WO2021047347A1 - 基于自适应自抗扰比例积分的直流输电系统控制方法及系统 - Google Patents

基于自适应自抗扰比例积分的直流输电系统控制方法及系统 Download PDF

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WO2021047347A1
WO2021047347A1 PCT/CN2020/109224 CN2020109224W WO2021047347A1 WO 2021047347 A1 WO2021047347 A1 WO 2021047347A1 CN 2020109224 W CN2020109224 W CN 2020109224W WO 2021047347 A1 WO2021047347 A1 WO 2021047347A1
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control
transmission system
proportional
disturbance
rejection
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PCT/CN2020/109224
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English (en)
French (fr)
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吴通华
郑玉平
王小红
戴魏
李新东
刘其朴
孙国强
赵志强
侯小凡
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国电南瑞科技股份有限公司
国电南瑞南京控制系统有限公司
国家电网有限公司
国网重庆市电力公司
南瑞集团有限公司
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Publication of WO2021047347A1 publication Critical patent/WO2021047347A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • the invention relates to the technical field of direct current transmission system control, in particular to a direct current transmission system control method and system based on adaptive auto-disturbance rejection proportional integral.
  • HVDC transmission is widely used because of its outstanding advantages in the field of cross-regional, large-capacity, asynchronous grid interconnection transmission, and has important strategic significance for promoting my country's "West-to-East power transmission, North-South mutual supply, and national interconnection".
  • the thyristor based on the commutation of the semi-controlled device cannot be turned off through the control gate level and needs to rely on the grid voltage to restore the blocking ability. Therefore, the commutation failure has become a key factor to curb the continued development of DC transmission. Only 1-9 of 2017 In June, commutation failure of DC occurred 20 times due to AC failure in East China. With the increase of DC transmission capacity, short-term power interruption caused by commutation failure seriously threatens the safe and stable operation of the AC system.
  • Commutation failure is related to many factors, such as AC bus voltage, commutation reactance, DC current, conversion ratio of the converter transformer, and advanced firing angle. Among them, the voltage drop caused by the ground fault of the AC bus is the main reason for the commutation failure. Generally speaking, the first commutation failure is unavoidable, and the short-term commutation failure can usually be restored to normal commutation after the fault is cleared. If the fault is not cleared in time, the DC system is prone to continuous commutation failure during the commutation failure recovery process. Continuous commutation failure will cause the DC system to be blocked and power transmission to be interrupted, which will result in the flow of the AC grid and the malfunction of the protection.
  • the current methods to suppress continuous commutation failure are mainly focused on prediction and topology improvement. There are few cases of continuous commutation failure analysis and control strategies to suppress commutation failure. However, the fact is that the DC control link is during the commutation failure period. It has sufficient regulation effect. Compared with suppressing single commutation failure of DC transmission, suppressing continuous commutation failure is more conducive to improving system stability.
  • One method is to add a virtual resistance module to the control system to limit the rapid increase of the DC current during the system recovery phase after the commutation failure, so as to suppress the continuous commutation failure, and it has a certain effect.
  • the virtual resistance current limiter introduces harmonic currents into the control link, causing large fluctuations in the current command.
  • Another method is to design a DC current self-regulation based on the lack of virtual commutation area based on the sag of the commutation voltage and the surge of the DC current after the fault occurs, so as to cause a gap in the time area of the commutation voltage.
  • this method requires an integral delay of the virtual commutation time ⁇ t, which makes the control command unable to respond in time, which affects its suppression of continuous commutation failure.
  • the other entry point to suppress the commutation failure is to analyze the low-voltage current-limiting link.
  • ADRC Auto Disturbance Rejection Control
  • this method does not take into account the impact of the high-frequency flutter and communication delay caused by the discrete system on the differential tracker, and this method is not suitable for improving the commutation failure problem of the DC transmission system. Improving the anti-disturbance control module.
  • the present invention proposes a DC transmission system control method and system based on adaptive auto-disturbance-rejection proportional integral, and applies the adaptive auto-disturbance-rejection proportional-integral controller to the constant current on the rectifier side of the DC system
  • the control and the constant turn-off angle control on the inverter side improve the dynamic response speed and robust performance of the system when dealing with a wide range of disturbances, and effectively suppress the continuous commutation failure in the HVDC transmission system.
  • the present invention provides a DC transmission system control method based on adaptive auto-disturbance rejection proportional integral, which is characterized in that it includes the following steps:
  • Discrete processing is carried out for the auto-disturbance-rejection proportional-integral controller to obtain an adaptive auto-disturbance-rejection proportional-integral controller;
  • the constant current control on the rectifier side and the constant cut-off angle control on the inverter side in the DC system are realized.
  • the discretization processing is performed on the auto-disturbance-rejection proportional-integral controller, and obtaining the adaptive auto-disturbance-rejection proportional-integral controller includes:
  • the active disturbance rejection proportional integral controller consists of three important parts: tracking differentiator TD, extended state observer ESO and nonlinear state error feedback structure NLSEF, v(t) is the input signal, TD tracks and softens the input signal to obtain
  • the generalized differential signals of each order v 1 (t)...v n (t), z(t) are the output signals of the extended state observer, which include n+1 output signals z 1 (t),..., z n + 1 (t), e (t) is the error signal, the error signal corresponding to each order of e 1 (t), ..., e n (t), u (t) as a control signal, w (t ) Is the disturbance signal, and y(t) is the output signal;
  • the specific algorithm of the adaptive active disturbance rejection proportional integral controller SAADR-PI can be expressed as:
  • v 1 (k) is the first-order differential signal obtained at TD at k sampling time, which is a differentiable smooth signal
  • v 2 (k) dv 1 (k)/dt
  • v 2 (k) is k sampling time TD
  • the second-order differential signal obtained v 1 (k+1) is the first-order differential signal obtained at TD at k+1 sampling time
  • h is the integration step
  • h 0 is the parameter that determines the filtering effect when the input signal is contaminated by noise
  • fhan The actual parameter r in the function is the input adjustment parameter;
  • the fhan(v 1 ,v 2 ,r,h) function is:
  • v 1 and v 2 represent the two formal parameters of the fhan function.
  • v 1 (k)-v(k) and v 2 (k) are passed as actual parameters to the fhan function call;
  • fhan function The formal parameters r and h in are adjustment parameters; d, d 0 , y, a and a 0 in the fhan function are only used as intermediate variables to participate in some operations within the function, and have no specific practical meaning;
  • z 1 (k), z 2 (k) indicate that the ESO at sampling time k corresponds to the system state observation value of y(k) and first-order y 1 (k), z 1 (k) tracks y(k), z 2 (k) Tracking the first-order y 1 (k), z 3 (k) represents the observed value of the extended state of the ESO at the k sampling time, which is the result of the extended state observer tracking the object's uncertain factors and external disturbance information; e(k) represents the error between the first-order system state observation value z 1 (k) and the output y(k) at sampling time k; ⁇ 01 , ⁇ 02 , ⁇ 01 , ⁇ 02 , ⁇ 03 , and ⁇ 0 are time k
  • the actual adjustment parameter called by the fal function, b 0 is the estimated value of the uncertain function b;
  • the fal function used in the formula is a special nonlinear structure, and the fal function expression is as follows:
  • e, ⁇ , ⁇ represent the three formal parameters of the fal function
  • the formal parameter e represents the error signal of the incoming function
  • the formal parameter ⁇ is a constant that affects the tracking effect
  • the formal parameter ⁇ is a constant that affects the filtering effect
  • e 1 (k) and e 2 (k) are the transitional processes v 1 (k) and v 2 (k) arranged at time k and the system output estimates z 1 (k) and z 2 (k).
  • First-order error and second-order error, u(k) is the control signal at time k.
  • the non-linear actual parameters ⁇ 1 , ⁇ 2 , ⁇ and the actual parameters k P , k D are selected to realize the non-linearity of the "integral series" object. Linear control.
  • the realization of the constant current control on the rectifier side and the constant cut-off angle control on the inverter side in the DC system based on the adaptive active disturbance rejection proportional integral controller includes:
  • the constant current control target on the rectifier side and the constant turn-off angle control target on the inverter side in the DC system are realized.
  • obtaining the mathematical model of the DC transmission system includes:
  • L dr ⁇ is the total impedance on the rectifier side
  • X r is the commutation reactance on the rectifier side
  • L di ⁇ is the total impedance on the inverter side
  • X i is the commutation reactance on the inverter side
  • C dc is the DC capacitor
  • V ar is the AC on the rectifier side.
  • Bus voltage R d is the DC resistance
  • V ai is the inverter side AC bus voltage
  • I dr is the rectifier side DC current
  • V c is the DC capacitor voltage
  • I di is the inverter side DC current
  • ⁇ is the rectifier side lagging trigger angle
  • ⁇ is the leading trigger angle of the inverter side;
  • T ⁇ and T ⁇ represent the ⁇ and ⁇ trigger delay time output by the control links of the rectifier side and the inverter side
  • ⁇ 0 and ⁇ 0 are the reference values for the lagging trigger angle of the rectifier side and the leading trigger angle of the inverter side.
  • determining the constant current control target on the rectifier side and the constant turn-off angle control target on the inverter side includes:
  • the control target is that the rectifier side DC current I dr can quickly and accurately track the current command I d_order , and the control target can be transformed into the expected error output y r to be 0, as in the formula ( 9) Shown:
  • Equation (10) For the inverter side of the DC transmission system, the constant cut-off angle control is adopted.
  • the control objective is that the inverter side cut-off angle ⁇ can quickly and accurately track the cut-off angle command ⁇ 0 , that is, the expected error output y i is 0, such as Equation (10) shows:
  • the realization of the constant current control target on the rectifier side and the constant turn-off angle control target on the inverter side in the DC system based on the adaptive active disturbance rejection proportional integral controller includes:
  • Equation 12 satisfies the SAADR-PI standard type, and the derivation of equations (11) ⁇ (14) realizes the use of second-order SAADR-PI as the constant current control strategy of the DC system;
  • the present invention also provides a DC transmission system control system based on adaptive auto-disturbance rejection proportional integral, which is characterized in that it includes a controller design module and a DC transmission system control module;
  • the controller design module is used to discretize the auto-disturbance-rejection proportional-integral controller to obtain an adaptive auto-disturbance-rejection proportional-integral controller;
  • the DC transmission system control module is used to realize the constant current control on the rectifier side and the constant cut-off angle control on the inverter side in the DC system based on the adaptive auto-disturbance rejection proportional integral controller.
  • the beneficial effect achieved by the present invention is: the present invention redesigns the adaptive auto-disturbance rejection proportional integral controller for the PI controller in the traditional control framework, and takes into account that the discrete system gives the differential tracker
  • the high frequency chattering and communication delay can automatically adjust the PI parameters through the fal function to keep the system adaptive.
  • the discretization of the control principle meets the needs of computer simulation. Applying the adaptive auto-disturbance-rejection proportional-integral controller to the constant current control of the rectifier side and the constant cut-off angle control of the inverter side of the DC system can improve the dynamic response speed and robust performance of the system when dealing with a wide range of disturbances. Effectively suppress the continuous commutation failure in the HVDC transmission system.
  • Figure 1 is the control block diagram of the active disturbance rejection algorithm
  • Figure 2 is the main topology diagram of the CIGRE HVDC test model
  • Figure 3 is a Cigre HVDC control block diagram using linear PI control
  • Figure 4 is a closed-loop control block diagram of the HVDC transmission system using SAADR-PI controller
  • Figure 8 is a statistical diagram of single-phase ground fault simulation results under different ground reactance and fault time
  • Figure 9 is a statistical diagram of simulation results of two-phase short-circuit faults under different ground reactance and fault time
  • Figure 10 is a statistical diagram of the simulation results of a two-phase short-circuit ground fault under different ground reactance and fault time.
  • a DC transmission system control method based on adaptive auto-disturbance rejection proportional integral of the present invention includes the following steps:
  • Step 1 Discretize the auto-disturbance-rejection proportional-integral controller to obtain an adaptive auto-disturbance-rejection proportional-integral controller (SAADR-PI).
  • SAADR-PI adaptive auto-disturbance-rejection proportional-integral controller
  • the PI parameters can be automatically adjusted through the fal function, and on the other hand, it is discretized Process to meet the needs of computer simulation;
  • Active disturbance rejection proportional integral controller is composed of three important parts: Tracking Differentiator (TD), Extended State Observer (ESO) and Nonlinear State Error Feedback (NLSEF) .
  • TD Tracking Differentiator
  • ESO Extended State Observer
  • NLSEF Nonlinear State Error Feedback
  • SAADR-PI adaptive active disturbance rejection proportional integral controller
  • TD represents the n-order tracking differentiator
  • ESO represents the n+1-order extended state observer
  • NLSEF represents the n-th order nonlinear state error feedback structure
  • Plant represents the nonlinear uncertain object
  • v(t) is the input signal
  • TD Track and soften the input signal get its generalized differential signals v 1 (t)...v n (t)
  • z(t) is the output signal of the extended state observer, which contains n+1 output signals z 1 (t), ..., z n + 1 (t)
  • e (t) is the error signal
  • u(t) is the control signal
  • w(t) is the disturbance signal
  • y(t) is the output signal.
  • the constant current control of the DC transmission control system can be controlled by the first-order system of the SAADR-PI controller, and the constant turn-off angle control can be controlled by the second-order system of the SAADR-PI controller.
  • the SAADR-PI controller is applied to the feasibility analysis of the DC transmission system, so the reasoning process of the n-order system will not be repeated. Only the second-order system is used as an example for reasoning.
  • the second-order control system of the SAADR-PI controller is In the formula, f, w, and b functions are all uncertain functions, and y represents output.
  • the specific algorithm of SAADR-PI controller can be expressed as:
  • v 1 (k) is the first-order differential signal obtained at TD at k sampling time, which is a differentiable smooth signal
  • v 2 (k) dv 1 (k)/dt
  • v 2 (k) is k sampling time TD
  • the second-order differential signal obtained v 1 (k+1) is the first-order differential signal obtained at TD at k+1 sampling time
  • h is the integration step
  • h 0 is the parameter that determines the filtering effect when the input signal is contaminated by noise
  • fhan The actual parameter r in the function is the input adjustment parameter.
  • the fhan(v 1 ,v 2 ,r,h) function is:
  • v 1 and v 2 represent the two formal parameters of the fhan function.
  • v 1 (k)-v(k) and v 2 (k) are passed as actual parameters to the fhan function call.
  • the formal parameters r and h in the fhan function are adjustment parameters.
  • the d, d 0 , y, a and a 0 in the fhan function are only used as intermediate variables to participate in some operations inside the function, and have no specific practical meaning.
  • z 1 (k), z 2 (k) indicate that the ESO at sampling time k corresponds to the system state observation value of y(k) and first-order y 1 (k), z 1 (k) tracks y(k), z 2 (k) Tracking the first-order y 1 (k), z 3 (k) represents the observed value of the extended state of the ESO at the sampling time k, which is the result of the extended state observer tracking the object's uncertain factors and external disturbance information.
  • e(k) represents the error between the first-order system state observation value z 1 (k) and the output y(k) at the sampling time k.
  • ⁇ 01 , ⁇ 02 , ⁇ 01 , ⁇ 02 , ⁇ 03 , ⁇ 0 are the actual adjustment parameters called by the fal function at time k
  • b 0 is the estimated value of the uncertain function b.
  • the fal function used in the formula is a special non-linear structure, which is the core part of ESO.
  • the parameters of the extended state observer can be selected appropriately through tracking, which has good adaptability.
  • the fal function expression is as follows:
  • e, ⁇ , ⁇ represent the three formal parameters of the fal function
  • the formal parameter e represents the error signal of the incoming function
  • the formal parameter ⁇ is a constant related to the tracking effect, which is inversely proportional to the tracking effect, but it decreases
  • the filtering effect will become worse
  • the formal parameter ⁇ is a constant that affects the filtering effect, which is proportional to the filtering effect, but its increase also increases the tracking delay.
  • e 1 (k), e 2 (k) are the transitional processes v 1 (k), v 2 (k) arranged at time k and the system output estimates z 1 (k), z 2 (k).
  • First-order error and second-order error, u(k) is the control signal at time k.
  • the non-linear actual parameters ⁇ 1 , ⁇ 2 , ⁇ and the actual parameters k P , k D are selected to realize the non-linearity of the "integral series" object. Linear control.
  • Step 2 Establish a corresponding mathematical model for the HVDC transmission system
  • T ⁇ and T ⁇ represent the ⁇ and ⁇ trigger delay time output by the control links of the rectifier side and the inverter side
  • ⁇ 0 and ⁇ 0 are the reference values for the lagging trigger angle of the rectifier side and the leading trigger angle of the inverter side.
  • Step 3 Based on the mathematical model of the HVDC transmission system derived in Step 2, in order to achieve the control purpose of the DC system, the control objectives of the rectifier side and the inverter side are determined as follows:
  • the control target is that the rectifier side DC current I dr can quickly and accurately track the current command I d_order , and the control target can be transformed into the expected error output y r to be 0, as in the formula ( 9) Shown:
  • Equation (10) For the inverter side of the DC transmission system, the constant cut-off angle control is adopted.
  • the control objective is that the inverter side cut-off angle ⁇ can quickly and accurately track the cut-off angle command ⁇ 0 , that is, the expected error output y i is 0, such as Equation (10) shows:
  • Step 4 Based on the SAADR-PI controller algorithm deduced in step 1, through the deformation and derivation of the DC system detailed model formula obtained in step 2, and closely combining with the control target determined in step 3, the SAADR-PI controller algorithm is analyzed The feasibility of applying to DC transmission system.
  • Equation 12 satisfies the SAADR-PI standard type, and the derivation of equations (11) ⁇ (14) realizes the use of second-order SAADR-PI as the constant current control strategy of the DC system.
  • Step 5 Based on the DC system control target in Step 3 and the applicability of the SAADR-PI controller verified in Step 4 in the DC control system, replace the original linear PI controller of the HVDC transmission system with the SAADR-PI controller.
  • FIG. 3 in the accompanying drawings is a high-voltage DC transmission control system using traditional linear PI control, which mainly includes low-voltage current limiter (Voltage Dependent Current Order Limiter, VDCOL), DC current control (Current Control Amplifier, CCA), and DC voltage controller ( Voltage Control Amplifier (VCA), Constant Extinction Angle (CEA) control, and other trigger limit links, etc.
  • VDCOL Voltage Dependent Current Order Limiter
  • CCA Current Control Amplifier
  • VCA Voltage Control Amplifier
  • CEA Constant Extinction Angle
  • I d_rec represents the DC current on the rectifier side, which is different from the DC control command I do_rec
  • the error value is input to the traditional linear PI controller (the dashed box in Figure 3 represents the part) to achieve constant current control on the rectifier side.
  • ⁇ _inv represents the switch-off angle of the inverter side, which is different from the set switch-off angle, and the error value enters the traditional linear PI controller for adjustment to realize the fixed switch-off angle control of the inverter side.
  • the International Conference on Large Power Grids (CIGRE) High Voltage Direct Current Transmission (HVDC) Standard Test Model (CIGRE HVDC) is the first standard model for HVDC control research proposed by the HVDC System Control Working Group of the HVDC Tie Line Research Committee.
  • the CIGRE HVDC standard test model is built on PSCAD simulation software to verify the effect of the control method provided by the present invention on suppressing the continuous commutation failure of DC transmission.
  • the schematic diagram of the main circuit of the CIGRE HVDC standard test model is shown in Figure 2. The figure shows a double-ended DC with a 12-pulse converter unit and DC unipolar operation.
  • the short circuit ratio (SCR) of the AC system is 2.5.
  • the power supply voltage of the sending end is 383kV
  • the power supply voltage of the receiving end is 215kV.
  • the unit of resistance is ⁇
  • the unit of inductance is H
  • the unit of capacitance is ⁇ F.
  • a grounding fault is applied to the inverter bus on the inverter side, and the adjustable ground inductance value L f is used to simulate the situation where the AC system fault is at different distances from the commutation bus.
  • the smaller the ground inductance value the closer the AC system fault is to the commutation bus. The more serious. Simulate and analyze the response of the following three control methods in different AC system fault cases on the inverter side:
  • Control method I Only use the CIGRE HVDC standard test model control link.
  • Control method II A virtual resistance current limit method is added on the basis of the control link of the CIGRE HVDC standard test model.
  • Control method III the SAADR-PI controller provided by the present invention is adopted.
  • the control method I and control method II are used to compare with the control method III proposed in this paper to verify the effect of the proposed algorithm in suppressing the continuous commutation failure of HVDC transmission. Focus on the response of physical quantities such as turn-off angle, DC current, DC voltage, and DC transmission power after a fault. Among them, the turn-off angle response curve is used to judge whether the DC transmission has failed commutation; the DC current, DC voltage, and transmission power response curves are used to observe the dynamic process during the fault.
  • control method II it is effective to adopt appropriate control methods, such as control method II.
  • the virtual resistance is used to make the VDCL act in advance, but the first commutation failure is still unavoidable.
  • the control method III effectively avoids the first commutation failure and continuous commutation failure. Since the controller does not change the original control frame, the inverter side still adopts the constant cut-off angle control during the failure period, and the DC voltage is always constant during the AC voltage drop. About 0.9pu, the power level is also 0.9pu, but the rated operating point is restored within 0.1s after the fault is cleared, which reflects the effective tracking ability of the SAADR-PI controller and meets the actual project operation needs.
  • Figures 8 to 10 show the statistics of simulation results under three asymmetric faults: single-phase grounding, two-phase short-circuit and two-phase short-circuit grounding.
  • the initial time is a cycle of 20ms, stepped every 2ms, from 4s to 4.018s.
  • the ground reactance varies from 0.5H to 1.5H.
  • the present invention also provides a direct current transmission system control system based on adaptive auto-disturbance rejection proportional integral, which is characterized by a controller design module and a direct current transmission system control module;
  • the controller design module is used to discretize the auto-disturbance-rejection proportional-integral controller to obtain an adaptive auto-disturbance-rejection proportional-integral controller;
  • the DC transmission system control module is used to realize the constant current control on the rectifier side and the constant cut-off angle control on the inverter side in the DC system based on the adaptive auto-disturbance rejection proportional integral controller.
  • the invention improves the original linear control system of the high-voltage direct current transmission system, effectively improves the performance of the control system, and improves the commutation failure problem existing in the system.
  • a DC transmission system control strategy based on the adaptive auto disturbance rejection proportional integral method is designed to improve the system The accuracy of tracking the trigger angle command under internal and external disturbances.
  • this application can be provided as methods, systems, or computer program products. Therefore, this application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.
  • computer-usable storage media including but not limited to disk storage, CD-ROM, optical storage, etc.
  • These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device.
  • the device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.
  • These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment.
  • the instructions provide steps for implementing the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

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Abstract

本发明公开了一种基于自适应自抗扰比例积分的直流输电系统控制方法及系统，方法包括以下步骤：针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器；基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制。本发明将自适应自抗扰比例积分控制器运用在直流系统的整流侧定电流控制以及逆变侧的定关断角控制，提高系统应对大范围扰动时的动态响应速度和鲁棒性能，有效抑制高压直流输电系统中的连续换相失败。

Description

基于自适应自抗扰比例积分的直流输电系统控制方法及系统 技术领域
本发明涉及直流输电系统控制技术领域，具体涉及一种基于自适应自抗扰比例积分的直流输电系统控制方法及系统。
背景技术
高压直流输电以其在跨区域、大容量、异步电网互联输电领域具有突出优点而被广泛应用，对于推广我国“西电东送、南北互供、全国联网”具有重要战略意义。然而，基于半控型器件换相的晶闸管无法通过控制门级使其关断，需要依靠电网电压恢复阻断能力，因此换相失败成为遏制直流输电继续发展的关键因素，仅2017年1—9月，中国华东地区因交流故障导致直流发生换相失败20次。而随着直流传输容量的增大，由换相失败引发的短暂功率中断等问题严重威胁交流系统的安全稳定运行。
换相失败与很多因素有关，例如交流母线电压、换相电抗、直流电流、换流变压器变比、超前触发角等。其中交流母线由于接地故障导致的电压跌落是引起换相失败的主要原因。一般而言，首次换相失败难以避免，而短时的换相失败在故障清除后，通常能够恢复正常换相。若故障未及时清除，直流系统在换相失败恢复过程当中极易出现连续换相失败。连续换相失败会造成直流系统闭锁、功率传输中断，从而导致交流电网潮流窜动、保护误动作。
目前抑制连续换相失败的方法主要集中在预测和拓扑结构改进上，对连续换相失败分析和通过控制策略来抑制换相失败的情况较少，然而事实情况是直流控制环节在换相失败期间有充分的调节作用，相比于抑制直流输电单次换相 失败，抑制连续换相失败更有利于提高系统稳定性。一种方法是通过在控制系统中添加虚拟电阻模块，在换相失败后的系统恢复阶段，通过限制直流电流快速增大，来抑制连续换相失败，且有一定的效果。然而，虚拟电阻电流限制器将谐波电流引入了控制环节，使电流指令产生较大波动，因此在不对称故障下应用时，此方法会受到一定的制约。另外一种方法是，根据故障发生后会出现换相电压的暂降以及直流电流的激增，以导致换相电压时间面积出现缺口，从而设计一种基于虚拟换相面积缺乏量的直流电流自调节方法。然而该方法需要经过虚拟换相时长Δt的积分延时，使得控制指令不能及时响应，影响其对连续换相失败的抑制。抑制换相失败的其他切入点是从低压限流环节进行分析，这种方法认为输入量直流电压的剧烈波动是造成触发角指令波动的主要原因，从而引发连续换相失败，而变化相对缓慢的交流母线电压更适合作为输入量。然而，这种方法没有认识到引发电气量波动的内在机理。
上面所述的几种控制策略没能从机理上对连续换相失败问题进行改进，高压直流输电系统在受到扰动时表现出非线性、多变量强耦合特性，而传统控制框架中PI控制是典型的线性控制，因此需要重新设计控制器以提高暂态期间直流控制系统的响应能力。
自抗扰控制(Auto Disturbance Rejection Control，ADRC)是一种不依赖被控对象精确数学模型的新型控制技术，能自动检测系统受到的内外扰动，并及时补偿被控对象，即使控制对象遇到不确定性扰动或者参数发生变化时也能收到良好的控制效果，具有较强的适应性和鲁棒性，ADRC已在火电机组汽门和励磁调节中获得一些应用。对于自抗扰技术应用在高压直流输电系统方面，自抗扰控制利用扩张状态观测器提取扰动信号，并补偿到输入中，获得了良好的 控制效果。但是此方法未考虑到离散系统给微分跟踪器带来的高频颤振和通信时延带来的影响，且该方法不适用于改善直流输电系统的换相失败问题，因此需要对现有自抗扰控制模块进行改进。
发明内容
本发明为了克服现有技术中的不足，提出一种基于自适应自抗扰比例积分的直流输电系统控制方法及系统，将自适应自抗扰比例积分控制器运用在直流系统的整流侧定电流控制以及逆变侧的定关断角控制，提高系统应对大范围扰动时的动态响应速度和鲁棒性能，有效抑制高压直流输电系统中的连续换相失败。
为解决上述技术问题，本发明提供了一种基于自适应自抗扰比例积分的直流输电系统控制方法，其特征是，包括以下步骤：
针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器；
基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制。
进一步的，所述针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器包括：
自抗扰比例积分控制器由三个重要部分组成：跟踪微分器TD、扩张状态观测器ESO和非线性状态误差反馈结构NLSEF，v(t)为输入信号，TD跟踪并柔化输入信号，得到其各阶广义微分信号v 1(t)...v n(t)，z(t)为扩张状态观测器输出信号，其包含n+1个输出信号z 1(t),...,z n+1(t)，e(t)为误差信号，对应的各阶误差信号为e 1(t),...,e n(t)，u(t)为控制信号，w(t)为扰动信号，y(t)为输出信号；
针对自抗扰比例积分控制器进行了离散化处理；
自适应自抗扰比例积分控制器SAADR-PI的具体算法可表示为：
(1)根据离散化需求，设v(k)是k采样时刻对应的输入信号，引入fhan函数并对原有自抗扰比例积分控制器中的微分器TD进行离散化处理，v(k)经过微分器TD便可以获得二阶系统下的各阶微分信号：
Figure PCTCN2020109224-appb-000001
其中，v 1(k)是k采样时刻TD获得的1阶微分信号，是可微的光滑信号，v 2(k)＝dv 1(k)/dt，v 2(k)是k采样时刻TD获得的2阶微分信号，v 1(k+1)是k+1采样时刻TD获得的1阶微分信号，h为积分步长，h 0为输入信号被噪声污染时决定滤波效果的参数，fhan函数中的实际参数r为输入的调节参数；
fhan(v 1,v 2,r,h)函数为：
Figure PCTCN2020109224-appb-000002
Figure PCTCN2020109224-appb-000003
其中v 1和v 2表示fhan函数的两个形式参数，对应在公式1中，是将v 1(k)-v(k)和v 2(k)作为实际参数传给fhan函数调用；fhan函数中的形式参数r和h为调节参数；fhan函数中的d、d 0、y、a以及a 0仅作为中间变量参与函数内部的一些运算，无具体的实际意义；
(2)以k采样时刻的输入量u(k)和k采样时刻的输出量y(k)进行观测，系统状态和扩张状态(总扰动)可表示为：
Figure PCTCN2020109224-appb-000004
其中，z 1(k)，z 2(k)表示k采样时刻ESO对应于y(k)和一阶y 1(k)的系统状态观测值，z 1(k)跟踪y(k)，z 2(k)跟踪一阶y 1(k)，z 3(k)表示k采样时刻ESO的扩张状态观测值，是扩张状态观测器针对对象的不确定因素以及外扰动信息而跟踪作用的结果；e(k)表示k采样时刻一阶系统状态观测值z 1(k)和输出y(k)之间的误差；α 01，α 02，β 01，β 02，β 03，δ 0为k时刻被fal函数调用的实际调节参数，b 0为不确定函数b的估计值；
式中用到的fal函数是一种特殊的非线性结构，fal函数表达式如下：
Figure PCTCN2020109224-appb-000005
式中，e、α、δ表示fal函数的三个形式参数，形式参数e表示传入函数的误差信号，形式参数α为影响跟踪效果有关的常数，形式参数δ为影响滤波效果的常数；
(3)状态误差反馈控制律
Figure PCTCN2020109224-appb-000006
其中，e 1(k)、e 2(k)是k时刻安排的过渡过程v 1(k)、v 2(k)和系统输出估计z 1(k)、 z 2(k)之间的一阶误差和二阶误差，u(k)为k时刻的控制信号，通过合理选择非线性实际参数α 1、α 2、δ以及实际参数k P、k D实现对“积分串联型”对象的非线性控制。
进一步的，所述基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制包括：
获取直流输电系统的数学模型；
基于直流输电系统的数学模型，确定整流侧的定电流控制目标以及逆变侧的定关断角控制目标；
基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制目标以及逆变侧的定关断角控制目标。
进一步的，获取直流输电系统的数学模型包括：
高压直流输电系统，其动态方程采用如下详细的数学模型：
Figure PCTCN2020109224-appb-000007
其中，L drΣ为整流侧总阻抗，X r为整流侧换相电抗，L diΣ为逆变侧总阻抗，X i为逆变侧换相电抗，C dc为直流电容，V ar为整流侧交流母线电压，R d为直流电阻，V ai为逆变侧交流母线电压，I dr为整流侧直流电流，V c为直流电容电压，I di为逆变侧直流电流，α为整流侧滞后触发角，β为逆变侧超前触发角；
考虑到直流系统整流侧和逆变侧控制环节输出的α和β存在触发延迟，有：
Figure PCTCN2020109224-appb-000008
式中，T α和T β表示整流侧和逆变侧控制环节输出的α和β触发延迟时间，α 0和β 0为整流侧滞后触发角和逆变侧超前触发角的参考值。
进一步地，基于直流输电系统的数学模型，确定整流侧的定电流控制目标以及逆变侧的定关断角控制目标包括：
对于直流输电系统的整流侧，采用定电流控制，其控制目标为整流侧直流电流I dr能够快速准确地跟踪电流指令I d_order，控制目标可转化为期望的误差输出y r为0，如式(9)所示：
y r＝I dr-I d_order＝0            (9)
对于直流输电系统的逆变侧，采用定关断角控制，其控制目标为逆变侧关断角γ能够快速准确地跟踪关断角指令γ 0，即期望的误差输出y i为0，如式(10)所示：
Figure PCTCN2020109224-appb-000009
进一步的，基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制目标以及逆变侧的定关断角控制目标包括：
基于直流输电系统的数学模型，将式7两边进行求导并与式8进行联立，可得：
Figure PCTCN2020109224-appb-000010
式(11)与式(8)联立，即可得到输入输出标准形式：
Figure PCTCN2020109224-appb-000011
其中，
Figure PCTCN2020109224-appb-000012
Figure PCTCN2020109224-appb-000013
式12满足SAADR-PI标准型，式(11)～(14)的推导实现了用二阶SAADR-PI来作为直流系统的定电流控制策略；
对于逆变侧定关断角控制进行推导，可得
Figure PCTCN2020109224-appb-000014
与式8联立，即可得到输入输出标准形式：
Figure PCTCN2020109224-appb-000015
其中，
Figure PCTCN2020109224-appb-000016
Figure PCTCN2020109224-appb-000017
式(15)～(18)的推导实现了用一阶SAADR-PI来作为直流系统的逆变侧定关断角控制策略。
相应的，本发明还提供了一种基于自适应自抗扰比例积分的直流输电系统控制系统，其特征是，包括控制器设计模块和直流输电系统控制模块；
控制器设计模块，用于针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器；
直流输电系统控制模块，用于基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制。
与现有技术相比，本发明所达到的有益效果是：本发明针对传统控制框架中PI控制器，重新设计了自适应自抗扰比例积分控制器，并考虑到离散系统给微分跟踪器带来的高频颤振以及通信时延，一方面可通过fal函数自动调节PI参数使系统保持自适应能力，另一方面对控制原理进行离散化处理满足了计算机仿真需求。将自适应自抗扰比例积分控制器运用在直流系统的整流侧定电流控制以及逆变侧的定关断角控制上，可以提高系统应对大范围扰动时的动态响应速度和鲁棒性能，可以有效抑制高压直流输电系统中的连续换相失败。
附图说明
图1是自抗扰算法控制框图；
图2是CIGRE HVDC测试模型主要拓扑图；
图3是采用线性PI控制的Cigre HVDC控制框图；
图4是采用SAADR-PI控制器的高压直流输电系统闭环控制框图；
图5是逆变侧换流母线单相接地故障(接地电感Lf＝0.89H，故障持续0.5s)仿真图；
图6是逆变侧换流母线两相相间短路(接地电感Lf＝1.12H，故障持续0.5s)仿真图；
图7是逆变侧换流母线两相接地短路故障(接地电感Lf＝0.95H，故障持续0.5s)仿真图；
图8是不同接地电抗和故障时间下单相接地故障仿真结果统计图；
图9是不同接地电抗和故障时间下两相短路故障仿真结果统计图；
图10是不同接地电抗和故障时间下两相短路接地故障仿真结果统计图。
具体实施方式
下面结合附图对本发明作进一步描述。以下实施例仅用于更加清楚地说明本发明的技术方案，而不能以此来限制本发明的保护范围。
本发明的一种基于自适应自抗扰比例积分的直流输电系统控制方法，参见图1所示，包括以下步骤：
步骤1：针对自抗扰比例积分控制器，进行了离散化处理，获得自适应自抗扰比例积分控制器(SAADR-PI)，一方面可通过fal函数自动调节PI参数，另一方面离散化处理满足计算机仿真需求；
自抗扰比例积分控制器由三个重要部分组成：跟踪微分器(Tracking Differentiator,TD)、扩张状态观测器(Extended State Observer,ESO)和非线性状态误差反馈结构(Nonlinear State Error Feedback，NLSEF)。考虑到跟踪微分器TD在计算机上实现时，必须采用离散算法。针对自抗扰比例积分控制器，进行了离散化处理，获得自适应自抗扰比例积分控制器(SAADR-PI)。也就是说，SAADR-PI控制器组成结构虽然与自抗扰比例积分控制器一致，但自抗扰比例积分控制器的跟踪微分器中最速控制综合函数fhan函数进行了离散化处理，自抗扰比例积分控制器中的扩张状态观测器和非线性状态误差反馈结构也同样延续了离散化处理。
自抗扰比例积分控制器具体框图如附图中图1所示。图中，TD表示n阶跟踪微分器，ESO表示n+1阶扩张状态观测器，NLSEF表示n阶非线性状态误差反馈结构，Plant表示非线性不确定对象，v(t)为输入信号，TD跟踪并柔化输入信号，得到其各阶广义微分信号v 1(t)...v n(t)，z(t)为扩张状态观测器输出信号，其 包含n+1个输出信号z 1(t),...,z n+1(t)，e(t)为误差信号，在图中对应的各阶误差信号为e 1(t),...,e n(t)，u(t)为控制信号，w(t)为扰动信号，y(t)为输出信号。
因直流输电控制系统的定电流控制可以用SAADR-PI控制器的一阶系统进行控制，定关断角控制可以用SAADR-PI控制器的二阶系统进行控制，具体详细推理步骤可参照步骤4中SAADR-PI控制器应用于直流输电系统的可行性分析，所以不再对n阶系统的推理过程进行赘述，仅以二阶系统为例进行推理，SAADR-PI控制器的二阶控制系统为
Figure PCTCN2020109224-appb-000018
式中f、w、b函数均为不确定函数，y表示输出。
SAADR-PI控制器的具体算法可表示为：
(1)根据离散化需求，设v(k)是k采样时刻对应的输入信号，引入fhan函数并对原有自抗扰比例积分控制器中的微分器TD进行离散化处理，v(k)经过微分器TD便可以获得二阶系统下的各阶微分信号：
Figure PCTCN2020109224-appb-000019
其中，v 1(k)是k采样时刻TD获得的1阶微分信号，是可微的光滑信号，v 2(k)＝dv 1(k)/dt，v 2(k)是k采样时刻TD获得的2阶微分信号，v 1(k+1)是k+1采样时刻TD获得的1阶微分信号，h为积分步长，h 0为输入信号被噪声污染时决定滤波效果的参数，fhan函数中的实际参数r为输入的调节参数。
fhan(v 1,v 2,r,h)函数为：
Figure PCTCN2020109224-appb-000020
Figure PCTCN2020109224-appb-000021
其中v 1和v 2表示fhan函数的两个形式参数，对应在公式1中，是将v 1(k)-v(k)和v 2(k)作为实际参数传给fhan函数调用。fhan函数中的形式参数r和h为调节参数。fhan函数中的d、d 0、y、a以及a 0仅作为中间变量参与函数内部的一些运算，无具体的实际意义。
(2)以k采样时刻的输入量u(k)和k采样时刻的输出量y(k)进行观测，系统状态和扩张状态(总扰动)可表示为：
Figure PCTCN2020109224-appb-000022
其中，z 1(k)，z 2(k)表示k采样时刻ESO对应于y(k)和一阶y 1(k)的系统状态观测值，z 1(k)跟踪y(k)，z 2(k)跟踪一阶y 1(k)，z 3(k)表示k采样时刻ESO的扩张状态观测值，是扩张状态观测器针对对象的不确定因素以及外扰动信息而跟踪作用的结果。e(k)表示k采样时刻一阶系统状态观测值z 1(k)和输出y(k)之间的误差。α 01，α 02，β 01，β 02，β 03，δ 0为k时刻被fal函数调用的实际调节参数，b 0为不确定函数b的估计值。
式中用到的fal函数是一种特殊的非线性结构，是ESO的核心部分，可以通过跟踪来适当的选择扩张状态观测器的参数，具有较好的自适应性。fal函数表达式如下：
Figure PCTCN2020109224-appb-000023
式中，e、α、δ表示fal函数的三个形式参数，形式参数e表示传入函数的误差信号，，形式参数α为影响跟踪效果有关的常数，与跟踪效果成反比，但其减小的同时滤波效果会变差；形式参数δ为影响滤波效果的常数，与滤波效果成正比，但其增加的同时也增加了跟踪的延迟。当信号误差较小时，fal函数产生较小的反馈增益，在误差较大时，产生较大的反馈增益，较好地满足了系统稳定性及快速性的需求。
(3)状态误差反馈控制律
Figure PCTCN2020109224-appb-000024
其中，e 1(k)、e 2(k)是k时刻安排的过渡过程v 1(k)、v 2(k)和系统输出估计z 1(k)、z 2(k)之间的一阶误差和二阶误差，u(k)为k时刻的控制信号，通过合理选择非线性实际参数α 1、α 2、δ以及实际参数k P、k D实现对“积分串联型”对象的非线性控制。
步骤2：针对高压直流输电系统，建立其相应的数学模型；
针对高压直流输电系统，其动态方程采用如下详细的数学模型：
Figure PCTCN2020109224-appb-000025
考虑到直流系统整流侧和逆变侧控制环节输出的α和β存在触发延迟，有：
Figure PCTCN2020109224-appb-000026
式中，T α和T β表示整流侧和逆变侧控制环节输出的α和β触发延迟时间，α 0和β 0为整流侧滞后触发角和逆变侧超前触发角的参考值。
以上涉及到的参数定义如下表所示。
表1 高压直流输电系统中参数含义
Figure PCTCN2020109224-appb-000027
步骤3：基于步骤2推导出的高压直流输电系统数学模型，为实现对直流系 统的控制目的，确定整流侧和逆变侧的控制目标如下：
对于直流输电系统的整流侧，采用定电流控制，其控制目标为整流侧直流电流I dr能够快速准确地跟踪电流指令I d_order，控制目标可转化为期望的误差输出y r为0，如式(9)所示：
y r＝I dr-I d_order＝0            (9)
对于直流输电系统的逆变侧，采用定关断角控制，其控制目标为逆变侧关断角γ能够快速准确地跟踪关断角指令γ 0，即期望的误差输出y i为0，如式(10)所示：
Figure PCTCN2020109224-appb-000028
步骤4：基于步骤1推导出的SAADR-PI控制器算法，通过对步骤2得到的直流系统详细模型公式的变形与推导，并与步骤3确定的控制目标紧密结合，分析SAADR-PI控制器算法应用于直流输电系统的可行性。
基于步骤2直流输电系统的数学模型，将式7两边进行求导并与式8进行联立，可得：
Figure PCTCN2020109224-appb-000029
式(11)与式(8)联立，即可得到输入输出标准形式：
Figure PCTCN2020109224-appb-000030
其中，
Figure PCTCN2020109224-appb-000031
Figure PCTCN2020109224-appb-000032
式12满足SAADR-PI标准型，式(11)～(14)的推导实现了用二阶SAADR-PI来作为直流系统的定电流控制策略。
对于逆变侧定关断角控制进行推导，可得
Figure PCTCN2020109224-appb-000033
与式8联立，即可得到输入输出标准形式：
Figure PCTCN2020109224-appb-000034
其中，
Figure PCTCN2020109224-appb-000035
Figure PCTCN2020109224-appb-000036
式(15)～(18)的推导实现了用一阶SAADR-PI来作为直流系统的逆变侧定关断角控制策略。
步骤5：基于步骤3的直流系统控制目标与步骤4验证的SAADR-PI控制器在直流控制系统的可适用性，将高压直流输电系统的原有线性PI控制器替换为SAADR-PI控制器。
附图中的图3是运用传统线性PI控制的高压直流输电控制系统，主要包括低压限流(Voltage Dependent Current Order Limiter,VDCOL)、直流电流控制(Current Control Amplifier,CCA)、直流电压控制器(Voltage Control Amplifier,VCA)、定关断角(Constant Extinction Angle,CEA)控制及其它触发限制环节等。图中I d_rec表示整流侧直流电流，与直流控制指令I do_rec进行做差，误差值输入至 传统线性PI控制器(图3中虚线框表示部分)，实现整流侧定电流控制。整流侧除了定电流控制外，还包含低压限流VDCL控制。γ _inv表示逆变侧的关断角，与设定的关断角作差，误差值进入传统线性PI控制器进行调节，实现逆变侧定关断角控制。
将所设计的SAADR-PI控制器应用到高压直流输电系统中的整流侧定电流和逆变侧定关断角控制策略中，亦即将图3中的传统线性PI控制器替换为SAADR-PI控制器，至于不将逆变侧的定电流控制PI环节同样进行改进，是因为逆变侧很少处于定电流控制状态，仅在整流侧交流母线电压大幅下降时才会启动，因此和本文考虑的情况完全不同。PI控制器替换后的直流系统闭环控制框图如图4所示，图中右侧虚线框部分即为SAADR-PI控制器。
实施例
国际大电网会议(CIGRE)高压直流输电(HVDC)标准测试模型(CIGRE HVDC)是直流联络线研究委员会HVDC系统控制工作组提出的第一个用于HVDC控制研究的标准模型。在PSCAD仿真软件上搭建CIGRE HVDC标准测试模型，验证本发明所提控制方法对于抑制直流输电连续换相失败所起的作用。CIGRE HVDC标准测试模型的主电路示意图如图2所示，图中所示为双端直流，采用12脉动换流单元，且直流单极运行，交流系统短路比(Short Circuit Ratio,SCR)在2.5左右，送端电源电压为383kV，受端电源电压为215kV。对于图中所示参数，电阻单位为Ω，电感单位H，电容单位为μF。
下表为测试模型的主要参数见表2。
表2 测试模型的主要参数
Figure PCTCN2020109224-appb-000037
Figure PCTCN2020109224-appb-000038
下表为控制策略的参数整定见表3。
标3 控制策略的参数
Figure PCTCN2020109224-appb-000039
Figure PCTCN2020109224-appb-000040
在逆变侧换流母线处施加接地故障，用可调接地电感值L f模拟交流系统故障距换流母线不同距离的情况，接地电感值越小表示交流系统故障距离换流母线越近，故障越严重。分别对以下3种控制方法在不同逆变侧交流系统故障案例下的响应情况进行仿真分析：
控制方法I：仅采用CIGRE HVDC标准测试模型控制环节。控制方法II：在CIGRE HVDC标准测试模型控制环节的基础上增加虚拟电阻电流限制方法。控制方法III：采用本发明所提的SAADR-PI控制器。利用控制方法I和控制方法II分别与本文所提控制方法III进行对比，以验证所提算法在抑制直流输电连续换相失败的作用。着重考察关断角、直流电流、直流电压、直流传输功率等物理量在故障后的响应情况。其中，关断角响应曲线用来判断直流输电是否换相失败；直流电流、直流电压、传输功率响应曲线用来观察故障期间的动态过程。
为了方便对比，将以上几种物理量在3种控制方法下的响应曲线放于同一坐标系下。图中Conventional PI表示控制方法I，Virtual Resist表示控制方法II，SAADR-PI表示控制方法III。
设逆变侧换流母线在4s时发生单相接地故障，接地电感L f＝0.89H，故障持续0.5s。该故障条件下，采用三种控制方法时各自电气量仿真结果如图5所示。由图5可知，控制方法I下关断角两次降为0°，对应直流输电发生连续两次换相失败。由于直流输电首次换相失败距离逆变侧交流系统故障时间很短，直流系统控制环节动作效果有限，故障后直流输电首次换相失败难以避免，但采取合适的控制方法，如控制方法II能有效避免直流输电第二次换相失败，通过虚拟电阻提前使得VDCL动作，但是仍无法避免首次换相失败。而控制方法III有效避免了首次换相失败以及连续换相失败，由于控制器未改变原有控制框架，因此故障期间逆变侧仍采取定关断角控制，交流电压跌落期间导致直流电压一直在0.9pu左右，功率水平也在0.9pu，但是在故障清除后的0.1s内恢复到额定运行点，这体现了SAADR-PI控制器的有效跟踪能力，满足实际工程运行需要。
同理，对交流系统施加两相相间短路以及两相接地短路故障，故障电感分别设置为1.12H与0.95H，得到系统仿真波形如图6和图7所示。由图可见，与单相接地故障情况类似，所提算法能够成功抑制首次换相失败与连续换相失败的发生，且故障后0.1s内恢复初始运行功率。
由于换相失败发生的概率与故障初始时间有密切关系，因此有必要考察相同故障下不同故障初始时间对控制策略性能的影响。图8～图10展示了在单相接地、两相相间短路以及两相短路接地三种不对称故障下的仿真结果数据统计。初始时间为一个周波20ms，每2ms步进，从4s到4.018s。接地电抗变化范围为0.5H～1.5H。图8～图10中空心圆圈代表CIGRE标准测试模型没有发生换相失败，实心圆圈代表在所提控制策略下未发生换相失败，空心方框代表所提控制策略下仅发生首次换相失败，实心方块代表发生两次以上的连续换相失败。由图8～ 图10可见，在4.006s和4.016s时刻最容易发生连续换相失败，这是因为此时阀即将换相或正在换相期间，因此控制策略还来不及响应；其余时刻在故障非常严重，交流电压跌落已导致无法继续换相情况下，也会发生连续换相失败。
相应的，本发明还提供了一种基于自适应自抗扰比例积分的直流输电系统控制系统，其特征是，控制器设计模块和直流输电系统控制模块；
控制器设计模块，用于针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器；
直流输电系统控制模块，用于基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制。
本发明对高压直流输电系统的原有线性控制系统进行改进，有效提高了控制系统的性能，改善了系统存在的换相失败问题。
考虑到线性PI控制器无法良好地控制高压直流输电系统这类非线性系统，根据自抗扰控制器基本原理，设计一种基于自适应自抗扰比例积分方法的直流输电系统控制策略，提高系统在内外扰动下对触发角指令跟踪的精度。
本领域内的技术人员应明白，本申请的实施例可提供为方法、系统、或计算机程序产品。因此，本申请可采用完全硬件实施例、完全软件实施例、或结合软件和硬件方面的实施例的形式。而且，本申请可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器、CD-ROM、光学存储器等)上实施的计算机程序产品的形式。
本申请是参照根据本申请实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或 方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。
以上所述仅是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明技术原理的前提下，还可以做出若干改进和变型，这些改进和变型也应视为本发明的保护范围。

Claims (7)

  1. 基于自适应自抗扰比例积分的直流输电系统控制方法，其特征是，包括以下步骤：
    针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器；
    基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制。
  2. 根据权利要求1所述的基于自适应自抗扰比例积分的直流输电系统控制方法，其特征是，所述针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器包括：
    自抗扰比例积分控制器由三个重要部分组成：跟踪微分器TD、扩张状态观测器ESO和非线性状态误差反馈结构NLSEF，v(t)为输入信号，TD跟踪并柔化输入信号，得到其各阶广义微分信号v 1(t)...v n(t)，z(t)为扩张状态观测器输出信号，其包含n+1个输出信号z 1(t),...,z n+1(t)，e(t)为误差信号，对应的各阶误差信号为e 1(t),...,e n(t)，u(t)为控制信号，w(t)为扰动信号，y(t)为输出信号；
    针对自抗扰比例积分控制器进行了离散化处理；
    自适应自抗扰比例积分控制器SAADR-PI的具体算法可表示为：
    (1)根据离散化需求，设v(k)是k采样时刻对应的输入信号，引入fhan函数并对原有自抗扰比例积分控制器中的微分器TD进行离散化处理，v(k)经过微分器TD便可以获得二阶系统下的各阶微分信号：
    Figure PCTCN2020109224-appb-100001
    其中，v 1(k)是k采样时刻TD获得的1阶微分信号，是可微的光滑信号， v 2(k)＝dv 1(k)/dt，v 2(k)是k采样时刻TD获得的2阶微分信号，v 1(k+1)是k+1采样时刻TD获得的1阶微分信号，h为积分步长，h 0为输入信号被噪声污染时决定滤波效果的参数，fhan函数中的实际参数r为输入的调节参数；
    fhan(v 1,v 2,r,h)函数为：
    Figure PCTCN2020109224-appb-100002
    Figure PCTCN2020109224-appb-100003
    其中v 1和v 2表示fhan函数的两个形式参数，对应在公式1中，是将v 1(k)-v(k)和v 2(k)作为实际参数传给fhan函数调用；fhan函数中的形式参数r和h为调节参数；fhan函数中的d、d 0、y、a以及a 0仅作为中间变量参与函数内部的一些运算，无具体的实际意义；
    (2)以k采样时刻的输入量u(k)和k采样时刻的输出量y(k)进行观测，系统状态和扩张状态(总扰动)可表示为：
    Figure PCTCN2020109224-appb-100004
    其中，z 1(k)，z 2(k)表示k采样时刻ESO对应于y(k)和一阶y 1(k)的系统状态观测值，z 1(k)跟踪y(k)，z 2(k)跟踪一阶y 1(k)，z 3(k)表示k采样时刻ESO的扩张状态 观测值，是扩张状态观测器针对对象的不确定因素以及外扰动信息而跟踪作用的结果；e(k)表示k采样时刻一阶系统状态观测值z 1(k)和输出y(k)之间的误差；α 01，α 02，β 01，β 02，β 03，δ 0为k时刻被fal函数调用的实际调节参数，b 0为不确定函数b的估计值；
    式中用到的fal函数是一种特殊的非线性结构，fal函数表达式如下：
    Figure PCTCN2020109224-appb-100005
    式中，e、α、δ表示fal函数的三个形式参数，形式参数e表示传入函数的误差信号，形式参数α为影响跟踪效果有关的常数，形式参数δ为影响滤波效果的常数；
    (3)状态误差反馈控制律
    Figure PCTCN2020109224-appb-100006
    其中，e 1(k)、e 2(k)是k时刻安排的过渡过程v 1(k)、v 2(k)和系统输出估计z 1(k)、z 2(k)之间的一阶误差和二阶误差，u(k)为k时刻的控制信号，通过合理选择非线性实际参数α 1、α 2、δ以及实际参数k P、k D实现对“积分串联型”对象的非线性控制。
  3. 根据权利要求1所述的基于自适应自抗扰比例积分的直流输电系统控制方法，其特征是，所述基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制包括：
    获取直流输电系统的数学模型；
    基于直流输电系统的数学模型，确定整流侧的定电流控制目标以及逆变侧的定关断角控制目标；
    基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制目标以及逆变侧的定关断角控制目标。
  4. 根据权利要求3所述的基于自适应自抗扰比例积分的直流输电系统控制方法，其特征是，获取直流输电系统的数学模型包括：
    高压直流输电系统，其动态方程采用如下详细的数学模型：
    Figure PCTCN2020109224-appb-100007
    其中，L drΣ为整流侧总阻抗，X r为整流侧换相电抗，L diΣ为逆变侧总阻抗，X i为逆变侧换相电抗，C dc为直流电容，V ar为整流侧交流母线电压，R d为直流电阻，V ai为逆变侧交流母线电压，I dr为整流侧直流电流，V c为直流电容电压，I di为逆变侧直流电流，α为整流侧滞后触发角，β为逆变侧超前触发角；
    考虑到直流系统整流侧和逆变侧控制环节输出的α和β存在触发延迟，有：
    Figure PCTCN2020109224-appb-100008
    式中，T α和T β表示整流侧和逆变侧控制环节输出的α和β触发延迟时间，α 0和β 0为整流侧滞后触发角和逆变侧超前触发角的参考值。
  5. 根据权利要求4所述的基于自适应自抗扰比例积分的直流输电系统控制方法，其特征是，基于直流输电系统的数学模型，确定整流侧的定电流控制目 标以及逆变侧的定关断角控制目标包括：
    对于直流输电系统的整流侧，采用定电流控制，其控制目标为整流侧直流电流I dr能够快速准确地跟踪电流指令I d_order，控制目标可转化为期望的误差输出y r为0，如式(9)所示：
    y r＝I dr-I d_order＝0  (9)
    对于直流输电系统的逆变侧，采用定关断角控制，其控制目标为逆变侧关断角γ能够快速准确地跟踪关断角指令γ 0，即期望的误差输出y i为0，如式(10)所示：
    Figure PCTCN2020109224-appb-100009
  6. 根据权利要求5所述的基于自适应自抗扰比例积分的直流输电系统控制方法，其特征是，基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制目标以及逆变侧的定关断角控制目标包括：
    基于直流输电系统的数学模型，将式7两边进行求导并与式8进行联立，可得：
    Figure PCTCN2020109224-appb-100010
    式(11)与式(8)联立，即可得到输入输出标准形式：
    Figure PCTCN2020109224-appb-100011
    其中，
    Figure PCTCN2020109224-appb-100012
    Figure PCTCN2020109224-appb-100013
    式12满足SAADR-PI标准型，式(11)～(14)的推导实现了用二阶SAADR-PI来作为直流系统的定电流控制策略；
    对于逆变侧定关断角控制进行推导，可得
    Figure PCTCN2020109224-appb-100014
    与式8联立，即可得到输入输出标准形式：
    Figure PCTCN2020109224-appb-100015
    其中，
    Figure PCTCN2020109224-appb-100016
    Figure PCTCN2020109224-appb-100017
    式(15)～(18)的推导实现了用一阶SAADR-PI来作为直流系统的逆变侧定关断角控制策略。
  7. 根据权利要求1-6任一项所述的基于自适应自抗扰比例积分的直流输电系统控制方法的直流输电系统控制系统，其特征是，包括控制器设计模块和直流输电系统控制模块；
    控制器设计模块，用于针对自抗扰比例积分控制器进行了离散化处理，获得自适应自抗扰比例积分控制器；
    直流输电系统控制模块，用于基于自适应自抗扰比例积分控制器实现直流系统中整流侧的定电流控制以及逆变侧的定关断角控制。
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