CN113162095B - Direct-current voltage control method of multi-terminal flexible direct-current system - Google Patents

Direct-current voltage control method of multi-terminal flexible direct-current system Download PDF

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CN113162095B
CN113162095B CN202110046091.2A CN202110046091A CN113162095B CN 113162095 B CN113162095 B CN 113162095B CN 202110046091 A CN202110046091 A CN 202110046091A CN 113162095 B CN113162095 B CN 113162095B
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converter
direct
controller
voltage
flexible direct
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CN113162095A (en
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窦飞
蔡晖
张成龙
刘柏良
彭竹弈
赵菲菲
许偲轩
黄成辰
葛乐
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Nanjing Institute of Technology
State Grid Jiangsu Electric Power Co Ltd
Economic and Technological Research Institute of State Grid Jiangsu Electric Power Co Ltd
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Nanjing Institute of Technology
State Grid Jiangsu Electric Power Co Ltd
Economic and Technological Research Institute of State Grid Jiangsu Electric Power Co Ltd
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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
    • H02J3/38—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
    • H02J2203/20—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]

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  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention relates to a direct-current voltage control method of a multi-terminal flexible direct-current system, which specifically comprises the following steps: firstly, modeling analysis is carried out on a multi-end flexible direct current system, and a modeled object comprises: a wind farm, a PQ converter and a multi-terminal flexible direct current system of a main converter; secondly, a controller is designed by applying a norm control method, and the method allows the controlled local direct-current voltage to change correspondingly according to the scheduling requirement, so that the control precision of the direct-current voltage of the system is improved; and finally, simulating the system by adopting the control method through MATLAB/SIMULINKR, and verifying the feasibility and effectiveness of the control strategy. Has the advantages that: the power storage can be effectively managed in the form of a wind turbine by adopting the norm controller for voltage regulation, and the robustness and the control precision of the system are improved.

Description

Direct-current voltage control method of multi-terminal flexible direct-current system
Technical Field
The invention relates to the field of power electronics, in particular to a direct-current voltage control method of a multi-terminal flexible direct-current system.
Background
Since the fifty years High Voltage Direct Current (HVDC) transmission systems have been built and operated, Voltage Source Converters (VSC) have only been applied to high voltage direct current transmission systems in the late 90s, although two multi-terminal VSC-HVDC projects have been operated in china, the control of the direct voltage is still the focus of research. The multi-terminal VSC-HVDC system is controlled by direct voltage through only one converter. The remaining converters are operated in a fast active/Passive (PQ) control mode. The droop control method is the expansion of power frequency droop characteristics adopted by the synchronous generator. The main disadvantage of this control logic is that multi-terminal hvdc (mtdc) power flow control is not accurate enough due to the constant droop coefficient employed.
The delivered power of multiple MTDC systems operating globally is derived from a decentralized offshore wind farm. Modern WTGs are considered to be one of the fastest, most efficient power generators. Recent improvements in wind energy prediction accuracy are greatly reducing prediction errors and maintaining sufficient reserves to overcome wind power uncertainty is making wind energy resources more similar to traditional thermal power resources.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a direct-current voltage control method of a multi-terminal flexible direct-current system, which adopts H ∞ The norm controller is used for regulating the voltage, can effectively manage power reserve in the form of a wind turbine, and improves the robustness and control accuracy of the system, and is specifically realized by the following technical scheme:
the direct-current voltage control method of the multi-terminal flexible direct-current system is further designed to comprise the following steps of:
step 1) modeling analysis is carried out on the multi-terminal flexible direct current system, and the modeled objects comprise: the method comprises the steps that a wind power plant, a PQ converter and a multi-terminal flexible direct current system of a main converter are used for obtaining a multi-terminal flexible direct current system and a nonlinear model of the wind power plant;
step 2) carrying out linearization processing on the multi-terminal flexible direct current system and the nonlinear model of the wind power plant to obtain a multi-terminal flexible direct current system and a linear model of the wind power plant;
step 3) based on H ∞ Norm control method constructs linear H ∞ And the controller is used for correspondingly changing the controlled local direct-current voltage according to the scheduling requirement, so that the control precision of the direct-current voltage of the system is improved.
The direct current voltage control method of the multi-terminal flexible direct current system is further designed in that in the step 2), nonlinear functions of the multi-terminal flexible direct current system and the wind driven generator are respectively constructed according to the formulas (1) and (2);
Figure GDA0003783553880000021
wherein i L1 ，i L3 The inductive currents in the main converter and the PQ converter respectively; the upper point represents the derivative with respect to time;
Figure GDA0003783553880000022
Figure GDA0003783553880000023
the direct-current voltage of the converter connected with the wind power plant is the direct-current voltage of the main converter, the PQ converter and the converter; i.e. i s ，i m ，i wf The current in the main converter, the PQ converter and the converter connected with the wind power plant are respectively; p i s ，P i m ，P wf The power converter comprises a main converter, a PQ converter and output power in a converter connected with a wind power plant;
the nonlinear model is described as a function of a standard linear state variable x, a disturbance input w, and a controlled input u:
Figure GDA0003783553880000024
wherein the control output y is the direct voltage of the wind farm terminal;
obtaining deviation values delta x, delta w, delta u and delta y of x, w, u and y and corresponding balance values according to the formula (3);
Figure GDA0003783553880000025
where A is a constant matrix, B 1 Is a constant matrix, B 2 Is a constant matrix, C 2 Is a constant matrix, D 21 Is a constant matrix, D 22 Is a matrix of constants.
The direct-current voltage control method of the multi-end flexible direct-current system is further designed in that in the step 3), a combination formula (3) is combined, and a linear H is constructed according to a formula (4) ∞ A controller for controlling the operation of the electronic device,
Figure GDA0003783553880000026
wherein, A K Is a constant matrix, B K Is a constant matrix, C K Is a constant matrix, D K Is a constant matrix, x k Is linearization H ∞ The state variables of the controller,
Figure GDA0003783553880000027
Is linearization H ∞ Derivative of the state variable of the controller.
The direct-current voltage control method of the multi-terminal flexible direct-current system is further designed in such a way that an objective function delta z is introduced to enable the linearity H to be linear ∞ Controller disturbance output minimization, setting
Figure GDA0003783553880000028
And delta beta are respectively used as the disturbance of the local direct-current voltage balance value and the nominal pitch angle of the wind power plant terminal; filter state ξ including β in δ z β Derivative of (2)
Figure GDA0003783553880000029
To limit the bandwidth of the controller output pitch control signals to keep its slew rate below 8/s.
The direct-current voltage control method of the multi-terminal flexible direct-current system is further designed in such a way that the direct-current voltage control method is used for inhibiting
Figure GDA0003783553880000031
Eliminating delta beta high frequency fast changing component, obtaining transfer function of first order high pass filter according to formula (5) (taking initial condition xi) β (0)＝0)：
Figure GDA0003783553880000032
Wherein Γ (·) represents the laplace transform of the signal, and the filter state variables are derived from equation (6)
Figure GDA0003783553880000033
The time derivative of (a) of (b),
Figure GDA0003783553880000034
wherein the time constant T is 1,
Figure GDA0003783553880000035
is xi β And δ β, the disturbance output δ z being selected as a weighted parameterization of the disturbance output of the form:
Figure GDA0003783553880000036
wherein, the positive weight c 1 、c 2 And c 3 And all control parameters used in subsequent simulations, as in table 1;
TABLE 1
Figure GDA0003783553880000037
The invention has the following advantages:
the direct-current voltage control method of the multi-terminal flexible direct-current system adopts H ∞ The norm controller performs voltage regulation, can effectively manage power reserve in the form of a wind turbine, and improves the robustness and control accuracy of the system.
Drawings
Fig. 1 is a topological structure diagram of a multi-terminal direct current transmission (MTDC) system.
Fig. 2 is a view showing a structure of a WTG model.
FIG. 3 is a graph of power as a function of rotational speed. Wherein (a) is related to the wind speed beta being 0, and (b) is related to the pitch change when the wind speed is 12 m/s.
FIG. 4 is a DC voltage calibration plot on a wind farm terminal.
Fig. 5 is a graph of simulation results of the controlled nonlinear MTDC model. Wherein (a) the amount of standby usage and (b) power redistribution within the MTDC.
Detailed Description
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.
In the embodiment based on H, as shown in FIG. 1 ∞ The direct-current voltage control method of the controlled multi-terminal flexible direct-current system comprises the following steps:
step 1) firstly, carrying out modeling analysis on a multi-terminal flexible direct current system, wherein the objects to be modeled comprise the multi-terminal flexible direct current system (MTDC), a wind power plant and a main converter.
And 2) carrying out linearization treatment on the established MTDC and wind power plant nonlinear model according to the multi-terminal flexible direct current system established in the step 1.
Step 3) adopting H according to the MTDC and wind power field linearization model in the step 2 ∞ The norm control method is used for designing the controller, allows the controlled local direct-current voltage to change correspondingly according to the scheduling requirement, improves the control precision of the direct-current voltage of the system, and finally verifies the feasibility and the existence of the control method through simulationHigh effect. Each step is described in further detail below:
in step 1, a three-terminal MTDC system is selected, and the system consists of a wind power plant, a PQ converter and a main converter station. Fig. 1 shows a modeling approach of MTDC, with a nominal voltage of the common dc link of ± 200 kV. All devices associated with the wind farm are identified by a superscript wf, all devices associated with the PQ converter are identified by a superscript m, and all devices associated with the main converter are identified by a superscript s. The size of the capacitors on the dc side of each converter should be equal to the equivalent capacitance of a Modular Multilevel Converter (MMC).
The link between the equations of the different subsystems is provided by the active power injected into the MTDC. The current flowing into each converter station is:
Figure GDA0003783553880000051
wherein i s ，i m ，i wf The current in the main converter, the PQ converter and the converter connected with the wind power plant are respectively; p i s ，P i m ，P wf The power converter comprises a main converter, a PQ converter and output power in a converter connected with a wind power plant;
Figure GDA0003783553880000052
respectively, a main converter, a PQ converter, and a DC voltage in a converter connected to the wind farm.
And sufficient MMC equivalent capacitance is ensured, and the direct-current voltage on each converter terminal represents 1 transient variable. As shown in fig. 1, the state equation can be written as:
Figure GDA0003783553880000053
wherein i L1 ，i L3 The inductive currents in the main converter and the PQ converter respectively; the upper point represents the derivative with respect to time;
because i is L2 ＝i L1 +i L3 ，i L2 Linearly dependent on the other two DC current states, so that the current i can be eliminated L2 . Thus, a non-linear relationship appears to relate voltage to injected power.
The dc current state is given by:
Figure GDA0003783553880000054
Figure GDA0003783553880000055
wherein: d ═ L 1 L 2 +L 1 L 3 +L 2 L 3 ；L 1 ，L 2 ，L 3 The wind power station comprises a main converter, a PQ converter and an inductor in a converter connected with a wind power station; r 1 ，R 2 ，R 3 The resistance values of the main converter, the PQ converter and the converter connected with the wind power plant are respectively;
Figure GDA0003783553880000061
which are the derivatives of the inductor currents in the main converter and the PQ converter, respectively.
The offshore wind farm is connected through a high-voltage direct-current power transmission network, and is an offshore alternating-current power grid with a converter station controlled in a grid-connected mode, namely, voltage amplitude and frequency are controlled to serve as ideal voltage sources. Thus, the injected power of the high voltage direct current transmission network is not controlled by the high voltage direct current converter, but is only regulated by the wind power plant. The power delivered by the offshore wind farm to the high voltage dc grid can easily be expressed as the sum of the power generated by the different WTGs, assuming no losses of the offshore ac grid occur. 100 identical 2 megawatt permanent magnet synchronous wind driven generators are adopted.
The WTG is continuously operated at the maximum of the power curve, depending on the wind speed or pitch angle. Fig. 3 shows the shift variation of the power curve. On the power curve, only pitch adjustments are used to eliminate the load of the turbine, rather than moving left and right on the power curve. As shown in fig. 2, the desired speed setting for the rotor is determined by Maximum Power Point Tracking (MPPT) logic using a two-dimensional look-up table, i.e. taking into account the wind speed v and pitch angle β.
The terminal voltage need not be described in terms of machine variables. The voltage of the motor is driven by internal current control logic and external MPPT logic, which is implemented on the q-axis (torque axis). As shown in figure 2 of the drawings, in which,
Figure GDA0003783553880000062
it represents torque as a function of q-axis current only. Thus, three state variables
Figure GDA0003783553880000063
And
Figure GDA0003783553880000064
as the current dq axis quadrature component, it can be expressed as:
Figure GDA0003783553880000065
wherein the content of the first and second substances,
Figure GDA0003783553880000066
reference values representing d-axis and q-axis current components; i is d ，I q Actual values representing d-axis and q-axis current components;
Figure GDA0003783553880000067
is the motor speed reference value given in the look-up table; omega r Is the actual value of the motor speed;
Figure GDA0003783553880000068
is a constant.
Rotor oscillation equation:
Figure GDA0003783553880000069
coefficient of power C p Expressed as:
Figure GDA0003783553880000071
in the formula: beta is the pitch angle, lambda i Is a function of lambda (tip speed ratio).
The internal power output equation given between the wind farm state variable and the MTDC system state variable is as follows:
Figure GDA0003783553880000072
the state space of the main converter can be expressed as:
Figure GDA0003783553880000073
wherein the current controller defines two new state variables
Figure GDA0003783553880000074
And
Figure GDA0003783553880000075
satisfies the following conditions:
Figure GDA0003783553880000076
the expression for the d-axis state current is as follows:
Figure GDA0003783553880000077
the form of the internal power output equation to the MTDC system is expressed as:
Figure GDA0003783553880000078
in the step 2: equations of state (2) and (5) show the non-linear functions of MTDC and WTG. Thus, the nonlinear model is described as a function of a standard linear state variable x, a disturbance input w, and a controlled input u:
Figure GDA0003783553880000079
wherein the control output y is the dc voltage at the wind farm terminal.
The state vector x (t) is represented as:
x(t)＝[(x wf ) T (x m ) T (x MTDC ) T ] T
wherein: subvector x wf 、x m And x MTDC Respectively related to the wind farm, the main converter and the MTDC, as shown in the following formula:
Figure GDA0003783553880000081
Figure GDA0003783553880000082
Figure GDA0003783553880000083
writing the input in vector form yields:
Figure GDA0003783553880000084
u＝β
linear Time Invariant (LTI) H taking into account non-linear objects ∞ And (4) designing a controller. Since this state space controller design requires a linearized model, the present embodiment constructs a linearized model of the MTDC object that surrounds a set of equilibrium values for the MTDC that form equilibrium state x eq . This is chosen as the normal operating point for the MTDC, with a fixed wind speed of 12m/s (here the example is simplified assuming constant wind speed), and a wind farm power output of 75% of the rated output (corresponding to β at a given wind speed) nom Pitch blade angle of approximately 4 °), perturbing the input nominal value w nom ＝[49.8×10 6 100×10 6 0] T For these values of beta nom And w nom By solving the equation f (x) eq ,β nom ,w nom ) The equilibrium point x of the nonlinear MTDC model is obtained as 0 eq . The relevant jacobian matrix for f in equation (12) is calculated by calculating the partial derivatives of f (x, w, u) with respect to vectors x, w, and u, and calculating at the equilibrium point. In summary, a linear time-invariant model is obtained:
Figure GDA0003783553880000085
wherein δ x, δ w and δ u represent the deviation of the quantities x, w and u from the corresponding equilibrium/nominal values; can be expressed as: δ x ═ x-x eq ，δw＝w-w nom ，δu＝β-β nom 。
In step 3, for H ∞ The design of the controller introduces an objective function deltaz, namely the disturbance output is minimized. Selecting
Figure GDA0003783553880000086
And delta beta is respectively used as the disturbance of the local direct voltage balance value and the nominal pitch angle of the wind power plant terminal. In addition, δ z includes filter state ξ of β β Derivative of (2)
Figure GDA0003783553880000091
To limit the bandwidth of the controller output pitch control signals to keep its slew rate below 8/s. Variable xi β Which may be considered the output of a first order high pass filter, whose input is δ β. Suppression of
Figure GDA0003783553880000092
Is one kind of eliminating delta beta high frequency fast varying componentAn alternative approach. The transfer function of a first order high pass filter is given by (taking the initial condition xi) β (0)＝0)：
Figure GDA0003783553880000093
Where Γ (·) represents the laplace transform of the signal. Back to the time domain, the filter state variables
Figure GDA0003783553880000094
The time derivative of (a) is given by:
Figure GDA0003783553880000095
wherein the time constant T is 1. Note from the formula (15)
Figure GDA0003783553880000096
Is xi β And δ β, and then selecting the disturbance output δ z as a weighted parameterization of the disturbance output of the form:
Figure GDA0003783553880000097
wherein, the positive weight c 1 、c 2 And c 3 And all control parameters used in subsequent simulations, as shown in table 1.
The linear H of MTDC was designed using the model in equation (13) ∞ And a controller. Can be expressed as follows:
Figure GDA0003783553880000098
initial condition x K (0) The controller order is 0, which is the same as the order of the controlled linearized MTDC model, i.e. 16 in the simulation case. The reality of the MTDC shown in FIG. 4 is that since the controller is designed based on a linearized modelThe control signal u is:
u＝β nom +δu (17)
according to the controller designed by the method, a simulation test shown in FIG. 1 is constructed to verify the superiority of the controller.
Wind farm at fixed wind speed of 12m/s, at beta nom A fixed wind speed of approximately 4 deg. drives, initially 100MW of power is delivered by the main converter, the remaining 50MW being used for the power of the PQ converter and the losses of the various resistances.
Fig. 5 (a) shows a PQ converter (P) i s ) A frequency of 20MW each regulates the interference at t 10s and t 30 s. A power ramp order of 1250MW/s was used in the simulation. As shown in the third graph of fig. 5 (a), the main converter is not affected by a frequency regulation load exceeding the minimum deviation. This is due to the release of approximately 3.6MJ by the DC capacitance, and H ∞ The fine tuning response of the controller when the pitch angle of the blade is adjusted improves the robustness of the system.
At 50s and 70s, the main converter needs to restore the wind farm reserve since the PQ converter has a new power output, which means that
Figure GDA0003783553880000101
A change occurs. The 50MW power shortage can be recovered as soon as possible by the grid side frequency converter. Even if the power is reduced by 20MW, the dynamic speed of the power output of the main converter is faster because the PI structures of the d-axis of the main controller are cascaded. Finally 20MW of power is injected to the main grid side at 90 s. In this case, the disturbance is limited to the ac side of the main converter due to the effective decoupling between the controllers. This shows the effectiveness of the controller on the main inverter in both frequency and voltage regulation.
Fig. 5 (b) shows the effect of a standard power redistribution operation on the designed controller. At 10 seconds, the PQ converter and the main converter exchange 450MW power at a rate of ± 20MW/s, bringing the PQ converter to its transmission capacity limit. In actual operation, the power supply loop of the main converter, such as xi in the bottom diagram of fig. 5 (b) Pg m shows that a new one needs to be foundA balance point. However, at the beginning and at the end of the ramping process, some disturbances occur, affecting the dc voltage and the pitch angle. Therefore, if the PQ converters on the MTDC are to exchange power, the power ramp need not be severely limited. Finally at the end of the simulation, a new balance point is found, but the injected power of the wind farm is slightly larger (smaller β) due to the higher losses on the MTDC.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (4)

1. A direct-current voltage control method of a multi-terminal flexible direct-current system is characterized by comprising the following steps:
step 1) modeling analysis is carried out on the multi-end flexible direct current system, and the modeled objects comprise: the method comprises the steps that a wind power plant, a PQ converter and a multi-terminal flexible direct current system of a main converter are used for obtaining a multi-terminal flexible direct current system and a nonlinear model of the wind power plant;
step 2) carrying out linearization treatment on the multi-end flexible direct current system and the nonlinear model of the wind power plant to obtain a multi-end flexible direct current system and a linear model of the wind power plant;
step 3) based on H ∞ Norm control method constructs linear H ∞ The controller is used for correspondingly changing the controlled local direct-current voltage according to the scheduling requirement, so that the control precision of the direct-current voltage of the system is improved;
in the step 2), non-linear functions of the multi-end flexible direct current system and the wind driven generator are respectively constructed according to the formula (1) and the formula (2);
Figure FDA0003783553870000011
wherein i L1 ，i L3 The inductive currents in the main converter and the PQ converter respectively; the upper point represents the derivative with respect to time;
Figure FDA0003783553870000012
the direct current voltage in the main converter, the PQ converter and the converter connected with the wind power plant are respectively; i.e. i s ，i m ，i wf The current in the main converter, the PQ converter and the converter connected with the wind power plant are respectively; p i s ，P i m ，P wf The power converter comprises a main converter, a PQ converter and output power in a converter connected with a wind power plant;
the nonlinear model is described as a function of a standard linear state variable x, a disturbance input w, and a controlled input u:
Figure FDA0003783553870000013
wherein the control output y is the dc voltage at the wind farm terminal;
obtaining deviation values deltax, deltaw, deltau and deltay of x, w, u and y and corresponding balance values according to the formula (3);
Figure FDA0003783553870000014
where A is a constant matrix, B 1 Is a constant matrix, B 2 Is a constant matrix, C 2 Is a constant matrix, D 21 Is a constant matrix, D 22 Is a matrix of constants.
2. The method for controlling the direct current voltage of the multi-terminal flexible direct current system according to claim 1, wherein in step 3), in accordance with formula (3), a linear H is constructed according to formula (4) ∞ A controller for controlling the operation of the electronic device,
Figure FDA0003783553870000021
wherein A is K Is a constant matrix, B K Is a constant matrix, C K Is a constant matrix, D K Is a constant matrix, x k Is linearization H ∞ The state variables of the controller,
Figure FDA0003783553870000022
Is linearizing H ∞ Derivative of the state variable of the controller.
3. The method for controlling the DC voltage of the multi-terminal flexible DC system according to claim 2, wherein an objective function δ z is introduced to make the linearity H ∞ Controller disturbance output minimization, setting
Figure FDA0003783553870000023
And delta beta are respectively used as the disturbance of the local direct-current voltage balance value and the nominal pitch angle of the wind power plant terminal; filter state ξ including β in δ z β Derivative of (2)
Figure FDA0003783553870000024
To limit the bandwidth of the controller output pitch control signals to keep its slew rate below 8/s.
4. The method of claim 3, wherein the DC voltage control of the multi-terminal flexible DC system is performed by suppressing
Figure FDA0003783553870000025
Eliminating delta beta high-frequency fast-changing components, and obtaining a transfer function of a first-order high-pass filter according to an equation (5):
Figure FDA0003783553870000026
wherein Γ (·) represents the laplace transform of the signal, and the filter state variables are derived from equation (6)
Figure FDA0003783553870000027
Taking the initial condition xi β (0)＝0，
Figure FDA0003783553870000028
Wherein the time constant T is 1,
Figure FDA0003783553870000029
is xi β And δ β, the disturbance output δ z being selected as a weighted parameterization of the disturbance output of the form:
Figure FDA00037835538700000210
wherein, the positive weight c 1 、c 2 And c 3 And all control parameters used in subsequent simulations, as in table 1;
TABLE 1
Figure FDA0003783553870000031
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106410835A (en) * 2016-10-12 2017-02-15 北京科东电力控制系统有限责任公司 Power grid simulation realization method of multi-terminal flexible direct-current transmission system
CN107302224A (en) * 2017-07-17 2017-10-27 南京南瑞集团公司 A kind of multi-terminal direct current transmission system current conversion station control method based on interior point method
CN111711217A (en) * 2020-05-21 2020-09-25 东北电力大学 Direct-current voltage control method of multi-terminal flexible direct-current system facing alternating-current power fluctuation

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106410835A (en) * 2016-10-12 2017-02-15 北京科东电力控制系统有限责任公司 Power grid simulation realization method of multi-terminal flexible direct-current transmission system
CN107302224A (en) * 2017-07-17 2017-10-27 南京南瑞集团公司 A kind of multi-terminal direct current transmission system current conversion station control method based on interior point method
CN111711217A (en) * 2020-05-21 2020-09-25 东北电力大学 Direct-current voltage control method of multi-terminal flexible direct-current system facing alternating-current power fluctuation

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