CN104993495A - Active power filter direct current control method suitable for condition of weak power grid - Google Patents

Active power filter direct current control method suitable for condition of weak power grid Download PDF

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CN104993495A
CN104993495A CN201510354312.7A CN201510354312A CN104993495A CN 104993495 A CN104993495 A CN 104993495A CN 201510354312 A CN201510354312 A CN 201510354312A CN 104993495 A CN104993495 A CN 104993495A
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CN104993495B (en
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张晓滨
张攀
程思雨
杨波
段建东
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Xian University of Technology
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30Reactive power compensation
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40Arrangements for reducing harmonics

Abstract

The invention discloses an active power filter direct current control method suitable for the condition of a weak power grid. The method is implemented according to the following steps: Step 1. voltage of a PCC point of a weak power grid system, inverter direct current side voltage, an instantaneous value of load current and an instantaneous value of current emitted by the inverter are collected; Step 2.the collected instantaneous values and the instantaneous value of current emitted by the inverter are processed through a conditioning circuit and is input to a DSP to be converted to digital signals; Step 3. the DSP processes the digital signals to obtain instruction current signals of the active power filter; Step 4. the DSP performs hysteresis comparison on the instruction current signals and the digital signals, and is controlled to emit PWM waves; and Step 5. the emitted PWM waves are sent to a drive circuit of an IGBT module of the inverter, the inverter is controlled to emit current according to the instruction current signals, and harmonic waves and reactive power in a power grid system are compensated according to the emitted current. The active power filter direct current control method suitable for the condition of the weak power grid effectively and accurately compensates reactive current and harmonic current of a load.

Description

Be applicable to the Active Power Filter-APF Direct Current Control method under weak grid conditions
Technical field
The invention belongs to electric and electronic technical field, relate to the Active Power Filter-APF Direct Current Control method be applicable under weak grid conditions.
Background technology
Along with fossil energy is day by day deficient, environmental problem is day by day serious, and clean regenerative resource is more and more paid attention to.Therefore distributed generation system is as one of the main application mode of regenerative resource, and the ratio in electrical network improves constantly.According to electric network composition, the impedance of electrical network determines primarily of lower powered converter and distribution line impedance.The increase of distributed power source makes electrical network under different service conditionss, and impedance be can not ignore and changed in a wider scope, and electrical network presents light current net characteristic.The extensive use of power electronic equipment simultaneously can bring day by day serious electric energy to pollute to electrical network, and usual using active electric-power filter (Active Power Filter and APF) is administered.And for light current net, flow through by harmonic current the background harmonics that electric network impedance causes because common tie point (Point of Common Coupling and PCC) voltage contains, to be therefore usually expressed as distortion uneven for PCC voltage.Therefore apply the improvement that APF carries out the quality of power supply in light current net, the problem that needs solve is: APF in PCC voltage distortion imbalance and when there is frequency deviation, can detect harmonic and reactive currents and compensate real-time and accurately.
For the real-time detection of harmonic and reactive currents, most widely used is at present instantaneous reactive power theory (Instantaneous Reactive Power Theory and IRP Theory) and extended method thereof and synchronous coordinate system method (Synchronous Reference Frame and SRF Method).But IRP theory is not suitable for the unbalanced state of PCC voltage distortion.Although the extended method of IRP and SRF method do not affect by voltage distortion or non-equilibrium state, need the real-time phase detecting positive sequence fundamental voltage.The distortion imbalance of PCC voltage brings larger difficulty to the real-time phase detecting positive sequence fundamental voltage.Although Phase Lock Technique comparatively advanced at present can meet above-mentioned condition to a certain extent, they implement mostly more complicated, need accurate parameter designing, and have certain delay, and these are all unfavorable for the practical application in engineering.
Another main direction of studying that compensation dynamic is APF is improved by eliminating detection time delay.Adaptive nonlinear control is adopted to eliminate the impact of systems axiol-ogy time delay on compensation effect.Adopt the mode of repetitive controller auto modification to eliminate the impact of time delay, but its dynamic responding speed is comparatively slow, cannot meets when system power fluctuates and compensate requirement.Adopt fuzzy logic controller, the intelligent algorithms such as synovial membrane controller carry out PREDICTIVE CONTROL to eliminate the impact detecting time delay.Although said method effectively eliminates the impact of time delay for compensation effect, implement comparatively complicated.
Summary of the invention
The object of the present invention is to provide the Active Power Filter-APF Direct Current Control method be applicable under weak grid conditions, solving traditional Direct Current Control cannot the problem of accurate compensation harmonic wave and reactive power under weak grid conditions.
The technical solution adopted in the present invention is, is applicable to the Active Power Filter-APF Direct Current Control method under weak grid conditions, implements according to following steps:
Step 1, gathers weak network system PCC point place voltage e a, e band e cinstantaneous value, DC side voltage of converter v dcinstantaneous value, load current i la, i lband i lcinstantaneous value, and the current i that inverter sends ca, i cband i ccinstantaneous value;
Step 2, by the e collected a, e b, e c, v dc, i la, i lband i lcinstantaneous value, and the current i that inverter sends ca, i cband i ccinstantaneous value is input in dsp processor after modulate circuit process, is digital signal e by A/D module converts a, e b, e c, v dc, i la, i lb, i lc, i ca, i cband i cc;
Step 3, dsp processor passes through digital signal e a, e b, e c, v dc, i la, i lband i lcprocess, obtain the instruction current signal i of Active Power Filter-APF refa, i refb, i refc;
Step 4, dsp processor is by instruction current signal i refa, i refb, i refcwith digital signal i ca, i cband i cccarry out stagnant chain rate comparatively, and the PWM module of control DSP sends PWM ripple;
Step 5, the PWM ripple sent by dsp processor is sent to the drive circuit of the IGBT module of inverter, and control inverter is according to instruction current signal i refa, i refb, i refcsend electric current, according to the harmonic wave sent in the weak network system of current compensation and reactive power.
Feature of the present invention is also,
The instruction current signal obtaining Active Power Filter-APF in step 3 is specifically implemented according to following steps:
1) instantaneous value of system PCC point voltage and load current is respectively:
e a = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + ) + E m - sin ( m ω t + θ e m - ) ] e b = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + - 2 π / 3 ) + E m - sin ( m ω t + θ e m - + 2 π / 3 ) ] e c = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + + 2 π / 3 ) + E m - sin ( m ω t + θ e m - - 2 π / 3 ) ] - - - ( 1 )
In formula (1), (2): m, n are harmonic number ,+represent positive sequence ,-represent negative phase-sequence; ω is angular speed, and t is the time, for positive sequence m subharmonic voltage amplitude, for negative phase-sequence m subharmonic voltage amplitude, for the initial phase angle of negative phase-sequence m subharmonic voltage, for the initial phase angle of positive sequence m subharmonic voltage, for positive sequence nth harmonic current amplitude, for negative phase-sequence nth harmonic current amplitude, for the initial phase angle of negative phase-sequence nth harmonic electric current, for the initial phase angle of positive sequence nth harmonic electric current;
2) voltage of PCC point and load current instantaneous value are converted to two-phase rest frame;
The coordinate figure that the voltage of PCC point is fastened in two-phase static coordinate is:
e α e β = C a b c _ α β e a e b e c = 3 / 2 Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + ) + E m - sin ( m ω t + θ e m - ) 3 / 2 Σ m = 1 ∞ [ - E m + cos ( m ω t + θ e m + ) + E m - cos ( m ω t + θ e m - ) - - - ( 3 )
In formula (3), (4): C a b c _ α β = 2 3 1 - 1 2 - 1 2 0 3 2 - 3 2 ;
3) be converted to voltage vector according to the locus between two-phase rest frame and rotating coordinate system, coordinate figure that current phasor is fastened at rotational coordinates;
The coordinate figure that voltage vector is fastened at rotational coordinates is:
e x e y = C α β _ x y e α e β = 3 / 2 Σ m = 1 ∞ { E m + cos [ ( m - 1 ) ωt + θ e m + - γ ] - E m - cos [ ( m + 1 ) ω t + θ e m - + γ ] } - 3 / 2 Σ m = 1 ∞ { E m + sin [ ( m - 1 ) ω t + θ e m + - γ ] + E m - sin [ ( m + 1 ) ω t + θ e m - + γ ] } - - - ( 5 )
In formula (5), C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
The coordinate figure that current phasor is fastened at rotational coordinates is:
4) adopt low pass filter to extract the coordinate figure fastened at rotational coordinates of voltage vector, obtaining the coordinate figure that PCC point voltage and load current fundamental positive sequence fasten at rotational coordinates is:
In formula (7), for the amplitude of fundamental positive sequence voltage, electric current, for the initial phase angle of fundamental positive sequence voltage, electric current, γ is the initial phase angle of xy coordinate system;
5) according to 3) and 4) in obtain voltage, electric current fundamental positive sequence with fundamental positive sequence voltage in the same way with the coordinate figure that the rotational coordinates of rotating speed is fastened, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is
Obtain active current according to the definition of active current again, expression is as follows:
In formula (8),
The coordinate figure that then active current is being fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage is:
i p L x = i p cos ( θ 1 + - γ ) = ( e x 1 + i x 1 + + e y 1 + i y 1 + ) e x 1 + ( e x 1 + ) 2 + ( e y 1 + ) 2 i p L y = i p sin ( θ 1 + - γ ) = ( e x 1 + i x 1 + + e y 1 + i y 1 + ) e x 1 + ( e x 1 + ) 2 + ( e y 1 + ) 2 - - - ( 9 )
6) according to the deviation of DC voltage and desired value, application PI controller obtains the active current i needed for voltage control pdc, then according to 3) and 4) in the coordinate figure fastened at rotational coordinates of the PCC point voltage fundamental positive sequence that obtains, by i pdcalso project to xy coordinate system, its coordinate figure is respectively:
i p d c x = i p d c × e x e x 2 + e y 2 i p d c y = i p d c × e y e x 2 + e y 2 - - - ( 10 )
By i pdccomponent on xy coordinate system joins the component of load active current on xy axial coordinate respectively, then the active current of system consumption at the coordinate figure of xy coordinate system is:
i p x = i p L x + i p d c x i p y = i p L y + i p d c y - - - ( 11 )
7) active current is carried out at the coordinate figure fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage the three-phase instantaneous value that matrix inverse transformation obtains active current to be respectively:
In formula (12), C x y _ α β = C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
8) 7 are deducted with the load current three-phase instantaneous value collected) the three-phase instantaneous value of system active current that obtains, obtain the instruction current signal of Active Power Filter-APF,
i r e f a = i L a - i p a i r e f b = i L b - i p b i r e f c = i L c - i p c . - - - ( 13 )
When PCC electric voltage frequency is displaced to ω ' by ω, the instruction current signal obtaining Active Power Filter-APF in step 3 is specifically implemented according to following steps:
1) instantaneous value of system PCC point voltage and load current is respectively:
e a = Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + ) + E m - sin ( mω ′ t + θ e m - ) ] e b = Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + - 2 π / 3 ) + E m - sin ( mω ′ t + θ e m - + 2 π / 3 ) ] e c = Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + + 2 π / 3 ) + E m - sin ( mω ′ t + θ e m - - 2 π / 3 ) ] - - - ( 14 )
In formula (14), (15), m, n are harmonic number ,+represent positive sequence ,-represent negative phase-sequence; ω 0for angular speed, t is the time, for positive sequence m subharmonic voltage amplitude, for negative phase-sequence m subharmonic voltage amplitude, for the initial phase angle of negative phase-sequence m subharmonic voltage, for the initial phase angle of positive sequence m subharmonic voltage, for positive sequence nth harmonic current amplitude, for negative phase-sequence nth harmonic current amplitude, for the initial phase angle of negative phase-sequence nth harmonic electric current, for the initial phase angle of positive sequence nth harmonic electric current;
2) voltage of PCC point and load current instantaneous value are converted to two-phase rest frame;
The coordinate figure that the voltage of PCC point is fastened in two-phase static coordinate is:
e α e β = C a b c _ α β e a e b e c = 3 / 2 Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + ) + E m - sin ( mω ′ t + θ e m - ) 3 / 2 Σ m = 1 ∞ [ - E m + cos ( mω ′ t + θ e m + ) + E m - cos ( mω ′ t + θ e m - ) - - - ( 16 )
In formula (16), (17), C a b c _ α β = 2 3 1 - 1 2 - 1 2 0 3 2 - 3 2 ;
3) be converted to voltage vector according to the locus between two-phase rest frame and rotating coordinate system, coordinate figure that current phasor is fastened at rotational coordinates;
The coordinate figure that voltage vector is fastened at rotational coordinates is:
e x e y = C α β _ x y e α e β = 3 / 2 Σ m = 1 ∞ { E m + cos [ ( mω ′ - ω ) t + θ e m + - γ ] - E m - cos [ ( mω ′ + ω ) t + θ e m - + γ ] } - 3 / 2 Σ m = 1 ∞ { E m + sin [ ( mω ′ - ω ) t + θ e m + - γ ] + E m - sin [ ( mω ′ + ω ) t + θ e m - + γ ] } - - - ( 18 )
In formula (18), C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) , γ is the first angle of xy coordinate system;
The coordinate figure that current phasor is fastened at rotational coordinates is:
4) adopt low pass filter to extract the coordinate figure fastened at rotational coordinates of voltage vector, obtaining the coordinate figure that PCC point voltage and load current fundamental positive sequence fasten at rotational coordinates is:
In formula (20), for the amplitude of fundamental positive sequence voltage, electric current, for the initial phase angle of fundamental positive sequence voltage, electric current, γ is the initial phase angle of xy coordinate system;
5) according to 3) and 4) in obtain voltage, electric current fundamental positive sequence with fundamental positive sequence voltage in the same way with the coordinate figure that the rotational coordinates of rotating speed is fastened, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is
Active current expression formula is obtained again as follows according to the definition of active current:
In formula (21),
The coordinate figure that then active current is being fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage is:
6) according to the deviation of DC voltage and desired value, application PI controller obtains the active current i needed for voltage control pdc, then according to the coordinate figure that the PCC point voltage fundamental positive sequence obtained in step 3.4 is fastened at rotational coordinates, by i pdcalso project to xy coordinate system, its coordinate figure is respectively:
i p d c x = i p d c × e x e x 2 + e y 2 i p d c y = i p d c × e y e x 2 + e y 2 - - - ( 23 )
By i pdccomponent on xy coordinate system joins the component of load active current on xy axial coordinate respectively, then the active current of system consumption at the coordinate figure of xy coordinate system is:
i p x = i p L x + i p d c x i p y = i p L y + i p d c y - - - ( 24 )
7) active current is carried out at the coordinate figure fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage the three-phase instantaneous value that matrix inverse transformation obtains active current to be respectively:
In formula (25), C x y _ α β = C α β _ x y = sin ( ω t + γ ) - cos ( ω t + γ ) - cos ( ω t + γ ) - sin ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
8) deduct 7 with the load current three-phase instantaneous value collected) in the three-phase instantaneous value of system active current that obtains, obtain the instruction current signal of Active Power Filter-APF,
i r e f a = i L a - i p a i r e f b = i L b - i p b i r e f c = i L c - i p c . - - - ( 26 )
The invention has the beneficial effects as follows: the present invention is applicable to the Active Power Filter-APF Direct Current Control method under weak grid conditions, can complete dynamic tracing compensation within an electric cycle, dynamic response characteristic is good.Not by the impact of weak line voltage generation frequency deviation.When weak network system is in stable state, APF can the idle and harmonic current of accurate compensation load effectively, does not need to use phase-locked loop, significantly reduce detection time delay, ensure that the dynamic that APF compensates in whole control procedure.
Accompanying drawing explanation
Fig. 1 is APF main circuit topological structure figure in the Active Power Filter-APF Direct Current Control method under the present invention is applicable to weak grid conditions;
Fig. 2 be in the Active Power Filter-APF Direct Current Control method step 3 under the present invention is applicable to weak grid conditions two-phase rest frame to and two-phase xy rotating coordinate system;
Fig. 3 is the APF control strategy block diagram in the Active Power Filter-APF Direct Current Control method under the present invention is applicable to weak grid conditions;
Fig. 4 is the simulation waveform of weak network system PCC point voltage;
Fig. 5 is the simulation waveform of light current net system load electric current;
Fig. 6 is the simulation waveform of system A phase PCC point voltage and light current net system power before compensating;
Fig. 7 is the simulation waveform of system A phase PCC point voltage and light current net system power after compensating;
Fig. 8 is the fft analysis of system A phase PCC point voltage and light current net system power before compensating;
Fig. 9 is the fft analysis of system A phase PCC point voltage and light current net system power after compensating;
The simulation waveform of load current when Figure 10 is light current net system load sudden change;
The simulation waveform of inverter current trace command electric current when Figure 11 is light current net system load sudden change;
System A phase PCC point voltage after Figure 12 compensates when being light current net system load sudden change and the simulation waveform of light current net system power;
System A phase PCC point voltage after Figure 13 compensates when being weak network system generation+5Hz frequency deviation and the simulation waveform of light current net system power;
System A phase PCC point voltage after Figure 14 compensates when being weak network system generation-5Hz frequency deviation and the fft analysis of light current net system power;
System A phase PCC point voltage after Figure 15 compensates when being weak network system generation+5Hz frequency deviation and the simulation waveform of light current net system power;
System A phase PCC point voltage after Figure 16 compensates when being weak network system generation-5Hz frequency deviation and the fft analysis of light current net system power.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.
The invention provides the Active Power Filter-APF Direct Current Control method be applicable under weak grid conditions, implement according to following steps:
Step 1, gathers weak network system PCC point place voltage e a, e band e cinstantaneous value, DC side voltage of converter v dcinstantaneous value, load current i la, i lband i lcinstantaneous value, and the current i that inverter sends ca, i cband i ccinstantaneous value;
Step 2, by the e collected a, e b, e c, v dc, i la, i lband i lcinstantaneous value, and the current i that inverter sends ca, i cband i ccinstantaneous value is input in dsp processor after modulate circuit process, is digital signal e by A/D module converts a, e b, e c, v dc, i la, i lb, i lc, i ca, i cband i cc;
Step 3, dsp processor passes through digital signal e a, e b, e c, v dc, i la, i lband i lcprocess, obtain the instruction current signal i of Active Power Filter-APF refa, i refb, i refc;
The instruction current signal obtaining Active Power Filter-APF in step 3 is specifically implemented according to following steps:
1) instantaneous value of system PCC point voltage and load current is respectively:
e a = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + ) + E m - sin ( m ω t + θ e m - ) ] e b = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + - 2 π / 3 ) + E m - sin ( m ω t + θ e m - + 2 π / 3 ) ] e c = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + + 2 π / 3 ) + E m - sin ( m ω t + θ e m - - 2 π / 3 ) ] - - - ( 1 )
In formula (1), (2): m, n are harmonic number ,+represent positive sequence ,-represent negative phase-sequence; ω is angular speed, and t is the time, for positive sequence m subharmonic voltage amplitude, for negative phase-sequence m subharmonic voltage amplitude, for the initial phase angle of negative phase-sequence m subharmonic voltage, for the initial phase angle of positive sequence m subharmonic voltage, for positive sequence nth harmonic current amplitude, for negative phase-sequence nth harmonic current amplitude, for the initial phase angle of negative phase-sequence nth harmonic electric current, for the initial phase angle of positive sequence nth harmonic electric current;
2) voltage of PCC point and load current instantaneous value are converted to two-phase rest frame;
The coordinate figure that the voltage of PCC point is fastened in two-phase static coordinate is:
e α e β = C a b c _ α β e a e b e c = 3 / 2 Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + ) + E m - sin ( m ω t + θ e m - ) ] 3 / 2 Σ m = 1 ∞ [ - E m + cos ( m ω t + θ e m + ) + E m - cos ( m ω t + θ e m - ) ] - - - ( 3 )
In formula (3), (4): C a b c _ α β = 2 3 1 - 1 2 - 1 2 0 3 2 - 3 2 ;
3) be converted to voltage vector according to the locus between two-phase rest frame and rotating coordinate system, coordinate figure that current phasor is fastened at rotational coordinates;
The coordinate figure that voltage vector is fastened at rotational coordinates is:
e x e y = C α β _ x y e α e β = 3 / 2 Σ m = 1 ∞ { E m + cos [ ( m - 1 ) ω t + θ e m + - γ ] - E m - cos [ ( m + 1 ) ω t + θ e m - + γ ] } - 3 / 2 Σ m = 1 ∞ { E m + sin [ ( m - 1 ) ω t + θ e m + - γ ] + E m - sin [ ( m + 1 ) ω t + θ e m - + γ ] } - - - ( 5 )
In formula (5), C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
The coordinate figure that current phasor is fastened at rotational coordinates is:
4) adopt low pass filter to extract the coordinate figure fastened at rotational coordinates of voltage vector, obtaining the coordinate figure that PCC point voltage and load current fundamental positive sequence fasten at rotational coordinates is:
In formula (7), for the amplitude of fundamental positive sequence voltage, electric current, for the initial phase angle of fundamental positive sequence voltage, electric current, γ is the initial phase angle of xy coordinate system;
5) according to 3) and 4) in obtain voltage, electric current fundamental positive sequence with fundamental positive sequence voltage in the same way with the coordinate figure that the rotational coordinates of rotating speed is fastened, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is
Obtain active current according to the definition of active current again, expression is as follows:
In formula (8),
The coordinate figure that then active current is being fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage is:
i p L x = i p cos ( θ 1 + - γ ) = ( e x 1 + i x 1 + + e y 1 + i y 1 + ) e x 1 + ( e x 1 + ) 2 + ( e y 1 + ) 2 i p L y = i p sin ( θ 1 + - γ ) = ( e x 1 + i x 1 + + e y 1 + i y 1 + ) e x 1 + ( e x 1 + ) 2 + ( e y 1 + ) 2 - - - ( 9 )
6) according to the deviation of DC voltage and desired value, application PI controller obtains the active current i needed for voltage control pdc, then according to 3) and 4) in the coordinate figure fastened at rotational coordinates of the PCC point voltage fundamental positive sequence that obtains, by i pdcalso project to xy coordinate system, its coordinate figure is respectively:
i p d c x = i p d c × e x e x 2 + e y 2 i p d c y = i p d c × e y e x 2 + e y 2 - - - ( 10 )
By i pdccomponent on xy coordinate system joins the component of load active current on xy axial coordinate respectively, then the active current of system consumption at the coordinate figure of xy coordinate system is:
i p x = i p L x + i p d c x i p y = i p L y + i p d c y - - - ( 11 )
7) active current is carried out at the coordinate figure fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage the three-phase instantaneous value that matrix inverse transformation obtains active current to be respectively:
In formula (12), C x y _ α β = C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
8) 7 are deducted with the load current three-phase instantaneous value collected) the three-phase instantaneous value of system active current that obtains, obtain the instruction current signal of Active Power Filter-APF,
i r e f a = i L a - i p a i r e f b = i L b - i p b i r e f c = i L c - i p c . - - - ( 13 )
When PCC electric voltage frequency is displaced to ω ' by ω, the instruction current signal obtaining Active Power Filter-APF in step 3 is specifically implemented according to following steps:
1) instantaneous value of system PCC point voltage and load current is respectively:
e a = Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + ) + E m - sin ( mω ′ t + θ e m - ) ] e b = Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + - 2 π / 3 ) + E m - sin ( mω ′ t + θ e m - + 2 π / 3 ) ] e c = Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + + 2 π / 3 ) + E m - sin ( mω ′ t + θ e m - - 2 π / 3 ) ] - - - ( 14 )
In formula (14), (15), m, n are harmonic number ,+represent positive sequence ,-represent negative phase-sequence; ω 0for angular speed, t is the time, for positive sequence m subharmonic voltage amplitude, for negative phase-sequence m subharmonic voltage amplitude, for the initial phase angle of negative phase-sequence m subharmonic voltage, for the initial phase angle of positive sequence m subharmonic voltage, for positive sequence nth harmonic current amplitude, for negative phase-sequence nth harmonic current amplitude, for the initial phase angle of negative phase-sequence nth harmonic electric current, for the initial phase angle of positive sequence nth harmonic electric current;
2) voltage of PCC point and load current instantaneous value are converted to two-phase rest frame;
The coordinate figure that the voltage of PCC point is fastened in two-phase static coordinate is:
e α e β = C a b c _ α β e a e b e c = 3 / 2 Σ m = 1 ∞ [ E m + sin ( mω ′ t + θ e m + ) + E m - sin ( mω ′ t + θ e m - ) 3 / 2 Σ m = 1 ∞ [ - E m + cos ( mω ′ t + θ e m + ) + E m - cos ( mω ′ t + θ e m - ) - - - ( 16 )
In formula (16), (17), C a b c _ α β = 2 3 1 - 1 2 - 1 2 0 3 2 - 3 2 ;
3) be converted to voltage vector according to the locus between two-phase rest frame and rotating coordinate system, coordinate figure that current phasor is fastened at rotational coordinates;
The coordinate figure that voltage vector is fastened at rotational coordinates is:
e x e y = C α β _ x y e α e β = 3 / 2 Σ m = 1 ∞ { E m + cos [ ( mω ′ - ω ) t + θ e m + - γ ] - E m - cos [ ( mω ′ + ω ) t + θ e m - + γ ] } - 3 / 2 Σ m = 1 ∞ { E m + sin [ ( mω ′ - ω ) t + θ e m + - γ ] + E m - sin [ ( mω ′ + ω ) t + θ e m - + γ ] } - - - ( 18 )
In formula (18), C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) , γ is the first angle of xy coordinate system;
The coordinate figure that current phasor is fastened at rotational coordinates is:
4) adopt low pass filter to extract the coordinate figure fastened at rotational coordinates of voltage vector, obtaining the coordinate figure that PCC point voltage and load current fundamental positive sequence fasten at rotational coordinates is:
In formula (20), for the amplitude of fundamental positive sequence voltage, electric current, for the initial phase angle of fundamental positive sequence voltage, electric current, γ is the initial phase angle of xy coordinate system;
5) according to 3) and 4) in obtain voltage, electric current fundamental positive sequence with fundamental positive sequence voltage in the same way with the coordinate figure that the rotational coordinates of rotating speed is fastened, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is
Active current expression formula is obtained again as follows according to the definition of active current:
In formula (21),
The coordinate figure that then active current is being fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage is:
6) according to the deviation of DC voltage and desired value, application PI controller obtains the active current i needed for voltage control pdc, then according to the coordinate figure that the PCC point voltage fundamental positive sequence obtained in step 3.4 is fastened at rotational coordinates, by i pdcalso project to xy coordinate system, its coordinate figure is respectively:
i p d c x = i p d c × e x e x 2 + e y 2 i p d c y = i p d c × e y e x 2 + e y 2 - - - ( 23 )
By i pdccomponent on xy coordinate system joins the component of load active current on xy axial coordinate respectively, then the active current of system consumption at the coordinate figure of xy coordinate system is:
i p x = i p L x + i p d c x i p y = i p L y + i p d c y - - - ( 24 )
7) active current is carried out at the coordinate figure fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage the three-phase instantaneous value that matrix inverse transformation obtains active current to be respectively:
In formula (25), C x y _ α β = C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
8) deduct 7 with the load current three-phase instantaneous value collected) in the three-phase instantaneous value of system active current that obtains, obtain the instruction current signal of Active Power Filter-APF,
i r e f a = i L a - i p a i r e f b = i L b - i p b i r e f c = i L c - i p c . - - - ( 26 )
Step 4, dsp processor is by instruction current signal i refa, i refb, i refcwith digital signal i ca, i cband i cccarry out stagnant chain rate comparatively, and the PWM module of control DSP sends PWM ripple;
Step 5, the PWM ripple sent by dsp processor is sent to the drive circuit of the IGBT module of inverter, and control inverter is according to instruction current signal i refa, i refb, i refcsend electric current, according to the harmonic wave sent in the weak network system of current compensation and reactive power.
The present invention is applicable in the Active Power Filter-APF Direct Current Control method under weak grid conditions, Active Power Filter-APF, i.e. APF, adopts the voltage source inverter of phase three-wire three, the structure be connected with light current net as shown in Figure 1, e a, e b, e cfor the voltage at PCC point place, i sa, i sb, i scfor the electric current that PCC point absorbs from electrical network, i la, i lb, i lcfor the electric current that nonlinear load absorbs, i ca, i cb, i ccfor the electric current that inverter sends, R, L, C are respectively connection impedance and the DC bus capacitor of inverter.Z ga, Z gb, Z gcfor electric network impedance.
The present invention is applicable to the Active Power Filter-APF Direct Current Control method under weak grid conditions, and be deduced a kind of rotating vector detection method based on virtual synchronous coordinate system according to the vectorial property of voltage and current, coordinate transform as shown in Figure 2.Employing and the synchronized homodromal xy coordinate system of PCC point fundamental positive sequence voltage instead of the dq coordinate system in conventional method, initial phase angle due to xy coordinate system can be arbitrary value, therefore do not need PLL to carry out phase-angle detection, the matrix corresponding to the Coordinate Conversion of Fig. 2 is:
C α β _ x y = s i n ( ω t + γ ) - c o s ( ω t + γ ) - c o s ( ω t + γ ) - s i n ( ω t + γ ) - - - ( 27 )
In formula (27), γ is the angle of positive sequence fundamental voltage and x-axis.
The voltage of PCC point and load current are transformed on virtual synchronous coordinate system xy, the coordinate figure of its correspondence is:
e x = 3 / 2 Σ m = 1 ∞ { E m + cos [ ( m - 1 ) ω t + θ e m + - γ ] - E m - cos [ ( m + 1 ) ω t + θ e m - + γ ] } e y = 3 / 2 Σ m = 1 ∞ { - E m + sin [ ( m - 1 ) ω t + θ e m + - γ ] - E m - sin [ ( m + 1 ) ω t + θ e m - + γ ] } - - - ( 28 )
Positive sequence fundamental voltage and the coordinate figure of current phasor on xy coordinate system is obtained through low pass filter:
Therefore under xy coordinate system, the real component of positive sequence fundamental current is:
Carry out inverse transformation to testing result, the real component obtaining positive sequence fundamental current is:
Can find that the value at virtual rotating coordinate system angle can not affect testing result by above-mentioned testing result.
The DC capacitor voltage fluctuation of APF not only can affect its compensation effect, and can affect the stability of whole system.Start at APF, in the dynamic process such as grid-connected and load switching, be necessary to the control of its DC voltage.According to the deviation of DC voltage and desired value in Traditional control strategy, application PI controller obtains the active current i needed for voltage control pdc, and joined the closed-loop control namely realizing DC voltage in load current d axle component.
Although xy coordinate system and the synchronized rotating Vortex of dq coordinate system, exist angle γ between it and positive sequence fundamental voltage, and become when γ value is, the present invention is by i pdcalso project to xy coordinate system, its coordinate figure is respectively:
i p d c x = i p d c × e x e x 2 + v y 2 i p d c y = i p d c × e y e x 2 + e y 2 - - - ( 33 )
By i pdccomponent on xy coordinate system joins the component of load active current on xy axial coordinate respectively, realizes the DC voltage closed-loop control with equivalence in Traditional control.
As shown in Figure 3, weak network system PCC voltage distortion and under uneven condition, APF no longer needs application PLL (i.e. phase-locked loop) to detect voltage-phase, because this reducing the complexity of control algolithm, reduce the detection time delay introduced by PLL simultaneously, effectively improve the performance of APF.
When the light current net system cloud gray model containing a large amount of distributed power source is in isolated island situation, because unbalanced power can cause line voltage frequency deviation, the present invention is equally applicable to this kind of situation.Supposing that electrical network fundamental voltage frequency is displaced to ω ' by ω, can there is frequency deviation in corresponding electric current equally, obtains positive sequence fundamental voltage and the coordinate figure of current phasor on xy coordinate system is after transforming to virtual synchronous coordinate system through low pass filter:
Under xy coordinate system, the real component of positive sequence fundamental current is:
Therefore the real component of three-phase positive sequence fundamental current is:
As can be seen from formula (36), when PCC point voltage generation frequency deviation, the present invention can accurately carry out current detecting.
Emulate system shown in Figure 1 at Matlab/Simulink software, PCC point voltage superposes negative phase-sequence 5 times by positive sequence fundamental voltage and positive sequence 7 subharmonic voltage is formed, and load is the uncontrollable rectification circuit of three-phase bridge, and concrete system emulation parameter is as shown in table 1:
Table 1 system emulation parameter
Utilize Matlab/Simulink software, according to the system emulation parameter in table 1, obtain the simulation result figure shown in Fig. 4-16;
Fig. 4, Fig. 5 are respectively the PCC point voltage before APF input and load current waveform.Wherein the perunit value of negative phase-sequence 5 subharmonic voltage is 0.3, and the perunit value of positive sequence 7 subharmonic voltage is 0.15.
Fig. 6, Fig. 7, Fig. 8, Fig. 9 are respectively APF control method and compensate the waveform of forward and backward PCC point A phase voltage and electrical network inflow PCC point electric current and the fft analysis result of electric current.Before APF puts into operation, the total harmonic distortion factor of inflow current is 25.66%, and there is certain phase angle difference between voltage and current, and system power factor is 0.886; After APF puts into operation, the current total harmonic distortion rate that electrical network flows into PCC point is reduced to 1.71%, and electric current and positive sequence fundamental voltage same-phase, system power factor brings up to 1.0, the present invention is when weak network system is in stable state, and APF can the idle and harmonic current of accurate compensation load effectively.
Weak network system is put in the load of 0.5s non-linear hour and is twice, and Figure 10, Figure 11, Figure 12 sets forth load current waveform, the current waveform of the A phase current that APF exports and reference value waveform and weak network system PCC point A phase voltage and electrical network inflow.Show that APF adopts the present invention, can complete dynamic tracing compensation within an electric cycle, dynamic response characteristic is good.
Figure 13, Figure 14 sets forth light current net system voltage when 0.5s under generation ± 5Hz offset frequency situation, PCC point voltage and electrical network flow into the waveform of PCC point electric current, Figure 15, Figure 16 sets forth the fft analysis of electric current, can find out from Figure 13,14,15 and 16 when system voltage generation frequency deviation, electrical network inflow current after compensation can keep and voltage in phase through the adjustment of one-period, and total harmonic distortion factor is respectively 2.45%, 2.04%.Therefore the present invention is not by the impact of weak line voltage generation frequency deviation.

Claims (3)

1. be applicable to the Active Power Filter-APF Direct Current Control method under weak grid conditions, it is characterized in that, implement according to following steps:
Step 1, gathers weak network system PCC point place voltage e a, e band e cinstantaneous value, DC side voltage of converter v dcinstantaneous value, load current i la, i lband i lcinstantaneous value, and the current i that inverter sends ca, i cband i ccinstantaneous value;
Step 2, by the e collected a, e b, e c, v dc, i la, i lband i lcinstantaneous value, and the current i that inverter sends ca, i cband i ccinstantaneous value is input in dsp processor after modulate circuit process, is digital signal e by A/D module converts a, e b, e c, v dc, i la, i lb, i lc, i ca, i cband i cc;
Step 3, dsp processor passes through digital signal e a, e b, e c, v dc, i la, i lband i lcprocess, obtain the instruction current signal i of Active Power Filter-APF refa, i refb, i refc;
Step 4, dsp processor is by instruction current signal i refa, i refb, i refcwith digital signal i ca, i cband i cccarry out stagnant chain rate comparatively, and the PWM module of control DSP sends PWM ripple;
Step 5, the PWM ripple sent by dsp processor is sent to the drive circuit of the IGBT module of inverter, and control inverter is according to instruction current signal i refa, i refb, i refcsend electric current, according to the harmonic wave sent in the weak network system of current compensation and reactive power.
2. the Active Power Filter-APF Direct Current Control method be applicable under weak grid conditions according to claim 1, it is characterized in that, the instruction current signal obtaining Active Power Filter-APF in step 3 is specifically implemented according to following steps:
1) instantaneous value of system PCC point voltage and load current is established to be respectively:
e a = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + ) + E m - sin ( m ω t + θ e m - ) ] e b = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + - 2 π / 3 ) + E m - sin ( m ω t + θ e m - + 2 π / 3 ) ] e c = Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + + 2 π / 3 ) + E m - sin ( m ω t + θ e m - - 2 π / 3 ) ] - - - ( 1 )
In formula (1), (2): m, n are harmonic number ,+represent positive sequence ,-represent negative phase-sequence; ω is angular speed, and t is the time, for positive sequence m subharmonic voltage amplitude, for negative phase-sequence m subharmonic voltage amplitude, for the initial phase angle of negative phase-sequence m subharmonic voltage, for the initial phase angle of positive sequence m subharmonic voltage, for positive sequence nth harmonic current amplitude, for negative phase-sequence nth harmonic current amplitude, for the initial phase angle of negative phase-sequence nth harmonic electric current, for the initial phase angle of positive sequence nth harmonic electric current;
2) voltage of PCC point and load current instantaneous value are converted to two-phase rest frame;
The coordinate figure that the voltage of PCC point is fastened in two-phase static coordinate is:
e α e β = C a b c _ α β = e a e b e c = 3 / 2 Σ m = 1 ∞ [ E m + sin ( m ω t + θ e m + ) + E m - sin ( m ω t + θ e m - ) ] 3 / 2 Σ m = 1 ∞ [ - E m + cos ( m ω t + θ e m + ) + E m - cos ( m ω t + θ e m - ) ] - - - ( 3 )
In formula (3), (4): C a b c _ α β = 2 3 1 - 1 2 - 1 2 0 3 2 - 3 2 ;
3) be converted to voltage vector according to the locus between two-phase rest frame and rotating coordinate system, coordinate figure that current phasor is fastened at rotational coordinates;
The coordinate figure that voltage vector is fastened at rotational coordinates is:
e x e y = C α β _ x y e α e β = 3 / 2 Σ m = 1 ∞ { E m + cos [ ( m - 1 ) ω t + θ e m + - γ ] - E m - cos [ ( m + 1 ) ω t + θ e m - + γ ] } - 3 / 2 Σ m = 1 ∞ { E m + sin [ ( m - 1 ) ω t + θ e m + - γ ] + E m - sin [ ( m + 1 ) ω t + θ e m - + γ ] } - - - ( 5 )
In formula (5), C α β _ x y = sin ( ω t + γ ) - cos ( ω t + γ ) - cos ( ω t + γ ) - sin ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
The coordinate figure that current phasor is fastened at rotational coordinates is:
4) adopt low pass filter to extract the coordinate figure fastened at rotational coordinates of voltage vector, obtaining the coordinate figure that PCC point voltage and load current fundamental positive sequence fasten at rotational coordinates is:
In formula (7), for the amplitude of fundamental positive sequence voltage, electric current, for the initial phase angle of fundamental positive sequence voltage, electric current, γ is the initial phase angle of xy coordinate system;
5) according to 3) and 4) in obtain voltage, electric current fundamental positive sequence with fundamental positive sequence voltage in the same way with the coordinate figure that the rotational coordinates of rotating speed is fastened, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is
Obtain active current according to the definition of active current again, expression is as follows:
In formula (8),
The coordinate figure that then active current is being fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage is:
i p L x = i p cos ( θ 1 + - γ ) = ( e x 1 + i x 1 + + e y 1 + i y 1 + ) e x 1 + ( e x 1 + ) 2 + ( e y 1 + ) 2 i p L y = i p sin ( θ 1 + - γ ) - ( e x 1 + i x 1 + + e y 1 + i y 1 + ) e y 1 + ( e x 1 + ) 2 + ( e y 1 + ) 2 - - - ( 9 )
6) according to the deviation of DC voltage and desired value, application PI controller obtains the active current i needed for voltage control pdc, then according to 3) and 4) in the coordinate figure fastened at rotational coordinates of the PCC point voltage fundamental positive sequence that obtains, by i pdcalso project to xy coordinate system, its coordinate figure is respectively:
i p d c x = i p d c × e x e x 2 + e y 2 i p d c y = i p d c × e y e x 2 + e y 2 - - - ( 10 )
By i pdccomponent on xy coordinate system joins the component of load active current on xy axial coordinate respectively, then the active current of system consumption at the coordinate figure of xy coordinate system is:
i p x = i p L x + i p d c x i p y = i p L y + i p d c y - - - ( 11 )
7) active current is carried out at the coordinate figure fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage the three-phase instantaneous value that matrix inverse transformation obtains active current to be respectively:
In formula (12), C x y _ α β = C α β _ x y = sin ( ω t + γ ) - cos ( ω t + γ ) - cos ( ω t + γ ) - sin ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
8) 7 are deducted with the load current three-phase instantaneous value collected) the three-phase instantaneous value of system active current that obtains, obtain the instruction current signal of Active Power Filter-APF,
i r e f a = i L a - i p a i r e f b = i L b - i p b i r e f c = i L c - i p c . - - - ( 13 )
3. the Active Power Filter-APF Direct Current Control method be applicable under weak grid conditions according to claim 1, it is characterized in that, when PCC electric voltage frequency is displaced to ω ' by ω, the instruction current signal obtaining Active Power Filter-APF in step 3 is specifically implemented according to following steps:
1) instantaneous value of system PCC point voltage and load current is established to be respectively:
e a = Σ m = 1 ∞ [ E m + sin ( m ω ′ t + θ em + ) + E m - sin ( m ω ′ t + θ em - ) ] e b = Σ m = 1 ∞ [ E m + sin ( m ω ′ t + θ em + - 2 π / 3 ) + E m - sin ( m ω ′ t + θ em - + 2 π / 3 ) ] e c = Σ m = 1 ∞ [ E m + sin ( m ω ′ t + θ em + + 2 π / 3 ) + E m - sin ( m ω ′ t + θ em - - 2 π / 3 ) ] - - - ( 14 )
In formula (14), (15), m, n are harmonic number ,+represent positive sequence ,-represent negative phase-sequence; ω 0for angular speed, t is the time, for positive sequence m subharmonic voltage amplitude, for negative phase-sequence m subharmonic voltage amplitude, for the initial phase angle of negative phase-sequence m subharmonic voltage, for the initial phase angle of positive sequence m subharmonic voltage, for positive sequence nth harmonic current amplitude, for negative phase-sequence nth harmonic current amplitude, for the initial phase angle of negative phase-sequence nth harmonic electric current, for the initial phase angle of positive sequence nth harmonic electric current;
2) voltage of PCC point and load current instantaneous value are converted to two-phase rest frame;
The coordinate figure that the voltage of PCC point is fastened in two-phase static coordinate is:
e α e β = C a b c _ α β = e a e b e c = 3 / 2 Σ m = 1 ∞ [ E m + sin ( m ω ′ t + θ em + ) + E m - sin ( m ω ′ t + θ em - ) ] 3 / 2 Σ m = 1 ∞ [ - E m + cos ( m ω ′ t + θ em + ) + E m - cos ( m ω ′ t + θ em - ) ] - - - ( 16 )
In formula (16), (17), C a b c _ α β = 2 3 1 - 1 2 - 1 2 0 3 2 - 3 2 ;
3) be converted to voltage vector according to the locus between two-phase rest frame and rotating coordinate system, coordinate figure that current phasor is fastened at rotational coordinates;
The coordinate figure that voltage vector is fastened at rotational coordinates is:
e x e y = C α β _ x y e α e β = 3 / 2 Σ m = 1 ∞ { E m + cos [ ( m ω ′ - ω ) t + θ e m + - γ ] - E m - cos [ ( m ω ′ + ω ) t + θ e m - + γ ] } - 3 / 2 Σ m = 1 ∞ { E m + sin [ ( m ω ′ - ω ) t + θ e m + - γ ] + E m - sin [ ( m ω ′ + ω ) t + θ e m - + γ ] } - - - ( 18 )
In formula (18), C α β _ x y = sin ( ω t + γ ) - cos ( ω t + γ ) - cos ( ω t + γ ) - sin ( ω t + γ ) , γ is the first angle of xy coordinate system;
The coordinate figure that current phasor is fastened at rotational coordinates is:
4) adopt low pass filter to extract the coordinate figure fastened at rotational coordinates of voltage vector, obtaining the coordinate figure that PCC point voltage and load current fundamental positive sequence fasten at rotational coordinates is:
In formula (20), for the amplitude of fundamental positive sequence voltage, electric current, for the initial phase angle of fundamental positive sequence voltage, electric current, γ is the initial phase angle of xy coordinate system;
5) according to 3) and 4) in obtain voltage, electric current fundamental positive sequence with fundamental positive sequence voltage in the same way with the coordinate figure that the rotational coordinates of rotating speed is fastened, the angle obtained between the fundamental positive sequence of voltage and the fundamental positive sequence of electric current is
Active current expression formula is obtained again as follows according to the definition of active current:
In formula (21),
The coordinate figure that then active current is being fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage is:
6) according to the deviation of DC voltage and desired value, application PI controller obtains the active current i needed for voltage control pdc, then according to the coordinate figure that the PCC point voltage fundamental positive sequence obtained in step 3.4 is fastened at rotational coordinates, by i pdcalso project to xy coordinate system, its coordinate figure is respectively:
i p d c x = i p d c × e x e x 2 + e y 2 i p d c y = i p d c × e y e x 2 + e y 2 - - - ( 23 )
By i pdccomponent on xy coordinate system joins the component of load active current on xy axial coordinate respectively, then the active current of system consumption at the coordinate figure of xy coordinate system is:
i p x = i p L x + i p d c x i p y = i p L y + i p d c y - - - ( 24 )
7) active current is carried out at the coordinate figure fastened with the rotational coordinates of rotating speed in the same way with fundamental positive sequence voltage the three-phase instantaneous value that matrix inverse transformation obtains active current to be respectively:
In formula (25), C x y _ α β = C α β _ x y = sin ( ω t + γ ) - cos ( ω t + γ ) - cos ( ω t + γ ) - sin ( ω t + γ ) , γ is the initial phase angle of xy coordinate system;
8) deduct 7 with the load current three-phase instantaneous value collected) in the three-phase instantaneous value of system active current that obtains, obtain the instruction current signal of Active Power Filter-APF,
i r e f a = i L a - i p a i r e f b = i L b - i p b i r e f c = i L c - i p c . - - - ( 26 )
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