CN114709828A - New energy converter power filtering method based on VMD-moving average filtering - Google Patents
New energy converter power filtering method based on VMD-moving average filtering Download PDFInfo
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- H—ELECTRICITY
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses a VMD-sliding average filtering-based new energy converter power filtering method, which belongs to the field of grid-connected converter control. The invention effectively inhibits the influence of the broadband harmonic waves on the system and improves the stability of the system under the system operation condition of the multi-time scale broadband oscillation characteristic of the new energy converter.
Description
Technical Field
The invention belongs to the field of grid-connected converter control, and particularly relates to a new energy converter power filtering method based on VMD-moving average filtering.
Background
With the rapid development of large-scale new energy power generation and high-voltage direct-current transmission, the power grid presents a weak power grid characterized by low inertia and short-circuit ratio. The traditional current control type new energy grid-connected converter adopts a direct current control strategy decoupled from the power grid frequency, a current control instruction is generated by tracking control of the maximum power point of an outer ring, the equivalent rotary inertia is small, frequency and voltage support cannot be provided for a system, the grid-related capacity is insufficient, and the problems of shutdown and grid disconnection are caused easily. The voltage control type new energy converter can simulate the primary frequency modulation, the voltage regulation characteristic and the virtual inertia of the synchronous generator through a control algorithm, can provide frequency and voltage support for a high-permeability new energy power generation system so as to improve the stability of the new energy converter and a grid-connected system thereof, and has wide theoretical research and engineering application prospects.
The access of a large number of new energy converters enables the system to present a multi-time scale broadband oscillation characteristic, and brings a serious challenge to the stable and high-efficiency operation of a new energy grid-connected power generation system, in order to effectively attenuate broadband harmonics generated in instantaneous power when the system with the multi-time scale broadband oscillation characteristic operates, and effectively prevent the output voltage quality and the control performance of the new energy converter from being influenced by the broadband harmonics of the system, a first-order low-pass filter is adopted, the cut-off frequency of the filter is generally designed to be within 1/10 of power frequency or twice of the power frequency, however, for the broadband oscillation system having broadband components from several hertz to thousands of hertz, in order to filter low-frequency harmonics, the cut-off frequency of the first-order low-pass filter needs to be further reduced, but the lower filter cut-off frequency reduces the response speed of the output power, power overshoot may be induced and even system oscillation instability may result. Therefore, in order to improve the operation stability of the voltage control type new energy converter under broadband oscillation and the grid-connected system thereof, the optimization of instantaneous power filtering in the converter control algorithm is very necessary.
At present, for the problem of harmonic components caused when the new energy converter outputs instantaneous active and reactive power, a scholars analyzes and proposes a solution, for example:
1. the problem is that the average value of instantaneous power in a half power frequency period is used for modeling in the literature ("modeling and parameter design of a virtual synchronous generator power ring", Wuheng, Runxingfeng, Lushipeng, etc. "(Chinese electro-mechanical engineering journal, 2015 volume 35, 24 th period 6508-page 6518) and the influence of VSG control parameters on a model is analyzed in detail based on the established model to indicate the influence of the change of rotational inertia J on the stability and the dynamic performance of active power and the influence of the change of inertia coefficient K on the stability and the dynamic performance of reactive power, and a method for designing the VSG control parameters according to the requirements of system cutoff frequency and phase angle can quickly and accurately calculate corresponding control parameters is provided, but the method has the following defects: the system under multi-time scale broadband oscillation has multi-modal and time-varying characteristics, and relates to the global complex problem of multi-electrical equipment.
2. The title "A Practical Secondary Frequency Control Strategy for Virtual Synchronous generators", Su H, Lin H, et al, IEEE Transactions on Smart Grid ", vol.11, No.3, pp.2734-2736, May 2020" ("a Practical Secondary Frequency Control Strategy for Virtual Synchronous generators", "IEEE institute of Electrical and electronics systems", 2020 No. 11, 11 th volume, 11 rd volume, 3 rd page 3 2734 and 2736) and (three-phase converter Small-Signal modeling and analysis of Virtual Synchronous Generator characteristics ", face Wu, Liu Zheng Man, Xuzheng, Suzhou, Nippon, Zhang, North China electric Power university (Nature science edition), 2016, 43 rd volume, 3 rd pages 1-8) establish a single VSG with inductive load, and analyze the small signal with respect to the impedance of a plurality of parameters including the low-pass characteristic and the low-pass characteristic of a system, however, the method has the following defects: the influence rule and the optimization method of the first-order low-pass filter on the system characteristics are not further analyzed.
In summary, in the prior art, the following problems also exist:
1. for a system under multi-time scale broadband oscillation, the harmonic frequency range is wide, and subsynchronous harmonic components generated by the system cannot be economically and effectively filtered in the prior art;
2. the instantaneous power filtering of the converter output mainly adopts a first-order low-pass filter, and if the first-order low-pass filter is used for filtering sub-synchronous harmonic components in a system, the cut-off frequency needs to be reduced, and the response speed of the output power can be reduced by the lower cut-off frequency;
disclosure of Invention
The invention aims to solve the problem of broadband harmonic optimization of instantaneous active power and instantaneous reactive power output in a new energy converter control algorithm based on droop control or virtual synchronous generator control in a high-permeability new energy grid-connected power generation system, and provides a new energy converter power filtering method based on VMD-sliding average filtering, so that the influence of system broadband harmonic on the output voltage quality and control performance of a new energy converter is effectively avoided, and the stability of the converter and a grid-connected system thereof is improved.
In order to achieve the purpose, the invention provides a new energy converter power filtering method based on VMD-moving average filtering, which comprises the following steps:
the calculation formulas of the instantaneous active power P and the instantaneous reactive power Q output by the converter are respectively as follows:
Firstly, constructing a constraint variation problem of instantaneous active power P and a constraint variation problem of instantaneous reactive power Q, wherein expressions of the constraint variation problems are respectively as follows:
wherein, { PβK is the number of resolved modal components, P is the set of K modal components resolved by the instantaneous active power P, β 1,2βThe beta-th modal component decomposed for the instantaneous active power P is recorded as the active power modal component Pβ;{QβIs the set of K modal components of the instantaneous reactive power Q decomposition, QβThe beta-th modal component of the instantaneous reactive power Q decomposition is recorded as the reactive power modal component Qβ;{ωpβThe central frequency is a set of central frequencies corresponding to K modal components of instantaneous active power P decomposition, { omega }qβThe central frequency set corresponding to K modal components of the instantaneous reactive power Q decomposition is adopted, t is time, delta (t) is a Dirac function, the symbol is a convolution operator, pi is a circumferential rate, j is an imaginary number unit,to partially derivative the function with respect to time t,is a two-norm square operation, Pβ(t) is the active power modal component PβActive power, Q, corresponding to time tβ(t) is the reactive power modal component QβCorresponding reactive power at the time t; omegapβIs an active power modal component PβCorresponding center frequency, ωqβAs reactive power modal component QβA corresponding center frequency;
secondly, solving the constraint variation problem of the constructed instantaneous active power P to obtain K modal components of the instantaneous active power P decomposition, and recording the minimum frequency value of the K modal components of the instantaneous active power P decomposition as a characteristic active modal component
Solving the constraint variation problem of the constructed instantaneous reactive power Q to obtain K modal components of the instantaneous reactive power Q decomposition, and recording the one with the minimum frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive modal component
Step 4, the characteristic active mode obtained in the step 3 is processedAnd characteristic reactive modeUsing a moving average filtering algorithmProcessing to obtain active DC componentAnd a reactive DC componentThe method comprises the following specific steps:
setting the width of a window to be N;
characteristic active modeSliding storage is carried out on the window in a unit control period, and then the characteristic active mode in the windowThe number of the numerical value is N, and the characteristic active mode of the window is recordedHas an ith value ofCharacteristic active modeN values ofPerforming arithmetic average to obtain active DC component
Characteristic reactive modeSliding storage is carried out on the window in a unit control period, and then the characteristic reactive mode in the windowThe number of the numerical values is N, andcharacteristic reactive mode of the windowHas a j value ofCharacteristic reactive modeN values ofCarrying out arithmetic average to obtain reactive direct current component
where ω is a converter frequency command obtained by droop control, EdFor d-axis voltage closed-loop commands obtained by droop control, omega*For the frequency of the power frequency of the converter, E*M is the active power droop coefficient of the converter, r is the reactive power droop coefficient of the converter, P is the rated voltage of the converter in no-loadNRated active power, Q, for the output of the converterNRated reactive power is output for the converter;
Make q axle voltage closed loop instruction Eq=0;
D-axis voltage closed-loop instruction E obtained through droop controldAnd the d-axis component E of the output voltageodObtaining the inductive current I of the d-axis bridge arm of the converter through the voltage closed-loop control of the d-axisldr(ii) a Closed-loop command E of q-axis voltageqAnd the converter output voltage q-axis component EoqObtaining the inductive current I of a q-axis bridge arm of the converter through the voltage closed-loop control of a q-axislqrThe d-axis voltage closed-loop control equation and the q-axis voltage control equation are respectively as follows:
wherein, KpvAs a voltage closed-loop proportional regulator coefficient, KiIs a voltage closed loop integral regulator coefficient;
the d-axis bridge arm of the converter induces current IldrD-axis component I of bridge arm inductance currentldObtaining an output signal E of a d-axis of the converter through d-axis bridge arm inductance current closed-loop controldi(ii) a Inducing current I to q-axis bridge arm of converterlqrQ-axis component I of bridge arm inductive currentlqObtaining an output signal E of a q axis of the converter through q axis bridge arm inductance current closed-loop controlqiThe d-axis bridge arm inductance current closed-loop control equation and the q-axis bridge arm inductance current control equation are respectively as follows:
Edi=(Ildr-ILd)Kpi
Eqi=(Ilqr-ILq)Kpi
wherein, KpiClosed-loop proportional adjustment coefficients of the inductive current of a bridge arm of the converter;
Emdi=Ed+Edi
Emqi=Eq+Eqi
modulating wave E under dq coordinate systemmdi,EmqiObtaining a modulation wave E under an alpha beta coordinate system through Park inverse transformationmαi,EmβiThen, the modulated wave E under the alpha beta coordinate system is usedmαi,EmβiObtaining a three-phase modulation wave E under an abc coordinate system through Clarke inverse transformationmai,Embi,EmciThe three-phase modulated wave Emai,Embi,EmciAnd the signal is used as a driving signal of the IGBT circuit after being modulated by the SPWM.
Preferably, the solving of the constrained variational problem constructed by the instantaneous active power P and the solving of the constrained variational problem constructed by the instantaneous reactive power Q in step 3 comprise the following steps:
(1) according to the constructed constraint variation problem, a secondary penalty factor alpha and an active Lagrange multiplication operator lambda are introducedpReactive Lagrange multiplier lambdaqChanging the constructed constraint variation problem into an unconstrained variation problem to obtain an augmented Lagrange expression of the unconstrained variation problem, wherein the augmented Lagrange expression of the instantaneous active power P is expressed as:
in the formula, λp(t) is the active Lagrange multiplier λpA temporal variation of (d); lambda [ alpha ]q(t) is the reactive Lagrange multiplier λqA temporal variation of (d);
(2) by using an alternative direction multiplier method, combining Parseval/Plancherel and Fourier equidistant transformation and alternately updatingFinding out minimum value points of the unconstrained variation problem, and obtaining the minimum value points through the (n + 1) th iteration updateThe detailed process is as follows:
where ω denotes a frequency domain variable, n is any one of C iterations, n is 1,2.. and C, C is the maximum number of iterations,is the instantaneous active power form on the corresponding frequency domain of the instantaneous active power P (t), and is marked as the instantaneous active power of the frequency domainIs the instantaneous reactive power form on the corresponding frequency domain of the instantaneous reactive power Q (t), and is recorded as the instantaneous reactive power form of the frequency domainIs instantaneous active power of frequency domainOf the beta modal component of (a) for the (n + 1) th iteration,is instantaneous reactive in frequency domainIs the (n + 1) th iteration of the beta modal component,andrepresenting frequency domain instantaneous activityOf the z-th modal component and the n-th iteration,andrepresenting frequency domain instantaneous reactive powerOf the ith modal component of (a), z 1,2, K,andis the active Lagrange multiplier lambdap(t) the corresponding n +1 th iteration and the active Lagrange multiplier after the nth iteration on the frequency domain,andis a reactive Lagrange multiplier lambdaq(t) corresponding to the (n + 1) th iteration on the frequency domain and the reactive Lagrange multiplication operator after the nth iteration, wherein tau is noise tolerance;
(3) setting a verification threshold epsilon, wherein epsilon is more than 0;
and carrying out the following judgment of termination iteration on the instantaneous active power P:
if it isAnd n is less than or equal to C, increasing the number of one iterationReturning to the step (2), performing the next iteration updating,
if it isOr n is more than C, stopping iteration, outputting K modal components of the instantaneous active power P decomposition, and taking the K modal components of the instantaneous active power P decomposition with the smallest frequency value as the characteristic active mode
And (3) judging the following termination iteration of the instantaneous reactive power Q:
if it isAnd n is less than or equal to C, increasing the iteration times, returning to the step (2), performing the next iteration update,
if it isOr n is more than C, stopping iteration, outputting K modal components of the instantaneous reactive power Q decomposition, and recording the one with the minimum frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode
Preferably, the modulated wave E in the dq coordinate system in step 7mdi,EmqiObtaining a modulation wave E under an alpha beta coordinate system through Park inverse transformationmαi,EmβiThe Park inverse transformation formula is as follows:
Emαi=Emdi cosθrefi-Emqisinθrefi
Emβi=Emdi sinθrefi+Emqi cosθrefi
wherein, thetarefiFor the converter phase angle command obtained by integrating the converter frequency command omega obtained by droop control, integrating operationThe calculation formula is as follows:
preferably, the modulated wave E in the α β coordinate system in step 7mαi,EmβiObtaining a three-phase modulation wave E under an abc coordinate system through Clarke inverse transformationmai,Embi,EmciThe Clarke inverse transformation formula is as follows:
Emai=Emαi
compared with the existing method adopting a first-order low-pass filter or a wave trap, the new energy converter power filtering method based on VMD-moving average filtering has the beneficial effects that:
1. the power filtering method has good processing effect on non-stationary and non-linear signals, and is a non-recursive modal variation and signal processing method;
2. the power filtering method eliminates the reduction of the output power response speed of the system caused by lower filtering cut-off frequency and the insufficiency of the dynamic characteristic of the converter;
3. the power filtering method adopts the moving average algorithm to filter the power output by the VMD decomposition, has good inhibiting effect on periodic interference, has high smoothness, is suitable for a high-frequency oscillation system, and is simple to design and implement.
Drawings
Fig. 1 is a block diagram of a control structure of a new energy converter.
Fig. 2 is an instantaneous active power waveform output by the new energy converter in a state of containing subsynchronous harmonic components and not being filtered.
Fig. 3 is an instantaneous active power waveform output by the new energy converter after being filtered by a first-order low-pass filter.
Fig. 4 shows an instantaneous active power waveform output by the new energy converter after VMD-moving average filtering.
Detailed Description
The present embodiment will be described in detail below with reference to the accompanying drawings.
In this embodiment, the bridge arm filter inductance of the new energy converter is L, and the bridge arm inductance current flowing through the bridge arm filter inductance is Ila,IlbFilter capacitance of CiThe phase voltage at the end of the filter capacitor is Eoa,EobThe line impedance between the output end of the converter and the PCC point is Zl. The specific parameters are as follows: the DC voltage is 600V, the rated output line voltage is 400V/50Hz, the bridge arm filter inductance value L is 0.5mH, and the filter capacitance value CiIs 90uF, line impedance Zl0.001+ j1.25 Ω, and a rated capacity of 100 KVar.
Fig. 1 is a control structure block diagram of the power filtering method of the new energy converter, and it can be seen from the diagram that the steps of the power filtering method of the invention are as follows:
Output voltage dq axis component Eod,EoqThe synchronous rotation coordinate transformation formula is as follows:
Eoα=-Eob
bridge arm inductive current dq axis component Ild,IlqThe synchronous rotation coordinate transformation formula is as follows:
Ilα=-Ilb
wherein, thetarefi-1The converter phase angle command for the previous calculation cycle.
The calculation formulas of the instantaneous active power P and the instantaneous reactive power Q output by the converter are respectively as follows:
Firstly, constructing a constraint variation problem of instantaneous active power P and a constraint variation problem of instantaneous reactive power Q, wherein expressions of the constraint variation problems are respectively as follows:
wherein, { PβK is the number of resolved modal components, P, K is the set of K modal components resolved by the instantaneous active power P, β 1,2βThe beta-th modal component decomposed for the instantaneous active power P is recorded as the active power modal component Pβ;{QβIs the set of K modal components of the instantaneous reactive power Q decomposition, QβThe beta-th modal component of the instantaneous reactive power Q decomposition is recorded as the reactive power modal component Qβ;{ωpβThe central frequency is a set of central frequencies corresponding to K modal components of instantaneous active power P decomposition, { omega }qβThe central frequency corresponding to K modal components of the instantaneous reactive power Q decomposition is set, t is time, delta (t) is a Dirac function, a symbol is a convolution operator, pi is a circumferential rate, j is an imaginary number unit,to partially derive the function over time t,is a two-norm square operation, Pβ(t) is the active power modal component PβActive power, Q, corresponding to time tβ(t) is the reactive power modal component QβCorresponding reactive power at the time t; omegapβIs an active power modal component PβCorresponding center frequency, ωqβAs reactive power modal component QβThe corresponding center frequency.
Secondly, solving the constraint variation of the constructed instantaneous active power PThe problem is that K modal components of instantaneous active power P decomposition are obtained, and one of the K modal components of the instantaneous active power P decomposition with the smallest frequency value is recorded as a characteristic active mode
Solving the constraint variation problem of the constructed instantaneous reactive power Q to obtain K modal components of the instantaneous reactive power Q decomposition, and recording the one with the minimum frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive modal component
Specifically, solving the constructed constraint variation problem of the instantaneous active power P and solving the constructed constraint variation problem of the instantaneous reactive power Q comprises the following steps:
(1) according to the constructed constraint variation problem, a secondary penalty factor alpha and an active Lagrange multiplication operator lambda are introducedpReactive Lagrange multiplier lambdaqChanging the constructed constraint variation problem into an unconstrained variation problem to obtain an augmented Lagrange expression of the unconstrained variation problem, wherein the augmented Lagrange expression of the instantaneous active power P is expressed as:
in the formula, λp(t) is the active Lagrange multiplier λpA temporal variation of (d); lambda [ alpha ]q(t) is the reactive Lagrange multiplier λqTime of change in time.
(2) By using an alternative direction multiplier method, combining Parseval/Plancherel and Fourier equidistant transformation and alternately updatingFinding out minimum value points of the unconstrained variation problem, and obtaining the minimum value points through the (n + 1) th iteration updateThe detailed process is as follows:
where ω denotes a frequency domain variable, n is any one of C iterations, n is 1,2.. and C, C is the maximum number of iterations,is the instantaneous active power form on the corresponding frequency domain of the instantaneous active power P (t), and is marked as the frequency domain instantaneous active powerIs the instantaneous reactive power form on the corresponding frequency domain of the instantaneous reactive power Q (t), and is recorded as the instantaneous reactive power form of the frequency domainIs instantaneous active power of frequency domainIs the (n + 1) th iteration of the beta modal component,is instantaneous reactive in frequency domainIs the (n + 1) th iteration of the beta modal component,andrepresenting frequency domain instantaneous activityThe (n + 1) th iteration and the (n) th iteration of the z-th modal component,andrepresenting frequency domain instantaneous reactive powerThe (n + 1) th and nth iterations of the z-th modal component of (a), z being 1,2, K,andis the active Lagrange multiplier lambdap(t) the corresponding n +1 th iteration and the active Lagrange multiplier after the nth iteration on the frequency domain,andis a reactive Lagrange multiplier lambdaq(t) the corresponding reactive Lagrange multiplication operators of the (n + 1) th iteration and the nth iteration on the frequency domain, wherein tau is the noise tolerance.
(3) Setting epsilon as a verification threshold, wherein epsilon is more than 0;
and (3) judging the following termination iteration for the instantaneous active power P:
if it isAnd n is less than or equal to C, increasing the iteration times, returning to the step (2) for next iteration updating,
if it isOr n is more than C, stopping iteration, outputting K modal components of instantaneous active power P decomposition, and recording the one with the minimum frequency value in the K modal components of the instantaneous active power P decomposition as a characteristic active modal component
And carrying out the following judgment of ending iteration on the instantaneous reactive power Q:
if it isAnd n is less than or equal to C, increasing the iteration times, returning to the step (2) for next iteration updating,
if it isOr n is more than C, stopping iteration, outputting K modal components of the instantaneous reactive power Q decomposition, and recording the one with the minimum frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode
In this embodiment, K is 5, α is 1000, and C is 500.
Step 4, the characteristic active mode obtained in the step 3 is processedAnd characteristic reactive modeProcessing by adopting a moving average filtering algorithm to obtain an active direct current componentAnd a reactive DC componentThe method comprises the following specific steps:
the window width is set to N.
Characteristic active modeSliding storage is carried out on the window in a unit control period, and then the characteristic active mode in the windowThe number of the numerical value is N, and the characteristic active mode of the window is recordedHas an ith value ofCharacteristic active modeN values ofPerforming arithmetic average to obtain active DC component
Characteristic reactive modeSliding storage is carried out on the window in a unit control period, and then the characteristic reactive mode in the windowThe number of the numerical value is N, and the characteristic reactive mode of the window is recordedHas a j value ofCharacteristic reactive modeN values ofCarrying out arithmetic average to obtain reactive direct current component
in the present embodiment, N is 200.
where ω is a converter frequency command obtained by droop control, EdFor d-axis voltage closed-loop commands obtained by droop control, omega*For the frequency of the power frequency of the converter, E*M is the active power droop coefficient of the converter, r is the reactive power droop coefficient of the converter, P is the rated voltage of the converter in no-loadNRated active power, Q, for the output of the converterNAnd rated reactive power is output by the converter.
In this embodiment, PN=100Kvar,ω*=314.159,E*=220V,m=3.14×10-5,r=1.1×10-4。
Q-axis voltage closed-loop command Eq=0。
D-axis voltage closed-loop instruction E obtained through droop controldAnd d-axis component E of output voltageodObtaining the inductive current I of the d-axis bridge arm of the converter through the voltage closed-loop control of the d-axisldr(ii) a Closed-loop command E of q-axis voltageqAnd the converter output voltage q-axis component EoqObtaining the inductive current I of a q-axis bridge arm of the converter through the voltage closed-loop control of a q-axislqrThe d-axis voltage closed-loop control equation and the q-axis voltage control equation are respectively as follows:
wherein, KpvAs a voltage closed-loop proportional regulator coefficient, KiIs a voltage closed loop integral regulator coefficient.
The d-axis bridge arm of the converter induces current IldrD-axis component I of bridge arm inductance currentldObtaining an output signal E of a d-axis of the converter through d-axis bridge arm inductance current closed-loop controldi(ii) a Inducing current I to q-axis bridge arm of converterlqrQ-axis component I of bridge arm inductive currentlqObtaining an output signal E of a q axis of the converter through q axis bridge arm inductance current closed-loop controlqiThe d-axis bridge arm inductance current closed-loop control equation and the q-axis bridge arm inductance current control equation are respectively as follows:
Edi=(Ildr-ILd)Kpi
Eqi=(Ilqr-ILq)Kpi
wherein, KpiAnd the closed-loop proportional adjustment coefficient of the inductive current of the bridge arm of the converter is obtained.
In this embodiment, Kpv=0.1,Ki=800,Kpi=0.6。
Emdi=Ed+Edi
Emqi=Eq+Eqi
modulating wave E under dq coordinate systemmdi,EmqiObtaining a modulation wave E under an alpha beta coordinate system through Park inverse transformationmαi,EmβiThen, the modulated wave E under the alpha beta coordinate system is usedmαi,EmβiObtaining a three-phase modulation wave E under an abc coordinate system through Clarke inverse transformationmai,Embi,EmciThe three-phase modulated wave Emai,Embi,EmciAnd the signal is used as a driving signal of the IGBT circuit after being modulated by the SPWM.
The Park inverse transformation formula and the Clarke inverse transformation formula are respectively as follows:
wherein, thetarefiFor a converter phase angle command obtained by integrating a converter frequency command omega obtained by droop control, a calculation formula of the integrating operation is as follows:
in order to prove the technical effect of the invention, the control method of the invention is simulated.
Fig. 2 is an instantaneous active power waveform output by the new energy converter in a state of containing subsynchronous harmonic components and not being filtered. As can be seen from fig. 2, the instantaneous active power oscillates sharply, and the frequency band of the harmonic components contained therein is wide.
Fig. 3 is a waveform of instantaneous active power output by the new energy converter after being filtered by a first-order low-pass filter. As can be seen from fig. 3, the response speed of the instantaneous active power is reduced, and the system is kept stable for about 2.2s, which reduces the stability margin of the system.
Fig. 4 shows an instantaneous active power waveform output by the new energy converter after VMD-moving average filtering. As can be seen from fig. 4, compared with the filtering effect of the conventional filter, the method can effectively reduce the influence of the harmonic waves under the broadband oscillation on the system, the output power can be quickly responded, the stability is maintained at about 1.8s, the problem of the reduction of the dynamic response of the output power due to the reduction of the cut-off frequency of the first-order low-pass filter is effectively solved, and the stability of the converter system is improved.
Claims (4)
1. A new energy converter power filtering method based on VMD-moving average filtering is characterized by comprising the following steps:
step 1, sampling output phase voltage E of a converteroa,EobAnd bridge arm inductive current Ila,IlbAnd respectively obtaining output voltage dq axis component E through synchronous rotating coordinate transformationod,EoqAnd bridge arm inductive current dq axis component Ild,IlqWherein d is an active axis and q is a reactive axis;
step 2, according to the output voltage dq axis component E in the step 1od,EoqAnd bridge arm inductive current dq axis component Ild,IlqCalculating to obtain instantaneous active power P and instantaneous reactive power Q output by the converter;
the calculation formulas of the instantaneous active power P and the instantaneous reactive power Q output by the converter are respectively as follows:
step 3, according to the instantaneous active power P and the instantaneous reactive power Q obtained in the step 2, utilizing a VMD algorithm, namely a variational modal decomposition algorithm to carry out the following processing to obtain the characteristic active modalAnd characteristic reactive mode
Firstly, constructing a constraint variation problem of instantaneous active power P and a constraint variation problem of instantaneous reactive power Q, wherein expressions of the constraint variation problems are respectively as follows:
wherein, { PβK is the number of resolved modal components, P, K is the set of K modal components resolved by the instantaneous active power P, β 1,2βThe beta-th modal component decomposed for the instantaneous active power P is recorded as the active power modal component Pβ;{QβIs the set of K modal components of the instantaneous reactive power Q decomposition, QβThe beta-th modal component of the instantaneous reactive power Q decomposition is recorded as the reactive power modal component Qβ;{ωpβThe central frequency is a set of central frequencies corresponding to K modal components of instantaneous active power P decomposition, { omega }qβThe central frequency corresponding to K modal components of the instantaneous reactive power Q decomposition is set, t is time, delta (t) is a Dirac function, a symbol is a convolution operator, pi is a circumferential rate, j is an imaginary number unit,to partially derive the function over time t,is a two-norm square operation, Pβ(t) is the active power modal component PβActive power, Q, corresponding to time tβ(t) is the reactive power modal component QβCorresponding reactive power at the time t; omegapβIs an active power modal component PβCorresponding center frequency, ωqβAs reactive power modal component QβA corresponding center frequency;
secondly, solving the constraint variation problem of the constructed instantaneous active power P to obtain K modal components of the instantaneous active power P decomposition, and recording the minimum frequency value of the K modal components of the instantaneous active power P decomposition as a characteristic active modal component
Solving the constraint variation problem of the constructed instantaneous reactive power Q to obtain K modal components of the instantaneous reactive power Q decomposition, and recording the one with the minimum frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive modal component
Step 4, the characteristic active mode obtained in the step 3 is processedAnd characteristic reactive modeProcessing by adopting a moving average filtering algorithm to obtain an active direct current componentAnd a reactive DC componentThe method comprises the following specific steps:
setting the width of a window to be N;
characteristic active modeSliding storage is carried out on the window in a unit control period, and then the characteristic active mode in the windowThe number of the numerical value is N, and the characteristic active mode of the window is recordedHas an ith value ofCharacteristic active modeN values ofPerforming arithmetic average to obtain active DC component
Characteristic reactive modeSliding storage is carried out on the window in a unit control period, and then the characteristic reactive mode in the windowThe number of the numerical value of (A) is N, and the characteristic reactive mode of the window is recordedHas a j value ofCharacteristic reactive modeN values ofCarrying out arithmetic average to obtain reactive direct current component
step 5, according to the active direct current component output in the step 4And a reactive DC componentThe droop control is respectively carried out on the active power-frequency and the reactive power-voltage, and the droop control equations are respectively as follows:
where ω is a converter frequency command obtained by droop control, EdFor d-axis voltage closed-loop commands obtained by droop control, omega*For the frequency of the power frequency of the converter, E*M is the active power droop coefficient of the converter, r is the reactive power droop coefficient of the converter, P is the rated voltage of the converter in no-loadNRated active power, Q, for the output of the converterNRated reactive power is output for the converter;
step 6, carrying out droop control on the converter frequency command omega obtained in the step 5 and carrying out droop control on the d-axis voltage closed-loop command EdObtaining an output signal E of a d axis of the converter through voltage and current double closed-loop controldiAnd the output signal E of the converter q-axisqi;
Make q axle voltage closed loop instruction Eq=0;
D-axis voltage closed-loop instruction E obtained through droop controldAnd the d-axis component E of the output voltageodObtaining the inductive current I of the d-axis bridge arm of the converter through the voltage closed-loop control of the d-axisldr(ii) a Closed-loop command E of q-axis voltageqAnd the converter output voltage q-axis component EoqObtaining the inductive current I of a q-axis bridge arm of the converter through the voltage closed-loop control of a q-axislqrThe d-axis voltage closed-loop control equation and the q-axis voltage control equation are respectively as follows:
wherein, KpvAs a voltage closed-loop proportional regulator coefficient, KiIs a voltage closed loop integral regulator coefficient;
the inductive current I of the d-axis bridge arm of the converterldrD-axis component I of bridge arm inductance currentldObtaining an output signal E of a d-axis of the converter through d-axis bridge arm inductance current closed-loop controldi(ii) a Inducing current I to q-axis bridge arm of converterlqrQ-axis component I of bridge arm inductive currentlqObtaining an output signal E of a q axis of the converter through q axis bridge arm induction current closed-loop controlqiThe d-axis bridge arm inductance current closed-loop control equation and the q-axis bridge arm inductance current control equation are respectively as follows:
Edi=(Ildr-ILd)Kpi
Eqi=(Ilqr-ILq)Kpi
wherein, KpiClosed-loop proportional adjustment coefficients of the inductive current of a bridge arm of the converter;
step 7, calculating a modulation wave E under the dq coordinate systemmdi,EmqiThe calculation formula is respectively:
Emdi=Ed+Edi
Emqi=Eq+Eqi
modulating wave E under dq coordinate systemmdi,EmqiObtaining a modulation wave E under an alpha beta coordinate system through Park inverse transformationmαi,EmβiThen, the modulated wave E under the alpha beta coordinate system is usedmαi,EmβiObtaining a three-phase modulation wave E under an abc coordinate system through Clarke inverse transformationmai,Embi,EmciThe three-phase modulated wave Emai,Embi,EmciAnd the signal is used as a driving signal of the IGBT circuit after being modulated by the SPWM.
2. The VMD-moving average filtering-based new energy converter power filtering method according to claim 1, wherein said solving the constrained variation problem of the constructed instantaneous active power P and solving the constrained variation problem of the constructed instantaneous reactive power Q in step 3 comprises the following steps:
(1) according to the constructed constraint variation problem, a secondary penalty factor alpha and an active Lagrange multiplication operator lambda are introducedpMultiplication operator lambda of reactive LagrangeqChanging the constructed constraint variation problem into an unconstrained variation problem to obtain an augmented Lagrange expression of the unconstrained variation problem, wherein the augmented Lagrange expression of the instantaneous active power P is expressed as:
in the formula, λp(t) is the active Lagrange multiplier λpA temporal variation of (d); lambda [ alpha ]q(t) is the reactive Lagrange multiplier λqA temporal variation of (d);
(2) by using an alternative direction multiplier method, combining Parseval/Plancherel and Fourier equidistant transformation and alternately updatingFinding out minimum value points of the unconstrained variation problem, and obtaining the minimum value points through the (n + 1) th iteration updateThe detailed process is as follows:
where ω denotes a frequency domain variable, n is any one of C iterations, n is 1,2.. and C, C is the maximum number of iterations,is the instantaneous active power form on the corresponding frequency domain of the instantaneous active power P (t), and is marked as the instantaneous active power of the frequency domainIs the instantaneous reactive power form on the corresponding frequency domain of the instantaneous reactive power Q (t), and is recorded as the instantaneous reactive power form of the frequency domainIs instantaneous active power of frequency domainOf the beta-th modal component of (1) < th > iteration,Is instantaneous reactive in frequency domainOf the beta modal component of (a) for the (n + 1) th iteration,andrepresenting frequency domain instantaneous activityThe (n + 1) th iteration and the (n) th iteration of the z-th modal component,andrepresenting frequency domain instantaneous reactive powerThe (n + 1) th and nth iterations of the z-th modal component of (a), z being 1,2, K,andis the active Lagrange multiplier lambdap(t) the corresponding n +1 th iteration and the active Lagrange multiplier after the nth iteration on the frequency domain,andis a reactive Lagrange multiplier lambdaq(t) corresponding to the (n + 1) th iteration on the frequency domain and the reactive Lagrange multiplication operator after the nth iteration, wherein tau is noise tolerance;
(3) setting a verification threshold epsilon, wherein epsilon is more than 0;
and carrying out the following judgment of termination iteration on the instantaneous active power P:
if it isAnd n is less than or equal to C, increasing the iteration times, returning to the step (2), performing the next iteration update,
if it isOr n is more than C, stopping iteration, outputting K modal components of the instantaneous active power P decomposition, and taking the K modal components of the instantaneous active power P decomposition with the smallest frequency value as the characteristic active mode
And carrying out the following judgment of ending iteration on the instantaneous reactive power Q:
if it isAnd n is less than or equal to C, increasing the iteration times, returning to the step (2), performing the next iteration update,
3. The VMD-sliding average filtering-based new energy converter power filtering method according to claim 1, characterized in that step 7 is a modulation wave E under dq coordinate systemmdi,EmqiObtaining a modulation wave E under an alpha beta coordinate system through Park inverse transformationmαi,EmβiThe Park inverse transformation formula is as follows:
Emαi=Emdicosθrefi-Emqisinθrefi
Emβi=Emdisinθrefi+Emqicosθrefi
wherein, thetarefiThe calculation formula of the integral operation is as follows:
4. the VMD-sliding average filtering-based new energy converter power filtering method according to claim 1, wherein step 7 is performed on the modulation wave E in the α β coordinate systemmαi,EmβiObtaining a three-phase modulation wave E under an abc coordinate system through Clarke inverse transformationmai,Embi,EmciThe Clarke inverse transformation formula is as follows:
Emai=Emαi
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