CN113258590A - Alternating current-direct current system staged voltage control method and system under high wind power permeability - Google Patents

Alternating current-direct current system staged voltage control method and system under high wind power permeability Download PDF

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CN113258590A
CN113258590A CN202110516295.8A CN202110516295A CN113258590A CN 113258590 A CN113258590 A CN 113258590A CN 202110516295 A CN202110516295 A CN 202110516295A CN 113258590 A CN113258590 A CN 113258590A
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CN113258590B (en
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张文
弓帅
李伟佳
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Shandong University
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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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F18/00—Pattern recognition
    • G06F18/20—Analysing
    • G06F18/23—Clustering techniques
    • 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
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • 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
    • 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
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    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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Abstract

The invention belongs to the field of intelligent power grids, and provides a method and a system for controlling voltage of an alternating current-direct current system in stages under high wind power permeability. In the emergency control stage, the voltage control variable of the next local area is determined by prediction and inter-area communication; the voltage control is then performed by model predictive control with the voltage deviation and control cost minimized as objective functions. In a preventive voltage control stage, reactive power replacement is carried out on the quick response equipment by utilizing a generator set and a parallel capacitor in the area, the standby margin of the quick response equipment is increased, and the capability of the system for dealing with sudden accidents is improved. Simulation results show that the strategy can improve the calculation efficiency of long-term voltage control and optimize the reactive power reserve of the system.

Description

Alternating current-direct current system staged voltage control method and system under high wind power permeability
Technical Field
The invention belongs to the field of intelligent power grids, and particularly relates to a method and a system for controlling voltage of an alternating current-direct current system in stages under high wind power permeability.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
With the construction and operation of large-scale offshore wind power plants in China, how to reasonably accept offshore wind power becomes one of the problems to be solved urgently in power systems. The connection mode of the wind power plant and the alternating current system is an important factor influencing the stability of alternating current voltage. The existing connection modes are divided into alternating current access, traditional direct current (LCC-HVDC) access and multi-terminal flexible direct current access (VSC-MTDC). The VSC-MTDC has the advantages of independent active and reactive control, frequency decoupling operation characteristics of a wind power plant and a land grid, capability of forming a multi-terminal direct current grid and the like, and becomes the best choice for the existing wind power grid connection.
With the proportion of the installed capacity of the wind power in the power generation of the power grid becoming larger and larger, the influence area of the wind power on the voltage of the power grid is also enlarged from a wind power feed-in point to the whole alternating current system. When wind power is fed into an alternating current and direct current power grid through the VSC-MTDC, voltage fluctuation of an alternating current system is even out of limit due to intermittence and fluctuation of the wind power. Wind power is fed into an alternating current power grid through different access points, the operating characteristics of alternating current systems of the feed points are different, and the requirement of multi-region multi-target control cannot be met by traditional centralized control. In order to improve the calculation efficiency of long-term voltage control, optimize the reactive power reserve of the system and ensure the voltage stability of the system, the method has important significance for researching the distributed voltage control method of the alternating current and direct current system under high wind power permeability.
According to the inventor, the distributed voltage control method of the alternating current-direct current system under the high wind power permeability has the following problems: (1) at present, in order to deal with uncertainty of renewable energy output, internal voltage regulation of a wind power plant, voltage control of a feed-in power grid and reactive power optimization are mainly researched, but research on long-term voltage control of an alternating current and direct current power grid under high wind power permeability is less. (2) The existing research only considers the emergency voltage control after the fault, and does not consider the optimization of the reactive standby of the system after the voltage enters the safety range. After the emergency voltage control, the fast response reactive power reserve is obviously reduced, if the reactive power replacement is not carried out, the system has no sufficient fast response reactive power reserve in the next control, and the voltage stability of the system is reduced. (3) In the existing long-term voltage instability control scheme, the control characteristic of flexible direct current cannot be fully exerted on the scene that a wind power plant is connected into an alternating current power grid through VSC-MTDC, and the long-term voltage stability of the system is reduced.
Disclosure of Invention
In order to solve the problems, the invention provides a staged voltage control method of an alternating current-direct current system under high wind power permeability. The method can effectively avoid voltage out-of-limit caused by wind power fluctuation, improve the calculation speed and ensure the long-term voltage stability of the system.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, a method for controlling voltage of an alternating current-direct current system in stages under high wind power permeability is disclosed, which comprises the following steps:
partitioning based on voltage sensitivity by using wind power prediction output data and taking a wind power access point as a clustering center;
acquiring the lowest node voltage information and the highest node voltage information in each area, and performing staged voltage control, wherein the staged voltage control comprises the following steps: an emergency control stage, which adopts an emergency control mode, and a preventive voltage control stage, which adopts a preventive voltage control mode;
in the emergency control stage, the voltage control quantity of the next local area is determined by prediction and inter-area communication; then, performing voltage control by using model predictive control with the minimum voltage deviation and control cost as an objective function; and in the preventive voltage control stage, reactive power replacement is carried out on the quick response equipment by utilizing the generator set and the parallel capacitor in the area, and the standby margin of the quick response equipment is increased.
And under the emergency control mode, judging whether reactive power and flexible direct current control quantity in the region can meet the voltage control requirement, if so, executing emergency voltage control in the region, if not, adding a reactive power control variable with the maximum voltage sensitivity among systems into a control sequence to carry out voltage coordination control among the regions, and if not, starting load shedding control.
According to the further technical scheme, when the partition based on the voltage sensitivity is carried out, the voltage sensitivity of a wind power access point to a PQ node is solved, and the PQ node is clustered to form a primary partition;
then solving the average voltage sensitivity of the PV node to the partition after the PQ node clustering;
and on the premise of ensuring connectivity, clustering the PV nodes to an area with the maximum average sensitivity.
According to the further technical scheme, when the staged voltage control is carried out, whether the deviation of the lowest node voltage information and the highest node voltage information in each area is larger than a first set value or not is judged, if the deviation is larger than the first set value, an emergency control mode is entered, if the deviation is not larger than the first set value, whether the deviation of the highest or lowest node voltage information and the set value is larger than a second set value or not is judged, if the deviation is larger than the second set value, a preventive voltage control mode is entered, and if the deviation is not larger than the first set value, a normal operation mode is regarded as not to be controlled.
In the emergency control mode, after being greatly disturbed, the emergency operation state is entered, the controller judges whether the reactive power reserve of the area can meet the control requirement, if not, the controller sends a request to an adjacent area, reactive equipment is added according to the voltage sensitivity until the control requirement is met, and then a quick response reactive device and multi-terminal flexible direct current access are used for voltage control, so that the voltage deviation and the control cost are minimized.
According to the further technical scheme, under the preventive voltage control mode, the system voltage is ensured to be within the safety range, and meanwhile, the standby margin of the quick-response reactive power equipment is increased through reactive power replacement.
In a further technical scheme, the emergency voltage control step in the emergency control mode is as follows:
step 1: when the deviation of the node voltage of the alternating current system and a set value is larger than a first set value, starting emergency voltage control;
step 2: solving the predicted track of the system in the prediction time domain and the track sensitivity of each control quantity;
and step 3: judging whether the reactive control quantity and the flexible direct active power control quantity in the area can meet the requirement of voltage control, if the reactive control quantity and the flexible direct active power control quantity in the area can not meet the requirement, increasing the reactive control quantity of adjacent areas, sequentially increasing the installation sensitivity until the requirement is met, and if the reactive control quantity and the flexible direct active power control quantity can not meet the requirement, starting load shedding control;
and 4, step 4: solving an emergency voltage control objective function to obtain an optimal control sequence of the voltage control optimization problem of the alternating current and direct current system;
and 5: and (3) rolling control: applying an optimal control sequence at the initial time of the next period of control sampling, detecting the system voltage, and if the system voltage meets the requirement, ending the calculation; otherwise, returning to the step 2.
According to the further technical scheme, the emergency voltage control objective function is minimum in voltage deviation and control cost.
In a further technical scheme, the preventive voltage control step in the preventive voltage control mode is as follows:
step 1: when the deviation of the alternating current system voltage and the set value is smaller than a second set value, starting preventive control;
step 2: solving the predicted track of the system in the prediction time domain and the track sensitivity of each control quantity;
and step 3: solving an objective function to obtain an optimal control sequence of the voltage control optimization problem of the alternating current and direct current system;
and 4, step 4: and applying an optimal control sequence at the initial moment of the next period of the control sampling. Detecting the system voltage, and if the system voltage meets the requirement, finishing the calculation; otherwise, returning to the step 2.
In a second aspect, a staged voltage control system for an ac/dc system under high wind power permeability is disclosed, comprising:
a partitioning module configured to: partitioning based on voltage sensitivity by using wind power prediction output data and taking a wind power access point as a clustering center;
a phased voltage control module configured to: acquiring the lowest node voltage information and the highest node voltage information in each area, and performing staged voltage control, wherein the staged voltage control comprises the following steps: an emergency control stage, which adopts an emergency control mode, and a preventive voltage control stage, which adopts a preventive voltage control mode;
in the emergency control stage, the voltage control quantity of the next local area is determined by prediction and inter-area communication; then, performing voltage control by using model predictive control with the minimum voltage deviation and control cost as an objective function; and in the preventive voltage control stage, reactive power replacement is carried out on the quick response equipment by utilizing the generator set and the parallel capacitor in the area, and the standby margin of the quick response equipment is increased.
And under the emergency control mode, judging whether reactive power and flexible direct current control quantity in the region can meet the voltage control requirement, if so, executing emergency voltage control in the region, if not, adding a reactive power control variable with the maximum voltage sensitivity among systems into a control sequence to carry out voltage coordination control among the regions, and if not, starting load shedding control.
In order to solve the above problem, a third aspect of the present invention provides a computer-readable storage medium.
A computer-readable storage medium, on which a computer program is stored, which program, when being executed by a processor, carries out the steps of the control method as described above.
In order to solve the above problem, a fourth aspect of the present invention provides a terminal device.
A terminal device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps in the control method as described above when executing the program.
The invention has the beneficial effects that:
the invention considers the wind power uncertainty and the influence of flexible direct current on the voltage stability of the alternating current system, fully utilizes the flexibility of the flexible direct current system on power modulation, designs a two-stage voltage control method of the alternating current and direct current system under high wind power permeability, and improves the long-term voltage stability of the system.
The high wind power permeability refers to the time when the installed wind power capacity accounts for the installed capacity of the regional power grid in a large percentage. In this case, the fluctuation and randomness of the wind power can cause the grid voltage to generate obvious fluctuation or even exceed the limit, and the voltage stability of the grid is endangered.
The invention provides a two-stage voltage control strategy, emergency voltage control is carried out by using fast reactive power equipment in the first stage, and the voltage stability of a system is ensured; reactive power replacement is carried out in the second stage of preventive voltage control, the fast response reactive power reserve margin of the system is increased, and the coping capability of the system after the system is disturbed again is improved.
The invention carries out voltage control through a distributed algorithm, and each area can be controlled only by communicating with adjacent areas, thereby reducing the dependence of the system on communication and improving the solving speed of the voltage optimization problem.
According to the method, the alternating current and direct current control quantity is coordinated and optimized by solving the quadratic programming problem of model predictive control, and the long-term voltage stability of the system is improved.
Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a flow chart of a two-stage voltage control framework of an AC/DC system under high wind power permeability according to an embodiment of the present invention;
FIG. 2 is a flow chart of emergency voltage control of the AC/DC system at high wind permeability according to the embodiment of the present invention;
FIG. 3 is a flow chart of voltage prevention control of the AC/DC system under high wind power permeability according to the embodiment of the present invention;
FIG. 4 is a diagram illustrating partitioning results provided by an embodiment of the present invention;
FIG. 5 is a wind farm predicted capacity curve.
Fig. 6 is a comparison between the weak bus voltage when the wind power output fluctuation arithmetic example system provided by the embodiment of the invention applies control and does not apply control.
Detailed Description
The invention is further described with reference to the following figures and examples.
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
Example one
As shown in fig. 1, the ac/dc system staged voltage control method under high wind power permeability includes the following steps:
step 1: acquiring wind power predicted output and real-time running state information of a power grid, and partitioning based on voltage sensitivity according to the acquired information;
step 2: obtaining the voltage information of all nodes in each area, and judging whether the maximum deviation of the voltage and the set value is more than delta VemerIf yes, the system enters an emergency control mode, and if not, the system enters a step 4;
and step 3: and judging whether the reactive power and flexible direct current control quantity in the region can meet the voltage control requirement. If so, performing in-zone emergency voltage control. And if the voltage cannot be met, adding a reactive control variable with the maximum voltage sensitivity among the systems into a control sequence to perform inter-area voltage coordination control, and if the voltage cannot be met, starting load shedding control. After the control is finished, returning to the step 2;
and 4, step 4: judging whether the maximum deviation of all node voltages of the system and a set value is more than delta V or notprvtIf the voltage is not greater than the preset voltage, the system enters a preventive voltage control mode, and if the voltage is not greater than the preset voltage, the system is regarded as a normal operation mode and is not controlled.
Note that Δ VemerGreater than Δ VprvtNamely, emergency voltage control is used when the voltage deviation is large; when smaller, preventative control is employed.
The influence of large-scale wind power access on the voltage stability of the alternating current system is considered, the flexibility and controllability of the VSC-MTDC are fully utilized, and the effectiveness and the rapidity of long-term voltage control are improved. In the first control stage, the system enters an emergency operation state after being greatly disturbed. First, the controller determines whether the reactive power reserve of the area can meet the control requirements. And if not, sending a request to an adjacent area, and increasing the reactive equipment according to the voltage sensitivity until the control requirement is met. The voltage control is then performed by the MPC using fast response reactive devices and VSC-MTDC with the goal of minimizing voltage deviation and control costs. The second control stage is preventive voltage control, the system voltage is ensured to be within a safety range, meanwhile, the standby margin of the quick response reactive power equipment is increased through reactive power replacement, and the response capability of the system to emergency events is improved.
In the step 1, wind power predicted output and power grid real-time running state information are obtained based on wide area measurement, and partitioning based on voltage sensitivity is carried out according to the obtained information;
specifically, in consideration of the scale of the ac/dc hybrid grid, the centralized control cannot meet the control requirements in terms of calculation time and multi-area independent control. It is necessary to divide the grid into a number of control areas according to the voltage sensitivity. Since wind power is fed into the alternating current system at different busbars through the VSC-MTDC, the control mode and parameters of each VSC converter will have different effects on the busbars at different positions. In order to clarify the influence area of each converter station, the wind power predicted output data is used, and the wind power access point is used as a clustering center to perform voltage sensitivity-based partitioning, which is shown in fig. 4. Clustering is divided into two steps, firstly, the voltage sensitivity of the wind power access point to the PQ node is solved, and the PQ node is clustered to form a primary partition. The voltage sensitivity is obtained by adopting a method of a Yaoyu matrix inverse matrix:
Figure BDA0003062364240000091
wherein, the delta P, the delta Q, the delta theta and the delta V are respectively the deviation of active power, reactive power, phase angle and voltage, J Jacobian matrix and Jpθ、Jpv、Jqθ、JqvA sub-matrix of the jacobian matrix.
In order to accurately account for the effect of active power on voltage, the complete decoupling of PQ is not considered here. Let Δ P be 0, the equation can be simplified as:
Figure BDA0003062364240000092
then, according to the sensitivity matrix S, the voltage sensitivity alpha between the nodes i and j is obtainedijThe PQ nodes are clustered into respective regions with the highest voltage sensitivity to wind access points.
Figure BDA0003062364240000093
In order to improve the effectiveness of the control, it is necessary to determine which control variables are most effective for each control region. And then solving the average voltage sensitivity of the PV node to the partition after the PQ node clustering:
Figure BDA0003062364240000094
in the formula, Sr,gAverage voltage sensitivity of PV node g to nodes within PQ partition r, nrIs the number of PQ nodes in the region r, alphakgThe voltage sensitivity of the PV node g to the PQ node k can be obtained by perturbation. And on the premise of ensuring connectivity, clustering the PV nodes to an area with the maximum average sensitivity. After partitioning, the optimization variables and the control dimension are obviously reduced compared with the original network, so that the solving time of the control optimization problem can be greatly reduced.
In steps 2 and 4, the power system is divided into normal, alarm and emergency states according to the maximum value of the deviation of the zone voltage from the reference value of 1.0p.u. Obtaining the operation state of the regional power grid based on wide-area measurement, and performing corresponding control, wherein the operation state is specifically classified as follows:
1) and (3) normal operation state: the deviation of the voltage from the reference value is less than the control deviation delta V of the preventive voltageprvtNo control is performed.
2) Warning the running state: voltage deviation greater than Δ VprvtBut still less than the emergency control startup deviation avemerThe system performs preventive voltage control to avoid voltage out-of-limit after being disturbed.
3) An emergency operation state: delta V when the voltage deviation is greater thanemerFirstly, the emergency voltage control is adopted to enable the system to enter an alert operation state, and then the preventive voltage control is adopted to enable the system to enter a normal operation state.
In step 3, calculating the regional reactive margin based on the wide-area measurement data to judge whether the regional reactive margin can meet the control requirement, if the regional reactive margin cannot meet the control requirement, adding a reactive control variable with the maximum voltage sensitivity among the systems into a control sequence to perform voltage coordination control among the regions, and if the regional reactive margin cannot meet the control requirement, starting load shedding control.
Specifically, when the deviation between the lowest or highest node voltage in the region and the reference value is more than Δ VemerThen, the emergency voltage control is started. Before control is implemented, whether reactive and flexible direct current active control quantity in the region can meet the control requirement or not is calculated
Figure BDA0003062364240000101
Figure BDA0003062364240000102
In the formula, SiSensitivity for control variables ui,ui,max,ui,minCurrent, maximum and minimum values of the control variable, NuIs the number of control variables, theta is a margin coefficient, V is the voltage amplitude before control,
Figure BDA0003062364240000103
andV limare the upper and lower limits of the emergency voltage control.
And when the reactive margin requirement cannot be met, adding the control variable with the maximum sensitivity of the adjacent region into the control sequence, and calculating again until the requirement is met. And after the reactive devices in the adjacent areas are all added into the control sequence, starting the LCC arc extinguishing angle and active power control, and if the voltage control requirements cannot be met, starting load shedding control. It is noted that all LCC-HVDC control needs to be performed on the basis of ensuring its commutation success, i.e. the extinction angle is larger than the critical extinction angle.
In an embodiment, as shown in fig. 2, a flow chart of emergency voltage control of an ac/dc system under high wind permeability is shown; the method comprises the following steps:
step 1: when the deviation of the node voltage of the alternating current system and the set value is more than delta VemerThen, the emergency voltage control is started.
Step 2: and solving the predicted track of the system in the prediction time domain and the track sensitivity of each control quantity.
And step 3: and judging whether the reactive control quantity and the flexible direct active power control quantity in the region can meet the requirement of voltage control, if not, increasing the reactive control quantity of adjacent regions, and sequentially increasing the installation sensitivity until the requirement is met. If the load is still not satisfied, load shedding control is started.
And 4, step 4: and solving the emergency voltage control objective function to obtain an optimal control sequence of the alternating current and direct current system voltage control optimization problem.
And 5: and (3) rolling control: and applying an optimal control sequence at the initial moment of the next period of the control sampling. Detecting the system voltage, and if the system voltage meets the requirement, finishing the calculation; otherwise, returning to the step 2.
In the embodiment, the large-scale wind power access enters an emergency operation state when the alternating current system is subjected to large disturbance, and emergency voltage control is adopted to ensure the voltage safety of the system. And determining an optimization variable through information interaction between the regions by taking the voltage deviation and the control cost as an objective function, and applying control.
In step 1, the voltage level of each partitioned area is determined based on the wide area measurement data, and whether emergency voltage control is required is determined.
In step 2, an implicit trapezoidal integration method and a Newton-Raphson method are applied to perform time domain simulation, and the voltage output trajectory of the system is predicted. And (4) obtaining the track sensitivity of each alternating current and direct current control quantity of the alternating current and direct current system to the load bus voltage through a Jacobian matrix obtained in time domain simulation.
The AC-DC system model is described by a differential-algebraic equation:
the power system model may be represented by a set of differential algebraic equations:
Figure BDA0003062364240000121
0＝g(x,y,λ)
wherein x represents the state variable of the system, y is an algebraic variable, and λ is a parametric variable.
Traditional direct current system model:
Figure BDA0003062364240000122
in the formula: vacR、VacIThe voltages of the commutation buses of the rectification station and the inversion station are respectively; vd0r、Vd0iThe no-load direct current voltages of the rectifier and the inverter are respectively; vdr、VdiDirect current voltages of a rectifier and an inverter respectively; i isdIs a direct line current; alpha and gamma are respectively the advanced trigger angle of the rectifier and the arc-quenching angle of the inverter; n is the number of six-pulse current-changing bridges; rdIs a direct current line resistor; kTr、KTiThe transformation ratios of the rectifier side converter transformer and the inverter side converter transformer are respectively; xcr、XciThe single-bridge phase-change reactance is respectively at the rectification side and the inversion side; pdcr、PdciRespectively the active power absorbed by the rectifier and the active power output by the inverter; qdcr、QdciRespectively absorbing reactive power of rectifier and inverterPower; porder、γorderThe control quantity setting values of the rectification side and the inversion side are respectively in a constant power-constant arc-quenching angle control mode.
Flexible direct current system model:
Figure BDA0003062364240000131
let α be arctan (R/X)L),
Figure BDA0003062364240000132
R and XLRespectively representing the equivalent resistance and reactance of the converter transformer, and Y is the equivalent admittance. The mathematical model for VSC-HVDC is then:
Pc、Qcfor the power absorbed by the converter station, Ps、QsFor power exchanged with an external AC system, UsFor ac system voltages, δ is the PMW modulation phase angle. Suppose that the DC voltage utilization of the PWM converter is
Figure BDA0003062364240000133
M is a modulation value, then
Figure BDA0003062364240000134
And calculating the track sensitivity of each bus voltage and the voltage sensitivity of the conventional direct current feed bus. Regarding a traditional direct current and flexible direct current system as a special load on the alternating current system side, modifying a steady-state power flow equation of a bus k connected with a current converter and a bus l of the alternating current system:
Figure BDA0003062364240000135
in the formula: the delta P and the delta Q are error column vectors of active power and reactive power in the load flow calculation process respectively; psAnd QsRespectively injecting active power and reactive power into the generator and the load at corresponding nodes; pdcAnd QdcInjecting active power and reactive power into direct current of a current conversion bus connected with the current converter; v and delta are the amplitude and phase angle of the AC bus voltage respectively; g and B are conductance and susceptance of corresponding elements of the node admittance matrix respectively.
For the traditional direct current, when two ends of a line are respectively connected to the current conversion buses i and J, the transmission power of a direct current system is irrelevant to the voltage phase angle of the current conversion buses, so that J in a tidal current Jacobian matrixPδAnd JQδRemaining unchanged, for corresponding elements (J) in the Jacobian matrixPV)m,nAnd (J)QV)m,nModification is carried out:
Figure BDA0003062364240000141
in the formula: j. the design is a squarePV' and JQV' modified jacobian submatrices J, respectivelyPVAnd JQV；
Figure BDA0003062364240000142
And
Figure BDA0003062364240000143
the sensitivity of the dc power to the amplitude of the dc bus voltage is traded.
Under the control mode of determining active power at the rectification side and determining the extinction angle at the inversion side, the sensitivity of the amplitude value of the converter bus voltage to the transmission power of the rectification station is as follows:
Figure BDA0003062364240000144
similarly, the sensitivity of the amplitude of the converter bus voltage to the transmission power of the inverter station is as follows:
Figure BDA0003062364240000151
for flexible direct current, the power inflow into the converter station is defined as positive and the outflow as negative. Because flexible direct current active and reactive decoupling is adjustable, the sensitivity of active and reactive control quantity to voltage is analyzed respectively as follows:
1) the active control mode is divided into a constant active power control mode and a constant direct current voltage control mode. When a fault occurs, the direct current voltage is set to be a fixed value and does not participate in alternating current and direct current coordination control as a control quantity, so that only the voltage sensitivity of the fixed active power control mode is analyzed.
When the active power set value of the converter station changes, the active power exchanged between the fixed direct-current voltage converter station and the alternating-current system is changed into the following power because the direct-current system obeys the active power balance:
Figure BDA0003062364240000152
in the formula: CV denotes a constant dc voltage converter station; ps,jAnd the setting value of the jth fixed active power converter station is shown, and the delta P shows the change quantity of the setting value of the fixed active power converter station. Delta PlossIs the loss of the dc network.
As can be seen from the above description, changing the set value of the active power of the converter station not only changes the active power of the converter station itself but also affects the active power of the fixed dc voltage converter station, and the active power changes at two locations have equal magnitude and opposite directions, and the sensitivity of the two locations can be obtained from the jacobian matrix.
2) The reactive control mode is divided into constant reactive power and constant alternating voltage. The voltage sensitivity of the output reactive power of each converter station to any alternating current bus can be obtained through a Jacobian matrix. For the control mode of the fixed alternating current voltage, the difference value of the reactive power output by different bus voltage set values can be obtained by a flexible direct current output power formula, and the difference value is multiplied by the sensitivity of the reactive power to the voltage, namely:
SU,i＝SQ,i*ΔQ
in the formula: sU,iIndicating the voltage sensitivity, S, of a fixed AC voltage set-point to the AC bus iQ,iThe voltage sensitivity of the reactive power to the ac bus i is shown, and Δ Q shows the amount of change in the reactive power corresponding to a change in the set value of the constant ac voltage.
And iteratively solving a differential-algebraic equation set of the AC/DC system model by adopting an implicit trapezoidal method and a Newton method which are commonly used in time domain simulation, so as to obtain a voltage prediction output trajectory of the AC/DC system, and solving the voltage trajectory sensitivity through a system Jacobian matrix in the time domain simulation process. The linear relationship between the input and the output of the system under the voltage stabilization control is expressed as follows:
Figure BDA0003062364240000161
in which the subscript k denotes the respective variable at tkThe value of the moment;
Figure BDA0003062364240000162
predicting a trajectory for the voltage;
Figure BDA0003062364240000163
is a change in the inputted control amount;
Figure BDA0003062364240000168
as voltage amplitude pairs
Figure BDA0003062364240000164
The trajectory sensitivity of (1).
In step 4, the objective function and constraints are as follows:
Figure BDA0003062364240000165
s.t.
Figure BDA0003062364240000166
ui,min≤uk,i≤ui,max k∈[1,Nc]
Δui,min≤Δuk,i≤Δui,max k∈[1,Nc]
Figure BDA0003062364240000167
in the formula, the objective function is divided into two parts: voltage deviation and control cost, omegaac,ωuThe voltage deviation and the weight coefficient of the control variable, respectively. k denotes a k-th control period. N is a radical ofp,NcRespectively, a prediction period and a control period.
Figure BDA0003062364240000171
Is the voltage reference at time k. Vk,V′kThe voltage amplitudes before and after the control at the k-th time are respectively. Under normal circumstances, V'kTaking the highest or lowest node voltage in the region, and V 'when the LCC receiving end converter station is contained in the region'kAnd taking the highest or lowest node voltage in the area and the bus node voltage at the LCC feed-in end.
Figure BDA0003062364240000172
Is the sensitivity of the ith control quantity to the voltage of the control quantity u at the kth time. Δ uk,iIs the amount of change in the ith control amount at the kth time. u. ofi,max,ui,minAre the upper and lower limit values of the controlled variable. Δ ui,max,Δui,minAre upper and lower limit values for a single change in the controlled variable. Pvsc,Qvsc,SvscThe active power, the reactive power and the capacity of the VSC converter station are respectively shown.
The randomness of wind can affect the voltage control effect of a power grid in a wind power feeding area, and the reason is that the predicted data and the real-time data have deviation. The traditional deterministic control method does not consider the random characteristic of wind power, so that the control effect is not ideal when the prediction deviation is large. The processing method has robust control, opportunity constraint and the like. The opportunity constraint is selected here because it can have better economy while considering the wind power impact on the grid voltage, the control is not over conservative. The constraints are defined as:
Figure BDA0003062364240000173
Vpis the current system voltage amplitude.
Figure BDA0003062364240000174
VpAn upper and lower limit, respectively, for acceptable system voltage amplitude. Sq，SwThe sensitivity of reactive power and wind power active power respectively. Δ Q, Δ PwRespectively, the reactive control quantity and the variable quantity of the wind power active power. Beta is the probability that needs to be satisfied.
The prediction error of the wind power output is assumed to follow a normal distribution with mean 0 and variance σ 2. PfIs the predicted value of wind power, PrThe probability is expressed as the formula if the total installed capacity of the wind power plant
σ2＝0.2Pf+0.02Pr
Figure BDA0003062364240000175
For the convenience of solving, the opportunity constraint can be converted into equivalent inequality constraint. The specific method comprises the steps of obtaining wind power prediction output and probability distribution of wind power prediction deviation, and setting confidence coefficient beta of constraint conditions. According to a normal distribution formula, under a certain probability distribution, corresponding wind power prediction deviation values under a certain confidence coefficient can be obtained, and opportunity constraints are converted into deterministic inequality constraints. And adding the same as a constraint condition into an optimization control problem.
Figure BDA0003062364240000181
Figure BDA0003062364240000182
In an embodiment, as shown in fig. 3, a control flow chart of the preventive voltage of the ac/dc system under high wind permeability is shown; the method comprises the following steps:
step 1: when the deviation of the AC system voltage and the set value is less than delta VprvtWhen so, preventive control is initiated.
Step 2: and solving the predicted track of the system in the prediction time domain and the track sensitivity of each control quantity.
And step 3: and solving a preventive voltage control objective function to obtain an optimal control sequence of the alternating current and direct current system voltage control optimization problem.
And 4, step 4: and (3) rolling control: and applying an optimal control sequence at the initial moment of the next period of the control sampling. Detecting the system voltage, and if the system voltage meets the requirement, finishing the calculation; otherwise, returning to the step 2.
In the embodiment, when the large-scale wind power access system is recovered to the warning range through the emergency voltage control after the alternating current system is in the emergency operation state due to large disturbance, the system voltage is in a safer state at the moment, and if the fast response reactive power resource is still used, the reactive power reserve of the system is unbalanced. When the system is disturbed again, the system cannot respond quickly. Therefore, the traditional generator and the parallel capacitor are required to replace a quick response reactive resource, so that the reactive power of the whole system is more balanced, more quick reactive power standby of the system is ensured, and the voltage stability of the system is improved.
In step 3, compared with the emergency control, the reactive standby term in the preventive control has a larger weight coefficient, and the control cost and the voltage fluctuation term have a smaller weight coefficient. The aim is to increase the reactive power reserve margin of the fast response equipment (VSC) when in preventive control, and simultaneously reduce the voltage fluctuation and the control cost, wherein the voltage fluctuation item is used as the soft constraint of the voltage.
Figure BDA0003062364240000191
Figure BDA0003062364240000192
ΔUmin≤|ΔUk|≤ΔUmax k∈[1,Np]
In the formula, ωuWeight coefficient, ω, for controlling costiIs the weight coefficient, ω, of the ith reactive marginacIs a weight coefficient of voltage fluctuation, thetai,kFor the reactive margin of the ith control variable at time k, VaveIs the average voltage over a period of time, QmaxAnd Q is the maximum and current values of the reactive power output, respectively.
FIG. 4 is a Nordic 32-based hybrid multi-feed AC/DC system. The partitioning method can obtain the partitioning result shown in fig. 4, and the power grid is partitioned into four areas. 4032-4044 AC line is changed into conventional DC transmission (LCC-HVDC). The rated capacity of an offshore wind farm is 3000MW, and the flexible direct current converter station VSC1, VSC2 and VSC3 correspond respectively to an alternating current power grid bus4012,4044,4062 fed through multi-end flexible direct current (VSC-MTDC), and the wind farm converter station is VSC 4. To maintain the balance of power generation and load, the load L1-L5(2750MW) in the center area was increased by a factor of 1.2. The original system generator g10(600MVA) and generator g17(530MVA) were deleted. The VSC1 and the VSC2 of the converter station are P-V droop control [69], the VSC2 is constant active control, and the VSC4 is constant frequency control. The specific control parameters of VSC-HVDC are:
VSC1(bus 4012): P-V droop control, Ps 600MW, Udc 1.0p.u., droop coefficient K6, constant reactive power control, Qs 255 Mvar.
VSC2(bus 4044): P-V droop control, Ps 550MW, Udc 0.99p.u., droop coefficient K6, constant reactive power control, Qs 0 Mvar.
3) VSC3(bus 4063): and the active power control is fixed, wherein Ps is 530MW, the alternating voltage control is fixed, and Us is 1.01p.u.
3) VSC4 (wind farm): constant frequency control: f is 50HZ, constant ac voltage control, Us is 1.01p.u.
Conventional DC voltage +/-500 kV and capacity 2000 MVA. And a filter and a parallel capacitance compensation device are respectively arranged on the rectification inversion side. The rectification side adopts constant direct-current voltage control, the inversion side adopts constant extinction angle control, and the initial extinction angle setting value is 18 degrees.
When the power grid normally operates, a fault does not occur, and due to the fluctuation of the wind power output, the partial bus voltage of the receiving-end alternating current system has larger fluctuation and even exceeds the limit, and the voltage needs to be controlled. The wind output curve is shown in fig. 5, and the voltage curve before and after control is shown in fig. 6. The voltage of the post control bus4044 is not out of limit. Within 80-300s, preferentially using reactive power control of the VSC converter station with the highest response speed to control the voltage to enable the voltage to be stabilized between 0.95-1.05 p.u, starting preventive reactive voltage control after 300s, increasing input of a parallel capacitor and a generator, reducing reactive power output of the VSC to increase reactive margin of the VSC converter station, and finally enabling the voltage to be stabilized between 1.01-1.03 p.u. When t is 100s, the voltage is out of limit, the control speed is fastest, the reactive power of the VSC2 converter station with the highest sensitivity is preferentially used, when t is 150s, the voltage reaches the highest value, and the reactive margin of the VSC converter station is the smallest and is 0.343. Within 300-900 s, the voltage is not out of limit, but the voltage fluctuation is large. At the moment, preventive voltage control is adopted, and the input of the generator and the parallel capacitor is gradually increased to replace the reactive power of the VSC converter station with quick response, so that the reactive margin of the converter station is increased, and enough quick response reactive standby power is reserved for emergency
Example two
This embodiment provides an alternating current-direct current system two-stage voltage control system under high wind-powered electricity generation permeability, includes:
a partitioning module configured to: partitioning based on voltage sensitivity by using wind power prediction output data and taking a wind power access point as a clustering center;
a phased voltage control module configured to: acquiring the lowest node voltage information and the highest node voltage information in each area, and performing staged voltage control, wherein the staged voltage control comprises the following steps: an emergency control stage, which adopts an emergency control mode, and a preventive voltage control stage, which adopts a preventive voltage control mode;
in the emergency control stage, the voltage control quantity of the next local area is determined by prediction and inter-area communication; then, performing voltage control by using model predictive control with the minimum voltage deviation and control cost as an objective function; and in the preventive voltage control stage, reactive power replacement is carried out on the quick response equipment by utilizing the generator set and the parallel capacitor in the area, and the standby margin of the quick response equipment is increased.
The partition module comprises: a sensitivity calculation module to: calculating the track sensitivity of each bus voltage and the voltage sensitivity of each control quantity to the DC feed-in bus by combining time domain simulation based on initial value information of the AC/DC system, the DC feed-in bus and the DC system under high wind power permeability;
a phased voltage control module comprising:
a control start judgment module for: judging whether to start emergency voltage control and preventive voltage control according to the regional voltage deviation;
an inter-region coordination control amount determination module for: calculating reactive margin in the area based on the wide area measurement data and determining whether to increase the participation coordination control amount between the areas or not based on the reactive margin;
an optimal control sequence solving module to: and respectively carrying out optimization solving on the corresponding optimal control sequences of the voltage stability coordination control aiming at respective control objective functions of the emergency voltage control and the preventive voltage control.
EXAMPLE III
The present embodiment provides a computer-readable storage medium on which a computer program is stored, which when executed by a processor implements the steps in the control method as in the first embodiment example above.
Example four
The embodiment provides a terminal device, which includes a memory, a processor and a computer program stored in the memory and capable of running on the processor, wherein the processor executes the program to implement the steps in the control method according to the first embodiment.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A staged voltage control method for an alternating current-direct current system under high wind power permeability is characterized by comprising the following steps:
partitioning based on voltage sensitivity by using wind power prediction output data and taking a wind power access point as a clustering center;
acquiring the lowest node voltage information and the highest node voltage information in each area, and performing staged voltage control, wherein the staged voltage control comprises the following steps: an emergency control stage, which adopts an emergency control mode, and a preventive voltage control stage, which adopts a preventive voltage control mode;
in the emergency control stage, the voltage control quantity of the next local area is determined by prediction and inter-area communication; then, performing voltage control by using model predictive control with the minimum voltage deviation and control cost as an objective function; and in the preventive voltage control stage, reactive power replacement is carried out on the quick response equipment by utilizing the generator set and the parallel capacitor in the area, and the standby margin of the quick response equipment is increased.
2. The method for controlling the voltage of the alternating current-direct current system in stages under the high wind power permeability of claim 1 is characterized in that when the partition based on the voltage sensitivity is carried out, the voltage sensitivity of a wind power access point to a PQ node is firstly solved, and the PQ node is clustered to form a primary partition;
then solving the average voltage sensitivity of the PV node to the partition after the PQ node clustering;
and on the premise of ensuring connectivity, clustering the PV nodes to an area with the maximum average sensitivity.
3. The method according to claim 1, wherein when the voltage control is performed in stages, based on the lowest node voltage information and the highest node voltage information in each region, it is determined whether the deviation from the set value is greater than a first set value, if so, the emergency control mode is entered, if not, the deviation from the set value is determined whether the deviation from the highest or lowest voltage is greater than a second set value, if so, the preventive voltage control mode is entered, and if not, the normal operation mode is determined and the control is not performed.
4. The method for controlling the voltage of the alternating current-direct current system in stages under the high wind power permeability as claimed in claim 1, wherein in the emergency control mode, after being greatly disturbed, the alternating current-direct current system enters an emergency operation state, the controller judges whether the reactive power reserve of the area can meet the control requirement, if the reactive power reserve of the area can not meet the control requirement, the controller sends a request to an adjacent area, increases reactive power equipment according to the voltage sensitivity until the control requirement is met, and then uses a fast response reactive power device and multi-terminal flexible direct current access to carry out voltage control, so that the voltage deviation and the control cost are minimized.
5. The method according to claim 1, wherein in the preventive voltage control mode, the reserve margin of the fast response reactive power equipment is increased by reactive power replacement while the system voltage is ensured within a safe range.
6. The method for controlling the voltage of the alternating current-direct current system in stages under the high wind power permeability of claim 1, wherein the emergency voltage control step in the emergency control mode is as follows:
step 1: when the deviation of the node voltage of the alternating current system and a set value is larger than a first set value, starting emergency voltage control;
step 2: solving the predicted track of the system in the prediction time domain and the track sensitivity of each control quantity;
and step 3: judging whether the reactive control quantity and the flexible direct active power control quantity in the area can meet the requirement of voltage control, if the reactive control quantity and the flexible direct active power control quantity in the area can not meet the requirement, increasing the reactive control quantity of adjacent areas, sequentially increasing the installation sensitivity until the requirement is met, and if the reactive control quantity and the flexible direct active power control quantity can not meet the requirement, starting load shedding control;
and 4, step 4: solving an emergency voltage control objective function to obtain an optimal control sequence of the voltage control optimization problem of the alternating current and direct current system;
and 5: and (3) rolling control: applying an optimal control sequence at the initial time of the next period of control sampling, detecting the system voltage, and if the system voltage meets the requirement, ending the calculation; otherwise, returning to the step 2.
7. The method for controlling the voltage of the alternating current-direct current system in stages under the high wind power permeability of claim 1, wherein the preventive voltage control step in the preventive voltage control mode is as follows:
step 1: when the deviation of the alternating current system voltage and the set value is smaller than a second set value, starting preventive control;
step 2: solving the predicted track of the system in the prediction time domain and the track sensitivity of each control quantity;
and step 3: solving an objective function to obtain an optimal control sequence of the voltage control optimization problem of the alternating current and direct current system;
and 4, step 4: and applying an optimal control sequence at the initial moment of the next period of the control sampling. Detecting the system voltage, and if the system voltage meets the requirement, finishing the calculation; otherwise, returning to the step 2.
8. Alternating current-direct current system is voltage control system stage by stage under high wind-powered electricity generation permeability, characterized by includes:
a partitioning module configured to: partitioning based on voltage sensitivity by using wind power prediction output data and taking a wind power access point as a clustering center;
a phased voltage control module configured to: acquiring the lowest node voltage information and the highest node voltage information in each area, and performing staged voltage control, wherein the staged voltage control comprises the following steps: an emergency control stage, which adopts an emergency control mode, and a preventive voltage control stage, which adopts a preventive voltage control mode;
in the emergency control stage, the voltage control quantity of the next local area is determined by prediction and inter-area communication; then, performing voltage control by using model predictive control with the minimum voltage deviation and control cost as an objective function; and in the preventive voltage control stage, reactive power replacement is carried out on the quick response equipment by utilizing the generator set and the parallel capacitor in the area, and the standby margin of the quick response equipment is increased.
9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the control method according to any one of the preceding claims 1 to 7.
10. A terminal device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the steps of the control method according to any of the preceding claims 1-7 are implemented when the program is executed by the processor.
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