A passive robust stability control method for offshore wind power dc transmission system

Abstract

The application discloses a passive robust stability control method for a marine wind power DC transmission system. The system comprises the following steps: obtaining a mathematical model of a voltage source converter in a marine wind power flexible DC grid-connected system in a stationary coordinate system; converting the mathematical model in the stationary coordinate system into a differential equation in a dq rotating coordinate system by using equivalent Park transformation; designing a real-time tracking equation for comprehensive interference terms, so as to realize accurate tracking of modeling errors in the differential equation in the dq rotating coordinate system; deducing the mathematical model of the voltage source converter into a differential equation form in a PCHD standard model; constructing an expected energy function of the PCHD standard model; and realizing passive robust control of the voltage source converter of the marine wind power flexible DC grid-connected system based on real-time tracking of interference according to the expected energy function of the system. The application is favorable for improving the safe and stable operation capacity of the marine wind power DC transmission system.

Description

Technical Field

[0001] This invention relates to the field of stability control of flexible DC systems, specifically a passive robust stability control method for offshore wind power DC transmission systems. Background Technology

[0002] Flexible DC transmission technology (VSC-HVDC) is a third-generation DC transmission system that combines power electronics, power systems, automatic control, and communication principles. Compared to traditional DC transmission, it utilizes fully controlled devices such as insulated-gate bipolar transistors (IGBTs) instead of semi-controlled devices like thyristors. This technology has seen rapid development and application in practical engineering projects in recent years. The development of flexible DC transmission technology plays a crucial role in promoting grid intelligence and the integration of new energy sources into the grid. Offshore wind power is characterized by its cleanliness, environmental friendliness, high resource stability, and high annual utilization hours, and its integration with flexible DC grid technology will lead to rapid development in the future. However, traditional offshore wind power flexible DC grid-connected systems use voltage source converters based on proportional-integral direct current control (PIC) with inner and outer loops. Its drawbacks include the use of trial-and-error methods to obtain parameters, lacking theoretical basis, and while the design may ensure system robustness, it often reduces the system's stable performance. Sudden power fluctuations can significantly impact the system's dynamic characteristics, including overshoot and settling time. Therefore, it is necessary to investigate novel control strategies to improve the robust stability of offshore wind power DC transmission systems under external disturbances.

[0003] Nonlinear control based on differential geometry theory has shown good performance in improving system dynamics. Existing literature uses back-propagation control methods based on feedback linearization in converters. However, this control method significantly reduces system robustness when the system modeling error is large. In recent years, passive control theory has been widely used in converter control design due to its advantages such as flexible adjustment, fast dynamic response, and good robustness. However, traditional passive control methods are still quite sensitive to modeling errors in the system.

[0004] A prior art method and system for robust DC voltage control when a voltage source converter is connected to a weak power grid (CN202111434555.3) does not consider external disturbances to system modeling errors when designing the robust control mode, thus affecting the accuracy of the model. Summary of the Invention

[0005] In view of this, this invention proposes a passive robust stability control method for offshore wind power DC transmission systems. First, a mathematical model of the voltage source converter in the stationary coordinate system of the offshore wind power flexible DC grid-connected system is written based on Kirchhoff's voltage law. Then, considering the modeling error, an equivalent Park transformation is used to convert the mathematical model into differential equations in the dq rotating coordinate system. Second, by setting a positive definite tracking gain value, the real-time tracking error is ensured to approach zero within a finite time, thereby designing a real-time tracking equation for the comprehensive disturbance term, achieving accurate tracking of the modeling error in the differential equations in the dq rotating coordinate system. Finally, a passive robust control method for the voltage source converter of the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking is designed. By defining the desired energy function under the PCHD (Port-Controlled Hamiltonian with Dissipation) standard model, the converter control input used to provide robust system stability is obtained, so that the energy at the system equilibrium point reaches a minimum value.

[0006] The objective of this invention is achieved by at least one of the following technical solutions.

[0007] A passive robust stability control method for offshore wind power DC transmission systems includes the following steps:

[0008] S1. Based on Kirchhoff's voltage law, a mathematical model of the voltage source converter (VSC) in the offshore wind power flexible DC grid-connected system is obtained in the stationary coordinate system.

[0009] S2. Considering modeling errors, the mathematical model in the stationary coordinate system obtained in step S1 is transformed into a differential equation in the dq rotating coordinate system using the equal Park transformation.

[0010] S3. By setting a positive definite tracking gain value, the real-time tracking error can be ensured to approach 0 within a finite time, thereby designing a real-time tracking equation for the comprehensive disturbance term and realizing accurate tracking of the modeling error in the differential equation under the dq rotating coordinate system.

[0011] S4. Derive the mathematical model of the voltage source converter (VSC) into differential equation form under the PCHD (Port-Controlled Hamiltonian with Dissipation) standard model;

[0012] S5. Construct the expected energy function of the PCHD standard model;

[0013] S6. Based on the system's desired energy function, derive the converter control input used to provide robust system stability, so that the energy of the system at the equilibrium point reaches a minimum value, thereby realizing passive robust control of the voltage source converter of the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking.

[0014] Furthermore, in step S1, a mathematical model of the voltage source converter of the offshore wind power flexible DC grid-connected system in the stationary coordinate system is written based on Kirchhoff's voltage law, as follows:

[0015] For voltage source converters (VSCs) in flexible DC grid-connected offshore wind power systems, U s and i s These represent the AC side voltage and current of the voltage source converter, U. c U is the output voltage of the voltage source converter; sa U sb U sc U s The instantaneous values ​​of phases A, B, and C, i a i b i c i s The instantaneous values ​​of phases A, B, and C, U ca U cb U cc U c The instantaneous values ​​of phases A, B, and C; assuming the three-phase voltages in the voltage source converter (VSC) are symmetrical, and neglecting the switching losses of the converter; based on the structure of the voltage source converter, using Kirchhoff's voltage law, the differential equation of VSC in the three-phase stationary coordinate system can be obtained as follows:

[0016]

[0017] Where L is the equivalent inductance of the converter, and R is the equivalent resistance of the converter.

[0018] Furthermore, in step S2, an equal Park transformation is used to convert the time-varying AC term in equation (1) into a constant DC term. Equation (1) is then transformed by Park and rewritten in matrix form, as follows:

[0019]

[0020] Among them, U sd U sq They are U s The d-axis and q-axis components in the dq coordinate system, U cd U cq They are U respectively c The d-axis and q-axis components in the dq coordinate system, i d iq They are i s d-axis and q-axis components in the dq coordinate system.

[0021] Furthermore, since the three-phase voltages are assumed to be symmetrical, the 0-axis component is zero after the Park transformation. After considering modeling errors and external disturbances, the time-domain expression of the mathematical model of the voltage source converter (VSC) is obtained from equation (2):

[0022]

[0023] Among them, w d and w q The system modeling error comprehensive disturbance terms for the d-axis and q-axis are respectively, w d and w q The upper bound of all is w max And satisfy the following relationship:

[0024]

[0025] In the formula, w d (t) and w q (t) represents the system modeling error comprehensive disturbance terms of the d-axis and q-axis at time t, respectively.

[0026] Furthermore, in step S3, by setting a positive definite tracking gain value, it is ensured that the real-time tracking error can approach 0 within a finite time, thereby designing a real-time tracking equation for the comprehensive disturbance term, and realizing accurate tracking of the modeling error in the differential equation under the dq rotating coordinate system, as follows:

[0027] Based on the mathematical model of equation (3), the real-time tracking equation for the comprehensive disturbance term w(t) is as follows:

[0028]

[0029] Among them, the system modeling error combined disturbance term w along the d-axis and q-axis d and w q The real-time tracking values ​​are respectively and The combined disturbance term w for system modeling errors along the d-axis and q-axis d and w q The tracking gain values ​​are k wd With k wq , and k wd >0, k wq >0; The intermediate variables of the real-time tracking equation are respectively and The converter currents i on the d-axis and q-axis represent the currents respectively. d and i qIntermediate variables; further, we can conclude that:

[0030]

[0031] Assuming the interference is constant and bounded, let the tracking error be:

[0032]

[0033] Equation (8) can be further written as:

[0034]

[0035] Calculated from equation (9) e d and e q These represent the tracking errors along the d-axis and q-axis, respectively, e d0 With e q0 These represent the initial tracking errors along the d-axis and q-axis, respectively, because k wd With k wq All are positive numbers, and the real-time tracking value is and It can approximate the actual value within a finite time, if k is increased. wd With k wq The value can speed up the real-time tracking of values ​​and reduce the time to converge to the actual value.

[0036] Furthermore, in step S4, the time-domain expression (3) of the mathematical model of the voltage source converter (VSC) is rewritten as a PCHD (Port-Controlled Hamiltonian with Dissipation) model:

[0037]

[0038] Where x, u, and y represent the state variables, control input variables, and system output variables of the PCHD model, respectively. Let x be the derivative of the state variable x; in the PCHD model, the Hamiltonian function H(x) is defined as the energy function, so that the system output y is passive under the control input variable u, thereby achieving the goal of robust and stable operation; the state variables and control input variables in the derivation of equation (10) are specifically expressed as:

[0039]

[0040] The disturbance is included in the control input, i.e.

[0041] Furthermore, the Hamiltonian function H(x) of the PCHD model is expressed as:

[0042]

[0043] Meanwhile, the interconnection matrix J(x) reflects the internal interconnection of the PCHD model, and the damping matrix... This reflects the dissipation of the PCHD model, and is expressed as follows:

[0044]

[0045] Where ω represents the fundamental frequency.

[0046] Furthermore, in step S5, since the objective of passive control is that the ideal equilibrium point of the PCHD standard model should satisfy asymptotic stability under the control input variable u, where the equilibrium point x * Defined as:

[0047]

[0048] in, i d * i q * Let x1, x2, and i represent respectively. d i q The equilibrium point state value;

[0049] Constructing the interconnection matrix J a Damping matrix and the closed-loop expected energy function H d (x):

[0050]

[0051] Where r1 and r2 are the parameters of the damping matrix, which are manually selected, and x * x and x represent the expected state variable and the actual state variable, respectively.

[0052] Furthermore, this makes the system energy at the equilibrium point extremely small, at which point the closed-loop system can be expressed as:

[0053]

[0054] Among them, J d (x) is the desired interconnection matrix; H is the desired damping matrix; d (x) is the desired energy function;

[0055] Among them, J d (x) and satisfy

[0056]

[0057] Furthermore, in step S6, the converter control input used to provide robust system stability is derived based on the expected energy function of the PCHD standard model, so that the energy of the system at the equilibrium point reaches a minimum value, thereby realizing passive robust control of the voltage source converter of the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking, as follows:

[0058] Based on the system's expected energy function and the PCHD standard model, the following is derived:

[0059]

[0060] Therefore, the control input variable u can be obtained as:

[0061]

[0062] Since the offshore wind power flexible DC grid-connected system is at its equilibrium point at this time, the energy of the offshore wind power flexible DC grid-connected system reaches a minimum value; therefore, the closed-loop system satisfies the condition of asymptotic robust stability; by using this control input u to control the converter, passive robust control of the voltage source converter of the offshore wind power flexible DC grid-connected system can be realized, thereby improving the stable operation capability of the offshore wind power flexible DC grid-connected system under external disturbances.

[0063] Compared with the prior art, the advantages of this invention are:

[0064] This invention proposes a passive robust stability control method for offshore wind power DC transmission systems. It establishes the system dynamic equations considering modeling errors and designs a passive robust control method for the voltage source converter of the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking. This method can significantly improve the system's stable operation capability under external disturbances. Attached Figure Description

[0065] Figure 1 This is a circuit structure diagram of a voltage source converter according to an embodiment of the present invention.

[0066] Figure 2 This is a schematic diagram of the simulation results of the active power of the system under conventional control in an embodiment of the present invention.

[0067] Figure 3 This is a schematic diagram of the simulation results of the active power of the system under the control of the present invention in an embodiment of the present invention.

[0068] Figure 4 This is a schematic diagram of the simulation results of the DC voltage of the system under the control of the present invention in an embodiment of the present invention. Detailed Implementation

[0069] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0070] To address the shortcomings or improvement needs of existing technologies, this invention proposes a passive robust stability control method for offshore wind power DC transmission systems. First, a mathematical model of the voltage source converter in the stationary coordinate system of the offshore wind power flexible DC grid-connected system is written based on Kirchhoff's voltage law. Then, considering modeling errors, an equivalent Park transformation is used to convert this mathematical model into differential equations in the dq rotating coordinate system. Second, by setting a positive definite tracking gain value, the real-time tracking error is ensured to approach zero within a finite time, thereby designing a real-time tracking equation for the comprehensive disturbance term, achieving accurate tracking of the modeling error in the differential equations in the dq rotating coordinate system. Finally, a passive robust control method for the voltage source converter of the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking is designed. By defining the desired energy function under the PCHD (Port-Controlled Hamiltonian with Dissipation) standard model, the converter control input used to provide robust system stability is obtained, minimizing the energy at the system's equilibrium point.

[0071] Example:

[0072] A passive robust stability control method for offshore wind power DC transmission systems includes the following steps:

[0073] S1. Based on Kirchhoff's voltage law, the mathematical model of the voltage source converter (VSC) in the offshore wind power flexible DC grid-connected system in the stationary coordinate system is obtained as follows:

[0074] For example Figure 1 The voltage source converter (VSC) in the offshore wind power flexible DC grid-connected system shown, U s and i s These represent the AC side voltage and current of the voltage source converter, U. c U is the output voltage of the voltage source converter; sa U sb U sc U s The instantaneous values ​​of phases A, B, and C, i a i b i c i s The instantaneous values ​​of phases A, B, and C, U ca U cb U cc U cThe instantaneous values ​​of phases A, B, and C; assuming the three-phase voltages in the voltage source converter (VSC) are symmetrical, and neglecting the switching losses of the converter; based on the structure of the voltage source converter, using Kirchhoff's voltage law, the differential equation of VSC in the three-phase stationary coordinate system can be obtained as follows:

[0075]

[0076] Where L is the equivalent inductance of the converter, and R is the equivalent resistance of the converter.

[0077] S2. Considering modeling errors, the mathematical model in the stationary coordinate system obtained in step S1 is transformed into a differential equation in the dq rotating coordinate system using the equal Park transformation.

[0078] Using the equal Park transformation, the time-varying AC term in equation (1) is converted into a constant DC term. The Park transformation of equation (1) is then performed and rewritten in matrix form, as follows:

[0079]

[0080] Among them, U sd U sq They are U s The d-axis and q-axis components in the dq coordinate system, U cd U cq They are U respectively c The d-axis and q-axis components in the dq coordinate system, i d i q They are i s d-axis and q-axis components in the dq coordinate system.

[0081] Since it is assumed that the three-phase voltages are symmetrical, the 0-axis component is zero after the Park transformation;

[0082] When a disturbance occurs in the system, it will also change the reference value of the inner loop current obtained by the VSC through the outer loop control. This kind of disturbance that affects the power balance is an external factor, so it can be regarded as an external disturbance. Secondly, due to measurement errors or changes in system components over time, the mathematical model parameters of equation (2) will not be accurate and will have a certain error with the actual parameters, so the model has uncertainty. In order to reduce the factors that affect the stability of system operation and control accuracy, it is necessary to study the external disturbances of the system in order to improve the system's ability to cope with sudden situations. Due to the time-varying characteristics of external disturbances and uncertainties in modeling, the disturbance term itself is an AC term with a high-order derivative, which increases the difficulty of tracking the disturbance.

[0083] After considering modeling errors and external disturbances, the time-domain expression of the mathematical model of the voltage source converter (VSC) is obtained from equation (2):

[0084]

[0085] Among them, w d and w q The system modeling error comprehensive disturbance terms for the d-axis and q-axis are respectively, w d and w q The upper bound of all is w max And satisfy the following relationship:

[0086]

[0087] In the formula, w d (t) and w q (t) represents the system modeling error comprehensive disturbance terms of the d-axis and q-axis at time t, respectively.

[0088] The combined disturbance term w for system modeling errors along the d-axis and q-axis d and w q The parameter errors and external power disturbances in the system model can be represented in the time-domain mathematical model. Next, appropriate control methods need to be adopted to reduce the impact of these disturbances on the system. Since it is difficult to measure these disturbances using conventional methods, this invention employs a real-time disturbance tracking method for observational compensation to improve the system's robustness.

[0089] S3. By setting a positive definite tracking gain value, the real-time tracking error can be ensured to approach 0 within a finite time. This allows for the design of a real-time tracking equation for the integrated disturbance term, achieving accurate tracking of the modeling error in the differential equation under the dq rotating coordinate system, as detailed below:

[0090] Based on the mathematical model of equation (3), the real-time tracking equation for the comprehensive disturbance term w(t) is as follows:

[0091]

[0092] Among them, the system modeling error combined disturbance term w along the d-axis and q-axis d and w q The real-time tracking values ​​are respectively and The combined disturbance term w for system modeling errors along the d-axis and q-axis d and w q The tracking gain values ​​are k wd With k wq , and k wd >0, k wq >0; The intermediate variables of the real-time tracking equation are respectively and The converter currents i on the d-axis and q-axis represent the currents respectively. d and iq Intermediate variables; further, we can conclude that:

[0093]

[0094] Assuming the interference is constant and bounded, let the tracking error be:

[0095]

[0096] Equation (8) can be further written as:

[0097]

[0098] Calculated from equation (9) e d and e q These represent the tracking errors along the d-axis and q-axis, respectively, e d0 With e q0 These represent the initial tracking errors along the d-axis and q-axis, respectively, because k wd With k wq All are positive numbers, and the real-time tracking value is and It can approximate the actual value within a finite time, if k is increased. wd With k wq The value of the gain can accelerate the real-time tracking speed and reduce the time to converge to the actual value. Increased noise and saturation effects may be caused by excessive gain.

[0099] S4. Derive the mathematical model of the voltage source converter (VSC) into differential equation form under the PCHD (Port-Controlled Hamiltonian with Dissipation) standard model;

[0100] The time-domain expression (3) of the mathematical model of the voltage source converter (VSC) is rewritten as a PCHD (Port-Controlled Hamiltonian with Dissipation) model:

[0101]

[0102] Where x, u, and y represent the state variables, control input variables, and system output variables of the PCHD model, respectively. Let x be the derivative of the state variable x; in the PCHD model, the Hamiltonian function H(x) is defined as the energy function, so that the system output y is passive under the control input variable u, thereby achieving the goal of robust and stable operation; the state variables and control input variables in the derivation of equation (10) are specifically expressed as:

[0103]

[0104] The disturbance is included in the control input, i.e.

[0105] Furthermore, the Hamiltonian function H(x) of the PCHD model is expressed as:

[0106]

[0107] Meanwhile, the interconnection matrix J(x) reflects the internal interconnection of the PCHD model, and the damping matrix... This reflects the dissipation of the PCHD model, and is expressed as follows:

[0108]

[0109] Where ω represents the fundamental frequency.

[0110] S5. Construct the expected energy function of the PCHD standard model;

[0111] Since the objective of passive control is to achieve asymptotic stability at the ideal equilibrium point of the PCHD standard model under the control input variable u, where the equilibrium point x * Defined as:

[0112]

[0113] in, i d * i q * Let x1, x2, and i represent respectively. d i q The equilibrium point state value;

[0114] Constructing the interconnection matrix J a Damping matrix and the closed-loop expected energy function H d (x):

[0115]

[0116] Where r1 and r2 are the parameters of the damping matrix, which are manually selected, and x * x and x represent the expected state variable and the actual state variable, respectively.

[0117] Furthermore, this makes the system energy at the equilibrium point extremely small, at which point the closed-loop system can be expressed as:

[0118]

[0119] Among them, J d(x) is the desired interconnection matrix; H is the desired damping matrix; d (x) is the desired energy function;

[0120] Among them, J d (x) and satisfy

[0121]

[0122] S6. Based on the system's desired energy function, derive the converter control input used to provide robust system stability, so that the energy at the system's equilibrium point is minimized. This achieves passive robust control of the voltage source converter in the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking, as detailed below:

[0123] Based on the system's expected energy function and the PCHD standard model, the following is derived:

[0124]

[0125] Therefore, the control input variable u can be obtained as:

[0126]

[0127] Since the offshore wind power flexible DC grid-connected system is at its equilibrium point at this time, the energy of the offshore wind power flexible DC grid-connected system reaches a minimum value; therefore, the closed-loop system satisfies the condition of asymptotic robust stability; by using this control input u to control the converter, passive robust control of the voltage source converter of the offshore wind power flexible DC grid-connected system can be realized, thereby improving the stable operation capability of the offshore wind power flexible DC grid-connected system under external disturbances.

[0128] In this embodiment, to verify that the adaptive passive robust control strategy has better dynamic response performance than PI control, a simulation model of an offshore wind power flexible DC grid-connected system was constructed in PSCAD / EMTDC. The voltage source converter (VSC) adopts a three-phase two-level circuit structure, with a system AC voltage of 110kV and a frequency of 50Hz. The transformer uses a Yy connection with a turns ratio of k1 / k2 = 110 / 10kV. The system transmission power is set to change after 4 seconds. The simulation results of the system active power under conventional control are as follows: Figure 2 As shown.

[0129] Example 2:

[0130] In this embodiment, a simulation model of an offshore wind power flexible DC grid-connected system was constructed using PSCAD / EMTDC. The voltage source converter (VSC) adopts a three-phase two-level circuit structure, with a system AC voltage of 110kV and a frequency of 50Hz. The transformer uses a Yy connection with a turns ratio of k1 / k2 = 110 / 10kV. The system's transmitted power is set to change after 4 seconds. The simulation results of the active power of the system under the proposed control are as follows: Figure 3 As shown.

[0131] Example 3:

[0132] In this embodiment, a simulation model of an offshore wind power flexible DC grid-connected system was constructed using PSCAD / EMTDC. The voltage source converter (VSC) adopts a three-phase two-level circuit structure, with a system AC voltage of 110kV and a frequency of 50Hz. The transformer uses a Yy connection with a turns ratio of k1 / k2 = 110 / 10kV. The system's transmitted power is set to change every 4 seconds. The simulation results of the DC voltage of the system under the proposed control are as follows: Figure 4 As shown.

[0133] The simulation results above show that the method proposed in this invention has better dynamic response characteristics, verifying the effectiveness of the control strategy proposed in this invention.

[0134] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A passive robust stability control method for offshore wind power DC transmission systems, characterized in that, Includes the following steps: S1. Based on Kirchhoff's voltage law, a mathematical model of the voltage source converter in the stationary coordinate system of the flexible DC grid-connected offshore wind power system is obtained. For voltage source converters (VSCs) in offshore wind power flexible DC grid-connected systems. U s and i s These represent the AC side voltage and current of the voltage source converter, respectively. U c This refers to the output voltage of the voltage source converter. U sa , U sb , U sc They are respectively U s The instantaneous values ​​of phases A, B, and C. i a , i b , i c They are respectively i s The instantaneous values ​​of phases A, B, and C. U ca , U cb , U cc They are respectively U c The instantaneous values ​​of phases A, B, and C are given; assuming the three-phase voltages in the voltage source converter (VSC) are symmetrical, and neglecting the switching losses of the converter; based on the structure of the voltage source converter, using Kirchhoff's voltage law, the differential equation of VSC in the three-phase stationary coordinate system can be derived as follows: (1) wherein, L L is the equivalent inductance value of the converter, and R is the equivalent resistance of the converter. S2. Considering modeling errors, the mathematical model in the stationary coordinate system obtained in step S1 is transformed into a differential equation in the dq rotating coordinate system using the equal Park transformation. The time-varying AC term in equation (1) is converted into a constant DC term using the equal Park transformation. Equation (1) is then transformed by Park and rewritten in matrix form, as follows: (2) in, U sd , U sq They are U s d-axis and q-axis components in the dq coordinate system U cd , U cq They are respectively U c d-axis and q-axis components in the dq coordinate system i d , i q They are i s d-axis and q-axis components in the dq coordinate system; S3. By setting a positive definite tracking gain value, the real-time tracking error can be ensured to approach 0 within a finite time, thereby designing a real-time tracking equation for the comprehensive disturbance term and realizing accurate tracking of the modeling error in the differential equation under the dq rotating coordinate system; Since it is assumed that the three-phase voltage is symmetrical, the 0-axis component is zero after the Park transformation; After considering the modeling error and external disturbance factors, the time-domain expression of the mathematical model of the voltage source converter (VSC) is obtained from equation (2): (3) in, w d and w q These are the combined disturbance terms of system modeling error on the d-axis and q-axis, respectively. w d and w q The upper bound is w max And satisfy the following relationship: (4) In the formula, and respectively represent the system modeling error comprehensive disturbance items of d-axis and q-axis at time t. By setting a positive definite tracking gain value, the real-time tracking error can be ensured to approach zero within a finite time. This allows for the design of a real-time tracking equation for the integrated disturbance term, achieving accurate tracking of the modeling error in the differential equation under the dq rotating coordinate system, as detailed below: According to the mathematical model of equation (3), the real-time tracking equation for the combined disturbance term w(t) is as follows: (6) Among them, the system modeling error combined disturbance term for the d-axis and q-axis w d and w q The real-time tracking values ​​are respectively and System modeling error combined disturbance term for d-axis and q-axis w d and w q The tracking gain values ​​are respectively and ,and , The intermediate variables of the real-time tracking equation are respectively and , representing the converter currents on the d-axis and q-axis, respectively. i d and i q Intermediate variables; further, we can conclude that: (7) Assuming the interference is constant and bounded, let the tracking error be: (8) Equation (8) can be further written as: (9) Calculated from equation (9) , , and They represent d shaft and q Axis tracking error, e d0 and e q0 They represent d shaft and q The initial tracking error of the axis, because and All are positive numbers, and the real-time tracking value is and It can approximate the actual value within a finite time; if it increases... and The value can speed up the real-time tracking of values ​​and reduce the time to converge to the actual value; S4. The mathematical model of the voltage source converter is derived into the differential equation form under the PCHD standard model; the time-domain expression (3) of the mathematical model of the voltage source converter (VSC) is rewritten into the PCHD (Port-Controlled Hamiltonian with Dissipation) model: (10) in, x , u and y These represent the state variables, control input variables, and system output variables of the PCHD model, respectively. State variables x The derivative; in the PCHD model, the Hamiltonian function is defined. H ( x As an energy function, it makes the system output quantity y Controlling input variables u The following is passive, thus achieving the goal of robust and stable operation; the state variables and control input variables in the derivation (10) are specifically expressed as follows: (11) wherein the perturbation quantity is contained in the control input, i.e. , ; The Hamiltonian function of the PCHD model H ( x ) is expressed as: (12) At the same time, the interconnection matrix J x reflects the internal interconnection of the PCHD model, and the damping matrix reflects the dissipation of the PCHD model, and are respectively expressed as:​ (13) wherein denotes the fundamental frequency; S5. Construct the expected energy function of the PCHD standard model; since the objective of passive control is to control the input variable... u Under ideal conditions, the PCHD standard model should achieve asymptotic stability at its equilibrium point, where the equilibrium point... x * Defined as: (14) wherein, , , , respectively represent , , , the equilibrium point state values of Constructing interconnection matrices , damping matrices and closed-loop desired energy functions H d ( x ): (15) where, and are parameters of the artificially valued damping matrix, and are the desired state variable and the actual state variable, respectively; such that the system energy is minimized at the equilibrium point, at which the closed-loop system can be represented as: (16) wherein, is a desired interconnection matrix; is a desired damping matrix; is a desired energy function; wherein and satisfies (17)； S6. Based on the system's expected energy function, the converter control input used to provide robust system stability is derived, so that the energy at the system's equilibrium point is minimized, thereby achieving passive robust control of the voltage source converter in the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking; Based on the expected energy function of the PCHD standard model, the converter control input used to provide robust system stability is derived, so that the energy at the system's equilibrium point is minimized, thereby achieving passive robust control of the voltage source converter in the offshore wind power flexible DC grid-connected system based on real-time disturbance tracking, as detailed below: Based on the system's expected energy function and the PCHD standard model, the following is derived: (18) Thus the control input variable u is given by: (19) Since the offshore wind power flexible DC grid-connected system is at the balance point at this time, the offshore wind power flexible DC grid-connected system energy obtains a minimum value; therefore, the closed-loop system meets the condition of asymptotic robust stability; the control input u The converter is controlled, so as to realize passive robust control of the offshore wind power flexible DC grid-connected system voltage source converter, and improve the stable operation ability of the offshore wind power flexible DC grid-connected system under external disturbance.

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