CN111987734A - Transient overvoltage two-stage optimization control method based on trajectory sensitivity - Google Patents

Transient overvoltage two-stage optimization control method based on trajectory sensitivity Download PDF

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CN111987734A
CN111987734A CN202010801827.8A CN202010801827A CN111987734A CN 111987734 A CN111987734 A CN 111987734A CN 202010801827 A CN202010801827 A CN 202010801827A CN 111987734 A CN111987734 A CN 111987734A
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control
voltage
transient overvoltage
direct current
stage
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王长江
姜涛
刘福锁
陈厚合
李雪
于洋
吕亚洲
郄朝辉
李兆伟
石渠
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NARI Group Corp
Northeast Electric Power University
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Northeast Dianli University
NARI Group Corp
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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
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • 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]

Abstract

The invention discloses a transient overvoltage two-stage optimization control method based on trajectory sensitivity, which comprises the following steps: constructing a two-stage optimization control model according to the trajectory sensitivity of the alternating current-direct current system and by combining the basic principle of the MPC; converting the model into a quadratic programming model taking the control quantity increment as an independent control variable by means of transient overvoltage and the track sensitivity of voltage in a recovery stage to the control quantity; aiming at a transient overvoltage instability scene of a direct current transmitting end system, solving the control quantity change of transient overvoltage prevention control in a quadratic programming model before a fault occurs, and applying the control quantity change to an alternating current-direct current system; and applying the change of the control quantity of the voltage control in the recovery stage to the recovery process of the alternating current-direct current system, and rolling and adjusting the control quantity until the transient overvoltage recovery process is operated in a safe range. The transient overvoltage suppression device can effectively suppress transient overvoltage of a direct current sending end system in a high-voltage direct current outward sending mode of wind power, and can ensure the safety of a transient overvoltage recovery process while suppressing the transient overvoltage of the direct current sending end system.

Description

Transient overvoltage two-stage optimization control method based on trajectory sensitivity
Technical Field
The invention relates to the field of safe and stable operation of an alternating current-direct current hybrid system, in particular to a transient overvoltage two-stage optimization control method based on trajectory sensitivity.
Background
The safe and stable operation of an AC/DC hybrid system is an important component of the safe and stable analysis of an electric power system, in recent years, a new energy power generation technology represented by wind power is rapidly developed, and when large-scale wind power is remotely transmitted to a load center through High Voltage Direct Currents (HVDC)[1-2]If large power disturbance such as short circuit, direct current blocking, commutation failure and the like of a receiving end alternating current system occurs, reactive balance of a direct current sending end system is broken, a large amount of surplus reactive power is gushed into the direct current sending end system, transient overvoltage of the direct current sending end system is easily caused, fan disconnection and chain reaction are caused, and safe and stable operation of an alternating current and direct current hybrid system is seriously threatened[3-4]. Therefore, the transient overvoltage of the direct current sending end system is restrained, and the method has important significance for improving the stability of the alternating current and direct current system containing large-scale wind power[5]。
At present, researches for suppressing transient overvoltage of a direct current transmission end system mainly focus on two aspects of adding an auxiliary device and optimizing a control system[6-8]. In the aspect of adding auxiliary devices, the voltage difference value between a fault and a normal condition can be compensated to a certain degree by configuring the auxiliary devices such as a dynamic reactive compensator, a dynamic voltage restorer, a phase modulator and the like, transient overvoltage is suppressed, fan off-line is avoided, and system investment is increased. In the aspect of optimizing a control system, transient overvoltage is suppressed from control parameters of a rectifying side current control link and a low-voltage current limiting link of an optimized direct current system based on a time domain simulation method. The above studies have been made from the viewpoint of adding an auxiliary device and improving the control of the device, and can suppress the transient overvoltage well, but the dynamic process of the transient overvoltage is fast and is likely to be accompanied by phenomena such as fan chain disconnection, and the control device needs a certain time delay from the reception of the control command to the device action, and it is difficult to ensure real-time suppression in the dynamic process of the transient overvoltage.
Therefore, research on the preventive control measures of the transient overvoltage is carried out, and the transient overvoltage of the direct current transmitting end system can be effectively avoided on the premise of ensuring the economy. Although the existing transient voltage prevention control can effectively improve the safety of the transient voltage, the prevention control research on the transient overvoltage of an alternating current and direct current sending end system is lacked, and the control measures mainly adopt the traditional control elements of an alternating current system and ignore the influence of the control elements such as direct current and wind power on the transient voltage[9-10]。
Disclosure of Invention
The invention provides a transient overvoltage two-stage optimization control method based on trajectory sensitivity, which can effectively inhibit transient overvoltage of a direct current transmission end system of wind power in a high-voltage direct current outward transmission mode, and can ensure the safety of a transient overvoltage recovery process while inhibiting the transient overvoltage of the direct current transmission end system, and is described in detail as follows:
a transient overvoltage two-stage optimization control method based on track sensitivity adopts two-stage optimization control of transient overvoltage and recovery stage voltage of a direct current sending end system, gives consideration to the risk of unsafe voltage in the recovery process of the direct current sending end system, and improves the transient voltage stability of the alternating current and direct current sending end system, and comprises the following steps:
constructing a two-stage optimization control model according to the trajectory sensitivity of the alternating current-direct current system and by combining the basic principle of the MPC;
converting the two-stage optimization control model into a quadratic programming model taking the control quantity increment as an independent control variable by means of transient overvoltage and the trace sensitivity of voltage in a recovery stage to the control quantity;
aiming at a transient overvoltage instability scene of a direct current transmitting end system, solving the control quantity change of transient overvoltage prevention control in a quadratic programming model before a fault occurs, and applying the control quantity change to an alternating current-direct current system;
and applying the change of the control quantity of the voltage control in the recovery stage to the recovery process of the alternating current-direct current system, and rolling and adjusting the control quantity until the transient overvoltage recovery process is operated in a safe range.
The quadratic programming model using the two-stage optimization control model with the control quantity increment as the independent control variable specifically comprises the following steps:
Figure BDA0002627673020000021
s.t.nVt,f(k+i)|k＝At,iΔUt(k)
Vt,r(k+i)|k＝at iVt,0(k)|k+(1-at i)cI
Figure BDA0002627673020000022
Vt,min≤Vt,0(k+N)|k+Vt,f(k+N)|k≤Vt,max
ut,min≤ut(k+j)|k≤ut,max
Δut,min≤Δut(k+j)|k≤Δut,max
in the formula, Vt0、VtfAnd VtrRespectively serving as a reference value, a variable quantity and a target value of the transient overvoltage, and respectively serving as a control measure implementation cost and a node voltage prediction deviation punishment in item 1 and item 2 of the objective function; a. thetFor transient overvoltage V of DC transmitting end systemtThe trajectory sensitivity matrix for the control quantity can be expressed as
Figure BDA0002627673020000023
Figure BDA0002627673020000024
Wherein Q is(o)、VF(p)、kT(q-r)、PHAnd PWThe transient overvoltage control quantity respectively represents the reactive power of a capacitor of a node o, the voltage reference value of a generator AVR of a node p, the transformer transformation ratio between a node q and a node r, the active power transmitted by the HVDC system and the active power of a double-fed wind power plant; delta UtA matrix of transient overvoltage variation at all control moments; a istThe speed degree of the reference track approaching the target value c can be adjusted for designing parameters; i is a unit vector; u. oftAnd Δ utRespectively the control quantity of the transient overvoltage and the variation quantity of the control quantity ut,max、ut,minEach represents utUpper and lower limits of, Δ ut,max、Δut,minEach represents DeltautUpper and lower limits of (d); vt,max、Vt,minRespectively an upper limit and a lower limit of transient overvoltage of a direct current sending end system; n is the number of discrete points of the involved voltage parameters; k. i and j are corresponding k, i and j discrete points.
Further, the recovery process of applying the control quantity change of the voltage control in the recovery stage to the ac/dc system specifically includes:
Figure BDA0002627673020000031
s.t.nVs,f(k+i)|k＝As,iΔUs(k)
Vs,r(k+i)|k＝as iVs,0(k)|k+(1-as i)cI
Figure BDA0002627673020000032
Vs,min≤Vs,0(k+i)|k+Vs,f(k+i)|k≤Vs,max
us,min≤us(k+j)|k≤us,max
Δus,min≤Δus(k+j)|k≤Δus,max
in the formula, Vs0、VsfAnd VsrRespectively representing a voltage reference value, a variable quantity and a target value in a recovery stage; a. thesFor the voltage V of the recovery stage of the DC transmitting end systemsThe trajectory sensitivity matrix for the control quantity can be expressed as
Figure BDA0002627673020000033
Figure BDA0002627673020000034
ΔUsA matrix formed by voltage increments in recovery stages at all control moments; a issDesign parameters for voltage control at the recovery stage; u. ofsAnd Δ usRespectively the controlled quantity of the voltage in the recovery stage and the variable quantity of the controlled quantity us,max、us,minEach represents usUpper and lower limits of, Δ us,max、Δus,minEach represents DeltausUpper and lower limits of (d); vs,max、Vs,minThe upper and lower limits of the voltage in the recovery phase.
The technical scheme provided by the invention has the beneficial effects that:
1. the method comprises the steps of constructing a two-stage control model of transient overvoltage based on Model Predictive Control (MPC) and trajectory sensitivity, solving the control quantity change of transient overvoltage prevention control before a fault occurs and applying the control quantity change to an AC/DC system aiming at a transient overvoltage instability scene of a DC transmitting end system to avoid serious transient overvoltage harm, applying the control quantity change of voltage control in a recovery stage to the recovery process of the AC/DC system if the voltage in the recovery stage is unsafe after control is implemented, and adjusting the control quantity in a rolling mode until the transient overvoltage recovery process is operated in a safe range;
2. according to the method, by means of the track sensitivity of transient overvoltage and recovery stage voltage of a direct current sending end system to the controlled variable, a traditional MPC optimization model is converted into a secondary planning model taking the controlled variable increment as an independent variable, and compared with a nonlinear model predictive control (NLMPC) method based on a quasi-steady-state equation, the method has the advantages that the model solving speed is high, and the regulating effect of direct current and wind power active controlled variable on the transient overvoltage and the recovery stage voltage is fully exerted;
3. in the transient overvoltage two-stage optimization control, the transient overvoltage peak value of the direct current sending end system is limited below 1.1p.u. by the transient overvoltage prevention control, the fan grid disconnection risk is reduced, the unsafe voltage node of the recovery stage can be adjusted to be close to the voltage safety range 1.0p.u. by the prediction control of the voltage of the recovery stage, so that the safety stability of the transient overvoltage and the voltage of the recovery stage of the direct current sending end system are considered, and reference can be provided for the transient voltage stability control of dispatching personnel.
Drawings
FIG. 1 is a flow chart of a transient overvoltage two-stage optimization control method based on trace sensitivity;
FIG. 2 is a schematic diagram of transient overvoltage prevention control;
FIG. 3 is a graph of node 25 voltage when no control is applied;
FIG. 4 is a graph of the effect of capacitor capacity on transient overvoltage;
FIG. 5 is a trace sensitivity of the transient overvoltage peak of node 25 to the control quantity;
FIG. 6 is a graph of node 25 voltage after applying preventative control;
FIG. 7 shows the voltage at node 25 after the 1 st control of the voltage during the recovery phase;
FIG. 8 is a voltage curve of different control methods after the 1 st control of the voltage at the recovery stage;
FIG. 9 shows the voltage at node 25 after the 2 nd control of the voltage during the recovery phase;
fig. 10 is a voltage curve of different control methods after the 2 nd control of the voltage in the recovery stage.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.
In order to solve the problem that transient overvoltage of a direct current sending end system generally occurs tens of milliseconds after fault removal and is difficult to control in a dynamic process in time, a control quantity change value can be obtained by solving a transient overvoltage prevention control model before a fault occurs, and control is applied to an alternating current-direct current system, so that the risk of transient overvoltage is avoided. The transient overvoltage prevention control of the direct current transmitting end system can reduce the transient overvoltage instability risk, but the voltage in the recovery stage is unsafe, so two-stage optimization control of the voltage of the direct current transmitting end system, namely prevention control of the transient overvoltage and prediction control of the voltage in the recovery stage, is required.
In view of the problems of insufficient transient overvoltage prevention and control research and complex model solution of the existing AC/DC transmitting end system, the track sensitivity method is applied to the transient overvoltage prevention and control, the complexity of the transient overvoltage optimization control model is reduced, two-stage optimization control of the transient overvoltage and the voltage in the recovery stage of the DC transmitting end system is adopted, the risk of unsafe voltage in the recovery process of the DC transmitting end system is considered, and the transient voltage stability of the AC/DC transmitting end system is improved.
Example 1
The embodiment of the invention provides a transient overvoltage two-stage optimization control method based on trajectory sensitivity, and referring to fig. 1, the method comprises the following steps:
101: analyzing the transient overvoltage generation reason of an AC/DC transmitting end system containing large-scale wind power, giving out track sensitivity and a basic principle of MPC, constructing a transient overvoltage two-stage control model by the MPC, and converting the nonlinear control model into a quadratic programming model taking control quantity increment as an independent control variable by means of the track sensitivity of transient overvoltage and recovery stage voltage to control quantity;
wherein, the nonlinear control model is a two-stage control model of transient overvoltage.
102: aiming at a transient overvoltage instability scene of a direct current transmitting end system, solving the control quantity change of transient overvoltage prevention control in a quadratic programming model before a fault occurs, and applying the control quantity change to an alternating current-direct current system;
103: if the voltage in the recovery stage is unsafe after the control is implemented, the control quantity change of the voltage control in the recovery stage is applied to the recovery process of the alternating current-direct current system in the same way, and the control quantity is adjusted in a rolling mode until the transient overvoltage recovery process is operated in a safe range.
Example 2
The scheme of example 1 is further described below with reference to specific calculation formulas and examples, which are described in detail below:
step 201: calculating the track sensitivity of the alternating current-direct current system;
the track sensitivity of the alternating current and direct current system can change constantly along with time, and influences of small changes of parameters on the running state of the alternating current and direct current system are reflected. The power system dynamic process may be represented as:
Figure BDA0002627673020000051
wherein x (t) and
Figure BDA0002627673020000052
respectively, a vector and a derivative of the system state variable at the time t; y (t) is a vector formed by algebraic variables at time t; u. ofa、udAnd uwControl variables of an AC system, a DC system and a wind farm, u ═ u [ [ u ] ]a，ud，uw]；x0、y0X (t) and y (t) at time t0F, g are the mapping relation. By means of phix(u，t)、Фy(u, t) represents the change tracks of the state variable and the algebraic variable of the AC-DC system:
Figure BDA0002627673020000061
x (t) and y (t) are defined as u ═ u0Is subjected to Taylor series expansion u0For a control quantity at a certain time, neglecting the higher-order terms of the control quantity variation Δ u, the state variable increment Δ x (t) and the algebraic variable increment Δ y (t) at the time t caused by Δ u can be approximately expressed as:
Figure BDA0002627673020000062
in the formula, xu(t)、yu(t) is the trajectory sensitivity of x (t), y (t) with respect to u. When Δ u is sufficiently small:
Figure BDA0002627673020000063
as can be seen from equation (4), when the system control amount changes Δ u, the trajectory sensitivity can be used to obtain the change trajectory of the system state variable and the algebraic variable, and there are two solving methods, namely, the analytic method and the perturbation method. Aiming at the characteristics of complex structure and higher equation dimension of a large-scale alternating current-direct current hybrid system, the perturbation method is generally adopted to solve the track sensitivity, the method is suitable for a complex black box system (known by the technical personnel in the field, and the embodiment of the invention does not need to be repeated for the situation), the characteristics of linearization and network topology of the system do not need to be considered, the approximate value of the track sensitivity is convenient to obtain, and the complicated numerical integration process of an analytic method is avoided.
The track sensitivity of the node voltage of the direct current sending end system to the controlled variable is calculated by adopting a perturbation method, the change area of the controlled variable can be divided into Z discrete time points, and the node electricity of the direct current sending end system at the ith discrete time pointPressure is ViAnd i is 1,2, …, Z, calculating the trajectory sensitivity of the direct current transmission end system voltage to the controlled variable by adopting a center difference method, a forward difference method and a reverse difference method (the forward difference method is adopted in the invention) of the formula (5), and selecting the controlled variable with a larger sensitivity value as the key controlled variable.
Figure BDA0002627673020000064
Wherein A isu,mDifference as center; a. theu,pIs a forward differential; a. theu,aIs a reverse difference; vi-1、ViAnd Vi+1The node voltages of the direct current sending end system at the i-1 th, i th and i +1 th discrete time points.
Step 202: providing a two-stage optimization control model according to the trajectory sensitivity of the alternating current-direct current system and by combining the basic principle of MPC;
the target function of the existing nonlinear MPC model comprehensively considers the deviation of the predicted track and the reference track at each sampling moment and the control cost of each control quantity, and the control model is as follows:
Figure BDA0002627673020000071
Figure BDA0002627673020000072
in the formula, Q and R are respectively weighted diagonal matrixes; y ismax、yminRespectively the upper limit and the lower limit of the controlled quantity; u. ofmax、uminRepresents the upper and lower limits of u, respectively; Δ umax、ΔuminUpper and lower limits for Δ u, respectively; y ispIs a predicted trajectory; y isrIs a reference track; m is the number of control cycles; n is the predicted period number; k represents the number of parameters.
According to the formula (6) and the formula (7), the traditional nonlinear MPC model needs to solve a complex nonlinear algebraic differential equation, the model solution is complex, in order to simplify the control model solution to improve the timeliness of predictive control, the MPC model can be converted into a quadratic programming model for solution by means of trajectory sensitivity, the complexity of the model solution is greatly reduced, and the transient voltage stability is improved by quickly giving the action quantity of a control element.
The selection principle of the control element is that in the transient overvoltage prevention control and recovery stage voltage prediction control stage of the direct current sending end system, the input sequence of the control element is determined according to the track sensitivity of the transient overvoltage and recovery stage voltage of the direct current sending end system to the controlled quantity, and when the voltage does not meet the requirement after a certain control measure is applied, other control measures are adopted for coordination control.
The specific method comprises the following steps:
(1) setting a controlled node as a direct current sending end system node h, and obtaining the node at t through time domain simulationk+1Temporal transient overvoltage prediction
Figure BDA0002627673020000073
And target value
Figure BDA0002627673020000074
(2) According to the trace sensitivity of transient overvoltage of the controlled node h to the controlled quantity and the maximum input quantity of the control element, t is calculatedk+1Maximum transient overvoltage control quantity delta V of time node ht (k+1)：
Figure BDA0002627673020000075
In the formula,. DELTA.Vt,j (k+1)Is composed of
Figure BDA0002627673020000076
The jth element of (1); Δ ut,jmaxThe maximum input amount of the jth control element in the transient overvoltage prevention control; a. thet,hjThe trace sensitivity of the transient overvoltage of the node h to the controlled variable j (i.e. the controlled variable calculated by the formula (5), where the specific physical meaning of the parameter in the formula (8) is given), at,hj＝(Vt,jmax(1)-Vt,jmax(0))/Δut,jWherein Δ ut,jFor the variation of the jth control element in the transient overvoltage prevention control, Vt,jmax(0)And Vt,jmax(1)The transient overvoltage amplitudes before and after the control quantity j is implemented respectively.
(3) Setting the maximum number of control elements that can be put in, in terms of Δ Vt (k+1)And (3) sequentially adding the medium elements from large to small, and determining the number of the control elements to be added according to the formula (9) if the transient overvoltage reaches a target value after M (less than the maximum number) control elements act.
Figure BDA0002627673020000081
In the formula (I), the compound is shown in the specification,
Figure BDA0002627673020000082
is DeltaVt (k+1)The jth element after sorting from big to small.
(4) If the transient overvoltage of the system does not meet the requirement after a certain control element is put into the limit number, other control elements are put into the system in sequence according to the sequence of the track sensitivity from large to small, and the selection method is similar.
(5) And if the voltage in the recovery stage is unsafe after the control is applied, performing the voltage control in the recovery stage, calculating the track sensitivity of the unsafe voltage node h in the recovery stage to the controlled variable, and selecting a control element by combining the formula (10) and the formula (11), wherein the specific implementation method is similar to the above.
Figure BDA0002627673020000083
Figure BDA0002627673020000084
In the formula,. DELTA.Vs,j (k+1)Is tk+1Maximum increment delta V of voltage at recovery stage of time node hs (k+1)The jth element of (1); a. thes,hjThe trace sensitivity of the unsafe voltage node h to the controlled variable j in the recovery stage; Δ us,jmaxThe maximum input amount of the jth control element in the control;
Figure BDA0002627673020000085
is DeltaVs (k+1)The jth element after sorting from big to small;
Figure BDA0002627673020000086
and
Figure BDA0002627673020000087
respectively, a predicted value and a target value of the voltage in the recovery stage.
Step 203: and (4) obtaining the prevention control of the transient overvoltage and the prediction control of the voltage in the recovery stage according to the models constructed by the formulas (6) and (7).
The invention mainly considers the suppression of the transient overvoltage amplitude, namely ensuring that the transient overvoltage peak value is lower than 1.1p.u., and ensuring the non-grid-disconnection operation of a fan, and can be expressed as follows:
Vh.max(tcl+tlim)＜Vlim (12)
in the formula, Vh.maxIs the transient overvoltage peak value of the node h; t is tclClearing the moment for the fault; t is tlimThe time from the fault clearance to the transient overvoltage peak value; vlim＝1.1p.u.。
The initial operation state of the system is changed, so that the peak value of the transient overvoltage after control is lower than 1.1p.u., and the fan is prevented from being disconnected. The transient overvoltage prevention control scheme is shown in FIG. 2, where y is the controlled quantity, Vh.max(0)And Vh.max(1)The transient overvoltage peak values of the node h before and after control are respectively. If the voltage in the recovery phase is unsafe after the transient overvoltage prevention control is applied, the control quantity is adjusted through the MPC idea to roll to implement control until the voltage is recovered to a safe level.
Track sensitivity A of transient overvoltage of direct current transmitting end system can be obtained by adopting track sensitivity construction methodsThe original nonlinear MPC mathematical models of equations (6) and (7) are reduced to quadratic programming models with control quantity increments as independent control variables as follows:
Figure BDA0002627673020000091
Figure BDA0002627673020000092
in the formula, Vt0、VtfAnd VtrRespectively serving as a reference value, a variable quantity and a target value of the transient overvoltage, and respectively serving as a control measure implementation cost and a node voltage prediction deviation punishment in item 1 and item 2 of the objective function; a. thetFor transient overvoltage V of DC transmitting end systemtThe trajectory sensitivity matrix for the control quantity can be expressed as
Figure BDA0002627673020000093
Figure BDA0002627673020000094
Wherein Q is(o)、VF(p)、kT(q-r)、PHAnd PWThe transient overvoltage control quantity respectively represents the reactive power of a capacitor of a node o, the voltage reference value of a generator AVR of a node p, the transformer transformation ratio between a node q and a node r, the active power transmitted by the HVDC system and the active power of a double-fed wind power plant; delta UtA matrix of transient overvoltage variation at all control moments; a istThe speed degree of the reference track approaching the target value c can be adjusted for designing parameters; i is a unit vector; u. oftAnd Δ utRespectively the control quantity of the transient overvoltage and the variation quantity of the control quantity ut,max、ut,minEach represents utUpper and lower limits of, Δ ut,max、Δut,minEach represents DeltautUpper and lower limits of (d);Vt,max、Vt,minrespectively an upper limit and a lower limit of transient overvoltage of a direct current sending end system; n is the number of discrete points of the involved voltage parameters; k. i and j are corresponding k, i and j discrete points.
When the transient overvoltage is prevented and controlled, if the voltage in the recovery stage is unsafe, a quadratic programming model of the voltage in the recovery stage can be constructed by adopting the same principle, so that the predictive control of the voltage in the recovery stage is realized, and the following steps are shown:
Figure BDA0002627673020000101
Figure BDA0002627673020000102
in the formula, Vs0、VsfAnd VsrRespectively representing a voltage reference value, a variable quantity and a target value in a recovery stage; a. thesFor the voltage V of the recovery stage of the DC transmitting end systemsThe trajectory sensitivity matrix for the control quantity can be expressed as
Figure BDA0002627673020000103
Figure BDA0002627673020000104
ΔUsA matrix formed by voltage increments in recovery stages at all control moments; a issDesign parameters for voltage control at the recovery stage; u. ofsAnd Δ usRespectively the controlled quantity of the voltage in the recovery stage and the variable quantity of the controlled quantity us,max、us,minEach represents usUpper and lower limits of, Δ us,max、Δus,minEach represents DeltausUpper and lower limits of (d); vs,max、Vs,minThe upper and lower limits of the voltage in the recovery phase.
Step 204: adjusting the control quantity to carry out the prediction control of the voltage model in the recovery stage, judging whether the voltage in the recovery stage is safe or not, and directly outputting the control quantity if the voltage in the recovery stage is safe; on the contrary, referring to fig. 1, the above operations are repeated to continuously adjust the control quantity to perform the voltage model prediction control in the recovery stage until the voltage in the recovery stage meets the condition.
Example 3
The following examples are presented to demonstrate the feasibility of the embodiments of examples 1 and 2, and are described in detail below:
the invention takes a modified IEEE39 node system as an example to verify the correctness and validity of the proposed control measures.
360 DFIGs (double-fed wind power plants are simulated by adopting a single-machine equivalent model) with 1.5MW are connected to the node 37; a CIGRE 500kV bipolar HVDC transmission system is added between the nodes 2 and 25. And a simulation model is built by means of Simulink/Matlab, and the simulation step length is 5e-5s (the simulation computer is configured with a CPU of Core i7-8550U, a main frequency of 1.80GHz and an internal memory of 8.00 GB). The generator adopts a 4-order model, AVR is arranged on each generator, the excitation system adopts a 4-order model, and the load adopts a constant impedance load model.
Firstly, the simulation of the transient overvoltage is analyzed. And a three-phase short-circuit fault occurs at the node 2 of the AC/DC receiving end system, the starting time of the fault is 8s, and the duration time of the fault is 0.1 s. Fig. 3 analyzes the voltage curve of the dc-link system node 25 when no control is applied. If no control is applied, the voltage value reaches 1.1p.u. at t-8.13 s, the node 25 starts to generate the transient overvoltage phenomenon, and the transient overvoltage reaches the maximum at t-8.17 s, and the peak value of the transient overvoltage is 1.2242 p.u..
The proposed control measures are adopted to carry out preventive control on the transient overvoltage of a direct current transmission system, voltage control is carried out on the system through preventive control actions when t is 0s, the voltage of a node 25 is ensured to be in the range of 1.0p.u. -1.10 p.u., key control elements are selected according to the track sensitivity of the transient overvoltage to each controlled variable, in order to explain the accuracy of the track sensitivity for the preventive control on the transient overvoltage, simulation analysis is carried out by taking a capacitor of a node 20 as an example, and the corresponding relation between the capacitor capacity and the transient overvoltage peak value is shown in fig. 4.
As can be seen from fig. 4, the capacitance of the capacitor connected to the node 20 changes linearly with the sensitivity of the transient overvoltage peak value when the interval [88Mvar, 108Mvar ] changes, while the change interval of the capacitor connected to the node 20 in the transient overvoltage prevention control is [92Mvar, 103Mvar ], which are both in the linear interval of the sensitivity, thereby proving the feasibility and accuracy of applying the trajectory sensitivity to the transient overvoltage prevention control.
The trace sensitivity of the transient overvoltage of the node 25 to each control quantity is shown in fig. 5, and the components participating in the control are determined by the sensitivity: capacitors at nodes 4, 20, 27, 28 and 29, excitation regulators at nodes 30, 32, 35, 38 and 39, transformers 2 to 30, 29 to 38, 6 to 31, 10 to 32 and 21 to 33, a direct current transmission system and a doubly-fed wind turbine. The maximum control variable quantity of each optimization of the capacitor is 10Mvar, the maximum control quantity is 20Mvar, and the maximum number of action stations of each optimization is 5; the maximum control variable quantity of each time of optimization of the generator terminal voltage is 0.04p.u., the maximum control quantity is 0.06p.u., and the maximum number of action stations of each time of optimization is 5; the maximum control variable quantity of each optimization of the transformer transformation ratio is 0.005p.u., the maximum control quantity is 0.0067 p.u., and the maximum number of action units is 5 in each optimization; the maximum control variable quantity of active power transmitted by the HVDC system in each optimization is 70MW, and the maximum control quantity is 100 MW; the maximum variation of active power of the wind power plant optimized each time is 30MW, and the maximum control quantity is 45 MW.
According to the transient overvoltage of the node 25 in the graph of fig. 5 to the transformation ratio k of the transformerTAnd generator terminal voltage reference value VFTrack sensitivity of, compared to the active power P transmitted by the HVDC systemHActive power P of wind power plantWThe track sensitivity of the sum capacitor reactive power Q is large, namely kTAnd VrefThe influence degree on the transient overvoltage peak value of the node 25 is more than PH、PWAnd Q is high. Therefore, when applying control, k is preferentially put inTAnd VrefIf the control requirement is not met, then sequentially adding PH、PWAnd Q. The change of the controlled variable after the transient overvoltage prevention control of the dc link system is shown in table 1.
TABLE 1 Change in control amount of transient overvoltage prevention control
Figure BDA0002627673020000111
Figure BDA0002627673020000121
FIG. 6 is a graph of node 25 voltage after preventive control has been applied to the AC/DC hybrid system. The transient overvoltage peak value of the node 25 is reduced from 1.2242p.u. to 1.0953p.u., namely, the transient overvoltage peak value is limited below 1.1p.u., so that the risk of fan disconnection is avoided.
As can be seen from fig. 6, after the dc link system applies the transient overvoltage prevention control, the voltage at the node 25 drops to 0.9211p.u. in the recovery phase, which is beyond the safe operating range of the voltage. The proposed dc-link system recovery phase voltage prediction control needs to be started to ensure that the recovery phase voltage at node 25 is operating within a safe range. And determining the elements participating in the control to be the capacitors of the nodes 27, 12, 20, 23 and 31, the excitation regulators of the nodes 30, 38, 39, 32 and 26, the transformers 2-30, 25-37, 29-38, 21-33 and 22-35, the direct-current transmission system and the doubly-fed wind turbine generator set according to the trace sensitivity of the voltage of the node 25 in the recovery stage to each control quantity. The maximum input amount of the control element is determined by the method and the transient overvoltage prevention control, and the application sequence of the control element is still the priority input kTAnd VrefIf the control requirement is not met, then sequentially adding PH、PWAnd Q. And comparing and analyzing the transient overvoltage recovery stage predictive control method with a quasi-steady-state equation-based nonlinear MPC, selecting the same control quantity for ensuring comparability, and obtaining the variable quantity of each control quantity in the 1 st control period through the optimal solution of a voltage predictive control model in the recovery stage of an AC/DC transmission system, as shown in Table 2.
TABLE 2 Change amount of control amount in 1 st control period
Figure BDA0002627673020000122
Figure BDA0002627673020000131
The real-time rolling optimization control effect of the predictive control is simulated by means of electromagnetic transient simulation, and the voltage change conditions of the direct current sending end system node 25 when no control is applied, transient overvoltage prevention control is applied, and the 1 st control of the voltage in the recovery stage is applied are contrastingly analyzed. When t is 11s, each control quantity in the 1 st control period of the predictive control model optimized solution is applied to the alternating current-direct current system, and a voltage curve of the direct current transmitting end system node 25 after the 1 st control is applied is obtained and is shown in fig. 7, while the voltage curve change of the invention and the NLMPC is shown in fig. 8.
As can be seen from fig. 7 and 8, when the proposed recovery stage voltage prediction control is performed for t 11s, the 1 st period control quantity is applied to the ac/dc system, the recovery stage voltage value of the node 25 is increased from 0.9211p.u. to 0.9738p.u., and the recovery stage voltage is increased from 0.9211p.u. to 0.9752p.u. after being controlled by the NLMPC, so that the prediction result has higher accuracy, the optimization time of the present invention is 1.093s in terms of the optimization time, while the NLMPC needs to repeatedly perform time-domain simulation in the prediction time domain to obtain an optimal control sequence, and the optimal control solving speed is slower. In summary, since the 1 st cycle control of both methods does not make the recovery phase voltage reach 1.0p.u, the 2 nd cycle control is required.
Further, the variation of each control quantity in the 2 nd control period is obtained by optimizing and solving the recovery stage voltage predictive control model, as shown in table 3.
TABLE 3 Change amount of control amount in 2 nd control period
Figure BDA0002627673020000132
And when t is 21s, applying the control quantity of the 2 nd control period of the predictive control model optimized solution to the system to obtain a node 25 voltage curve after the 2 nd control, wherein fig. 9 is the node 25 voltage curve after the 2 nd control, and fig. 10 is the voltage curve change of the invention and the NLMPC. As can be seen from FIGS. 9 and 10, the present invention makes the voltage value of the node 25 in the recovery phase rise from 0.9738p.u. to 1.0098p.u., and the optimization time is 1.091s, and the NLMPC can raise the voltage value of the node 25 in the recovery phase from 0.9752p.u. to 1.0115 p.u. Therefore, the two methods can enable the predicted voltage to reach the target value, namely the prediction control method can enable the voltage in the recovery stage to operate in a safe range, and further verify the validity of the voltage.
Reference to the literature
[1] Li national celebration, Liu Xian Chao, Zhan Song, and the like, a TWBS-HVDC direct current side short-circuit fault current calculation method [ J ] based on MMC, automation of an electric power system, 2020,44(05):91-100+290-294.
[2] Weeku, super-high-voltage, Lihui, and the like, the study on the alternating current transient voltage characteristics of the sending end of a hybrid direct current transmission system [ J ], the protection and control of a power system, 2019,47(17):125-132.
[3] Chen-Hou, Wang Changjiang river, Jiang Tao, etc. transient stability assessment of VSC-HVDC-containing AC/DC hybrid system based on port energy [ J ] proceedings of electrotechnology, 2018,33(03):498-511.
[4] Zhao Ming, Li Yongli, Sunwangyu, etc. the influence of commutation failure on the overvoltage at the sending end of an AC/DC hybrid system containing a wind farm [ J ] high voltage technology, 2019,45(11):3666-3673.
[5] The control system for inhibiting the HVDC sending end AC transient overvoltage optimizes the power grid technology, 2017,41(3) 721-728.
[6] The problem of fan off-grid caused by direct current fault of wind-fire bundling direct current outward conveying system is researched [ J ] power grid technology, 2015,39(12):3333-3338.
[7] Xie Shaji, Zhang Xing, Yang Shuying, etc. the double-fed wind driven generator high voltage ride through control strategy based on virtual impedance [ J ]. the Chinese Motor engineering Proc. 2012,32(27):16-23.
[8] The influence of the excitation auxiliary control function of the generator on the dynamic reactive power support capability of an extra-high voltage direct current transmission end is researched [ J ] power grid technology, 2018,42(07):2262-2272.
[9] Wu Ping, Chen Hao, Zhao Bing, et al, wind-light fire bundling AC-DC series-parallel connection delivery system interaction influence and stability research [ J ] power grid technology, 2016,40(07):1934-1942.
[10] Huang Yi Long, Xie Min, Liu Min Bo long term voltage stabilization control [ J ] is predicted based on a model that corrects trajectory sensitivity [ J ] power system automation, 2012,36(03):28-33.
In the embodiment of the present invention, except for the specific description of the model of each device, the model of other devices is not limited, as long as the device can perform the above functions.
Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (3)

1. A transient overvoltage two-stage optimization control method based on track sensitivity is characterized in that the method adopts two-stage optimization control of transient overvoltage and recovery stage voltage of a direct current sending end system, gives consideration to the risk of unsafe voltage in the recovery process of the direct current sending end system, and improves the transient voltage stability of the alternating current and direct current sending end system, and comprises the following steps:
constructing a two-stage optimization control model according to the trajectory sensitivity of the alternating current-direct current system and by combining the basic principle of the MPC;
converting the two-stage optimization control model into a quadratic programming model taking the control quantity increment as an independent control variable by means of transient overvoltage and the trace sensitivity of voltage in a recovery stage to the control quantity;
aiming at a transient overvoltage instability scene of a direct current transmitting end system, solving the control quantity change of transient overvoltage prevention control in a quadratic programming model before a fault occurs, and applying the control quantity change to an alternating current-direct current system;
and applying the change of the control quantity of the voltage control in the recovery stage to the recovery process of the alternating current-direct current system, and rolling and adjusting the control quantity until the transient overvoltage recovery process is operated in a safe range.
2. The two-stage transient overvoltage optimization control method based on trajectory sensitivity as claimed in claim 1, wherein the quadratic programming model using the two-stage optimization control model with control quantity increment as independent control variable is specifically:
Figure FDA0002627673010000011
s.t.nVt,f(k+i)|k＝At,iΔUt(k)
Vt,r(k+i)|k＝at iVt,0(k)|k+(1-at i)cI
Figure FDA0002627673010000012
Vt,min≤Vt,0(k+N)|k+Vt,f(k+N)|k≤Vt,max
ut,min≤ut(k+j)|k≤ut,max
Δut,min≤Δut(k+j)|k≤Δut,max
in the formula, Vt0、VtfAnd VtrRespectively serving as a reference value, a variable quantity and a target value of the transient overvoltage, and respectively serving as a control measure implementation cost and a node voltage prediction deviation punishment in item 1 and item 2 of the objective function; a. thetFor transient overvoltage V of DC transmitting end systemtA trajectory sensitivity matrix to the control quantity, expressed as
Figure FDA0002627673010000013
Figure FDA0002627673010000014
Wherein Q is(o)、VF(p)、kT(q-r)、PHAnd PWCapacitors representing the node o for the over-voltage transient controlReactive power, a generator AVR voltage reference value of a node p, a transformer transformation ratio between a node q and a node r, active power transmitted by the HVDC system and active power of a double-fed wind power plant; delta UtA matrix of transient overvoltage variation at all control moments; a istThe speed degree of the reference track approaching the target value c can be adjusted for designing parameters; i is a unit vector; u. oftAnd Δ utRespectively the control quantity of the transient overvoltage and the variation quantity of the control quantity ut,max、ut,minEach represents utUpper and lower limits of, Δ ut,max、Δut,minEach represents DeltautUpper and lower limits of (d); vt,max、Vt,minRespectively an upper limit and a lower limit of transient overvoltage of a direct current sending end system; n is the number of discrete points of the involved voltage parameters; k. i and j are corresponding k, i and j discrete points.
3. The two-stage transient overvoltage optimization control method based on the trajectory sensitivity as claimed in claim 1, wherein the recovery process of applying the control quantity variation of the voltage control in the recovery stage to the ac/dc system is specifically:
Figure FDA0002627673010000021
s.t.nVs,f(k+i)|k＝As,iΔUs(k)
Vs,r(k+i)|k＝as iVs,0(k)|k+(1-as i)cI
Figure FDA0002627673010000022
Vs,min≤Vs,0(k+i)|k+Vs,f(k+i)|k≤Vs,max
us,min≤us(k+j)|k≤us,max
Δus,min≤Δus(k+j)|k≤Δus,max
in the formula, Vs0、VsfAnd VsrRespectively representing a voltage reference value, a variable quantity and a target value in a recovery stage; a. thesFor the voltage V of the recovery stage of the DC transmitting end systemsA trajectory sensitivity matrix to the control quantity, expressed as
Figure FDA0002627673010000023
Figure FDA0002627673010000024
ΔUsA matrix formed by voltage increments in recovery stages at all control moments; a issDesign parameters for voltage control at the recovery stage; u. ofsAnd Δ usRespectively the controlled quantity of the voltage in the recovery stage and the variable quantity of the controlled quantity us,max、us,minEach represents usUpper and lower limits of, Δ us,max、Δus,minEach represents DeltausUpper and lower limits of (d); vs,max、Vs,minThe upper and lower limits of the voltage in the recovery phase.
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