CN114221358A - Transient current limiting method and system for realizing amplitude-frequency combined control based on virtual magnetic flux - Google Patents

Transient current limiting method and system for realizing amplitude-frequency combined control based on virtual magnetic flux Download PDF

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CN114221358A
CN114221358A CN202111552937.6A CN202111552937A CN114221358A CN 114221358 A CN114221358 A CN 114221358A CN 202111552937 A CN202111552937 A CN 202111552937A CN 114221358 A CN114221358 A CN 114221358A
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magnetic flux
current
virtual magnetic
frequency
amplitude
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CN114221358B (en
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袁小明
何维
张睿
龙涛
杨海瞳
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Huazhong University of Science and Technology
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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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy

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Abstract

The invention discloses a transient current limiting method and system for realizing amplitude-frequency combined control based on virtual magnetic flux, and belongs to the field of power systems. The method comprises the following steps: s1, calculating to obtain terminal voltage virtual magnetic flux T on the grid-connected side of the new energy equipment, wherein T is Vt/ωt，VtAnd ωtThe amplitude and the frequency of the terminal voltage are respectively; s2, designing an internal potential virtual magnetic flux T ', wherein T' ═ E/omega, and E and omega are the amplitude and the frequency of the internal potential respectively; s3, based on the internal potential virtual magnetic flux E/omega and the terminal voltage virtual magnetic flux Vt/ωtSetting the total current I limited on the filter inductor when the new energy equipment is in power grid faultgObtaining an active current instruction I at the grid-connected side end for constraint relationgdAnd a reactive current command IgqAnd the coordination distribution of active current and reactive current in the transient current limiting process is realized. Hair brushThe virtual magnetic flux is introduced to represent the joint change of the voltage amplitude and the frequency, so that the coordination distribution of reactive current and active current is realized, and finally the joint support of the voltage frequency and the amplitude of the power grid under the transient state current limiting is realized.

Description

Transient current limiting method and system for realizing amplitude-frequency combined control based on virtual magnetic flux
Technical Field
The invention belongs to the field of power systems, and particularly relates to a transient current limiting method and system for realizing amplitude-frequency combined control based on virtual magnetic flux.
Background
In order to construct a novel power system taking new energy power generation as a main body, the new energy power generation gradually replaces a thermal power generator and becomes a main power supply of the power system. The new energy power generation has urgent and practical requirements for maintaining the dynamic stability of the voltage amplitude and the frequency under various disturbances. However, new energy power generation is limited by its own power electronics over-current capability, requiring current limiting control during grid faults. How to realize the combined support of the voltage amplitude and the frequency of the power grid under the constraint condition of the new energy power generation current limitation is a significant problem in the future of power systems. The effective support of a well designed transient current-limiting control strategy on a power grid is an important requirement of a novel power system mainly based on new energy power generation.
However, current transient current limiting strategies are currently available, which are typically based on preferential reactive current injection or active current injection to limit current. These methods suffer from the drawback that the capacity allocation of active and reactive currents is relatively independent, i.e. the total current capacity allocation to active and reactive currents lacks a coordinated control mechanism; based on the defects, the traditional transient current-limiting control method has limitation on amplitude and frequency dynamics of grid voltage of a combined supporting novel power system, a role of supporting the grid is assisted, and certain power injection is realized on the grid through injected current. At this time, the amplitude and frequency of the new energy power generation can be set dynamically only by coordination control between reactive current and active current. Namely, the transient current-limiting control design idea taking single injection reactive current or active current as a direct design object is difficult to determine the amplitude and frequency dynamics of the potential in the new energy power generation, so that the transient current-limiting control design idea is not suitable for effectively and jointly supporting the amplitude and the frequency of the grid voltage.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a transient current limiting method and a transient current limiting system for realizing amplitude-frequency combined control based on virtual magnetic flux, and aims to realize the coordinated distribution of reactive current and active current in the transient current limiting control in a new energy power system, and further realize the combined support of the voltage frequency and the amplitude of a power grid under the transient current limiting.
To achieve the above object, according to an aspect of the present invention, there is provided a transient current limiting method for implementing amplitude-frequency joint control based on virtual magnetic flux, including the following steps:
s1, calculating to obtain terminal voltage virtual magnetic flux T on the grid-connected side of the new energy equipment, wherein T is Vt/ωt，VtAnd ωtThe amplitude and the frequency of the terminal voltage are respectively;
s2, designing an internal potential virtual magnetic flux T ', wherein T' ═ E/omega, and E and omega are the amplitude and the frequency of the internal potential respectively;
s3, based on the internal potential virtual magnetic flux E/omega and the terminal voltage virtual magnetic flux Vt/ωtSetting the total current I limited on the filter inductor when the new energy equipment is in power grid faultgObtaining an active current instruction I at the grid-connected side end for constraint relationgdAnd a reactive current command IgqAnd the coordination distribution of active current and reactive current in the transient current limiting process is realized.
Further, the active current instruction I is obtained by a fractional integration methodgdAnd a reactive current command Igq。
Further, the active current instruction IgdAnd a reactive current command IgqRespectively as follows:
Figure BDA0003418230450000021
Figure BDA0003418230450000022
wherein L isfIs the inductance value of the filter inductor.
Further, the internal potential virtual magnetic flux satisfies the following constraint condition:
Figure BDA0003418230450000031
wherein, ImaxIs the set maximum current value on the filter inductor.
Further, the internal potential virtual magnetic flux is:
Figure BDA0003418230450000032
wherein K, c is a constant, and K > 0, and A is a virtual flux control parameter.
Further, the magnitude V of the terminal voltage is calculated by vector compositiont。
Further, the magnitude V of the terminal voltagetComprises the following steps:
Figure BDA0003418230450000033
wherein v ista、vtb、vtcRespectively is three-phase instantaneous voltage at the grid-connected side.
Further, the frequency omega of the terminal voltage is obtained through phase-locked loop measurementt。
According to another aspect of the present invention, a transient current limiting system for implementing amplitude-frequency joint control based on virtual magnetic flux is provided, which includes the following modules:
the terminal voltage virtual magnetic flux calculation module is used for calculating and obtaining a terminal voltage virtual magnetic flux T on the grid-connected side of the new energy equipment, wherein T is Vt/ωt，VtAnd ωtThe amplitude and the frequency of the terminal voltage are respectively;
an internal potential virtual flux design module for obtaining an internal potential virtual flux T ', wherein T' ═ E/ω, and E and ω are the amplitude and frequency of the internal potential, respectively;
a current command design module for designing a current command based on the internal potential virtual magnetic flux E/omega and the terminal voltage virtual magnetic flux Vt/ωtSetting the total current I limited on the filter inductor when the new energy equipment is in power grid faultgObtaining an active current instruction I at the grid-connected side end for constraint relationgdAnd a reactive current command IgqAnd the coordination distribution of active current and reactive current in the transient current limiting process is realized.
Further, the active current instruction IgdAnd a reactive current command IgqRespectively as follows:
Figure BDA0003418230450000041
Figure BDA0003418230450000042
wherein L isfIs the inductance value of the filter inductor.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) according to the invention, the virtual magnetic flux is introduced to represent the combined change of the voltage amplitude and the frequency, the virtual magnetic flux of the voltage at the grid-connected side end of the new energy equipment and the designed internal potential virtual magnetic flux are measured, the total current limited on the filter inductor during the fault of the power grid is taken as the constraint, the active current and reactive current instruction values in the transient process are obtained, the coordinated distribution of the active current and the reactive current in the transient current limiting process is realized, and the effective combined support of the voltage amplitude and the frequency of the power grid is realized.
(2) The constraint condition met by the internal potential virtual magnetic flux designed by the invention can ensure that the active reactive current does not exceed the limited maximum current during the fault.
(3) The internal potential virtual magnetic flux designed by the invention, K is more than 0, and the output of inductive reactive current during the transient state is ensured.
In summary, the virtual magnetic flux is introduced to represent the joint change of the voltage amplitude and the frequency, so that the coordinated distribution of reactive current and active current is realized, and finally the joint support of the voltage frequency and the amplitude of the power grid under the transient state current limiting is realized.
Drawings
FIG. 1 is a flow chart of a transient current-limiting coordination control method for realizing internal potential amplitude-frequency joint control based on virtual magnetic flux according to the present invention;
FIG. 2 is a schematic diagram of the control method provided by the invention applied to a circuit based on a full-power fan grid-side converter;
FIG. 3 is a schematic diagram of measuring terminal voltage magnitude by a voltage vector measurement module;
FIG. 4 is a diagram illustrating a phase-locked loop structure used in the present invention;
FIG. 5 is a schematic diagram of an active current and reactive current command calculation module provided by the present invention;
FIG. 6 is a schematic diagram of a classic two-zone four-machine system;
FIG. 7 is a comparison of reactive current commands obtained by the current limiting control method of the present invention and the classical control method;
FIG. 8 is a comparison graph of fan terminal voltage amplitudes under a current limiting control method and a classical control method provided by the present invention;
FIG. 9 is a graph comparing the fan terminal voltage frequency response in the current limiting control method of the present invention with that in the classical control method;
FIG. 10 is a graph comparing the voltage amplitude of the load terminal in the current limiting control method of the present invention with the voltage amplitude of the load terminal in the classical control method;
fig. 11 is a comparison graph of the voltage frequency response of the load terminal under the current limiting control method provided by the present invention and the classical control method.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
21-Park converter, 22-PI controller and 23-integrator.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention relates to a demand of a power system taking new energy power generation as a main body for supporting the dynamic state of the voltage frequency and the amplitude of a power grid during the fault period of the new energy power generation and the defect of the existing transient current limiting control method.
As shown in fig. 1, the present invention provides a transient current limiting method and system for implementing amplitude-frequency joint control based on virtual magnetic flux, including:
s1, calculating to obtain terminal voltage virtual magnetic flux T of grid-connected side of new energy equipment (fan, photovoltaic and the like), wherein T is Vt/ωt，VtAnd ωtAmplitude and frequency of terminal voltage respectively;
wherein, the amplitude V of the voltage at the grid-connected side end is obtained by the measurement of the voltage vector measurement module and the phase-locked loop module respectivelytAnd frequency ω of grid-connected side-end voltaget。
S2 virtual magnetic flux V based on the terminal voltaget/ωtAnd the total current I limited on the filter inductor when the power grid of the new energy equipment failsgDesigning an internal potential virtual magnetic flux T ', wherein T' ═ E/ω, and E and ω are respectivelyThe magnitude and frequency of the internal potential;
s3, virtual magnetic flux E/omega based on the internal potential and terminal voltage virtual magnetic flux Vt/ωtWith the total current magnitude I limited on the filter inductancegThe active current instruction I at the grid-connected end is obtained by fractional integration for constraint relationgdAnd a reactive current command IgqAnd the coordination distribution of active current and reactive current in the transient current limiting process is realized. The active current instruction I obtained by the inventiongdAnd a reactive current command IgqRespectively as follows:
Figure BDA0003418230450000061
the quotient of the voltage amplitude and the frequency is defined as the virtual magnetic flux at the position, the quotient can be used for representing the combined change of the voltage amplitude and the frequency, and the voltage amplitude and the frequency are jointly controlled by the method.
In the actual dynamic process, the amplitude and the frequency of the voltage at each point of the grid-connected side end are changed instantaneously. In order to represent the combined change of the voltage amplitude and the frequency and carry out the combined control on the voltage amplitude and the frequency, the quotient of the voltage amplitude and the frequency is defined as the virtual magnetic flux at the position by taking the relation between the magnetic flux and the voltage amplitude and the rotating speed in the speed regulation of the motor as reference. Thus, the change in virtual flux actually reflects the combined dynamics of voltage amplitude and frequency. Meanwhile, the joint coordination control of the amplitude and the frequency of the internal potential can also be realized through the control of virtual magnetic flux of the internal potential. Thus, the virtual flux is a direct design object of the transient current limiting control.
As shown in fig. 2, in this embodiment, a full-power fan grid-side converter circuit is taken as an example, three-phase instantaneous voltage at a grid-connected point is measured and input to a voltage vector measurement module, so as to calculate a terminal voltage vector amplitude VtAnd measuring terminal voltage frequency omega at grid-connected point by using phase-locked loop moduletThereby obtaining a virtual magnetic flux V of the terminal voltaget/ωt(ii) a The circuit filter inductance can be regarded as a constant, and the transient current limiting control and the device energy can be realized in the case of power grid faultsForce specification, given the total current I flowing through the filter inductorgThen, through the final active current and reactive current commands obtained by the algorithm of the invention, the active current and reactive current commands are determined by the virtual magnetic flux E/ω of the internal potential. Therefore, the virtual magnetic flux becomes an index for determining the coordinated distribution of the active current and the reactive current in the transient process. The internal potential virtual magnetic flux is designed based on the constraint relation of the virtual magnetic flux change of the total current and the terminal voltage, different values of the internal potential virtual magnetic flux can be given according to the state of the power grid, and the command values of the active current and the reactive current are further determined in a coordinated mode.
Specifically, in step S1, the amplitude V of the grid-connected side voltage is measured by the voltage vector measurement module and the phase-locked loop module respectivelytAnd frequency ω of grid-connected side-end voltaget。
The voltage vector measurement module calculates the amplitude V of the grid-connected side end voltage through vector synthesist(i.e., the magnitude of the grid-side end voltage rotation vector). As shown in fig. 3, the amplitude V of the grid-connected side-end voltagetComprises the following steps:
Figure BDA0003418230450000071
wherein v ista、vtb、vtcThree-phase instantaneous voltages (A-phase instantaneous voltage, B-phase instantaneous voltage and C-phase instantaneous voltage) on the grid-connected side are respectively provided.
In this embodiment, the voltage vector is projected and calculated to synthesize the magnitude of the voltage rotation vector by taking the voltage rotation vector as an example in a three-phase stationary ABC coordinate system. In other embodiments, the amplitude of the grid-connected side end voltage may also be calculated by projection using a two-phase stationary α β coordinate system, a synchronous rotation dq coordinate system, or the like.
As shown in fig. 4, the frequency ω of the grid-connected side end voltage is measured by the phase-locked loop modulet. The phase-locked loop in this embodiment includes: a Park converter 21, a PI controller 22, and an integrator 23. The phase-locked loop realizes stator voltage orientation, and the input of the phase-locked loop is three-phase electricity at a grid-connected pointPressure (v)ta、vtb、vtc) The output is the d, q axis voltage components that characterize the port voltage vector magnitude and phase changes being tracked (noted:
Figure BDA0003418230450000081
Figure BDA0003418230450000082
). The transformation relation between the three-phase stationary coordinate system and the rotating dq coordinate system is shown in formula (2). Wherein theta ispRotating the phase of the dq coordinate system for a phase locked loop, C3s/2rIndicating that the three-phase stationary coordinate system is converted to the rotating dq coordinate system.
Figure BDA0003418230450000083
Wherein,
Figure BDA0003418230450000084
suppose that the three-phase voltages are respectively:
Figure BDA0003418230450000085
wherein, VsThe amplitude of the three-phase voltage, θ is the phase of the a-phase voltage, and γ is the phase error.
Then the components under the rotating dq coordinate system can be obtained by equation (2) as follows:
Figure BDA0003418230450000086
when theta ispWhen θ + γ, it is apparent that V issq0. Then theta is at this timepIs equal to the phase of the terminal voltage vector, and is corresponding
Figure BDA0003418230450000087
The voltage amplitude is represented. Thus, use is made ofThe resulting phase locked loop is constructed in principle. As shown in (3), the first step is,
Figure BDA0003418230450000088
the signal takes tracking the amplitude of the power grid as a target;
Figure BDA0003418230450000089
the signal takes tracking of the phase of the power grid as a target, the phase of the terminal voltage space rotation vector can be obtained through the PI controller and the integrator and fed back to the Park converter 11, and therefore tracking of the phase of the power grid is achieved. Based on the analysis of the phase-locked loop module, the electric quantity obtained by the PI controller through the q-axis component of the voltage vector output from the Park converter is the terminal voltage frequency value omega in the virtual magnetic flux of the required terminal voltaget。
According to the specific requirements of transient current limiting control and device capacity in the power grid fault, the limited total current I is givengThen, given the values of the virtual magnetic flux of the different internal potentials, the command values for the active and reactive currents can be determined in a coordinated manner.
Specifically, as shown in fig. 5, in step S3, the active current and reactive current command algorithm provided by the present invention is as follows:
virtual magnetic flux E/omega at internal potential and total current IgFilter inductance value LfTerminal voltage virtual magnetic flux Vt/ωtFor input, the active current and reactive current commands are obtained by a fractional integration method based on the constraint relation of the current on the filter inductor, and in other embodiments, the active current and reactive current commands can be calculated based on the constraint relation in other manners. In this embodiment, the mode of obtaining the active current and reactive current commands through fractional integration is specifically as follows:
inner potential vector E and terminal voltage vector VtCan be respectively expressed as:
Figure BDA0003418230450000091
Figure BDA0003418230450000092
wherein E and VtAmplitude of the internal potential and terminal voltage, omega and omega respectivelytFrequency of internal potential and terminal voltage, theta0And thetat0Are the initial phases of the internal potential and terminal voltage, respectively. According to the original relation between the current on the filter inductor and the voltage at two ends, the filter inductor (the inductance value is L)f) Current I flowing upwardsgComprises the following steps:
Figure BDA0003418230450000093
the integration is difficult to find for any time-varying frequency and amplitude, as shown in fig. 2 for the positive current direction. The invention can obtain the following results by performing fractional integration on the data:
Figure BDA0003418230450000101
in the above equation, it can be seen that the current obtained from the fractional integration is infinite. And under the time scale of the given current reactive current and active current instruction, for the analysis of the electromechanical dynamic stability problem of the power system (such as low-frequency oscillation of the power system), although the component related to the change rate of the amplitude/frequency and the higher derivative thereof is not 0, the influence is usually small, and the faster scale dynamic state, namely the current I is negligiblegIt can be simplified to consider only the first term current component in equation (7), which is expressed as follows:
Figure BDA0003418230450000102
equation (8) is further written when terminal voltage orientation is assumed:
Figure BDA0003418230450000103
wherein, ω isIAnd thetaI0Respectively representing the frequency and initial phase, I, of the current in the filter inductorgIs the magnitude of the current on the filter inductor (i.e. the total current flowing through the filter inductor in the event of a power grid fault). At this time, the active current command I can be obtainedgdAnd a reactive current command IgqRespectively as follows:
Figure BDA0003418230450000104
Figure BDA0003418230450000105
wherein:
Igd＝Igcos(∫(ωI-ωt)dt+θI0-θt0)
Igq＝Igsin(∫(ωI-ωt)dt+θI0-θt0)
Ed＝Ecos(∫(ω-ωt)dt+θ0-θt0)
Eq＝Esin(∫(ω-ωt)dt+θ0-θt0)
Igand E represent the magnitude of the total current and the magnitude of the internal potential, respectively.
Simplifying the formula (10) and the formula (11) simultaneously to obtain
Figure BDA0003418230450000111
The formula (12) reflects the basic relationship between the potential virtual magnetic flux and the terminal voltage virtual magnetic flux in the full-power fan and the active current and the reactive current in the dynamic process. At this time, the active current and reactive current commands may be further expressed as:
Figure BDA0003418230450000112
Figure BDA0003418230450000113
thus, the active current instruction and the reactive current instruction provided by the invention are obtained.
As can be seen from equations (13) and (14), the active current command and the reactive current command are functions of the internal potential virtual flux, the terminal voltage virtual flux, the filter inductance, and the total current amplitude. Since the virtual magnetic flux of the terminal voltage is measured by the voltage vector measuring module and the phase-locked loop module, the filter inductance can be regarded as a constant, and after the total current is given, the active current command and the reactive current command are determined by the virtual magnetic flux of the internal potential. After the virtual magnetic flux of the internal potential is given, the active current and the reactive current are uniquely determined. Therefore, the virtual magnetic flux becomes an index for determining the coordinated distribution of the active current and the reactive current in the transient process. According to the state of the power grid, given different values of the virtual magnetic flux of the internal potential, command values of active current and reactive current are determined in a coordinated mode.
It should be noted that, in the practical application process, if terminal voltage amplitude information at a grid-connected point needs to be measured for a specific new energy device, a required signal can be acquired by combining the specific control of the device to reduce the use of measuring elements, and the required measurement information can be acquired by combining the signal in the control of the specific device, which are the same in principle and do not hinder the application of the patent.
The following specifically describes the method of designing the internal potential virtual magnetic flux, i.e., the internal potential virtual magnetic flux E/ω in step S2.
As can be seen from equations (13) and (14), the current command values (command values of the active current and the reactive current) during the fault are determined by the internal potential virtual magnetic flux. However, the command value of the internal potential virtual magnetic flux cannot be arbitrarily taken. During a fault, an internal potential virtual flux that is too large or too small will cause the active reactive current determined by equations (13) and (14) to exceed the maximum current. Therefore, a selection range of the internal potential virtual magnetic flux needs to be determined. For reactive current there are:
-Imax≤Igq≤Imax (15)
then, it can be known from equation (14) that the virtual flux range of the internal potential should be:
Figure BDA0003418230450000121
wherein, ImaxIs the set maximum current value on the filter inductor.
It should be noted that the active current is obtained by subtracting the respective squares of the actual total current and the reactive current and then squaring, so that the active current command certainly meets the total current limit after the reactive current command meets the total current limit.
Therefore, under the condition that the constraint of the formula (16) is satisfied, the virtual magnetic flux of the internal potential is designed based on the virtual magnetic flux change of the terminal voltage, wherein the virtual magnetic flux of the internal potential is as follows:
Figure BDA0003418230450000122
and K is more than 0, inductive reactive current is output in the transient state period, A is a virtual magnetic flux control parameter, and the significance of A is that the virtual magnetic flux of the terminal voltage is compared with that of the terminal voltage, and when the virtual magnetic flux of the terminal voltage is lower, the difference value of the corresponding internal potential virtual magnetic flux and the virtual magnetic flux of the terminal voltage is larger. The amplitude and frequency joint dynamic state of the electric potential in the fan can be correspondingly adjusted according to the terminal voltage amplitude and frequency joint dynamic state. The constant c can be guaranteed to be at Vt/ωtWhen 1 is 0.9gqref0, wherein, IgqrefIs a Vt/ωtWhen the value is 0.9, the reactive current command value is obtained.
Specifically, when K (A-V)t/ωt)≤1-c/(LfImax) When formula (17) is brought into formula (13), V can be obtainedt/ωtReactive current command value I of 0.9gqrefAt this time, a filtering current flowsTotal current magnitude of inductor IgIs equal to the maximum current value Imax. After obtaining the reactive current command value, V is calculated by the formula (13)t/ωtActive current command value I when equal to 0.9gdref。
When K (A-V)t/ωt)＞1-c/(LfImax) At this time Vt/ωtReactive current command I at 0.9gqref＝-Imax，Vt/ωtThe active current command at 0.9 is 0.
To further illustrate the application of the present invention, the following provides a method of the present invention applied to a two-zone four-machine system, comparing the conventional classical reactive power priority transient current limiting control method with the transient current limiting control method based on virtual magnetic flux provided by the present invention through simulation, and now detailed below with reference to the accompanying drawings:
as shown in fig. 6, the schematic diagram of a classical two-zone four-machine system structure is to embody the main characteristics of new energy power generation, wherein G1 and G2 in the end region of the power transmission zone are full power fans, and G3 and G4 are synchronous generators. Setting a fault scene as follows: three-phase grounding short circuit faults occur in the No. 7 bus and the No. 8 bus single-circuit wire, the short-circuit resistance is 13 omega, and the grounding resistance is 0.1 omega. And the fault line is cut off after 0.17s of fault occurrence. Compared with the traditional classical reactive power priority transient current limiting control method and the transient current limiting control method based on virtual magnetic flux provided by the invention, the simulation is carried out. In the method provided by the invention, the value of K of the internal potential virtual magnetic flux is 3. To illustrate the supporting characteristics of the system voltage amplitude and frequency, the gain K of the conventional transient current limiting strategy is selectedvIs 3.6. Assuming that the terminal voltage frequency is constant, the reactive current output characteristics of both are as shown in fig. 7. It can be seen that the reactive current output characteristics of the two methods are relatively close under the assumption that the terminal voltage frequency is constant.
The simulation results are shown in fig. 8 to 11. Wherein fig. 8 and 9 are the voltage amplitude versus frequency variation at the G2 fan, and fig. 10 and 11 are the voltage amplitude versus frequency variation at the load node No. 7. It can be seen that there is a large variation in the instantaneous frequency of the grid voltage after a fault has occurred and after the fault has been removed, due to the lack of a synchronous generator in the send end region. After the fault occurs, the voltage drops rapidly, and the controller enters current-limiting transient current-limiting control after experiencing detection delay. It can be seen that both methods provide reactive injection to increase the level of voltage droop. Compared with the classical priority reactive current injection method, the method provided by the invention has obvious inhibition effect on the fluctuation of the frequency. After the fault occurs, the frequency deviation can be obviously reduced, and the frequency variation trend is smoother. The design method of the internal potential virtual magnetic flux provided by the invention enables the output reactive power to be smaller than that of a classical priority reactive current injection method, so that the voltage amplitude of the terminal voltage of the fan or the voltage amplitude of the load side is slightly lower, but the change of the overall voltage amplitude of the method provided by the invention is smoother.
Some time after the fault has been removed, the voltage in the classical control method does not return to the normal level immediately, but remains within a certain low voltage range. In this case, the method provided by the invention can obviously inhibit the fluctuation of the frequency. Because the load is subjected to the dynamic coupling effect of the voltage amplitude and the frequency, in the method provided by the invention, the amplitude voltage finally returns to the level before the fault, and the voltage of the classical priority reactive current injection method cannot be restored to the level before the fault. Simulation shows that under the constraint of limited capacity, the transient current-limiting control method based on the virtual magnetic flux can provide better combined support effect on the voltage amplitude and frequency change of the power grid.
The simulation shows that compared with the traditional method, the method can better support the voltage and the frequency of the power grid under the condition of lacking the synchronous generator.
Based on the transient current limiting method, the invention also provides a transient current limiting system for realizing amplitude-frequency combined control based on virtual magnetic flux, which comprises the following modules:
the terminal voltage virtual magnetic flux calculation module is used for calculating and obtaining a terminal voltage virtual magnetic flux T on the grid-connected side of the new energy equipment, wherein T is Vt/ωt，VtAnd ωtAmplitude and frequency of terminal voltage respectively;
an internal potential virtual flux design module, configured to obtain an internal potential virtual flux T ', where T' ═ E/ω, and E and ω are an amplitude and a frequency of the internal potential, respectively;
a current command design module for designing a current command based on the internal potential virtual flux E/omega and the terminal voltage virtual flux Vt/ωtThe total current I limited on the filter inductor is given when the new energy equipment power grid failsgObtaining an active current instruction I at the grid-connected side end for constraint relationgdAnd a reactive current command IgqAnd the coordination distribution of active current and reactive current in the transient current limiting process is realized.
Wherein the active current command IgdAnd a reactive current command IgqRespectively as follows:
Figure BDA0003418230450000151
Figure BDA0003418230450000152
the internal potential virtual magnetic flux E/omega satisfies the following constraint condition:
Figure BDA0003418230450000153
wherein, ImaxIs the set maximum current value on the filter inductor.
The internal potential virtual magnetic flux E/omega is as follows:
Figure BDA0003418230450000154
wherein K, c is a constant, and K > 0, and A is a virtual flux control parameter.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A transient current limiting method for realizing amplitude-frequency combined control based on virtual magnetic flux is characterized by comprising the following steps:
s1, calculating to obtain terminal voltage virtual magnetic flux T on the grid-connected side of the new energy equipment, wherein T is Vt/ωt，VtAnd ωtThe amplitude and the frequency of the terminal voltage are respectively;
s2, designing an internal potential virtual magnetic flux T ', wherein T' ═ E/omega, and E and omega are the amplitude and the frequency of the internal potential respectively;
s3, based on the internal potential virtual magnetic flux E/omega and the terminal voltage virtual magnetic flux Vt/ωtSetting the total current I limited on the filter inductor when the new energy equipment is in power grid faultgObtaining an active current instruction I at the grid-connected side end for constraint relationgdAnd a reactive current command IgqAnd the coordination distribution of active current and reactive current in the transient current limiting process is realized.
2. The transient current limiting method of claim 1 wherein the active current command I is obtained by fractional integrationgdAnd a reactive current command Igq。
3. The transient current limiting method of claim 2 wherein the active current command I isgdAnd a reactive current command IgqRespectively as follows:
Figure FDA0003418230440000011
Figure FDA0003418230440000012
wherein L isfIs the inductance value of the filter inductor.
4. The transient current limiting method of claim 3, wherein the internal potential virtual flux satisfies the following constraints:
Figure FDA0003418230440000013
wherein, ImaxIs the set maximum current value on the filter inductor.
5. The transient current limiting method of claim 4, wherein the internal potential virtual flux is:
Figure FDA0003418230440000021
wherein K, c is a constant, and K > 0, and A is a virtual flux control parameter.
6. The method of claim 5, wherein the magnitude V of the terminal voltage is calculated by vector synthesist。
7. The method of claim 6, wherein the magnitude V of the terminal voltage is greater than or equal to VtComprises the following steps:
Figure FDA0003418230440000022
wherein v ista、vtb、vtcRespectively is three-phase instantaneous voltage at the grid-connected side.
8. The method of claim 5, wherein the frequency ω of the terminal voltage is measured by a phase-locked loopt。
9. A transient current limiting system for realizing amplitude-frequency combined control based on virtual magnetic flux is characterized by comprising the following modules:
the terminal voltage virtual magnetic flux calculation module is used for calculating and obtaining a terminal voltage virtual magnetic flux T on the grid-connected side of the new energy equipment, wherein T is Vt/ωt，VtAnd ωtThe amplitude and the frequency of the terminal voltage are respectively;
an internal potential virtual flux design module for obtaining an internal potential virtual flux T ', wherein T' ═ E/ω, and E and ω are the amplitude and frequency of the internal potential, respectively;
a current command design module for designing a current command based on the internal potential virtual magnetic flux E/omega and the terminal voltage virtual magnetic flux Vt/ωtSetting the total current I limited on the filter inductor when the new energy equipment is in power grid faultgObtaining an active current instruction I at the grid-connected side end for constraint relationgdAnd a reactive current command IgqAnd the coordination distribution of active current and reactive current in the transient current limiting process is realized.
10. The transient current limiting system of claim 9 wherein the active current command IgdAnd a reactive current command IgqRespectively as follows:
Figure FDA0003418230440000031
Figure FDA0003418230440000032
wherein L isfIs the inductance value of the filter inductor.
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* Cited by examiner, † Cited by third party
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CN110350551A (en) * 2019-06-11 2019-10-18 华中科技大学 A kind of direct amplitude-frequency control method and system of grid-connected converting means electric current of voltage-source type

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