CN106501574A - A kind of novel active power filter harmonic current detecting method - Google Patents

Abstract

The invention discloses a kind of new A PF harmonic current detecting method, voltage to points of common connection in the three-phase power grid voltage unbalanced system that collects, by the relation after introducing conductance factor representation voltage on line side and compensation between current on line side, fundamental positive sequence voltage effective value is tried to achieve according to Active Power Filter-APF power conservation principle, simultaneously by the construction Lagrangian between grid current harmonic content and line voltage, target grid electric current is drawn by the method for seeking extreme value, and make the difference with load current and negate and can be compensated current instruction value, so as to realize the Power Control to Active Power Filter-APF, and then control signal is generated by PWM technology, the output of control Active Power Filter-APF.The present invention replaces the phase voltage in traditional algorithm using the fundamental positive sequence of voltage so that the change synchronous with the holding of the fundamental positive sequence of voltage of the system power waveform after compensation, so as to overcome the problem that harmonic wave can not be completely eliminated when line voltage distorts.

Description

A kind of novel active power filter harmonic current detecting method

Technical field

The invention belongs to the control technology field of power electronic equipment.Specifically, the present invention relates to a kind of be based on electrical network The acquisition methods of the harmonic current of the Active Power Filter-APF of parameter.

Background technology

Active Power Filter-APF (APF：Active power filter) application in power distribution network mainly has two sides Face：Improve system power factor and regulating system voltage.Although all it is to system by Active Power Filter-APF in terms of the two Middle injecting reactive current is realizing, but the purpose for compensating is different, and the method which is realized is also different, but the detection of harmonic current is real The key factor of existing APF control effects.

Active Power Filter-APF mainly includes major loop and control loop two parts, its operation principle can be briefly described as Under：First, Harmonic currents detection module is analyzed detection to harmonic source, requires to obtain accordingly according to different system balances Harmonic wave command signal；Then, current follow-up control circuit is using harmonic wave command signal as reference signal, by current control circuit The drive signal of main circuit is obtained with modulation module；Finally, the benefit under the control of drive signal, needed for main circuit generation system Repay electric current.The electric current of electrical network is flowed through comprising harmonic source load current and Active Power Filter-APF compensation electric current two parts, two kinds of electricity Stream superposition after, just obtain harmonic content extremely low, be similar to sine power network current.

Harmonic wave command signal is the foundation that Active Power Filter-APF is compensated, the performance of harmonic wave command signal extraction algorithm Quality is related to the final compensation effect of active power filter system.Preferably harmonic wave command signal extract can in real time with With the change that harmonic source is loaded, detecting exactly needs the harmonic wave command signal of compensation.

At present, the anti-therapy of Harmonic currents detection mainly has following several：

(1) the digital assay method based on FFT

FFT (Fast Fourier Transformation) i.e. fast Fourier decomposition methods.By to periodic harmonic wave Electric current carries out fast Fourier decomposition, obtains the harmonic wave command signal needed for system balance.The method can extract arbitrarily secondary Harmonic signal, and not by mains frequency change affected；But the method can only be detected to periodic harmonic signal, and examine Need to carry out substantial amounts of mathematical computations during survey, rapidity is poor.Therefore, the method can not be used for harmonic source and frequently change System.

(2) self adaptation Harmonic detection

Adaptation theory is applied to field of signal processing earliest, for extracting original from the signal containing additive noise Signal.Self adaptation harmonic wave command signal extraction algorithm is a kind of closed loop detection method based on adaptive interference cancelling principle, leads to Cross the parameter that study constantly changes sef-adapting filter so that the output valve infinite approach harmonic wave command signal of wave filter.From Adapting to detection method has its advantage：Do not affected by system voltage frequency, waveform change, applied widely, strong robustness.But, Adaptive process is the process for constantly approaching target, its convergence rate and system initial state, the Mathematical Modeling that selects and Using optiaml ciriterion related, therefore, system dynamic responding speed is slow.

(3) detection method based on instantaneous reactive power theory

Instantaneous reactive power theory is the most typical with p-q methods and ip-iq methods, and two methods are obtained by coordinate transform Predefined instantaneous real, fictitious power.When voltage waveform equally exists distortion, using the calculated electricity of p-q detection algorithms Contain and voltage identical harmonic component in stream fundamental wave；And now using in the calculated current first harmonics of ip-iq detection methods simultaneously These harmonic components are not contained.But need to carry out multiple changes in coordinates during the use of the method, amount of calculation is larger；With When, the introducing of low pass filter also reduces the rapidity of harmonic detecting.

(4) synchronization detection method

Synchronized harmonics command signal extraction algorithm is in harmonic wave command signal extraction process with single-phase load currents as analysis Object, considers threephase load harmonic wave and system balance requirement again after extracting the harmonic wave command signal in every phase, so as to Obtain the reference harmonic command signal for meeting system balance requirement.For three-phase system generally speaking, synchronization detection method is with system Power-balance for detection target, will not be excessive concern per phase current decomposition computation.For three-phase unsymmetrical winding, synchronous inspection Angle of the survey method from three-phase power balance, not only can be with the idle and positive sequence harmonic point in the load of compensation harmonic source Amount, moreover it is possible to the asymmetric degree in good improvement system.Traditional synchronized harmonics command signal extraction algorithm is according to three-phase When harmonic current command signal calculated by balanced dynamometer, the phase and amplitude information for using voltage signal is needed；According to electricity Pressure infomation detection algorithm is incorrect, then can introduce very big detection time delay, affects the rapidity and accuracy of harmonic detecting.

(5) other harmonic detecting methods (include that the harmonic wave based on artificial neural network (Neural Network, NN) is instructed Extraction method, FBD harmonic waves instruction extraction method, the harmonic wave based on analog filter instruct extraction method etc.).

The theory deduction of aforementioned several conventional harmonic wave instruction extraction algorithms and checking be all balanced with three-phase power grid voltage and Premised on undistorted.But in actual application, the continuous superposition accumulation of harmonic signal can cause the distortion of voltage, electrical network Break down or some specific operations under can equally cause the imbalance of three-phase voltage；Now, above-mentioned harmonic wave command signal is carried The accuracy and precision for taking strategy can be affected.The present invention needs measurement electricity for conventional synchronization harmonic wave instruction extraction algorithm The drawbacks of pressure signal, propose a kind of improved synchronized harmonics and instruct extraction algorithm, it is to avoid conventional synchronization harmonic wave command signal is carried The drawbacks of taking algorithm and need detection voltage amplitude；Meanwhile, appropriate adjustment control targe can be required according to compensation, control mode is cleverer Living, with very strong practicality.

Content of the invention

According to the deficiencies in the prior art, the present invention provides a kind of novel active power filter harmonic current detecting method, Its objective is that Active Power Filter-APF is used conventional methods carries out harmonic current when considering that electrical network has non-equilibrium state Detection, may result in and testing result occur and deviation occur or can not detect harmonic wave and idle component, new detection completely Method can not only realize line voltage distortion time-harmonic wave current detecting, and using the balance component in distorted voltage as synchronous electricity Pressure, improves the asymmetric degree of three-phase current, improves the compensation effect of Active Power Filter-APF.

The present invention is realized by technical scheme below：

A kind of novel active power filter harmonic current detecting method, it is characterised in that：The method is comprised the following steps：

Step one：Three-phase power grid voltage, the three-phase phase current of load-side and active electric power at collection points of common connection The DC capacitor voltage of wave filter；

Step 2：According to the three-phase power grid voltage at the points of common connection for collecting, fundamental wave is obtained using coordinate transformation method Positive sequence voltage signal, in the three-phase phase current to points of common connection three-phase power grid voltage and load-side, carry out Clark conversion and Park is converted, and utilizes Instantaneous Power Theory, is calculated and is loaded the average active power p absorbed from grid side_avgAnd active electric power The average loss p of wave filter work_loss；

Step 3：Virtual value processing module is sent into the points of common connection three-phase power grid voltage for collecting to process, construction one The individual Lagrangian object function for meeting grid current harmonic aberration rate and the restriction of Voltage Harmonic aberration rate, should by solving Object function obtains the apparent energy minimum of a value of Active Power Filter-APF, so as to try to achieve conductance factor G_n, and then try to achieve target electricity Net electric current；

Step 4：Target grid electric current and threephase load side electric current are made the difference and is negated and can just be compensated current-order Value, calculates the reactive power that can just obtain system needs compensation through instruction current follow-up control circuit；

Step 5：Current follow-up control circuit is tracked using compensating current instruction value as reference signal by instruction current Control circuit and SVPWM module obtain the drive signal of main circuit；The last control in pwm pulse drive signal Under system so that the compensation electric current needed for main circuit generation system.

Preferably, the specific implementation of the target grid electric current in step 3 is：The inspection of the target grid electric current Surveying includes two parts：First, using the extracting method based on coordinate transform and Instantaneous Power Theory, meeting three-phase power grid voltage Demand for control during balance；Second, when in three-phase power grid voltage unbalanced system, by net side electricity after voltage on line side with compensation Conductance factor G is introduced between stream_n, during according to Active Power Filter-APF steady operation, system power conserva-tion principle constructs one Meet the Lagrangian of power conservation and percent harmonic distortion restrictive condition；Again by solving to the function, mesh is drawn Mark power network current.

Preferably, the voltage of three-phase power grid voltage points of common connection is expressed as：

In formula：χ=a, b, c；H=highest overtone orders；E_xnThe virtual value of each harmonic voltage；φ_xnEach harmonic The initial phase angle of voltage；

Load-side three-phase current is expressed as：

In formula：θ is that phaselocked loop locks phase angle, Δ θ=θ-ω t, C₂₃=C₃₂ ^-1, I_n、The virtual value of each primary current with Initial phase angle, i_pFor the active component of current,For i_pDC component,

The DC capacitor voltage of Active Power Filter-APF is：

U_dc≥3e_sx(c).

Preferably, positive sequence voltage is separated, at points of common connection, the balance component of voltage is represented by formula：

Wherein：e′_sxnThe n balance of voltage component extracted in unbalance voltage.

Preferably, in Active Power Filter-APF compensation system, complete Harmonics elimination is that load harmonic is fully compensated, Obtain synchronous with net side fundamental voltage, standard sine power network current；Unity power factor compensation is with High Power Factor For the purpose of, the current on line side with actual electric network voltage in phase, i.e. voltage and current synchronization is obtained, when electrical network is asymmetric or even deposits In distortion, now power network current equally contains the harmonic wave of corresponding number of times；

In order to show the relation after voltage on line side and compensation between current on line side, conductance factor G is introduced_n；

As the component of voltage that extracts and target grid current value are three-phase symmetricals, therefore three-phase chooses identical Conductance factor G_n.

Preferably, can be obtained according to Active Power Filter-APF power conservation principle：

Wherein, p_avgLoad average active power, is obtained by threephase load electric current and line voltage according to instantaneous power principle ?；p_lossThe average loss of Active Power Filter-APF work, for stablizing Active Power Filter-APF DC voltage；E′_sn—n The virtual value of component is balanced in subharmonic voltage, works as n=1, E '_s1Represent fundamental positive sequence voltage effective value, E '_snCalculating formula be,

Preferably, by introducing electricity percent harmonic distortion limit value, THD is used_io、THD_ieThe actual electric current of expression system is strange, Even-order harmonic aberration rate, THD_vo、THD_veThe odd, even subharmonic aberration rate of the actual voltage of expression system, constructs object function, Square value of this value for apparent energy：

Wherein,

Preferably, when band carries one timing of situation, obtain a system and meeting power conservation and percent harmonic distortion restriction Under the conditions of minimum Apparent Power, apparent energy is less, then power factor is higher；The method of asking of power minimum passes through to build glug Bright day function asks conditional extremum to obtain conductance factor G_n,

Formula (i) is brought in formula (e), draws target grid electric current, make the difference with load current and negate and can just be compensated Current instruction value.

Preferably, the THD_iomaxAnd THD_iemaxSelection, meet following condition：

THD in formula_iostdAnd THD_iestdThe grid current harmonic aberration rate that respectively GB is limited.

Beneficial effect of the present invention：

The drawbacks of present invention needs measurement voltage signal for conventional synchronization harmonic wave instruction extraction algorithm, proposes a kind of improvement Harmonic wave instruction extraction algorithm, it is to avoid the drawbacks of conventional synchronization harmonic wave command signal extraction algorithm needs detection voltage amplitude； Remain able to accurately detect harmonic wave when three-phase power grid voltage is uneven, compensation effect is excellent, meanwhile, can be required according to compensation suitable When adjustment control targe, control mode is more flexible, with very strong practicality；Can basis in the case of unbalanced source voltage Different compensation demands adjust control targe, realize complete Harmonics elimination or unity power factor compensation.

Conductance factor G is being introduced after voltage on line side and compensation between current on line side_n, when being worked according to Active Power Filter-APF Power conservation principle, constructs a Lagrangian for meeting power conservation and percent harmonic distortion restrictive condition.Pass through again The function is solved, target grid electric current can be drawn, can quickly calculate compensation current instruction value.

Increased the rapidity of the voltage-controlled dynamic stability performance of Active Power Filter-APF access point and voltage compensation.

Description of the drawings

Fig. 1 is ip-iq method harmonic detecting schematic diagrams；

Fig. 2 is reference synchronization coordinate system phaselocked loop general principle flow chart；

Fig. 3 is to extract fundamental positive sequence voltage flow chart using coordinate transform；

Fig. 4 is improved active filter harmonic current detection method schematic diagram；

The harmonic current waveforms that Fig. 5 is detected using ip-iq methods when being unbalanced source voltage；

The harmonic current waveforms detected using improvement detection method when Fig. 6 is unbalanced source voltage；

When Fig. 7 selects HF to compensate, net side three-phase current comparison of wave shape before and after compensation；

When Fig. 8 selects HF to compensate, during using improving detection method detection harmonic wave, current on line side harmonic content value (a) after compensation； DC voltage waveform (b), net side power factor (c)；

When Fig. 9 selects UPF to compensate, A phase line voltages, current waveform (a), net side power factor (b).

Specific embodiment

Below in conjunction with accompanying drawing, by specific embodiment, the present invention is further illustrated.

Existing conventional harmonic wave command signal extracts the proposition of strategy and theory deduction, verification process are all based on three-phase Grid balance, symmetrically carry out.When unbalanced source voltage in system, these harmonic wave command signals extract tactful whether can also It is fast and accurate that to carry out harmonic detecting unknown.The present invention as a example by the widest ip-iq detection methods of practical engineering application, Analysis impact of the unbalanced power supply to harmonic detecting.

As shown in figure 1, in figure, C₃₂, C represent Clark transformation matrixs and Park transformation matrixs respectively.

In formula, ω electrical network angular frequencys.

Assume that three-phase symmetrical, detected load current are：

In formula, I_n、The virtual value of each primary current and initial phase angle.

The distortionless situation of line voltage

When grid voltage waveform is not distorted, three-phase voltage is symmetrical and is represented by following form:

In formula, E_1mThe single-phase peak value of line voltage, i.e. electrical network fundamental voltage amplitude；

Load current is transformed under synchronous rotating frame：

In formula, i_p、i_qElectric current is active, idle component.

In formula, symbol during n=3k+1, is taken, during n=3k-1, remove symbol, k=0,1,2....

i_p、i_qLow-pass filtered device LPF (Low Pass Filter, LPF) is obtained：

In formula,—i_p、i_qDC component.

Can be obtained by Fig. 2-1 again：

In formula, i_af、i_bf、i_cfFundametal compoment in each phase load electric current is represented respectively；C₂₃=C₃₂ ^-1.Work as active electric power When wave filter is simultaneously used for compensation harmonic and idle component, only i need to be disconnected_qPassage, now：

Exactly equal to fundamental active component.

There is the situation of distortion in line voltage

In formula (2-2), the ω t in transformation matrix are and e_aCorresponding phase angle, can be obtained by phaselocked loop.Work as electrical network When voltage is distorted, the angle that phaselocked loop draws no longer is strict ω t, below with reference synchronization coordinate system phaselocked loop Analytic explanation in addition as a example by (Synchronous Reference Frame Phase Locked Loop, SRF-PLL).

As shown in Fig. 2 when line voltage is balanced, which is first transformed to-β through Clarke with (2-4) by voltage expression Coordinate system：

It is transformed under synchronous rotating frame by park conversion again：

In formula, θ is that phaselocked loop locks phase angle, makes line voltage actual phase ω t=θ^*, then formula (2-11) further indicate that For：

Understand, when lock is mutually accurate, i.e. θ^*=θ, voltage q axle components are zero.Therefore control voltage component, makes e_q ^*=0 reaches During to stable state, you can realize PGC demodulation.

After line voltage is distorted, from symmetrical components theory analysis, remove in voltage waveform and contain positive sequence network Outward, also containing substantial amounts of negative phase-sequence and zero-sequence network.For three-phase three-line system, as zero sequence is not turned on path, therefore can Only consider positive sequence therein and negative sequence network.Voltage signal is obtained by each frequency component linear superposition, therefore in follow-up reason In by derivation, process, only considers the positive sequence in fundamental signal and negative sequence network to simplify the analysis.

It is assumed that the line voltage being distorted is represented with formula (2-13).

In formula, V₁、V₁The amplitude of fundamental wave positive and negative sequence voltage, φ are represented respectively₁、φ₂Fundamental wave positive and negative sequence voltage is represented respectively Initial phase.

After formula (2-10), (2-11) accordingly transform to d-q reference axis, expression is as follows：

If according further to the lock facies principle of SRF-PLL, the phase angle locked during stable state：

It can be seen that, when line voltage contains distortion, the angle drawn during phaselocked loop stable state has no longer been fundamental positive sequence voltage Phase place.

Assume that the deviation between actual lock phase angle and ω t is Δ θ, i.e. Δ θ=θ-ω t, then：

This up-to-date style (2-7) is expressed as：

Again its contravariant is changed to and can be obtained under three-phase a-b-c coordinate systems：

It can be seen that, if only compensation harmonic electric current, ip-iq methods do not receive electrical network distortion effects.

But when compensation harmonic simultaneously and reactive current is needed, formula (2-9) is changed into：

Fundamental active component in the load current for detecting is wrong, it is seen that ip-iq methods are no longer suitable in such cases Harmonics and reactive current detection.

Fundamental positive sequence voltage is extracted using coordinate transform, its principle is identical with ip-iq harmonic component extraction methods, such as Fig. 3 Shown, the nth harmonic voltage under reference synchronization coordinate system is represented by：

In formula, e_dn、e_qnNth harmonic d-axis and quadrature axis component.

e_dn、e_qnFurther it is represented by again：

In formula,The corresponding DC component of nth harmonic, i.e., the balance component in nth harmonic； N time The corresponding AC compounent of harmonic wave, i.e. unbalanced component in nth harmonic.

Therefore, the balance component e ' in nth harmonic under Static Synchronous referential_snIt is represented by：

Obviously, when phaselocked loop lock phase angle is positive sequence voltage phase of fundamental wave angle, can be extracted by method shown in Fig. 3 Fundamental positive sequence voltage.But, when line voltage is asymmetric or even containing distortion, from SRF-PLL principle analysis, lock phase angle Degree is no longer the phase information of fundamental positive sequence voltage.Lower surface analysis locks impact of the phase angular deviation to fundamental positive sequence voltage subtraction.

It is assumed that in the case of unbalanced source voltage, between the angle of SRF-PLL lock phases and fundamental positive sequence voltage phase angle Deviation be Δ θ, the same formula of unbalanced electric grid voltage expression formula (2-10), being transformed to has under rotational coordinates：

Again its contravariant is changed under a-b-c coordinate systems, is obtained：

It can be seen that this fundamental positive sequence voltage subtraction method is not affected by phaselocked loop angular deviation, can apply it to During unbalanced power supply among the extraction of fundamental positive sequence voltage, this is also which relative to one of advantage of other extracting methods.

During unbalanced source voltage, improved harmonic detecting method is：

As shown in figure 4, in three-phase power grid voltage unbalanced system points of common connection (Point of Common Coupling, PCC) voltage be represented by：

In formula, x=a, b, c；N overtone orders；H highest overtone orders；E_xnThe virtual value of each harmonic voltage； φ_xnThe initial phase angle of each harmonic voltage.

According to separating to positive sequence voltage, at points of common connection, the balance component of voltage is represented by：

In formula, e '_sxnThe n balance of voltage component extracted in unbalance voltage.

In Active Power Filter-APF compensation system, the standard of compensation has two：Complete Harmonics elimination (HF) and specific work Rate factor compensation (UPF).The former compensation purpose is that load harmonic is fully compensated, and obtains and net side fundamental voltage same-phase , the power network current of standard sine；The latter is for the purpose of High Power Factor, obtains the net side with actual electric network voltage in phase Electric current, i.e. voltage and current synchronization, when electrical network is asymmetric or even there is distortion, now power network current equally contains corresponding number of times Harmonic wave.

In order to show the relation after voltage on line side and compensation between current on line side, conductance factor G is introduced_n.

As the component of voltage that extracts and target grid current value are three-phase symmetricals, therefore three-phase chooses identical Conductance factor G_n.

From Active Power Filter-APF operation principle, theoretically do not consume during Active Power Filter-APF steady operation Work(power, can be drawn according to power conservation principle：

In formula, p_avgLoad average active power, can be according to instantaneous power principle by threephase load electric current and line voltage Obtain；p_lossThe average loss of APF work, for stablizing APF DC voltages；E′_snComponent is balanced in nth harmonic voltage Virtual value, work as n=1, E '_s1Represent fundamental positive sequence voltage effective value.

E′_snCalculating refer to following formula and obtain：

Electricity percent harmonic distortion can be limited within limits all in engineering.Assume the odd, even subharmonic that engineering is limited The current distortion rate upper limit is respectively THD_iomax、THD_iemax.Actual odd, even subharmonic aberration rate THD of system_io、THD_ieFor：

Should then meet：

Generally, THD_iomaxAnd THD_iemaxSelection, meet following condition：

THD in formula_iostdAnd THD_iestdThe grid current harmonic aberration rate that respectively GB is limited, THD_voAnd THD_veFor reality The voltage harmonic aberration rate on border.

Introduce THD_iomaxAnd THD_iemaxRather than null value is defined as directly, it is to meet some to power factor command Strict occasion.If now grid voltage waveform is that then net side is electric containing distortion, except fundamental wave also has other higher hamonic waves Stream also needs the higher hamonic wave containing corresponding content to meet unity power factor.The purpose of do so is exactly to contain in the harmonic wave for allowing Power factor is improved in the range of amount as far as possible.

Limiting value of the grid current harmonic content in allowed band be：

I.e.：

An object function, square value of this value for apparent energy can be constructed：

When band carries the timing of situation one, a system is obtained in the case where power conservation and percent harmonic distortion restrictive condition is met most Little apparent energy, apparent energy are less, then power factor is higher.The method of asking of power minimum can pass through to build Lagrangian Conditional extremum is asked to obtain.Formula (2-46), (2-53) are respectively constraint equation：

In formula, γ₁、γ₂、γ₃Lagrangian.

Above-mentioned equation is to G₁、G_o、G_eSeek single order local derviation and can obtain with conditional equation simultaneous：

G₃=G₅=...=G_o(2-57)

G₂=G₄=...=G_e(2-58)

(2-58) bring formula (2-57) into (2-56) to obtain：

In formula

Solution (2-59)～(2-61) has：

Target grid electric current is drawn by bringing formula (2-45) into, is made the difference with load current and is negated and can be compensated electric current Command value.

Embodiment：

Using Matlab softwares, the present invention is emulated.System emulation parameter setting is as follows：The uncontrollable rectification of three-phase Bridge 8 Europe resistance of band are used as harmonic source；DC side busbar voltage value is set to 180V；DC side bus capacitor is 2200uF；Load-side Smoothing reactor 0.45mH；Active Power Filter-APF AC filter inductance 1.5mH；Switching frequency is set to 12.5kHz；Active electrical Force filter system is put in 0.06s.

The harmonic wave for improving that detection method is detected is given when Fig. 5 gives unbalanced source voltage using ip-iq methods and Fig. 6 Current waveform, substantially can be seen that the harmonic current waveforms detected using improved method more comprehensively from figure；Fig. 7 gives choosing When selecting HF compensation, net side three-phase current comparison of wave shape before and after compensation, after system input, is reached within the time less than a cycle Stable, and the power network current after compensating is the power frequency sinusoidal current of three-phase symmetrical, waveform is undistorted；Fig. 8 gives selection HF and mends When repaying, during using improving detection method detection harmonic wave, current on line side harmonic content value, DC voltage waveform, net side work(after compensation Rate factor, it can be seen that grid current harmonic aberration rate is reduced to 3.77% by 30.78% before compensating, meets electrical network Require, DC side voltage regulation result is good, ripple voltage very little.Meet DC side busbar voltage stable requirement when APF works, choosing When selecting HF and compensating, the power factor of net side substantially meets the standard that power factor is 1 between 97% to 1；Fig. 9 gives choosing When selecting UPF compensation, A phase line voltages, current waveform, the waveform of net side power factor, it can be seen that ripple before and after compensation Shape phase place is basically identical, and power factor is maintained between 0.99 to 1.

Effect has reached following target：Using the balance component in distorted voltage as synchronizing voltage, three-phase current is improved Asymmetric degree, while can need to select complete Harmonics elimination (HF) or unity power factor control (UPF) according to compensation.

Claims (9)

1. a kind of novel active power filter harmonic current detecting method, it is characterised in that：The method is comprised the following steps：

Step one：Three-phase power grid voltage, the three-phase phase current of load-side and active power filtering at collection points of common connection The DC capacitor voltage of device；

Step 2：According to the three-phase power grid voltage at the points of common connection for collecting, fundamental positive sequence is obtained using coordinate transformation method Voltage signal, in the three-phase phase current to points of common connection three-phase power grid voltage and load-side, carries out Clark conversion and Park becomes Change, and utilize Instantaneous Power Theory, calculate and load the average active power p absorbed from grid side_avgAnd Active Power Filter-APF The average loss p of work_loss；

Step 3：Virtual value processing module is sent into the points of common connection three-phase power grid voltage for collecting to process, one is constructed completely The Lagrangian object function that sufficient grid current harmonic aberration rate and Voltage Harmonic aberration rate are limited, by solving the target Function obtains the apparent energy minimum of a value of Active Power Filter-APF, so as to try to achieve conductance factor G_n, and then try to achieve target grid electricity Stream；

Step 4：Target grid electric current and threephase load side electric current are made the difference and are negated and just can be compensated current instruction value, The reactive power that can just obtain system needs compensation is calculated through instruction current follow-up control circuit；

Step 5：Current follow-up control circuit to compensate current instruction value as reference signal, by instruction current tracing control Circuit and SVPWM module obtain the drive signal of main circuit；Finally under the control of pwm pulse drive signal, So that the compensation electric current needed for main circuit generation system.

2. a kind of novel active power filter harmonic current detecting method according to claim 1, it is characterised in that step The specific implementation of the target grid electric current in rapid three is：The detection of the target grid electric current includes two parts：

First, using the extracting method based on coordinate transform and Instantaneous Power Theory, meeting when three-phase power grid voltage is balanced and controlling Demand；

Second, when in three-phase power grid voltage unbalanced system, by introducing between current on line side after voltage on line side and compensation Conductance factor G_n, during according to Active Power Filter-APF steady operation, system power conserva-tion principle constructs one and meets power and keeps The Lagrangian of permanent and percent harmonic distortion restrictive condition；Again by solving to the function, target grid electric current is drawn.

3. a kind of novel active power filter harmonic current detecting method according to claim 1, it is characterised in that：

The voltage of three-phase power grid voltage points of common connection is expressed as：

$e_{sx}=\sqrt{2}\underset{n=1}{\overset{h}{\Σ}}{E}_{xn}sin(n\mathrm{\ω}t+{\mathrm{\φ}}_{xn})---\left(a\right)$

In formula：χ=a, b, c；H=highest overtone orders；E_xnThe virtual value of each harmonic voltage；φ_xnEach harmonic voltage Initial phase angle；

Load-side three-phase current is expressed as：

In formula：θ is that phaselocked loop locks phase angle, Δ θ=θ-ω t, C₂₃=C₃₂ ^-1, I_n、Virtual value and first phase for each primary current Angle, i_pFor the active component of current,For i_pDC component,

$C_{32}=\frac{2}{3}\left[\begin{array}{ccc}1& -1/2& -1/2\\ 0& \sqrt{3}/2& -\sqrt{3}/2\end{array}\right],C=\left[\begin{array}{cc}\sin \left(\mathrm{\ω}t+\mathrm{\Δ}\mathrm{\θ}\right)& -\cos \left(\mathrm{\ω}t+\mathrm{\Δ}\mathrm{\θ}\right)\\ -\cos \left(\mathrm{\ω}t+\mathrm{\Δ}\mathrm{\θ}\right)& -\sin \left(\mathrm{\ω}t+\mathrm{\Δ}\mathrm{\θ}\right)\end{array}\right];$

The DC capacitor voltage of Active Power Filter-APF is：

U_dc≥3e_sx(c).

4. a kind of novel active power filter harmonic current detecting method according to claim 3, it is characterised in that：

Positive sequence voltage is separated, at points of common connection, the balance component of voltage is represented by formula：

$e_{sx}^{\′}=\underset{n=1}{\overset{h}{\Σ}}{e}_{sxn}^{\′}---\left(d\right)$

Wherein：e′_sxnThe n balance of voltage component extracted in unbalance voltage.

5. a kind of novel active power filter harmonic current detecting method according to claim 4, it is characterised in that：? In Active Power Filter-APF compensation system, complete Harmonics elimination is that load harmonic is fully compensated, and obtains and net side fundamental voltage The power network current of synchronous, standard sine；Unity power factor compensation is for the purpose of High Power Factor, obtains and actual electricity The current on line side of net voltage in phase, i.e. voltage and current synchronization, when electrical network is asymmetric or even there is distortion, now electrical network is electric The stream equally harmonic wave containing corresponding number of times；

In order to show the relation after voltage on line side and compensation between current on line side, conductance factor G is introduced_n；

$\left\{\begin{array}{cc}{i}_{sx}^{*}=G_1{e^{\′}}_{sx1},& HF\\ i_{sx}^{*}=G_1{e^{\′}}_{sx1}+\underset{n=2}{\overset{h}{\mathrm{\Σ}}}{G}_n{e^{\′}}_{sxn},& UPF\end{array}\right.---\left(e\right)$

As the component of voltage that extracts and target grid current value are three-phase symmetricals, therefore three-phase chooses identical conductance Factor G_n.

6. a kind of novel active power filter harmonic current detecting method according to claim 5, it is characterised in that root Can obtain according to Active Power Filter-APF power conservation principle：

$\frac{p_{loss}+p_{avg}}{3}-\underset{n=1}{\overset{h}{\Σ}}{G}_n{E}_{sn}^{\′2}=0---\left(f\right)$

Wherein, p_avgLoad average active power, is obtained by threephase load electric current and line voltage according to instantaneous power principle； p_lossThe average loss of Active Power Filter-APF work, for stablizing Active Power Filter-APF DC voltage；E′_snN time The virtual value of component is balanced in harmonic voltage, works as n=1, E '_s1Represent fundamental positive sequence voltage effective value, E '_snCalculating formula be,

$E_{sn}^{\′}=\sqrt{\frac{{\stackrel{\‾}{e}}_{dn}^2+{\stackrel{\‾}{e}}_{qn}^2}{2}}---\left(g\right).$

7. a kind of novel active power filter harmonic current detecting method according to claim 6, it is characterised in that：Logical Introducing electricity percent harmonic distortion limit value is crossed, THD is used_io、THD_ieThe odd, even subharmonic aberration rate of the actual electric current of expression system, THD_vo、THD_veThe odd, even subharmonic aberration rate of the actual voltage of expression system, constructs object function, and this value is apparent energy Square value：

$f=\underset{n=1}{\overset{h}{\Σ}}{E}_{sn}^{\′2}\underset{n=1}{\overset{h}{\Σ}}{G}_n^2{E}_{sn}^{\′2}---\left(h\right)$

Wherein,

8. a kind of novel active power filter harmonic current detecting method according to claim 7, it is characterised in that：When Band carries one timing of situation, obtains minimum apparent work(of the system in the case where power conservation and percent harmonic distortion restrictive condition is met Rate, apparent energy are less, then power factor is higher；The method of asking of power minimum seeks conditional extremum by building Lagrangian Obtain conductance factor G_n,

$\left\{\begin{array}{c}{G}_1=\frac{p_{loss}+p_{avg}}{3E_{s1}^2\left(1+{\mathrm{THD}}_{io\max }{\mathrm{THD}}_{vo}+{\mathrm{THD}}_{ie\max }{\mathrm{THD}}_{ve}\right)}\\ G_o=\frac{{\mathrm{THD}}_{io\max }}{{\mathrm{THD}}_{vo}}{G}_1\\ G_e=\frac{{\mathrm{THD}}_{ie\max }}{{\mathrm{THD}}_{ve}}{G}_1\end{array}\right.---\left(i\right)$

Wherein, THD_iomax、THD_iemaxFor the odd, even subharmonic current aberration rate upper limit, formula (i) is brought in formula (e), draws target Power network current, is made the difference with load current and is negated.

9. a kind of novel active power filter harmonic current detecting method according to claim 8, it is characterised in that：Institute State THD_iomaxAnd THD_iemaxSelection, meet following condition：

${\mathrm{THD}}_{iomax}=\left\{\begin{array}{cc}{\mathrm{THD}}_{iostd},& {\mathrm{THD}}_{iostd}<{\mathrm{THD}}_{vo}\\ {\mathrm{THD}}_{vo},& else\end{array}\right.$

${\mathrm{THD}}_{iemax}=\left\{\begin{array}{cc}{\mathrm{THD}}_{iestd},& {\mathrm{THD}}_{iestd}<{\mathrm{THD}}_{ve}\\ {\mathrm{THD}}_{ve},& else\end{array}\right.$

THD in formula_iostdAnd THD_iestdThe grid current harmonic aberration rate that respectively GB is limited.