CN114709828B - 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
- 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
- H02J3/01—Arrangements for reducing harmonics or ripples
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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
- H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
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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
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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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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses a new energy converter power filtering method based on VMD-moving average filtering, which belongs to the field of grid-connected converter control. According to the invention, under the condition that the system with the broadband oscillation characteristics of multiple time scales is operated by the new energy converter, the influence of broadband harmonic waves on the system is effectively inhibited, and the stability of the system is improved.
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 low short circuit ratio. The traditional current control type new energy grid-connected converter adopts a direct current control strategy decoupled with the frequency of a power grid, a current control instruction is generated by tracking control of the maximum power point of an outer ring, the equivalent moment of inertia is small, and the current control type new energy grid-connected converter has the problems that frequency and voltage support cannot be provided for a system, the grid-related capacity is insufficient, shutdown and grid disconnection are easy, and the like. The voltage control type new energy converter can simulate primary frequency modulation, voltage regulation characteristics and 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 system presents a multi-time scale broadband oscillation characteristic due to the access of a large number of new energy converters, a serious challenge is brought to the stable and efficient operation of the new energy grid-connected power generation system, the traditional voltage control type new energy converters based on droop control or Virtual Synchronous Generator (VSG) control are used for effectively attenuating broadband harmonic waves generated in instantaneous power when the system with the multi-time scale broadband oscillation characteristic operates, the influence of the output voltage quality and the control performance of the new energy converters by the broadband harmonic waves of the system is effectively avoided, a first-order low-pass filter is usually adopted, the cut-off frequency of the filter is generally designed to be within 1/10 of the power frequency or twice the power frequency, however, the cut-off frequency of the first-order low-pass filter needs to be further reduced for the broadband oscillation system, and the lower filter cut-off frequency is used for reducing the response speed of the output power, so that the power overshoot can be caused, and even the oscillation instability of the system is caused. Therefore, in order to improve the operation stability of the voltage control type new energy converter and the grid-connected system thereof under broadband oscillation, the instantaneous power filtering optimization in the converter control algorithm is necessary.
At present, aiming at the harmonic component problem caused when the new energy converter outputs instantaneous active and reactive power, a scholars analyze and put forward solutions, for example:
1. The model is built by using the average value of instantaneous power in a half power frequency period in the literature (modeling and parameter design of a virtual synchronous generator power ring, wu Heng, ruan Xinbo, yang Dongsheng, chen Xinran, zhong Qingchang, lv Zhipeng and the like, and the average value of instantaneous power in a half power frequency period is used in the literature (Chinese motor engineering journal, 35 th edition 24 pages 6508-6518) of 2015), the influence of VSG control parameters on the model is analyzed in detail based on the established model, the influence of the change of rotational inertia J on the stability and dynamic performance of active power and the influence of the change of inertia coefficient K on the stability and dynamic performance of reactive power are pointed out, and a method for designing the VSG control parameters according to the requirements of the cut-off frequency and phase angle margin of the system is provided, but the method is insufficient: the system under the multi-time scale broadband oscillation has the characteristics of multiple modes and time variation, is a global complex problem related to multiple electrical equipment, and cannot effectively filter out components containing active power and reactive power characteristics respectively.
2. The problem is "A Practical Secondary Frequency Control Strategy for Virtual Synchronous Generator",Jiang K,Su H,Lin H,et al,"IEEE Transactions on Smart Grid",vol.11,no.3,pp.2734-2736,May 2020,(" a practical virtual synchronous generator secondary frequency control strategy ', "IEEE school journal of smart grid, volume 11, 5 th month, 3 rd phase 2734-2736 pages) and (three-phase converter small signal modeling and analysis of virtual synchronous generator characteristics', yan Xiangwu, liu Zhengnan, xu Hengbo, su Xiao, ren Yalong, zhang Bo, north China university school journal (Nature science edition), volume 43, 3 rd phase 1-8 pages of 2016) and other documents, a small signal fine model of a single VSG load with resistance is established, and the influence of various parameters on system characteristics is analyzed, including the relation between the cut-off frequency of a first-order low-pass filter and the position of a system characteristic root, but the method is not as follows: the influence rule and the optimization method of the first-order low-pass filter on the system characteristics are not further analyzed.
In summary, the following problems also exist in the prior art:
1. For a system under multi-time scale broadband oscillation, the harmonic frequency range is wider, and the prior art cannot economically and effectively filter out subsynchronous harmonic components generated by the system;
2. The output instantaneous power of the converter is filtered by a first-order low-pass filter, and if the first-order low-pass filter is required to filter out the subsynchronous harmonic components in the system, the cut-off frequency is required to be reduced, and the response speed of the output power is reduced due to the lower cut-off frequency;
Disclosure of Invention
The invention aims at the problem of wideband 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, which effectively avoids the influence of wideband harmonic of a system on the output voltage quality and control performance of a new energy converter and improves the stability of the converter and a grid-connected system thereof.
In order to achieve the above purpose, the invention provides a new energy converter power filtering method based on VMD-moving average filtering, comprising the following steps:
Step 1, sampling output phase voltage E oa,Eob and bridge arm inductance current I la,Ilb of the converter, and respectively obtaining output voltage dq axis component E od,Eoq and bridge arm inductance current dq axis component I ld,Ilq through synchronous rotation coordinate transformation, wherein d is an active axis, and q is a reactive axis;
Step 2, calculating to obtain instantaneous active power P and instantaneous reactive power Q output by the converter according to the output voltage dq axis component E od,Eoq and the bridge arm inductance current dq axis component I ld,Ilq in the step 1;
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, the VMD algorithm, namely the variational modal decomposition algorithm is utilized to carry out the following processing to obtain the characteristic active mode And 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 the expressions are as follows:
wherein { P β } is a set of K modal components of the instantaneous active power P decomposition, β=1, 2..K, K is the number of modal components of the instantaneous active power P decomposition, P β is the β -th modal component of the instantaneous active power P decomposition, denoted as active power modal component P β;{Qβ } is a set of K modal components of the instantaneous reactive power Q decomposition, Q β is the β -th modal component of the instantaneous reactive power Q decomposition, denoted as reactive power modal component Q β;{ωpβ } is a set of center frequencies corresponding to K modal components of the instantaneous active power P decomposition, { ω qβ } is a set of center frequencies corresponding to K modal components of the instantaneous reactive power Q decomposition, t is time, δ (t) is a Dirac function, symbol is a convolution operator, pi is a circumference ratio, j is an imaginary unit, To determine the partial derivative of the function with respect to time t,/>For the two-norm square operation, P β (t) is the active power corresponding to the active power modal component P β at the time t, and Q β (t) is the reactive power corresponding to the reactive power modal component Q β at the time t; omega pβ is the center frequency corresponding to the active power modal component P β, omega qβ is the center frequency corresponding to the reactive power modal component Q β;
Secondly, solving the constructed constraint variation problem of the instantaneous active power P to obtain K modal components decomposed by the instantaneous active power P, and taking one marked as a characteristic active mode with the minimum frequency value in the K modal components decomposed by the instantaneous active power P
Solving the constructed constraint variation problem of the instantaneous reactive power Q to obtain K modal components of the instantaneous reactive power Q decomposition, and taking one with the smallest frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode
Step 4, for the characteristic active mode obtained in step3And characteristic reactive mode/>Processing by adopting a moving average filtering algorithm to obtain an active direct current component/>And reactive DC component/>The method comprises the following steps:
setting the width of the window as N;
Let the characteristic active mode Sliding storage is carried out on the window in a unit control period, so that characteristic active modes/>The number of the numerical values is N, and the characteristic active mode/>, of the window is recordedThe i-th value of/>Characterizing active modality/>N values/>Performing arithmetic average to obtain active DC component/>
Make characteristic reactive modeSliding storage is carried out on the window in a unit control period, so that characteristic reactive mode/>, in the windowThe number of the numerical values is N, and the characteristic reactive mode/>, of the window is recordedThe j-th value is/>Characteristic reactive mode/>N values/>Performing arithmetic average to obtain reactive DC component/>
Active DC componentAnd reactive DC component/>The expressions of (2) are respectively:
Step5, according to the active DC component output in step4 And reactive DC component/>Droop control is respectively carried out on active-frequency and reactive-voltage, and droop control equations are respectively as follows:
Wherein ω is a converter frequency instruction obtained by droop control, E d is a d-axis voltage closed-loop instruction obtained by droop control, ω * is a power frequency of the converter, E * is a rated voltage of the converter when no load is applied, m is an active power droop coefficient of the converter, r is a reactive power droop coefficient of the converter, P N is an output rated active power of the converter, and Q N is an output rated reactive power of the converter;
step 6, obtaining an output signal E di of the d axis of the converter and an output signal E qi of the q axis of the converter through voltage and current double closed-loop control by using the converter frequency command omega obtained through droop control and the d axis voltage closed-loop command E d obtained through droop control obtained in the step 5;
Let q-axis voltage closed loop command E q = 0;
d-axis voltage closed-loop instruction E d and output voltage d-axis component E od obtained through droop control are subjected to d-axis voltage closed-loop control, so that d-axis bridge arm inductance current I ldr of the converter is obtained; the q-axis voltage closed-loop instruction E q and the q-axis component E oq of the output voltage of the converter are subjected to q-axis voltage closed-loop control to obtain the q-axis bridge arm inductance current I lqr of the converter, and a d-axis voltage closed-loop control equation and a q-axis voltage control equation of the q-axis bridge arm inductance current I lqr are respectively as follows:
Wherein, K pv is the voltage closed-loop proportional regulator coefficient, and K i is the voltage closed-loop integral regulator coefficient;
carrying out closed-loop control on the d-axis bridge arm inductance current I ldr and the bridge arm inductance current d-axis component I ld of the current transformer through the d-axis bridge arm inductance current to obtain an output signal E di of the d axis of the current transformer; the q-axis bridge arm inductance current I lqr and the q-axis bridge arm inductance current component I lq of the current transformer are subjected to q-axis bridge arm inductance current closed-loop control to obtain an output signal E qi of the q-axis of the current transformer, and a d-axis bridge arm inductance current closed-loop control equation and a q-axis bridge arm inductance current control equation are respectively:
Edi＝(Ildr-ILd)Kpi
Eqi＝(Ilqr-ILq)Kpi
Wherein K pi is the closed-loop proportional adjustment coefficient of the bridge arm inductance current of the converter;
Step 7, calculating a modulated wave E mdi,Emqi under the dq coordinate system, wherein the calculation formulas are respectively as follows:
Emdi＝Ed+Edi
Emqi＝Eq+Eqi
And performing Park inverse transformation on the modulated wave E mdi,Emqi under the dq coordinate system to obtain a modulated wave E mαi,Emβi under the alpha beta coordinate system, performing Clarke inverse transformation on the modulated wave E mαi,Emβi under the alpha beta coordinate system to obtain a three-phase modulated wave E mai,Embi,Emci under the abc coordinate system, and performing SPWM (sinusoidal pulse width modulation) on the three-phase modulated wave E mai,Embi,Emci to obtain a driving signal of the IGBT circuit.
Preferably, the solving the constraint variation problem constructed by the instantaneous active power P and the solving the constraint variation problem constructed by the instantaneous reactive power Q described in the step 3 include the steps of:
(1) According to the constructed constraint variation problem, introducing a secondary penalty factor alpha, an active Lagrange multiplier lambda p and a reactive Lagrange multiplier lambda q, and changing the constructed constraint variation problem into an unconstrained variation problem to obtain an augmented Lagrange expression of the constraint variation problem, wherein the augmented Lagrange expression of the instantaneous active power P is expressed as:
Where λ p (t) is the time variation of the active Lagrange multiplier λ p; lambda q (t) is the time variation of the reactive Lagrange multiplier lambda q;
(2) By combining the alternate direction multiplier method with Parseval/PLANCHEREL and Fourier equidistant transformation and by alternate updating Finding out minimum value points of unconstrained variation problems, and obtaining/>, through n+1st iteration updateThe detailed process of (2) is as follows:
Is updated by the n+1st iteration to obtain The detailed process of (2) is as follows:
where ω represents the frequency domain variance, n is any one of C iterations, n=1, 2,.., Is the instantaneous active power form on the frequency domain corresponding to the instantaneous active power P (t), and is recorded as the instantaneous active power of the frequency domainIs the instantaneous reactive power form on the frequency domain corresponding to the instantaneous reactive power Q (t), and is recorded as the frequency domain instantaneous reactive power/>Is the instantaneous active power of the frequency domain/>N+1st iteration of the beta-th modal component,/>For the frequency domain instantaneous reactive power/>N+1st iteration of the beta-th modal component,/>And/>Representing the instantaneous active power of the frequency domain/>N+1th and nth iterations,/>, of the z-th modal componentAnd/>Representing frequency domain instantaneous reactive power/>N+1th and nth iterations of the z-th modal component, z=1, 2AndIs the active Lagrange multiplier lambda p (t) corresponding to the n+1st iteration and the active Lagrange multiplier after the n iterationAnd/>The method is a reactive Lagrange multiplier lambda q (t) corresponding to the n+1th iteration and the n-th iteration on the frequency domain, and tau is the noise margin;
(3) Setting a verification threshold epsilon, wherein epsilon is more than 0;
the following determination for terminating the iteration is made for the instantaneous active power P:
If it is And n is less than or equal to C, increasing the iteration times for one time, returning to the step (2), carrying out the next iteration update,
If it isOr n is larger than C, terminating the iteration, outputting K modal components decomposed by the instantaneous active power P, and taking one with the smallest frequency value out of the K modal components decomposed by the instantaneous active power P as a characteristic active mode/>
The following determination to terminate the iteration is made for the instantaneous reactive power Q:
If it is And n is less than or equal to C, increasing the iteration times for one time, returning to the step (2), carrying out the next iteration update,
If it isOr n is more than C, terminating the iteration, outputting K modal components of the instantaneous reactive power Q decomposition, and taking one with the smallest frequency value out of the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode/>
Preferably, the modulated wave E mdi,Emqi in the dq coordinate system in step 7 is subjected to Park inverse transformation to obtain a modulated wave E mαi,Emβi in the αβ coordinate system, where Park inverse transformation formula is as follows:
Emαi＝Emdi cosθrefi-Emqisinθrefi
Emβi＝Emdi sinθrefi+Emqi cosθrefi
Wherein, θ refi is a converter phase angle instruction obtained by integrating a converter frequency instruction ω obtained by droop control, and a calculation formula of the integrating operation is:
Preferably, the modulating wave E mαi,Emβi in the αβ coordinate system in step 7 is subjected to Clarke inverse transformation to obtain a three-phase modulating wave E mai,Embi,Emci in the abc coordinate system, where the Clarke inverse transformation formula is as follows:
Emai＝Emαi
under the condition of broadband harmonic wave generated when a system with multi-time scale broadband oscillation characteristics operates, the VMD-moving average filtering-based new energy converter power filtering method has the following beneficial effects compared with the existing method adopting a first-order low-pass filter or a trap filter:
1. the power filtering method has good processing effect on non-stationary and nonlinear signals, and is a non-recursive modal variation and signal processing method;
2. The power filtering method eliminates the reduction of the response speed of the output power and the insufficient dynamic characteristics of the converter, which are generated by the system due to lower filtering cut-off frequency;
3. The power filtering method filters the power decomposed and output by the VMD by adopting a moving average algorithm, has good inhibition effect on periodic interference, has high smoothness, is suitable for a high-frequency oscillation system, and is simple in design and realization.
Drawings
Fig. 1 is a control structure block diagram of a new energy converter.
Fig. 2 is a waveform of instantaneous active power output from the new energy converter in an unfiltered state including subsynchronous harmonic components.
Fig. 3 is a waveform of instantaneous active power output by the new energy converter after filtering by the first-order low-pass filter.
Fig. 4 is a waveform of instantaneous active power output from the new energy converter after VMD-moving average filtering.
Detailed Description
The present embodiment will be described in detail with reference to the accompanying drawings.
In this embodiment, the bridge arm filter inductance of the new energy converter is L, the bridge arm inductance current flowing through the new energy converter is I la,Ilb, the filter capacitance is C i, the phase voltage at the filter capacitance end is E oa,Eob, and the line impedance between the converter output end and the PCC point is Z l. 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, the filter capacitance value C i is 90uF, the line impedance Z l =0.001+j1.25Ω, and the rated capacity is 100KVar.
Fig. 1 is a control structure block diagram of a power filtering method of a new energy converter according to the present invention, and as can be seen from the figure, the steps of the power filtering method according to the present invention are as follows:
Step 1, sampling an output phase voltage E oa,Eob and a bridge arm inductance current I la,Ilb of the converter, and respectively obtaining an output voltage dq axis component E od,Eoq and a bridge arm inductance current dq axis component I ld,Ilq through synchronous rotation coordinate transformation, wherein d is an active axis, and q is a reactive axis.
The synchronous rotation coordinate transformation formula of the output voltage dq axis component E od,Eoq is:
Eoα＝-Eob
The synchronous rotation coordinate transformation formula of the bridge arm inductance dq axis component I ld,Ilq is as follows:
Ilα＝-Ilb
Wherein, θ refi-1 is the converter phase angle instruction of the previous calculation cycle.
And 2, calculating to obtain the instantaneous active power P and the instantaneous reactive power Q output by the converter according to the output voltage dq axis component E od,Eoq and the bridge arm inductance current dq axis component I ld,Ilq in the step 1.
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, the VMD algorithm, namely the variational modal decomposition algorithm is utilized to carry out the following processing to obtain the characteristic active mode And 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 the expressions are as follows:
wherein { P β } is a set of K modal components of the instantaneous active power P decomposition, β=1, 2..K, K is the number of modal components of the instantaneous active power P decomposition, P β is the β -th modal component of the instantaneous active power P decomposition, denoted as active power modal component P β;{Qβ } is a set of K modal components of the instantaneous reactive power Q decomposition, Q β is the β -th modal component of the instantaneous reactive power Q decomposition, denoted as reactive power modal component Q β;{ωpβ } is a set of center frequencies corresponding to K modal components of the instantaneous active power P decomposition, { ω qβ } is a set of center frequencies corresponding to K modal components of the instantaneous reactive power Q decomposition, t is time, δ (t) is a Dirac function, symbol is a convolution operator, pi is a circumference ratio, j is an imaginary unit, To determine the partial derivative of the function with respect to time t,/>For the two-norm square operation, P β (t) is the active power corresponding to the active power modal component P β at the time t, and Q β (t) is the reactive power corresponding to the reactive power modal component Q β at the time t; omega pβ is the center frequency corresponding to the active power modal component P β, and omega qβ is the center frequency corresponding to the reactive power modal component Q β.
Secondly, solving the constructed constraint variation problem of the instantaneous active power P to obtain K modal components decomposed by the instantaneous active power P, and taking one marked as a characteristic active mode with the minimum frequency value in the K modal components decomposed by the instantaneous active power P
Solving the constructed constraint variation problem of the instantaneous reactive power Q to obtain K modal components of the instantaneous reactive power Q decomposition, and taking one with the smallest frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode
Specifically, the method for solving the constructed constraint variation problem of the instantaneous active power P and the constructed constraint variation problem of the instantaneous reactive power Q comprises the following steps:
(1) According to the constructed constraint variation problem, introducing a secondary penalty factor alpha, an active Lagrange multiplier lambda p and a reactive Lagrange multiplier lambda q, and changing the constructed constraint variation problem into an unconstrained variation problem to obtain an augmented Lagrange expression of the constraint variation problem, wherein the augmented Lagrange expression of the instantaneous active power P is expressed as:
Where λ p (t) is the time variation of the active Lagrange multiplier λ p; lambda q (t) is the time variation of the reactive Lagrange multiplier lambda q.
(2) By combining the alternate direction multiplier method with Parseval/PLANCHEREL and Fourier equidistant transformation and by alternate updatingFinding out minimum value points of unconstrained variation problems, and obtaining/>, through n+1st iteration updateThe detailed process of (2) is as follows:
Is updated by the n+1st iteration to obtain The detailed process of (2) is as follows:
/>
where ω represents the frequency domain variance, n is any one of C iterations, n=1, 2,.., Is the instantaneous active power form on the frequency domain corresponding to the instantaneous active power P (t), and is recorded as the instantaneous active power of the frequency domainIs the instantaneous reactive power form on the frequency domain corresponding to the instantaneous reactive power Q (t), and is recorded as the frequency domain instantaneous reactive power/>Is the instantaneous active power of the frequency domain/>N+1st iteration of the beta-th modal component,/>For the frequency domain instantaneous reactive power/>N+1st iteration of the beta-th modal component,/>And/>Representing the instantaneous active power of the frequency domain/>N+1th and nth iterations,/>, of the z-th modal componentAnd/>Representing frequency domain instantaneous reactive power/>N+1th and nth iterations of the z-th modal component, z=1, 2AndIs the active Lagrange multiplier lambda p (t) corresponding to the n+1st iteration and the active Lagrange multiplier after the n iterationAnd/>The method is a reactive Lagrange multiplier lambda q (t) corresponding to the n+1th iteration and the reactive Lagrange multiplier after the n iteration, and tau is the noise margin.
(3) Setting epsilon as a verification threshold value, wherein epsilon is more than 0;
the following determination for terminating the iteration is made for the instantaneous active power P:
If it is And n is less than or equal to C, increasing the iteration times for one time, returning to the step (2), carrying out the next iteration update,
If it isOr n is larger than C, terminating the iteration, outputting K modal components decomposed by the instantaneous active power P, and taking one with the smallest frequency value out of the K modal components decomposed by the instantaneous active power P as a characteristic active mode/>
The following determination to terminate the iteration is made for the instantaneous reactive power Q:
If it is And n is less than or equal to C, increasing the iteration times for one time, returning to the step (2), carrying out the next iteration update,
If it isOr n is more than C, terminating the iteration, outputting K modal components of the instantaneous reactive power Q decomposition, and taking one with the smallest frequency value out of the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode/>
In this embodiment, k=5, α=1000, and c=500.
Step 4, for the characteristic active mode obtained in step3And characteristic reactive mode/>Processing by adopting a moving average filtering algorithm to obtain an active direct current component/>And reactive DC component/>The method comprises the following steps: /(I)
The window width is set to N.
Let the characteristic active modeSliding storage is carried out on the window in a unit control period, so that characteristic active modes/>The number of the numerical values is N, and the characteristic active mode/>, of the window is recordedThe i-th value of/>Characterizing active modality/>N values/>Performing arithmetic average to obtain active DC component/>
Make characteristic reactive modeSliding storage is carried out on the window in a unit control period, so that characteristic reactive mode/>, in the windowThe number of the numerical values is N, and the characteristic reactive mode/>, of the window is recordedThe j-th value is/>Characteristic reactive mode/>N values/>Performing arithmetic average to obtain reactive DC component/>
Active DC componentAnd reactive DC component/>The expressions of (2) are respectively:
in the present embodiment, n=200.
Step5, according to the active DC component output in step4And reactive DC component/>Droop control is respectively carried out on active-frequency and reactive-voltage, and droop control equations are respectively as follows:
Wherein ω is a converter frequency command obtained through droop control, E d is a d-axis voltage closed-loop command obtained through droop control, ω * is a power frequency of the converter, E * is a rated voltage of the converter when no load is applied, m is an active power droop coefficient of the converter, r is a reactive power droop coefficient of the converter, P N is an output rated active power of the converter, and Q N is an output rated reactive power of the converter.
In this embodiment, P N＝100Kvar,ω*＝314.159,E*＝220V,m＝3.14×10-5,r＝1.1×10-4.
And 6, obtaining an output signal E di of the d axis of the converter and an output signal E qi of the q axis of the converter through voltage and current double closed-loop control by using the converter frequency command omega obtained through droop control and the d axis voltage closed-loop command E d obtained through droop control obtained in the step 5.
Let q-axis voltage closed loop command E q =0.
D-axis voltage closed-loop instruction E d and output voltage d-axis component E od obtained through droop control are subjected to d-axis voltage closed-loop control, so that d-axis bridge arm inductance current I ldr of the converter is obtained; the q-axis voltage closed-loop instruction E q and the q-axis component E oq of the output voltage of the converter are subjected to q-axis voltage closed-loop control to obtain the q-axis bridge arm inductance current I lqr of the converter, and a d-axis voltage closed-loop control equation and a q-axis voltage control equation of the q-axis bridge arm inductance current I lqr are respectively as follows:
/>
Where K pv is the voltage closed-loop proportional regulator coefficient and K i is the voltage closed-loop integral regulator coefficient.
Carrying out closed-loop control on the d-axis bridge arm inductance current I ldr and the bridge arm inductance current d-axis component I ld of the current transformer through the d-axis bridge arm inductance current to obtain an output signal E di of the d axis of the current transformer; the q-axis bridge arm inductance current I lqr and the q-axis bridge arm inductance current component I lq of the current transformer are subjected to q-axis bridge arm inductance current closed-loop control to obtain an output signal E qi of the q-axis of the current transformer, and a d-axis bridge arm inductance current closed-loop control equation and a q-axis bridge arm inductance current control equation are respectively:
Edi＝(Ildr-ILd)Kpi
Eqi＝(Ilqr-ILq)Kpi
Wherein K pi is the closed-loop proportional adjustment coefficient of the bridge arm inductance current of the converter.
In this embodiment, K pv＝0.1,Ki＝800,Kpi =0.6.
Step 7, calculating a modulated wave E mdi,Emqi under the dq coordinate system, wherein the calculation formulas are respectively as follows:
Emdi＝Ed+Edi
Emqi＝Eq+Eqi
And performing Park inverse transformation on the modulated wave E mdi,Emqi under the dq coordinate system to obtain a modulated wave E mαi,Emβi under the alpha beta coordinate system, performing Clarke inverse transformation on the modulated wave E mαi,Emβi under the alpha beta coordinate system to obtain a three-phase modulated wave E mai,Embi,Emci under the abc coordinate system, and performing SPWM (sinusoidal pulse width modulation) on the three-phase modulated wave E mai,Embi,Emci to obtain a driving signal of the IGBT circuit.
The Park inverse transformation formula and the Clarke inverse transformation formula are respectively as follows:
Wherein, θ refi is a converter phase angle instruction obtained by integrating a converter frequency instruction ω obtained by droop control, and a calculation formula of the integrating operation is:
In order to demonstrate the technical effect of the present invention, the control method of the present invention was simulated.
Fig. 2 is a waveform of instantaneous active power output from the new energy converter in an unfiltered state including subsynchronous harmonic components. As can be seen from fig. 2, the instantaneous active power oscillation is intense, and the frequency band of the contained harmonic component is wider.
Fig. 3 is a waveform of instantaneous active power output by the new energy converter after filtering by the 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 remains stable for about 2.2s, reducing the stability margin of the system.
Fig. 4 is a waveform of instantaneous active power output from 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 wave under the broadband oscillation on the system, the output power can quickly respond, and the stability is kept at about 1.8s, so that the problem that the dynamic response of the output power is reduced 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. The power filtering method of the new energy converter based on VMD-moving average filtering is characterized by comprising the following steps:
Step 1, sampling output phase voltage E oa,Eob and bridge arm inductance current I la,Ilb of the converter, and respectively obtaining output voltage dq axis component E od,Eoq and bridge arm inductance current dq axis component I ld,Ilq through synchronous rotation coordinate transformation, wherein d is an active axis, and q is a reactive axis;
Step 2, calculating to obtain instantaneous active power P and instantaneous reactive power Q output by the converter according to the output voltage dq axis component E od,Eoq and the bridge arm inductance current dq axis component I ld,Ilq in the step 1;
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, the VMD algorithm, namely the variational modal decomposition algorithm is utilized to carry out the following processing to obtain the characteristic active mode And 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 the expressions are as follows:
wherein { P β } is a set of K modal components of the instantaneous active power P decomposition, β=1, 2..K, K is the number of modal components of the instantaneous active power P decomposition, P β is the β -th modal component of the instantaneous active power P decomposition, denoted as active power modal component P β;{Qβ } is a set of K modal components of the instantaneous reactive power Q decomposition, Q β is the β -th modal component of the instantaneous reactive power Q decomposition, denoted as reactive power modal component Q β;{ωpβ } is a set of center frequencies corresponding to K modal components of the instantaneous active power P decomposition, { ω qβ } is a set of center frequencies corresponding to K modal components of the instantaneous reactive power Q decomposition, t is time, δ (t) is a Dirac function, symbol is a convolution operator, pi is a circumference ratio, j is an imaginary unit, To derive the partial derivative of the function with respect to time t,For the two-norm square operation, P β (t) is the active power corresponding to the active power modal component P β at the time t, and Q β (t) is the reactive power corresponding to the reactive power modal component Q β at the time t; omega pβ is the center frequency corresponding to the active power modal component P β, omega qβ is the center frequency corresponding to the reactive power modal component Q β;
Secondly, solving the constructed constraint variation problem of the instantaneous active power P to obtain K modal components decomposed by the instantaneous active power P, and taking one marked as a characteristic active mode with the minimum frequency value in the K modal components decomposed by the instantaneous active power P
Solving the constructed constraint variation problem of the instantaneous reactive power Q to obtain K modal components of the instantaneous reactive power Q decomposition, and taking one with the smallest frequency value in the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode
Step 4, for the characteristic active mode obtained in step3And characteristic reactive mode/>Processing by adopting a moving average filtering algorithm to obtain an active direct current component/>And reactive DC component/>The method comprises the following steps:
setting the width of the window as N;
Let the characteristic active mode Sliding storage is carried out on the window in a unit control period, so that characteristic active modes/>The number of the numerical values is N, and the characteristic active mode/>, of the window is recordedThe i-th value of/>Characterizing active modality/>N values/>Performing arithmetic average to obtain active DC component/>
Make characteristic reactive modeSliding storage is carried out on the window in a unit control period, so that characteristic reactive mode/>, in the windowThe number of the numerical values is N, and the characteristic reactive mode/>, of the window is recordedThe j-th value is/>Characteristic reactive mode/>N values/>Performing arithmetic average to obtain reactive DC component/>
Active DC componentAnd reactive DC component/>The expressions of (2) are respectively:
Step5, according to the active DC component output in step4 And reactive DC component/>Droop control is respectively carried out on active-frequency and reactive-voltage, and droop control equations are respectively as follows:
Wherein ω is a converter frequency instruction obtained by droop control, E d is a d-axis voltage closed-loop instruction obtained by droop control, ω * is a power frequency of the converter, E * is a rated voltage of the converter when no load is applied, m is an active power droop coefficient of the converter, r is a reactive power droop coefficient of the converter, P N is an output rated active power of the converter, and Q N is an output rated reactive power of the converter;
step 6, obtaining an output signal E di of the d axis of the converter and an output signal E qi of the q axis of the converter through voltage and current double closed-loop control by using the converter frequency command omega obtained through droop control and the d axis voltage closed-loop command E d obtained through droop control obtained in the step 5;
Let q-axis voltage closed loop command E q = 0;
d-axis voltage closed-loop instruction E d and output voltage d-axis component E od obtained through droop control are subjected to d-axis voltage closed-loop control, so that d-axis bridge arm inductance current I ldr of the converter is obtained; the q-axis voltage closed-loop instruction E q and the q-axis component E oq of the output voltage of the converter are subjected to q-axis voltage closed-loop control to obtain the q-axis bridge arm inductance current I lqr of the converter, and a d-axis voltage closed-loop control equation and a q-axis voltage control equation of the q-axis bridge arm inductance current I lqr are respectively as follows:
Wherein, K pv is the voltage closed-loop proportional regulator coefficient, and K i is the voltage closed-loop integral regulator coefficient;
carrying out closed-loop control on the d-axis bridge arm inductance current I ldr and the bridge arm inductance current d-axis component I ld of the current transformer through the d-axis bridge arm inductance current to obtain an output signal E di of the d axis of the current transformer; the q-axis bridge arm inductance current I lqr and the q-axis bridge arm inductance current component I lq of the current transformer are subjected to q-axis bridge arm inductance current closed-loop control to obtain an output signal E qi of the q-axis of the current transformer, and a d-axis bridge arm inductance current closed-loop control equation and a q-axis bridge arm inductance current control equation are respectively:
Edi＝(Ildr-ILd)Kpi
Eqi＝(Ilqr-ILq)Kpi
Wherein K pi is the closed-loop proportional adjustment coefficient of the bridge arm inductance current of the converter;
Step 7, calculating a modulated wave E mdi,Emqi under the dq coordinate system, wherein the calculation formulas are respectively as follows:
Emdi＝Ed+Edi
Emqi＝Eq+Eqi
And performing Park inverse transformation on the modulated wave E mdi,Emqi under the dq coordinate system to obtain a modulated wave E mαi,Emβi under the alpha beta coordinate system, performing Clarke inverse transformation on the modulated wave E mαi,Emβi under the alpha beta coordinate system to obtain a three-phase modulated wave E mai,Embi,Emci under the abc coordinate system, and performing SPWM (sinusoidal pulse width modulation) on the three-phase modulated wave E mai,Embi,Emci to obtain a driving signal of the IGBT circuit.
2. The VMD-moving average filtering-based new energy converter power filtering method according to claim 1, wherein the solving the constraint variation problem of the constructed instantaneous active power P and the solving the constraint variation problem of the constructed instantaneous reactive power Q in step 3 comprises the steps of:
(1) According to the constructed constraint variation problem, introducing a secondary penalty factor alpha, an active Lagrange multiplier lambda p and a reactive Lagrange multiplier lambda q, and changing the constructed constraint variation problem into an unconstrained variation problem to obtain an augmented Lagrange expression of the constraint variation problem, wherein the augmented Lagrange expression of the instantaneous active power P is expressed as:
Where λ p (t) is the time variation of the active Lagrange multiplier λ p; lambda q (t) is the time variation of the reactive Lagrange multiplier lambda q;
(2) By combining the alternate direction multiplier method with Parseval/PLANCHEREL and Fourier equidistant transformation and by alternate updating Finding out minimum value points of unconstrained variation problems, and obtaining/>, through n+1st iteration updateThe detailed process of (2) is as follows:
Is updated by the n+1st iteration to obtain The detailed process of (2) is as follows:
Where ω represents the frequency domain variance, n is any one of C iterations, n=1, 2,.., Is the instantaneous active power form on the frequency domain corresponding to the instantaneous active power P (t), and is recorded as the instantaneous active power of the frequency domainIs the instantaneous reactive power form on the frequency domain corresponding to the instantaneous reactive power Q (t), and is recorded as the frequency domain instantaneous reactive power/>Is the instantaneous active power of the frequency domain/>N+1st iteration of the beta-th modal component,/>For the frequency domain instantaneous reactive power/>N+1st iteration of the beta-th modal component,/>And/>Representing the instantaneous active power of the frequency domain/>N+1th and nth iterations,/>, of the z-th modal componentAnd/>Representing frequency domain instantaneous reactive power/>N+1th and nth iterations of the z-th modal component, z=1, 2AndIs the active Lagrange multiplier lambda p (t) corresponding to the n+1st iteration and the active Lagrange multiplier after the n iterationAnd/>The method is a reactive Lagrange multiplier lambda q (t) corresponding to the n+1th iteration and the n-th iteration on the frequency domain, and tau is the noise margin;
(3) Setting a verification threshold epsilon, wherein epsilon is more than 0;
the following determination for terminating the iteration is made for the instantaneous active power P:
If it is And n is less than or equal to C, increasing the iteration times for one time, returning to the step (2), carrying out the next iteration update,
If it isOr n is larger than C, terminating the iteration, outputting K modal components decomposed by the instantaneous active power P, and taking one with the smallest frequency value out of the K modal components decomposed by the instantaneous active power P as a characteristic active mode/>
The following determination to terminate the iteration is made for the instantaneous reactive power Q:
If it is And n is less than or equal to C, increasing the iteration times for one time, returning to the step (2), carrying out the next iteration update,
If it isOr n is more than C, terminating the iteration, outputting K modal components of the instantaneous reactive power Q decomposition, and taking one with the smallest frequency value out of the K modal components of the instantaneous reactive power Q decomposition as a characteristic reactive mode/>
3. The VMD-moving average filtering-based new energy converter power filtering method according to claim 1, wherein in step 7, the modulated wave E mdi,Emqi in the dq coordinate system is subjected to Park inverse transformation to obtain a modulated wave E mαi,Emβi in the αβ coordinate system, and a Park inverse transformation formula is as follows:
Emαi＝Emdicosθrefi-Emqisinθrefi
Emβi＝Emdisinθrefi+Emqicosθrefi
Wherein, θ refi is a converter phase angle instruction obtained by integrating a converter frequency instruction ω obtained by droop control, and a calculation formula of the integrating operation is:
4. the VMD-moving average filtering-based new energy converter power filtering method according to claim 1, wherein in step 7, the modulated wave E mαi,Emβi in the αβ coordinate system is subjected to Clarke inverse transformation to obtain a three-phase modulated wave E mai,Embi,Emci in the abc coordinate system, and the Clarke inverse transformation formula is as follows:
Emai＝Emαi
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