CN104184147A - Filtering method of stationary synchronous compensator (SVG) - Google Patents

Abstract

Disclosed is a filtering method of a stationary synchronous compensator (SVG). According to actual compensation currents output by the SVG in a last cycle, the virtual generation current Iref (i.e., a theoretical sampling value) of a current sampling point is obtained; according to a sampling fluctuation value X allowed by a system under a design requirement, the value range |i-Iref|<=X of the compensation current i of the sampling point is obtained, and the compensation current of the sampling point is filtered according to this. The filtering method provided by the invention, under the condition that a physical filter device is not additionally arranged, realizes front filtering on interference current and greatly reduces the application cost of the invention; through a design of ingenious determine logic, the actual compensation current of the current sampling point can be determined in real time, the front filtering can be rapidly completed, a time delay almost does not exist, and the filtering method has an actual application value; and low pass filtering is then carried out on current signals which are already subjected to the front filtering in the method provided by the invention, such that the filtering effect can be greatly improved.

Description

A kind of filtering method of STATCOM

Technical field

The present invention relates to a kind of filtering method of STATCOM.

Background technology

In order to administer electric design power quality problem, power department has been installed reactive power compensator in low-voltage distribution platform district in recent years.These reactive power compensators, taking the dynamic switching principle of capacitor group as main, all exist switching differential.Because low-voltage network load variations is larger, in underload situation, due to the existence of switching extreme difference, compensating reactive power vacancy that cannot be correct in a lot of situations.

STATCOM (STATCOM-Static Synchronous Compensator, the domestic SVG of being commonly called as) capacitive and lagging reactive power can be in extremely rapid succession provided, realize voltage and Reactive Power Control fast, ensure power system stability, efficient, high-quality ground operation, be widely used in recent years in electric power system.The direct user oriented of low-voltage network, must ensure provides qualified electric power for user.SVG more flexibly compensating reactive power vacancy, administer harmonic wave, improve three-phase imbalance, be specially adapted to low-voltage distribution platform district.Compared with traditional reactive power compensator, SVG has and the advantage such as regulates continuously, harmonic wave is little, loss is low, range of operation is wide, reliability is high, governing speed is fast, since coming out, has just got the attention and degree of flying development.

In addition, along with the paces that intelligent grid is built, China has started the initiatively research work of power distribution network.Research shows that active power distribution network need to rely on power distribution network Survey of Flexible AC Transmission System Technology, use trend, the regulation voltage and idle of D-STATCOM flexible allocation power distribution network, support the access of renewable distribution power, micro-electrical network, make power distribution network obtain more economical, efficient operational effect.

But low-voltage network construction is economic, practical to the requirement of device therefor, there is higher cost performance.In the past due to the low capacity SVG product towards low-voltage network not, and general SVG product cost is higher, is not suitable for the requirement of low-voltage network.Therefore, be subject to the restriction of price factor at low-voltage network SVG equipment, be not widely applied.The low-voltage network SVG equipment of new generation high performance-price ratio, has become a very urgent task.

For the use of STATCOM, need to use filter to filter offset current, the method that uses conventional filter to adopt, that to extend time lag be cost in order to obtain good filter effect, and time delay cross conference cause current oscillation increase, being reflected in current waveform is exactly the obvious wider width of waveform, has reduced the filter effect of filter, thereby can reduce low voltage distribution network electric energy quality.In order to eliminate above-mentioned interference in the time calculating instantaneous power, need the filter of better effects if.

Summary of the invention

The present invention wants technical solution problem to be: overcome prior art shortcoming, a kind of filtering method of STATCOM is proposed, before low-pass filtering, increase one-level software screening method, first filtering manifest error sampled point, then carry out low-pass filtering algorithm, can greatly improve filtering speed and filter effect.

In order to solve the problems of the technologies described above, the technical scheme that the present invention proposes is: a kind of filtering method of STATCOM, comprises the steps:

The 1st step, obtain the actual offset current of all sampled points of SVG output in a cycle on current sampling point, the actual offset current of y sampled point $I_y^{\&prime;}=\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right],$ Y=1,2 ..., Y, Y is the sampling number of a upper cycle;

The 2nd step, the actual offset current I ' that the 1st step is obtained _ytake turns doing three-dimensional static coordinate conversion, three-dimensional rotation transformation of coordinates, obtain the N subharmonic equivalent transformation electric current under three-dimensional rotation coordinate: $I_{N,y}^{\&prime;\&prime;\&prime;}=\left[\begin{array}{c}{I}_d^{N,y}\\ I_q^{N,y}\\ I_0^{N,y}\end{array}\right],$ In formula, the number of times that N is harmonic wave, represent respectively the current component of y the N subharmonic equivalent transformation electric current under actual offset current three-dimensional rotation coordinate on d, q, 0 axle;

The 3rd step, the harmonic number M that need to compensate for system respectively, the current component of the M subharmonic equivalent transformation electric current of the actual offset current to all sampled points of a upper cycle on q axle average and take advantage of in sin (2 π M50), obtaining the idle component of the M subharmonic of a upper cycle;

The 4th step, the idle component of described M subharmonic is made to rotary/static coordinate inverse transformation, three phase static coordinate inverse transformation successively, obtain the M subharmonic offset current reference value of current sampling point $I_{\mathrm{ref}}^M=\left[\begin{array}{c}{I}_{\mathrm{aref}}^M\\ I_{\mathrm{bref}}^M\\ I_{\mathrm{cref}}^M\end{array}\right],$ Wherein be respectively M subharmonic A, B, the C phase offset current reference value of current sampling point, then by cumulative the M subharmonic offset current reference value of the current sampling point virtual generation electric current that obtains current sampling point

$I_{\mathrm{ref}}=\left[\begin{array}{c}{I}_{\mathrm{aref}}\\ I_{\mathrm{bref}}\\ I_{\mathrm{cref}}\end{array}\right]=\left[\begin{array}{c}\mathrm{\&Sigma;}{I}_{\mathrm{aref}}^M\\ \mathrm{\&Sigma;}{I}_{\mathrm{bref}}^M\\ \mathrm{\&Sigma;}{I}_{\mathrm{cref}}^M\end{array}\right];$

The 5th step, utilize I _ref± X filters the actual offset current of current sampling point as threshold, if the actual offset current of current sampling point $i=\left[\begin{array}{c}{i}_a\\ I_b\\ I_c\end{array}\right]$ Meet | i _a-I _aref|≤X and | i _b-I _bref|≤X and | i _c-I _cref|≤X, the actual offset current i of current sampling point is sent into next stage low pass filter and carry out low-pass filtering, filter otherwise set it as disturbance current, wherein in formula, U _dcfor the voltage that maintains of SVG DC capacitor, K is upper and lower bridge arm duty ratio poor of the SVG bridge circuit of a upper cycle; θ is the corresponding current waveform anglec of rotation of current sampling point, T is the time in sampling interval, L is the inductance value that SVG connects inductance, if certain phase or the heterogeneous threshold of crossing of the actual offset current of current sampling point, utilize the threshold current value of corresponding phase to replace interference phase current, complete the correction to disturbance current, and revised electric current is sent into next stage low pass filter and carry out low-pass filtering, the corresponding current waveform anglec of rotation θ=z*2 of current sampling point π/Y, z is the sampled point sequence number of current sampling point place sinusoidal current waveform.。

The filtering method of a kind of STATCOM of the present invention, can not suddenly change based on electric current in inductance, and the principle that in electric capacity, voltage can not suddenly change, according to the virtual generation electric current I of the actual offset current acquisition current sampling point of SVG output in a upper cycle _ref(being theoretical sampled value), the sampling undulating value X that the system of then obtaining can allow under designing requirement, final basis | i-I _ref|≤X draws the span of sampled point offset current i, if the offset current actual value i of current sampling point meets | and i-I _ref|≤X, offset current actual value i is sent into next stage low pass filter and carry out low-pass filtering, filter otherwise set it as disturbance current.

The filtering method of a kind of STATCOM of the present invention, also has following improvement:

1, on current sampling point, in a cycle, y actual offset current acquisition methods of SVG output is as follows: sample constantly with assigned frequency, on current sampling point, in a cycle, the three-phase offset current of y sampled point is $I_y=\left[\begin{array}{c}{I}_{a,y}\\ I_{b,y}\\ I_{c,y}\end{array}\right]$ And center line offset current I _n,y; The actual offset current of SVG output in a cycle on current sampling point $I_y^{\&prime;}=\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right]=\left[\begin{array}{c}{I}_{a,y}\\ I_{b,y}\\ I_{c,y}\end{array}\right]-I_{z,y},$ In formula $I_{z,y}=\frac{I_{a,y}+I_{b,y}+I_{c,y}+I_{n,y}}{4}.$

2, the first-harmonic equivalent transformation electric current under three-dimensional rotation coordinate and each harmonic equivalent transformation electric current acquisition methods are as follows:

First to actual offset current I ' _ydo three-dimensional static coordinate conversion, obtain the three-dimensional rest frame equivalent transformation electric current of y actual offset current:

$I_y^{\&prime;\&prime;}=\left[\begin{array}{c}{I}_{\mathrm{\&alpha;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&beta;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&gamma;},y}^{\&prime;\&prime;}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}\end{array}\right]\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right],$

I in formula " _{α, y}, I " _{β, y}, I " _{γ, y}be respectively the current value component of equivalent transformation electric current on α, β, γ axle under the three-dimensional rest frame of y actual offset current;

Three-dimensional rest frame equivalent transformation electric current I to described y actual offset current again " _ycarry out three-dimensional rotation transformation of coordinates, the N subharmonic equivalent transformation electric current under the three-dimensional rotation coordinate of y actual offset current of acquisition:

$I_{N,y}^{\&prime;\&prime;\&prime;}=\left[\begin{array}{c}{I}_d^{N,y}\\ I_q^{N,y}\\ I_0^{N,y}\end{array}\right]=\left[\begin{array}{ccc}\cos (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& \sin (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& 0\\ -\sin (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& \cos (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& 0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{c}{I}_{\mathrm{\&alpha;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&beta;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&gamma;},y}^{\&prime;\&prime;}\end{array}\right],$

In formula, the number of times that N is harmonic wave, represent respectively the current component of N subharmonic equivalent transformation electric current on d, q, 0 axle under the three-dimensional rotation coordinate of y actual offset current.

Filtering method of the present invention has been realized the preposition filtration to disturbance current under the prerequisite of not setting up physical filter part, greatly reduces application cost of the present invention; The present invention has designed decision logic cleverly, has realized the real-time judge to the actual offset current of current sampling point, can complete rapidly pre-filtering, has hardly time delay, is that filtering method of the present invention has actual application value; And the present invention proposes the scheme that disturbance current is revised, guarantee the reliable and stable output of SVG, can impact compensation not export because lasting disturbance current exists; Current signal after pre-filtering of the present invention carries out low-pass filtering again, can greatly improve filter effect, and having overcome conventional method dependence raising hardware cost or having extended time lag is the defect of cost with boostfiltering effect.

Brief description of the drawings

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

Fig. 1 is the flow chart of filtering method embodiment of the present invention

Fig. 2 is the mutually virtual generation electric current of A and boundary curve schematic diagram.

Fig. 3-a is traditional filtering algorithm SVG compensation after-current waveform schematic diagram.

Fig. 3-b is the filtering method SVG compensation after-current waveform schematic diagram of the embodiment of the present invention.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention will be further described.

As shown in Figure 1, be the filtering method flow chart of embodiment of the present invention STATCOM, the present embodiment comprises the steps:

The 1st step, obtain the actual offset current of all sampled points of SVG output in a cycle on current sampling point, the actual offset current of y sampled point $I_y^{\&prime;}=\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right],$ Y=1,2 ..., Y, Y is the sampling number of a upper cycle; In this example, a cycle sampled point number is 128.

In this step, on current sampling point, in a cycle, y actual offset current acquisition methods of SVG output is as follows: sample constantly with assigned frequency, on current sampling point, in a cycle, the three-phase offset current of y sampled point is $I_y=\left[\begin{array}{c}{I}_{a,y}\\ I_{b,y}\\ I_{c,y}\end{array}\right]$ And center line offset current I _n,y; The actual offset current of SVG output in a cycle on current sampling point $I_y^{\&prime;}=\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right]=\left[\begin{array}{c}{I}_{a,y}\\ I_{b,y}\\ I_{c,y}\end{array}\right]-I_{z,y},$ In formula $I_{z,y}=\frac{I_{a,y}+I_{b,y}+I_{c,y}+I_{n,y}}{4}.$

The 2nd step, the actual offset current I ' that the 1st step is obtained _ytake turns doing three-dimensional static coordinate conversion, three-dimensional rotation transformation of coordinates, obtain the N subharmonic equivalent transformation electric current under three-dimensional rotation coordinate: $I_{N,y}^{\&prime;\&prime;\&prime;}=\left[\begin{array}{c}{I}_d^{N,y}\\ I_q^{N,y}\\ I_0^{N,y}\end{array}\right],$ In formula, the number of times that N is harmonic wave, represent respectively the current component of y the N subharmonic equivalent transformation electric current under actual offset current three-dimensional rotation coordinate on d, q, 0 axle.

In this step, the first-harmonic equivalent transformation electric current under three-dimensional rotation coordinate and each harmonic equivalent transformation electric current acquisition methods are as follows:

First to actual offset current I ' _ydo three-dimensional static coordinate conversion, obtain the three-dimensional rest frame equivalent transformation electric current of y actual offset current:

$I_y^{\&prime;\&prime;}=\left[\begin{array}{c}{I}_{\mathrm{\&alpha;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&beta;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&gamma;},y}^{\&prime;\&prime;}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}\end{array}\right]\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right],$

I in formula " _{α, y}, I " _{β, y}, I " _{γ, y}be respectively the current value component of equivalent transformation electric current on α, β, γ axle under the three-dimensional rest frame of y actual offset current;

Three-dimensional rest frame equivalent transformation electric current I to described y actual offset current again " _ycarry out three-dimensional rotation transformation of coordinates, the N subharmonic equivalent transformation electric current under the three-dimensional rotation coordinate of y actual offset current of acquisition:

$I_{N,y}^{\&prime;\&prime;\&prime;}=\left[\begin{array}{c}{I}_d^{N,y}\\ I_q^{N,y}\\ I_0^{N,y}\end{array}\right]=\left[\begin{array}{ccc}\cos (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& \sin (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& 0\\ -\sin (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& \cos (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& 0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{c}{I}_{\mathrm{\&alpha;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&beta;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&gamma;},y}^{\&prime;\&prime;}\end{array}\right],$

In formula, the number of times that N is harmonic wave, represent respectively the current component of N subharmonic equivalent transformation electric current on d, q, 0 axle under the three-dimensional rotation coordinate of y actual offset current.

The 3rd step, the harmonic number M that need to compensate for system respectively, the current component of the M subharmonic equivalent transformation electric current of the actual offset current to all sampled points of a upper cycle on q axle average and take advantage of in sin (2 π M50), obtaining the idle component of the M subharmonic of a upper cycle.

For different equipment, the harmonic number that system need to compensate is not quite similar, and embodiment is taking common three phase full bridge controllable silicon rectification type load as example, waveform contains a large amount of harmonic components, but mainly with 5 times, 7 times, 11 times is for 13 times main, contains a small amount of 17,19 subharmonic, according to this algorithm, emphasis consideration 5 times, 7 times, 11 times, 13 order harmonic components.Motor load is mainly that fundamental wave reactive power content is larger, and three-phase four-wire system user various times harmonics likely exists.May there is above odd harmonic 12 times in 12 pulse three phase rectifying installations.This routine target compensation is the electric current of controllable silicon intermediate frequency furnace, M=1,5,7,11,13.The present embodiment SVG output current one cycle has 128 sampled points, in a cycle, there is the idle transient component of 128 first-harmonics (1 subharmonic), 128 idle transient components of 5 subharmonic, 128 idle transient components of 7 subharmonic, 128 idle transient components of 11 subharmonic, 128 idle transient components of 13 subharmonic.128 fundamental wave reactive power transient components are averaging and take advantage of the sine value in the corresponding anglec of rotation, obtain the idle component of first-harmonic, in like manner can obtain the idle component of all each harmonics that need compensation.

The 4th step, the idle component of described M subharmonic is made to rotary/static coordinate inverse transformation, three phase static coordinate inverse transformation successively, obtain the M subharmonic offset current reference value of current sampling point $I_{\mathrm{ref}}^M=\left[\begin{array}{c}{I}_{\mathrm{aref}}^M\\ I_{\mathrm{bref}}^M\\ I_{\mathrm{cref}}^M\end{array}\right],$ Wherein be respectively M subharmonic A, B, the C phase offset current reference value of current sampling point, then by cumulative the M subharmonic offset current reference value of the current sampling point virtual generation electric current that obtains current sampling point

$I_{\mathrm{ref}}=\left[\begin{array}{c}{I}_{\mathrm{aref}}\\ I_{\mathrm{bref}}\\ I_{\mathrm{cref}}\end{array}\right]=\left[\begin{array}{c}\mathrm{\&Sigma;}{I}_{\mathrm{aref}}^M\\ \mathrm{\&Sigma;}{I}_{\mathrm{bref}}^M\\ \mathrm{\&Sigma;}{I}_{\mathrm{cref}}^M\end{array}\right].$

The 5th step, utilize I _ref± X filters the actual offset current of current sampling point as threshold, if the actual offset current of current sampling point $i=\left[\begin{array}{c}{i}_a\\ I_b\\ I_c\end{array}\right]$ Meet | i _a-I _aref|≤X and | i _b-I _bref|≤X and | i _c-I _cref|≤X, the actual offset current i of current sampling point is sent into next stage low pass filter and carry out low-pass filtering, filter otherwise set it as disturbance current, wherein in formula, U _dcfor the voltage that maintains of SVG DC capacitor, K is upper and lower bridge arm duty ratio poor of the SVG bridge circuit of a upper cycle; θ is the corresponding current waveform anglec of rotation of current sampling point, θ=z*2 π/Y, and z is the sampled point sequence number of current sampling point place sinusoidal current waveform, and T is the time in sampling interval, and L is the inductance value that SVG connects inductance.

Taking A, mutually as example, as shown in Figure 2, middle curve is the mutually virtual generation electric current I of A of current sampling point _aref(being theoretical sampled value) is with respect to the function curve of time; The boundary curve of reaching the standard grade is I _aref+ X, the boundary curve that rolls off the production line is I _aref-X, the sampling fluctuation maximum that X can allow under designing requirement for system.The offset current actual value of reaching the standard grade boundary curve and roll off the production line between boundary curve is retained, and send into next stage low pass filter and carry out low-pass filtering; Otherwise setting it as disturbance current filters; Respectively the offset current actual value of B phase, C phase is filtered in the same way.

For the compensation of better more stable realization to system, the present embodiment is revised disturbance current, specific practice is: in the 5th step, if certain phase or the heterogeneous threshold of crossing of the actual offset current of current sampling point, utilize the threshold current value of corresponding phase to replace interference phase current, complete the correction to disturbance current, and revised electric current is sent into next stage low pass filter and carry out low-pass filtering.Suppose that A phase offset current actual value is greater than I _aref+ X, revised A phase disturbance current equals I _aref+ X, if A phase offset current actual value is less than I _aref-X, revised A phase disturbance current equals I _aref-X, revises B phase, C phase disturbance current in the same way.

The present embodiment carries out low-pass filtering to traditional low-pass filtering with after the inventive method is carried out pre-filtering again and contrasts, and filter effect refers to as shown in Fig. 3-a and Fig. 3-b.As seen from the figure: use conventional filter in order to reach same filter effect, filtering delay-time is excessive, the algorithm adopting for the direct control mode of instantaneous value electric current, time delay is crossed conference and is caused current oscillation to increase, can see the obvious wider width of waveform in Fig. 3-a, and Fig. 3-b shows after employing filtering method of the present invention, because time delay is less, embody current waveform by transient current algorithm obviously thinner.

In addition to the implementation, the present invention can also have other execution modes.All employings are equal to the technical scheme of replacement or equivalent transformation formation, all drop on the protection range of requirement of the present invention.

Claims (3)

1. a filtering method for STATCOM, comprises the steps:

The 1st step, obtain the actual offset current of all sampled points of SVG output in a cycle on current sampling point, the actual offset current of y sampled point $I_y^{\&prime;}=\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right],$ Y=1,2 ..., Y, Y is the sampling number of a upper cycle;

The 2nd step, the actual offset current I ' that the 1st step is obtained _ytake turns doing three-dimensional static coordinate conversion, three-dimensional rotation transformation of coordinates, obtain the N subharmonic equivalent transformation electric current under three-dimensional rotation coordinate: $I_{N,y}^{\&prime;\&prime;\&prime;}=\left[\begin{array}{c}{I}_d^{N,y}\\ I_q^{N,y}\\ I_0^{N,y}\end{array}\right],$ In formula, the number of times that N is harmonic wave, represent respectively the current component of y the N subharmonic equivalent transformation electric current under actual offset current three-dimensional rotation coordinate on d, q, 0 axle;

The 3rd step, the harmonic number M that need to compensate for system respectively, the current component of the M subharmonic equivalent transformation electric current of the actual offset current to all sampled points of a upper cycle on q axle average and take advantage of in sin (2 π M50), obtaining the idle component of the M subharmonic of a upper cycle;

The 4th step, the idle component of described M subharmonic is made to rotary/static coordinate inverse transformation, three phase static coordinate inverse transformation successively, obtain the M subharmonic offset current reference value of current sampling point $I_{\mathrm{ref}}^M=\left[\begin{array}{c}{I}_{\mathrm{aref}}^M\\ I_{\mathrm{bref}}^M\\ I_{\mathrm{cref}}^M\end{array}\right],$ Wherein be respectively M subharmonic A, B, the C phase offset current reference value of current sampling point, then by cumulative the M subharmonic offset current reference value of the current sampling point virtual generation electric current that obtains current sampling point

$I_{\mathrm{ref}}=\left[\begin{array}{c}{I}_{\mathrm{aref}}\\ I_{\mathrm{bref}}\\ I_{\mathrm{cref}}\end{array}\right]=\left[\begin{array}{c}\mathrm{\&Sigma;}{I}_{\mathrm{aref}}^M\\ \mathrm{\&Sigma;}{I}_{\mathrm{bref}}^M\\ \mathrm{\&Sigma;}{I}_{\mathrm{cref}}^M\end{array}\right];$

The 5th step, utilize I _ref± X filters the actual offset current of current sampling point as threshold, if the actual offset current of current sampling point $i=\left[\begin{array}{c}{i}_a\\ I_b\\ I_c\end{array}\right]$ Meet | i _a-I _aref|≤X and | i _b-I _bref|≤X and | i _c-I _cref|≤X, the actual offset current i of current sampling point is sent into next stage low pass filter and carry out low-pass filtering, filter otherwise set it as disturbance current, wherein in formula, U _dcfor the voltage that maintains of SVG DC capacitor, K is upper and lower bridge arm duty ratio poor of the SVG bridge circuit of a upper cycle; θ is the corresponding current waveform anglec of rotation of current sampling point, T is the time in sampling interval, L is the inductance value that SVG connects inductance, if certain phase or the heterogeneous threshold of crossing of the actual offset current of current sampling point, utilize the threshold current value of corresponding phase to replace interference phase current, complete the correction to disturbance current, and revised electric current is sent into next stage low pass filter and carry out low-pass filtering, the corresponding current waveform anglec of rotation θ=z*2 of current sampling point π/Y, z is the sampled point sequence number of current sampling point place sinusoidal current waveform.

2. the filtering method of STATCOM according to claim 1, it is characterized in that y the actual offset current acquisition methods that on current sampling point, in a cycle, SVG exports is as follows: sample constantly with assigned frequency, on current sampling point, in a cycle, the three-phase offset current of y sampled point is $I_y=\left[\begin{array}{c}{I}_{a,y}\\ I_{b,y}\\ I_{c,y}\end{array}\right]$ And center line offset current I _n,y; The actual offset current of SVG output in a cycle on current sampling point $I_y^{\&prime;}=\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right]=\left[\begin{array}{c}{I}_{a,y}\\ I_{b,y}\\ I_{c,y}\end{array}\right]-I_{z,y},$ In formula $I_{z,y}=\frac{I_{a,y}+I_{b,y}+I_{c,y}+I_{n,y}}{4}.$

3. the filtering method of STATCOM according to claim 1, is characterized in that first-harmonic equivalent transformation electric current and the each harmonic equivalent transformation electric current acquisition methods under three-dimensional rotation coordinate is as follows:

First to actual offset current I ' _ydo three-dimensional static coordinate conversion, obtain the three-dimensional rest frame equivalent transformation electric current of y actual offset current:

$I_y^{\&prime;\&prime;}=\left[\begin{array}{c}{I}_{\mathrm{\&alpha;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&beta;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&gamma;},y}^{\&prime;\&prime;}\end{array}\right]=\sqrt{\frac{2}{3}}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{2}}\end{array}\right]\left[\begin{array}{c}{I}_{a,y}^{\&prime;}\\ I_{b,y}^{\&prime;}\\ I_{c,y}^{\&prime;}\end{array}\right],$

I in formula " _{α, y}, I " _{β, y}, I " _{γ, y}be respectively the current value component of equivalent transformation electric current on α, β, γ axle under the three-dimensional rest frame of y actual offset current;

Three-dimensional rest frame equivalent transformation electric current I to described y actual offset current again " _ycarry out three-dimensional rotation transformation of coordinates, the N subharmonic equivalent transformation electric current under the three-dimensional rotation coordinate of y actual offset current of acquisition:

$I_{N,y}^{\&prime;\&prime;\&prime;}=\left[\begin{array}{c}{I}_d^{N,y}\\ I_q^{N,y}\\ I_0^{N,y}\end{array}\right]=\left[\begin{array}{ccc}\cos (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& \sin (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& 0\\ -\sin (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& \cos (2\&CenterDot;\mathrm{\&pi;}\&CenterDot;N\&CenterDot;50)& 0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{c}{I}_{\mathrm{\&alpha;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&beta;},y}^{\&prime;\&prime;}\\ I_{\mathrm{\&gamma;},y}^{\&prime;\&prime;}\end{array}\right],$

In formula, the number of times that N is harmonic wave, represent respectively the current component of N subharmonic equivalent transformation electric current on d, q, 0 axle under the three-dimensional rotation coordinate of y actual offset current.