CN113346540A - Method, system, medium and equipment for stabilizing balance point of grid-connected voltage source type current converter - Google Patents

Method, system, medium and equipment for stabilizing balance point of grid-connected voltage source type current converter Download PDF

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CN113346540A
CN113346540A CN202110573010.4A CN202110573010A CN113346540A CN 113346540 A CN113346540 A CN 113346540A CN 202110573010 A CN202110573010 A CN 202110573010A CN 113346540 A CN113346540 A CN 113346540A
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phase
vsc
axis
balance point
voltage source
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CN113346540B (en
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李宇骏
杜正春
张雨萌
陆艺源
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Xian Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

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Abstract

The invention discloses a method, a system, a medium and equipment for stabilizing balance points of a grid-connected voltage source type converter, wherein a mathematical model that VSC (voltage source converter) containing a phase-locked loop is connected into an infinite system through a power transmission line is established; determining active power P output at the appointed VSC according to a system steady state equationrefAnd reactive power QrefThe balance point of the lower system; establishing a linearization model of the system at the balance point according to the mathematical model and the balance point; and obtaining an analytic condition for stabilizing the balance point of the grid-connected VSC according to the linear model, and realizing the stabilization of the balance point of the grid-connected voltage source converter.

Description

Method, system, medium and equipment for stabilizing balance point of grid-connected voltage source type current converter
Technical Field
The invention belongs to the technical field of electric power, and particularly relates to a method, a system, a medium and equipment for stabilizing a balance point of a grid-connected voltage source type converter.
Background
In recent years, the influence of a Phase Lock Loop (PLL) on the stability of a grid-connected Voltage Source Converter (VSC) has attracted much attention in the power industry. A variety of stability analysis methods, such as an eigenvalue analysis method, an impedance-based analysis (IMA), a passivity analysis method, and the like, have been used by the predecessors to study the stability of the grid-connected inverter. These studies indicate that shortening the electrical distance of the VSC from the system, reducing the load, increasing the reactive power output of the VSC, and reducing the bandwidth of the PLL control all improve the stability of the system.
In addition, based on modal analysis and IMA discovery, an excessively high PLL scaling factor negatively affects system stability, thereby lowering the power transmission limit of VSCs. Although the stability of the grid-connected inverter can be numerically analyzed by repeated characteristic value calculation or multiple Nyquist graphs and other methods, and the parameter range of the VSC controller for ensuring the stability of the system is obtained, the methods do not obtain the parameter of the VSC controller for ensuring the stability of the system, the electrical distance between the VSC and an infinite system and the analytical relationship among the operation modes of the system. In other words, the existing stability analysis method does not provide a sufficient condition for stabilizing the system equilibrium point.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method, a system, a medium and equipment for stabilizing a balance point of a grid-connected voltage source converter aiming at the defects in the prior art, qualitatively judging the influence of parameters of a VSC controller, the electrical distance between the VSC and an infinite system and the stability of the system operation mode, judging the stability of the system through simple quantitative calculation, and guiding the parameter design of the VSC controller and the formulation of the system operation mode.
The invention adopts the following technical scheme:
the method for stabilizing the balance point of the grid-connected voltage source type converter comprises the following steps:
s1, establishing a mathematical model of the VSC with the phase-locked loop connected to the infinite system through the power transmission line;
s2, determining that the active power P is output at the appointed VSC according to the steady state equation of the VSC with the phase-locked loop when the VSC is connected into an infinite system through the power transmission linerefAnd reactive power QrefThe VSC with the lower phase-locked loop is connected to a balance point of an infinite system through a power transmission line;
s3, establishing a linear model of the VSC with the phase-locked loop connected to the infinite system at the balance point through the transmission line according to the mathematical model established in the step S1 and the balance point determined in the step S2;
and S4, obtaining an analysis condition for stabilizing the balance point of the grid-connected VSC according to the linear model established in the step S3, and realizing the stabilization of the balance point of the grid-connected voltage source type converter.
Specifically, in step S1, the d-q coordinate system and the x-y coordinate system are controlled at angular velocities ω and ω, respectivelysRotating anticlockwise, wherein the d axis leads to theta degrees before the x axis; the infinite system is a three-phase symmetrical voltage source, and the mathematical model of the infinite system is specifically as follows:
Figure BDA0003083248710000021
Figure BDA0003083248710000022
Figure BDA0003083248710000023
Figure BDA0003083248710000024
wherein the content of the first and second substances,
Figure BDA0003083248710000031
is xdThe derivative with respect to the time t,
Figure BDA0003083248710000032
is xqThe derivative with respect to the time t,
Figure BDA0003083248710000033
is composed of
Figure BDA0003083248710000034
The derivative with respect to time is that of,
Figure BDA0003083248710000035
is composed of
Figure BDA0003083248710000036
The derivative with respect to time is that of,
Figure BDA0003083248710000037
integral of, xqIs composed of
Figure BDA0003083248710000038
The integral of (a) is calculated,
Figure BDA0003083248710000039
for the scaling factor of the phase-locked loop,
Figure BDA00030832487100000310
is the integral coefficient of the phase-locked loop,
Figure BDA00030832487100000311
is the q-axis voltage of the common connection point,
Figure BDA00030832487100000312
for common connection point d-axis voltage, UsLThe effective value of the line voltage of the three-phase symmetrical voltage source; rcAnd LcRespectively the resistance and inductance of the phase reactor; rlAnd LlRespectively the resistance and inductance of the transmission line;
Figure BDA00030832487100000313
and
Figure BDA00030832487100000314
proportional coefficients and integral coefficients of the d axis and the q axis are respectively controlled by the inner ring current;
Figure BDA00030832487100000315
and
Figure BDA00030832487100000316
respectively d-axis and q-axis currents through the phase reactors,
Figure BDA00030832487100000317
and
Figure BDA00030832487100000318
reference values for d-axis and q-axis currents flowing through the phase reactors, respectively.
Specifically, in step S2, the steady state equation of the system is specifically:
Figure BDA00030832487100000319
wherein R islIs the inductance, omega, of a phase reactorsIs the angular velocity, L, of the bus under the original fixed systemlIs the inductance of the transmission line and is,
Figure BDA00030832487100000320
for a steady state value of the d-axis current through the phase reactor,
Figure BDA00030832487100000321
is the square of the effective value of the line voltage of the three-phase symmetrical voltage source.
Specifically, in step S3, the linearization model of the system at the equilibrium point is specifically:
Figure BDA00030832487100000322
Figure BDA00030832487100000323
Figure BDA00030832487100000324
Figure BDA00030832487100000325
wherein the content of the first and second substances,
Figure BDA00030832487100000326
for the scaling factor of the phase-locked loop,
Figure BDA00030832487100000327
for a steady state value of the d-axis current through the phase reactor,
Figure BDA00030832487100000328
is composed of
Figure BDA00030832487100000329
The increment of (a) is increased by (b),
Figure BDA00030832487100000330
the steady-state value of d-axis voltage of infinite voltage source is delta theta, delta x is delta x, and LlIs the inductance of the transmission line, LcIs the inductance of the phase reactor, Δ xqIs xqIncrement of, ωsIs the angular velocity under the original fixed system,
Figure BDA00030832487100000331
is composed of
Figure BDA00030832487100000332
Increment of (A), RlIs the resistance of the transmission line, RcIs the resistance of the phase reactor and,
Figure BDA0003083248710000041
the scaling factor of the q-axis is controlled for the inner loop current,
Figure BDA0003083248710000042
is composed of
Figure BDA0003083248710000043
The increment of (c).
Specifically, in step S4, the characteristic equation of the system is determined according to the linearized model established in step S3, and the sufficient condition for obtaining the stable system equilibrium point is obtained by solving the characteristic equation of the system by using the dada theorem:
Figure BDA0003083248710000044
wherein the content of the first and second substances,
Figure BDA0003083248710000045
is the integral coefficient of the phase-locked loop,
Figure BDA0003083248710000046
is the proportionality coefficient of the phase-locked loop, LlIs the inductance of the transmission line and is,
Figure BDA0003083248710000047
for a steady state value of the d-axis current through the phase reactor,
Figure BDA0003083248710000048
the voltage steady state value of the d-axis of the infinite voltage source is obtained.
Further, the characteristic equation of the system is as follows:
Bd(s)Bq(s)D(s)＝0
Figure BDA0003083248710000049
Figure BDA00030832487100000410
Figure BDA00030832487100000411
wherein L iscIs the inductance of the phase reactor, s is the laplace operator,
Figure BDA00030832487100000412
controlling the proportionality coefficient of the d-axis for the inner loop current, RcIs the resistance of the phase reactor and,
Figure BDA00030832487100000413
for inner loop current controlIntegral coefficient of d-axis, s1，s2，s3，s4，s5，s6For the six roots of the characteristic equation of the system,
Figure BDA00030832487100000414
the scaling factor of the q-axis is controlled for the inner loop current,
Figure BDA00030832487100000415
the integral coefficient of the q-axis is controlled for the inner loop current,
Figure BDA00030832487100000416
is the proportionality coefficient of the phase-locked loop, LlIs the inductance of the transmission line and is,
Figure BDA00030832487100000417
for a steady state value of the d-axis current through the phase reactor,
Figure BDA00030832487100000418
the voltage steady state value of the d-axis of the infinite voltage source is obtained.
Another technical solution of the present invention is a system for stabilizing a balance point of a grid-connected voltage source converter, including:
the digital model module is used for establishing a mathematical model of the VSC containing the phase-locked loop, which is accessed to an infinite system through the power transmission line;
the balance module determines that the active power P is output at the appointed VSC according to a system steady state equationrefAnd reactive power QrefThe VSC with the lower phase-locked loop is connected to a balance point of an infinite system through a power transmission line;
the linear module is used for establishing a linear model of the VSC containing the phase-locked loop at a balance point by connecting the VSC into an infinite system through the power transmission line according to the mathematical model established by the digital model module and the balance point determined by the balance module;
and the stabilization module is used for obtaining an analytic condition for stabilization of the balance point of the grid-connected VSC according to the linearization model established by the linearity module, so that stabilization of the balance point of the grid-connected voltage source type converter is realized.
Another aspect of the present invention is a computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by computing apparatus, cause the computing apparatus to perform any of the grid connected voltage source converter balance point stabilization methods.
Another technical solution of the present invention is a computing device, including:
one or more processors, memory, and one or more programs stored in the memory and configured for execution by the one or more processors, the one or more programs including the instructions for performing any of the grid connected voltage source converter balancing point stabilization methods.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention relates to a method for stabilizing balance points of a grid-connected voltage source converter, which comprises the steps of firstly establishing a mathematical model that VSC (voltage source converter) containing PLL (phase locked loop) is connected into an infinite system through a power transmission line; then obtaining a steady state equation of the system and solving a balance point of the system according to a control target; further obtaining a linearization model of the system at a balance point; and finally, solving a characteristic equation of the system, and deriving the essential condition for stabilizing the balance point of the grid-connected VSC. Compared with the prior art, the invention has the following advantages: the obtained essential condition for stabilizing the balance point of the grid-connected Voltage Source Converter (VSC) is analyzed, so that the method is simple and visual; the influence of VSC controller parameters, the electrical distance between the VSC and an infinite system and the system operation mode on the stability can be qualitatively analyzed, and a system instability mechanism is disclosed; the stability of the system can be judged by simple quantitative calculation.
Further, a mathematical model that VSC with a phase-locked loop is connected to an infinite system through a power transmission line is established. The classical general model is convenient for obtaining the analysis essential condition of the stability of the balance point of the grid-connected Voltage Source Converter (VSC), and can be applied to systems using the VSC with a phase-locked loop as an important component in wind energy and photovoltaic power generation, flexible alternating current transmission systems, high-voltage direct current and the like.
Furthermore, the VSC containing the phase-locked loop is solved and is accessed without the phase-locked loop through the power transmission lineThe steady state equation of the finite system can be used for solving the active power P output at the specified VSC according to the steady state equationrefAnd reactive power QrefEquilibrium point of the lower system (steady state operating point).
Furthermore, a linear model of the VSC with the phase-locked loop, which is connected to an infinite system at a balance point through the power transmission line, is solved so as to solve a characteristic equation of the system.
Furthermore, a characteristic equation of the VSC with the phase-locked loop connected into an infinite system through the power transmission line is given, and as the real parts of all roots of the system balance point stability equivalent to the system characteristic equation are less than zero, sufficient conditions for the system balance point stability can be obtained by utilizing the Weddar theorem.
Further, the analysis essential condition that the balance point of the grid-connected Voltage Source Converter (VSC) is stable is obtained, and the analysis essential condition is simple and visual. The analytic relation among the VSC controller parameters, the electrical distance between the VSC and the infinite system and the system operation mode is reflected, the key factors influencing the system stability can be qualitatively analyzed, the system instability mechanism is revealed, the system stability can be quantitatively analyzed, and the parameter design and the system operation mode formulation of the VSC controller are guided.
In conclusion, the essential condition for stabilizing the balance point of the grid-connected VSC provided by the invention is rigorous in theory, concise and intuitive, and can be used for qualitative and quantitative analysis of system stability and guidance of parameter design of a VSC controller and formulation of a system operation mode.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a flow chart of the present invention;
fig. 2 is a circuit diagram of a VSC connected to an infinite system via a transmission line;
FIG. 3 is a schematic view of d-q rotational coordinates with angular velocity ω;
FIG. 4 is a block diagram of a transfer function of a phase locked loop;
FIG. 5 is a graph of a root trajectory analysis of dominant eigenvalues.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
The invention provides a method for stabilizing balance points of a grid-connected Voltage Source Converter, which comprises the steps of establishing a mathematical model that the grid-connected Voltage Source Converter (VSC) containing PLL is connected into an infinite system through a transmission line; then obtaining a steady state equation of the system and solving a balance point of the system according to a control target; further obtaining a linearization model of the system at a balance point; and finally, solving a characteristic equation of the system, deducing a sufficient condition for stabilizing the balance point of the grid-connected Voltage Source Converter (VSC), and establishing an analytic relation among the parameters of a Voltage Source Converter (VSC) controller, the electrical distance between the VSC and an infinite system and the system operation mode according to the sufficient condition, so that the method can be used for qualitatively analyzing key factors influencing the stability of the balance point, disclosing a system instability mechanism and quantitatively analyzing the stability of the system. The research finds that: the small electrical distance and light load between a Voltage Source Converter (VSC) and an infinite system are favorable for the stability of the system; the PLL proportionality coefficient ensuring the stability of the balance point has an upper bound and a lower bound, and the integral coefficient has an upper bound. The balance point stability essential condition of the grid-connected Voltage Source Converter (VSC) disclosed by the invention is rigorous in theory, concise and intuitive, is an effective tool for analyzing the stability of the grid-connected Voltage Source Converter (VSC), and can be used for parameter design of a Voltage Source Converter (VSC) controller and system operation mode formulation.
Referring to fig. 1, the method for stabilizing the balance point of the grid-connected voltage source converter according to the present invention includes the following steps:
s1, establishing a mathematical model that a Voltage Source Converter (VSC) containing a phase-locked loop (PLL) is connected to an infinite system through a transmission line;
the inverter voltage is assumed to be three-phase symmetric and there is no harmonic injection. Furthermore, VSCs are powered by dc power supplies, ignoring dc side dynamics. Referring to fig. 2, a network equation of the VSC connected to the infinite system via the transmission line in the d-q coordinate system is:
Figure BDA0003083248710000091
Figure BDA0003083248710000092
wherein the content of the first and second substances,
Figure BDA0003083248710000093
wherein the content of the first and second substances,
Figure BDA0003083248710000094
is composed of
Figure BDA0003083248710000095
The derivative with respect to time is that of,
Figure BDA0003083248710000096
is composed of
Figure BDA0003083248710000097
The derivative with respect to time is that of,
Figure BDA0003083248710000098
is the q-axis voltage of the common connection point,
Figure BDA0003083248710000099
the voltage of the axis d of the common connection point is a line voltage effective value of a three-phase symmetrical voltage source; rcAnd LcRespectively the resistance and inductance of the phase reactor; rlAnd LlRespectively the resistance and inductance of the transmission line;
Figure BDA00030832487100000910
and
Figure BDA00030832487100000911
d-axis and q-axis currents flowing through the phase reactors, respectively; and omega is the angular speed of the d-q axis.
Based on the operating principle of VSC, the reference value for the current control of the phase reactor can be expressed as
Figure BDA00030832487100000912
And
Figure BDA00030832487100000913
the inner loop current control equation is as follows:
Figure BDA00030832487100000914
Figure BDA00030832487100000915
substituting (3) into (1) to obtain:
Figure BDA00030832487100000916
referring to fig. 3, another d-q rotation coordinate having an angular velocity ω is introduced so that the current flowing through the phase reactor can be effectively controlled.
In the present invention, the d-axis leads the x-axis by an angle θ.
Figure BDA00030832487100000917
Wherein the content of the first and second substances,
Figure BDA0003083248710000101
referring to fig. 4, to ensure the normal operation of the VSC, the PLL obtains the accurate phase angle of the common node voltage. The assumption is that the common junction voltage direction is aligned with the d-axis.
The dynamic equation for a PLL is as follows:
Figure BDA0003083248710000102
substituting (5) and (6) into (2) to obtain:
Figure BDA0003083248710000103
the active power and the reactive power output by a voltage source type converter (VSC) are as follows:
Figure BDA0003083248710000104
wherein the d-q coordinate system and the x-y coordinate system are respectively based on angular velocities omega and omegasRotating anticlockwise, wherein the d axis leads to theta degrees before the x axis; the infinite system is a three-phase symmetrical voltage source, and the effective value of the line voltage is UsL；RcAnd LcRespectively the resistance and inductance of the phase reactor; rlAnd LlRespectively the resistance and inductance of the transmission line;
Figure BDA0003083248710000105
and
Figure BDA0003083248710000106
proportional coefficients and integral coefficients of the d axis and the q axis are respectively controlled by the inner ring current;
Figure BDA0003083248710000107
and
Figure BDA0003083248710000108
respectively d-axis and q-axis currents through the phase reactors,
Figure BDA0003083248710000109
and
Figure BDA00030832487100001010
respectively, reference values thereof.
The differential equations (4) to (6) and the algebraic equation (7) are mathematical models of the system.
The classical general model is convenient for obtaining the analysis essential condition of the stability of the balance point of the grid-connected Voltage Source Converter (VSC), and can be applied to systems using the VSC with a phase-locked loop as an important component in wind energy and photovoltaic power generation, flexible alternating current transmission systems, high-voltage direct current and the like.
S2, determining a voltage source type converter (VSC) at a specified voltage according to the steady state equation of the VSC with the phase-locked loop connected to an infinite system through the power transmission line) Output active power PrefAnd reactive power QrefThe balance point of the lower system (steady state operating point);
Figure BDA0003083248710000111
Figure BDA0003083248710000112
Figure BDA0003083248710000113
combining (10) and (11) to obtain:
Figure BDA0003083248710000114
the active power P output at the specified VSC is obtained by the formularefAnd reactive power QrefEquilibrium point of the lower system (steady state operating point). A linear model of the VSC with the phase-locked loop, which is connected to an infinite system through the power transmission line, at the balance point can be deduced according to the balance point.
S3, establishing a linear model of the VSC with the phase-locked loop connected to the infinite system at the balance point through the transmission line according to the mathematical model established in the step S1 and the balance point determined in the step S2;
linearizing (4) - (7) at the equilibrium point to obtain:
Figure BDA0003083248710000115
Figure BDA0003083248710000116
Figure BDA0003083248710000117
Figure BDA0003083248710000118
wherein the content of the first and second substances,
Figure BDA0003083248710000119
for the scaling factor of the phase-locked loop,
Figure BDA00030832487100001110
for a steady state value of the d-axis current through the phase reactor,
Figure BDA00030832487100001111
is composed of
Figure BDA00030832487100001112
The increment of (a) is increased by (b),
Figure BDA00030832487100001113
the steady-state value of d-axis voltage of infinite voltage source is delta theta, delta x is delta x, and LlIs the inductance of the transmission line, LcIs the inductance of the phase reactor, Δ xqIs xqIncrement of, ωsIs the angular velocity under the original fixed system,
Figure BDA0003083248710000121
is composed of
Figure BDA0003083248710000122
Increment of (A), RlIs the resistance of the transmission line, RcIs the resistance of the phase reactor and,
Figure BDA0003083248710000123
the scaling factor of the q-axis is controlled for the inner loop current,
Figure BDA0003083248710000124
is composed of
Figure BDA0003083248710000125
The increment of (c).
The method is characterized in that a linear model of an infinite system at a balance point is accessed through a power transmission line according to VSC (voltage source converter) containing a phase-locked loop, so that a characteristic equation of the system can be solved, and because the system balance point is stable and is equivalent to the real parts of all roots of the system characteristic equation and are less than zero, sufficient conditions for the system balance point to be stable can be obtained by utilizing the Wedd's theorem.
And S4, obtaining an analysis condition for stabilizing the balance point of the grid-connected VSC according to the linearization model established in the step S3, realizing the stabilization of the balance point of the grid-connected voltage source type converter, and setting parameters of the grid-connected voltage source type converter in a stable domain range according to the analysis condition to ensure that the VSC containing the phase-locked loop is connected to the balance point of an infinite system through the power transmission line to be stabilized.
Combining (13) and (14) to obtain:
Figure BDA0003083248710000126
Figure BDA0003083248710000127
combining (14) to (17) to obtain:
D(s)Δθ＝0 (19)
based on (17) to (19), the characteristic equation of the system is as follows:
Figure BDA0003083248710000128
Bd(s)Bq(s)D(s)＝0 (21)
because the system balance point stability is equivalent to the real parts of all roots of the system characteristic equation and are less than zero, the essential conditions for obtaining the system balance point stability by utilizing the Vida theorem are as follows:
Figure BDA0003083248710000129
and is
Figure BDA00030832487100001210
(22) Is additionally written as
Figure BDA0003083248710000131
The analytic relation among VSC controller parameter, VSC and infinity system electrical distance, the system operation mode three is reflected to the above formula, both can qualitative analysis influence the key factor of system stability, disclose system instability mechanism, but also quantitative analysis system stability guides VSC controller parameter design and system operation mode to formulate.
As seen from (23), once
Figure BDA0003083248710000132
Or
Figure BDA0003083248710000133
Beyond the stability region, the equilibrium point is unstable, i.e.
Figure BDA0003083248710000134
The analysis conditions are concise and intuitive, and the stability of the VSC with the phase-locked loop when the VSC is connected to an infinite system balance point through the power transmission line can be ensured by setting the parameters of the grid-connected voltage source type converter within the stable domain according to the analysis conditions.
In another embodiment of the present invention, a system for stabilizing a balance point of a grid-connected voltage source converter is provided, which can be used to implement the method for stabilizing a balance point of a grid-connected voltage source converter.
The digital model module is used for establishing a mathematical model of the VSC with the phase-locked loop, which is accessed to an infinite system through the power transmission line;
the balance module determines that the output of the designated VSC is equal to the output of the designated VSC according to the steady state equation of the infinite system accessed by the VSC containing the phase-locked loop through the power transmission lineWork power PrefAnd reactive power QrefThe VSC with the lower phase-locked loop is connected to a balance point of an infinite system through a power transmission line;
the linear module is used for establishing a linear model of the VSC containing the phase-locked loop at a balance point by connecting the VSC into an infinite system through the power transmission line according to the mathematical model established by the digital model module and the balance point determined by the balance module;
and the stabilization module is used for obtaining an analytic condition for stabilization of the balance point of the grid-connected VSC according to the linearization model established by the linearity module, so that stabilization of the balance point of the grid-connected voltage source type converter is realized.
In yet another embodiment of the present invention, a terminal device is provided that includes a processor and a memory for storing a computer program comprising program instructions, the processor being configured to execute the program instructions stored by the computer storage medium. The Processor may be a Central Processing Unit (CPU), or may be other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable gate array (FPGA) or other Programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, etc., which is a computing core and a control core of the terminal, and is adapted to implement one or more instructions, and is specifically adapted to load and execute one or more instructions to implement a corresponding method flow or a corresponding function; the processor provided by the embodiment of the invention can be used for the operation of the method for stabilizing the balance point of the grid-connected voltage source type converter, and comprises the following steps:
establishing a mathematical model of a VSC (voltage source converter) containing a phase-locked loop, which is accessed to an infinite system through a power transmission line; determining that the active power P is output at the appointed VSC according to the steady state equation of the VSC containing the phase-locked loop and the infinite system connected to the transmission linerefAnd reactive power QrefThe VSC with the lower phase-locked loop is connected to a balance point of an infinite system through a power transmission line; establishing a linear model of the VSC with the phase-locked loop at a balance point by connecting the VSC with an infinite system through a transmission line according to the mathematical model and the balance point; deriving grid-tie from linearized modelsAnd the stable analysis condition of the VSC balance point realizes the stability of the balance point of the grid-connected voltage source type converter.
In still another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a Memory device in a terminal device and is used for storing programs and data. It is understood that the computer readable storage medium herein may include a built-in storage medium in the terminal device, and may also include an extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also, one or more instructions, which may be one or more computer programs (including program code), are stored in the memory space and are adapted to be loaded and executed by the processor. It should be noted that the computer-readable storage medium may be a high-speed RAM memory, or may be a non-volatile memory (non-volatile memory), such as at least one disk memory.
The processor can load and execute one or more instructions stored in the computer readable storage medium to realize the corresponding steps of the method for stabilizing the balance point of the grid-connected voltage source type converter in the embodiment; one or more instructions in the computer-readable storage medium are loaded by the processor and perform the steps of:
establishing a mathematical model of a VSC (voltage source converter) containing a phase-locked loop, which is accessed to an infinite system through a power transmission line; determining that the active power P is output at the appointed VSC according to the steady state equation of the VSC containing the phase-locked loop and the infinite system connected to the transmission linerefAnd reactive power QrefThe VSC with the lower phase-locked loop is connected to a balance point of an infinite system through a power transmission line; establishing a linear model of the VSC with the phase-locked loop at a balance point by connecting the VSC with an infinite system through a transmission line according to the mathematical model and the balance point; and obtaining an analytic condition for stabilizing the balance point of the grid-connected VSC according to the linear model, and realizing the stabilization of the balance point of the grid-connected voltage source converter.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The proposed stable condition was verified by the case where the VSC was connected to a stand-alone infinite system via a transmission line. The basic capacity of the simulation system is 200MVA, and the rated system voltage is 220 kV. The line adopts a classical RL model, and the line resistance and the line inductance are respectively 0.05pu and 0.5 pu. Further, the resistance and inductance of the phase reactor are 0.005pu and 0.15pu, respectively. The proportional and integral gains of the current inner loop control are designed to 57.77 and 605.
Referring to FIG. 5, FIG. 5 illustrates the difference
Figure BDA0003083248710000161
Then, the system dominates the change track of the real part of the eigenvalue. As can be seen from fig. 5(a), the larger the active power output by the VSC, the weaker the system stability,
Figure BDA0003083248710000162
the narrower the stability region. And increasing the reactive power can improve the stability of the system. As can be seen from fig. 5(b), increasing the VSC electrical distance from the infinite system will impair system stability.
Figure BDA0003083248710000163
Too large or too small can lead to system instability, larger
Figure BDA0003083248710000164
May impair system stabilityI.e. by
Figure BDA0003083248710000165
Has an upper and a lower boundary
Figure BDA0003083248710000166
Has an upper bound and once
Figure BDA0003083248710000167
Exceeds the critical value given by (24), whether or not
Figure BDA0003083248710000168
How to take values is not stable.
In summary, according to the method for stabilizing the balance point of the grid-connected voltage source type converter, the analytic relationship among the parameters of the VSC controller, the electrical distance between the VSC and an infinite system and the system operation mode for ensuring the stability of the balance point is established; the small electrical distance and light load of the VSC and an infinite system are beneficial to the stability of the system and are consistent with the research results of the predecessors; the PLL proportionality coefficient ensuring the stability of the balance point has an upper bound and a lower bound, and the integral coefficient has an upper bound.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims (9)

1. The method for stabilizing the balance point of the grid-connected voltage source type converter is characterized by comprising the following steps of:
s1, establishing a mathematical model of the VSC with the phase-locked loop connected to the infinite system through the power transmission line;
s2, determining that the active power P is output at the appointed VSC according to the steady state equation of the VSC with the phase-locked loop when the VSC is connected into an infinite system through the power transmission linerefAnd reactive power QrefThe VSC with the lower phase-locked loop is connected to a balance point of an infinite system through a power transmission line;
s3, establishing a linear model of the VSC with the phase-locked loop connected to the infinite system at the balance point through the transmission line according to the mathematical model established in the step S1 and the balance point determined in the step S2;
and S4, obtaining an analysis condition for stabilizing the balance point of the grid-connected VSC according to the linear model established in the step S3, and realizing the stabilization of the balance point of the grid-connected voltage source type converter.
2. The method of claim 1, wherein in step S1, the d-q coordinate system and the x-y coordinate system are respectively at angular velocities ω and ωsRotating anticlockwise, wherein the d axis leads to theta degrees before the x axis; the infinite system is a three-phase symmetrical voltage source, and the mathematical model of the infinite system is specifically as follows:
Figure FDA0003083248700000011
Figure FDA0003083248700000012
Figure FDA0003083248700000013
Figure FDA0003083248700000014
wherein the content of the first and second substances,
Figure FDA0003083248700000015
is xdThe derivative with respect to the time t,
Figure FDA0003083248700000016
is xqThe derivative with respect to the time t,
Figure FDA0003083248700000017
is composed of
Figure FDA0003083248700000018
The derivative with respect to time is that of,
Figure FDA0003083248700000019
is composed of
Figure FDA00030832487000000110
The derivative with respect to time is that of,
Figure FDA00030832487000000111
integral of, xqIs composed of
Figure FDA00030832487000000112
The integral of (a) is calculated,
Figure FDA00030832487000000113
for the scaling factor of the phase-locked loop,
Figure FDA0003083248700000021
is the integral coefficient of the phase-locked loop,
Figure FDA0003083248700000022
is the q-axis voltage of the common connection point,
Figure FDA0003083248700000023
for common connection point d-axis voltage, UsLThe effective value of the line voltage of the three-phase symmetrical voltage source; rcAnd LcRespectively the resistance and inductance of the phase reactor; rlAnd LlRespectively the resistance and inductance of the transmission line;
Figure FDA0003083248700000024
and
Figure FDA0003083248700000025
proportional coefficients and integral coefficients of the d axis and the q axis are respectively controlled by the inner ring current;
Figure FDA0003083248700000026
and
Figure FDA0003083248700000027
respectively d-axis and q-axis currents through the phase reactors,
Figure FDA0003083248700000028
and
Figure FDA0003083248700000029
reference values for d-axis and q-axis currents flowing through the phase reactors, respectively.
3. The method according to claim 1, wherein in step S2, the steady state equation of the system is specifically:
Figure FDA00030832487000000210
wherein R islIs the inductance, omega, of a phase reactorsIs the angular velocity, L, of the bus under the original fixed systemlIs the inductance of the transmission line and is,
Figure FDA00030832487000000211
for a steady state value of the d-axis current through the phase reactor,
Figure FDA00030832487000000212
is the square of the effective value of the line voltage of the three-phase symmetrical voltage source.
4. The method according to claim 1, wherein in step S3, the system linearization model at the balance point is specifically:
Figure FDA00030832487000000213
Figure FDA00030832487000000214
Figure FDA00030832487000000215
Figure FDA00030832487000000216
wherein the content of the first and second substances,
Figure FDA00030832487000000217
for the scaling factor of the phase-locked loop,
Figure FDA00030832487000000218
for a steady state value of the d-axis current through the phase reactor,
Figure FDA00030832487000000219
is composed of
Figure FDA00030832487000000220
The increment of (a) is increased by (b),
Figure FDA00030832487000000221
the steady-state value of d-axis voltage of infinite voltage source is delta theta, delta x is delta x, and LlIs the inductance of the transmission line, LcIs the inductance of the phase reactor, Δ xqIs xqIncrement of, ωsIs the angular velocity under the original fixed system,
Figure FDA00030832487000000222
is composed of
Figure FDA00030832487000000223
Increment of (A), RlIs the resistance of the transmission line, RcIs the resistance of the phase reactor and,
Figure FDA0003083248700000031
the scaling factor of the q-axis is controlled for the inner loop current,
Figure FDA0003083248700000032
is composed of
Figure FDA0003083248700000033
The increment of (c).
5. The method according to claim 1, wherein in step S4, the eigen equation of the system is determined according to the linearized model established in step S3, and the solution of the eigen equation of the system using the dada theorem yields the essential condition that the system equilibrium point is stable:
Figure FDA0003083248700000034
wherein the content of the first and second substances,
Figure FDA0003083248700000035
is the integral coefficient of the phase-locked loop,
Figure FDA0003083248700000036
is the proportionality coefficient of the phase-locked loop, LlIs the inductance of the transmission line and is,
Figure FDA0003083248700000037
for a steady state value of the d-axis current through the phase reactor,
Figure FDA0003083248700000038
the voltage steady state value of the d-axis of the infinite voltage source is obtained.
6. The method of claim 5, wherein the system's characteristic equation is as follows:
Bd(s)Bq(s)D(s)＝0
Figure FDA0003083248700000039
Figure FDA00030832487000000310
Figure FDA00030832487000000311
wherein L iscIs the inductance of the phase reactor, s is the laplace operator,
Figure FDA00030832487000000312
controlling the proportionality coefficient of the d-axis for the inner loop current, RcIs the resistance of the phase reactor and,
Figure FDA00030832487000000313
controlling the integral coefficient of the d-axis, s, for the inner loop current1，s2，s3，s4，s5，s6For the six roots of the characteristic equation of the system,
Figure FDA00030832487000000314
the scaling factor of the q-axis is controlled for the inner loop current,
Figure FDA00030832487000000315
the integral coefficient of the q-axis is controlled for the inner loop current,
Figure FDA00030832487000000316
is the proportionality coefficient of the phase-locked loop, LlIs the inductance of the transmission line and is,
Figure FDA00030832487000000317
for a steady state value of the d-axis current through the phase reactor,
Figure FDA00030832487000000318
the voltage steady state value of the d-axis of the infinite voltage source is obtained.
7. A grid-connected voltage source type converter balance point stabilizing system is characterized by comprising:
the digital model module is used for establishing a mathematical model of the VSC containing the phase-locked loop, which is accessed to an infinite system through the power transmission line;
the balance module determines that the active power P is output at the appointed VSC according to a system steady state equationrefAnd reactive power QrefThe VSC with the lower phase-locked loop is connected to a balance point of an infinite system through a power transmission line;
the linear module is used for establishing a linear model of the VSC containing the phase-locked loop at a balance point by connecting the VSC into an infinite system through the power transmission line according to the mathematical model established by the digital model module and the balance point determined by the balance module;
and the stabilization module is used for obtaining an analytic condition for stabilization of the balance point of the grid-connected VSC according to the linearization model established by the linearity module, so that stabilization of the balance point of the grid-connected voltage source type converter is realized.
8. A computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by a computing device, cause the computing device to perform any of the methods of claims 1-7.
9. A computing device, comprising:
one or more processors, memory, and one or more programs stored in the memory and configured for execution by the one or more processors, the one or more programs including instructions for performing any of the methods of claims 1-7.
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