A kind of big capacity series connection type active electric power filter
Technical field
The utility model belongs to the electric-power filter technical field, is specifically related to a kind of big capacity series connection type active electric power filter.
Background technology
Up to now, Active Power Filter-APF mainly contains three classes: the first kind is a shunt active power filter; Second class is active filter and the passive filter series connection back mode in parallel with electrical network; The 3rd class is the passive hybrid filter that adds series active in parallel.First and second class filter all needs to detect in real time harmonic current, produces harmonic current with combining, and has implemented certain degree of difficulty.The utility model people utility model in 1999 based on the serial active filter (seeing ZL99120103.5, December 4 1999 applying date) of flux compensation, it belongs to above-mentioned the 3rd class filter.Theory analysis and the experimental study that carries out with various harmonic sources show, when the current first harmonics of fundamental current that injects at the series transformer secondary side and primary side satisfies the fundamental flux compensation condition, this series transformer approaches zero to the equiva lent impedance of first-harmonic, and harmonic wave is presented high impedance, thereby force harmonic current to inject the passive filter branch road.No matter,, filter effect is preferably arranged all still to the current mode harmonic source to the voltage-type harmonic source.But, promptly have only a Zhi Luxiang series transformer secondary winding to inject the fundamental current of compensation because series transformer has only a secondary winding in this filter.If when needed primary side current was big, secondary side current also can be bigger, owing to be subjected to the restriction of existing switching device capacity just can not produce jumbo active filter.
Summary of the invention
The purpose of this utility model is to provide a kind of big capacity series connection type active electric power filter that can overcome above-mentioned defective, and it is fundamental current that this filter does not only need to detect the single-frequency electric current, and response is stable, and can be applicable to the high-voltage large current operating mode.
For realizing above-mentioned utility model purpose, a kind of big capacity series connection type active electric power filter mainly is made up of three unit: fundamental Current's Detection unit I, compensating fundamental wave electric current generating unit II and series transformer III; Fundamental Current's Detection unit I comprises the current transformer that is positioned on the electrical network bus, and the fundamental Current's Detection link that is connected with the current transformer output, and this unit detects fundamental current signal i from the distortion current waveform of bus
1SDescribed compensating fundamental wave electric current generating unit II is made of N identical compensating fundamental wave electric current generation subelement II ', N≤500, its input is connected with the output of unit I, and each subelement II ' produces N equal and opposite in direction, phase place is identical, and with fundamental current signal i
1SThe fundamental current i of antiphase
2/ N is from motion tracking fundamental current signal; The secondary side of series transformer III is provided with N winding, the number of turn of each winding is identical, physical dimension equates, each winding is connected with subelement II ' among the corresponding compensating fundamental wave electric current generating unit II, a windings in series makes first-harmonic main flux Φ ml ≈ 0 in the series transformer III iron core in the electrical network bus.
The utility model has kept the advantage of prior art, only need from power network current, detect fundamental current, utilize compensation arrangement to produce identical with detected fundamental current frequency, as a to be in proportion offset current, produce harmonic current and compare with existing detection harmonic current, tracking, respond more stable, easier realization.
In addition, the utility model also has the advantage of following two aspects:
(1) the utility model is provided with N winding at the series transformer secondary side, and each winding disposes an offset current generation subelement, is total to N subelement, and the sine-wave current equal and opposite in direction of this N subelement generation (is i
2/ N), phase place is identical, but with primary side current in the first-harmonic antiphase, thereby can utilize the element manufacturing of low voltage, less electric current to be applicable to serial active filter under high pressure, the big electric current operating mode.
(2) the utility model is connected on the series transformer first side winding in the electrical network bus, when all import equal and opposite in direction, current i that phase place is identical in N winding of series transformer secondary side
2During/N, can make in the series transformer iron core first-harmonic main flux be approximately zero, at primary side AX port fundamental current is zero impedance (or very Low ESR), thereby filter first-harmonic capacity be less.Because it is excitation impedance (a very big impedance) to harmonic current, thereby stop filtered circuit to scurry into electrical network, thereby the harmonic wave capacity of device is also very little, integrates, the filter capacity is less.
Description of drawings
The Filter Structures schematic diagram that Fig. 1 provides for the utility model;
Fig. 2 unites the structural representation of use for the utility model filter and parallel connection type passive filter;
Fig. 3 is the structural representation of a kind of embodiment of the utility model filter.
Embodiment
Below in conjunction with accompanying drawing the utility model is described in further detail.
As shown in Figure 1, the said serial active filter of the utility model mainly is made up of three unit: fundamental Current's Detection unit I, compensating fundamental wave electric current generating unit II and series transformer III.Fundamental Current's Detection unit I comprises the current transformer 2 that is positioned on the electrical network bus 1, and the fundamental Current's Detection link 3 that is connected with current transformer 2 outputs.Compensating fundamental wave electric current generating unit II is made of the individual identical compensating fundamental wave electric current generation subelement II ' of N (N≤500).Series transformer III, its secondary side are provided with N winding, and the number of turn of each winding is Wax, and physical dimension is identical.
The operation principle of above-mentioned filter is:
(1) current sensor 2 is delivered to distortion current (i) waveform of electrical network bus 1 in the fundamental Current's Detection link 3, detects its fundamental current signal i from the current waveform of distortion
1S
(2) will be from fundamental Current's Detection unit I detected fundamental current signal i
1S, being transported among each the compensating fundamental wave electric current generation subelement II ' among the compensating fundamental wave electric current generating unit II, each subelement II ' is according to the fundamental current signal i that receives
1SProduce fundamental current i
2/ N, and from motion tracking i
1SCompensating fundamental wave electric current generation subelement II ' can utilize existing electric current to realize with the technology of combining.
(3) with subelement II
1' the fundamental current i that takes place
2/ N delivers to the 1st secondary winding a of series transformer
1x
1In, with subelement II
2' the fundamental current i that takes place
2/ N delivers to the 2nd secondary winding a of serializer
2x
2In; With subelement II
N' the fundamental current i that takes place
2/ N delivers in N secondary winding of series transformer.
Obviously, the sine-wave current equal and opposite in direction, the phase place that are transported to each secondary winding are identical, but with the fundamental current i of electrical network bus
1Antiphase makes primary side in the iron core, secondary side winding first-harmonic magnetomotive force in a basic balance,
Promptly
Be W
AXi
1+ W
Axi
2≈ 0
Thereby, make first-harmonic main flux Φ ml ≈ 0 in the series transformer III iron core
Series transformer III is at grid side first-harmonic pressure drop UAX ≈ 0
And be high impedance ZAx (n)=nZm (1) [Zm (1) is series transformer (net side) first-harmonic excitation impedance] for the nth harmonic electric current, so series transformer III stops harmonic current to scurry into electric power system.
As shown in Figure 2, above-mentioned filter can be united use with parallel connection type passive filter IV, constitutes the series hybrid mode filter, also can unite use with shunt active power filter, constitutes hybrid active filter.
Fig. 1, filter shown in Figure 2 all are a kind of single-phase series type active filters, can adopt three cover single phase filters to constitute the three-phase serial active filter.
Fig. 3 is an embodiment, compensating fundamental wave electric current generation subelement II ' adopts the current tracking technology, specifically comprises five links: branch current distributes link 6, feedback current to detect link 7, Current Control link 8, PWM control and drives link 9 and inverter and switching frequency filter 10.5 is harmonic load among the figure, and inverter and switching frequency filter 10 comprise inverter 4 and switching frequency filter LdCd.
Fundamental current signal i from 3 outputs of fundamental Current's Detection link
1SOutput to branch current and distribute link 6, produce fundamental current signal i
1S/ N (sine wave signal); Feedback current detects link 7 and receives sine-wave current i
2The signal of/N produces feedback current signal i
1f, Current Control link 8 is according to i
1S/ N and i
1fTwo current signal control PWM control and drive link 9, produce driving command and drive inverter 4, close frequency, sine wave output current i through switching frequency filter Ld Cd filtering again
2/ N.
Among Fig. 3, TA2 is a current sensor, belongs to feedback current and detects link 7.
Persons skilled in the art can adopt multiple concrete mode that the utility model is realized according to above-mentioned disclosed content.