CN113746129A - Impedance model obtaining method and device for direct-drive wind power plant through LCC-HVDC sending-out system - Google Patents
Impedance model obtaining method and device for direct-drive wind power plant through LCC-HVDC sending-out system Download PDFInfo
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- H—ELECTRICITY
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- 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
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- H02J3/381—Dispersed generators
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- 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
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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
- H02J2003/365—Reducing harmonics or oscillations in HVDC
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- 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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Abstract
The invention provides an impedance obtaining method and device for a direct-drive wind power plant through an LCC-HVDC sending-out system, which can accurately obtain system impedance, thereby providing a model basis for stability analysis and optimization of the sending-out system. According to the method, the subsynchronous and supersynchronous coupling relation is considered, the positive sequence impedance and the coupling impedance of the direct-drive wind power plant, the alternating current power grid and the LCC-HVDC transmitting end system are respectively obtained through the acquisition module, the acquisition module and the calculation module, and the impedance of the whole direct-drive wind power plant in a full frequency band through the LCC-HVDC transmitting end system is calculated, so that the stability of the system is accurately analyzed. The device is easy to operate, the subsynchronous and supersynchronous coupling relation is considered, the positive sequence impedance and the coupling impedance of the direct-drive wind power plant in a full frequency band through the LCC-HVDC sending-out system can be accurately obtained, the obtained impedance model is more accurate and comprehensive, and the stability of the system is more accurate and effective to analyze.
Description
Technical Field
The invention belongs to the technical field of direct-current high-voltage power transmission systems, and particularly relates to a method and a device for obtaining an impedance model of a direct-drive wind power plant through an LCC-HVDC (low-voltage capacitor-high-voltage direct-current) sending-out system.
Background
Wind power in China develops rapidly, and installed capacity rises year by year. However, wind resources and electricity load centers are distributed in a reverse direction in regions, and the problem that the distribution of a power generation supply side and an electricity demand side of wind power is unbalanced is obvious. The remote, large-scale and highly centralized wind power delivery construction becomes a main mode for wind power development and utilization in China at present and in a considerable period of time in the future. The traditional LCC-HVDC transmission technology has a dominant position in the current stage and the future high-voltage direct-current construction due to the advantage of large-capacity power during long-distance transmission. In the research of high-voltage direct current construction and development of a national power grid, wind power of northeast and northwest (including Xinjiang) bases needs to be sent out through LCC-HVDC, and a plurality of projects are put into operation or under construction. However, the transmission distance is long, the local power grid strength is weakened due to large-scale centralized wind power integration, the power electronic power system features are remarkable due to the large number of devices such as converters, and Sub-synchronous Oscillation (SSO) problems possibly caused by interaction between a wind power plant and the HVDC occur. Direct-drive Permanent Magnet Synchronous Generator (D-PMSG) is used on a large scale due to the advantages of large single machine power, strong low-voltage ride through capability and the like. However, no effective solution has been proposed for impedance acquisition of direct-drive wind farms via LCC-HVDC send-out engineering. As the project scale of direct-drive wind power plants sent out through LCC-HVDC is increased, a method and a device for obtaining an impedance model of a system are needed to be effectively sent out, so that the stability of the system is evaluated.
Disclosure of Invention
In view of the above, the invention provides an impedance obtaining method and an impedance obtaining device for a direct-drive wind power plant through an LCC-HVDC sending-out system, which can accurately obtain system impedance, thereby providing a model basis for stability analysis and optimization of the sending-out system.
In order to achieve the above object, the method for obtaining the system impedance model of the direct-drive wind farm sent out through the LCC-HVDC comprises the following steps:
step 2, obtaining alternating current power grid parameters including power frequency voltage, line length and line inductance resistance parameters;
step 3, obtaining LCC-HVDC transmitting end system parameters including direct current line inductance resistance, direct current side capacitance and alternating current measurement reactive compensation capacitance;
obtaining rectifier station controller parameters, including a phase-locked loop transfer function and control parameters, a direct current controller PI link transfer function and control parameters, a direct current feedback gain transfer function and control parameters, a direct current voltage reference value, a direct current reference value and a trigger angle reference value;
step 4, operating the grid-connected system to enable the grid-connected system to operate at a steady-state working point, and then acquiring a system steady-state value, wherein the system steady-state value comprises direct-drive wind power plant output power, alternating current weak grid output power, LCC rectifier station input power, power frequency voltage of a public coupling point and direct-drive wind power plant output power frequency current;
and 5, obtaining impedance models of the direct-drive wind power plant, the alternating current power grid and the LCC-HVDC transmitting end system according to the obtained direct-drive wind power plant converter parameters, the LCC rectifier station parameters and the system steady state values, and obtaining positive sequence impedance and coupling impedance of each part when a disturbance voltage signal with fp frequency exists through the impedance model transfer function.
And 6, carrying out parallel calculation on the impedance of the direct-drive wind power plant and the impedance model of the LCC-HVDC transmitting end system to obtain the positive sequence impedance and the coupling impedance of the direct-drive wind power plant through the LCC-HVDC transmitting end system.
Calculating an impedance model of the direct-drive wind power plant according to the direct-drive wind power plant converter parameters obtained in the steps 1 and 3 and the system steady state value, wherein the impedance model comprises positive sequence impedance and coupling impedance, and the calculation method comprises the following steps:
in the formula:
direct-drive wind power plant system positive sequence impedance;
coupling impedance of positive sequence voltage and negative sequence current of direct-drive wind power plant system, I1The peak value of the wave phase current of the alternating side group; m1Is the fundamental wave peak value of the modulation signal; kmIs the modulation ratio; t isPLL(s) is a phase-locked loop closed-loop transfer function; omega1Is the fundamental angular frequency; vdcIs the dc side voltage amplitude; hi(s) is the current loop transfer function; cf is a filter capacitor; lf is a filter inductor; kd is a decoupling coefficient; s is a differential operator.
Calculating an LCC-HVDC transmitting end system impedance model comprising positive sequence impedance and coupling impedance according to the LCC rectifier station parameters obtained in the step 2 and the step 3 and the system steady state value, wherein the calculating method comprises the following steps:
wherein,
the positive sequence impedance of the rectifier station system,
coupling impedance, V, of positive-sequence voltage and negative-sequence current of a rectifier station systema(s) is the positive sequence voltage of the system, Ia(s)、Ia(s2) Respectively positive sequence current and negative sequence current of the system, P is power grid fundamental frequency active power, Q is power grid fundamental frequency reactive power, S is P + jQ is apparent power,
for the phase angle of the fundamental current of the grid, omega1＝2πf1Wherein f is1Is a fundamental frequency, K is a positive integer, KTFor transformer transformation ratio, Dp(s) is the flip-flop perturbation function, s is the differential operator, CRFor reactive compensation of the capacitance, s, of the LCC1Being differential operators at positive sequence frequency, ZdcFor DC line impedance, the initial firing angle α1＝α0+5 pi/6, superscript "+" indicates conjugation, | | | is a parallel symbol;
the DC side circuit impedance is:
wherein L isd,RdRespectively, inductance and resistance of the DC transmission line, CdcIs a DC side capacitor.
The invention also provides a device for acquiring the system impedance model of the direct-drive wind farm sent out by the LCC-HVDC, which comprises a first acquisition module, a second acquisition module, a third acquisition module, an acquisition module and a calculation module;
the first acquisition module is used for acquiring direct-drive wind power plant converter parameters, and the parameters comprise a filter inductance capacitor and a control parameter value;
the second acquisition module is used for acquiring alternating current power grid parameters including line length and inductance-capacitance distribution parameters;
the third acquisition module is used for acquiring LCC-HVDC transmitting end system parameters including direct current line inductance resistance, direct current side capacitance, alternating current measurement reactive compensation capacitance and rectifier station controller parameters;
the acquisition module is used for acquiring a system steady state value, including the power of a direct-drive wind power plant, an alternating current weak power grid and an LCC rectification station and the power frequency voltage and current of each point;
and the calculation module is used for obtaining an impedance model of the direct-drive wind power plant through the LCC-HVDC sending system according to the obtained direct-drive wind power plant converter parameters, the LCC rectifier station parameters and the system steady state value, and calculating to obtain the positive sequence impedance and the coupling impedance of the system in the wideband through the impedance model transfer function.
Wherein the apparatus further comprises a memory and a communication interface;
the first acquisition module, the second acquisition module, the third acquisition module, the acquisition module and the calculation module form a processor;
a memory for a storage device to run a computer program;
the communication interface has a man-machine interaction function, receives system parameter data from the outside, uploads the system parameter data to the communication bus, or obtains a genetic algorithm optimization result of the direct-drive wind power plant sent out of the system through LCC-HVDC from the communication bus, and transmits the data to an external upper computer and the STATCOM controller;
the processor has the functions of data interaction input and output, information acquisition, parameter calculation and optimization result calculation, accesses or calls a computer program stored in the memory through the communication bus, and then executes the computer program.
Has the advantages that:
according to the method, the subsynchronous and supersynchronous coupling relation is considered, the positive sequence impedance and the coupling impedance of the direct-drive wind power plant, the alternating current power grid and the LCC-HVDC transmitting end system are respectively obtained through the acquisition module, the acquisition module and the calculation module, and the impedance of the whole direct-drive wind power plant in a full frequency band through the LCC-HVDC transmitting end system is calculated, so that the stability of the system is accurately analyzed.
The device for acquiring the impedance model of the direct-drive wind power plant through the LCC-HVDC sending-out system is very simple and easy to operate, considers the subsynchronous and supersynchronous coupling relation, can accurately acquire the positive sequence impedance and the coupling impedance of the direct-drive wind power plant through the LCC-HVDC sending-out system in a full frequency band, is more accurate and comprehensive in the acquired impedance model, is more accurate and effective in analyzing the stability of the system, makes up the defect that the model acquisition is not accurate in the stability analysis of the direct-drive wind power plant through the LCC-HVDC sending-out system in the current research, and provides an important basis for the design and grid connection of the direct-drive wind power plant through the LCC-HVDC sending-out system.
Drawings
FIG. 1 is a flow chart of impedance acquisition of a direct drive wind farm system through LCC-HVDC transmission according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of an impedance model acquisition device of a direct-drive wind farm through an LCC-HVDC sending-out system according to an embodiment of the present invention.
Fig. 3 is a topological structure diagram of a direct-drive wind farm sending system through LCC-HVDC in the embodiment of the present invention.
Fig. 4 is a control structure diagram of a current loop of a converter at the machine side of the direct-drive wind turbine generator system in the embodiment of the invention.
Fig. 5 is a block diagram of the control of the trigger pulse of the LCC rectifier station according to the embodiment of the present invention.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
The method and the device for acquiring the impedance model of the direct-drive wind power plant through the LCC-HVDC sending-out system can accurately acquire the positive sequence impedance and the coupling impedance of the direct-drive wind power plant through the LCC-HVDC sending-out system in the full frequency band, consider the subsynchronous and supersynchronous coupling relation, obtain more accurate and comprehensive impedance model, are more accurate and effective for analyzing the stability of the system, make up the defect that the model acquisition is not inaccurate in the stability analysis of the direct-drive wind power plant through the LCC-HVDC sending-out system in the current research, and provide important basis for the design and the grid connection of the direct-drive wind power plant through the LCC-HVDC sending-out system.
Fig. 1 is a flow chart of direct-drive wind farm impedance model acquisition through an LCC-HVDC transmission system, the method comprising the steps of:
And step 2, obtaining alternating current power grid parameters (through the second obtaining module 102), wherein the alternating current power grid parameters comprise power frequency voltage, line length and line inductance resistance parameters.
Step 3, obtaining LCC-HVDC transmitting end system parameters including direct current line inductance resistance, direct current side capacitance and alternating current measurement reactive compensation capacitance (through a third obtaining module 103);
and acquiring rectifier station controller parameters including a phase-locked loop transfer function and control parameters, a direct current controller PI link transfer function and control parameters, a direct current feedback gain transfer function and control parameters, a direct current voltage reference value, a direct current reference value and a trigger angle reference value.
And 4, operating the grid-connected system to enable the grid-connected system to operate at a steady-state working point, and then acquiring a system steady-state value (through an acquisition module 104), wherein the system steady-state value comprises direct-drive wind power plant output power, alternating-current weak grid output power, LCC rectifier station input power, power frequency voltage of a public coupling point and direct-drive wind power plant output power frequency current.
And 5, obtaining impedance models of the direct-drive wind power plant, the alternating current power grid and the LCC-HVDC transmitting end system (through the calculation module 105) according to the obtained direct-drive wind power plant converter parameters, the LCC rectifier station parameters and the system steady state values, and obtaining positive sequence impedance and coupling impedance of each part when a disturbance voltage signal with fp frequency exists through the impedance model transfer function.
In step 6, the direct-drive wind power plant impedance and the impedance model of the LCC-HVDC transmitting end system are calculated in parallel (through the calculating module 105) to obtain the positive sequence impedance and the coupling impedance of the direct-drive wind power plant through the LCC-HVDC transmitting end system.
Further, in an embodiment of the present invention, an impedance model of the direct-drive wind farm is calculated according to the direct-drive wind farm converter parameters obtained in step 1 and step 3 and the system steady-state values, the impedance model includes positive sequence impedance and coupling impedance, and the calculation method includes:
in the formula:
direct-drive wind power plant system positive sequence impedance;
coupling impedance of positive sequence voltage and negative sequence current of direct-drive wind power plant system, I1The peak value of the wave phase current of the alternating side group; m1Is the fundamental wave peak value of the modulation signal; kmIs the modulation ratio; t isPLL(s) is a phase-locked loop closed-loop transfer function; omega1Is the fundamental angular frequency; vdcIs the dc side voltage amplitude; hi(s) is the current loop transfer function; cf is a filter capacitor; lf is a filter inductor; kd is a decoupling coefficient; s is a differential operator.
Further, in an embodiment of the present invention, an LCC-HVDC transmitting end system impedance model is calculated according to the LCC rectifier station parameters obtained in step 2 and step 3 and the system steady state values, and the calculation method includes:
wherein,
the positive sequence impedance of the rectifier station system,
coupling impedance, V, of positive-sequence voltage and negative-sequence current of a rectifier station systema(s) is the positive sequence voltage of the system, Ia(s)、Ia(s2) Respectively positive sequence current and negative sequence current of the system, P is power grid fundamental frequency active power, Q is power grid fundamental frequency reactive power, S is P + jQ is apparent power,
for the phase angle of the fundamental current of the grid, omega1＝2πf1Wherein f is1Is a fundamental frequency, K is a positive integer, KTFor transformer transformation ratio, Dp(s) is the flip-flop perturbation function, s is the differential operator, CRFor reactive compensation of the capacitance, s, of the LCC1Being differential operators at positive sequence frequency, ZdcFor DC line impedance, the initial firing angle α1＝α0+5 pi/6, superscript "+" indicates conjugation, | | | is a parallel symbol;
the DC side circuit impedance is:
wherein L isd,RdRespectively, inductance and resistance of the DC transmission line, CdcIs a DC side capacitor.
Wherein L isd,RdIs an inductive resistance, C, of a direct current transmission linedcIs a DC side capacitor.
FIG. 2 is a schematic structural diagram of an impedance model acquisition device of a direct-drive wind farm through an LCC-HVDC transmission system. And further calculating the impedance value of the direct-drive wind power plant in the full frequency band through the LCC-HVDC transmission system through the impedance model transfer function.
The device comprises a processor 201, a memory 202 and a communication interface 203, wherein the processor 201 calls a computer program stored in the memory 202, and the computer program can realize the acquisition and collection functions by executing the functions of each module;
the processor 201 has functions of interactive input and output, measurement acquisition and parameter calculation, and mainly comprises an acquisition module, an acquisition module and a calculation module. The processor 201 calls and executes the computer program stored in the memory 202 through the communication bus, so that the acquisition module receives system parameters of all parts of the direct-drive wind power plant sent out of the system through the LCC-HVDC from the communication bus; the acquisition module acquires a system operation steady-state value through a sensor; the calculation module reads the data of the acquisition module and the acquisition module, calculates the positive sequence impedance and the coupling impedance of the direct-drive wind power plant system transmitted out through the LCC-HVDC according to the obtained data, and uploads the result to the communication bus;
a memory 202, the storage device running the computer program. The processor 201 may access or invoke the computer program stored in the memory 202 through the communication bus.
And the communication interface 203 has a man-machine interaction function. The communication interface receives system parameter data from the outside and uploads the system parameter data to a communication bus; or the communication interface obtains the positive sequence impedance and the coupling impedance of the direct-drive wind power plant through the LCC-HVDC sending system from the communication bus and transmits data to the outside.
The processor 201 includes a first obtaining module 101, a second obtaining module 102, a third obtaining module 103, an acquiring module 104, and a calculating module 105. The first obtaining module 101 is used for obtaining parameters of a direct-drive wind power plant converter, wherein the parameters include a filter inductor capacitor and a control parameter value; a second obtaining module 102, configured to obtain ac power grid parameters, including a line length and an inductor-capacitor distribution parameter; a third obtaining module 103, configured to obtain LCC-HVDC transmission end system parameters, including a dc line inductance resistance, a dc side capacitance, an ac measurement reactive compensation capacitance value, and rectifier controller parameters; the acquisition module 104 is used for acquiring system steady state values, including power of a direct-drive wind power plant, an alternating current weak power grid and an LCC rectification station, and power frequency voltage and current of each point; and the calculation module 105 is used for obtaining an impedance model of the direct-drive wind power plant through the LCC-HVDC sending system according to the obtained direct-drive wind power plant converter parameters, the LCC rectifier station parameters and the system steady state value, and calculating to obtain the positive sequence impedance and the coupling impedance of the system in the wideband through the impedance model transfer function.
Fig. 3 is a topological structure diagram of a direct-drive wind farm sending system through LCC-HVDC, wherein: v. ofg，igFor AC mains voltage and output current, Rg，LgIs a power grid resistance inductor; i.e. iL,idcAC/DC side current, L, for LCC-HVDC transmitting terminald,RdFor dc transmission linesResistance of the line inductor, CdcA direct current side capacitor; cR,iRThe filter capacitor and the current thereof on the alternating current side of the LCC-HVDC are used for reducing the steady-state harmonic wave on the alternating current side of the system; i.e. isAnd outputting current for the direct-drive wind power plant.
FIG. 4 is a view of a current loop control structure of a machine side converter of a direct-drive wind turbine generator, Hri(s) is the PI transfer function of the machine side converter current controller.
Signals, M, are respectively given to the dq-axis current loopsds、MqsOutput of modulated signal for current loop, KrdIs a decoupling factor. The mathematical expression for the current loop is thus as follows:
FIG. 5 is a block diagram of LCC rectifier station trigger pulse control, Gim(s) is a first order filter of the form 1/(1+ Ts); hio(s) is a PI controller of the form kip+kiiS; the phase control part is used for receiving the trigger signal angle alpha and the reference signal angle thetalAnd compares them to generate a corresponding trigger pulse.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. 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 (5)
1. A method for obtaining an impedance model of a system sent out by a direct-drive wind field through LCC-HVDC is characterized by comprising the following steps:
step 1, obtaining direct-drive wind power plant converter parameters including a converter filter inductor, a filter capacitor and a direct current link capacitance value; obtaining converter controller parameters including a current controller PI link transfer function and control parameters, a phase-locked loop transfer function and control parameters, a direct current voltage reference value and an alternating current reference value;
step 2, obtaining alternating current power grid parameters including power frequency voltage, line length and line inductance resistance parameters;
step 3, obtaining LCC-HVDC transmitting end system parameters including direct current line inductance resistance, direct current side capacitance and alternating current measurement reactive compensation capacitance;
obtaining rectifier station controller parameters, including a phase-locked loop transfer function and control parameters, a direct current controller PI link transfer function and control parameters, a direct current feedback gain transfer function and control parameters, a direct current voltage reference value, a direct current reference value and a trigger angle reference value;
step 4, operating the grid-connected system to enable the grid-connected system to operate at a steady-state working point, and then acquiring a system steady-state value, wherein the system steady-state value comprises direct-drive wind power plant output power, alternating current weak grid output power, LCC rectifier station input power, power frequency voltage of a public coupling point and direct-drive wind power plant output power frequency current;
and 5, obtaining impedance models of the direct-drive wind power plant, the alternating current power grid and the LCC-HVDC transmitting end system according to the obtained direct-drive wind power plant converter parameters, the LCC rectifier station parameters and the system steady state values, and obtaining positive sequence impedance and coupling impedance of each part when a disturbance voltage signal with fp frequency exists through the impedance model transfer function.
And 6, carrying out parallel calculation on the impedance of the direct-drive wind power plant and the impedance model of the LCC-HVDC transmitting end system to obtain the positive sequence impedance and the coupling impedance of the direct-drive wind power plant through the LCC-HVDC transmitting end system.
2. The method for obtaining the impedance model of the direct-drive wind farm system sent out through the LCC-HVDC according to claim 1, wherein the impedance model of the direct-drive wind farm is calculated according to the direct-drive wind farm converter parameters obtained in the steps 1 and 3 and the system steady-state values, the impedance model comprises positive sequence impedance and coupling impedance, and the calculation method comprises the following steps:
in the formula:
direct-drive wind power plant system positive sequence impedance;
coupling impedance of positive sequence voltage and negative sequence current of direct-drive wind power plant system, I1The peak value of the wave phase current of the alternating side group; m1Is the fundamental wave peak value of the modulation signal; kmIs the modulation ratio; t isPLL(s) is a phase-locked loop closed-loop transfer function; omega1Is the fundamental angular frequency; vdcIs the dc side voltage amplitude; hi(s) is the current loop transfer function; cf is a filter capacitor; lf is a filter inductor; kd is a decoupling coefficient; s is a differential operator.
3. The method for obtaining the impedance model of the direct-drive wind farm system sent out through the LCC-HVDC transmission system according to claim 1, wherein an LCC-HVDC transmission end system impedance model is calculated according to the LCC rectifier station parameters obtained in the steps 2 and 3 and the steady state value of the system, the LCC-HVDC transmission end system impedance model comprises a positive sequence impedance and a coupling impedance, and the calculation method comprises the following steps:
wherein,
the positive sequence impedance of the rectifier station system,
coupling impedance, V, of positive-sequence voltage and negative-sequence current of a rectifier station systema(s) is the positive sequence voltage of the system, Ia(s)、Ia(s2) Respectively positive sequence current and negative sequence current of the system, P is power grid fundamental frequency active power, Q is power grid fundamental frequency reactive power, S is P + jQ is apparent power,
for the phase angle of the fundamental current of the grid, omega1＝2πf1Wherein f is1Is a fundamental frequency, K is a positive integer, KTFor transformer transformation ratio, Dp(s) is the flip-flop perturbation function, s is the differential operator, CRFor reactive compensation of the capacitance, s, of the LCC1Being differential operators at positive sequence frequency, ZdcFor DC line impedance, the initial firing angle α1＝α0+5 pi/6, superscript "+" indicates conjugation, | | | is a parallel symbol;
the DC side circuit impedance is:
wherein L isd,RdRespectively, inductance and resistance of the DC transmission line, CdcIs a DC side capacitor.
4. A direct-drive wind field system impedance model acquisition device sent out through LCC-HVDC is characterized by comprising a first acquisition module, a second acquisition module, a third acquisition module, an acquisition module and a calculation module;
the first acquisition module is used for acquiring direct-drive wind power plant converter parameters, and the parameters comprise a filter inductance capacitor and a control parameter value;
the second acquisition module is used for acquiring alternating current power grid parameters including line length and inductance-capacitance distribution parameters;
the third acquisition module is used for acquiring LCC-HVDC transmitting end system parameters including direct current line inductance resistance, direct current side capacitance, alternating current measurement reactive compensation capacitance and rectifier station controller parameters;
the acquisition module is used for acquiring a system steady state value, including the power of a direct-drive wind power plant, an alternating current weak power grid and an LCC rectification station and the power frequency voltage and current of each point;
and the calculation module is used for obtaining an impedance model of the direct-drive wind power plant through the LCC-HVDC sending system according to the obtained direct-drive wind power plant converter parameters, the LCC rectifier station parameters and the system steady state value, and calculating to obtain the positive sequence impedance and the coupling impedance of the system in the wideband through the impedance model transfer function.
5. The direct drive wind farm of claim 1, wherein the system impedance model acquisition device is sent out via LCC-HVDC, wherein the device further comprises a memory and a communication interface;
the first acquisition module, the second acquisition module, the third acquisition module, the acquisition module and the calculation module form a processor;
a memory for a storage device to run a computer program;
the communication interface has a man-machine interaction function, receives system parameter data from the outside, uploads the system parameter data to the communication bus, or obtains a genetic algorithm optimization result of the direct-drive wind power plant sent out of the system through LCC-HVDC from the communication bus, and transmits the data to an external upper computer and the STATCOM controller;
the processor has the functions of data interaction input and output, information acquisition, parameter calculation and optimization result calculation, accesses or calls a computer program stored in the memory through the communication bus, and then executes the computer program.
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