Switching control method and system for black start and islanded operation of wind power converter

Abstract

This invention relates to the field of wind power converter control, and provides a method and system for switching control between black start and islanded operation of a wind power converter. Before responding to a closing command, the method first predicts the new steady-state operating point to be reached after load connection, including steady-state values ​​such as PCC voltage and converter output current, based on the electrical parameters of the load to be connected. Then, it calculates the corresponding state values ​​that the integrators of the voltage and current loop PI controllers inside the converter should possess at the new steady-state operating point. Finally, at the instant the circuit breaker closing signal is issued, these pre-calculated integrator state values ​​are synchronously preset into the controller's integrator. In this way, the controller's internal state is already near the new steady state at the moment of load connection, thus skipping the transient process of response lag and error accumulation in traditional PI controllers, achieving a smooth transition from no-load to loaded, and effectively suppressing voltage and frequency surges during the switching process.

Description

Technical Field

[0001] This invention relates to the field of wind power converter control technology, and in particular to a switching control method and system for black start and islanded operation of a wind power converter. Background Technology

[0002] With the development of new energy technologies, wind power is playing an increasingly important role in the power system. To enhance grid resilience and power supply capabilities to remote or weak grids, wind turbines are required to have black start and islanding capabilities. Wind power converters with grid-connected control functions can autonomously establish the voltage and frequency of the local grid without relying on external large grid support, achieving no-load voltage establishment. After the grid-connected converter successfully establishes the no-load voltage, the system needs to smoothly transition from this no-load state to the loaded islanding operation state. A key step in this process is connecting the first critical load, such as an on-site transformer, collector line, or other auxiliary equipment. However, existing technologies face significant technical challenges when performing this switching operation. When the circuit breaker at the point of common coupling (PCC) closes, connecting a load that is not energized, the system's equivalent impedance and power demand undergo a step change. Especially when connecting inductive loads such as transformers, the system instantaneously demands a large amount of reactive power to establish the magnetic field, accompanied by an active power surge, which causes drastic fluctuations in voltage and frequency at the PCC point.

[0003] Existing wind power converter control strategies typically employ feedback control loops based on PI regulators. An inherent characteristic of these controllers is hysteresis response. That is, they can only begin adjusting their control output after detecting a drop in the PCC voltage. The integral element in the PI regulator requires time to accumulate error, leading to a delay in control response. When load surges are significant, this delayed response causes the converter's output current to rapidly reach its hardware saturation limit. At this point, the voltage loop loses its effective control capability and cannot effectively support the PCC voltage. This switching process from no-load to load is often accompanied by significant voltage drops and frequency oscillations. These transient shocks may even trigger the converter's overcurrent or undervoltage protection, leading to switching failure and preventing a successful transition from black start to stable islanded operation. Summary of the Invention

[0004] The present invention aims to solve at least one of the problems existing in the prior art, and provides a method and system for switching control between black start and islanded operation of wind power converter.

[0005] One aspect of the present invention provides a switching control method for black start and islanded operation of a wind power converter, comprising: A system stability flag is generated based on the acquired PCC three-phase voltage and PCC frequency; In response to the system stability flag being true, the load parameters of the load to be connected are identified to obtain the equivalent resistance and equivalent inductance of the load to be connected. The steady-state operating point is predicted based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching, so as to obtain the steady-state value of the dq-axis current and the steady-state value of the dq-axis PCC voltage after switching. The controller integral state is preset based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. The preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator are written into the integrator in the controller, and a circuit breaker closing signal is generated.

[0006] Another aspect of the present invention provides a switching control system for black start and islanded operation of a wind power converter, comprising: The system stability flag generation module is used to generate a system stability flag based on the acquired PCC three-phase voltage and PCC frequency; The load parameter identification module is used to identify the load parameters of the load to be connected in response to the system stability flag being true, so as to obtain the equivalent resistance and equivalent inductance of the load to be connected. The steady-state operating point prediction module is used to predict the steady-state operating point based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching, so as to obtain the steady-state value of the dq-axis current and the steady-state value of the dq-axis PCC voltage after switching. The controller integral state preset module is used to preset the controller integral state based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching, so as to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. The circuit breaker closing signal generation module is used to write the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator into the integrator in the controller, and generate the circuit breaker closing signal.

[0007] Compared with existing technologies, this invention, before responding to the closing command, first predicts the new steady-state operating point to be reached after the load is connected by establishing a system steady-state model based on the electrical parameters of the load to be connected. This new steady-state operating point includes steady-state values ​​such as PCC voltage and converter output current. Then, it calculates the corresponding state values ​​that the integrators of the voltage loop and current loop PI controllers inside the converter should possess under this new steady-state operating point. Finally, at the instant the circuit breaker closing signal is issued, these pre-calculated integrator state values ​​are synchronously preset into the controller's integrator. In this way, the controller's internal state is already near the new steady state at the moment the load is connected, thus skipping the transient process of response lag and error accumulation in traditional PI controllers, achieving a smooth transition from no-load to load, and effectively suppressing voltage and frequency surges during the switching process. Attached Figure Description

[0008] One or more embodiments are illustrated by way of example with the corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0009] Figure 1 A flowchart of a switching control method for black start and islanded operation of a wind power converter according to an embodiment of the present invention; Figure 2 This is a data flow diagram illustrating the switching control method between black start and islanded operation of a wind power converter according to an embodiment of the present invention. Figure 3 This is a flowchart illustrating the steady-state operating point prediction method for the black start and islanded operation switching control of a wind power converter according to an embodiment of the present invention, based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching, to obtain the steady-state value of the dq-axis current and the steady-state value of the dq-axis PCC voltage after switching. Figure 4 This is a flowchart illustrating the switching control method for black start and islanded operation of a wind power converter according to an embodiment of the present invention. The method involves presetting the controller integral state based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching, to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. Figure 5 This is a block diagram of a switching control system for black start and islanded operation of a wind power converter according to an embodiment of the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the various embodiments of the present invention to facilitate a better understanding of the invention. However, the technical solutions claimed in the present invention can be implemented even without these technical details and with various variations and modifications based on the following embodiments. The division of the various embodiments below is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction.

[0011] As indicated in the specification and claims of this invention, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0012] While this invention makes various references to certain modules in systems according to embodiments of the invention, any number of different modules can be used and run on user terminals and / or servers. The modules described are merely illustrative, and different aspects of the systems and methods may use different modules.

[0013] This invention uses flowcharts to illustrate the operations performed by the system according to embodiments of the invention. It should be understood that the preceding or following operations are not necessarily performed in precise order. Instead, various steps can be processed in reverse order or simultaneously, as needed. Furthermore, other operations can be added to these processes, or one or more steps can be removed from them.

[0014] After a wind power converter achieves black start and establishes no-load voltage, a smooth transition to islanded operation under load is required. Existing technologies, when switching to the first critical load such as a transformer or line, can cause severe voltage drops and frequency oscillations at the point of common coupling (PCC) due to the step change in system impedance and power demand, potentially even leading to system instability. This transient impact is mainly due to the reliance on lagging feedback regulation by traditional controllers, which cannot provide active support at the moment of impact. Therefore, this invention proposes a switching control method and system for wind power converters between black start and islanded operation. This method pre-calculates the new steady state after the switch before load connection and allows the controller to skip the transient response process, thereby achieving a smooth switch. Specifically, this invention first obtains the electrical parameters of the load to be connected, such as equivalent resistance and equivalent inductance, after the system has stabilized under no-load voltage. Then, using these parameters and the converter's own model, a steady-state equivalent circuit model of the system after switching is constructed, and steady-state operating point prediction is performed to calculate the steady-state values ​​of the dq-axis current and the dq-axis PCC voltage that the system will reach after the load is connected. Next, the key step of this invention is to reverse-calculate the state value that the voltage loop PI controller integrator should have under the new steady state based on the predicted new steady-state current value. At the same time, combining the predicted steady-state current, converter parameters, and the voltage reference value before switching, the integrator preset state value required by the current loop PI controller integrator to cancel the decoupling term and maintain the internal potential is calculated. Finally, when the controller responds to the load switching command, these calculated dq-axis integrator preset state values ​​of the voltage loop and current loop are synchronously written into the corresponding integrator register in the controller at the same time as the output circuit breaker closing signal.

[0015] Figure 1 This is a flowchart of a switching control method for black start and islanded operation of a wind power converter according to an embodiment of the present invention. Figure 2 This is a data flow diagram illustrating the switching control method for black start and islanded operation of a wind power converter according to an embodiment of the present invention. (In conjunction with...) Figure 1 and Figure 2According to an embodiment of the present invention, a switching control method for black start and islanded operation of a wind power converter includes the following steps: S100, generating a system stability flag based on the acquired PCC three-phase voltage and PCC frequency; S200, in response to the system stability flag being true, identifying the load parameters of the load to be connected to obtain the equivalent resistance and equivalent inductance of the load to be connected; S300, predicting the steady-state operating point based on the equivalent resistance, equivalent inductance, and reference values ​​of the dq-axis voltage before switching to obtain... S400: Obtain the steady-state values ​​of the dq-axis current and the PCC voltage of the dq-axis after switching; S500: Based on the steady-state values ​​of the dq-axis current, the PCC voltage of the dq-axis after switching, and the reference value of the dq-axis voltage before switching, preset the controller integral state to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator; S500: Write the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator into the integrator in the controller and generate the circuit breaker closing signal.

[0016] Specifically, in step S100, a system stability flag is generated based on the acquired PCC three-phase voltage and PCC frequency. It is understood that after the wind power converter achieves black-start no-load voltage build-up, its output voltage and frequency must first reach a stable state for subsequent load switching operations to have a controllable basis. If load connection is performed during a transient process where the voltage or frequency is not yet stable, it will lead to superimposed impacts, preventing the system from establishing a stable new operating point and potentially causing the entire switching process to fail. Therefore, in the technical solution of this invention, a system stability flag is generated based on the acquired PCC three-phase voltage and PCC frequency to determine in real time whether the black-start no-load voltage build-up process has been completed and to confirm whether the system is in a ready state suitable for executing the next load switching step. This ensures that subsequent steady-state operating point prediction and controller state presets are calculated based on a valid, non-transient initial condition, while avoiding switching operations performed when the system itself is unstable, thus improving the reliability and success rate of the entire black-start to islanded operation switching process.

[0017] More specifically, in a specific example of the present invention, the process of generating a system stability flag is as follows: First, three-phase AC voltage waveform data at the point of common coupling (PCC) is continuously collected. The collected three-phase voltage data is input to a phase-locked loop (PLL) module or a frequency amplitude detection unit. Through dq transformation and PLL processing, the fundamental amplitude of the current PCC voltage and the system frequency are calculated in real time. Subsequently, the calculated PCC voltage amplitude is compared with a preset voltage stability range, such as 0.99 to 1.01 times the rated voltage, and the calculated system frequency is compared with a preset frequency stability range, such as 49.9 Hz to 50.1 Hz of the rated frequency. A timer is introduced, and the system is considered to have reached a no-load stable state only when the PCC voltage amplitude and the system frequency are simultaneously and continuously maintained within their respective preset stability ranges for a preset stability duration, such as 1 second. After all the above conditions are met, a system stability flag with a Boolean value of true is generated. This system stability flag is passed to the subsequent load parameter identification step as a permission signal to initiate the switching operation. If any condition is not met, the flag remains false or is cleared to zero.

[0018] Specifically, in step S200, in response to the system stability flag being true, the load parameter identification of the load to be connected is performed to obtain the equivalent resistance and equivalent inductance of the load to be connected. It is understood that the accuracy of subsequent steady-state operating point prediction and controller state preset fundamentally depends on the precise understanding of the electrical characteristics of the load to be connected. If the load parameters are unknown or inaccurate, the predicted new steady-state operating point will deviate from the actual value, leading to an error in the calculated integrator preset state, thus preventing smooth switching. Therefore, in the technical solution of this invention, in response to the system stability flag being true, the load parameter identification of the load to be connected is further performed to obtain the equivalent resistance and equivalent inductance of the load to be connected, thereby providing the necessary quantitative input parameters for the subsequent solution of the system steady-state model. This ensures the accuracy of the steady-state operating point prediction, provides a reliable data foundation for the reverse calculation of the controller integrator state, and is a prerequisite for realizing the entire feedforward control strategy.

[0019] More specifically, in a specific example of the present invention, when the response system stability flag is true, the controller first receives an identifier of a load to be connected. This identifier corresponds to a specific device to be connected, such as a certain box-type transformer or a certain section of collector line. After obtaining the identifier, its electrical parameters can be determined through one of two implementation methods. In the first implementation method, the identifier of the load to be connected is used as an index key to query a pre-configured load parameter database in the controller's internal memory. This load parameter database stores the equivalent resistance and equivalent inductance values ​​of various key loads in the wind farm measured during offline calibration or at the factory. The query operation retrieves the equivalent resistance and equivalent inductance of the load to be connected corresponding to the identifier and transmits them to the subsequent prediction calculation step. That is, identifying the load parameters of the load to be connected to obtain the equivalent resistance and equivalent inductance of the load to be connected includes: querying and retrieving the corresponding equivalent resistance and equivalent inductance of the load to be connected from the load parameter database based on the identifier of the load to be connected. In the second implementation method, an online identification strategy is adopted. With the main circuit breaker remaining open, a dedicated detection unit is activated. This detection unit injects a preset detection signal, with an intensity lower than the protection action threshold, into the load to be connected, while the load side is still unenergized. This signal can be a voltage or current signal of a specific frequency. Simultaneously, the measurement unit collects the voltage and current response data generated on the load by the detection signal. Finally, based on the collected voltage and current response signals, the equivalent resistance and equivalent inductance of the load to be connected are calculated in real time using an online identification algorithm, such as an impedance measurement or system identification method.

[0020] Specifically, in step S300, steady-state operating point prediction is performed based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching to obtain the steady-state values ​​of the dq-axis current and the dq-axis PCC voltage after switching. It is understood that the effectiveness of the controller internal state preset strategy adopted in this invention depends on prior knowledge of the new equilibrium state the system will reach after load connection. If the target steady-state operating point is unknown, an accurate target value cannot be provided for the subsequent reverse calculation of the controller integrator state. Therefore, in the technical solution of this invention, steady-state operating point prediction is further performed based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching. This allows for the quantitative calculation of the values ​​at which the current and PCC voltage will stabilize in the dq rotating coordinate system after the load is connected by establishing and solving a system steady-state equivalent circuit model including the converter and the load to be connected. This provides two key, quantitative calculation bases for the subsequent controller integral state preset steps: the steady-state value of the dq-axis current after the switch and the steady-state value of the dq-axis PCC voltage after the switch. This set of data forms the basis for the reverse derivation of the preset states of the voltage loop and current loop integrators, ensuring the accuracy of the feedforward control strategy.

[0021] Figure 3 This is a flowchart illustrating the steady-state operating point prediction based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching, to obtain the steady-state values ​​of the dq-axis current and the dq-axis PCC voltage after switching, according to an embodiment of the present invention. Figure 3 As shown, step S300 includes: S310, constructing a system model matrix based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the resistance and inductance of the equivalent impedance on the converter side to obtain the total system impedance matrix and the load impedance matrix; S320, predicting the steady-state current after switching based on the total system impedance matrix and the reference value of the dq-axis voltage before switching to obtain the steady-state value of the dq-axis current after switching; S330, predicting the point of common coupling voltage after switching based on the load impedance matrix and the steady-state value of the dq-axis current after switching to obtain the steady-state value of the dq-axis PCC voltage after switching.

[0022] In step S310, a system model matrix is ​​constructed based on the equivalent resistance and inductance of the load to be connected, as well as the resistance and inductance of the equivalent impedance on the converter side, to obtain the total system impedance matrix and the load impedance matrix. It is understood that subsequent steady-state operating point prediction requires solving a system of linear equations describing the new steady state in the dq rotating coordinate system to calculate the current and voltage after switching. If only scattered resistance and inductance parameters are available without integrating them into a systematic mathematical model, efficient and standardized matrix operations cannot be performed. Therefore, in the technical solution of this invention, a system model matrix is ​​further constructed based on the equivalent resistance and inductance of the load to be connected, as well as the resistance and inductance of the equivalent impedance on the converter side, to transform the algebraic equations describing the electrical characteristics of the system in the dq coordinate system into a standardized matrix form. This provides two core mathematical operators—the total system impedance matrix and the load impedance matrix—for the subsequent current and voltage prediction steps, simplifying and standardizing the steady-state solution calculation process.

[0023] More specifically, in a specific example of the present invention, the process of constructing the system model matrix is ​​as follows: First, obtain the equivalent resistance of the load to be connected obtained in the previous steps. Equivalent inductance of the load to be connected and the resistance of the converter-side equivalent impedance stored in the controller. ,inductance and the system's rated angular frequency Next, the system total impedance matrix is ​​constructed. The resistance of the equivalent impedance on the converter side is then calculated. Equivalent resistance of the load to be connected The sum of these gives the total resistance, which is the inductance of the equivalent impedance on the converter side. Equivalent inductance of the load to be connected The total inductance is obtained by adding the values. Then, the total resistance is used as the diagonal element of the matrix, and the coupling terms of the total inductance are added. and As off-diagonal elements, construct a 2×2 system total impedance matrix. Simultaneously, construct the load impedance matrix. The equivalent resistance of the load to be connected is... As a diagonal element, the coupling term of the load inductance is... and As off-diagonal elements, a 2×2 load impedance matrix is ​​constructed. Finally, the generated total system impedance matrix and load impedance matrix are output for use in subsequent steady-state prediction steps.

[0024] In step S320, steady-state current prediction after switching is performed based on the system total impedance matrix and the reference value of the dq-axis voltage before switching to obtain the steady-state value of the dq-axis current after switching. It is understood that after the constructed system total impedance matrix describes the transmission relationship from the converter's internal potential to the output current, a definite voltage excitation source is needed as input to solve for the current response of the system in the new steady state. This current response is a crucial intermediate variable for subsequent calculations of the PCC voltage and for inferring the controller state. Therefore, in the technical solution of this invention, steady-state current prediction after switching is further performed based on the system total impedance matrix and the reference value of the dq-axis voltage before switching. This allows for the quantitative calculation of the d-axis and q-axis steady-state current components flowing out of the converter after load connection by solving the linear equations representing the new steady-state electrical relationship. This provides a known current input for the subsequent PCC voltage prediction step and provides an accurate target reference value for the pre-calculation of the voltage loop integrator state.

[0025] More specifically, in a specific example of the present invention, the process for predicting the steady-state current after switching is as follows: First, obtain the total system impedance matrix constructed in the preceding steps, and the dq-axis voltage reference value used by the controller in the black-start no-load voltage build-up steady state before switching. In this embodiment, the controller's dq rotating coordinate system is synchronized with the PCC voltage vector; therefore, the d-axis voltage reference value... Corresponding to the voltage amplitude, the q-axis voltage reference value is set to 0. Vector The excitation source vector used to solve for the converter's internal potential in the new steady state is based on the assumption that the goal of the switching action is to maintain this internal potential constant. Subsequently, a set of steady-state equations describing the relationship between the converter's internal potential, the system's total impedance, and the steady-state current after switching is established. This set of steady-state equations takes the following matrix form: ; In this system of steady-state equations, This represents the steady-state value of the d-axis current after the switch. This represents the steady-state value of the q-axis current after the switch. The reference value for the d-axis voltage before switching. The total impedance matrix of the system is... The resistance is the equivalent impedance on the converter side. The inductance is the equivalent impedance on the converter side. The equivalent resistance of the load to be connected. The equivalent inductance of the load to be connected, The system's rated angular frequency is given. Finally, by solving this system of two linear equations in two variables, for example using matrix inversion or Cramer's rule, the unique solution is obtained. and The values ​​are calculated and output as the steady-state values ​​of the dq-axis current after switching.

[0026] That is, based on the system's total impedance matrix and the reference value of the dq-axis voltage before switching, the steady-state current after switching is predicted to obtain the steady-state value of the dq-axis current after switching, including: The following formula is used to predict the steady-state current after switching: ; in, This represents the steady-state value of the d-axis current after the switch. This represents the steady-state value of the q-axis current after the switch. The reference value for the d-axis voltage before switching. The total impedance matrix of the system is... The resistance is the equivalent impedance on the converter side. The inductance is the equivalent impedance on the converter side. The equivalent resistance of the load to be connected. The equivalent inductance of the load to be connected, This is the system's rated angular frequency.

[0027] In step S330, the post-switching point of common coupling (PCC) voltage is predicted based on the load impedance matrix and the steady-state value of the dq-axis current after switching to obtain the steady-state value of the PCC voltage. It is understood that the dq-axis current output by the converter in the new steady state has been calculated, but this current is based on the assumption of maintaining a constant potential within the converter. Therefore, it is necessary to further calculate the actual voltage drop across the load impedance to determine the final steady-state voltage of the PCC. Therefore, in the technical solution of this invention, the post-switching PCC voltage is further predicted based on the load impedance matrix and the steady-state value of the dq-axis current after switching, thereby accurately calculating the d-axis and q-axis voltage components of the PCC point after switching using Ohm's law in the dq coordinate system. This allows the acquisition of the steady-state value of the PCC voltage after switching. This data can be used to evaluate the feasibility of the switching operation, such as determining whether the predicted PCC voltage drop is within the allowable range; if it exceeds the range, the switching is terminated. Furthermore, it provides crucial feedback and verification information for more advanced iterative prediction algorithms or state observers.

[0028] More specifically, in a specific example of the present invention, the process for predicting the point of common coupling voltage after switching is as follows: First, obtain the load impedance matrix constructed in the previous steps, and the steady-state value of the dq-axis current after switching, which was just calculated, i.e. and Subsequently, a steady-state equation describing the relationship between the PCC voltage, load impedance, and steady-state current is established. This steady-state equation shows that the dq-axis voltage vector of the PCC is equal to the product of the load impedance matrix and the dq-axis current vector. This set of equations is expressed in the following matrix form: ; Where, vector These are the steady-state values ​​of the d-axis PCC voltage and the q-axis PCC voltage after the switching, which are to be solved. These are the known steady-state values ​​of the dq-axis current after switching. The equivalent resistance of the load to be connected. The equivalent inductance of the load to be connected, The system's rated angular frequency, This is the load impedance matrix. Finally, by performing matrix multiplication, the solution is obtained. and The specific values ​​are then used as the steady-state values ​​of the dq-axis PCC voltage after switching.

[0029] That is, based on the load impedance matrix and the steady-state value of the dq-axis current after switching, the voltage at the point of common coupling after switching is predicted to obtain the steady-state value of the dq-axis PCC voltage after switching, including: The following formula is used to predict the voltage at the point of common coupling after the switchover: ; in, This represents the steady-state value of the d-axis PCC voltage after switching. This represents the steady-state value of the q-axis PCC voltage after the switch. This is the load impedance matrix.

[0030] For example, in a black start scenario at a wind farm, the load to be connected is an on-site collection transformer. The previous step has predicted the steady-state current required to excite this unloaded transformer. and The steady-state current is mainly composed of inductive reactive components. Multiplying this current value by the load impedance matrix representing the transformer impedance yields the calculated... and This allows the controller to predict the actual voltage amplitude and phase angle at the PCC point at the moment of closing. The controller can compare the predicted actual voltage amplitude with a preset undervoltage protection threshold, such as 0.9 times the rated voltage. If the predicted actual voltage value is lower than the undervoltage protection threshold, the controller can actively abort the switching operation and issue an alarm, thereby avoiding switching failure or system crash due to excessive drop in PCC voltage. It should be noted that this verification step is not involved in the calculation formula of the controller integrator preset value, but is used to assess and suppress switching risks before closing, ensuring the safety and success rate of the switching.

[0031] Specifically, in step S400, the controller integral state is preset based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching, to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. It is understandable that the internal state of the PI regulator in the converter controller, especially its integral stage, corresponds to a specific steady-state operating point of the system. When switching from no-load to load, if the integrator state does not change accordingly, but instead relies on feedback error to accumulate from the original no-load state corresponding to zero current output to adapt to the new load demand, this accumulation process itself will manifest as voltage drops and oscillations during the system switching transient. Therefore, in the technical solution of this invention, the controller integral state is further preset based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching, to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. This allows the complete electrical quantities characterizing the new system steady state predicted in the preceding steps to be used to reverse-calculate the internal state values ​​that the integrators in the voltage and current loops must possess at the new equilibrium point. It should be noted that the steady-state value of the dq-axis PCC voltage after switching does not directly participate in the calculation of the integrator preset value. Its role is in the feasibility judgment and strategy optimization before closing the circuit, used to predict the PCC voltage drop / rise and decide whether to proceed to this step or adjust control parameters such as virtual impedance before prediction. In this way, at the instant of physical closing, these calculated preset state values ​​can be directly written into the controller register, causing the controller's internal state to transition to a state close to or equal to the state required for the new steady-state operating point. This eliminates the need for the controller to undergo a transient accumulation process, fundamentally eliminating transient shocks caused by controller response lag, and ensuring the smoothness of the switching process and the stability of the PCC voltage.

[0032] Figure 4 This is a flowchart illustrating the controller integral state preset values ​​for the voltage loop dq-axis integrator and the current loop dq-axis integrator, based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching, according to an embodiment of the present invention. Figure 4As shown, step S400 includes: S410, using the steady-state value of the d-axis current after switching as the preset state value of the voltage loop d-axis integrator, and using the steady-state value of the q-axis current after switching as the preset state value of the voltage loop q-axis integrator; S420, calculating the current decoupling feedforward compensation voltage term and the cross-decoupling feedforward voltage term to offset the coupling effect between the d and q axes based on the steady-state value of the d and q axis currents after switching; S430, calculating the preset state value of the current loop d and q axis integrator based on the reference value of the d and q axis voltages before switching, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term.

[0033] In step S410, the steady-state value of the switched d-axis current is used as the preset state value of the voltage loop d-axis integrator, and the steady-state value of the switched q-axis current is used as the preset state value of the voltage loop q-axis integrator. It can be understood that in a typical voltage-current dual closed-loop control structure of a converter, the output of the outer voltage loop is the dq-axis current reference value of the inner current loop. According to the steady-state control principle of the PI regulator, when the system enters a new steady-state operating point, the input error of the voltage loop, i.e., the difference between the PCC voltage reference value and the actual PCC voltage value, will approach zero. At this time, the output of the proportional element in the PI regulator is also zero, and its entire steady-state output, equal to the new steady-state dq-axis current reference value, is entirely accumulated and maintained by its integral element. Therefore, in the technical solution of this invention, the steady-state value of the switched d-axis current is further used as the preset state value of the voltage loop d-axis integrator, and the steady-state value of the switched q-axis current is used as the preset state value of the voltage loop q-axis integrator, thereby directly setting the internal state necessary for the voltage loop integrator under the new steady state. In this way, the output of the voltage loop can immediately jump to the new steady-state current reference value at the moment of switching, that is, the predicted steady-state value of the dq axis current after switching, thereby eliminating the response delay caused by the integration accumulation of the voltage loop and providing the inner current loop with an instant and accurate tracking command.

[0034] More specifically, in a specific example of the present invention, the processing of the preset voltage loop integrator state is as follows: First, the calculated steady-state value of the d-axis current after switching is obtained from the preceding steady-state operating point prediction step. and the steady-state value of the q-axis current after switching These two values ​​represent the steady-state output current required by the converter to maintain PCC voltage stability after load connection. Subsequently, in the controller's software algorithm, the d-axis integrator accumulator register and q-axis integrator accumulator register, used to store the voltage outer loop PI regulator state, are located. Then, the acquired d-axis current steady-state value after switching is... As an assignment instruction, this is to be written into the d-axis integrator's accumulator register to replace its integration state under no-load conditions (zero current). Simultaneously, the acquired steady-state value of the q-axis current after the switch will be... The data is ready to be written to the q-axis integrator accumulator register. These two assignment operations are temporarily stored and configured to be executed simultaneously with the circuit breaker closing signal in subsequent synchronous execution steps to ensure that the control state of the voltage loop remains precisely synchronized with the state changes of the physical system.

[0035] In step S420, based on the steady-state value of the dq-axis current after switching, a cross-decoupling feedforward voltage term is calculated to offset the coupling effect between the d and q axes, resulting in the d-axis current decoupling feedforward compensation voltage term and the q-axis current decoupling feedforward compensation voltage term. It is understood that when modeling and controlling the converter in the dq rotating coordinate system, there is a cross-coupling effect between the voltage and current equations of the d and q axes caused by the system angular frequency and the converter-side inductance. Specifically, changes in the q-axis current cause disturbances in the d-axis voltage, and vice versa. When calculating the preset state of the current loop integrator, this predictable coupled voltage component existing in the new steady state must be separated from the overall internal potential target in order to deduce the steady-state component purely borne by the PI integrator. Therefore, in the technical solution of this invention, a current decoupling feedforward compensation voltage term is further calculated based on the steady-state value of the dq-axis current after switching to counteract the coupling effect between the d and q axes. This quantitatively calculates the coupling voltage values ​​existing in the d-axis and q-axis control channels under the new steady-state current. This provides accurate compensation data for the next step of calculating the current loop integrator preset state, ensuring that the calculated integrator state value has eliminated known coupling effects, thereby improving the accuracy of the preset.

[0036] More specifically, in a specific example of the present invention, the process of calculating the current decoupling feedforward compensation voltage term is as follows: First, the steady-state value of the d-axis current after switching is obtained from the preceding steady-state operating point prediction step. and the steady-state value of the q-axis current after switching Simultaneously, the system's rated angular frequency is obtained from the controller parameter library. Inductance and the equivalent impedance of the converter side Subsequently, the d-axis current decoupling feedforward compensation voltage term is calculated, which is done by... , and Multiply them and take their opposites to get Simultaneously, the q-axis current decoupling feedforward compensation voltage term is calculated, which is done by... , and Multiply, we get Finally, the calculated d-axis current decoupling feedforward compensation voltage term and q-axis current decoupling feedforward compensation voltage term are output and used for the final calculation of the current loop integrator preset state value in the next step.

[0037] In step S430, the preset state value of the current loop dq-axis integrator is calculated based on the pre-switching dq-axis voltage reference value, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term. It is understood that the steady-state output value of the inner current loop PI regulator must be superimposed with the feedforward compensation voltage term used to offset the dq-axis coupling effect; together, they constitute the total internal potential required by the converter under the new steady-state condition. Therefore, given the total internal potential target (i.e., the pre-switching dq-axis voltage reference value) and the calculated decoupling feedforward compensation voltage term, the voltage component purely borne by the PI integrator must be solved in reverse by subtraction. Therefore, in the technical solution of this invention, the preset state value of the current loop dq-axis integrator is further calculated based on the pre-switching dq-axis voltage reference value, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term, thereby accurately determining the precise preset state values ​​in the current loop d-axis and q-axis integrators under the new steady-state operating point. In this way, it can be ensured that when these preset state values ​​and the decoupled feedforward terms work together in the new steady state, their combined control output is exactly equal to the converter internal potential required for the new steady state. This enables the current loop to instantaneously and accurately track the new steady-state current command given by the voltage outer loop, achieving shockless current switching.

[0038] More specifically, in a specific example of the present invention, the process of calculating the preset state value of the current loop dq-axis integrator is as follows: First, obtain the d-axis voltage reference value before switching. And confirm that the q-axis voltage reference value is 0 before switching. Simultaneously, obtain the d-axis current decoupling feedforward compensation voltage term calculated in the previous steps. The decoupling feedforward compensation voltage term with q-axis current is... Subsequently, the preset state value of the d-axis integrator of the current loop is calculated, and the calculation formula is as follows: ; in, The preset state values ​​are for the d-axis integrator of the current loop. The physical meaning of this calculation formula, which specifies the reference value for the d-axis voltage before switching, is that the steady-state value that the d-axis integrator needs to handle is equal to the target total d-axis voltage. Subtract the coupling voltage term between the d and q axes At the same time, the preset state value of the current loop q-axis integrator is calculated, and the calculation formula is as follows: ; in, This calculation is for the preset state value of the current loop q-axis integrator. The physical meaning of the formula is that the steady-state value that the q-axis integrator needs to handle is equal to the target 0 for the total q-axis voltage minus the coupling voltage term between the d and q axes. ,Right now Here, The inductance is the equivalent impedance on the converter side. The system's rated angular frequency, and These are the steady-state current values ​​on the q-axis and d-axis after the switch, respectively. For example, when switching to an unloaded transformer, the predicted values ​​are... That is, the reactive current component will be very large, and That is, the active current component is relatively small. This step will calculate a larger one. Correction value and a smaller This ensures that the state of the current loop integrator is precisely matched to the characteristics of this highly inductive, low-active-power load.

[0039] That is, based on the reference value of the dq-axis voltage before switching, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term, the preset state value of the current loop dq-axis integrator is calculated, including: The preset state value of the current loop dq-axis integrator is calculated using the following formula: ; ; in, The preset state values ​​are for the d-axis integrator of the current loop. The preset state values ​​are for the q-axis integrator of the current loop. The reference value for the d-axis voltage before switching. This is the feedforward compensation voltage term for d-axis current decoupling. The inductance is the equivalent impedance on the converter side. The system's rated angular frequency, This represents the steady-state value of the q-axis current after the switch. This is the feedforward compensation voltage term for q-axis current decoupling. This represents the steady-state value of the d-axis current after switching.

[0040] Specifically, in step S500, the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator are written into the integrator in the controller, and a circuit breaker closing signal is generated. It is understood that the preset state values ​​of the integrator calculated in the preceding steps are only target data stored in the controller's memory, while the converter's control loop still operates based on the integral values ​​under no-load conditions. For this feedforward control strategy to be effective, these predicted target data must be written into the controller's actual operating register at precise times, and this writing operation must be highly consistent with the timing of the physical load connection. Therefore, in the technical solution of this invention, the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator are further written into the integrator in the controller, and a circuit breaker closing signal is generated, serving as the final execution instruction for the entire feedforward switching strategy, ensuring that the transition of the controller's internal state and the change of the physical system's state occur simultaneously. In this way, the controller's internal integrator is already at or close to the new steady-state operating point the instant it senses the load connection, thus avoiding a transient process of accumulating errors from zero. This achieves active suppression of switching shocks and ensures a smooth transition of the PCC voltage.

[0041] More specifically, in a specific example of the present invention, the synchronous execution process of step S500 is as follows: First, after the controller completes the calculation of all integrator preset state values, it waits for a specific control clock synchronization signal, such as the start time of the next pulse width modulation cycle or control sampling cycle. Upon receiving the control clock synchronization signal, the controller performs two parallel operations within one control cycle: On the one hand, the preset state values ​​of the voltage loop d-axis integrator, voltage loop q-axis integrator, current loop d-axis integrator, and current loop q-axis integrator calculated in the previous steps are atomically written and loaded into the integral accumulation registers of the corresponding voltage loop and current loop PI regulators in the digital signal processor, respectively, to overwrite the original no-load integral state; on the other hand, within the same control cycle, the controller outputs a high-level or pulse signal through one of its general-purpose input / output ports, which is transmitted to the closing coil of the physical circuit breaker. The synchronous execution of these two operations ensures that the internal state of the converter controller is ready when the circuit breaker physical contacts are closed and the load is connected to the system, so that it can immediately output the active and reactive current required to match the new load, and the transient drop and oscillation of PCC voltage are effectively suppressed.

[0042] In summary, the switching control method for black start and islanded operation of a wind power converter according to an embodiment of the present invention is explained. Before responding to the closing command, it first predicts the new steady-state operating point to be reached after the load is connected by establishing a system steady-state model based on the electrical parameters of the load to be connected. This new steady-state operating point includes steady-state values ​​such as PCC voltage and converter output current. Then, it calculates the corresponding state values ​​that the integrators of the voltage loop and current loop PI controllers inside the converter should possess under this new steady-state operating point. Finally, at the instant the circuit breaker closing signal is issued, these pre-calculated integrator state values ​​are synchronously preset into the integrator of the controller. In this way, the controller's internal state is already near the new steady state at the moment of load connection, thereby skipping the transient process of response lag and error accumulation in traditional PI controllers, realizing a smooth transition from no-load to load, and effectively suppressing voltage and frequency surges during the switching process.

[0043] The present invention also provides a switching control system for black start and islanded operation of a wind power converter.

[0044] Figure 5 This is a block diagram of a switching control system for black start and islanded operation of a wind power converter according to an embodiment of the present invention. Figure 5 As shown, the switching control system 100 for black start and islanded operation of a wind power converter according to an embodiment of the present invention includes: a system stability flag generation module 110, used to generate a system stability flag based on the acquired PCC three-phase voltage and PCC frequency; a load parameter identification module 120, used to identify the load parameters of the load to be connected in response to the system stability flag being true, so as to obtain the equivalent resistance and equivalent inductance of the load to be connected; and a steady-state operating point prediction module 130, used to predict the steady-state operating point based on the equivalent resistance and equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching. The system predicts the steady-state values ​​of the dq-axis current and the PCC voltage of the dq-axis after the switch. A controller integral state preset module 140 is used to preset the controller integral state based on the steady-state values ​​of the dq-axis current, the PCC voltage of the dq-axis after the switch, and the reference value of the dq-axis voltage before the switch, to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. A circuit breaker closing signal generation module 150 is used to write the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator into the integrator in the controller and generate a circuit breaker closing signal.

[0045] For example, the steady-state operating point prediction module 130 includes: The system model matrix construction unit is used to construct the system model matrix based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the resistance and inductance of the equivalent impedance on the converter side to obtain the total system impedance matrix and the load impedance matrix. The steady-state current prediction unit is used to predict the steady-state current after switching based on the total system impedance matrix and the reference value of the dq-axis voltage before switching, so as to obtain the steady-state value of the dq-axis current after switching. The common coupling point voltage prediction unit is used to predict the common coupling point voltage after switching based on the load impedance matrix and the steady-state value of the dq-axis current after switching, so as to obtain the steady-state value of the dq-axis PCC voltage after switching.

[0046] For example, the controller integral state preset module 140 includes: The preset state value setting unit is used to set the steady-state value of the d-axis current after switching as the preset state value of the voltage loop d-axis integrator, and the steady-state value of the q-axis current after switching as the preset state value of the voltage loop q-axis integrator. The decoupling feedforward voltage calculation unit is used to calculate the current decoupling feedforward compensation voltage term to offset the coupling effect between the d and q axes based on the steady-state value of the d-q axis current after switching. The cross-decoupling feedforward voltage is used to obtain the d-axis current decoupling feedforward compensation voltage term and the q-axis current decoupling feedforward compensation voltage term. The current loop dq-axis integrator preset state value calculation unit is used to calculate the current loop dq-axis integrator preset state value based on the dq-axis voltage reference value before switching, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term. The specific implementation method of the switching control system 100 for black start and islanded operation of wind power converter provided in this embodiment of the invention can be found in the switching control method for black start and islanded operation of wind power converter provided in this embodiment of the invention, and will not be repeated here.

[0047] The black-start and islanding switching control system 100 for wind power converters according to embodiments of the present invention can be implemented in various types of computing devices or control units. For example, it can be deployed in the main controller of a wind power converter, the central controller of a wind turbine generator, or a dedicated wind farm-level industrial computer. In one possible implementation, the black-start and islanding switching control system 100 for wind power converters according to embodiments of the present invention can be integrated into the computing device as a software module and / or a hardware module. For example, the switching control system 100 can be a software module in the control firmware of the computing device or control unit, or it can be a dedicated control algorithm program developed for the computing device or control unit. Of course, the switching control system 100 can also be one of many hardware modules of the computing device or control unit, for example, implemented as dedicated digital signal processor logic, field-programmable gate array circuits, or application-specific integrated circuits.

[0048] Those skilled in the art will understand that the above embodiments are specific implementations of the present invention, and in practical applications, various changes can be made in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A switching control method for black start and islanded operation of a wind power converter, characterized in that, include: A system stability flag is generated based on the acquired PCC three-phase voltage and PCC frequency; In response to the system stability flag being true, the load parameters of the load to be connected are identified to obtain the equivalent resistance and equivalent inductance of the load to be connected. The steady-state operating point is predicted based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching, so as to obtain the steady-state value of the dq-axis current and the steady-state value of the dq-axis PCC voltage after switching. The controller integral state is preset based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. The preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator are written into the integrator in the controller, and a circuit breaker closing signal is generated.

2. The switching control method for black start and islanded operation of a wind power converter according to claim 1, characterized in that, The load parameters of the load to be connected are identified to obtain the equivalent resistance and equivalent inductance of the load to be connected, including: Based on the identifier of the load to be connected, the equivalent resistance and equivalent inductance of the load to be connected are retrieved from the load parameter database.

3. The switching control method for black start and islanded operation of a wind power converter according to claim 1, characterized in that, Steady-state operating point prediction is performed based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching to obtain the steady-state values ​​of the dq-axis current and the dq-axis PCC voltage after switching, including: Based on the equivalent resistance and inductance of the load to be connected, as well as the resistance and inductance of the equivalent impedance on the converter side, a system model matrix is ​​constructed to obtain the total system impedance matrix and the load impedance matrix. The steady-state current after switching is predicted based on the total system impedance matrix and the reference value of the dq-axis voltage before switching, so as to obtain the steady-state value of the dq-axis current after switching. Based on the load impedance matrix and the steady-state value of the dq-axis current after switching, the voltage at the point of common coupling after switching is predicted to obtain the steady-state value of the PCC voltage on the dq-axis after switching.

4. The switching control method for black start and islanded operation of a wind power converter according to claim 3, characterized in that, Based on the system total impedance matrix and the pre-switching dq-axis voltage reference value, the steady-state current after switching is predicted to obtain the steady-state value of the dq-axis current after switching, including: The following formula is used to predict the steady-state current after switching: ； in, This represents the steady-state value of the d-axis current after the switch. This represents the steady-state value of the q-axis current after the switch. The reference value for the d-axis voltage before switching. The total impedance matrix of the system is... The resistance is the equivalent impedance on the converter side. The inductance is the equivalent impedance on the converter side. The equivalent resistance of the load to be connected. The equivalent inductance of the load to be connected, This is the system's rated angular frequency.

5. The switching control method for black start and islanded operation of a wind power converter according to claim 4, characterized in that, Based on the load impedance matrix and the steady-state value of the dq-axis current after switching, the voltage at the point of common coupling (PCC) after switching is predicted to obtain the steady-state value of the dq-axis PCC voltage after switching, including: The following formula is used to predict the voltage at the point of common coupling after the switchover: ； in, This represents the steady-state value of the d-axis PCC voltage after switching. This represents the steady-state value of the q-axis PCC voltage after the switch. This is the load impedance matrix.

6. The switching control method for black start and islanded operation of a wind power converter according to claim 1, characterized in that, Based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching, the controller integral state is preset to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator, including: The steady-state value of the d-axis current after switching is used as the preset state value of the d-axis integrator of the voltage loop, and the steady-state value of the q-axis current after switching is used as the preset state value of the q-axis integrator of the voltage loop. Based on the steady-state value of the dq-axis current after switching, the current decoupling feedforward compensation voltage term used to cancel the coupling effect between the dq axes is calculated to obtain the d-axis current decoupling feedforward compensation voltage term and the q-axis current decoupling feedforward compensation voltage term. Based on the reference values ​​of the dq-axis voltage before switching, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term, the preset state values ​​of the current loop dq-axis integrator are calculated.

7. The switching control method for black start and islanded operation of a wind power converter according to claim 6, characterized in that, Based on the pre-switching dq-axis voltage reference value, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term, the preset state values ​​of the current loop dq-axis integrator are calculated, including: The preset state value of the current loop dq-axis integrator is calculated using the following formula: ； ； in, The preset state values ​​are for the d-axis integrator of the current loop. The preset state values ​​are for the q-axis integrator of the current loop. The reference value for the d-axis voltage before switching. This is the feedforward compensation voltage term for d-axis current decoupling. The inductance is the equivalent impedance on the converter side. The system's rated angular frequency, This represents the steady-state value of the q-axis current after the switch. This is the feedforward compensation voltage term for q-axis current decoupling. This represents the steady-state value of the d-axis current after switching.

8. A switching control system for black start and islanded operation of a wind power converter, characterized in that, include: The system stability flag generation module is used to generate a system stability flag based on the acquired PCC three-phase voltage and PCC frequency; The load parameter identification module is used to identify the load parameters of the load to be connected in response to the system stability flag being true, so as to obtain the equivalent resistance and equivalent inductance of the load to be connected. The steady-state operating point prediction module is used to predict the steady-state operating point based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the reference value of the dq-axis voltage before switching, so as to obtain the steady-state value of the dq-axis current and the steady-state value of the dq-axis PCC voltage after switching. The controller integral state preset module is used to preset the controller integral state based on the steady-state value of the dq-axis current after switching, the steady-state value of the dq-axis PCC voltage after switching, and the reference value of the dq-axis voltage before switching, so as to obtain the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator. The circuit breaker closing signal generation module is used to write the preset state values ​​of the voltage loop dq-axis integrator and the current loop dq-axis integrator into the integrator in the controller, and generate the circuit breaker closing signal.

9. The switching control method for black start and islanded operation of a wind power converter according to claim 8, characterized in that, The steady-state operating point prediction module includes: The system model matrix construction unit is used to construct the system model matrix based on the equivalent resistance of the load to be connected, the equivalent inductance of the load to be connected, and the resistance and inductance of the equivalent impedance on the converter side to obtain the total system impedance matrix and the load impedance matrix. The steady-state current prediction unit is used to predict the steady-state current after switching based on the total system impedance matrix and the reference value of the dq-axis voltage before switching, so as to obtain the steady-state value of the dq-axis current after switching. The common coupling point voltage prediction unit is used to predict the common coupling point voltage after switching based on the load impedance matrix and the steady-state value of the dq-axis current after switching, so as to obtain the steady-state value of the dq-axis PCC voltage after switching.

10. The switching control method for black start and islanded operation of a wind power converter according to claim 8, characterized in that, The controller integral state preset module includes: The preset state value setting unit is used to set the steady-state value of the d-axis current after switching as the preset state value of the voltage loop d-axis integrator, and the steady-state value of the q-axis current after switching as the preset state value of the voltage loop q-axis integrator. The decoupling feedforward voltage calculation unit is used to calculate the current decoupling feedforward compensation voltage term to offset the coupling effect between the d and q axes based on the steady-state value of the d-q axis current after switching. The cross-decoupling feedforward voltage is used to obtain the d-axis current decoupling feedforward compensation voltage term and the q-axis current decoupling feedforward compensation voltage term. The current loop dq-axis integrator preset state value calculation unit is used to calculate the current loop dq-axis integrator preset state value based on the dq-axis voltage reference value before switching, the d-axis current decoupling feedforward compensation voltage term, and the q-axis current decoupling feedforward compensation voltage term.

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