CN104682390A - Alternating current (AC) hybrid active power filter system for high-voltage direct current (DC) transmission, and control method thereof - Google Patents

Alternating current (AC) hybrid active power filter system for high-voltage direct current (DC) transmission, and control method thereof Download PDF

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Publication number
CN104682390A
CN104682390A CN201510033171.9A CN201510033171A CN104682390A CN 104682390 A CN104682390 A CN 104682390A CN 201510033171 A CN201510033171 A CN 201510033171A CN 104682390 A CN104682390 A CN 104682390A
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China
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filter
voltage
current
level converter
modular multi
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李勇
韩继业
段义隆
张明敏
罗隆福
曹一家
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Hunan University
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Hunan University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H02J2003/365—Reducing harmonics or oscillations in HVDC
    • Y—GENERAL 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/20—Active power filtering [APF]
    • Y—GENERAL 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention provides an alternating current (AC) hybrid active power filter system for high-voltage direct current (DC) transmission, and a control method of the AC hybrid active power filter system. The AC hybrid active power filter system is applied to a high-voltage DC transmission system, and comprises a passive power filter and an active power filter which are connected with each other, wherein an output end of the passive power filter is directly connected with AC sides of convertor stations at two ends of a high-voltage DC output power system; the passive power filter comprises three groups of single-tuned passive filters, wherein each group of single-tuned passive filter is correspondingly connected with one phase of the AC sides of the convertor stations; the single-tuned passive filter groups have a series resonance characteristic; the active power filter comprises a modular multi-level converter and a controller connected with the modular multi-level converter; a DC end of the modular multi-level converter is connected with a capacitor in parallel. After the AC hybrid active power filter system and the control method of the system are adopted, the equipment investment and the operation and maintenance cost are effectively reduced, the electric energy loss generated by unit capacity can be reduced, and the economy of a high-voltage DC transmission AC filtering device can be improved.

Description

For interchange hybrid active power filter and the control method thereof of high voltage direct current transmission
Technical field
The present invention relates to harmonic wave control and the reactive power compensation of high voltage direct current transmission interchange, more particularly, relate to a kind of interchange hybrid active power filter for high voltage direct current transmission and control method thereof.
Background technology
The distribution of China's power load and power generation energy resource is very unbalanced, and eastern region load is many and the energy is few, and northwest, the southwest energy is many and load is few.Setting up thermoelectricity, Hydropower Base at energy centre, Large Copacity, is at a distance the better approach of this contradiction of solution to load center by power delivery.This just needs to set up national energy source passage, carries out the deployment of " transferring electricity from the west to the east, north and south supplies mutually, on national network ".High voltage direct current transmission can at a distance, Large Copacity electric energy transmitting, be applicable to large regional grid asynchronous interconnected, have power loss little, circuit cost is low, and power adjustments rapid flexible, does not exist the advantages such as system instability, is at home and abroad widely applied.What the current conversion station of high voltage direct current transmission adopted usually is 12 pulse conversion devices, and it produces 12n ± 1 time characteristic harmonics at AC.These harmonic currents; not only affect the quality of electric energy; and all can produce serious interference to the power equipment in electrical network itself, electrical network, metering device, protective device, neighbouring communication system; therefore, to the research of high voltage direct current transmission harmonic filtration method be an important subject of DC transmission system.
At present, in solution high voltage direct current transmission AC power quality problem, main filtering technique comprises the pulse number and passive filtering that increase current converter.Can reduce the constituent of characteristic harmonics by increasing the pulse number of current converter and improve the number of times of most low order characteristic harmonics, thus characteristic harmonics content is reduced, but this will cause the wiring of transformer very complicated, nor economical.Passive filtering is because apparatus structure is fairly simple, design and manufaction ratio is easier to, and initial investment cost is lower, is widely applied in systems in practice.But the Filtering Efficacy of passive filter is easily subject to the impact of system side impedance.When line voltage exists harmonic wave, when electric power networks structure changes, likely cause the series/parallel resonance between filter impedance and system impedance, this not only affects electric power system stability, and limits the performance of filtering performance.In addition, although passive filtering can suppress specific subharmonic, but to low-order harmonic, there is amplification, and capacitor parameters passing in time easily changes, this can cause tuned frequency to offset, for avoiding and system impedance generation resonance in addition when designing passive filter, usually adopt the humorous design of offset, thus the filtering performance that impact is actual.
Summary of the invention
The object of the invention is to overcome above-mentioned defect of the prior art, a kind of interchange hybrid active power filter for high voltage direct current transmission and control method thereof are provided, fundamentally solve the technical barrier that conventional active filtering system directly cannot be applied in high voltage direct current transmission ac filter; Effective reduction equipment investment and operation expense, reduce the electric energy loss that unit capacity produces, and improves the economy of high voltage direct current transmission (HVDC, High-Voltage Direct Current) AC filter installation.
For achieving the above object, technical scheme provided by the invention is as follows:
For an interchange hybrid active power filter for high voltage direct current transmission, comprise interconnective passive filter and active filter; The output of described passive filter directly connects the AC that high voltage direct current exports electric system two ends current conversion station;
Described passive filter comprises three groups of single tuning passive filter groups, and wherein each group single tuning passive filter group correspondence connects a phase of current conversion station AC, and described single tuning passive filter group has series resonance characteristics;
Described active filter comprises modular multi-level converter and coupled controller, a DC terminal capacitor in parallel of described modular multi-level converter; The input of each one group of single tuning passive filter group that is connected of modular multi-level converter ac output end, the output of single tuning passive filter group is connected to the corresponding phase on current conversion station AC;
Described modular multi-level converter comprises three unsteady flow bridges, and the output of each unsteady flow bridge is respectively as a phase of three-phase alternating current output, and each unsteady flow bridge comprises a positive convertor arm, a negative convertor arm and two filter reactors; Each convertor arm comprises the power modules of multiple positive-negative series successively;
In each unsteady flow bridge, the anode of positive convertor arm is connected to the direct current anode of modular multi-level converter, and the negative terminal of positive convertor arm is connected to the output of unsteady flow bridge by a filter reactor; The negative terminal of negative convertor arm is connected to the direct current negative terminal of modular multi-level converter, and the anode of negative convertor arm is connected to the output of unsteady flow bridge by another filter reactor;
The control output end of described controller is connected with each power modules in modular multi-level converter, for controlling the switch of each power modules, and then change the quantity of the power modules effectively worked in each convertor arm, the compensating signal exported with control module Multilevel Inverters.
Further, described single tuning passive filter group comprises 11 single tuned filters parallel with one another, 13 single tuned filters, 23 single tuned filters, 25 single tuned filters.
Further, described passive filter is issued to series resonance state at specific subfrequency, is capacitive under fundamental frequency simultaneously, the reactive power that compensating non-linear load consumes;
Passive filter is while carrying out filtering, and bear all fundamental voltages, active filter bears fundamental voltage hardly; Often organizing in single tuning passive filter group, there is h single tuned filter of series resonance characteristics at design capacitance device C hwith reactor L hduring parameter, meet following condition:
jh ω 1 L h - 1 jh ω 1 C h = 0 C h = Q C ( h ) ( h 2 - 1 ) ( V 2 ω 1 ) h 2 L h = 1 h 2 ω 1 2 C h
In formula, the fundamental voltage that V bears for h single tuned filter, Q c (h)for the reactive power compensation capacity that h single tuned filter provides, ω 1for first-harmonic angular frequency.
Further, modular multi-level converter is controlled so as to a harmonic current control type voltage source U under the effect of controller ch, it is equivalent to add virtual resistance K at system primary side, the voltage U that modular multi-level converter will export chfollowing relation should be met:
U ch＝KI sh
Wherein, K is the equivalent virtual resistance of modular multi-level converter, I shfor the harmonic current of current conversion station AC in the HVDC (High Voltage Direct Current) transmission system that on-line checkingi goes out.
To a control method for the above-described hybrid active power filter for high voltage direct current transmission, comprise the following steps:
S1, Harmonic currents detection;
S2, outer shroud voltage control;
The command signal of S3, calculating active filter output voltage;
S4, Pressure and Control: comprise alternate Pressure and Control and power modules Pressure and Control;
S5, loop current suppression;
S6, phase-shifting carrier wave are modulated.
Further, described S1 comprises: HVDC (High Voltage Direct Current) transmission system two ends AC a phase voltage through phase-locked loop for whole control system provides synchronizing signal; HVDC (High Voltage Direct Current) transmission system two ends AC three-phase current through DQ conversion and high pass filter after, by the projection of harmonic component on DQ axle in remaining three-phase current.
Further, in described S4, the method of power modules Pressure and Control comprises: the instantaneous value detecting the electric current of upper and lower brachium pontis in real time, when power component is to common DC bus active power of output, namely electric capacity is discharged, otherwise, then electric capacity is charged, obtain the correction of individual capacitor voltages thus, this correction is superimposed upon on the reference voltage of the upper and lower brachium pontis of modular multi-level converter.
Further, described S5 comprises: adopt the rotation transformation of two frequency multiplication negative phase-sequences that two frequency multiplication circulation are separated into two DC component, after described two DC component and the reference value of circulation DQ axle component being done poor comparison, through pi regulator, the feedforward amount introducing voltage again realizes the decoupling zero of circulation, by obtaining the amount of unbalance of builtin voltage after coordinate transform, finally in the voltage command signal of upper and lower brachium pontis, this voltage-drop compensation is fallen.
Further, described S6 comprises:
For the N number of submodule in each brachium pontis, controller all produces N bar triangular carrier, make the N bar triangular carrier of each brachium pontis remove the 1/N triangular carrier cycle successively, 360 °/N phase angle, then with superposed modular multi-level converter (MMC) voltage between phases correction u aref, individual capacitor voltages correction u brefwith loop current suppression unbalanced component u crefafter upper and lower bridge arm voltage modulating wave compare, produce N group PWM ripple signal, respectively a driving N submodule unit, determine that they drop into or excise.
Compared with prior art, beneficial effect of the present invention is:
(1) in this system, passive filter is issued to series resonance state at specific subfrequency, and in capacitive under fundamental frequency, plays main harmonic filtration and inactive power compensation, and bear most of fundamental voltage.Therefore modular multi-level converter only bears harmonic voltage, will greatly reduce the capacity of active filter, reduce system investments.
(2) be connected in series containing the active filter of modular multi-level converter and passive filter, play auxiliary filter effect.It can increase the filtering bandwidth of passive filter, for the HVDC (High Voltage Direct Current) transmission system that system frequency fluctuation range is larger, passive filter effectively can be suppressed in the problem departing from humorous the brought filtering performance decline of offset under rated frequency, improve the filter effect of passive filter.
(3) with use merely compared with passive filter (namely removing the active filter in native system), the harmonic current that native system can effectively suppress HVDC (High Voltage Direct Current) transmission system AC harmonic voltage to excite in circulation transformer side, and to interact the series resonance problem produced with passive filter.
(4) main circuit of active filter adopts modular multi-level converter, depending on the compensation capacity of HVDC (High Voltage Direct Current) transmission system AC, by changing the quantity of the power modules of each brachium pontis series connection of modular multi-level converter, adjust the voltage scope of application of current transformer neatly, reach the object of dynamic compensation.
Accompanying drawing explanation
Fig. 1 is the schematic diagram of a kind of interchange hybrid active power filter for high voltage direct current transmission provided by the invention;
Fig. 2 is the structural representation of the modular multi-level converter in the present invention;
Fig. 3 is the electrical block diagram of the power modules in the present invention;
Fig. 4 is the single-phase winding diagram of system of the present invention;
Fig. 5 is the one phase equivalent circuit figure of Fig. 4;
Fig. 6 is control method schematic diagram provided by the invention;
Fig. 7 is the circuit theory diagrams of alternate Pressure and Control part in control method provided by the invention;
Fig. 8 is the circuit theory diagrams of power modules Pressure and Control part in control method provided by the invention;
Fig. 9 is the circuit theory diagrams of loop current suppression part in control method provided by the invention.
Embodiment
Below in conjunction with drawings and Examples, a kind of interchange hybrid active power filter for high voltage direct current transmission of the present invention and control method thereof are described further.
Embodiment 1
Please refer to Fig. 1 to Fig. 5, Fig. 1 is the interchange hybrid active power filter for high voltage direct current transmission provided by the invention, and described hybrid active power filter 2 comprises interconnective passive filter 4 and active filter 3; The direct carry of passive filter 4 output is on the public exchange bus of current conversion station both sides, HVDC (High Voltage Direct Current) transmission system two ends.
Particularly, in prior art, Inverter Station 64 that described HVDC (High Voltage Direct Current) transmission system comprises converter transformer 62, doube bridge 12 pulses converting plant 63 and doube bridge 12 is pulsed.Doube bridge 12 converting plant 63 and doube bridge 12 Inverter Station 64 of pulsing of pulsing is interconnected; Pulse converting plant 63 and a converter transformer 62 of doube bridge 12 is connected to form a current conversion station; Pulse Inverter Station 64 of doube bridge 12 is connected to form another current conversion station with another converter transformer 62; The AC of two current conversion stations is connected with AC transmission system 61 respectively by public exchange bus, for converting the alternating current in AC transmission system 61 to direct current, after being sent to reception place by overhead wire or cable, restoring into alternating current and send into another AC transmission system 61.In the embodiment of the present invention, on the public exchange bus of each current conversion station of HVDC (High Voltage Direct Current) transmission system, each connection one exchanges hybrid active power filter 2.
Particularly, described passive filter 4 comprises three groups of single tuning passive filter groups 5, and wherein each group single tuning passive filter group 5 correspondence connects a phase of public exchange bus.Described single tuning passive filter group 5 has series resonance characteristics; Each group single tuning passive filter group 5 comprises 11 single tuned filters parallel with one another, 13 single tuned filters, 23 single tuned filters, 25 single tuned filters, passive filter 4 is issued to the state of series resonance at specific subfrequency, be capacitive under fundamental frequency simultaneously, the reactive power that compensating non-linear load consumes; Be mainly used to suppress the harmonics electric current that in HVDC (High Voltage Direct Current) transmission system, two ends current conversion station produces at AC, and take into account the function of reactive power compensation.
Described active filter 3 comprises modular multi-level converter (MMC, Modular Multilevel Converter) and coupled controller 6, a DC terminal capacitor in parallel of described modular multi-level converter (MMC) is as direct current and exchange the energy storage device changed.The input of each one group of single tuning passive filter group 5 that is connected of modular multi-level converter (MMC) ac output end, the output of single tuning passive filter group 5 is connected to the corresponding phase on public exchange bus.Active filter 3 act as the filtering performance improving passive filter 4, the series/parallel resonance of damped harmonic system.
The structured flowchart of the modular multi-level converter (MMC) that the main circuit of active filter 3 in the present invention adopts has been shown in Fig. 2.Particularly, described modular multi-level converter (MMC) comprises A phase unsteady flow bridge, B phase unsteady flow bridge and C phase unsteady flow bridge, and the output of each unsteady flow bridge is respectively as a phase of three-phase alternating current output.
Wherein, each unsteady flow bridge comprises a positive convertor arm, a negative convertor arm and two filter reactors 12; Each convertor arm comprises the power modules 11 of multiple positive-negative series successively, namely the anode of a power modules 11 is connected to the negative terminal of another power modules 11, multiple power modules 11 connects successively, and the power modules 11 being positioned at two ends forms anode and the negative terminal of convertor arm respectively., positive convertor arm comprises the multiple power modules 11 being numbered SM1 to SMN in the present embodiment as shown in Figure 2, and negative convertor arm comprises the multiple power modules 11 being numbered SMN+1 to SM2N; Namely the quantity comprising power modules 11 in positive convertor arm and negative convertor arm is equal.
Further, in each unsteady flow bridge, the anode of positive convertor arm is connected to the direct current anode of modular multi-level converter (MMC), and then is connected to the anode of capacitor 9, and the negative terminal of positive convertor arm is connected to the output of unsteady flow bridge by a filter reactor 12; The negative terminal of negative convertor arm is connected to the direct current negative terminal of modular multi-level converter (MMC), and then is connected to the negative terminal of capacitor 9, and the anode of negative convertor arm is connected to the output of unsteady flow bridge by another filter reactor 12.
As shown in Figure 3, each power modules 11 comprises direct current capacitor C, the first switching device VT1, second switch device VT2, the first fly-wheel diode VD1 and the second fly-wheel diode VD2 to the concrete structure of power modules 11; Wherein, described first switching device VT1 and second switch device VT2 is full-control type semiconductor switch device;
The collector electrode of the first switching device VT1 is connected with the negative electrode of the first fly-wheel diode VD1, and the emitter of the first switching device VT1 is connected with the anode of the first fly-wheel diode VD1; The collector electrode of second switch device VT2 is connected with the negative electrode of the second fly-wheel diode VD2, and the emitter of second switch device VT2 is connected with the anode of the second fly-wheel diode VD2; The anode of direct current capacitor C is connected with the collector electrode of the first switching device VT1, and the negative terminal of direct current capacitor C is connected with the emitter of second switch device VT2; The emitter of the first switching device VT1 is as the anode of power modules 11, and the emitter of second switch device VT2 is as the negative terminal of power modules 11.
The control output end of described controller 6 is connected with each power modules 11 in modular multi-level converter (MMC), for controlling the switch of each power modules 11, and then change the quantity of the power modules 11 effectively worked in each convertor arm, the compensating signal exported with control module Multilevel Inverters (MMC).Particularly, switching device work in each power modules 11 transmitted control signal in driver module Multilevel Inverters (MMC) by controller 6, makes modular multi-level converter (MMC) export and the compensating signal that harmonic current size is identical, direction is contrary on public exchange bus.
In addition, play direct current and the capacitor 9 exchanging translation function, the harmonic electric energy of each phase can be stored on the one hand, galvanic current pressure also can be provided as inverter on the other hand.
Modular multi-level converter (MMC) becomes a harmonic current control type controlled voltage source under the influence of control 6, by changing the quantity of the power modules of the upper series connection of modular multi-level converter (MMC) each brachium pontis (general names of two convertor arms namely on a unsteady flow bridge), adjust the voltage scope of application of current transformer neatly, fundamentally solve active filter system and directly cannot be applied in technical barrier in HVDC (High Voltage Direct Current) transmission system.
After modular multi-level converter (MMC) becomes a harmonic current control type controlled voltage source under the effect of controller, be mainly the AC of current conversion station in HVDC (High Voltage Direct Current) transmission system and virtual resistance is provided, improve the filter effect of passive filter 4, and greatly can reduce the possibility of system generation series/parallel resonance.Hybrid active power filter provided by the invention takes full advantage of the filtering potential of passive filter 4, its active part only provides the effect improving system filter characteristic, therefore greatly reduce active part capacity, its equipment investment of effective reduction and operation expense, reduce the electric energy loss that unit capacity produces, improve the economy of AC filter installation in HVDC (High Voltage Direct Current) transmission system.Therefore compared with traditional mixed filtering system, active filter 3 is successfully applied to HVDC (High Voltage Direct Current) transmission system by the present invention, overcome the drawback that tradition has no chance filter, achieve the harmonic current that dynamic compensation HVDC (High Voltage Direct Current) transmission system two ends exchange, and carry out certain reactive power compensation.
Introduce Harmonic suppression Theory of the present invention below.
In the present invention, passive filter 4 all reaches series resonance state under specific subfrequency, is capacitive under fundamental frequency simultaneously, the reactive power that compensating non-linear load consumes; That is, passive filter 4 is while carrying out filtering, bears all fundamental voltages, and active filter 3 bears fundamental voltage hardly.Often organizing in single tuning passive filter group 5, there is h single tuned filter of series resonance characteristics at design capacitance device C hwith reactor L hduring parameter, meet following condition:
jh ω 1 L h - 1 jh ω 1 C h = 0 C h = Q C ( h ) ( h 2 - 1 ) ( V 2 ω 1 ) h 2 L h = 1 h 2 ω 1 2 C h
In formula, the fundamental voltage that V bears for h single tuned filter, Q c (h)for the reactive power compensation capacity that h single tuned filter provides, ω 1for first-harmonic angular frequency.Consider the technical scheme of embodiments of the invention, h gets 11,13,23 and 25 respectively, corresponding 11 single tuned filters, 13 single tuned filters, 23 single tuned filters and 25 single tuned filters.
Fig. 4 is the single-phase winding diagram of native system, and modular multi-level converter (MMC) is controlled so as to a harmonic current control type voltage source U under the influence of control 6 ch, it is equivalent to add virtual resistance K at system primary side, fundamentally can eliminate the series resonance of passive filter 4, and can increase the bandwidth of passive filter 4 filtering harmonic current.The voltage U that modular multi-level converter (MMC) will export chfollowing relation should be met:
U ch＝KI sh
Wherein, K is the equivalent virtual resistance of modular multi-level converter (MMC), I shfor the harmonic current of current conversion station AC in the HVDC (High Voltage Direct Current) transmission system that on-line checkingi goes out.
Only consider reactor L helectric current I lhcompensation characteristic time, the voltage supposing current conversion station AC in HVDC (High Voltage Direct Current) transmission system is for sinusoidal wave.The then harmonic component I of current conversion station ac-side current in HVDC (High Voltage Direct Current) transmission system sh, hybrid active power filter and HVDC (High Voltage Direct Current) transmission system the harmonic voltage U exchanging tie point place th, modular multi-level converter (MMC) AC output voltage U chprovided by following three formulas:
I sh = Z F Z s + Z F + K I Lh - - - ( 1 )
U Th = U S - Z s I sh = - Z F Z s Z s + Z F + K I Lh - - - ( 2 )
U ch = KI sh = KZ F Z s + Z F + K I Lh - - - ( 3 )
In formula, Z sfor the equiva lent impedance of current conversion station in HVDC (High Voltage Direct Current) transmission system, Z ffor the equiva lent impedance of h single tuned filter, I lhfor reactor L in h single tuned filter helectric current, U sfor the AC equivalent voltage source of current conversion station in HVDC (High Voltage Direct Current) transmission system.
From formula (1), for I sh, the one phase equivalent circuit of Fig. 4 can turn the form of Fig. 5 into, is found out by figure, and this is equivalent to Z sbe connected in series a crosstalk resistance K.If K>> ∣ is Z f∣, then the harmonic current I produced by current conversion station shlC filter will be flowed into.If K>> ∣ is Z s∣, then filtering characteristic is determined by K.In addition, K also plays damping Z sand Z fthe effect of parallel resonance.This shows that virtual resistance K value its filter effect larger is better, due to the harmonic current I that current conversion station AC in HVDC (High Voltage Direct Current) transmission system produces shitself is very large, causes the voltage U that modular multi-level converter (MMC) will export after being multiplied by gain K on this basis chjust quite high, common two level and three level filtering system cannot meet requirement of the present invention, therefore present invention employs modular multi-level converter (MMC).The present invention can by changing the quantity of the power modules of each brachium pontis series connection of modular multi-level converter (MMC), adjust the voltage scope of application of current transformer neatly, realize the object of dynamic filtering HVDC (High Voltage Direct Current) transmission system AC harmonic current and reactive power compensation.
Embodiment 2
Present embodiments provide the control method of the hybrid active power filter described in a kind of embodiment 1, this control method realizes primarily of controller 6, in order to realize good harmonic filtration and reactive power compensation, voltage stabilizing, all pressure and loop current suppression effect.
As shown in Figure 6, described method its comprise the following steps:
S1, Harmonic currents detection;
S2, outer shroud voltage control;
The command signal of S3, calculating active filter output voltage;
S4, Pressure and Control: comprise alternate Pressure and Control and power modules Pressure and Control;
S5, loop current suppression;
S6, phase-shifting carrier wave are modulated.
Particularly, in described S1, the method for Harmonic currents detection comprises: HVDC (High Voltage Direct Current) transmission system two ends AC a phase voltage v sasuccessively through overvoltage phase-locked loop and sin & cos generator, for whole controller 6 provides synchronizing signal; HVDC (High Voltage Direct Current) transmission system two ends AC three-phase current i sa, i sb, i sccurrent component i under DQ conversion converts DQ coordinate to dand i q, then after high pass filter, by remaining i sa, i sb, i scthe projection of middle harmonic component on DQ axle with (i.e. i d, i qin alternating current component).
In described S2, because native system outer shroud voltage control is different from the shunt active power filter be used alone, the controlled quentity controlled variable now in direct voltage closed loop is Δ Q instead of Δ P.Because LC passive filter is capacitive to first-harmonic, its current i fbe ahead of the voltage of supply terminals, active filter only has output one and i fsynchronous fundamental voltage, current/voltage that could be advanced thus produces active power and controls DC capacitor voltage.Therefore, the voltage-controlled method of outer shroud comprises: by direct voltage command quantity v dc* with its measured value v dcdifference inject the Q axis AC current component of S1 through PI adjuster realize the meritorious exchange of HVDC (High Voltage Direct Current) transmission system and modularization level current transformer (MMC) DC side.
In described S3, the method calculating the command signal of active filter output voltage comprises: by the current component on the DQ axle after synthesis in S2 with current i under anti-DQ shift conversion is ABC coordinate system sh; For modularization level current transformer is controlled to harmonic current control type voltage source, need three-phase current i by the harmonic current command signal in S1 after anti-DQ conversion shbe multiplied with virtual resistance K, and by output signal U *as the reference value of the upper and lower bridge arm voltage of modularization level current transformer.
Described S4 comprises alternate Pressure and Control and power modules Pressure and Control.As shown in Figure 7, the alternate pressure equalizing control method of described modular multi-level converter (MMC) comprising: adoption rate resonant controller (PR) realizes the error free tracking to the alternating current component of circulation, by the suppression to circulation, thus realize the balance of voltage between phases.In Fig. 8, u areffor modular multi-level converter (MMC) voltage between phases correction, u creffor submodule capacitor voltage reference value each in modular multi-level converter (MMC) brachium pontis, u cavfor modular multi-level converter (MMC) each brachium pontis Neutron module capacitance voltage mean value, i pfor the upper bridge arm current of modular multi-level converter (MMC), i nfor bridge arm current under modular multi-level converter (MMC).
As shown in Figure 8, in described S4, the method for power modules Pressure and Control comprises: after each submodule capacitor voltage reference signal and actual detection signal obtain error signal after doing difference, then after PI controller, obtain the error of corresponding submodule.Because the current instruction value of upper and lower brachium pontis is different, the direction of upper and lower bridge arm current determines inflow or the output of energy, this control method is by detecting the instantaneous value of the electric current of upper and lower brachium pontis in real time, when power component is to common DC bus active power of output, namely electric capacity is discharged, otherwise, then electric capacity is charged, obtains the correction u of individual capacitor voltages thus bref, secondary correction is superimposed upon on the reference voltage of modular multi-level converter (MMC) upper and lower brachium pontis, thus achieves the Balance route of each capacitance voltage.Wherein sign represents the output 1 when i >=0, exports as-1 as i < 0.In Fig. 8, u creffor submodule capacitor voltage reference value each in modular multi-level converter (MMC) brachium pontis, u cjfor the capacitance voltage value of each submodule that reality detects, i is modular multi-level converter (MMC) the bridge arm current value of actual detection, wherein i pfor upper bridge arm current, i nfor lower bridge arm current.
As shown in Figure 9, in described S5, the method of loop current suppression comprises: adopt the rotation transformation of two frequency multiplication negative phase-sequences that two frequency multiplication circulation are separated into two DC component, after described two DC component and the reference value of circulation DQ axle component being done poor comparison, through ratio-integral controller (PI), the feedforward amount introducing voltage again realizes the decoupling zero of circulation, finally in the voltage command signal of upper and lower brachium pontis, this voltage-drop compensation is fallen by the amount of unbalance obtaining builtin voltage after coordinate transform, the effect suppressing circulation can be reached, realize the suppression to alternate circulation.In this enforcement control method, the reference value of circulation all gets zero as requested.
In described S6, the method of phase-shifting carrier wave modulation comprises: for the N number of submodule in each brachium pontis, controller all produces N bar triangular carrier, the N bar triangular carrier of each brachium pontis is made to remove the 1/N triangular carrier cycle successively, 360 °/N phase angle, then with superposed modular multi-level converter (MMC) voltage between phases correction u aref, individual capacitor voltages correction u brefwith loop current suppression unbalanced component u crefafter upper and lower bridge arm voltage modulating wave compare, produce N group PWM ripple signal, respectively a driving N submodule unit, determine that they drop into or excise.
The above embodiment only have expressed several execution mode of the present invention, and it describes comparatively concrete and detailed, but therefore can not be interpreted as the restriction to the scope of the claims of the present invention.It should be pointed out that for the person of ordinary skill of the art, without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection range of patent of the present invention should be as the criterion with claims.

Claims (9)

1. for an interchange hybrid active power filter for high voltage direct current transmission, it is characterized in that: comprise interconnective passive filter and active filter; The output of described passive filter directly connects the AC that high voltage direct current exports electric system two ends current conversion station;
Described passive filter comprises three groups of single tuning passive filter groups, and wherein each group single tuning passive filter group correspondence connects a phase of current conversion station AC, and described single tuning passive filter group has series resonance characteristics;
Described active filter comprises modular multi-level converter and coupled controller, a DC terminal capacitor in parallel of described modular multi-level converter; The input of each one group of single tuning passive filter group that is connected of modular multi-level converter ac output end, the output of single tuning passive filter group is connected to the corresponding phase on current conversion station AC;
Described modular multi-level converter comprises three unsteady flow bridges, and the output of each unsteady flow bridge is respectively as a phase of three-phase alternating current output, and each unsteady flow bridge comprises a positive convertor arm, a negative convertor arm and two filter reactors; Each convertor arm comprises the power modules of multiple positive-negative series successively;
In each unsteady flow bridge, the anode of positive convertor arm is connected to the direct current anode of modular multi-level converter, and the negative terminal of positive convertor arm is connected to the output of unsteady flow bridge by a filter reactor; The negative terminal of negative convertor arm is connected to the direct current negative terminal of modular multi-level converter, and the anode of negative convertor arm is connected to the output of unsteady flow bridge by another filter reactor;
The control output end of described controller is connected with each power modules in modular multi-level converter, for controlling the switch of each power modules, and then change the quantity of the power modules effectively worked in each convertor arm, the compensating signal exported with control module Multilevel Inverters.
2. hybrid active power filter according to claim 1, is characterized in that: described single tuning passive filter group comprises 11 single tuned filters parallel with one another, 13 single tuned filters, 23 single tuned filters, 25 single tuned filters.
3. hybrid active power filter according to claim 1, is characterized in that: described passive filter is issued to series resonance state at specific subfrequency, is capacitive under fundamental frequency simultaneously, the reactive power that compensating non-linear load consumes;
Passive filter is while carrying out filtering, and bear all fundamental voltages, active filter bears fundamental voltage hardly; Often organizing in single tuning passive filter group, there is h single tuned filter of series resonance characteristics at design capacitance device C hwith reactor L hduring parameter, meet following condition:
jh &omega; 1 L h - 1 jh &omega; 1 C h = 0 C h = Q C ( h ) ( h 2 - 1 ) ( V 2 &omega; 1 ) h 2 L h = 1 h 2 &omega; 1 2 C h
In formula, the fundamental voltage that V bears for h single tuned filter, Q c (h)for the reactive power compensation capacity that h single tuned filter provides, ω 1for first-harmonic angular frequency.
4. hybrid active power filter according to claim 1, is characterized in that: modular multi-level converter is controlled so as to a harmonic current control type voltage source U under the effect of controller ch, it is equivalent to add virtual resistance K at system primary side, the voltage U that modular multi-level converter will export chfollowing relation should be met:
U ch＝KI sh
Wherein, K is the equivalent virtual resistance of modular multi-level converter, I shfor the harmonic current of current conversion station AC in the HVDC (High Voltage Direct Current) transmission system that on-line checkingi goes out.
5., to a control method for the arbitrary described hybrid active power filter for high voltage direct current transmission of Claims 1-4, it is characterized in that: comprise the following steps:
S1, Harmonic currents detection;
S2, outer shroud voltage control;
The command signal of S3, calculating active filter output voltage;
S4, Pressure and Control: comprise alternate Pressure and Control and power modules Pressure and Control;
S5, loop current suppression;
S6, phase-shifting carrier wave are modulated.
6. method according to claim 5, is characterized in that: described S1 comprises: HVDC (High Voltage Direct Current) transmission system two ends AC a phase voltage through phase-locked loop for whole control system provides synchronizing signal; HVDC (High Voltage Direct Current) transmission system two ends AC three-phase current through DQ conversion and high pass filter after, by the projection of harmonic component on DQ axle in remaining three-phase current.
7. method according to claim 5, it is characterized in that: in described S4, the method of power modules Pressure and Control comprises: the instantaneous value detecting the electric current of upper and lower brachium pontis in real time, when power component is to common DC bus active power of output, namely electric capacity is discharged, otherwise, then electric capacity is charged, obtain the correction of individual capacitor voltages thus, this correction is superimposed upon on the reference voltage of the upper and lower brachium pontis of modular multi-level converter.
8. method according to claim 5, it is characterized in that: described S5 comprises: adopt the rotation transformation of two frequency multiplication negative phase-sequences that two frequency multiplication circulation are separated into two DC component, after described two DC component and the reference value of circulation DQ axle component being done poor comparison, through pi regulator, the feedforward amount introducing voltage again realizes the decoupling zero of circulation, by obtaining the amount of unbalance of builtin voltage after coordinate transform, finally in the voltage command signal of upper and lower brachium pontis, this voltage-drop compensation is fallen.
9. method according to claim 5, is characterized in that: described S6 comprises:
For the N number of submodule in each brachium pontis, controller all produces N bar triangular carrier, make the N bar triangular carrier of each brachium pontis remove the 1/N triangular carrier cycle successively, 360 °/N phase angle, then with superposed modular multi-level converter (MMC) voltage between phases correction u aref, individual capacitor voltages correction u brefwith loop current suppression unbalanced component u crefafter upper and lower bridge arm voltage modulating wave compare, produce N group PWM ripple signal, respectively a driving N submodule unit, determine that they drop into or excise.
CN201510033171.9A 2015-01-22 2015-01-22 Alternating current (AC) hybrid active power filter system for high-voltage direct current (DC) transmission, and control method thereof Pending CN104682390A (en)

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