CN105490275A - Parallel hybrid active filter and quality detection method thereof - Google Patents

Abstract

The embodiment of the invention discloses a parallel hybrid active filter, which includes an active apparatus and a passive apparatus connected between a three-phase power grid and a non-linear load in a parallel. The passive apparatus includes a passive filter group and a compensation capacitor, which are connected between the three-phase power grid and the non-linear load in a parallel. The active apparatus includes two DC-side capacitors and an inverter, the DC-side capacitors are identical in capacitance, and the two DC-side capacitors are connected in series and then connected to the inverter in parallel. The inverter includes two bridge arms that are connected in parallel, and each bridge arm includes two IGBTs connected in series. A midpoint of series connection of the two DC-side capacitors and a midpoint of the bridge arms are in parallel connection between the three-phase power grid and the non-linear load. The novel parallel hybrid active filter has the great harmonic wave inhibition and reactive compensation properties.

Description

A kind of Shunt Hybrid Active Power Filter and quality determining method thereof

Technical field

The present invention relates to active power filtering technical field, particularly relate to a kind of Shunt Hybrid Active Power Filter and quality determining method thereof.

Background technology

Harmonic wave makes the production of electric energy, the efficiency of transmission and utilization reduces, and make device of overheating of electrical, produce vibration & noise, and make ageing of insulation, useful life shortens, and even breaks down or burns.Harmonic wave can cause electric power system local parallel resonant or series resonance, harmonic content is amplified, causes the equipment burnouts such as capacitor.Harmonic wave also can cause relaying protection and automatics misoperation, and electric energy metrical is caused confusion.Outside for electric power system, harmonic wave can produce severe jamming to communication equipment and electronic equipment.Along with the use of a large amount of nonlinear-load, cause harmonic pollution in electric power system more and more serious, harmonic loss also increases day by day, also day by day serious on the impact of China's saving energy and decreasing loss.

At present existing many scholars and research institution are studied harmonics restraint, and conventional harmonics restraint means are in electrical network, install passive filter (PPF), active filter (APF) or passive filter and the comprehensive hybrid active filter (HAPF) of active filter.But in middle-and-high voltage system, independent passive filter can only carry out filtering to specific subharmonic, and there is the problem that compensation capacity is less and price is high in independent active filter.Therefore hybrid active filter becomes the focus of current practical application.

In prior art, hybrid active filter is applicable to mesohigh electrical network, and can carry out jumbo reactive power compensation, but hybrid active filter is in running, and its inverter losses is comparatively large, and package unit cost is higher.

Summary of the invention

Provide a kind of Shunt Hybrid Active Power Filter and quality determining method thereof in the embodiment of the present invention, to solve hybrid active filter of the prior art in running, inverter losses is large, the problem that package unit cost is high.

In order to solve the problems of the technologies described above, the embodiment of the invention discloses following technical scheme:

Embodiments provide a kind of Shunt Hybrid Active Power Filter, comprise and be parallel to active device between three phase network and nonlinear load and passive device, wherein,

Described passive device comprises passive filter group and compensation condenser, and described passive filter group and compensation condenser are parallel between three phase network and nonlinear load respectively;

Described active device comprises two DC bus capacitors and inverter, the capacitance of described DC bus capacitor is equal, be connected with described inverter parallel after two described DC bus capacitor series connection, described inverter comprises two groups of brachium pontis parallel with one another, and described brachium pontis comprises the IGBT of two series connection; The mid point of two DC bus capacitor serial connections and the mid point of described brachium pontis are parallel between described three phase network and nonlinear load.

Preferably, described active device also comprises the coupling transformer and one group of passive filter that are connected in series, and described coupling transformer and described passive filter are all connected in series with described active device.

Preferably, described active device also comprises the injection electric capacity for the jumbo reactive power of compensate for slower.

Preferably, the output of described active device is in series with the three pole reactor of the frequency glitches caused for filtering switching device break-make.

A quality determining method for Shunt Hybrid Active Power Filter, requires the arbitrary described Shunt Hybrid Active Power Filter of 1-4 for test right, comprising:

Calculate electrical network reference current;

According to described electrical network reference current, calculate the error amount of power network current;

According to the error amount of described power network current, determine the scale of precision of Shunt Hybrid Active Power Filter.

Preferably, described calculating electrical network reference current, comprising:

Obtain single-phase mains voltage and single-phase power network current;

According to described single-phase mains voltage and single-phase power network current, calculate the parameter G of susceptance character;

According to described parameter G and described single-phase mains voltage, calculate electrical network reference current.

Preferably, the error amount of power network current is the difference between described single-phase power network current and described electrical network reference current.

Preferably, the described error amount according to described power network current, determine the scale of precision of Shunt Hybrid Active Power Filter, comprising:

Prestore the error threshold scope corresponding with credit rating;

According to error amount, search the error threshold scope corresponding with described error amount;

The credit rating corresponding with described error amount is determined according to error threshold scope.

From above technical scheme, the Shunt Hybrid Active Power Filter that the embodiment of the present invention provides, comprise and be parallel to active device between three phase network and nonlinear load and passive device, wherein, described passive device comprises passive filter group and compensation condenser, and described passive filter group and compensation condenser are parallel between three phase network and nonlinear load respectively; Described active device comprises two DC bus capacitors and inverter, the capacitance of described DC bus capacitor is equal, be connected with described inverter parallel after two described DC bus capacitor series connection, described inverter comprises two groups of brachium pontis parallel with one another, and described brachium pontis comprises the IGBT of two series connection; The mid point of two DC bus capacitor serial connection mid points and described brachium pontis is parallel between described three phase network and threephase load.The present invention proposes a kind of structure of novel Shunt Hybrid Active Power Filter, the cost of package unit can be reduced further, cardinal principle is: active inverter adopts three-phase four construction of switch, decreases the quantity of switching device, reduces the loss of inverter simultaneously; Have employed a kind of harmonic detecting method of monophase current in addition, decrease the use of corresponding detection means and control performer, the detection computations time significantly reduces.Emulation experiment and engineer applied all demonstrate the validity of this structure.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, for those of ordinary skills, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

The topological structure schematic diagram of a kind of Shunt Hybrid Active Power Filter that Fig. 1 provides for the embodiment of the present invention;

The structural representation of the inverter of a kind of three-phase four switch that Fig. 2 provides for the embodiment of the present invention;

The single-phase electric model schematic of one that Fig. 3 provides for the embodiment of the present invention;

The equivalent circuit diagram of a kind of parallel connection mixed type active filter system that Fig. 4 provides for the embodiment of the present invention;

A kind of Shunt Hybrid Active Power Filter quality determining method schematic flow sheet that Fig. 5 provides for the embodiment of the present invention;

A kind of schematic flow sheet calculating electrical network reference current that Fig. 6 provides for the embodiment of the present invention;

The scale of precision determination schematic flow sheet of a kind of Shunt Hybrid Active Power Filter that Fig. 7 provides for the embodiment of the present invention;

Fig. 8 (a) for the embodiment of the present invention provide a kind of compensate before power network current oscillogram;

Fig. 8 (b) for the embodiment of the present invention provide a kind of compensate after power network current oscillogram;

Fig. 1-Fig. 8 (b), symbol represents:

1-three phase network, 2-nonlinear load, 3-passive device, 4-injects electric capacity, 5-coupling transformer, 6-three pole reactor, 7-inverter, 71-DC bus capacitor, the impedance of 72-IGBT, 8-output filter, the equivalent voltage source of 9-coupling transformer valve side.

Embodiment

Technical scheme in the present invention is understood better in order to make those skilled in the art person, below in conjunction with the accompanying drawing in the embodiment of the present invention, technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, should belong to the scope of protection of the invention.

First aspect

See Fig. 1, for the topological structure schematic diagram of a kind of Shunt Hybrid Active Power Filter that the embodiment of the present invention provides, comprise and be parallel to active device between three phase network 1 and nonlinear load 2 and passive device 3, described passive device 3 comprises passive filter group and compensation condenser, and described passive filter group and compensation condenser are parallel between three phase network 1 and nonlinear load 2 respectively; Described active device comprises two DC bus capacitors 71 and inverter 7, the capacitance of described DC bus capacitor 71 is equal, two described DC bus capacitors 71 are connected in parallel with described inverter 7 after connecting, described inverter 7 is three-phase four switching voltage type inverter, is the pulse width modulation inverter based on self-turn-off device.

Described active device also comprises the coupling transformer 5 and one group of passive filter that are connected in series, and described coupling transformer 5 and described passive filter are all connected in series with described active device.

Described active device also comprises the injection electric capacity 4 for the jumbo reactive power of compensate for slower.

The output of described active device is in series with the three pole reactor 6 of the frequency glitches caused for filtering switching device break-make.

Active device is made up of DC bus capacitor 71 and three-phase four switching voltage type inverter (VSC), VSC is the pulse-width modulation (PulseWidthModulation based on self-turn-off device, PWM) inverter, active device is connected in series by coupling transformer 5 and one group of passive filter and is parallel to electrical network.

Passive device 3 bears the fundamental voltage of the overwhelming majority, and active device injects the harmonic current needing to compensate.Whole system structure is simple, better can administer the harmonic wave in high-power electrical network, can compensate jumbo reactive power simultaneously.Its maximum advantage is that the fundamental voltage that active device bears is low, and the capacity of required inverter 7 is little.Shunt Hybrid Active Power Filter carries out the static compensation of reactive power by compensation condenser, and passive filter in parallel can the harmonic current of the jumbo reactive power of compensate for slower and filtering specific times, by active device and the common harmonic inhabitation of passive device 3.Fundamental reactive current can not flow into coupling transformer 5 and inverter 7 substantially, make this filter have the reactive power compensation planning of larger capacity, jumbo harmonic inhibition capability and less inverter capacity concurrently, be more suitable for the harmonic wave control requirement of large industrial enterprise.

As shown in Figure 2, the structural representation of the inverter of a kind of three-phase four switch provided for the embodiment of the present invention.Described inverter 7 comprises two groups of brachium pontis parallel with one another, and described brachium pontis comprises the IGBT72 of two series connection; The mid point of two DC bus capacitor 71 serial connections and the mid point of described brachium pontis are parallel between described three phase network 1 and nonlinear load 2.

Compared with three-phase six inverter bridge of routine, the inverter 7 that the embodiment of the present invention provides decreases two switching devices, is change the electric capacity that capacitance is original twice into by the electric capacity of DC side.Inverter 7 phase is wherein drawn from the mid point of DC side two electric capacity, change by having 4 IGBT72 (InsulatedGateBipolarTransistor, insulated gate bipolar transistor) IPM (IntelligentPowerModule of switching tube, Intelligent Power Module) electric capacity that module is equal with two capacitances constructs three-phase inverting circuit, is equivalent to change in three-phase three brachium pontis (6 IGBT switching tubes) into electric capacity brachium pontis mutually.

The compound full-control type voltage driven type power semiconductor that IGBT72 is made up of BJT (BipolarJunctionTransistor double pole triode) and MOS (Metal-Oxid-Semiconductor insulating gate type field effect tube), IGBT72 has the advantage that the little and saturation pressure of driving power reduces, and being applicable to very much being applied to direct voltage is that 600V and above converter system are as fields such as alternating current machine, frequency converter, Switching Power Supply, lighting circuit, Traction Drives.

The AC voltage that can be obtained three-phase Four-switch converter by Kirchoff s voltage theorem is:

$\left\{\begin{array}{c}{u}_{aN}=u_{an}+u_{nN}\\ u_{bN}=u_{bn}+u_{nN}\\ u_{cN}=u_{nN}\end{array}\right.---\left(1\right)$

To the three-phase system of balance, have

u _aN+u _bN+u _cN＝0(2)

Formula (2) is substituted into formula (1) can obtain:

$u_{nN}=-\frac{u_{an}+u_{bn}}{3}---\left(3\right)$

Therefore, the voltage equation of Hybrid Shunt Active Power Filter is:

$\left\{\begin{array}{c}{u}_{aN}=\frac{2u_{an}-u_{bn}}{3}\\ u_{bN}=\frac{2u_{bn}-u_{an}}{3}\\ u_{cN}=-\frac{u_{an}+u_{bn}}{3}\end{array}\right.---\left(4\right)$

Wherein,

In Fig. 2, N is coupling transformer valve side neutral point, Z _a, Z _b, Z _cfor the impedance of output filter, n is the mid point of DC bus capacitor.Corresponding with Fig. 2, then in formula (1)-Shi (5), u _anrefer to the voltage between a point and n point, u _bnrefer to the voltage between b point and n point, u _cnrefer to the voltage between c point and n point, u _aNrefer to the voltage between a point and N point, u _bNrefer to the voltage between b point and N point, u _cNrefer to the voltage between c point and N point, u _nNrefer to the voltage between n point and N point, u _c1refer to electric capacity C ₁voltage, u _c2refer to electric capacity C ₂voltage, T _a1, T _a2, T _b1, T _b2refer to the voltage on 4 IGBT elements, T _a1∧ u _c1represent T _a1and u _c1between magnitude of voltage, T _a2∧ u _c2represent T _a2and u _c2between magnitude of voltage, T _b1∧ u _c1represent T _b1and u _c1between magnitude of voltage, T _b2∧ u _c2represent T _b2and u _c2between magnitude of voltage.

As can be seen from voltage equation (4), as long as control A, B two phase voltage, C phase voltage just indirectly controls, and therefore inverter can adopt three-phase four construction of switch completely.In the engineer applied of reality, this inverter structure only need control the break-make of four switch elements, thus effectively can reduce the part executive component of detection system and control system, and can reduce the cost of the power consumption of active device, failure rate and switching device.

The one phase equivalent circuit of the hybrid active filter that the embodiment of the present invention provides as shown in Figure 3.Nonlinear load is counted as a harmonic current source I _l, U _sfor system power source voltage, active device is controlled as a desirable controlled voltage source U _c, n is coupling transformer no-load voltage ratio.In circuit, the definition of other each electricity and direction are also as shown in Figure 3, wherein I _s, I _l, I _p, I _c, I _i, I _fbe respectively grid branch electric current, load branch electric current, parallel passive branch current, active device output current, injection branch electric current, fundamental series resonance branch current, Z _s, Z _p, Z _c0, Z _f, Z _cbe respectively electric network impedance, passive leg impedance, inject condensance, first-harmonic resonance branch impedance, output filter impedance.

According to kirchhoff electric current and voltage theorem, have:

$\left\{\begin{array}{c}{U}_S=I_S{Z}_S+I_P{Z}_P\\ I_S=I_L+I_P+I_i\\ I_P{Z}_P=I_f{Z}_f+I_i{Z}_{C0}\\ I_f=I_i+I_C\\ U_C=I_C{Z}_C+I_f{Z}_f\end{array}\right.---\left(6\right)$

Abbreviation equation group (6):

I _S(K ₁Z _S+K ₂Z _S+K ₁Z _P)-I _LK ₁+U _CZ _f-(K ₁+K ₂)U _S＝0(7)

In formula, $\left\{\begin{array}{c}{K}_1=Z_C{Z}_f+Z_{C0}{Z}_L+Z_{C0}{Z}_C\\ K_2=Z_P(Z_f+Z_C)\end{array}\right.---\left(8\right)$

From formula (7), as long as conservative control inverter output harmonic wave voltage U _csize, then can effectively reduce mains by harmonics electric current I _scontent.Adopt the control strategy according to mains by harmonics electric current herein, i.e. control U _c=KI _s, K controls multiplication factor.Then formula (7) can abbreviation be:

$I_S=\frac{K_1/K_1+K_2}{Z_S+\frac{K_1{Z}_P+{\mathrm{KZ}}_f}{K_1+K_2}}{I}_L+\frac{U_S}{Z_S+\frac{K_1{Z}_P+{\mathrm{KZ}}_f}{K_1+K_2}}---\left(9\right)$

By formula (9) can instead release adopt carry out the control strategy of control inverter output voltage according to mains by harmonics electric current time, the one phase equivalent circuit of whole system, as shown in Figure 4.

Wherein, equiva lent impedance $Z^{\′}=\frac{K_1(Z_P-1)+{\mathrm{KZ}}_f}{K_1+K_2}---\left(9\right)$

As shown in Figure 4, the output impedance that this control strategy is equivalent in fact by controlling active device carrys out the equivalent harmonic impedance increasing electrical network.The harmonic impedance of electrical network is larger, then force load harmonic more to flow into passive filter, thus improves the filter effect of whole system.Meanwhile, the harmonic compensation characteristic of passive filter is larger by the impact of electric network impedance, and electric network impedance is larger, and the filter effect of passive filter is better.Therefore this control strategy further improves the grid-connected performance of passive filter while improving whole system filter effect.

On the other hand, corresponding with a kind of Hybrid Shunt Active Power Filter embodiment provided by the invention, present invention also offers a kind of quality determining method of Shunt Hybrid Active Power Filter.What the embodiment of the present invention carried out quality testing employing to shunt mixed type wave filter is Direct Current Control method based on power network current error.See Fig. 5, concrete steps comprise:

Step S101: calculate electrical network reference current.

Concrete, see Fig. 6, step S101 comprises:

Step S201: obtain single-phase mains voltage and single-phase power network current.

Step S202: according to described single-phase mains voltage and single-phase power network current, calculates the parameter G of susceptance character.

Step S203: according to described parameter G and described single-phase mains voltage, calculates electrical network reference current.

Step S102: according to described electrical network reference current, calculates the error amount of power network current.

Concrete derivation is as follows:

Define single-phase electrical network current i _s:

i _s＝i _f+i _h＝Gu _s+i _h(10)

I in formula _hthe summation of harmonic and reactive currents, i _fbe fundamental current, G is the parameter representing susceptance character.I _hequal 0 after being compensated, then have electrical network reference current and the summation i of harmonic and reactive currents _hmeet formula (11), wherein, T is electrical network power frequency.

$1/T{\∫}_0^T{u}_s{i}_{h}dt=0---\left(11\right)$

i _h＝i _s-i _f＝i _s-Gu _s(12)

By formula (12) formula to be entered (11), have:

$1/T{\∫}_0^T{u}_s(i_s-{\mathrm{Gu}}_s)dt=0---\left(13\right)$

Therefore obtaining parameter G is:

$G=\frac{1/T{\∫}_0^T{u}_s{i}_{s}dt}{1/T{\∫}_0^T{u}_s^{2}dt}=\frac{{\∫}_0^T{u}_s{i}_{s}dt}{{\∫}_0^T{u}_s^{2}dt}---\left(14\right)$

Parameter G determines, and electrical network reference current just can determine.

The inverter that the embodiment of the present invention adopts is three-phase four switch, only need detect biphase current.From analysis above, electrical network A phase current error and B phase current error are respectively:

${\mathrm{\Δi}}_{sa}=i_{sa}-i_{sa}^{*}---\left(15\right)$

${\mathrm{\Δi}}_{sb}=i_{sb}-i_{sb}^{*}---\left(16\right)$

Step S103: according to the error amount of described power network current, determines the scale of precision of Shunt Hybrid Active Power Filter.

Concrete, the error amount of power network current is the difference between described single-phase power network current and described electrical network reference current.See Fig. 7, concrete implementation step comprises:

Step S301: prestore the error threshold scope corresponding with credit rating.

Step S302: according to error amount, searches the error threshold scope corresponding with described error amount.

Step S303: determine the credit rating corresponding with described error amount according to error threshold scope.

This algorithm is based upon on the basis of monophase current harmonic detecting, therefore can directly apply in single phase system, three-phase three-wire system and three-phase four-wire system.The embodiment of the present invention adopts the high-power Shunt Hybrid Active Power Filter of three-phase Four-switch converter structure, for harmonic wave control and the reactive power compensation problem of the non-linear smelting equipment of enterprise, trys out in certain massive casting enterprise.

Certain massive casting enterprise 10kV intermediate frequency furnace smelting equipment rectifying device capacity is 9.54MVA, 24 pulse wave rectifiers are formed by secondary triangle misphase, reactive requirement when intermediate frequency furnace load is 6MW is 4.032MVar, and 23,25,47 and 49 subharmonic current content are respectively 14.57A, 12.75A, 3.94A and 3.44A.The parallel hybrid active filter designed herein, design parameter is as follows: system active installed capacity is 300kVA; Inverter adopts the power model F4-150R12KS4 that rated voltage is 1200V, rated current is 150A, and the C phase of inverter is made up of the electric capacity of DC side two 10000uF/1000V; Control section take DSP2812 as core; Output filter parameter is 1mH; The transformer phase voltage transformation ratio that active filter is coupled to passive filter is 2:1; Passive device is made up of 23,25 filter branch, and 23 passive leg electric capacity are 10uF, and inductance is 1.92mH, and 25 passive leg electric capacity are 10uF, and inductance is 1.62mH.

Drop into power network current waveform that is front and 2s after dropping into respectively as shown in Fig. 8 (a), Fig. 8 (b).As can be seen from the figure, after system puts into operation, power network current waveform is improved as close to sinusoidal wave by distorted waveform, and the harmonic component in power network current greatly reduces.

It should be noted that, in this article, the such as relational terms of " first " and " second " etc. and so on is only used for an entity or operation to separate with another entity or operating space, and not necessarily requires or imply the relation that there is any this reality between these entities or operation or sequentially.And, term " comprises ", " comprising " or its any other variant are intended to contain comprising of nonexcludability, thus make to comprise the process of a series of key element, method, article or equipment and not only comprise those key elements, but also comprise other key elements clearly do not listed, or also comprise by the intrinsic key element of this process, method, article or equipment.When not more restrictions, the key element limited by statement " comprising ... ", and be not precluded within process, method, article or the equipment comprising described key element and also there is other identical element.

The above is only the specific embodiment of the present invention, those skilled in the art is understood or realizes the present invention.To be apparent to one skilled in the art to the multiple amendment of these embodiments, General Principle as defined herein can without departing from the spirit or scope of the present invention, realize in other embodiments.Therefore, the present invention can not be restricted to these embodiments shown in this article, but will meet the widest scope consistent with principle disclosed herein and features of novelty.

Claims (8)

1. a Shunt Hybrid Active Power Filter, is characterized in that, comprises and is parallel to active device between three phase network (1) and nonlinear load (2) and passive device (3), wherein,

Described passive device (3) comprises passive filter group and compensation condenser, and described passive filter group and compensation condenser are parallel between three phase network (1) and nonlinear load (2) respectively;

Described active device comprises two DC bus capacitors (71) and inverter (7), the capacitance of described DC bus capacitor (71) is equal, be connected in parallel with described inverter (7) after two described DC bus capacitor (71) series connection, described inverter (7) comprises two groups of brachium pontis parallel with one another, and described brachium pontis comprises the IGBT (72) of two series connection; The mid point of the mid point that two DC bus capacitors (71) are connected in series and described brachium pontis is parallel between described three phase network (1) and nonlinear load (2).

2. Shunt Hybrid Active Power Filter according to claim 1, it is characterized in that, described active device also comprises the coupling transformer (5) and one group of passive filter that are connected in series, and described coupling transformer (5) and described passive filter are all connected in series with described active device.

3. Shunt Hybrid Active Power Filter according to claim 1, is characterized in that, described active device also comprises the injection electric capacity (4) for the jumbo reactive power of compensate for slower.

4. Shunt Hybrid Active Power Filter according to claim 1, is characterized in that, the output of described active device is in series with the three pole reactor (6) of the frequency glitches caused for filtering switching device break-make.

5. a quality determining method for Shunt Hybrid Active Power Filter, requires the arbitrary described Shunt Hybrid Active Power Filter of 1-4 for test right, it is characterized in that, comprising:

Calculate electrical network reference current;

According to described electrical network reference current, calculate the error amount of power network current;

According to the error amount of described power network current, determine the scale of precision of Shunt Hybrid Active Power Filter.

6. the quality determining method of Shunt Hybrid Active Power Filter according to claim 5, is characterized in that, described calculating electrical network reference current, comprising:

Obtain single-phase mains voltage and single-phase power network current;

According to described single-phase mains voltage and single-phase power network current, calculate the parameter G of susceptance character;

According to described parameter G and described single-phase mains voltage, calculate electrical network reference current.

7. the quality determining method of Shunt Hybrid Active Power Filter according to claim 6, is characterized in that, the error amount of power network current is the difference between described single-phase power network current and described electrical network reference current.

8. the quality determining method of Shunt Hybrid Active Power Filter according to claim 5, is characterized in that, the described error amount according to described power network current, determines the scale of precision of Shunt Hybrid Active Power Filter, comprising:

Prestore the error threshold scope corresponding with credit rating;

According to error amount, search the error threshold scope corresponding with described error amount;

The credit rating corresponding with described error amount is determined according to error threshold scope.