CN113794240B - Method and system for judging synchronization stability of power electronic equipment - Google Patents

Method and system for judging synchronization stability of power electronic equipment Download PDF

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CN113794240B
CN113794240B CN202111344471.0A CN202111344471A CN113794240B CN 113794240 B CN113794240 B CN 113794240B CN 202111344471 A CN202111344471 A CN 202111344471A CN 113794240 B CN113794240 B CN 113794240B
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CN113794240A (en
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孙华东
王姝彦
徐式蕴
毕经天
王一鸣
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China Electric Power Research Institute Co Ltd CEPRI
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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
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Abstract

The invention discloses a method and a system for judging the synchronization stability of power electronic equipment, wherein the method comprises the following steps: acquiring operation data of the power electronic equipment in the operation process in real time; determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data; judging whether two balance points exist or not according to the first voltage vector length and the first reference voltage vector length, and obtaining a judgment result; when the judgment result indicates that two balance points exist, determining an unstable balance point according to a stable balance point criterion; determining the length of a second reference voltage vector corresponding to the unstable equilibrium point; and determining a second voltage vector length of the grid-connected point after the fault occurs based on the operation data, and determining that the system is subjected to synchronous instability when the second voltage vector length is smaller than a second reference voltage vector length. The method has good observability, and provides a new means and a new mode for judging the synchronization stability of the power electronic equipment under large disturbance.

Description

Method and system for judging synchronization stability of power electronic equipment
Technical Field
The present invention relates to the field of power system synchronization stability determination technologies, and in particular, to a method and a system for determining synchronization stability of power electronic devices.
Background
The grid-connected mechanism of the power electronic equipment is different from that of the traditional synchronous machine, and the switching control and the nonlinearity of the system under large disturbance increase the difficulty in judging the synchronous stability of the power electronic equipment. Therefore, under the background of high permeability of new energy, a method for judging the targeted synchronization stability is urgently needed to be provided according to a control strategy of the power electronic equipment.
In the study of the problem of large-disturbance synchronous stability of power electronic equipment in which a Phase Locked Loop (PLL) is synchronized with a power grid, the existing stability analysis and discrimination methods mainly focus on an equal-area method, a direct method for constructing a lyapunov function, and a phase plane analysis method. The equal-area method can intuitively reveal the transient synchronous stability mechanism of the converter, and has important guiding significance for improving the design of the synchronous stability of the converter; the Lyapunov function obtained by the construction method can enlarge the relatively conservative attraction domain of the equal-area method; the phase plane analysis method can draw a phase diagram of a second-order dynamic system, is a numerical method essentially, and can visually display an attraction domain and an unstable limit ring of a stable balance point. However, the research objects of the current analysis method are the included angle between the d axis of the phase-locked loop controller and the voltage of the power grid, and the angle is a function related to the state variable and time of the phase-locked loop controller and is not easy to obtain.
Generally, for a method for judging the synchronization stability of power electronic equipment, a method for judging the observation quantity which is easy to obtain is still lacked at present.
Disclosure of Invention
The invention provides a method and a system for judging the synchronization stability of power electronic equipment, which are used for solving the problem of quickly and accurately judging the synchronization stability of the power electronic equipment.
In order to solve the above problem, according to an aspect of the present invention, there is provided a synchronization stability determination method for a power electronic device, the method including:
acquiring operation data of the power electronic equipment in the operation process in real time;
determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data;
judging whether two balance points exist according to the first voltage vector length and the first reference voltage vector length and a balance point criterion, and obtaining a judgment result;
when the judgment result indicates that two balance points exist, determining an unstable balance point according to a stable balance point criterion;
determining a second reference voltage vector length corresponding to the unstable equilibrium point;
and determining the length of a second voltage vector of the grid-connected point after the fault occurs based on the real-time operation data of the power electronic equipment, and determining that the system is subjected to synchronous instability when the length of the second voltage vector is smaller than the length of a second reference voltage vector.
Preferably, the determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data includes:
Figure 254879DEST_PATH_IMAGE001
，
Figure 703178DEST_PATH_IMAGE002
，
Figure 499227DEST_PATH_IMAGE003
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; i is VSC output current; zgConnecting points for VSC to AC system impedance;
Figure 425595DEST_PATH_IMAGE004
the voltage of the power grid at the moment of fault occurrence; delta0Is the value of delta angle at steady state before failure; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault;
Figure 771125DEST_PATH_IMAGE005
the output current of the VSC is in steady state before the fault;
Figure 124746DEST_PATH_IMAGE006
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 673670DEST_PATH_IMAGE007
the impedance angle from the VSC grid-connected point to the AC system in the steady state before the fault;
Figure 403729DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 603766DEST_PATH_IMAGE009
is the pre-fault grid voltage; δ = θPLL controller-θg，θPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate systemgIs UgThe included angle between the two-phase static coordinate system and a beta axis negative half shaft; u shapePCCOriented on the positive d-axis half and the q-axis leads the d-axis by 90 deg..
Preferably, the balance point criterion comprises:
Figure 393868DEST_PATH_IMAGE010
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; determining that there are two balance points when the balance point criterion is satisfied; otherwise, it is determined that one or no balance point exists.
Preferably, wherein said determining an unstable equilibrium point based on a stable equilibrium point criterion comprises:
for any balance point, if any balance point meets the criterion of stable balance point
Figure 430088DEST_PATH_IMAGE011
Determining any balance point as a stable balance point; otherwise, determining any balance point as an unstable balance point;
wherein, deltaeAn included angle between a d axis of the PLL controller corresponding to any balance point and a voltage vector of a grid-connected point; by solving for
Figure 698258DEST_PATH_IMAGE012
To obtain deltaeI is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
Preferably, the determining the length of the second reference voltage vector corresponding to the unstable equilibrium point includes:
Figure 752802DEST_PATH_IMAGE013
，
wherein, UUEPThe vector length of the second reference voltage is I, and the I is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
According to another aspect of the present invention, there is provided a synchronization stability determination system for a power electronic device, the system including:
the operation data acquisition unit is used for acquiring operation data of the power electronic equipment in the operation process in real time;
the first calculation unit is used for determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data;
the balance point judging unit is used for judging whether two balance points exist according to the first voltage vector length and the first reference voltage vector length and a balance point criterion to obtain a judgment result;
an unstable equilibrium point determining unit, configured to determine an unstable equilibrium point according to a stable equilibrium point criterion when the determination result indicates that two equilibrium points exist;
the second calculation unit is used for determining the length of a second reference voltage vector corresponding to the unstable equilibrium point;
and the synchronous stability judging unit is used for determining the second voltage vector length of the grid-connected point after the fault occurs based on the real-time operation data of the power electronic equipment, and determining that the system is subjected to synchronous instability when the second voltage vector length is smaller than the second reference voltage vector length.
Preferably, the first calculation unit, based on the operation data, determines a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs, and includes:
Figure 713805DEST_PATH_IMAGE001
，
Figure 689851DEST_PATH_IMAGE002
，
Figure 246865DEST_PATH_IMAGE003
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; i is VSC output current; zgConnecting points for VSC to AC system impedance;
Figure 421495DEST_PATH_IMAGE004
the voltage of the power grid at the moment of fault occurrence; delta0For fail-safe stateThe value of the delta angle; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault;
Figure 553399DEST_PATH_IMAGE005
the output current of the VSC is in steady state before the fault;
Figure 813479DEST_PATH_IMAGE006
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 705343DEST_PATH_IMAGE007
the impedance angle from the VSC grid-connected point to the AC system in the steady state before the fault;
Figure 734478DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 240546DEST_PATH_IMAGE009
is the pre-fault grid voltage; δ = θPLL controller-θg，θPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate systemgIs UgThe included angle between the two-phase static coordinate system and a beta axis negative half shaft; u shapePCCOriented on the positive d-axis half and the q-axis leads the d-axis by 90 deg..
Preferably, the balance point criterion comprises:
Figure 722343DEST_PATH_IMAGE010
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; determining that there are two balance points when the balance point criterion is satisfied; otherwise, it is determined that one or no balance point exists.
Preferably, the unstable equilibrium point determining unit determines the unstable equilibrium point according to a stable equilibrium point criterion, including:
for any balance point, if any balance point meets the criterion of stable balance point
Figure 886739DEST_PATH_IMAGE011
Determining any balance point as a stable balance point; otherwise, determining any balance point as an unstable balance point;
wherein, deltaeAn included angle between a d axis of the PLL controller corresponding to any balance point and a voltage vector of a grid-connected point; by solving for
Figure 35961DEST_PATH_IMAGE012
To obtain deltaeI is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
Preferably, the determining, by the second calculating unit, a second reference voltage vector length corresponding to the unstable equilibrium point includes:
Figure 509668DEST_PATH_IMAGE013
，
wherein, UUEPThe vector length of the second reference voltage is I, and the I is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgTo failThe impedance angle from the VSC grid-connected point to the alternating current system; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
The invention provides a method and a system for judging the synchronization stability of power electronic equipment, which are used for judging a balance point according to a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs; determining the unstable balance point and the length of a second reference voltage vector corresponding to the unstable balance point; determining a second voltage vector length of a grid-connected point after a fault occurs based on the real-time operation data of the power electronic equipment, and determining that the system is subjected to synchronous instability when the second voltage vector length is smaller than a second reference voltage vector length; the method of the invention judges the synchronous stability of the power electronic equipment based on the space vector, and focuses on the vector constraint relation when the angle changes from the view point of the external characteristic of the voltage, thereby establishing the relation between the voltage with stronger observability and the synchronous stability of the converter which is difficult to observe, forming the synchronous stability criterion of the voltage form, judging whether a balance point exists during the fault period and whether transient instability leading to an unstable balance point occurs by calculating and monitoring the voltage of the power electronic equipment in real time, having good observability, and providing a new means and a new mode for judging the synchronous stability under the large disturbance of the power electronic equipment.
Drawings
A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
fig. 1 is a flowchart of a synchronization stability determination method 100 for a power electronic device according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a VSC grid-connected system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a control structure of a PLL controller according to an embodiment of the present invention;
FIG. 4 is a schematic view of various angles according to an embodiment of the present invention;
FIG. 5 is a vector diagram before failure according to an embodiment of the present invention;
FIG. 6 is a space vector relationship for synchronous stability analysis during a fault according to an embodiment of the present invention;
FIGS. 7(a), 7(b) and 7(c) are δ according to an embodiment of the present invention, respectively0>|θZg+θIA vector diagram when l;
FIGS. 8(a), 8(b) and 8(c) are δ according to an embodiment of the present invention, respectively0<|θZg+θIA vector diagram when l;
FIG. 9 is a schematic diagram of a stable equilibrium point and an unstable equilibrium point according to an embodiment of the present invention;
FIG. 10 is a flow chart of synchronization stability determination according to an embodiment of the present invention;
FIG. 11 is a simulation result of condition 1 according to an embodiment of the present invention;
FIG. 12 shows simulation results for condition 2 according to an embodiment of the present invention;
FIG. 13 is a simulation result for condition 3 according to an embodiment of the present invention;
fig. 14 is a schematic structural diagram of a synchronization stability determination system 1400 of a power electronic device according to an embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Fig. 1 is a flowchart of a synchronization stability determination method 100 for a power electronic device according to an embodiment of the present invention. As shown in fig. 1, the method for determining synchronization stability of power electronic equipment according to the embodiment of the present invention determines synchronization stability of power electronic equipment based on space vectors, focuses on vector constraint relation when angle changes from the perspective of external characteristics of voltage, establishes a link between voltage with strong observability and synchronization stability of a converter that is not easy to observe, forms a synchronization stability criterion in a voltage form, and determines whether a balance point exists during a fault and whether transient instability leading to an unstable balance point occurs by calculating and monitoring the voltage of the power electronic equipment in real time, so that good observability is achieved, and a new means and a new manner are provided for determining synchronization stability under large disturbance of the power electronic equipment. The method 100 for determining synchronization stability of power electronic equipment according to the embodiment of the present invention starts from step 101, and obtains operation data of the power electronic equipment in an operation process in real time in step 101.
In the embodiment of the invention, the operation data of the electronic equipment needs to be monitored in real time, so that the calculation of the synchronization stability judgment is carried out according to the acquired operation data. The simulation calculation can be performed through a Voltage Source Converter (VSC) grid-connected system model structure established by a single-machine equivalence method to obtain the operation data, and the operation data of the power electronic device in actual work can also be obtained. The operational data includes: pre-fault grid voltage, pre-fault equivalent resistance, pre-fault equivalent reactance, pre-fault d-axis current and q-axis current, grid voltage during fault, equivalent resistance during fault, equivalent reactance during fault, d-axis current and q-axis current during fault as determined by a low voltage ride through strategy.
In step 102, a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs are determined based on the operation data.
Preferably, the determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data includes:
Figure 682023DEST_PATH_IMAGE001
，
Figure 633798DEST_PATH_IMAGE002
，
Figure 388259DEST_PATH_IMAGE003
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; i is VSC output current; zgConnecting points for VSC to AC system impedance;
Figure 298446DEST_PATH_IMAGE004
the voltage of the power grid at the moment of fault occurrence; delta0Is the value of delta angle at steady state before failure; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault;
Figure 754835DEST_PATH_IMAGE005
the output current of the VSC is in steady state before the fault;
Figure 713564DEST_PATH_IMAGE006
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 306219DEST_PATH_IMAGE007
the impedance angle from the VSC grid-connected point to the AC system in the steady state before the fault;
Figure 872461DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 81725DEST_PATH_IMAGE009
is the pre-fault grid voltage; δ = θPLL controller-θg，θPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate systemgIs UgThe included angle between the two-phase static coordinate system and a beta axis negative half shaft; u shapePCCOriented on the positive d-axis half and the q-axis leads the d-axis by 90 deg..
In step 103, according to the first voltage vector length and the first reference voltage vector length, whether two balance points exist is judged according to a balance point criterion, and a judgment result is obtained.
Preferably, the balance point criterion comprises:
Figure 640883DEST_PATH_IMAGE010
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; determining that there are two balance points when the balance point criterion is satisfied; otherwise, it is determined that one or no balance point exists.
The embodiment of the invention aims at the power electronic equipment which adopts the phase-locked loop to keep synchronization, and the reasoning process for determining the first voltage vector length and the first reference voltage vector length is as follows: firstly, establishing a Voltage Source Converter (VSC) grid-connected system model structure based on a single-machine equivalence method, and then analyzing a space vector relation of a VSC grid-connected system according to a grid-connected system model to determine the space vector relation; a first voltage vector length, a first reference voltage vector length, and a criterion that there are two equilibrium points are then determined based on the space vector relationship.
Fig. 2 is a model structure of a Voltage Source Converter (VSC) grid-connected system established by a single-machine equivalent method. Wherein, UcFor VSC AC side voltage, UPCCFor VSC point-of-connection voltages, UgFor AC system voltage, Zc=Rc+jωLcFor VSC converter outlet to point of connection impedance, Zg=Rg+jωLgThe impedance from a VSC grid-connected point to an alternating current system, I is VSC output current, and the sampling voltage of the PLL controller is grid-connected point voltage. The subscript dq indicates the electrical quantity on the coordinate axis of the PLL controller dq, the subscript abc indicates the electrical quantity on the three-phase stationary coordinate system, the subscript 0 indicates the electrical quantity at steady state before failure, and the superscript indicates the reference value.
FIG. 3 is a PLL controller control block diagram in which U is specifiedPCCOriented on the positive half axis of the d-axis with the q-axis leading the d-axis by 90 DEG omegaPLL controllerFor PLL controller d-axis angular velocity, omegagFor the mains voltage UgAngular velocity of (a), thetaPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate system, and the delta omega = omegaPLL controller-ωg，Ki、KpRespectively, an integral coefficient and a proportional coefficient of the PI link. The second order equation controlled by the PLL controller is:
Figure 556886DEST_PATH_IMAGE014
（1）
fig. 4 is a schematic view of the angles. Wherein, thetagIs UgAngle delta = theta with the negative half axis of the beta axis of the two-phase stationary coordinate systemPLL controller-θgThen the second order control equation of the PLL controller can be converted into:
Figure 277717DEST_PATH_IMAGE015
（2）
neglecting the dynamic state of the alternating current circuit, substituting the delta angle to obtain a simplified expression of a voltage equation from a grid-connected point to a main circuit of a power grid under a PLL controller dq coordinate system, wherein the simplified expression is as follows:
Figure 459431DEST_PATH_IMAGE016
（3）
and obtaining a second-order motion equation with delta as a variable from a control equation and a voltage equation:
Figure 822279DEST_PATH_IMAGE017
（4）
wherein the equivalent inertia is:
Figure 655106DEST_PATH_IMAGE018
（5）
the equivalent damping is:
Figure 546839DEST_PATH_IMAGE019
（6）
the equivalent acceleration torque is:
Figure 215849DEST_PATH_IMAGE020
（7）
the equivalent deceleration torque is:
Figure 116809DEST_PATH_IMAGE021
（8）
the main circuit voltage equation of equation (3) is expressed in the following form:
Figure 741825DEST_PATH_IMAGE022
（9）
wherein,
Figure 70038DEST_PATH_IMAGE023
（10）
the following steps are provided:
Figure 210033DEST_PATH_IMAGE024
(11)
thus, the vector relationship can be expressed as:
Figure 665416DEST_PATH_IMAGE025
(12)
the VSC output power is:
Figure 207256DEST_PATH_IMAGE026
(13)
according to the power equation, u is in the dq coordinate axis relation used by the invention before faultPCCq=0, for activating new energy, i* dPositive, the new energy is not reactive in general, i* q=0, at this time, θI0=0，θZg0+θI0Is positive. U under steady statePCC0Oriented at dPLL controllerOn the positive half shaft of the shaft, d can be obtained by vector relationPLL controllerShaft and Ug0Angle delta of0Is positive. The vector relationship in steady state before failure is shown in fig. 5.
During fault, on the premise that phase locking of the phase-locked loop is successful, uPCCq=0, in order to meet the requirement of new energy to generate reactive power during low voltage ride through, i* qIs negative, and in general, when the voltage drop degree is deeper, the new energy does not generate active power or generates a small amount of active power, i.e. i* dIs positive, and i* d<<|i* qL, thus during a fault thetaIIs negative and is close to-90 deg..
The following assumptions are made in the scene that the fault is a direct voltage drop and the fault is not cleared:
1) short time after faultWithin the middle, omegaPLL controller ≈ωgCan be converted into | Zg|、θZgConsidered as a constant.
2) During fault i* d、i* qDetermined by the low voltage ride through strategy and is constant, then I and thetaIIs a constant.
The space vector relationship for the synchronous stability analysis during a fault can be derived from the foregoing basic assumptions, as shown in fig. 6. Wherein, IZgRelative to dPLL controllerThe amplitude of the shaft is unchanged, and the included angle is unchanged; voltage UgAfter falling, the amplitude is unchanged, andPLL controllerThe included angle delta of the shaft moves according to a second-order motion equation; from IZg、UgResultant vector UPCCIs on a circle, the amplitude varies with delta.
In FIG. 6, the system presence balance point is represented by U during the faultPCCCan be reacted with dPLL controllerWith coincident axes, i.e. UPCCCircle at the end point and dPLL controllerThe axes intersect. When the system has a point of equilibrium, it is not possible for the fault period to transition to a new steady state.
First, the value δ of the pre-failure δ angle is calculated from fig. 50Comprises the following steps:
Figure 706370DEST_PATH_IMAGE027
(14)
wherein,
Figure 599240DEST_PATH_IMAGE028
the output current of the VSC is in steady state before the fault;
Figure 592735DEST_PATH_IMAGE029
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 723502DEST_PATH_IMAGE030
the impedance angle from the VSC grid-connected point to the AC system in the steady state before the fault;
Figure 393517DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 773683DEST_PATH_IMAGE031
is the pre-fault grid voltage.
During fault IZgAnd dPLL controllerThe angle of the axes being thetaZg+θIFrom the foregoing analysis, θZg+θIIs negative. The numerical value delta before the fault is kept on the assumption that the delta angle does not change suddenly at the moment of the fault0. In FIGS. 6 and 7, the circle of the green dotted line is UPCCThe circle with the end point and the orange dotted line is UgStarting point as center of circle, from the starting point to dPLL controllerThe length of the vertical axis is a circle with a radius. The subscript 0+ represents the electrical quantity immediately after the occurrence of the fault.
By comparing delta0And | θZg+θIThe magnitude of | can be obtained when δ0>|θZg+θIWhen the system has only one balance point, two balance points and no balance point, the vector relations are respectively shown in fig. 7(a), 7(b) and 7 (c); when delta0<|θZg+θIIn | the system, the vector relationship of only one balance point, two balance points and no balance point is shown in fig. 8(a), 8(b) and 8(c), respectively.
In fig. 7 and 8, one vector represents U at the instant after the occurrence of the faultPCCIt is named as UPCC_0+. A reference voltage vector (U) reflecting the existence of an equilibrium pointEEP) Falls on the small circle and Ug0+On the intersection of the straight lines. As can be seen from fig. 7 and 8, there is a balance point in the system during a fault, i.e. there is a UPCCAnd dPLL controllerWhen there is a possibility of overlapping, the radius of the large circle is always equal to or larger than the radius of the small circle in the figure.Due to UPCC_0+And UEEPFalls on two circles, so the existence of a balance point is also judged by the length of the two vectors: when U is turnedPCC_0+ =UEEPWhen the system is in use, only one balance point exists; when U is turnedPCC_0+> UEEPWhen the system is in use, two balance points exist; when U is turnedPCC_0+ < UEEPThe system has no balance point.
Due to UPCC_0+Following Ug0+Varies in size, and UEEPAnd Ug0+Is not related to the size of U, thereforeEEPMay be used as a threshold value to reflect the existence of an equilibrium point.
In fig. 7 and 8, the vector UEEPCan be expressed as:
Figure 305290DEST_PATH_IMAGE002
(15)
vector UPCC_0+Can be expressed as:
Figure 24984DEST_PATH_IMAGE001
(16)
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; i is VSC output current; zgConnecting points for VSC to AC system impedance;
Figure 865901DEST_PATH_IMAGE004
the voltage of the power grid at the moment of fault occurrence; delta0Is the value of delta angle at steady state before failure; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault;
Figure 467784DEST_PATH_IMAGE005
the output current of the VSC is in steady state before the fault;
Figure 317928DEST_PATH_IMAGE006
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 439599DEST_PATH_IMAGE007
the impedance angle from the VSC grid-connected point to the AC system in the steady state before the fault;
Figure 451417DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 478279DEST_PATH_IMAGE009
is the pre-fault grid voltage; δ = θPLL controller-θg，θPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate systemgIs UgThe included angle between the two-phase static coordinate system and a beta axis negative half shaft; u shapePCCOriented on the positive d-axis half and the q-axis leads the d-axis by 90 deg..
Thus, the voltage value U immediately after the occurrence of the passing fault can be determinedPCC_0+Judging whether the system has a balance point after the fault occurs, wherein the criterion for obtaining that the system has two balance points is as follows:
Figure 866535DEST_PATH_IMAGE010
(17)
and if the first voltage vector length and the first reference voltage vector length satisfy the formula, determining that two balance points exist in the system. When the system has no balance point or only one balance point, the synchronous stability can not be recovered.
In the embodiment of the invention, after system parameters, system working conditions and operation faults are determined, a first voltage vector length and a first reference voltage vector length of a grid-connected point when the faults occur are determined according to the operation data, and then whether two balance points exist is judged according to a balance point criterion according to the first voltage vector length and the first reference voltage vector length.
In step 104, when the determination result indicates that two balance points exist, an unstable balance point is determined according to a stable balance point criterion.
Preferably, wherein said determining an unstable equilibrium point based on a stable equilibrium point criterion comprises:
for any balance point, if any balance point meets the criterion of stable balance point
Figure 357559DEST_PATH_IMAGE011
Determining any balance point as a stable balance point; otherwise, determining any balance point as an unstable balance point;
wherein, deltaeAn included angle between a d axis of the PLL controller corresponding to any balance point and a voltage vector of a grid-connected point; by solving for
Figure 279293DEST_PATH_IMAGE012
To obtain deltaeI is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
When the condition of two equilibrium points is met during the fault, in the dynamic process, if the delta always moves near the stable equilibrium point in the transient process and is finally stabilized on the point, the system can be recovered to be stable after large disturbance; once δ crosses the unstable equilibrium point, the system destabilizes after a large disturbance. Therefore, it is necessary to determine the unstable equilibrium point.
At equilibrium point deltaeLinear state variables in the linear state equation are Δ δ and Δ ω:
Figure 59030DEST_PATH_IMAGE032
(18)
if and only if all eigenvalues satisfy that the real part is less than 0, the balance point is stable, and thus the criterion for obtaining the stable balance point is as follows:
Figure 782135DEST_PATH_IMAGE033
(19)
namely:
Figure 862087DEST_PATH_IMAGE011
(20)
from the above formula, δeBelongs to (2k pi-pi/2, 2k pi + pi/2), and when k belongs to Z, deltaeThe angle corresponding to the stable equilibrium point is outside this range the unstable equilibrium point.
Thus, for any equilibrium point, if that equilibrium point satisfies the stable equilibrium point criterion
Figure 232019DEST_PATH_IMAGE011
Determining any balance point as a stable balance point; otherwise, determining any balance point as an unstable balance point. Wherein by solving in equation (9)
Figure 233473DEST_PATH_IMAGE012
To obtain deltaeI is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
In step 105, a second reference voltage vector length corresponding to the unstable equilibrium point is determined.
Preferably, the determining the length of the second reference voltage vector corresponding to the unstable equilibrium point includes:
Figure 963532DEST_PATH_IMAGE013
，
wherein, UUEPThe vector length of the second reference voltage is I, and the I is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
In step 106, based on the real-time operation data of the power electronic device, determining a second voltage vector length of a grid-connected point after a fault occurs, and determining that the system is in synchronous instability when the second voltage vector length is smaller than a second reference voltage vector length.
The calculation according to equation (20) yields δ in fig. 9e_1To stabilize the equilibrium point, δe_2Is the unstable equilibrium point. Dotted line circle is UPCCThe circle of the endpoint, the second reference voltage (U) corresponding to the unstable equilibrium pointUEP) The vector length of (d) is:
Figure 163569DEST_PATH_IMAGE013
(21)
when U is turnedPCCIs less than U in lengthUEPWhen δ is destabilized beyond the unstable equilibrium point.
Thus, in an embodiment of the present invention,firstly, calculating a second reference voltage vector length corresponding to an unstable equilibrium point, and then determining a second voltage vector length U of a grid-connected point after a fault occurs based on real-time operation data of the power electronic equipmentPCCCompare UPCCAnd UUEPAnd (4) judging whether synchronous instability occurs or not. In the dynamic monitoring process, UPCCOnce the second voltage vector length is satisfied to be less than the second reference voltage vector length, then:
UPCC＜UUEP,
it may be determined that the system is out of sync stability and otherwise it is determined that the system is able to recover sync stability.
The calculation method of the second voltage vector length is the same as the calculation method of the first voltage vector length, and is not described herein again.
As shown in fig. 10, the process of determining synchronization stability based on a simulation model according to the embodiment of the present invention includes: simulating according to given system parameters, initial operation conditions and fault types to obtain U when fault occursPCC_0+And UEEP(ii) a If U isPCC_0+Greater than UEEPDetermining that no balance point exists and determining that large disturbance instability occurs; if U isPCC_0+Less than or equal to UEEPIf so, calculating balance points, determining whether two balance points exist, and if so, determining a stable balance point and an unstable balance point; calculating a second reference voltage U corresponding to the unstable equilibrium pointUEP(ii) a For U after faultPCCMonitoring if U existsPCC＜UUEPIf so, determining that disturbance instability occurs, otherwise, determining that the system can recover synchronous stability.
In order to verify the feasibility of the invention, a single VSC infinite system is established by utilizing PSCAD/EMTDC for simulation verification, wherein the working condition 1 is that no balance point exists during the fault, the working condition 2 is that the balance point exists and is recovered to be stable during the fault, and the working condition 3 is that the balance point exists but is unstable during the fault. The operating regime 1 and operating regime 2 system parameters are shown in table 1. During a fault, condition 1 sets id=0，iq=1p.u., I =1p.u., θI= -90 °; working condition 2 set id=0，iq=0.45p.u., I =0.45p.u., θIAnd = 90. Set condition 3 during fault UgAnd =0.02p.u., and the other parameters are the same as those in the working condition 2.
TABLE 1 Condition 1 and Condition 2 System parameter Table
Figure 953671DEST_PATH_IMAGE034
Working condition 1:
calculate UEEP=0.1306，UPCC_0+=0.1184, having UPCC_0+<UEEPAnd by combining with the criterion of existence of the balance point, the system can be judged to have no balance point during the fault period, and the synchronization stability is lost. U shapePCCThe simulation result of the sum delta angle is shown in fig. 11, the divergence of the delta angle is unstable, and the simulation result is consistent with the judgment result of the criterion.
Working condition 2:
calculate UEEP=0.0588，UPCC_0+=0.0698, having UPCC_0+>UEEPAnd the balance point of the system during the fault period can be judged by combining the criterion of existence of the balance point. Calculate UUEP=0.0117。UPCCThe results of the simulation of the sum delta angle are shown in FIG. 12, U in the dynamic processPCCIs not always less than UUEPAnd the instability criterion is not met, the delta angular oscillation is converged, and the simulation result is consistent with the criterion judgment result.
Working condition 3:
calculate UEEP=0.0588，UPCC_0+=0.0598, having UPCC_0+>UEEPAnd the balance point of the system during the fault period can be judged by combining the criterion of existence of the balance point. Calculate UUEP=0.0287。UPCCThe simulation results of the sum angle are shown in FIG. 13, where U exists in the dynamic processPCC<UUEPAnd the instability criterion is met, the delta angle divergence instability is met, and the simulation result is consistent with the criterion judgment result.
Fig. 14 is a schematic structural diagram of a synchronization stability determination system 1400 of a power electronic device according to an embodiment of the present invention. As shown in fig. 14, a synchronization stability determination system 1400 for a power electronic device according to an embodiment of the present invention includes: an operation data acquisition unit 1401, a first calculation unit 1402, a balance point determination unit 1403, an unstable balance point determination unit 1404, a second calculation unit 1405, and a synchronization stability determination unit 1406.
Preferably, the operation data acquiring unit, 1401 is configured to acquire operation data of the power electronic device in real time during operation.
Preferably, the first calculating unit 1402 is configured to determine a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs, based on the operation data.
Preferably, the determining, by the first calculating unit 1402, the first voltage vector length and the first reference voltage vector length of the grid-connected point when the fault occurs based on the operation data includes:
Figure 724312DEST_PATH_IMAGE001
，
Figure 258061DEST_PATH_IMAGE002
，
Figure 312605DEST_PATH_IMAGE003
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; i is VSC output current; zgConnecting points for VSC to AC system impedance;
Figure 273608DEST_PATH_IMAGE004
the voltage of the power grid at the moment of fault occurrence; delta0Is the value of delta angle at steady state before failure; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idControl of the VSC output current I during PLL for fault periods, respectivelyA q-axis component and a d-axis component under a dq coordinate system of the controller;
Figure 984075DEST_PATH_IMAGE005
the output current of the VSC is in steady state before the fault;
Figure 72248DEST_PATH_IMAGE006
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 246877DEST_PATH_IMAGE007
the impedance angle from the VSC grid-connected point to the AC system in the steady state before the fault;
Figure 316464DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 576544DEST_PATH_IMAGE009
is the pre-fault grid voltage; δ = θPLL controller-θg，θPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate systemgIs UgThe included angle between the two-phase static coordinate system and a beta axis negative half shaft; u shapePCCOriented on the positive d-axis half and the q-axis leads the d-axis by 90 deg..
Preferably, the balance point determining unit 1403 is configured to determine, according to the length of the first voltage vector and the length of the first reference voltage vector, whether two balance points exist according to a balance point criterion, and obtain a determination result.
Preferably, the balance point criterion comprises:
Figure 452096DEST_PATH_IMAGE010
，
wherein, UPCC_0+Is the first voltage vector lengthDegree; u shapeEEPIs a first voltage reference vector length; determining that there are two balance points when the balance point criterion is satisfied; otherwise, it is determined that one or no balance point exists.
Preferably, the unstable equilibrium point determining unit 1404 is configured to determine an unstable equilibrium point according to a stable equilibrium point criterion when the determination result indicates that two equilibrium points exist.
Preferably, the unstable equilibrium point determining unit 1404, according to the stable equilibrium point criterion, determines the unstable equilibrium point, including:
for any balance point, if any balance point meets the criterion of stable balance point
Figure 231965DEST_PATH_IMAGE011
Determining any balance point as a stable balance point; otherwise, determining any balance point as an unstable balance point;
wherein, deltaeAn included angle between a d axis of the PLL controller corresponding to any balance point and a voltage vector of a grid-connected point; by solving for
Figure 3611DEST_PATH_IMAGE012
To obtain deltaeI is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
Preferably, the second calculating unit 1405 is configured to determine a second reference voltage vector length corresponding to the unstable equilibrium point.
Preferably, the second calculating unit 1405, determining the length of the second reference voltage vector corresponding to the unstable equilibrium point, includes:
Figure 750988DEST_PATH_IMAGE013
，
wherein, UUEPThe vector length of the second reference voltage is I, and the I is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
Preferably, the synchronization stability determining unit 1406 is configured to determine, based on real-time operation data of the power electronic device, a second voltage vector length of a grid-connected point after the fault occurs, and determine that the system is synchronized and unstable when the second voltage vector length is smaller than a second reference voltage vector length.
The synchronization stability determination system 1400 of the power electronic device according to the embodiment of the present invention corresponds to the synchronization stability determination method 100 of the power electronic device according to another embodiment of the present invention, and is not described herein again.
The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
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.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.

Claims (4)

1. A method for judging synchronization stability of power electronic equipment is characterized by comprising the following steps:
acquiring operation data of the power electronic equipment in the operation process in real time;
determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data;
judging whether two balance points exist according to the first voltage vector length and the first reference voltage vector length and a balance point criterion, and obtaining a judgment result;
when the judgment result indicates that two balance points exist, determining an unstable balance point according to a stable balance point criterion;
determining a second reference voltage vector length corresponding to the unstable equilibrium point;
determining a second voltage vector length of a grid-connected point after a fault occurs based on the real-time operation data of the power electronic equipment, and determining that the system is subjected to synchronous instability when the second voltage vector length is smaller than a second reference voltage vector length;
wherein the determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data comprises:
Figure 877898DEST_PATH_IMAGE001
，
Figure 258195DEST_PATH_IMAGE002
，
Figure 884348DEST_PATH_IMAGE003
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; i is VSC output current; zgConnecting points for VSC to AC system impedance;
Figure 599363DEST_PATH_IMAGE004
the voltage of the power grid at the moment of fault occurrence; delta0Is the value of delta angle at steady state before failure; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault;
Figure 484011DEST_PATH_IMAGE005
the output current of the VSC is in steady state before the fault;
Figure 233662DEST_PATH_IMAGE006
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 47028DEST_PATH_IMAGE007
the impedance angle from the VSC grid-connected point to the AC system in the steady state before the fault;
Figure 983760DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 688411DEST_PATH_IMAGE009
is the pre-fault grid voltage; δ = θPLL controller-θg，θPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate systemgIs UgThe included angle between the two-phase static coordinate system and a beta axis negative half shaft; u shapePCCOriented on the positive half shaft of the d shaft, and the q shaft leads the d shaft by 90 degrees;
wherein the balance point criterion comprises:
Figure 216869DEST_PATH_IMAGE010
，
wherein, when the balance point criterion is satisfied, it is determined that two balance points exist; otherwise, determining that one or no balance point exists;
wherein determining an unstable equilibrium point based on the stable equilibrium point criterion comprises:
for any balance point, if any balance point meets the criterion of stable balance point
Figure 715983DEST_PATH_IMAGE011
Determining any balance point as a stable balance point; otherwise, determining any balance point as an unstable balance point;
wherein, deltaeAn included angle between a d axis of the PLL controller corresponding to any balance point and a voltage vector of a grid-connected point; by solving for
Figure 140011DEST_PATH_IMAGE012
To obtain deltae， UgIs an ac system voltage.
2. The method of claim 1, wherein determining the length of the second reference voltage vector corresponding to the unstable equilibrium point comprises:
Figure 133506DEST_PATH_IMAGE013
，
wherein, UUEPThe vector length of the second reference voltage is I, and the I is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
3. A system for determining synchronization stability of a power electronic device, the system comprising:
the operation data acquisition unit is used for acquiring operation data of the power electronic equipment in the operation process in real time;
the first calculation unit is used for determining a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data;
the balance point judging unit is used for judging whether two balance points exist according to the first voltage vector length and the first reference voltage vector length and a balance point criterion to obtain a judgment result;
an unstable equilibrium point determining unit, configured to determine an unstable equilibrium point according to a stable equilibrium point criterion when the determination result indicates that two equilibrium points exist;
the second calculation unit is used for determining the length of a second reference voltage vector corresponding to the unstable equilibrium point;
the synchronous stability judging unit is used for determining the length of a second voltage vector of a grid-connected point after a fault occurs based on the real-time operation data of the power electronic equipment, and determining that the system is subjected to synchronous instability when the length of the second voltage vector is smaller than the length of a second reference voltage vector;
the first calculating unit determines a first voltage vector length and a first reference voltage vector length of a grid-connected point when a fault occurs based on the operation data, and includes:
Figure 264273DEST_PATH_IMAGE001
，
Figure 934289DEST_PATH_IMAGE002
，
Figure 94881DEST_PATH_IMAGE003
，
wherein, UPCC_0+Is a first voltage vector length; u shapeEEPIs a first voltage reference vector length; i is VSC output current; zgConnecting points for VSC to AC system impedance;
Figure 406913DEST_PATH_IMAGE004
the voltage of the power grid at the moment of fault occurrence; delta0Is the value of delta angle at steady state before failure; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault;
Figure 939657DEST_PATH_IMAGE005
the output current of the VSC is in steady state before the fault;
Figure 954143DEST_PATH_IMAGE006
impedance from a VSC grid-connected point to an alternating current system in a steady state before a fault;
Figure 431392DEST_PATH_IMAGE007
VSC grid-connected point-to-alternating current system in steady state before faultThe impedance angle of (d);
Figure 796383DEST_PATH_IMAGE008
is the output current angle theta of VSC under dq coordinate system of PLL controller in steady state before faultI0=arctan(iq0/id0)，iq0And id0Respectively representing a q-axis component and a d-axis component of VSC output current I in a dq coordinate system of a PLL controller before fault steady state;
Figure 167321DEST_PATH_IMAGE009
is the pre-fault grid voltage; δ = θPLL controller-θg，θPLL controllerIs the angle between the d axis of the PLL controller and the negative half axis of the beta axis of the two-phase static coordinate systemgIs UgThe included angle between the two-phase static coordinate system and a beta axis negative half shaft; u shapePCCOriented on the positive half shaft of the d shaft, and the q shaft leads the d shaft by 90 degrees;
wherein the balance point criterion comprises:
Figure 913560DEST_PATH_IMAGE010
，
wherein, when the balance point criterion is satisfied, it is determined that two balance points exist; otherwise, determining that one or no balance point exists;
wherein, the unstable equilibrium point determining unit determines the unstable equilibrium point according to a stable equilibrium point criterion, including:
for any balance point, if any balance point meets the criterion of stable balance point
Figure 19051DEST_PATH_IMAGE011
Determining any balance point as a stable balance point; otherwise, determining any balance point as an unstable balance point;
wherein, deltaeAn included angle between a d axis of the PLL controller corresponding to any balance point and a voltage vector of a grid-connected point; by solving for
Figure 407307DEST_PATH_IMAGE012
To obtain deltae， UgIs an ac system voltage.
4. The system of claim 3, wherein the second computing unit determining the length of the second reference voltage vector corresponding to the unstable equilibrium point comprises:
Figure 681687DEST_PATH_IMAGE013
，
wherein, UUEPThe vector length of the second reference voltage is I, and the I is VSC output current; zgConnecting points for VSC to AC system impedance; thetaZgThe impedance angle from a VSC grid-connected point to an alternating current system during a fault; thetaIIs the output current angle, theta, of the VSC in the dq coordinate system of the PLL controller during a faultI=arctan(iq/id)，iqAnd idRespectively representing a q-axis component and a d-axis component of VSC output current I under a dq coordinate system of a PLL controller during a fault; u shapegIs an ac system voltage.
CN202111344471.0A 2021-11-15 2021-11-15 Method and system for judging synchronization stability of power electronic equipment Active CN113794240B (en)

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