CN114069681B - Input impedance modeling method, system, computer equipment and storage medium - Google Patents

Input impedance modeling method, system, computer equipment and storage medium Download PDF

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CN114069681B
CN114069681B CN202111258702.6A CN202111258702A CN114069681B CN 114069681 B CN114069681 B CN 114069681B CN 202111258702 A CN202111258702 A CN 202111258702A CN 114069681 B CN114069681 B CN 114069681B
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current
converter
relation
voltage
linearization
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CN114069681A (en
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孙鹏伟
周保荣
姚文峰
张帆
袁豪
张野
李俊杰
陈雁
翟鹤峰
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CSG Electric Power Research Institute
China Southern Power Grid Co Ltd
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CSG Electric Power Research Institute
China Southern Power Grid 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
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Hardware Design (AREA)
  • Evolutionary Computation (AREA)
  • Geometry (AREA)
  • General Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Inverter Devices (AREA)
  • Rectifiers (AREA)

Abstract

The invention relates to the technical field of stability analysis of power systems, and discloses an input impedance modeling method, an input impedance modeling system, computer equipment and a storage medium. According to the method, a mathematical model of a high-voltage direct current end-transmitting system is built according to three-phase full-wave bridge rectification current in the end-transmitting system, linearization is carried out on the mathematical model, meanwhile, the influence of phase-locked loop control on the mathematical model of the end-transmitting system is considered, an LCC-HVDC end-transmitting system small signal model considering the phase-locked loop is formed together, and finally input impedance is obtained through the model. The method for establishing the input impedance model by the linearization method under the synchronous rotation coordinate system has the advantages of simple modeling process and clear physical meaning, can be used for analyzing the harmonic stability and subsynchronous oscillation risk of the system, and also solves the problem that the influence of the system parameters on the stability is difficult to analyze by the traditional method.

Description

Input impedance modeling method, system, computer equipment and storage medium
Technical Field
The invention relates to the technical field of stability analysis of power systems, in particular to a method, a system, computer equipment and a storage medium for modeling input impedance of a high-voltage direct-current transmission end system under a synchronous rotation coordinate system.
Background
With the wide application of high-voltage direct current (HVDC) power transmission systems in western electric east transmission and power grid interconnection, harmonic transmission and amplification of converters are called potential hazards which threaten power grid stability. In the practical application construction of the high-voltage direct-current system, the power grid commutation converter LCC is widely applied to various high-voltage direct-current systems because the technology is mature and the construction cost is lower than that of other types of high-voltage direct-current power transmission. However, the rich harmonics created by the non-linear nature of the power electronics in LCCs pose a potential threat to the stability of the ac-dc interconnect system.
In order to facilitate analysis of harmonic transmission in an LCC-HVDC system, modeling of the LCC is required, and since a thyristor-based three-phase full-wave bridge rectifier is generally adopted by a transmitting-end converter of the LCC-HVDC, a certain difficulty exists in linearization modeling of the LCC-HVDC due to strong nonlinear characteristics of semi-controlled devices and mutual coupling of a direct current network and an alternating current network. The current common modeling method comprises a switching function model, a three-pulse wave model and the like, but both methods have certain limitations. Although the switching function model can better reflect the transfer relation of harmonic waves at two sides of the converter, the built model is not stable enough and has the defect of insufficient precision; the three-pulse wave model is mainly used for calculating the harmonic wave at the direct current side, and the harmonic current transmitted to the alternating current side at the direct current side is complex to calculate.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide an input impedance modeling method, an input impedance modeling system, computer equipment and a storage medium of an LCC-HVDC (high-speed direct current) power transmission end system under a synchronous rotation coordinate system, wherein the influences of a main circuit, a power transmission end converter control system and a phase-locked loop are comprehensively considered, and the LCC-HVDC power transmission end system is used for analyzing harmonic stability and subsynchronous oscillation risk of the system.
In a first aspect, an embodiment of the present invention provides a method for modeling input impedance of an LCC-HVDC transmission end system in a synchronous rotation coordinate system, where the method includes:
building an LCC-HVDC transmitting end system, wherein the LCC-HVDC transmitting end system comprises a converter which is a three-phase full-wave bridge rectifier circuit, and the converter comprises 3 common-anode thyristors and 3 common-cathode thyristors;
acquiring a voltage relation, a current relation and an active power relation of an alternating current side and a direct current side of the converter under a synchronous rotation coordinate system, and linearizing the voltage relation, the current relation and the active power relation at a steady-state point to respectively obtain a first linearization relation among the voltages, the currents and the active power of the alternating current side and the direct current side of the converter;
obtaining the expression relation of phase-locked loop errors and the conversion relation between the trigger angle reference value and the trigger angle actual value according to phase-locked loop control in the LCC-HVDC transmitting end system;
According to the first linearization relation, the phase-locked loop error is considered, and a second linearization relation among the alternating-current side outlet voltage, the current of the current converter and the voltage of the converting bus is obtained;
obtaining a third linearization relation among the alternating current side outlet voltage, the current of the current-direction converter and the voltage of the converting bus under a synchronous rotation coordinate system according to an alternating current circuit model of the LCC-HVDC transmitting end system;
obtaining a linearization relation of the converter bus voltage and the current flowing to the converter under a synchronous rotation coordinate system according to the second linearization relation and the third linearization relation, and taking the ratio of the converter bus voltage to the current flowing to the converter as the input impedance of the converter bus to the direct current side;
and obtaining the linearization relation between the current of the current converter and the voltage of the current converting bus under a synchronous rotation coordinate system according to a circuit model from the current converting bus to the alternating current side in the LCC-HVDC power transmission end system, obtaining the input admittance of the current converting bus looking at the alternating current side according to the linearization relation between the current of the current converter and the voltage of the current converting bus, and inverting the input admittance to obtain the input impedance of the voltage converting bus looking at the alternating current side.
Further, the step of obtaining the voltage relationship, the current relationship and the active power relationship of the ac side and the dc side of the converter in the synchronous rotation coordinate system, and linearizing the voltage relationship, the current relationship and the active power relationship at a steady-state point to obtain a first linearization relationship among the voltages, the currents and the active power of the ac side and the dc side of the converter, respectively, includes:
acquiring a first conversion relation between the direct current voltage at the rectifying side outlet of the converter, the direct current voltage at the inverting side outlet and the direct current voltage at the alternating side outlet and a second conversion relation between the current flowing to the converter and the direct current under a synchronous rotation coordinate system;
taking the active power at the direct current side as the active power at the alternating current side to obtain a third conversion relation among the direct current, the outlet voltage at the alternating current side and the current flowing to the converter;
linearizing the first conversion relation, the second conversion relation and the third conversion relation at steady-state points to respectively obtain linearization relations among the direct current, the alternating current side outlet voltage and the actual value of the current converter trigger angle, linearization relations among the direct current and the current flowing to the current converter, and linearization relations among the direct current, the alternating current side outlet voltage and the current flowing to the current converter;
The linearization relation among the direct current, the alternating current side outlet voltage and the current converter trigger angle actual value is calculated by adopting the following formula:
wherein the superscript r denotes a vector in the synchronous rotation coordinate system, the superscript (0) denotes a steady state value of the variable, and Δ is a small disturbance near the steady state value, I dc Is direct current, U is the outlet voltage of the alternating current side of the converter, R is the resistance of the direct current line, U d Is a plurality of U r The real part of U q Is a plurality of U r Alpha is the actual value of the firing angle of the converter, Δα=Δα ord +Δθ, wherein,
wherein alpha is ord Is the trigger angle reference value of the converter, H 1 (s) is a first-order inertial link, H 2 (s) is PI link, P ref S is a complex variable after Laplacian transformation and is a direct current active power reference value;
wherein θ is the phase-locked loop output signal, H 3 (s) is PI link, U c,d For converting bus voltage U c The real part of U c,q For converting bus voltage U c Delta theta is the phase-locked loop error;
calculating the linearization relation between the direct current and the current flowing to the converter by adopting the following formula:
wherein I is r(0) For synchronizing steady state values of current flowing to the converter under the rotating coordinate system, I d Is complex I r Real part of I q Is complex I r Is the imaginary part of (2);
calculating a linearization relationship among the direct current, the alternating current side outlet voltage and the flowing current to the converter current by adopting the following formula:
In U dc,i Is the dc voltage at the inverter side outlet.
Further, the step of obtaining the expression relation of the phase-locked loop error and the conversion relation between the trigger angle reference value and the trigger angle actual value according to the phase-locked loop control in the LCC-HVDC transmitting end system comprises the following steps:
according to active power control in the LCC-HVDC transmitting end system, obtaining a linearization relation of a trigger angle reference value;
according to phase-locked loop control in the LCC-HVDC transmitting end system, a fourth conversion relation between a phase-locked loop output signal and a converter bus voltage under a converter rotating coordinate system is obtained;
obtaining a fifth conversion relation between the converter busbar voltage and the phase-locked loop output signal under the synchronous rotation coordinate system according to the corresponding relation between the synchronous rotation coordinate system and the converter rotation coordinate system;
obtaining an expression relation of phase-locked loop errors according to the fourth conversion relation and the fifth conversion relation;
and taking the sum of the trigger angle reference value and the phase-locked loop error as an actual trigger angle value.
Further, the step of obtaining a second linearization relationship among the ac side outlet voltage, the current flowing to the converter and the voltage of the converter bus according to the first linearization relationship and considering the phase-locked loop error includes:
Combining the first conversion relation, the second conversion relation, the third conversion relation and the conversion relation between the trigger angle reference value and the trigger angle actual value to obtain a second linearization relation among the alternating current side outlet voltage, the current of the current-to-converter and the voltage of the converting bus taking into account phase-locked loop errors;
the second linearization relation among the alternating current side outlet voltage, the current of the flow direction converter and the voltage of the converting bus is calculated by adopting the following formula: :
wherein:
u is the vector form of the outlet voltage of the alternating current side, I is the vector form of the current flowing to the converter, U c In the form of a vector of commutation bus voltages.
Further, the step of obtaining a third linearization relationship among the ac side outlet voltage, the current of the current converter and the voltage of the converting bus in the synchronous rotation coordinate system according to the ac circuit model of the LCC-HVDC transmitting terminal system includes:
according to an alternating current circuit model in the LCC-HVDC transmitting end system, obtaining a conversion relation among the voltage of the converter bus, the outlet voltage of the alternating current side and the current of the flowing current converter under a static coordinate system;
Converting the conversion relation under the static coordinate system into a synchronous rotation coordinate system;
converting the conversion relation under the synchronous rotation coordinate system into a vector form and linearizing to obtain a third linearization relation among the converter busbar voltage, the alternating current side outlet voltage and the current of the current-to-converter;
wherein the third linearization relationship is calculated using the formula:
where s is complex variable after Laplacian transformation, ω 1 The power frequency angular velocity is the power frequency angular velocity, and L is the equivalent impedance of the converter.
Further, the input impedance of the converter bus to the dc side is calculated using the following formula:
wherein:
further, the step of obtaining the linearization relation between the current of the current converter and the voltage of the current converting bus in the synchronous rotation coordinate system according to the circuit model from the current converting bus to the ac side in the LCC-HVDC power transmission system, obtaining the input admittance of the current converting bus looking at the ac side according to the linearization relation between the current of the current converter and the voltage of the current converting bus, and inverting the input admittance to obtain the input impedance of the voltage converting bus looking at the ac side includes:
obtaining a conversion relation between the current of the current converter and the voltage of the current converting bus in a static coordinate system according to a circuit model from the current converting bus to an alternating current side in an LCC-HVDC (high-speed direct current) transmitting end system;
Converting the conversion relation into a synchronous rotation coordinate system;
converting the conversion relation under the synchronous rotation coordinate system into a vector form and linearizing to obtain a linearization relation between the current of the current converter and the voltage of the converter bus, obtaining the input admittance of the converter bus looking to the alternating current side according to the linearization relation, and inverting the input admittance to obtain the input impedance of the converter bus looking to the alternating current side;
wherein the linearization relationship is calculated using the following formula:
wherein C is the equivalent parallel capacitance of the alternating current filter and the reactive compensation device, L s The equivalent impedance of the alternating current power grid is E, and E is the equivalent power supply of the alternating current power grid at the transmitting endVoltage of Y 1 I.e. the input admittance of the converter bus to the ac side, for Y 1 Inversion is carried out, and the following steps are obtained:
i.e. the input impedance of the converter bus looking at the ac side.
In a second aspect, an embodiment of the present invention provides an input impedance modeling system of an LCC-HVDC transmission end system in a synchronous rotation coordinate system, the system comprising:
the system comprises a power transmission end system building module, a power transmission end system control module and a power transmission end control module, wherein the power transmission end system building module is used for building an LCC-HVDC power transmission end system, the LCC-HVDC power transmission end system comprises a current converter which is a three-phase full-wave bridge rectifier circuit, and the current converter comprises 3 common-anode thyristors and 3 common-cathode thyristors;
The first linearization relation calculation module is used for acquiring a voltage relation, a current relation and an active power relation of an alternating current side and a direct current side of the converter under a synchronous rotation coordinate system, linearizing the voltage relation, the current relation and the active power relation at a steady-state point to respectively obtain a first linearization relation among the voltages, the currents and the active power of the alternating current side and the direct current side of the converter;
the expression and conversion relation calculation module is used for obtaining the expression relation of phase-locked loop errors and the conversion relation between the trigger angle reference value and the trigger angle actual value according to phase-locked loop control in the LCC-HVDC transmitting end system;
the second linearization relation calculation module is used for obtaining a second linearization relation among the alternating-current side outlet voltage, the current of the current converter and the voltage of the converting bus by considering the phase-locked loop error according to the first linearization relation;
the third linearization relation calculation module is used for obtaining a third linearization relation among the alternating current side outlet voltage, the flow direction converter current and the converter bus voltage under a synchronous rotation coordinate system according to an alternating current circuit model of the LCC-HVDC transmitting end system;
The direct current side input impedance calculation module is used for obtaining the linearization relation of the voltage of the converter bus and the current flowing to the converter under a synchronous rotation coordinate system according to the second linearization relation and the third linearization relation, and taking the ratio of the voltage of the converter bus and the current flowing to the converter as the input impedance of the converter bus to the direct current side;
and the alternating current side input impedance calculation module is used for obtaining the linearization relation between the current of the current converter and the voltage of the current converting bus under a synchronous rotation coordinate system according to a circuit model from the current converting bus to the alternating current side in the LCC-HVDC transmitting end system, obtaining the input admittance of the current converting bus looking at the alternating current side according to the linearization relation between the current of the current converter and the voltage of the current converting bus, and inverting the input admittance to obtain the input impedance of the voltage converting bus looking at the alternating current side.
In a third aspect, embodiments of the present invention further provide a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the above method when executing the computer program.
In a fourth aspect, embodiments of the present invention also provide a computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the above method.
The application provides an input impedance modeling method, an input impedance modeling system, computer equipment and a storage medium of an LCC-HVDC transmitting end system under a synchronous rotation coordinate system. According to the method, a mathematical model of a high-voltage direct current end-transmitting system is built according to three-phase full-wave bridge rectification current in the end-transmitting system, linearization is carried out on the mathematical model, meanwhile, the influence of phase-locked loop control on the mathematical model of the end-transmitting system is considered, an LCC-HVDC end-transmitting system small signal model considering the phase-locked loop is formed together, and finally input impedance is obtained through the model. The method for establishing the input impedance model by the linearization method under the synchronous rotation coordinate system has the advantages of simple modeling process and clear physical meaning, can be used for analyzing the harmonic stability and subsynchronous oscillation risk of the system, and also solves the problem that the influence of the system parameters on the stability is difficult to analyze by the traditional method.
Drawings
FIG. 1 is a schematic flow chart of an input impedance modeling method according to an embodiment of the present invention;
Fig. 2 is a topology structure diagram of an LCC-HVDC transmission end system in accordance with an embodiment of the present invention;
fig. 3 is a flowchart of step S20 in fig. 1;
fig. 4 is a flowchart of step S30 in fig. 1;
FIG. 5 is a schematic diagram of an active power control flow in an embodiment of the present invention;
FIG. 6 is a schematic diagram of a phase locked loop control flow in an embodiment of the invention;
fig. 7 is a flowchart of step S50 in fig. 1;
fig. 8 is a flowchart of step S70 in fig. 1;
FIG. 9 is a diagram of the relationship between input impedance and input admittance;
FIG. 10 is a schematic diagram of an input impedance modeling system in accordance with an embodiment of the present invention;
fig. 11 is an internal structural view of a computer device in the embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1, a method for modeling input impedance of an LCC-HVDC transmission end system in a synchronous rotation coordinate system according to a first embodiment of the present invention includes steps S10 to S60:
and step S10, building an LCC-HVDC transmitting end system, wherein the LCC-HVDC transmitting end system comprises a converter which is a three-phase full-wave bridge rectifier circuit, and the converter comprises 3 common-anode thyristors and 3 common-cathode thyristors.
The topology structure diagram of the LCC-HVDC power transmission system in this embodiment is shown in FIG. 2, wherein E is the voltage of the equivalent power supply of the power transmission AC network, L s Is equivalent impedance of AC power grid, I s U for current flowing from AC network to converter bus c To commutate bus voltage, I c Is the current flowing through the AC filter, I is the current flowing to the converter, L is the equivalent impedance of the converter, U is the outlet voltage of the AC side of the converter, U dc,r For rectifying side-outlet DC voltage, U dc,i For the inversion side outlet DC voltage, I dc The direct current, R is the direct current line resistance, C is the equivalent parallel capacitance of the alternating current filter and the reactive compensation device, and the direct current electric quantity is the average value under the quasi-steady state, and the parameter is used in the follow-up formula, and the parameter meaning will not be repeated.
As can be seen from fig. 2, the converter in the feed-end system is a three-phase full-wave bridge rectifier circuit, and is composed of 3 thyristors with common anodes and 3 thyristors with common cathodes, so as to realize conversion from ac to dc. The input impedance modeling method in the embodiment ignores the influence of the resistance of the alternating current system, the direct current filter and the phase change link of the converter on the model, and considers U when analyzing the input impedance dc,i The control method has the advantages that the control method is kept constant, the converter adopts an active power control mode in a normal working state, the control is realized by controlling the conduction time of 6 thyristors, the physical meaning of the model is clearer, and linearization is convenient under a synchronous rotation coordinate system.
Step S20, obtaining a voltage relation, a current relation and an active power relation of an alternating current side and a direct current side of the converter under a synchronous rotation coordinate system, and linearizing the voltage relation, the current relation and the active power relation at a steady-state point to respectively obtain a first linearization relation among the voltages, the currents and the active power of the alternating current side and the direct current side of the converter.
According to the circuit structure of the converter, the relation between the voltages and the currents at two sides of the converter and the relation between the active power can be obtained, and the specific steps are shown in fig. 3:
Step S201, obtaining a first conversion relationship between the dc voltage at the rectifying side, the dc voltage at the inverting side and the ac side of the converter and a second conversion relationship between the current flowing to the converter and the dc current in the synchronous rotation coordinate system.
According to the conversion relationship between the dc voltage and the ac voltage at the two sides of the 6-pulse full-bridge inverter and the conversion relationship between the current at the two sides in fig. 2, the following formula can be obtained:
wherein, the superscript r is expressed as a vector under a synchronous rotation coordinate system, U d And U q For plural ac side outlet voltages U in synchronous rotation coordinate system r Real and imaginary parts of (i.e. U) r ＝U d +jU q The same I d And I q For the real and imaginary parts of the current I flowing to the converter, |i r I is I r Alpha is the actual value of the converter firing angle, Δα=Δα ord +Δθ, wherein,
wherein alpha is ord Is the trigger angle reference value of the converter, H 1 (s) is a first-order inertial link, H 2 (s) is PI link, P ref S is a complex variable after Laplacian transformation and is a direct current active power reference value;
in which θ is the phase-locked loop output signalNumber H 3 (s) is PI link, U c,d For converting bus voltage U c The real part of U c,q For converting bus voltage U c Delta theta is the phase-locked loop error;
The conversion relation expression between the rectifying side outlet direct current voltage and the inverting side outlet voltage in the direct current side of the converter and the conversion relation expression between the alternating side outlet voltage are clearly shown in the formula (1), and the relation among the three voltages can be seen to also relate to the actual value of the trigger angle of the converter, wherein the specific calculation process of the delta alpha expression is described in detail in the following steps. And the expression (2) is the expression relationship between the current flowing to the converter and the direct current. The relation between the direct-current and alternating-current voltages at the two sides of the converter is clearly expressed through the formulas (1) and (2), and meanwhile, the subsequent linearization of parameters is facilitated.
Step S202, taking the active power at the dc side as the active power at the ac side, to obtain a third conversion relationship among the dc current, the outlet voltage at the ac side, and the current flowing to the inverter.
Since the active loss of the converter is ignored in the present embodiment, the active power on the dc side can be equal to the active power on the ac side, and the active power on both sides is denoted by P:
P＝(U dc,i +I dc R)I dc ＝3(U d I d +U q I q ) (3)
the converter used in the formula (3) is a 6-pulse full-bridge converter, so that a calculation formula of the active power of the direct current side and the active power of the alternating current side of the converter can be obtained, that is, another expression relationship between the voltage and the current at two sides of the converter is obtained. The mathematical model of the transmitting end system can be formed by the formulas (1), (2) and (3), so that the basis of the input impedance modeling method of the embodiment is formed, and the relation between the voltage and the current is further calculated on the basis.
Step S203, linearizing the first conversion relationship, the second conversion relationship, and the third conversion relationship at steady-state points to obtain linearization relationships among the dc current, the ac side outlet voltage, and the actual value of the trigger angle of the converter, linearization relationships among the dc current and the current flowing to the converter, and linearization relationships among the dc current, the ac side outlet voltage, and the current flowing to the converter.
Through the two steps, the direct current I under the synchronous rotation coordinate system is obtained dc Three different conversion expression relations among the alternating current side outlet voltage U and the current I flowing to the converter, because the LCC-HVDC transmitting end system is a nonlinear system, in order to facilitate modeling of input impedance, we are at a steady-state pointLinearizing equations (1) (2) (3) to obtain equations (4) (5) (6), wherein superscript (0) represents the steady state value of the variable and Δ represents the small perturbation of the steady state value attachment, the linearized equation is as follows:
by linearizing the formulas (1), (2) and (3), the end-feeding system of the nonlinear system has a linearization expression relationship, so that the model is convenient to build. Wherein the calculation of the actual value of the firing angle will be described in detail in the following steps.
And step S30, obtaining the expression relation of the phase-locked loop error and the conversion relation between the trigger angle reference value and the trigger angle actual value according to the phase-locked loop control in the LCC-HVDC transmitting end system.
The conversion relation between the voltages at both sides of the converter obtained in step S20, that is, the actual value of the firing angle of the converter is referred to in equation (4), so, as shown in fig. 4, the actual value of the firing angle needs to be obtained through active power control and phase-locked loop control:
and step S301, obtaining the linearization representation of the trigger angle reference value according to active power control in the LCC-HVDC transmitting end system.
As can be seen from equation (4), at DC current I dc The relation between the ac side outlet voltage U and the actual value of the firing angle a is included, and in practice in steady state conditions the firing angle of the converter is typically between 12.5 deg. and 17.5 deg..
The reference value of the trigger angle is obtained by an active power control link, as shown in FIG. 5, wherein P ref Is a direct current active power reference value, I dcref Is the reference value of direct current, alpha ord Is the trigger angle reference value of the converter, H 1 (s) is a first-order inertial link, H 2 (s) is PI link, namely:
wherein T is u Is a time constant, K p2 Is a proportionality coefficient, K i2 S is the complex variable after Laplacian transformation, and s is the integral coefficient.
The reference value of the converter firing angle can be derived from fig. 5:
will H 1 (s) and H 2 (s) into the formula (7 a), the trigger angle reference value alpha can be obtained ord And direct current I dc And then linearizing the relation expression to obtain a linearization expression of the converter trigger angle reference value:
when the error of the triggering device is ignored, the error between the triggering angle reference value and the triggering angle actual value is derived from the phase locked loop.
And step S302, obtaining a fourth conversion relation between the phase-locked loop output signal and the voltage of the converting bus under the rotating coordinate system of the converter according to the phase-locked loop control in the LCC-HVDC transmitting end system.
As shown in fig. 6, in the phase-locked loop control flow diagram, the commutation bus voltage U c Expressed in the converter rotation coordinate system asThe superscript c denotes the converter rotational coordinate system, ω 1 For the power frequency angular velocity, deltaω is the power frequency angular velocity error, abc/dq module represents park transformation, θ is the phase-locked loop output signal, H 3 (s) is a PI link, and the formula is as follows:
wherein k is p3 Is a proportionality coefficient, k i3 Is an integral coefficient.
According to the phase-locked loop control, a relational expression between a phase-locked loop output signal and a converter bus voltage under a converter rotation coordinate system can be obtained:
Step S303, obtaining a fifth conversion relation between the converter busbar voltage and the phase-locked loop output signal under the synchronous rotation coordinate system according to the corresponding relation between the synchronous rotation coordinate system and the converter rotation coordinate system.
The conversion relation of the converter busbar voltage under two coordinates can be obtained by the corresponding relation of the synchronous rotation coordinate system and the converter rotation coordinate system:
the formula (9) is obtained after further conversion:
step S304, according to the fourth conversion relation and the fifth conversion relation, the expression relation of the phase-locked loop error is obtained.
The conversion relation between the converter bus voltage and the phase-locked loop output signal in the synchronous rotation coordinate system can be obtained by obtaining the formulas (8) and (10) and bringing the converter bus voltage in the converter rotation coordinate system in the formula (10) into the formula (8), and the linearization expression of the phase-locked loop output signal, namely the expression relation of the phase-locked loop error, is obtained after linearization of the conversion relation:
and step S305, taking the sum of the trigger angle reference value and the phase-locked loop error as an actual trigger angle value.
Since the error of the phase-locked loop affects the actual value of the firing angle of the converter valve, the actual value of the firing angle can be obtained by formulas (7) and (11):
Δα＝Δα ord +Δθ (12)
And (3) carrying the formulas (7) and (11) into the formula (12) to obtain a linearization expression of the actual value of the trigger angle, namely, the formula (12) analyzes the influence of phase-locked loop control on the mathematical model of the LCC-HVDC transmitting end system.
Since the actual value of the trigger angle is used in the formula (4) obtained in the above step, and the actual value of the trigger angle is related to the output signal of the phase-locked loop, the formulas (4) (5) (6) and (12) together form the small signal model of the LCC-HVDC transmitting end system considering the phase-locked loop.
And step S40, according to the first linearization relation, taking the phase-locked loop error into consideration to obtain a second linearization relation among the AC side outlet voltage, the current of the current-to-converter and the voltage of the converter bus.
After the small signal model of the transmitting end system is obtained, further conversion calculation is needed to be carried out on the expression in the model, in the above steps, the linearization relation between the direct current and the alternating current side outlet voltage and the actual value of the triggering angle of the formula (4), the linearization relation between the direct current and the current flowing to the converter, and the linearization relation between the direct current and the alternating current side outlet voltage and the current flowing to the converter are obtained, and the simultaneous combination calculation is carried out according to the three different linearization relations, so that the second linearization relation among the alternating current side outlet voltage, the current flowing to the converter and the voltage of the converting bus, which take the phase-locked loop error into consideration, can be obtained, and the specific procedures are as follows:
Firstly, carrying out simultaneous calculation on the formula (5) and the formula (6), so as to obtain a linearization relation between the current flowing to the converter and the outlet voltage at the alternating current side:
wherein:
then, the formulas (4), (5), (7), (11), (12) are simultaneously calculated to obtain a linearization relation among the direct current, the alternating current side outlet voltage and the converter bus voltage:
wherein:
converting equations (13) and (14) into vector and matrix form, obtaining the linearization relation of the vector form between the AC side outlet voltage and the current-direction converter voltage and the converter bus voltage:
that is, after the small signal model of the transmitting end system is converted for a plurality of times in the steps, a relational expression with very clear meaning among the outlet voltage of the alternating current side, the current of the current converter and the voltage of the converting bus is finally obtained.
And step S50, obtaining a third linearization relation among the AC side outlet voltage, the current of the current converter and the voltage of the converting bus under a synchronous rotation coordinate system according to an AC circuit model of the LCC-HVDC transmitting end system.
In the above steps, the linearization relationship among the ac side outlet voltage, the current flowing to the inverter and the voltage of the converting bus in the synchronous rotation coordinate system is obtained through the circuit structure of the inverter, and the relationship among the three in the stationary coordinate system can be obtained according to the ac circuit model of the transmitting end system, therefore, the three needs to be converted into the synchronous rotation coordinate system, and the specific steps are shown in fig. 7:
And step S501, obtaining a conversion relation among the converter busbar voltage, the alternating-current side outlet voltage and the current of the flow direction converter under a static coordinate system according to an alternating-current circuit model in the LCC-HVDC transmitting end system.
From the ac circuit in the LCC-HVDC transmission system topology shown in fig. 1, the relationship among the converter bus voltage, ac side outlet voltage and current to the converter in the stationary coordinate system can be obtained:
wherein the superscript s denotes a stationary coordinate system.
Step S502, converting the conversion relation under the stationary coordinate system into a synchronous rotation coordinate system.
According to the corresponding relation between the synchronous rotation coordinate system and the static coordinate system, the formula (16 a) is transferred to the synchronous rotation coordinate system:
step S503, converting the conversion relationship in the synchronous rotation coordinate system into a vector form and linearizing, so as to obtain a third linearization relationship of the converter bus voltage, the ac side outlet voltage and the current of the current-to-converter.
The expression (16) is expressed in a vector form, and is obtained after linearization:
that is, by linearization, a clear relational expression in the ac circuit between the converter bus voltage, the ac side outlet voltage, and the current flowing to the converter can be obtained.
And step S60, obtaining the linearization relation of the voltage of the converter bus and the current flowing to the converter under a synchronous rotation coordinate system according to the second linearization relation and the third linearization relation, and taking the ratio of the voltage of the converter bus to the current flowing to the converter as the input impedance of the converter bus to the direct current side.
Two linearization relations between the ac side outlet voltage, the current flowing to the converter and the voltage of the converter bus, namely formulas (15) and (17), are obtained through the above steps, and for this purpose, we perform simultaneous calculation on formulas (15) and (17) and convert the two linearization relations between the voltage of the converter bus and the current flowing to the converter:
wherein:
equation (18) clearly shows the relationship between the converter bus voltage and the current flowing to the converter, that is, the ratio of the converter bus voltage to the current flowing to the converter can be obtained by simple conversion of equation (18):
z in the formula (19) r I.e. the input impedance of the converter bus looking to the dc side. The input impedance model established through the steps is clear in physical meaning, and the modeling process is not too complex.
And step S70, obtaining a linearization relation between the current of the current converter and the voltage of the current converting bus under a synchronous rotation coordinate system according to a circuit model from the current converting bus to the alternating current side in the LCC-HVDC transmitting end system, obtaining an input admittance of the current converting bus looking at the alternating current side according to the linearization relation between the current of the current converter and the voltage of the current converting bus, and inverting the input admittance to obtain the input impedance of the voltage converting bus looking at the alternating current side.
By steps S10-S60 we get the input impedance from the converter bus to the dc side, whereas in practice the input impedance in LCC-HVDC transmission system also includes the converter bus to the ac side, so we need to calculate the input impedance of the other side by the steps as in fig. 9:
and step 701, obtaining a conversion relation between the current of the current converter and the voltage of the current converting bus under a static coordinate system according to a circuit model from the current converting bus to the alternating current side in the LCC-HVDC transmitting end system.
According to the circuit of the LCC-HVDC transmission system with the converter bus line looking to the ac side shown in fig. 1, the conversion relationship between the current flowing to the converter and the voltage of the converter bus line in the stationary coordinate system can be obtained:
step S702, converting the conversion relationship into a synchronous rotation coordinate system.
Since linearization of the sine quantity in the stationary coordinate system is difficult, it is necessary to convert it into the synchronous coordinate system, and the equation (20 a) is converted into:
and the steady-state down-conversion result is a direct current when the formula is down-converted from a static coordinate system to a synchronous rotation coordinate system, so that further linearization processing is convenient to follow.
Step S703, converting the conversion relationship in the synchronous rotation coordinate system into a vector form and linearizing the vector form to obtain a linearization relationship between the current of the current converter and the voltage of the converter bus, obtaining an input admittance of the converter bus looking at the ac side according to the linearization relationship, and inverting the input admittance to obtain an input impedance of the converter bus looking at the ac side.
For ease of calculation, we convert the parameters in equation (20) from complex form to vector form and perform linearization:
equation (21) also clearly shows the linearization relationship between the current flowing to the converter and the voltage of the converter bus, and Y can be seen from equation (21) 1 I.e. the input admittance of the converter bus to the ac side, for Y 1 Inversion is carried out, and the following steps are obtained:
i.e. the input impedance of the converter bus looking at the ac side.
Through steps S10-S70, an input impedance model of the LCC-HVDC transmitting terminal system is established under the synchronous rotation coordinate system, wherein the input impedance model comprises an input impedance of a current conversion bus looking at a direct current side and an input impedance of the current conversion bus looking at an alternating current side, and the model established through the method is clear in physical meaning and solves the problem that the influence of system parameters on stability is difficult to analyze in the traditional method.
From the formulas (18), (19) and (21), a flow chart of the relationship between the input impedance of the converter bus to the dc side and the input impedance of the converter bus to the ac side as shown in fig. 9 can be obtained, and from this chart, the open loop transfer function of the input impedance model of the present embodiment can be obtained:
the stability of the system can be determined according to the formula (22) using a multivariate nyquist criterion, and the specific determination process can refer to the conventional steps of the multivariate nyquist criterion, which are not described herein.
Compared with the conventional switching function model or the three-pulse wave model and other established models, the input impedance modeling method provided by the embodiment of the invention is not stable enough and is insufficient in precision, the LCC-HVDC transmitting end system mathematical model under the synchronous rotation coordinate system is established, the modeling method is made to take the influence of phase-locked loop control on the transmitting end system mathematical model into consideration, and the LCC-HVDC transmitting end system small signal model taking the phase-locked loop into consideration is formed, so that the input impedance modeling method is obtained, the modeling process is simple, the physical meaning is clear, the method can be used for analyzing the harmonic stability and subsynchronous oscillation risk of the system, and the problem that the influence of system parameters on the stability is difficult to analyze in the conventional method is also overcome.
Referring to fig. 10, based on the same inventive concept, a second embodiment of the present invention provides an input impedance modeling system, including:
a power transmission system building module 10, configured to build an LCC-HVDC power transmission system, where the LCC-HVDC power transmission system includes a converter that is a three-phase full-wave bridge rectifier circuit, and the converter includes 3 common-anode thyristors and 3 common-cathode thyristors;
the first linearization relation calculation module 20 is configured to obtain a voltage relation, a current relation and an active power relation of an ac side and a dc side of the converter in a synchronous rotation coordinate system, and linearize the voltage relation, the current relation and the active power relation at a steady-state point to obtain a first linearization relation between the voltages, the currents and the active power of the ac side and the dc side of the converter, respectively;
the expression and conversion relation calculation module 30 is configured to obtain an expression relation of a phase-locked loop error and a conversion relation between a trigger angle reference value and a trigger angle actual value according to phase-locked loop control in the LCC-HVDC transmission end system;
a second linearization relation calculating module 40, configured to obtain a second linearization relation among the ac side outlet voltage, the current flowing to the converter, and the voltage of the converter bus, in consideration of the phase-locked loop error according to the first linearization relation;
A third linearization relation calculation module 50, configured to obtain a third linearization relation among the ac side outlet voltage, the current of the current-to-converter, and the voltage of the converter bus in a synchronous rotation coordinate system according to an ac circuit model of the LCC-HVDC transmission end system;
a dc side input impedance calculating module 60, configured to obtain a linearization relationship between the voltage of the converter bus and the current flowing to the converter under a synchronous rotation coordinate system according to the second linearization relationship and the third linearization relationship, and take a ratio of the voltage of the converter bus and the current flowing to the converter as an input impedance of the converter bus to look at the dc side;
and the ac side input impedance calculating module 70 is configured to obtain a linearization relationship between the current of the converter and the voltage of the converter bus in the synchronous rotation coordinate system according to a circuit model from the converter bus to the ac side in the LCC-HVDC power transmission system, obtain an input admittance of the converter bus looking at the ac side according to the linearization relationship between the current of the converter and the voltage of the converter bus, and invert the input admittance to obtain an input impedance of the converter bus looking at the ac side.
The technical features and technical effects of the input impedance modeling system provided by the embodiment of the present invention are the same as those of the method provided by the embodiment of the present invention, and are not described herein. The various modules in the input impedance modeling system described above may be implemented in whole or in part by software, hardware, and combinations thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
Referring to FIG. 11, in one embodiment, an internal architecture diagram of a computer device, which may be a terminal or a server in particular. The computer device includes a processor, a memory, a network interface, a display, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is executed by a processor to implement a method of modeling input impedance. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, can also be keys, a track ball or a touch pad arranged on the shell of the computer equipment, and can also be an external keyboard, a touch pad or a mouse and the like.
It will be appreciated by those of ordinary skill in the art that the architecture shown in fig. 11 is merely a block diagram of some of the architecture relevant to the present application and is not intended to limit the computer device on which the present application may be implemented, and that a particular computing device may include more or fewer components than those shown in the middle, or may combine certain components, or have the same arrangement of components.
In addition, the embodiment of the invention also provides computer equipment, which comprises a memory, a processor and a computer program stored on the memory and capable of running on the processor, wherein the processor realizes the steps of the method when executing the computer program.
Furthermore, the embodiment of the invention also provides a computer readable storage medium, on which a computer program is stored, which when being executed by a processor, implements the steps of the method.
In summary, the embodiments of the present invention provide a method, a system, a computer device, and a storage medium for modeling input impedance, where the method includes building an LCC-HVDC transmission system, where the LCC-HVDC transmission system includes a converter that is a three-phase full-wave bridge rectifier circuit, and where the converter includes 3 common-anode thyristors and 3 common-cathode thyristors; acquiring a voltage relation, a current relation and an active power relation of an alternating current side and a direct current side of the converter under a synchronous rotation coordinate system, and linearizing the voltage relation, the current relation and the active power relation at a steady-state point to respectively obtain a first linearization relation among the voltages, the currents and the active power of the alternating current side and the direct current side of the converter; obtaining the expression relation of phase-locked loop errors and the conversion relation between the trigger angle reference value and the trigger angle actual value according to phase-locked loop control in the LCC-HVDC transmitting end system; according to the first linearization relation, the phase-locked loop error is considered, and a second linearization relation among the alternating-current side outlet voltage, the current of the current converter and the voltage of the converting bus is obtained; obtaining a third linearization relation among the alternating current side outlet voltage, the current of the current-direction converter and the voltage of the converting bus under a synchronous rotation coordinate system according to an alternating current circuit model of the LCC-HVDC transmitting end system; obtaining a linearization relation of the converter bus voltage and the current flowing to the converter under a synchronous rotation coordinate system according to the second linearization relation and the third linearization relation, and taking the ratio of the converter bus voltage to the current flowing to the converter as the input impedance of the converter bus to the direct current side; and obtaining the linearization relation between the current of the current converter and the voltage of the current converting bus under a synchronous rotation coordinate system according to a circuit model from the current converting bus to the alternating current side in the LCC-HVDC power transmission end system, obtaining the input admittance of the current converting bus looking at the alternating current side according to the linearization relation between the current of the current converter and the voltage of the current converting bus, and inverting the input admittance to obtain the input impedance of the voltage converting bus looking at the alternating current side. The method for establishing the input impedance model by the linearization method under the synchronous rotation coordinate system has the advantages of simple modeling process and clear physical meaning, can be used for analyzing the harmonic stability and subsynchronous oscillation risk of the system, and also solves the problem that the influence of the system parameters on the stability is difficult to analyze by the traditional method.
In this specification, each embodiment is described in a progressive manner, and all the embodiments are directly the same or similar parts referring to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments. It should be noted that, any combination of the technical features of the foregoing embodiments may be used, and for brevity, all of the possible combinations of the technical features of the foregoing embodiments are not described, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples only represent a few preferred embodiments of the present application, which are described. And are specific and detailed herein, but are not to be construed as limiting the scope of the invention. It should be noted that modifications and substitutions can be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and substitutions should also be considered to be within the scope of the present application. Therefore, the protection scope of the patent application is subject to the protection scope of the claims.

Claims (10)

1. An input impedance modeling method of an LCC-HVDC transmitting end system under a synchronous rotation coordinate system is characterized by comprising the following steps:
building an LCC-HVDC transmitting end system, wherein the LCC-HVDC transmitting end system comprises a converter which is a three-phase full-wave bridge rectifier circuit, and the converter comprises 3 common-anode thyristors and 3 common-cathode thyristors;
acquiring a voltage relation, a current relation and an active power relation of an alternating current side and a direct current side of the converter under a synchronous rotation coordinate system, and linearizing the voltage relation, the current relation and the active power relation at a steady-state point to respectively obtain a first linearization relation among the voltages, the currents and the active power of the alternating current side and the direct current side of the converter;
obtaining the expression relation of phase-locked loop errors and the conversion relation between the trigger angle reference value and the trigger angle actual value according to phase-locked loop control in the LCC-HVDC transmitting end system;
according to the first linearization relation, the phase-locked loop error is considered, and a second linearization relation among the alternating-current side outlet voltage, the current of the current converter and the voltage of the converting bus is obtained;
obtaining a third linearization relation among the alternating current side outlet voltage, the current of the current-direction converter and the voltage of the converting bus under a synchronous rotation coordinate system according to an alternating current circuit model of the LCC-HVDC transmitting end system;
Obtaining a linearization relation of the converter bus voltage and the current flowing to the converter under a synchronous rotation coordinate system according to the second linearization relation and the third linearization relation, and taking the ratio of the converter bus voltage to the current flowing to the converter as the input impedance of the converter bus to the direct current side;
and obtaining the linearization relation between the current of the current converter and the voltage of the current converting bus under a synchronous rotation coordinate system according to a circuit model from the current converting bus to the alternating current side in the LCC-HVDC power transmission end system, obtaining the input admittance of the current converting bus looking at the alternating current side according to the linearization relation between the current of the current converter and the voltage of the current converting bus, and inverting the input admittance to obtain the input impedance of the voltage converting bus looking at the alternating current side.
2. The method for modeling input impedance of LCC-HVDC transmission end system in accordance with claim 1, wherein said step of obtaining voltage relationship, current relationship and active power relationship of ac side and dc side of said inverter in synchronous rotation coordinate system and linearizing said voltage relationship, current relationship and active power relationship at steady-state point to obtain first linearization relationship between voltage, current and active power of ac side and dc side of said inverter, respectively, comprises:
Acquiring a first conversion relation between the direct current voltage at the rectifying side outlet of the converter, the direct current voltage at the inverting side outlet and the direct current voltage at the alternating side outlet and a second conversion relation between the current flowing to the converter and the direct current under a synchronous rotation coordinate system;
taking the active power at the direct current side as the active power at the alternating current side to obtain a third conversion relation among the direct current, the outlet voltage at the alternating current side and the current flowing to the converter;
linearizing the first conversion relation, the second conversion relation and the third conversion relation at steady-state points to respectively obtain linearization relations among the direct current, the alternating current side outlet voltage and the actual value of the current converter trigger angle, linearization relations among the direct current and the current flowing to the current converter, and linearization relations among the direct current, the alternating current side outlet voltage and the current flowing to the current converter;
the linearization relation among the direct current, the alternating current side outlet voltage and the current converter trigger angle actual value is calculated by adopting the following formula:
wherein the superscript r denotes a vector in the synchronous rotation coordinate system, the superscript (0) denotes a steady state value of the variable, and Δ is a small disturbance near the steady state value, I dc Is direct current, U is the outlet voltage of the alternating current side of the converter, R is the resistance of the direct current line, U d Is a plurality of U r The real part of U q Is a plurality of U r Alpha is the actual value of the firing angle of the converter, Δα=Δα ord +Δθ, wherein,
wherein alpha is ord Is the trigger angle reference value of the converter, H 1 (s) is a first-order inertial link, H 2 (s) is PI link, P ref S is a complex variable after Laplacian transformation and is a direct current active power reference value;
wherein θ is the phase-locked loop output signal, H 3 (s) is PI link, U c,d For converting bus voltage U c The real part of U c,q For converting bus voltage U c Delta theta is the phase-locked loop error;
calculating the linearization relation between the direct current and the current flowing to the converter by adopting the following formula:
wherein I is r(0) For synchronizing steady state values of current flowing to the converter under the rotating coordinate system, I d Is complex I r Real part of I q Is complex I r Is the imaginary part of (2);
calculating a linearization relationship among the direct current, the alternating current side outlet voltage and the flowing current to the converter current by adopting the following formula:
in U dc,i Is the dc voltage at the inverter side outlet.
3. The method for modeling the input impedance of the LCC-HVDC transmission end system in the synchronous rotation coordinate system according to claim 2, wherein the step of obtaining the expression relationship of the phase-locked loop error and the conversion relationship between the trigger angle reference value and the trigger angle actual value according to the phase-locked loop control in the LCC-HVDC transmission end system comprises:
According to active power control in the LCC-HVDC transmitting end system, obtaining a linearization relation of a trigger angle reference value;
according to phase-locked loop control in the LCC-HVDC transmitting end system, a fourth conversion relation between a phase-locked loop output signal and a converter bus voltage under a converter rotating coordinate system is obtained;
obtaining a fifth conversion relation between the converter busbar voltage and the phase-locked loop output signal under the synchronous rotation coordinate system according to the corresponding relation between the synchronous rotation coordinate system and the converter rotation coordinate system;
obtaining an expression relation of phase-locked loop errors according to the fourth conversion relation and the fifth conversion relation;
and taking the sum of the trigger angle reference value and the phase-locked loop error as an actual trigger angle value.
4. The method for modeling input impedance of LCC-HVDC transmission end system in accordance with claim 3, wherein said step of obtaining a second linearization relationship among the ac side outlet voltage, the current of the inverter, and the voltage of the commutation bus in consideration of the phase-locked loop error according to the first linearization relationship comprises:
combining the first conversion relation, the second conversion relation, the third conversion relation and the conversion relation between the trigger angle reference value and the trigger angle actual value to obtain a second linearization relation among the alternating current side outlet voltage, the current of the current-to-converter and the voltage of the converting bus taking into account phase-locked loop errors;
Calculating a second linearization relationship between the ac side outlet voltage, the current to the converter and the converter bus voltage using the formula:
wherein:
u is the vector form of the outlet voltage of the alternating current side, I is the vector form of the current flowing to the converter, U c In the form of a vector of commutation bus voltages.
5. The method for modeling input impedance of LCC-HVDC transmission end system in accordance with claim 3, wherein said step of obtaining a third linearization relationship among said ac side outlet voltage, said current to inverter and said voltage of said commutation bus in synchronous rotation coordinate system based on an ac circuit model of said LCC-HVDC transmission end system comprises:
according to an alternating current circuit model in the LCC-HVDC transmitting end system, obtaining a conversion relation among the voltage of the converter bus, the outlet voltage of the alternating current side and the current of the flowing current converter under a static coordinate system;
converting the conversion relation under the static coordinate system into a synchronous rotation coordinate system;
converting the conversion relation under the synchronous rotation coordinate system into a vector form and linearizing to obtain a third linearization relation among the converter busbar voltage, the alternating current side outlet voltage and the current of the current-to-converter;
Wherein the third linearization relationship is calculated using the formula:
where s is complex variable after Laplacian transformation, ω 1 The power frequency angular velocity is the power frequency angular velocity, and L is the equivalent impedance of the converter.
6. The method for modeling the input impedance of an LCC-HVDC transmission end system in a synchronous rotation coordinate system according to claim 3, wherein the input impedance of the converter bus to the dc side is calculated by using the following formula:
wherein:。
7. the method for modeling input impedance of an LCC-HVDC transmission terminal system in a synchronous rotation coordinate system according to claim 1, wherein the step of obtaining a linearization relationship between the current of the flowing inverter and the voltage of the converting bus in the synchronous rotation coordinate system according to a circuit model of the converting bus to the ac side in the LCC-HVDC transmission terminal system, obtaining an input admittance of the converting bus to the ac side according to the linearization relationship between the current of the flowing inverter and the voltage of the converting bus, and inverting the input admittance to obtain an input impedance of the converting bus voltage to the ac side comprises:
obtaining a conversion relation between the current of the current converter and the voltage of the current converting bus in a static coordinate system according to a circuit model from the current converting bus to an alternating current side in an LCC-HVDC (high-speed direct current) transmitting end system;
Converting the conversion relation into a synchronous rotation coordinate system;
converting the conversion relation under the synchronous rotation coordinate system into a vector form and linearizing to obtain a linearization relation between the current of the current converter and the voltage of the converter bus, obtaining the input admittance of the converter bus looking to the alternating current side according to the linearization relation, and inverting the input admittance to obtain the input impedance of the converter bus looking to the alternating current side;
wherein the linearization relationship is calculated using the following formula:
wherein C is the equivalent parallel capacitance of the alternating current filter and the reactive compensation device, L s Is the equivalent impedance of the alternating current power grid, E is the voltage of an equivalent power supply of the alternating current power grid of the transmitting end, Y 1 I.e. the input admittance of the converter bus to the ac side, for Y 1 Inversion is carried out, and the following steps are obtained:
i.e. the input impedance of the converter bus looking at the ac side.
8. An input impedance modeling system of an LCC-HVDC transmission end system in a synchronous rotation coordinate system, comprising:
the system comprises a power transmission end system building module, a power transmission end system control module and a power transmission end control module, wherein the power transmission end system building module is used for building an LCC-HVDC power transmission end system, the LCC-HVDC power transmission end system comprises a current converter which is a three-phase full-wave bridge rectifier circuit, and the current converter comprises 3 common-anode thyristors and 3 common-cathode thyristors;
The first linearization relation calculation module is used for acquiring a voltage relation, a current relation and an active power relation of an alternating current side and a direct current side of the converter under a synchronous rotation coordinate system, linearizing the voltage relation, the current relation and the active power relation at a steady-state point to respectively obtain a first linearization relation among the voltages, the currents and the active power of the alternating current side and the direct current side of the converter;
the expression and conversion relation calculation module is used for obtaining the expression relation of phase-locked loop errors and the conversion relation between the trigger angle reference value and the trigger angle actual value according to phase-locked loop control in the LCC-HVDC transmitting end system;
the second linearization relation calculation module is used for obtaining a second linearization relation among the alternating-current side outlet voltage, the current of the current converter and the voltage of the converting bus by considering the phase-locked loop error according to the first linearization relation;
the third linearization relation calculation module is used for obtaining a third linearization relation among the alternating current side outlet voltage, the flow direction converter current and the converter bus voltage under a synchronous rotation coordinate system according to an alternating current circuit model of the LCC-HVDC transmitting end system;
The direct current side input impedance calculation module is used for obtaining the linearization relation of the voltage of the converter bus and the current flowing to the converter under a synchronous rotation coordinate system according to the second linearization relation and the third linearization relation, and taking the ratio of the voltage of the converter bus and the current flowing to the converter as the input impedance of the converter bus to the direct current side;
and the alternating current side input impedance calculation module is used for obtaining the linearization relation between the current of the current converter and the voltage of the current converting bus under a synchronous rotation coordinate system according to a circuit model from the current converting bus to the alternating current side in the LCC-HVDC transmitting end system, obtaining the input admittance of the current converting bus looking at the alternating current side according to the linearization relation between the current of the current converter and the voltage of the current converting bus, and inverting the input admittance to obtain the input impedance of the voltage converting bus looking at the alternating current side.
9. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor implements the steps of the method according to any one of claims 1 to 7 when the computer program is executed by the processor.
10. A computer readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, implements the steps of the method of any of claims 1 to 7.
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