Grid-connected converter fault transient process control parameter security domain determination method and device

Abstract

The invention provides a grid-connected converter fault transient process control parameter security domain determination method and device, and relates to the technical field of power systems. The grid-connected converter fault transient process control parameter safety domain determination method comprises the following steps: solving a power system equation of a target phase-locked loop by using structural parameters of a target power grid, and obtaining a first analytical expression of an output phase of the target phase-locked loop in a low-voltage ride-through stage after a short-circuit fault occurs in the target power grid; according to the first analytical expression, determining a low-pass phase-locked stability constraint; wherein the low-voltage ride-through phase-locked stable constraint is used for constraining that the output phase of the target phase-locked loop is not out of step in the low-voltage ride-through stage; determining a first parameter domain of a control parameter of the target grid-connected converter according to the low-pass phase-locked stability constraint; and determining a control parameter security domain of the target grid-connected converter based on the first parameter domain. According to the method, the safety domain of the control parameters of the grid-connected converter can be efficiently and accurately determined, so that the short-circuit fault ride-through capability of the grid-connected converter is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method and apparatus for determining the safety domain of control parameters for transient fault processes in grid-connected converters. Background Technology

[0002] The power system is undergoing a profound transformation from the traditional model dominated by synchronous generators to a new type of power system dominated by power electronic devices. Among these, the voltage source converter (VSC), as the core interface equipment for new energy grid integration, is crucial for the safety and reliability of the power system. However, when a short-circuit fault occurs in the grid, the VSC enters a low voltage ride-through (LVRT) state. At this time, the phase-locked loop (PLL) may become unstable due to voltage drops, or the unit may be disconnected from the grid due to transient overvoltages after the fault is cleared. All of these pose serious threats to the safety of the power system.

[0003] In existing PLL stability analysis, the traditional small disturbance criterion is based on the assumption that the deviation of the initial point is infinitesimal, which is too conservative and impractical in complex and ever-changing actual operating conditions; while large disturbance stability analysis focuses more on normal operating conditions and lacks targeted research on special operating conditions during LVRT.

[0004] Therefore, how to efficiently and accurately determine the safety domain of the control parameters of grid-connected converters in order to effectively improve the short-circuit fault ride-through capability of grid-connected converters is an urgent technical problem to be solved. Summary of the Invention

[0005] This invention provides a method and apparatus for determining the safety domain of control parameters during transient fault processes in grid-connected converters, thereby addressing the aforementioned deficiencies in the prior art and enabling efficient and accurate determination of the safety domain of control parameters for grid-connected converters, thus effectively improving the short-circuit fault ride-through capability of grid-connected converters.

[0006] This invention provides a method for determining the safety domain of control parameters for transient fault processes in grid-connected converters, comprising the following steps.

[0007] Using the structural parameters of the target power grid, the dynamic system equations of the target phase-locked loop (PLL) are solved to obtain a first analytical expression for the output phase of the target PLL during the low-voltage ride-through phase after a short-circuit fault in the target power grid. Based on the first analytical expression, a low-voltage ride-through stability constraint is determined; wherein, the low-voltage ride-through stability constraint is used to prevent the output phase of the target PLL from losing synchronization during the low-voltage ride-through phase. Based on the low-voltage ride-through stability constraint, a first parameter domain of the control parameters of the target grid-connected converter is determined. Based on the first parameter domain, a safety domain of the control parameters of the target grid-connected converter is determined; wherein, the target grid-connected converter is connected to the target power grid through a grid connection point, and the target PLL is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

[0008] According to the present invention, a method for determining the safety domain of control parameters for a grid-connected converter during a fault transient process includes: solving the dynamic system equations of a target phase-locked loop (PLL) using the structural parameters of the target power grid; obtaining a second analytical expression for the output phase of the target PLL at the moment the short-circuit fault is cleared; the method further includes: establishing a voltage phase relationship between the voltage at the grid connection point and the output phase of the target PLL based on the vector relationship of the grid connection point voltage; determining a transient overvoltage constraint based on the second analytical expression and the voltage phase relationship; wherein the transient overvoltage constraint is used to constrain the transient overvoltage at the input grid connection point of the target grid-connected converter to be lower than a safe voltage threshold; determining a second parameter domain of the control parameters of the target grid-connected converter based on the transient overvoltage constraint; and determining the safety domain of the control parameters of the target grid-connected converter based on the first parameter domain, including: determining the safety domain of the control parameters of the target grid-connected converter based on the intersection of the first parameter domain and the second parameter domain.

[0009] According to the present invention, a method for determining the safety domain of control parameters for transient fault processes of a grid-connected converter is provided. For a short-circuit fault in the target power grid, the implementation stages of the control strategy for the target grid-connected converter include: a first stage using a conventional control strategy before the short-circuit fault occurs; a second stage where a low-voltage ride-through control strategy has not yet been initiated after the short-circuit fault occurs; a third stage using a low-voltage ride-through control strategy; and a fourth stage where a low-voltage ride-through control strategy is still used after fault clearance. The dynamic system equation is a second-order differential equation of the output phase of the target phase-locked loop. The first analytical expression and the second analytical expression are obtained by sequentially applying the control parameters of the target grid-connected converter... In each implementation stage of the control strategy, based on the initial phase value of the target phase-locked loop in that implementation stage, the dynamic system equation of the target phase-locked loop is solved to obtain the analytical expression of that implementation stage; wherein, in each implementation stage, the initial phase value of the target phase-locked loop is the phase value of the target phase-locked loop at the last moment of the previous implementation stage; in each implementation stage, the initial phase derivative of the target phase-locked loop is the sum of the derivative of the phase value of the target phase-locked loop at the last moment of the previous implementation stage and its abrupt change; the analytical expression of the third stage is used as the first analytical expression; and the analytical expression of the fourth stage is used as the second analytical expression.

[0010] According to the present invention, a method for determining the safety domain of control parameters for transient fault processes of a grid-connected converter is provided. The first analytical expression consists of a steady-state phase and a phase oscillation term. The step of determining the low-voltage phase-locked loop stability constraint based on the first analytical expression includes: using differentiation operations to obtain the low-voltage phase-locked loop stability constraint based on the amplitude of the phase oscillation term in the first analytical expression.

[0011] According to the present invention, a method for determining the safety domain of control parameters for transient fault processes in a grid-connected converter is provided, wherein the first analytical expression is as follows: ; ; The step of obtaining the low-penetration phase-locked stability constraint based on the amplitude of the phase oscillation term in the first analytical expression using differentiation includes: taking the derivative of the square of the amplitude of the phase oscillation term and making the result of the differentiation less than zero, resulting in the low-penetration phase-locked stability constraint as shown below: ; in, For output phase; This is the steady-state phase; This is a phase oscillation term; This is the initial parameter for the amplitude of the phase oscillation term; The initial phase parameter for the phase oscillation term; For simplification; To match the target grid voltage , d axis, q Shaft current command value , and constants related to power grid structure parameters; The initial phase value of the target phase-locked loop during the low-pressure crossing phase; The initial value of the first-order phase derivative of the target phase-locked loop during the low-pressure crossing phase; and These are the proportional and integral coefficients of the PID controller in the target phase-locked loop control loop, respectively. For the voltage drop of the transmission line in steady state q Axial components; This represents the angular frequency of the phase oscillation of the phase-locked loop; t It is a time variable; This is the equivalent inductance value of the transmission line.

[0012] According to the present invention, a method for determining the safe domain of control parameters for transient fault processes in a grid-connected converter is provided, wherein the voltage phase relationship is as follows: ; in, for t The voltage at the grid connection point at any given time; The target grid voltage; The inductive reactance value of the target power grid line; The resistance value of the target power grid line; The output of the target grid-connected converter d shaft current; The output of the target grid-connected converter q shaft current; The target phase-locked loop outputs the phase; determining the transient overvoltage constraint based on the second analytical expression and the voltage phase relationship includes: substituting the second analytical expression into the voltage phase relationship, and making the value of the voltage phase relationship less than the safe voltage threshold, to obtain the transient overvoltage constraint as shown below: ; in, This is the safe voltage threshold.

[0013] The present invention also provides a device for determining the safety domain of control parameters for transient fault processes in grid-connected converters, comprising the following modules: The solution module is used to solve the dynamic system equations of the target phase-locked loop (PLL) using the structural parameters of the target power grid, and obtain a first analytical expression for the output phase of the target PLL during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid. A first determination module is used to determine the low-voltage ride-through stability constraint based on the first analytical expression; wherein the low-voltage ride-through stability constraint is used to prevent the output phase of the target PLL from losing synchronization during the low-voltage ride-through stage. A second determination module is used to determine a first parameter domain of the control parameters of the target grid-connected converter based on the low-voltage ride-through stability constraint. A third determination module is used to determine the safety domain of the control parameters of the target grid-connected converter based on the first parameter domain; wherein the target grid-connected converter is connected to the target power grid through a grid connection point, and the target PLL is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

[0014] The present invention also provides an electronic device, including 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 method for determining the safety domain of fault transient process control parameters of a grid-connected converter as described above.

[0015] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for determining the safety domain of control parameters for fault transient processes of grid-connected converters as described above.

[0016] The present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the method for determining the safety domain of control parameters for fault transient processes of grid-connected converters as described above.

[0017] The present invention provides a method and apparatus for determining the safety domain of control parameters during transient fault processes of a grid-connected converter. It utilizes the structural parameters of the target power grid to solve the dynamic system equations of the target phase-locked loop (PLL), obtaining a first analytical expression for the output phase of the target PLL during the low-voltage ride-through stage after a short-circuit fault in the target power grid. Based on this first analytical expression, a low-voltage ride-through stability constraint is determined. Based on this constraint, a first parameter domain of the control parameters of the target grid-connected converter is determined. Based on this first parameter domain, the safety domain of the control parameters of the target grid-connected converter is determined. Since the first analytical expression accurately describes the dynamic characteristics of the target PLL during low-voltage ride-through, the low-voltage ride-through stability constraint can be accurately determined. This constraint ensures that the target PLL does not lose synchronization during the low-voltage ride-through stage, effectively avoiding the risk of synchronization loss or oscillation. Therefore, based on the low-voltage ride-through stability constraint, the control parameter domain of the target grid-connected converter that allows the target PLL to reach a steady-state equilibrium point during low-voltage ride-through is determined. This allows for the efficient and accurate determination of the safety domain of the control parameters of the grid-connected converter, thereby effectively improving the short-circuit fault ride-through capability of the grid-connected converter. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is one of the flowcharts illustrating the method for determining the safety domain of control parameters during transient fault processes in grid-connected converters provided by this invention.

[0020] Figure 2 This is the second flowchart illustrating the method for determining the safety domain of control parameters during transient fault processes in grid-connected converters provided by this invention.

[0021] Figure 3 This is a schematic diagram of the control structure of the grid-connected converter provided by the present invention.

[0022] Figure 4 This is a schematic diagram illustrating the process of solving the safety domain of control parameters for a grid-connected converter that considers low-voltage ride-through phase-locked stability and transient overvoltage, as provided by the present invention.

[0023] Figure 5 Provided by the present invention d A schematic diagram of the safety domain of the shaft current reference command and the proportional coefficient of the phase-locked loop PID controller.

[0024] Figure 6 Provided by the present invention qA schematic diagram of the safety domain of the shaft current reference command and the integral coefficient of the phase-locked loop PID controller.

[0025] Figure 7 The simulation verification results are for the safe domain of control parameters under low-penetration phase-locked stability constraints provided by this invention.

[0026] Figure 8 The simulation verification results of the safe domain of the control parameters under transient overvoltage constraints provided by this invention.

[0027] Figure 9 This is a schematic diagram of the device for determining the safety domain of control parameters for fault transient processes of grid-connected converters provided by the present invention.

[0028] Figure 10 This is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] The following is combined with Figures 1-8 The present invention describes a method for determining the safety domain of control parameters for transient fault processes in grid-connected converters.

[0031] Figure 1 This is one of the flowcharts illustrating the method for determining the safety domain of control parameters during transient fault processes in grid-connected converters provided by this invention. Figure 1 As shown, the method includes the following: Step 101: Using the structural parameters of the target power grid, solve the dynamic system equations of the target phase-locked loop to obtain the first analytical expression of the output phase of the target phase-locked loop during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid.

[0032] In the specific implementation process, the target grid-connected converter is connected to the target power grid through the grid connection point, and the target phase-locked loop is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

[0033] A target grid-connected converter is a grid-connected converter used to realize the conversion and transmission of electrical energy and meet the grid connection requirements of the target power grid. In power systems, especially in the field of renewable energy grid connection, grid-connected converters (e.g., voltage source converters) serve as core interface devices, responsible for converting the electrical energy generated by renewable energy sources (such as wind and solar power) into AC power compatible with the target power grid and achieving synchronous grid-connected operation with the target power grid.

[0034] For example, in a wind power generation system, the electrical energy generated by the wind turbine is converted into alternating current (AC) that matches the frequency, phase, and voltage of the grid, achieving stable grid-connected output of wind energy. To ensure the safe operation of the power system, the grid-connected converter needs to have low-voltage ride-through capability, maintaining grid-connected operation when the grid voltage drops to prevent the wind turbine from disconnecting from the grid.

[0035] The target power grid refers to the power system to which a grid-connected converter (e.g., a voltage source grid-connected converter) is connected. This system may include various synchronous generators, power electronic equipment, and transmission lines.

[0036] The structural parameters of the target power grid include, but are not limited to, transmission line impedance and transmission line inductance.

[0037] The target phase-locked loop (PLL) (output phase is the control quantity used by the PLL to synchronize the output current phase of the grid-connected converter with the grid connection point voltage phase, and its stability is crucial to the grid-connected operation of the target grid-connected converter) is crucial.

[0038] The low-voltage ride-through phase refers to the ability of the target grid-connected converter to maintain grid connection and not disconnect from the grid when the grid voltage drops. This is crucial for the stable operation of the power system.

[0039] The target grid-connected converter control structure diagram is as follows: Figure 3 As shown in the figure, The active power output value of the target grid-connected converter; The active power on the DC side of the target grid-connected converter; For the target grid-connected converter DC-side capacitor; This is the DC-side capacitor voltage; This is the commanded value for the DC-side capacitor voltage; This refers to the voltage at the grid connection point; This is the voltage command value at the grid connection point; The target grid-connected converter's rated current; and These are the filter line currents. shaft and Axial components; and The target grid-connected converters are respectively shaft and Shaft current command value; This is the reactive current adjustment coefficient; The active current during the low-voltage ride-through of the target grid-connected converter; and The outer ring outputs are respectively shaft and shaft current; and The voltage at the grid connection point ( )of shaft and Axial components; and These are the internal potentials of the target grid-connected converter. shaft and Axial components; and The voltage at the grid connection point ( )of shaft and Axial components; The phase of the target phase-locked loop.

[0040] When a short-circuit fault occurs in the target power grid, in order to protect the equipment and maintain the stability of the power system, it is necessary to quickly switch the control strategy of the target grid-connected converter. The implementation stages of the control strategy include: the first stage of using the conventional control strategy before the short-circuit fault occurs, the second stage of using the low-voltage ride-through control strategy before the short-circuit fault occurs, the third stage of using the low-voltage ride-through control strategy, and the fourth stage of using the low-voltage ride-through control strategy after the fault is cleared.

[0041] During the low-voltage ride-through phase following a short-circuit fault in the target power grid, the control strategy of the target grid-connected converter changes from the second stage (e.g., ...). Figure 3 Switching from S1 and S2 as shown) to the third stage (e.g. Figure 3 As shown in S3 and S4): the outer loop uses constant current control, that is... , Meanwhile, since the inner current loop is much faster than the target PLL, the inner current loop is assumed to meet its control objective in real time when analyzing the stability of the target PLL. , At this point, the target grid-connected converter is simplified to a controlled current source model. The synchronous stability of the target grid-connected converter is determined by the dynamic characteristics of the target phase-locked loop, which can be described by the dynamic system equations.

[0042] Dynamic system equations are mathematical models describing the dynamic behavior of a system. They typically include the relationships between state variables, input variables, and output variables, and are used to analyze the system's stability and response characteristics. The dynamic system equations of a target phase-locked loop (PLL) are second-order differential equations of the PLL's output phase, used to describe the PLL's dynamic behavior. As an example, the formula is shown below: ; (1) in, The output phase of the target phase-locked loop; The steady-state phase of the target phase-locked loop; simplified quantity This represents the voltage drop across the transmission line in steady state. q Axial components; for d Shaft reference current command; and These are the proportional and integral coefficients of the PID (Proportional-Integral-Derivative) controller in the target phase-locked loop control loop, respectively. The target grid voltage.

[0043] If the target phase-locked loop is stable under small disturbances, it must satisfy: (1) an equilibrium point exists; (2) the eigenvalues ​​of the Jacobian matrix at the equilibrium point are all in the left half of the complex plane, as shown in the following formula.

[0044] (2) The above formula is the small disturbance criterion, which is applicable only when the system disturbance tends to be infinitesimal. However, in actual engineering, the deviation between the initial operating point and the equilibrium point of the target phase-locked loop is often not negligible. Even if the criterion is met, the system may still become unstable due to finite disturbances.

[0045] In the embodiments provided by the present invention, considering the deviation between the initial operating point and the equilibrium point of the target phase-locked loop, the dynamic system equations of the target phase-locked loop are solved to obtain the first analytical expression of the output phase of the target phase-locked loop during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid.

[0046] The first analytical expression is the analytical solution of the target phase-locked loop output phase obtained by mathematical methods during the low-voltage ride-through stage. It can be used to analyze the stability and dynamic behavior of the target phase-locked loop.

[0047] like Figure 4 As shown, for each implementation stage of the control strategy of the target grid-connected converter, based on the initial phase value of the target phase-locked loop in the implementation stage, the dynamic system equation of the target phase-locked loop is solved to obtain the analytical expression of the implementation stage.

[0048] In each implementation phase, the initial phase value of the target PLL is the phase value of the target PLL at the last moment of the previous implementation phase; in each implementation phase, the initial phase derivative of the target PLL is the sum of the derivative of the phase value of the target PLL at the last moment of the previous implementation phase and its abrupt change. The abrupt change of the phase derivative is expressed by the following formula: (3) At each implementation stage, if the dynamic system equations of the target phase-locked loop (PLL) have an equilibrium point, an approximate analytical solution can be obtained based on Taylor expansion and the multi-scale method, given the existence of the equilibrium point. If the dynamic system equations of the target PLL do not have an equilibrium point, they can be approximated as constant-coefficient differential equations and solved to obtain an approximate analytical solution.

[0049] Through the above solution process, the analytical expressions for the first, second, third, and fourth stages are obtained. The analytical expression for the fourth stage is used as the second analytical expression (for more details on the second analytical expression, see...). Figure 2 (Related content in the document).

[0050] The first analytical expression consists of steady-state phase and phase oscillation terms, and is shown below: ; (4) ; (5) in, For output phase; This is the steady-state phase; This is a phase oscillation term; This is the initial parameter for the amplitude of the phase oscillation term; The initial phase parameter for the phase oscillation term; For simplification; To match the target grid voltage , d axis, q Shaft current command value , and constants related to power grid structure parameters; The initial phase value of the target phase-locked loop during the low-pressure crossing phase; The initial value of the first-order phase derivative of the target phase-locked loop during the low-pressure crossing phase; and These are the proportional and integral coefficients of the PID controller in the target phase-locked loop control loop, respectively. For the voltage drop of the transmission line in steady state q Axial components; This represents the angular frequency of the phase oscillation of the phase-locked loop; t It is a time variable; This is the equivalent inductance value of the transmission line.

[0051] Step 102: Determine the low-voltage crossing phase-locked loop stability constraint according to the first analytical expression; wherein, the low-voltage crossing phase-locked loop stability constraint is used to constrain the output phase of the target phase-locked loop to not lose synchronization during the low-voltage crossing stage.

[0052] In some embodiments, the low-penetration phase-locked stability constraint can be obtained by using differentiation operations based on the amplitude of the phase oscillation term in the first analytical expression. Specifically, the low-penetration phase-locked stability constraint can be obtained by differentiating the square of the amplitude of the phase oscillation term and making the result of the differentiation operation less than zero.

[0053] use The square of the amplitude of the phase oscillation term in formula (3) is expressed as: (6) Differentiating the above expression and setting it to less than zero, we get: (7) when At that time, the amplitude of the phase oscillation term decreases with time. If it undergoes damped oscillations, it will eventually stabilize at the equilibrium point; conversely, It oscillates with increasing amplitude until it approaches the saddle point and then diverges. Therefore, it can be... As the stability criterion for the target phase-locked loop under non-infinite perturbations, the following is the low-penetration phase-locked loop stability constraint: (8) in, Represents the degree of disturbance, when When the disturbance is infinitesimal, the criterion obtained by formula (8) is completely consistent with the small disturbance stability criterion shown by formula (2); when When the disturbance is not infinitesimal, the safety domain of the parameter obtained by the criterion of formula (7) is smaller than the safety domain of the small disturbance obtained by formula (2), which strengthens the conservatism of the safety domain and meets the actual requirements.

[0054] In actual operation The value of needs to be estimated by solving for each implementation stage of the control strategy for the target grid-connected converter for short-circuit faults and by the phase continuity between implementation stages. The complete stability criterion is obtained by estimating the initial phase value of the target phase-locked loop in the third stage of the low-voltage ride-through control strategy.

[0055] In some embodiments, since The value of is related to the structural parameters and control parameters of the target grid-connected converter. The above calculation method can be improved as follows: (1) Set the Taylor expansion point of the dynamic system equation of the target phase-locked loop as the initial point of the low voltage ride-through stage, and emphasize the adjustment effect of the change of the initial point on the analytical solution. Within a certain disturbance, the fitting effect of the analytical expression can be better; (2) Use the control parameters of the target grid-connected converter ( ) represents the initial value parameter of the amplitude. and initial phase parameters And the initial amplitude parameter will be expressed using control parameters. and initial phase parameters Substituting these values ​​directly into the final analytical expression yields the result. Ultimately, the criterion can be rearranged into equation (6).

[0056] (9) Step 103: Determine the first parameter domain of the control parameters of the target grid-connected converter based on the low-voltage phase-locked loop stability constraint.

[0057] The first parameter domain is the set of control parameters that enable the target grid-connected converter to maintain phase-locked loop stability during the low-voltage ride-through phase. The control parameters of the target grid-connected converter include: d Shaft current reference command q Shaft current reference command, proportional coefficient and integral coefficient of phase-locked loop PID controller.

[0058] In practical implementation, the range of control parameters that satisfy the low-breakdown phase-locked loop stability constraint can be determined through various methods (e.g., mathematical analysis or numerical simulation). The range of control parameters that satisfy the low-breakdown phase-locked loop stability constraint is defined as the first parameter domain.

[0059] Step 104: Based on the first parameter domain, determine the control parameter safety domain of the target grid-connected converter.

[0060] In some embodiments, the first parameter domain can be used as the control parameter safety domain of the target grid-connected converter. The control parameters of the target grid-connected converter are then tuned based on the control parameter safety domain of the grid-connected converter.

[0061] In some embodiments, the control parameter safety domain of the target grid-connected converter can be determined based on the first parameter domain and combined with the second parameter domain obtained by combining the transient overvoltage constraint of the target grid-connected converter after the short-circuit fault in the target power grid is cleared. This control parameter safety domain can ensure the stability of the target phase-locked loop and avoid loss of synchronization during the voltage ride-through phase; and can also suppress the transient overvoltage of the target grid-connected converter within safe limits after the short-circuit fault is cleared. For a detailed description of this embodiment, please refer to the following... Figure 2 .

[0062] Figure 2 This is the second flowchart illustrating the method for determining the safety domain of control parameters during transient fault processes in grid-connected converters provided by this invention. Figure 2 As shown, the method includes the following: Step 201: Based on the vector relationship of the grid connection point voltage, establish the voltage phase relationship between the grid connection point voltage and the target phase-locked loop output phase.

[0063] The vector relationship of the grid connection point voltage is shown below: (10) Based on formula (9), the voltage phase relationship is obtained as follows: ; in, for t The voltage at the grid connection point at any given time; The target grid voltage; The inductive reactance value of the target power grid line; The resistance value of the target power grid line; For the output of the target grid-connected converter d shaft current; For the output of the target grid-connected converter q shaft current; The target phase-locked loop outputs the phase.

[0064] Step 202: Determine the transient overvoltage constraint based on the second analytical expression and the voltage phase relationship; wherein, the transient overvoltage constraint is used to constrain the transient overvoltage at the input grid connection point of the target grid-connected converter to be lower than the safe voltage threshold.

[0065] The second analytical expression is for the fourth stage, which still uses the low-voltage ride-through control strategy during fault clearing (see detailed description). Figure 1 The analytical solution of the target phase-locked loop output phase obtained by mathematical methods (related content in the document) can be used to analyze the phase output of the target phase-locked loop in the fourth stage.

[0066] The second analytical expression is obtained by solving the dynamic system equations of the target phase-locked loop using the structural parameters of the target power grid. For a detailed description, please refer to [link to relevant documentation]. Figure 1 The relevant descriptions in the text will not be repeated here.

[0067] In the specific implementation process, the second analytical expression is substituted into the voltage phase relationship, and the value of the voltage phase relationship is made less than the safe voltage threshold, resulting in the transient overvoltage constraint shown below: (11) in, This is the safe voltage threshold.

[0068] In practical implementation, a safe voltage threshold can be determined based on relevant standards. For example, current national standards for key technical indicators of high-voltage ride-through at renewable energy power plants require wind turbines to have a high-voltage ride-through capability of 1.25~1.3 pu / 0.5s (rated voltage / 0.5 seconds). A 0.5-second interval indicates that an abnormal voltage spike could lead to a large number of wind turbines disconnecting from the grid. Therefore, when the target grid includes wind turbines, a safe voltage threshold of 1.3 pu can be set to ensure the safe operation of the target grid under short-circuit faults.

[0069] When a short-circuit fault occurs in the target power grid, the control strategy of the target grid-connected converter needs to be switched quickly, including: rapidly switching from the conventional control strategy to the low-voltage ride-through (LVRT) control strategy after the short-circuit fault occurs; and rapidly switching from the LVRT control strategy back to the conventional control strategy after the short-circuit fault is cleared. However, in practice, the switching of the target grid-connected converter's control strategy cannot be completed instantaneously; there is a certain delay. In the fourth stage, where the LVRT control strategy is still used after the fault is cleared (see detailed description...),... Figure 1 (Related content in the text) Since the low voltage ride-through control strategy does not consider the changes in the target grid voltage and power after the short-circuit fault is cleared, it will cause the target grid-connected converter to output transient overvoltage. At this time, transient overvoltage can be limited to a safe range through transient overvoltage constraints.

[0070] Since voltage cannot change abruptly, if the transient overvoltage at the time of fault clearance is not higher than the safe voltage threshold (e.g., 1.3 pu), the overvoltage will not exceed the safe voltage threshold for a period of time. Therefore, the transient overvoltage at the time of fault clearance can be used as a constrained quantity. That is, the value of the first analytical expression at the time of fault clearance is substituted into the voltage phase relationship shown in formula (10), and it is set to be less than the safe voltage threshold to obtain the transient voltage constraint. Based on this transient voltage constraint, the target power grid is guaranteed to the greatest extent that no chain disconnection accident occurs after the short-circuit fault is restored.

[0071] The switching delay of the control strategy is random, ranging from tens to hundreds of milliseconds. As an example, the fault clearing time can be estimated using a 50ms control strategy switching delay (the time from the fault occurrence to the adoption of the low-voltage ride-through control strategy) and a 200ms short-circuit fault time. The transient voltage constraint is determined by setting it to be less than the safe voltage threshold.

[0072] Step 203: Determine the second parameter domain of the control parameters of the target grid-connected converter based on the transient overvoltage constraint.

[0073] The second parameter domain is the set of control parameters that enable the target grid-connected converter to output a safe transient overvoltage after the short-circuit fault is cleared. The control parameters of the target grid-connected converter include: d Shaft current reference command q Shaft current reference command, proportional coefficient and integral coefficient of phase-locked loop PID controller.

[0074] In practical implementation, the range of control parameters that satisfy the transient voltage constraint can be determined through various methods (e.g., mathematical analysis or numerical simulation). The range of control parameters that satisfy the transient voltage constraint is defined as the second parameter domain.

[0075] Step 204: Determine the control parameter safety domain of the target grid-connected converter based on the intersection of the first parameter domain and the second parameter domain.

[0076] For a detailed description of the first parameter field, see [link to relevant documentation]. Figure 1 The relevant content will not be repeated here.

[0077] In practical implementation, the intersection of the first and second parameter domains can be determined in various ways, without being limited by the description in this specification. The intersection of the first and second parameter domains is used as the intersection of the first and second parameter domains of the target grid-connected converter, thus determining the control parameter safety domain of the target grid-connected converter. This control parameter safety domain can satisfy the stability requirements of the target phase-locked loop during low-voltage ride-through and limit the transient overvoltage output of the target grid-connected converter to a safe range after fault clearance. For example, Figure 5 and Figure 6 The safety domain for the control parameters shown is the shaded area in the figure.

[0078] The following section, based on experimental results, illustrates the technical effectiveness of the method for determining the safety domain of control parameters for transient fault processes in grid-connected converters provided by this invention. Under the system parameter conditions shown in Table 1 below, the results are obtained from... Figure 5 and Figure 6 As can be seen, the shaded area represents the feasible parameter range, with the upper part being the phase-locked instability region and the lower part representing the parameter region where the transient overvoltage exceeds 1.3 pu at the fault clearing moment. The control parameters for different simulation conditions are shown in Table 2 below, and the simulation results are as follows. Figure 7 and Figure 8 As shown. Combined with Figure 7 and Figure 8 The predicted performance under each operating condition was obtained, and the simulation results verified the safety of the feasible range of parameters obtained in this invention.

[0079] Specifically, in Figure 5 In the figure, the phase response curves of the phase-locked loop (PLL) under different operating conditions clearly demonstrate that when the control parameters are within the feasible range, the target PLL can remain stable without instability. Meanwhile, Figure 6 The transient overvoltage levels under different operating conditions also verified the effectiveness of the transient voltage constraint proposed in this invention. That is, when the control parameters are within the range of feasible parameters, the transient overvoltage at the fault clearing time can be effectively suppressed below the safe voltage threshold (e.g., 1.3 pu), thereby avoiding unit cascading disconnection accidents caused by overvoltage.

[0080] In summary, the method for determining the safety domain of control parameters during transient fault processes of grid-connected converters provided by this invention has been fully verified through experimental results, demonstrating that the method can effectively guide the tuning of control parameters of the target grid-connected converter and effectively improve the stability and safety of the target power grid after a short-circuit fault.

[0081] Table 1 System Parameters

[0082] in, and These are the system's reference capacity and reference voltage, respectively. and These are the equivalent resistance and reactance values ​​of the transmission line, respectively. and These are the equivalent resistance and reactance values ​​of the filter circuit, respectively. Indicates the grounding admittance at the grid connection point; The target is the DC-side capacitor value of the grid-connected converter; and These are the grid connection point voltage reference command and the target grid-connected converter DC side voltage reference command, respectively. Indicates the target grid rated voltage; This indicates the fault voltage of the target power grid.

[0083] Table 2 Simulation Conditions

[0084] The following describes the device for determining the safe domain of control parameters for transient fault processes of grid-connected converters provided by the present invention. The device for determining the safe domain of control parameters for transient fault processes of grid-connected converters described below can be referred to in correspondence with the method for determining the safe domain of control parameters for transient fault processes of grid-connected converters described above.

[0085] Figure 9 This is a schematic diagram of the device for determining the safety domain of control parameters for fault transient processes of grid-connected converters provided by the present invention.

[0086] like Figure 9 As shown, the grid-connected converter fault transient process control parameter safety domain determination device 900 includes the following modules: The solver module 910 is used to solve the dynamic system equations of the target phase-locked loop using the structural parameters of the target power grid, and obtain the first analytical expression of the output phase of the target phase-locked loop during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid.

[0087] The first determining module 920 is used to determine the low-voltage crossing phase-locked loop stability constraint according to the first analytical expression; wherein the low-voltage crossing phase-locked loop stability constraint is used to constrain the output phase of the target phase-locked loop from losing synchronization during the low-voltage crossing phase.

[0088] The second determining module 930 is used to determine the first parameter domain of the control parameters of the target grid-connected converter based on the low-voltage phase-locked loop stability constraint.

[0089] The third determining module 940 is used to determine the control parameter safety domain of the target grid-connected converter based on the first parameter domain.

[0090] The target grid-connected converter is connected to the target power grid through a grid connection point, and the target phase-locked loop is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

[0091] Figure 10 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 10 As shown, the electronic device may include: a processor 1010, a communications interface 1020, a memory 1030, and a communications bus 1040, wherein the processor 1010, the communications interface 1020, and the memory 1030 communicate with each other through the communications bus 1040. Processor 1010 can call logic instructions in memory 1030 to execute a method for determining the safety domain of control parameters during transient faults in a grid-connected converter. This method includes: using structural parameters of the target grid, solving the dynamic system equations of the target phase-locked loop (PLL) to obtain a first analytical expression for the output phase of the target PLL during the low-voltage ride-through stage after a short-circuit fault in the target grid; determining a low-voltage ride-through stability constraint based on the first analytical expression; wherein the low-voltage ride-through stability constraint is used to prevent the output phase of the target PLL from losing synchronization during the low-voltage ride-through stage; determining a first parameter domain of the control parameters of the target grid-connected converter based on the low-voltage ride-through stability constraint; and determining the safety domain of the control parameters of the target grid-connected converter based on the first parameter domain; wherein the target grid-connected converter is connected to the target grid through a grid connection point, and the target PLL is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

[0092] Furthermore, the logical instructions in the aforementioned memory 1030 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0093] On the other hand, the present invention also provides a computer program product, which includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the method for determining the safety domain of control parameters for a grid-connected converter during a fault transient process provided by the above methods. This method includes: using the structural parameters of the target power grid, solving the dynamic system equations of the target phase-locked loop (PLL) to obtain a first analytical expression for the output phase of the target PLL during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid; determining a low-voltage ride-through stability constraint based on the first analytical expression; wherein the low-voltage ride-through stability constraint is used to constrain the output phase of the target PLL from losing synchronization during the low-voltage ride-through stage; determining a first parameter domain of the control parameters of the target grid-connected converter based on the low-voltage ride-through stability constraint; and determining the safety domain of the control parameters of the target grid-connected converter based on the first parameter domain; wherein the target grid-connected converter is connected to the target power grid through a grid connection point, and the target PLL is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

[0094] In another aspect, the present invention also provides a non-transitory computer-readable storage medium storing a computer program thereon. When executed by a processor, the computer program implements a method for determining the safety domain of control parameters for a grid-connected converter during a fault transient process, as provided by the methods described above. This method includes: using structural parameters of the target power grid, solving the dynamic system equations of a target phase-locked loop (PLL) to obtain a first analytical expression for the output phase of the target PLL during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid; determining a low-voltage ride-through stability constraint based on the first analytical expression; wherein the low-voltage ride-through stability constraint is used to constrain the output phase of the target PLL from losing synchronization during the low-voltage ride-through stage; determining a first parameter domain of the control parameters of the target grid-connected converter based on the low-voltage ride-through stability constraint; and determining the safety domain of the control parameters of the target grid-connected converter based on the first parameter domain; wherein the target grid-connected converter is connected to the target power grid through a grid connection point, and the target PLL is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

[0095] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0096] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the safety domain of control parameters during transient fault processes in a grid-connected converter, characterized in that, include: Using the structural parameters of the target power grid, the dynamic system equations of the target phase-locked loop are solved to obtain the first analytical expression of the output phase of the target phase-locked loop during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid; Based on the first analytical expression, a low-voltage crossover phase-locked loop (PLL) stability constraint is determined; wherein, the low-voltage crossover phase-locked loop stability constraint is used to constrain the target PLL output phase from losing synchronization during the low-voltage crossover phase; Based on the low-penetration phase-locked stability constraint, the first parameter domain of the control parameters of the target grid-connected converter is determined. Based on the first parameter domain, the control parameter safety domain of the target grid-connected converter is determined; The target grid-connected converter is connected to the target power grid through a grid connection point, and the target phase-locked loop is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

2. The method for determining the safety domain of control parameters for transient fault processes in grid-connected converters according to claim 1, characterized in that, The method utilizes the structural parameters of the target power grid to solve the dynamic system equations of the target phase-locked loop, and also obtains a second analytical expression for the output phase of the target phase-locked loop at the moment the short-circuit fault is cleared. The method further includes: Based on the vector relationship of the grid connection point voltage, establish the voltage phase relationship between the grid connection point voltage and the target phase-locked loop output phase; Based on the second analytical expression and the voltage phase relationship, a transient overvoltage constraint is determined; wherein, the transient overvoltage constraint is used to constrain the transient overvoltage at the input grid connection point of the target grid-connected converter to be lower than the safe voltage threshold. Based on the transient overvoltage constraint, determine the second parameter domain of the control parameters of the target grid-connected converter; The step of determining the control parameter safety domain of the target grid-connected converter based on the first parameter domain includes: The control parameter safety domain of the target grid-connected converter is determined based on the intersection of the first parameter domain and the second parameter domain.

3. The method for determining the safety domain of control parameters for transient fault processes in grid-connected converters according to claim 2, characterized in that, For a short-circuit fault in the target power grid, the implementation phases of the control strategy of the target grid-connected converter include: a first phase in which a conventional control strategy is used before the short-circuit fault occurs; a second phase in which a low-voltage ride-through control strategy is not activated before the short-circuit fault occurs; a third phase in which a low-voltage ride-through control strategy is used; and a fourth phase in which the low-voltage ride-through control strategy is still used after the fault is cleared. The dynamic system equation is a second-order differential equation for the output phase of the target phase-locked loop; The first parsing expression and the second parsing expression are obtained in the following way: For each implementation stage of the control strategy for the target grid-connected converter, based on the initial phase value of the target phase-locked loop in the implementation stage, the dynamic system equation of the target phase-locked loop is solved to obtain the analytical expression of the implementation stage; wherein, in each implementation stage, the initial phase value of the target phase-locked loop is the phase value of the target phase-locked loop at the last moment of the previous implementation stage; and in each implementation stage, the initial phase derivative of the target phase-locked loop is the sum of the derivative of the phase value of the target phase-locked loop at the last moment of the previous implementation stage and its abrupt change. The parsing expression of the third stage is used as the first parsing expression; The parsing expression of the fourth stage is used as the second parsing expression.

4. The method for determining the safety domain of control parameters for transient fault processes in grid-connected converters according to claim 3, characterized in that, The first analytical expression consists of steady-state phase and phase oscillation terms; The step of determining the low-penetration phase-locked stability constraint based on the first analytical expression includes: By using differentiation, the low-penetration phase-locked stability constraint is obtained based on the amplitude of the phase oscillation term in the first analytical expression.

5. The method for determining the safety domain of control parameters for transient fault processes in grid-connected converters according to claim 4, characterized in that, The first parsing expression is as follows: ； ； The step of obtaining the low-penetration phase-locked stability constraint by using differentiation operations based on the amplitude of the phase oscillation term in the first analytical expression includes: By taking the derivative of the square of the amplitude of the phase oscillation term and making the result of the derivative less than zero, the following low-penetration phase-locked stability constraint is obtained: ； in, For output phase; This is the steady-state phase; This is a phase oscillation term; This is the initial parameter for the amplitude of the phase oscillation term; The initial phase parameter for the phase oscillation term; For simplification; To match the grid connection point voltage , d axis, q Shaft current command value , and constants related to power grid structure parameters; The initial phase value of the target phase-locked loop during the low-pressure crossing phase; The initial value of the first-order phase derivative of the target phase-locked loop during the low-pressure crossing phase; and These are the proportional and integral coefficients of the PID controller in the target phase-locked loop control loop, respectively. For the voltage drop of the transmission line in steady state q Axial components; This represents the angular frequency of the phase oscillation of the phase-locked loop; t It is a time variable; This is the equivalent inductance value of the transmission line.

6. The method for determining the safety domain of control parameters for fault transient processes in grid-connected converters according to any one of claims 2 to 5, characterized in that, The voltage phase relationship is as follows: in, for t The voltage at the grid connection point at any given time; The target grid voltage; The inductive reactance value of the target power grid line; The resistance value of the target power grid line; The output of the target grid-connected converter d shaft current; The output of the target grid-connected converter q shaft current; The target phase-locked loop outputs the phase; The step of determining the transient overvoltage constraint based on the second analytical expression and the voltage phase relationship includes: Substituting the second analytical expression into the voltage phase relationship, and making the value of the voltage phase relationship less than the safe voltage threshold, the transient overvoltage constraint is obtained as follows: ； in, This is the safe voltage threshold.

7. A device for determining the safety domain of control parameters during transient fault processes in a grid-connected converter, characterized in that, include: The solver module is used to solve the dynamic system equations of the target phase-locked loop using the structural parameters of the target power grid, and obtain the first analytical expression of the output phase of the target phase-locked loop during the low-voltage ride-through stage after a short-circuit fault occurs in the target power grid. The first determining module is used to determine the low-voltage crossing phase-locked loop stability constraint according to the first analytical expression; wherein the low-voltage crossing phase-locked loop stability constraint is used to constrain the output phase of the target phase-locked loop to not lose synchronization during the low-voltage crossing phase; The second determining module is used to determine the first parameter domain of the control parameters of the target grid-connected converter based on the low-breakdown phase-locked stability constraint. The third determining module is used to determine the control parameter safety domain of the target grid-connected converter based on the first parameter domain; The target grid-connected converter is connected to the target power grid through a grid connection point, and the target phase-locked loop is used to synchronize the current phase output by the target grid-connected converter with the voltage phase of the grid connection point.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the method for determining the safety domain of control parameters for fault transient processes of grid-connected converters as described in any one of claims 1 to 6.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the method for determining the safety domain of control parameters for fault transient processes of grid-connected converters as described in any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the method for determining the safety domain of control parameters for fault transient processes of grid-connected converters as described in any one of claims 1 to 6.

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