain of the phase-locked loop during transient conditions, make up for the shortcomings of existing strategies, and enhance the synchronous stability of grid-following inverters during transient conditions. This is particularly suitable for transient synchronous stability control of inverters in high-proportion new energy power systems. Nonlinear compensation technology is used to solve the problem of phase-locked loop instability under strong grid disturbances, thereby improving the overall stability of the system.

[0045] In another exemplary embodiment of the present application, in step 102, coordinate conversion is performed on the grid voltage at the current moment to obtain the d-axis grid voltage and the q-axis grid voltage at the current moment, and a grid detection signal is determined based on the d-axis grid voltage, which specifically includes:

[0046] (2-1) The grid voltage at the current moment is transformed from the three-phase stationary coordinate system to the dq-axis coordinate system to obtain the d-axis grid voltage and q-axis grid voltage at the current moment.

[0047] (2-2) Compare the d-axis grid voltage with the preset voltage value to determine the grid detection signal.

[0048] When the d-axis grid voltage at the current moment is greater than the preset voltage value, the grid detection signal is a grid normal signal.

[0049] When the d-axis grid voltage at the current moment is less than the preset voltage value, the grid detection signal is a grid fault signal.

[0050] In another exemplary embodiment of the present application, in step 104, determining the stability margin judgment signal according to the power angle signal at the current moment specifically includes:

[0051] The power angle signal at the current moment is combined with By comparison, a stability margin judgment signal is obtained.

[0052] When the current power angle signal is greater than When , the stability margin judgment signal is a small stability margin judgment signal.

[0053] When the current power angle signal is less than When , the stability margin judgment signal is a large stability margin judgment signal.

[0054] In another exemplary embodiment of the present application, in step 105, the expression of the nonlinear model of the phase-locked loop based on the power angle signal is:

[0055]

[0056] in,

[0057] Where δ is the power angle signal, which is the difference between the phase angle of the phase-locked loop output and the grid voltage phase angle; Δω is the output value of the phase-locked loop PI regulator, that is, the difference between the phase-locked loop angular frequency and the rated angular frequency of the grid; g(δ) and f(δ) are defined as the restoring force and damping, respectively; K i Refers to the integral coefficient of the phase-locked loop PI regulator; K p Refers to the proportional coefficient of the phase-locked loop PI regulator; I sd Refers to the d-axis current amplitude; L g Refers to the grid inductance; U g Refers to the grid voltage amplitude; ω n Refers to the rated angular velocity of the grid voltage.

[0058] In another exemplary embodiment of the present application, in step 105, the expressions of the first nonlinear compensation and the second nonlinear compensation are expressed as follows:

[0059]

[0060] Wherein, K1(δ) represents the first nonlinear compensation amount; K2(δ) represents the second nonlinear compensation amount.

[0061] In another exemplary embodiment of the present application, in step 106, the phase angle of the phase-locked loop output is controlled using a PI regulator and expressions for the first nonlinear compensation and the second nonlinear compensation according to the amplitude of the q-axis grid voltage at the current moment, the power angle signal, and the stability margin judgment signal, specifically including:

[0062] (1) Substitute the power angle signal at the current moment into the expressions K1(δ) and K2(δ) of the first nonlinear compensation and the second nonlinear compensation to obtain the first nonlinear compensation amount and the second nonlinear compensation amount.

[0063] (2) Based on the phase-locked loop output phase at the current moment, the three-phase voltage at the common coupling point is converted from the three-phase stationary coordinate system (abc coordinate system) to the dq axis coordinate system (rotational synchronous coordinate system) to obtain the q axis voltage at the common coupling point at the current moment.

[0064] (3) The q-axis voltage of the common coupling point at the current moment is input into the phase-locked loop PI regulator to obtain the PI regulation output variable.

[0065] (4) The current PI adjustment output variable and the second nonlinear compensation amount are multiplied to obtain a third nonlinear compensation amount. Specifically, the current PI adjustment output variable and the second nonlinear compensation amount are multiplied to obtain the third nonlinear compensation amount.

[0066] (5) According to the amplitude of the q-axis grid voltage, the first nonlinear compensation amount, and the third nonlinear compensation amount at the current moment, the phase-locked loop PI regulator is applied to obtain the phase-locked loop output angular velocity at the next moment.

[0067] In another exemplary embodiment of the present application, in the above step (5), according to the amplitude of the q-axis grid voltage at the current moment, the first nonlinear compensation amount, and the third nonlinear compensation amount, the phase-locked loop PI regulator is applied to obtain the phase-locked loop output angular velocity at the next moment, which specifically includes:

[0068] (5-1) If the stability margin judgment signal is a large stability margin signal, the value obtained by subtracting the third nonlinear compensation amount from the amplitude of the q-axis grid voltage is input into the integral part of the PI regulator, and the amplitude of the q-axis grid voltage is input into the proportional part of the PI regulator. The output results of the integral part and the proportional part are added together and then added to the rated angular velocity of the grid to obtain the phase-locked loop output angular velocity at the next moment.

[0069] (5-2) If the stability margin judgment signal is a small stability margin signal, the value obtained by subtracting the third nonlinear compensation amount and the first nonlinear compensation amount from the amplitude of the q-axis grid voltage is input into the integral part of the PI regulator, and the amplitude of the q-axis grid voltage is input into the proportional part of the PI regulator. The output results of the integral part and the proportional part are added together and then added to the rated angular velocity of the grid to obtain the phase-locked loop output angular velocity at the next moment.

[0070] (5-3) Integrate the angular velocity output by the phase-locked loop at the next moment to obtain the output phase of the phase-locked loop at the next moment; the output phase of the phase-locked loop at the next moment is the output phase of the phase-locked loop after nonlinear compensation.

[0071] The present invention is based on the nonlinear model of the phase-locked loop. After analyzing the improved energy function with clear physical meaning (corresponding to the subsequent corresponding formulas (8), (9), (10), and (11)), a transient synchronization stabilization control strategy of the grid-following inverter based on nonlinear compensation is proposed. The transient synchronization stability of the grid-following inverter during the fault period can be increased. Among them, the traditional energy function takes into account the kinetic energy and potential energy of the system, but does not consider the dissipative effect of the work done by the damping force on the system. The improved energy function (corresponding to formula (8)) can reflect the influence of damping. The attraction domain estimated by this energy function is larger than that of the traditional energy function. Then, based on the improved energy function, mainly the stability criterion part (corresponding to formulas (9), (10), and (11)), according to the main factors limiting the stability criterion, a nonlinear compensation method is proposed.

[0072] The following is a detailed process of deriving the expressions of the first nonlinear compensation and the second nonlinear compensation from the nonlinear model of the phase-locked loop:

[0073] (1) Description of the nonlinear model of the phase-locked loop

[0074] During a grid fault, the grid-following inverter enters the low voltage ride-through control mode, the power outer loop in the vector control is unlocked, and the control mode is switched to constant current control. At the same time, considering the protection measures on the DC side, the DC side voltage U dc can be regarded as a constant. Based on these two assumptions, a simplified model of the grid-connected inverter system can be obtained, as shown in Figure 3 As shown. Figure 3 In, L f is the filter inductor, Z g is the grid impedance, U g is the grid voltage, i dqref is the current reference value of d and q axis, i abc 、u abc Indicates the instantaneous value of current and voltage at the point of common coupling (PCC), θ p is the output phase of the phase-locked loop.

[0075] For the convenience of analysis, define the state variable δ = θ p -θ g , δ is referred to as the power angle, where θ g is the grid voltage U g The phase of . Figure 3 U available g and PCC q-axis voltage U q The relationship is shown in formula (1).

[0076] U q =-U g sinδ+I q R g +I d ω p L g (1)

[0077] Where, I d represents the d-axis current, I q represents the q-axis current, R g Indicates the grid resistance, L g represents the grid inductance, ω p Indicates the phase-locked loop angular frequency.

[0078] Figure 4 This is a typical PLL control structure diagram. Among them, K p , K i Respectively represent the proportional gain and integral gain of the PI regulator of the phase-locked loop, ω n is the grid rated angular frequency, Δω is the difference between the phase-locked loop angular frequency and the grid rated angular frequency. Figure 4 We can get θp The expression of is shown in formula (2).

[0079] θ p =θ g +∫(K p U q +K i ∫U q ) (2)

[0080] Generally, the dynamics of the current loop are significantly faster than those of the phase-locked loop. When focusing on the impact of the dynamic characteristics of the phase-locked loop on the synchronization stability, it can be considered that the grid current can quickly track the current reference value, that is, the d-axis current I d =I dref , q-axis current I q =I qref , I dref Indicates the d-axis current reference value, I qref Represents the q-axis current reference value, so the nonlinear dynamic equation of the phase-locked loop expressed in power angle can be derived from equations (1) and (2). As shown in equation (3):

[0081]

[0082] Comparing the power angle swing equation of the synchronous motor, it is very obvious that this equation is somewhat similar to it, so equation (3) can be written as:

[0083]

[0084] Among them, P m Considered as equivalent mechanical power, P e Considered as equivalent electromagnetic power, D eq Considered as equivalent damping, M eq is regarded as equivalent inertia, and the expression is shown in formula (5).

[0085]

[0086] For formula (4), we can find that the steady-state solution is At this time, the phase-locked loop is synchronized with the power grid. When a serious fault occurs in the power grid, such as three-phase grounding, the electromagnetic power P e With damping D eq (δ) drops suddenly. The power imbalance causes the power angle δ to oscillate violently, thus deviating from the balance point. When the unbalanced power is too large or the fault lasts too long, even if the fault is removed, the power angle cannot return to the vicinity of the attraction domain, causing the inverter to become unstable.

[0087] (2) Transient synchronization stabilization control strategy of grid-following inverter based on nonlinear compensation

[0088] The stability problem under the above large disturbance cannot be analyzed using a linearized model, and the Lyapunov second method is generally used. Rewrite Equation (4) as:

[0089]

[0090] Where Δω is the difference between the PLL output angular velocity and the grid rated angular velocity; g(δ) corresponds to the unbalanced power P e -P m ; f(δ) is the damping function, ignoring the influence of grid resistance, its expressions are:

[0091]

[0092] Observing formula (4), we can propose the energy function:

[0093]

[0094] Where Ve refers to the energy function, which is the convention of the Lyapunov method, and u is the integral operator, which is the form when using variable upper limit integral. Because f() itself is a function of angle, integrating it with respect to angle will replace the variables in f().

[0095] According to Lyapunov's second method, the stability region needs to satisfy Except for the equilibrium point, V e > 0, the stability region of this system needs to satisfy the following formula:

[0096]

[0097] like Figure 5 As shown, the steady-state solution of formula (6) will be obtained into three solutions, among which δ0 is the equilibrium point, δ u and -2π+δ u It is an unstable equilibrium point close to the equilibrium point. According to the local La Salle invariance principle, the area enclosed by the dotted line is the stable domain. It can be found that under this energy function, the size of the stable domain will only be proportional to δ′. max Correlation, δ′ max The larger the critical energy V e The larger the value is, the larger the stability boundary range is, and the stronger the transient synchronization stability of the system is.

[0098] analyze Figure 5 It can be seen that the upper bound of the work angle δ′ under the improved energy function max Depend on The zero point of δ u For a certain equilibrium point, when g(δ) remains unchanged, δ u The value of is fixed, so we should analyze The value of the first solution to the right of δ0, and make it as close to δ as possible u From formula (9), Should satisfy the following conditions: u ) is greater than zero and is greater than zero when δ∈(-2π+δ u ,δ0) is less than zero, and when it is substituted into formula (7), formula (9) can be rewritten as:

[0099]

[0100] From formula (10), we can write δ′ max The expression is as follows:

[0101] δ′ max =min(δ u ,δ * ) (11)

[0102] Where, δ * Representing equations The first solution to the right of δ0.

[0103] The constraints of the Lyapunov second method in the framework of the surface energy function in formula (10) are essentially constraints on the damping function. The damping function constraint area can be drawn from (10), as shown in Figure 6 As shown in the figure, the pink area is the power angle range of formula (10), and the distance between the blue curve and the straight line represents Further observation Figure 6 It can be seen that, due to the nonlinear characteristics of the sine function, when δ>π / 2, It will decrease rapidly and become 0, at which point it reaches the power angle boundary δ′ max It can be seen that improving the nonlinear characteristics of damping can effectively increase δ′ max , thus expanding the range of the stable domain. When the damping increases, δ * Increase to greater than δ u When δ′ max will be affected by δ u Constraints. Figure 5 It can be seen that, affected by the sine function in g(δ), when δ>π / 2, the value of g(δ) decreases and is u Reaching 0, the nonlinear characteristics of the g(δ) curve will become the limiting δ′ max Therefore, if the nonlinear characteristics of the restoring force function g(δ) can be changed and δ u This will further broaden the stability domain.

[0104] According to the above analysis, the stability boundary of the system is mainly constrained by the nonlinear characteristics of the damping function and the restoring force. This application proposes a PLL improved control strategy based on the improved energy function stability criterion. By introducing additional control of the PLL, the nonlinear characteristics of the damping function f(δ) and the restoring force g(δ) can be effectively improved, thereby expanding the stability boundary of the system. The PLL control structure frame is improved during the fault period, such as Figure 7 shown.

[0105] Assume that the system function of the improved PLL is as follows:

[0106]

[0107] Where g c (δ) is the restoring force function after compensation; f c (δ) is the damping function after compensation.

[0108] Depend on Figure 7 And formula (12), we get g c (δ) and f c (δ) is expressed as follows:

[0109]

[0110] The expressions of K1(δ) and K2(δ) are:

[0111]

[0112] Equation (14) includes the grid voltage U which is usually difficult to obtain in the grid-connected system. g Considering the reactive power compensation of the grid-connected system during the fault ride-through period, in actual projects, a value greater than U g The grid connection point voltage U t Alternative U g This alternative method will increase the compensation amount, but it can avoid voltage estimation, and since U t with U g Closer, the compensation coefficient can be maintained to adapt to different fault depths.

[0113] After compensation, the expressions of restoring force and damping are:

[0114]

[0115] Since the above-mentioned improved energy function construction does not involve specific f(δ) and g(δ) functions, the stability criterion still holds for the improved PLL system, and the nonlinear effect is effectively weakened. The damping function and restoring force function curves before and after improvement are shown in Figure 2. Figure 8 and Figure 9 shown.

[0116] It should be pointed out that Figure 8 Based on the condition that the slope of the red line is greater than the slope of the black line, that is, K i I sd L g / (K p U g )<1. In order to meet this condition, the PI parameters of the PLL during the fault period need to be adjusted. Since the existing analysis is based on the existence of the equilibrium point, that is, g(δ)=0, there must be a solution, that is, satisfying U g ≥I sd ω n L g , from this we can get K i I sd L g / (K p U g )<1:

[0117]

[0118] Based on Equation (16), the PI parameters of the PLL can be adaptively adjusted during the fault period. Considering the increase of K p Will reduce the small signal stability of the system, and keep K p No change, only K is adjusted i .

[0119] Since the equilibrium point corresponds to the zero point of g(δ), compensation cannot be applied near the equilibrium point to avoid changing the equilibrium point. Since the grid impedance is unknown, the equilibrium point cannot be estimated, and the equilibrium point should be within the range of (0,π / 2), so K1(δ) compensation can be applied only when δ>π / 2. c The expression for (δ) should be changed to:

[0120]

[0121] In order to verify the effectiveness of the control strategy proposed in this application, a MATLAB / Simulink simulation platform is built as follows Figure 3 The simplified model of the grid-connected inverter system is shown in FIG. 1 , and the parameters used in the model are shown in Table 1.

[0122] Table 1 Simplified model parameters of wind turbine grid-connected system

[0123] parameter Parameter value parameter Parameter value Rated voltage 220V filter inductors 3mH Rated current 30 / 2A Grid inductance 6mH Rated frequency 50Hz Grid resistance 0.05Ω DC voltage 500V PLLP / I parameters 1 / 300

[0124] Set the grid voltage U when a fault occurs in the grid-connected system g At t = 0.1s, the current drops to 65V (balance point exists) and 46V (balance point does not exist) under two working conditions. During the fault period, the current command is I sd=20,I sq =0, the other parameters are the same as Table 1, and the simulation curves are obtained by using the unimproved PLL and the improved PLL proposed in this application. Figure 10 and Figure 11 As shown in the figure, u ta is the a-phase voltage of PCC, i sa is the a-phase current output by the inverter.

[0125] Figure 10 It shows that under the condition that the equilibrium point exists, after a fault occurs, the power angle oscillation of the grid-connected system using the unimproved PLL diverges, and synchronization instability occurs. After the instability, both the voltage and current become unstable; while the power angle oscillation of the grid-connected system using the improved PLL proposed in this application converges, and the voltage and current waveforms recover quickly. This proves that the control strategy proposed in this application can effectively suppress synchronization instability and improve transient synchronization stability under the condition that SEP (static equilibrium point) exists but there is still a risk of instability.

[0126] Figure 11 It shows that when the equilibrium point does not exist, after a fault occurs, the power angle of the wind power grid-connected system using the unimproved PLL oscillates and diverges rapidly, and synchronization instability occurs quickly after the fault; while the power angle oscillation of the grid-connected system using the improved PLL proposed in this application converges, and the voltage and current can still remain stable, which proves that the control strategy proposed in this application can still maintain a certain degree of synchronization stability when the equilibrium point does not exist.

[0127] In summary, Figure 10 and Figure 11 The analysis results show that the control strategy proposed in this application significantly enhances the transient synchronization stability of the grid-following inverter, and the power angle will not diverge within a certain range when the fault severity exceeds the boundary where the equilibrium point does not exist, which proves the effectiveness of the improved PLL control strategy proposed in this application.

[0128] The present application also provides an application scenario, which applies the above-mentioned grid-following inverter transient synchronization and stabilization control method based on nonlinear compensation. Specifically: the grid-following inverter transient synchronization and stabilization control method based on nonlinear compensation provided in this embodiment can be applied in new energy grid-connected control scenarios. The scenario includes a data acquisition link, a phase angle compensation link and a synchronization control link; the data acquisition link is used to collect the grid voltage and power angle signals at the current moment; the phase angle compensation link is used to calculate the phase-locked loop compensation output phase angle based on the collected grid voltage and power angle signals; the synchronization control link is used for the phase-locked loop compensation output phase angle to control the actual output of the phase-locked loop; the grid-following inverter transient synchronization and stabilization control method based on nonlinear compensation provided in this embodiment belongs to the phase angle compensation link.

[0129] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Figure 12 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O) and a communication interface. The processor, memory and input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store the compensated phase-locked loop output power angle. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a transient synchronous stabilization control method for a grid-following inverter based on nonlinear compensation is implemented.

[0130] Those skilled in the art will understand that Figure 12 The structure shown in the figure is merely a block diagram of a portion of the structure related to the solution of the present application and does not constitute a limitation on the computer device to which the solution of the present application is applied. A specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement. In an exemplary embodiment, a computer device is provided, including a memory and a processor. The memory stores a computer program, and the processor implements the steps of the above-mentioned method embodiments when executing the computer program.

[0131] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0132] In an exemplary embodiment, a computer program product is provided, including a computer program. When the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0133] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0134] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, database or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0135] The databases involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processors involved in the various embodiments provided herein may include, but are not limited to, general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic units, data processing logic units based on quantum computing, and the like.

[0136] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0137] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A transient synchronous stabilization control method for a grid-following inverter based on nonlinear compensation, characterized in that: include: Obtain the current grid voltage and power angle signals; Performing coordinate conversion on the grid voltage at the current moment to obtain the d-axis grid voltage and the q-axis grid voltage at the current moment, and determining a grid detection signal based on the d-axis grid voltage; the grid detection signal includes a grid normal signal and a grid fault signal; When the grid detection signal is a normal grid signal, the phase angle of the phase-locked loop output is controlled by a phase-locked loop PI regulator according to the amplitude of the q-axis grid voltage; When the power grid detection signal is a power grid fault signal, a stability margin judgment signal is determined according to the power angle signal at the current moment; Constructing a nonlinear model of a phase-locked loop based on a power angle signal, and deriving expressions of the first nonlinear compensation and the second nonlinear compensation according to the nonlinear model of the phase-locked loop; According to the amplitude of the q-axis grid voltage, the power angle signal and the stability margin judgment signal at the current moment, the phase angle output by the phase-locked loop is compensated and controlled using a PI regulator and expressions of the first nonlinear compensation and the second nonlinear compensation.

2. The method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to claim 1, characterized in that: Perform coordinate conversion on the grid voltage at the current moment to obtain the d-axis grid voltage and the q-axis grid voltage at the current moment, and determine the grid detection signal based on the d-axis grid voltage, specifically including: The grid voltage at the current moment is transformed from the three-phase stationary coordinate system to the dq-axis coordinate system to obtain the d-axis grid voltage and the q-axis grid voltage at the current moment; Comparing the d-axis grid voltage with a preset voltage value to determine a grid detection signal; When the d-axis grid voltage at the current moment is greater than the preset voltage value, the grid detection signal is a grid normal signal; When the d-axis grid voltage at the current moment is less than the preset voltage value, the grid detection signal is a grid fault signal.

3. The method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to claim 1, characterized in that: The stability margin judgment signal is determined according to the power angle signal at the current moment, specifically including: The power angle signal at the current moment is combined with Compare and obtain the stability margin judgment signal; When the current power angle signal is greater than When , the stability margin judgment signal is a small stability margin judgment signal; When the current power angle signal is less than When , the stability margin judgment signal is a large stability margin judgment signal.

4. The method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to claim 1, characterized in that: The expression of the nonlinear model of the phase-locked loop based on the power angle signal is: in, Where δ refers to the power angle signal, which is the difference between the phase angle of the phase-locked loop output and the phase angle of the grid voltage; Δω refers to the output value of the phase-locked loop PI regulator; g(δ) and f(δ) are defined as the restoring force and damping, respectively; K i Refers to the integral coefficient of the phase-locked loop PI regulator; K p Refers to the proportional coefficient of the phase-locked loop PI regulator; I sd Refers to the d-axis current amplitude; L g Refers to the equivalent impedance of the power grid; U g Refers to the grid voltage amplitude; ω n Refers to the rated angular velocity of the grid voltage.

5. The method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to claim 4, characterized in that: The expressions of the first nonlinear compensation and the second nonlinear compensation are: Wherein, K1(δ) represents the first nonlinear compensation amount; K2(δ) represents the second nonlinear compensation amount.

6. The method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to claim 3, characterized in that: According to the amplitude of the q-axis grid voltage, the power angle signal, and the stability margin judgment signal at the current moment, the phase angle output by the phase-locked loop is compensated and controlled using a PI regulator and expressions of the first nonlinear compensation and the second nonlinear compensation, specifically including: Substituting the power angle signal at the current moment into the expressions of the first nonlinear compensation and the second nonlinear compensation to obtain the first nonlinear compensation amount and the second nonlinear compensation amount; Based on the phase-locked loop output phase at the current moment, the three-phase voltage at the common coupling point is converted from the three-phase stationary coordinate system to the dq-axis coordinate system to obtain the q-axis voltage at the common coupling point at the current moment; Input the q-axis voltage of the common coupling point at the current moment into the phase-locked loop PI regulator to obtain the PI regulation output variable; The third nonlinear compensation value is obtained by adding the current PI adjustment output variable and the second nonlinear compensation value; According to the amplitude of the q-axis grid voltage at the current moment, the first nonlinear compensation amount, and the third nonlinear compensation amount, a phase-locked loop PI regulator is applied to obtain the phase-locked loop output angular velocity at the next moment.

7. The method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to claim 6, characterized in that: According to the amplitude of the q-axis grid voltage at the current moment, the first nonlinear compensation amount, and the third nonlinear compensation amount, the phase-locked loop PI regulator is applied to obtain the phase-locked loop output angular velocity at the next moment, specifically including: If the stability margin judgment signal is a large stability margin signal, the value obtained by subtracting the third nonlinear compensation amount from the amplitude of the q-axis grid voltage is input into the integral part of the PI regulator, and the amplitude of the q-axis grid voltage is input into the proportional part of the PI regulator. The output results of the integral part and the proportional part are added together and then added to the rated angular velocity of the grid to obtain the phase-locked loop output angular velocity at the next moment; If the stability margin judgment signal is a small stability margin signal, the value obtained by subtracting the third nonlinear compensation amount and the first nonlinear compensation amount from the amplitude of the q-axis grid voltage is input into the integral part of the PI regulator, and the amplitude of the q-axis grid voltage is input into the proportional part of the PI regulator. The output results of the integral part and the proportional part are added together and then added to the rated angular velocity of the grid to obtain the phase-locked loop output angular velocity at the next moment; The output angular velocity of the phase-locked loop at the next moment is integrated to obtain the output phase of the phase-locked loop at the next moment; the output phase of the phase-locked loop at the next moment is the output phase of the phase-locked loop after nonlinear compensation.

8. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the transient synchronous stabilization control method for a grid-following inverter based on nonlinear compensation according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to any one of claims 1 to 7 is implemented.

10. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the method for transient synchronous stabilization control of a grid-following inverter based on nonlinear compensation according to any one of claims 1 to 7 is implemented.

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