A method, system, and medium for bias current disturbance rejection in a soft direct current converter

Abstract

The present application relates to the technical field of power conversion control, and particularly relates to a HVDC converter bias current anti-disturbance suppression method, system and medium, the method comprising: collecting an AC side current signal of the HVDC converter, and determining a bias current representation quantity for representing a bias current state; according to a coupling relationship between the bias current representation quantity and a current control process, equivalent the bias current representation quantity to a bias disturbance quantity; constructing an extended state observation object based on the AC side current signal and the bias disturbance quantity, and obtaining a state observation result by observation; generating an anti-disturbance compensation quantity according to the state observation result, and adaptively correcting the anti-disturbance compensation quantity according to the bias current representation quantity; and applying the corrected anti-disturbance compensation quantity to a modulation control quantity to suppress the bias current. Through the present application, the problem that the bias current disturbance caused by the bias current cannot be accurately represented and dynamically compensated in the current control process of the existing HVDC converter, resulting in insufficient bias current suppression effect, is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of power conversion control technology, and in particular to a method, system and medium for suppressing bias current disturbances in a flexible DC converter. Background Technology

[0002] In flexible DC transmission systems, the flexible DC converter typically performs power conversion and regulation between the AC and DC systems. Modular multilevel converters are widely used in flexible DC transmission due to their high output waveform quality, adaptability to high-voltage and high-capacity scenarios, and flexible control. During the operation of a flexible DC converter, the AC side current not only reflects the normal current output state of the converter but may also include bias current components caused by differences in device parameters, control deviations, system disturbances, or changes in operating conditions. This bias current can alter the dynamic response characteristics of the converter's current control process and adversely affect modulation control and power conversion.

[0003] Existing technologies typically control converter current by acquiring current signals and employing conventional current feedback control, fixed parameter compensation, or error adjustment methods. However, these methods often treat bias current as a normal current deviation, failing to adequately characterize its disturbance properties based on the coupling relationship between bias current and the converter current control process. Furthermore, they struggle to monitor and adaptively compensate for dynamic changes in bias disturbances during operation, resulting in insufficient matching between the compensation amount and the actual bias current state, thus affecting the bias current suppression effect. Therefore, existing flexible DC converters suffer from the problem of inaccurately characterizing and dynamically compensating for disturbances caused by bias current during current control, leading to insufficient bias current suppression.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a method, system, and medium for suppressing bias current disturbances in a flexible DC converter, which can effectively solve the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for suppressing bias current disturbances in a flexible DC converter, the method comprising: Acquire the AC side current signal of the flexible DC converter, and determine the bias current characterization quantity used to characterize the bias current state of the flexible DC converter based on the AC side current signal. Based on the coupling relationship between the bias current characterization and the current control process of the flexible DC converter, the bias current characterization is equivalent to the bias disturbance acting on the current control process. An extended state observation object is constructed based on the AC side current signal and the bias disturbance, and the extended state observation object is observed to obtain state observation results including the bias disturbance. Based on the state observation results, an anti-disturbance compensation amount is generated to reduce the impact of the bias disturbance, and the anti-disturbance compensation amount is adaptively corrected based on the bias current characterization. The modified disturbance rejection compensation is applied to the modulation control of the flexible DC converter to suppress the bias current in the flexible DC converter.

[0007] Further, acquiring the AC side current signal and determining the bias current characterization parameters includes: The valve side of the modular multilevel converter in the flexible DC converter is used as the current acquisition location, and the three-phase current signal of the valve side of the modular multilevel converter is acquired. Determine the DC bias current component from the three-phase current signal that can characterize the DC bias state of the modular multilevel converter; The DC bias current component is used as the bias current characterization quantity for subsequent determination of the bias disturbance amount.

[0008] Further, determining the bias perturbation includes: Based on the relationship between the bias current characterization and the current output dynamics of the flexible DC converter, the disturbance effect of the bias current characterization on the current control process is determined. The bias current characterization is equivalent to the system equivalent disturbance acting on the current control process; A current disturbance model is established based on the equivalent disturbance of the system, and the equivalent disturbance of the system is converted into the bias disturbance.

[0009] Furthermore, obtaining the state observation results includes: Based on the AC side current signal and the current disturbance model used to characterize the bias disturbance, the current output, current change rate, and bias disturbance of the flexible DC converter are determined as the state quantities to be observed. The current output, the current change rate, and the bias disturbance are introduced into the linear extended state observer to construct the extended state observation object; The linear extended state observer is used to observe the extended state observation object in real time to obtain the state observation results, including the estimated results of the current output, the current change rate and the bias disturbance.

[0010] Further, generating the disturbance rejection compensation amount includes: Based on the estimated current output and current change rate from the state observation results, the state error feedback quantity is determined. Based on the estimation results of the bias disturbance in the state observation results, determine the disturbance compensation amount used to reduce the influence of the bias disturbance. A linear state error feedback control law is formed based on the state error feedback amount and the disturbance compensation amount, and a voltage compensation command is generated through the linear state error feedback control law. The voltage compensation command is used as the disturbance rejection compensation amount.

[0011] Furthermore, the adaptive correction of the disturbance rejection compensation amount includes: The bias current error is determined based on the aforementioned bias current characterization. The rate of change of bias error is determined based on the change in the bias current error; The bias current error and the rate of change of the bias error are input into the fuzzy controller, and the parameter correction amount used to correct the linear state error feedback control law is obtained through the fuzzy controller.

[0012] Furthermore, the disturbance rejection compensation amount is modified, including: The linear state error feedback control law is adjusted online based on the parameter correction amount used to correct the linear state error feedback control law, so as to obtain the adjusted linear state error feedback control law. The voltage compensation command, which is updated as the disturbance rejection compensation amount, is used by the adjusted linear state error feedback control law, so that the voltage compensation command is corrected as the bias current characterization value changes. The updated voltage compensation command is used as the revised disturbance rejection compensation amount.

[0013] Furthermore, the function of the modulation control quantity includes: Acquire the three-phase modulation wave signal of the flexible DC converter, and use the three-phase modulation wave signal as the modulation control quantity; The corrected anti-interference compensation amount is superimposed on the three-phase modulated wave signal to obtain the compensated three-phase modulated wave signal. The power conversion process of the flexible DC converter is adjusted according to the compensated three-phase modulation wave signal to suppress the bias current corresponding to the bias current characterization quantity.

[0014] A bias current disturbance rejection system for a flexible DC converter, the system comprising: The current characterization determination module acquires the AC side current signal of the flexible DC converter and determines the bias current characterization quantity used to characterize the bias current state of the flexible DC converter based on the AC side current signal. The bias disturbance equivalent module, based on the coupling relationship between the bias current characterization and the current control process of the flexible DC converter, converts the bias current characterization into a bias disturbance acting on the current control process. The extended state observation module constructs an extended state observation object based on the AC side current signal and bias disturbance, and observes the extended state observation object to obtain state observation results including the bias disturbance. The disturbance rejection compensation correction module generates a disturbance rejection compensation amount to reduce the influence of bias disturbance based on the state observation results, and adaptively corrects the disturbance rejection compensation amount based on the bias current characterization. The modulation compensation and suppression module applies the corrected disturbance rejection compensation amount to the modulation control amount of the flexible DC converter to suppress the bias current in the flexible DC converter.

[0015] A computer-readable storage medium storing a computer program, the computer program including program instructions that, when executed by a processor, can implement the aforementioned method for suppressing bias current in a flexible DC converter.

[0016] The technical solution of this invention can achieve the following technical effects: By acquiring the AC side current signal of the flexible DC converter, the bias current characterization quantity is determined. This bias current characterization quantity is then equated to the bias disturbance quantity in the current control process. Based on extended state observation and adaptive disturbance rejection compensation, the corrected compensation quantity is applied to the modulation control quantity, thereby achieving dynamic suppression of the bias current of the flexible DC converter. This effectively solves the problem that existing flexible DC converters are unable to accurately characterize and dynamically compensate for the disturbance caused by the bias current in the current control process, resulting in insufficient bias current suppression effect.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

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

[0019] Figure 1 This is a flowchart illustrating a method for suppressing bias current disturbances in a flexible DC converter. Figure 2 A model diagram of a modular multilevel converter; Figure 3 This is an overall control block diagram of the embodiment solution; Figure 4 This is a block diagram of fuzzy active disturbance rejection control. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] Example 1; like Figure 1 As shown, this application provides a method for suppressing bias current disturbances in a flexible DC converter, the method comprising: S10: Acquire the AC side current signal of the flexible DC converter and determine the bias current characterization quantity used to characterize the bias current state of the flexible DC converter based on the AC side current signal. S20: Based on the coupling relationship between the bias current characterization and the current control process of the flexible DC converter, the bias current characterization is equivalent to the bias disturbance acting on the current control process. S30: Construct an extended state observation object based on the AC side current signal and bias disturbance, and observe the extended state observation object to obtain state observation results including the bias disturbance. S40: Generate an anti-disturbance compensation amount to reduce the impact of bias disturbance based on the state observation results, and adaptively correct the anti-disturbance compensation amount based on the bias current characterization. S50: Apply the corrected disturbance rejection compensation amount to the modulation control amount of the flexible DC converter to suppress the bias current in the flexible DC converter.

[0023] Specifically, this embodiment provides a method for suppressing bias current disturbances in a flexible DC converter. This method can be applied to the control device of a flexible DC converter in a flexible DC transmission system. The flexible DC converter can be a modular multilevel converter. The control device achieves dynamic suppression of bias current by collecting, equivalence of disturbances, state observation, compensation correction and modulation control of the AC side current of the converter.

[0024] Specifically, during the operation of the flexible DC converter, the current signal on the AC side of the flexible DC converter is first acquired. The AC side current signal can be the three-phase current signal on the valve side of the modular multilevel converter. Based on the AC side current signal, a bias current characterization quantity that can reflect the bias current state of the flexible DC converter is extracted or determined. The bias current characterization quantity is used to characterize the bias state generated by the flexible DC converter during the current output process, so that the subsequent control process can no longer be adjusted based solely on the conventional current error, but can instead perform disturbance rejection and suppression based on the bias current state. After obtaining the bias current characterization, the influence of the bias current characterization on the current output dynamics is determined based on the coupling relationship between the bias current characterization and the current control process of the flexible DC converter. The bias current characterization is then equivalent to the bias disturbance acting on the current control process. Through this processing method, the influence of the bias current on the converter current control process can be uniformly incorporated into the disturbance characterization framework, transforming the bias current from a bias state that is difficult to compensate directly into an observable and compensable disturbance object. Subsequently, an extended state observation object is constructed based on the AC side current signal and the bias disturbance. In one specific implementation, the current output, current change rate, and bias disturbance of the flexible DC converter can be used as the state variables to be observed in the extended state observation object. The extended state observation object is then observed in real time using an extended state observer to obtain state observation results including the bias disturbance. The state observation results can reflect both the current output state of the flexible DC converter and the dynamic changes of the bias disturbance during operation. After obtaining the state observation results, an anti-disturbance compensation amount is generated based on the state observation results to reduce the influence of the bias disturbance. In one specific implementation, state error feedback and disturbance compensation can be formed based on the current output estimation results, current change rate estimation results, and bias disturbance estimation results in the state observation results, and a voltage compensation command is generated therefrom. The voltage compensation command serves as the anti-disturbance compensation amount to offset or reduce the influence of the bias disturbance on the current control process. Furthermore, to improve the adaptability of the disturbance rejection compensation amount to changes in operating conditions and bias current, the bias current error is determined based on the bias current characterization, and the bias error change rate is determined based on the change of the bias current error. Then, the disturbance rejection compensation amount is adaptively corrected based on the bias current error and the bias error change rate. In one specific implementation, the bias current error and the bias error change rate can be input into a fuzzy controller, and the control parameter correction amount can be obtained through the fuzzy controller. The control law that generates the disturbance rejection compensation amount is then adjusted online using the control parameter correction amount, so that the corrected disturbance rejection compensation amount can be dynamically updated as the bias current characterization changes. Finally, the corrected disturbance rejection compensation amount is applied to the modulation control amount of the flexible DC converter. In one specific implementation, the corrected disturbance rejection compensation amount can be superimposed on the three-phase modulation wave signal of the flexible DC converter to obtain the compensated modulation control amount. The power conversion process of the flexible DC converter is then adjusted according to the compensated modulation control amount, so that the flexible DC converter can compensate for bias disturbances in real time during operation, thereby suppressing the bias current in the flexible DC converter. The technical solution of this embodiment equates the bias current state to the bias disturbance in the current control process, and combines extended state observation and adaptive disturbance rejection compensation to dynamically suppress the bias disturbance, which can effectively improve the matching between the disturbance rejection compensation and the actual bias current state and improve the bias current suppression effect of the flexible DC converter.

[0025] The technical solution of this invention acquires the AC side current signal of the flexible DC converter to determine the bias current characterization quantity, and equates the bias current characterization quantity to the bias disturbance quantity in the current control process. Based on extended state observation and adaptive disturbance rejection compensation, the corrected compensation quantity is applied to the modulation control quantity, thereby realizing the dynamic suppression of the bias current of the flexible DC converter. This effectively solves the problem that existing flexible DC converters are difficult to accurately characterize and dynamically compensate for the disturbance caused by the bias current in the current control process, resulting in insufficient bias current suppression effect.

[0026] Furthermore, acquiring AC side current signals and determining bias current characterization parameters includes: The valve side of the modular multilevel converter in the flexible DC converter is used as the current acquisition location, and the three-phase current signal of the valve side of the modular multilevel converter is acquired. Determine the DC bias current component from the three-phase current signal that can characterize the DC bias state of the modular multilevel converter; The DC bias current component is used as a characterization of the bias current to help determine the bias disturbance.

[0027] Furthermore, determining the bias disturbance includes: Based on the relationship between the bias current characterization and the dynamic current output of the flexible DC converter, the disturbance effect of the bias current characterization on the current control process is determined. The bias current characterization is equivalent to the system equivalent disturbance acting on the current control process; A current disturbance model is established based on the system equivalent disturbance, and the system equivalent disturbance is used as a bias disturbance.

[0028] As a preferred embodiment of the above, the structure of the modular multilevel controller is as follows: Figure 2 As shown, according to Kirchhoff's current-voltage law, the mathematical model of the modular multilevel converter can be obtained as follows: ; In the formula, j is any one of the three phases, usually a, b, or c; Let j be the phase voltage on the AC side of phase j; The voltage of the upper arm of phase j; The voltage of the lower arm of phase j; Let j be the current in the upper arm of phase j; Let J be the current of the lower arm of phase j. These are the equivalent resistance parameters of the bridge arms. , The equivalent arm resistance of the upper and lower arms of the same phase in a modular multilevel converter is synthesized. The equivalent inductance parameters of the bridge arm are... , The equivalent arm inductance after combining the upper and lower arms of the same phase in a modular multilevel converter; Let be the rate of change of the current in the upper arm of phase j with respect to time; Let be the rate of change of the current in the lower arm of phase j with respect to time; This refers to the voltage at the neutral point or reference point on the AC side of the converter. This is the DC side voltage; Converting the above equation to its direct-axis and quadrature-axis components in a synchronous rotating coordinate system using three-phase alternating current or voltage, and then performing a Laplace transform, yields: ; In the formula, , The valve-side current is in dq-axis coordinates; The differential voltage in dq axis coordinates; The AC system voltage in dq axis coordinates; Synchronous rotational angular velocity; R is the equivalent resistance parameter of the modular multilevel converter in the dq coordinate system; L is the equivalent inductance parameter of the modular multilevel converter in the dq coordinate system; s is the Laplace operator; Based on the principles of automatic control, the mathematical model obtained after decoupling transformation is as follows: ; In the formula This is the reference value for the valve-side current in the dq synchronous rotating coordinate system. Reference value of differential mode voltage of bridge arm under dq axis; This refers to the proportional gain of the current controller; The integral coefficient of the current controller; The AC system voltage along the d-axis in the dq synchronous rotating coordinate system; The AC system voltage along the q-axis in the dq synchronous rotating coordinate system; To synchronize rotational angular velocity; Effective suppression of DC current on the converter transformer valve side is achieved by adding a DC bias suppression circuit to the controller. The strategy involves measuring and extracting the DC bias current from the three-phase AC current on the converter valve side, injecting the extracted DC bias current into the fuzzy active disturbance rejection controller, and superimposing the output onto the original three-phase modulated wave voltage to form a DC bias correction voltage. Figure 3 The diagram shows the overall control structure of this scheme, including AC three-phase current acquisition, DC bias current extraction, fuzzy active disturbance rejection controller compensation, power outer loop, current inner loop, dq / abc transformation, and superimposing the compensation results onto the three-phase modulation wave before entering the nearest level approximation modulation (NLM). The bias current control proposed in this scheme consists of two components: a linear extended observer (LESO) and a linear state error feedback (LSEF), and three parts: fuzzy control. Figure 4 Detailed demonstration Figure 3 The internal structure of the fuzzy active disturbance rejection controller includes a linear extended state observer, a linear state error feedback control law, a fuzzy controller, parameter corrections m1 and m2, a disturbance estimate z3, a control input gain 1 / b0, and a final control output y; the direct control paradigm is: ; in, Let y represent the second derivative of y, where y is the output of the controlled object, which in this scheme corresponds to the output of the DC bias current control loop. To estimate the input gain for control purposes; The control quantity output by the controller can be used in this scheme as a compensation control quantity to suppress DC bias current. The equivalent disturbance of the system is used to characterize the combined disturbance caused by the DC bias current and model uncertainties to the control process; the space state equation for direct control can be obtained as follows: ; In the formula, , , Let x1, x2, and x3 be the first derivatives of the state variables x1, x2, and x3 with respect to time, respectively; x1 is the differential of the output y; x2 is the differential of the output y; x3 is the differential of the output y; and h is the differential of the disturbance f.

[0029] Furthermore, obtaining state observation results includes: Based on the AC side current signal and the current disturbance model used to characterize the bias disturbance, the current output, current change rate and bias disturbance of the flexible DC converter are determined as the state variables to be observed. The current output, current change rate, and bias disturbance are introduced into the linear extended state observer to construct the extended state observation object; The linear extended state observer is used to observe the extended state observation object in real time, and the state observation results include the estimated results of current output, current change rate and bias disturbance.

[0030] Furthermore, generating interference immunity compensation includes: Based on the estimated current output and current change rate from the state observation results, determine the state error feedback quantity; Based on the estimation results of the bias disturbance in the state observation results, determine the disturbance compensation amount used to reduce the influence of the bias disturbance. A linear state error feedback control law is formed based on the state error feedback quantity and the disturbance compensation quantity, and a voltage compensation command is generated through the linear state error feedback control law. Use voltage compensation commands as disturbance rejection compensation quantities.

[0031] As a preferred embodiment of the above, in order to obtain the equivalent disturbance of the DC bias current to the control process in real time, it is necessary to construct a linear extended state observer to estimate the system state. In the linear extended state observer, the output of the controlled object, the rate of change of the output, and the equivalent disturbance of the system are observed as extended states, and the observed states are corrected by feedback using the deviation between the actual output and the estimated output. Thus, the following linear extended state observer equation is obtained: ; In the formula, z1, z2, and z3 are the outputs of LESO, tracking state variables x1, x2, and x3 respectively; β1, β2, and β3 are the state observer parameters. To estimate the input gain for control purposes; The control quantity output by the controller; The actual output of the controlled object; The output quantity estimated for the linear extended state observer; Let z1, z2, and z3 form the observation state vector; Linear state error feedback control law parameter configuration: When the observer converges, z1=e1=y, z2=e2= Where z1 is the estimate of the output y by the linear extended state observer, and z2 is the rate of change of the output by the linear extended state observer. Given the estimated value, e1 is the bias current error, and e2 is the rate of change of the bias error, the linear state error feedback control law equation is: ; ; in, The control input generated for the linear state error feedback control law; For the proportional feedback parameter in the linear state error feedback control law; These are the differential feedback parameters in the linear state error feedback control law; This is the estimate of the equivalent disturbance of the system by the linear extended state observer; To control the input gain parameter; Let y be the second derivative of the output quantity y; its corresponding differential equation is: ; in, This is the expression of the output quantity y after undergoing the Laplace transform; For the Laplace operator; This is the corresponding form of the second-order differential in the Laplace field; To control the input amount The expression after Laplace transform; combining the above equations, we get: ,in This is the expression of the reference input r after undergoing the Laplace transform; From the bandwidth method, we can obtain ,in Given the controller bandwidth, combining it with the above equation yields: ; By having equal corresponding coefficients, k p k d The parameters are tuned to: ; Linear expansion observer parameter configuration: The state-space equation of the system can be written as: ; in, Let x be the first derivative of the system state variable with respect to time. For system control input; This is the system output quantity; This is the system state matrix; Input matrix to the system; The system output matrix; the linearly extended observer equation can be written as: ; ; In the formula, This is the state estimation vector for the linearly extended state observer; The first derivative of the state estimation vector z with respect to time; The system output estimated by the linear extended state observer; The observer gain matrix; Output the estimation error; , This is the feedback gain parameter for the output estimation error in the linear extended state observer. This is the feedback gain parameter for estimating the rate of change of the output in the linear extended state observer. The feedback gain parameter is the equivalent system disturbance estimation error in the linear extended state observer. From the above formula, we can obtain: ; ; ; Define the estimation error e as: ; ; in, Let e ​​be the first derivative of the estimation error with respect to time; when the eigenvalues ​​of the matrix A-LC are less than 0, the estimation error e will approach zero as time increases.

[0032] Furthermore, the adaptive correction of disturbance rejection compensation includes: Determine the bias current error based on the bias current characterization; The rate of change of bias error is determined based on the change in bias current error; The bias current error and the rate of change of bias error are input into the fuzzy controller, and the parameter correction amount used to correct the linear state error feedback control law is obtained through the fuzzy controller.

[0033] As a preferred embodiment of the above, the characteristic equation of matrix A-LC is: ; in, These are the characteristic root variables in the characteristic equation; It is the identity matrix; This is the system state matrix; The observer gain matrix; The system output matrix; , , Let the feedback gain parameter be the linear extended state observer; let the characteristic equation be... In the formula Given the bandwidth of the linearly extended state observer, expansion yields: ; By comparing corresponding terms, we can obtain: ; In summary, in traditional linear active disturbance rejection control, the estimated value of the control input gain b0 and the controller bandwidth are determined by the tuning of controller parameters. Linear extended state observer bandwidth Traditional methods typically rely on empirical and trial-and-error approaches, which are time-consuming and struggle to guarantee global optimality. Therefore, fuzzy active disturbance rejection control (ADC) is introduced, using a fuzzy logic system to adaptively adjust parameters online for optimization. and Corresponding control law parameters This overcomes the limitations of traditional methods and improves the control accuracy and robustness of the system under varying operating conditions. This invention uses bias current error and the rate of change of bias error As the input correction value of the fuzzy controller, the parameter correction amount output by the fuzzy controller is... As output, dynamically adjust Where m1 is used to correct the proportional feedback parameter k in the linear state error feedback control law. p m2 is used to correct the differential feedback parameter k in the linear state error feedback control law. d This is to achieve online adaptive adjustment of control parameters. Simultaneously, each variable is divided into seven commonly used linguistic variable levels within its respective domain: {Negative Large (NB), Negative Medium (NM), Negative Small (NS), Zero (ZO), Positive Small (PS), Positive Medium (PM), Positive Large (PM)}. The bias error is then... The fuzzy subset universe of discourse is defined as [-1,1] and the rate of change of bias error. [-5,5], The fuzzy subset theory domain is defined as [-10, 10]. The theoretical domain is defined as [-20, 20]; the fuzzy control rule tables are shown in Table 1 and Table 2: Table 1

[0034] Table 2

[0035] Furthermore, the correction of interference immunity compensation includes: The linear state error feedback control law is adjusted online based on the parameter correction amount used to modify the linear state error feedback control law, and the adjusted linear state error feedback control law is obtained. The voltage compensation command, which is updated as the disturbance rejection compensation amount, is used by the adjusted linear state error feedback control law, so that the voltage compensation command is corrected as the bias current characterization value changes. The updated voltage compensation command is used as the revised disturbance rejection compensation amount.

[0036] As a preferred embodiment of the above, the fuzzy control parameter correction amount and Configuration of parameters k for linear state error feedback control law p k d By adding them together, we can obtain the parameters of the controller of the tuned system: ; in, These are the adjusted proportional feedback parameters; The differential feedback parameters are set; based on the given controller parameters, the final fuzzy active disturbance rejection controller output u is: ; In summary, this scheme provides a method for suppressing DC bias current in flexible DC transmission systems. A current disturbance state observer is constructed for direct bias current control, using the bias current as the input to the state observer and adjusting it using an error feedback controller. Based on this, the error e1 and the error change rate e2 are used as the two input variables of a fuzzy controller, with the control parameter correction values ​​m1 and m2 as the outputs. This achieves the requirement for online adaptive adjustment of LSEF parameters, improving the controller's control effect and anti-interference capability.

[0037] Furthermore, the functions of the modulation control quantity include: Acquire the three-phase modulation wave signal of the flexible DC converter and use the three-phase modulation wave signal as the modulation control quantity; The corrected disturbance rejection compensation is superimposed on the three-phase modulated wave signal to obtain the compensated three-phase modulated wave signal; The power conversion process of the flexible DC converter is adjusted according to the compensated three-phase modulation wave signal to suppress the bias current corresponding to the bias current characterization.

[0038] As a preferred embodiment of the above, after obtaining the corrected disturbance rejection compensation amount, the controller acquires the three-phase modulation wave signal of the main circuit of the flexible DC converter and uses the three-phase modulation wave signal as the modulation control quantity; then, the disturbance rejection compensation amount after dynamic compensation and adaptive correction is superimposed on the three-phase modulation wave signal to form the compensated three-phase modulation wave signal, which is used to generate the DC bias correction voltage; finally, the power conversion process of the flexible DC converter is adjusted according to the compensated three-phase modulation wave signal so that the DC bias correction voltage cancels the DC bias current on the valve side of the flexible DC converter, thereby suppressing the bias current corresponding to the bias current characterization quantity.

[0039] Example 2; Based on the same inventive concept as the flexible DC converter bias current disturbance rejection method in the foregoing embodiments, the present invention also provides a flexible DC converter bias current disturbance rejection system, the system comprising: The current characterization determination module acquires the AC side current signal of the flexible DC converter and determines the bias current characterization quantity used to characterize the bias current state of the flexible DC converter based on the AC side current signal. The bias disturbance equivalent module, based on the coupling relationship between the bias current characterization and the current control process of the flexible DC converter, converts the bias current characterization into a bias disturbance acting on the current control process. The extended state observation module constructs an extended state observation object based on the AC side current signal and bias disturbance, and observes the extended state observation object to obtain state observation results including the bias disturbance. The disturbance rejection compensation correction module generates a disturbance rejection compensation amount to reduce the influence of bias disturbance based on the state observation results, and adaptively corrects the disturbance rejection compensation amount based on the bias current characterization. The modulation compensation and suppression module applies the corrected disturbance rejection compensation amount to the modulation control amount of the flexible DC converter to suppress the bias current in the flexible DC converter.

[0040] The system described above in this invention can effectively implement a method for suppressing bias current disturbances in a flexible DC converter, and the technical effects it can achieve are as described in the above embodiments, which will not be repeated here.

[0041] Example 3; Based on the same inventive concept as the flexible DC converter bias current disturbance suppression method in the foregoing embodiments, the present invention also provides a computer-readable storage medium storing a computer program, the computer program including program instructions, which, when executed by a processor, can implement the flexible DC converter bias current disturbance suppression method.

[0042] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of the application as defined herein, and are to be considered as covering any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A method for suppressing bias current disturbances in a flexible DC converter, characterized in that, The method includes: Acquire the AC side current signal of the flexible DC converter, and determine the bias current characterization quantity used to characterize the bias current state of the flexible DC converter based on the AC side current signal. Based on the coupling relationship between the bias current characterization and the current control process of the flexible DC converter, the bias current characterization is equivalent to the bias disturbance acting on the current control process. An extended state observation object is constructed based on the AC side current signal and the bias disturbance, and the extended state observation object is observed to obtain state observation results including the bias disturbance. Based on the state observation results, an anti-disturbance compensation amount is generated to reduce the impact of the bias disturbance, and the anti-disturbance compensation amount is adaptively corrected based on the bias current characterization. The modified disturbance rejection compensation amount is applied to the modulation control amount of the flexible DC converter to suppress the bias current in the flexible DC converter; Obtaining the state observation results includes: Based on the AC side current signal and the current disturbance model used to characterize the bias disturbance, the current output, current change rate, and bias disturbance of the flexible DC converter are determined as the state quantities to be observed. The current output, the current change rate, and the bias disturbance are introduced into the linear extended state observer to construct the extended state observation object; The linear extended state observer is used to observe the extended state observation object in real time to obtain the state observation results, including the estimated results of the current output, the current change rate and the bias disturbance. Generating the disturbance rejection compensation amount includes: Based on the estimated current output and current change rate from the state observation results, the state error feedback quantity is determined. Based on the estimation results of the bias disturbance in the state observation results, determine the disturbance compensation amount used to reduce the influence of the bias disturbance. A linear state error feedback control law is formed based on the state error feedback amount and the disturbance compensation amount, and a voltage compensation command is generated through the linear state error feedback control law. The voltage compensation command is used as the disturbance rejection compensation amount.

2. The method for suppressing bias current disturbances in a flexible DC converter according to claim 1, characterized in that, Acquiring the AC side current signal and determining the bias current characterization parameters includes: The valve side of the modular multilevel converter in the flexible DC converter is used as the current acquisition location, and the three-phase current signal of the valve side of the modular multilevel converter is acquired. Determine the DC bias current component from the three-phase current signal that can characterize the DC bias state of the modular multilevel converter; The DC bias current component is used as the bias current characterization quantity for subsequent determination of the bias disturbance amount.

3. The method for suppressing bias current disturbances in a flexible DC converter according to claim 1, characterized in that, Determining the bias disturbance includes: Based on the relationship between the bias current characterization and the current output dynamics of the flexible DC converter, the disturbance effect of the bias current characterization on the current control process is determined. The bias current characterization is equivalent to the system equivalent disturbance acting on the current control process; A current disturbance model is established based on the equivalent disturbance of the system, and the equivalent disturbance of the system is converted into the bias disturbance.

4. The method for suppressing bias current disturbances in a flexible DC converter according to claim 1, characterized in that, Adaptive correction of the disturbance rejection compensation amount includes: The bias current error is determined based on the bias current characterization. The rate of change of bias error is determined based on the change in the bias current error; The bias current error and the rate of change of the bias error are input into the fuzzy controller, and the parameter correction amount used to correct the linear state error feedback control law is obtained through the fuzzy controller.

5. The method for suppressing bias current disturbances in a flexible DC converter according to claim 1, characterized in that, The correction of the interference immunity compensation amount includes: The linear state error feedback control law is adjusted online based on the parameter correction amount used to correct the linear state error feedback control law, so as to obtain the adjusted linear state error feedback control law. The voltage compensation command, which is updated as the disturbance rejection compensation amount, is used by the adjusted linear state error feedback control law, so that the voltage compensation command is corrected as the bias current characterization value changes. The updated voltage compensation command is used as the revised disturbance rejection compensation amount.

6. The method for suppressing bias current disturbances in a flexible DC converter according to claim 1, characterized in that, The function of the modulation control quantity includes: Acquire the three-phase modulation wave signal of the flexible DC converter, and use the three-phase modulation wave signal as the modulation control quantity; The corrected anti-interference compensation amount is superimposed on the three-phase modulated wave signal to obtain the compensated three-phase modulated wave signal. The power conversion process of the flexible DC converter is adjusted according to the compensated three-phase modulation wave signal to suppress the bias current corresponding to the bias current characterization quantity.

7. A bias current disturbance rejection system for a flexible DC converter, characterized in that, The system employing the bias current disturbance rejection method for flexible DC converters as described in claim 1, comprises: The current characterization determination module acquires the AC side current signal of the flexible DC converter and determines the bias current characterization quantity used to characterize the bias current state of the flexible DC converter based on the AC side current signal. The bias disturbance equivalent module, based on the coupling relationship between the bias current characterization and the current control process of the flexible DC converter, converts the bias current characterization into a bias disturbance acting on the current control process. The extended state observation module constructs an extended state observation object based on the AC side current signal and bias disturbance, and observes the extended state observation object to obtain state observation results including the bias disturbance. The disturbance rejection compensation correction module generates a disturbance rejection compensation amount to reduce the influence of bias disturbance based on the state observation results, and adaptively corrects the disturbance rejection compensation amount based on the bias current characterization. The modulation compensation and suppression module applies the corrected disturbance rejection compensation amount to the modulation control amount of the flexible DC converter to suppress the bias current in the flexible DC converter.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which includes program instructions that, when executed by a processor, implement the method for suppressing bias current of a flexible DC converter as described in any one of claims 1-6.

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