CN202395452U - Hybrid active power filter (APF) - Google Patents

Abstract

The utility model discloses a hybrid active power filter (APF). The hybrid APF comprises an APF, single-tuned passive power filters (PPFs) and an isolating transformer, wherein an inverter of the APF has a three-phase four-switch structure; two bridge arms are formed by four insulated gate bipolar transistor (IGBT) devices; a capacitor on a direct current side forms a third bridge arm; the output end of the APF is connected with the secondary side of the isolating transformer; the secondary side of the isolating transformer is connected in parallel with a fundamental wave shunt inductor; and the primary side of the isolating transformer is connected in series with a seventh single-tuned PPF, connected in parallel with a non-linear load and connected to a power grid. Main characteristic harmonics such as the fifth harmonic, the seventh harmonic and the eleventh harmonic which are caused by the non-linear load are filtered by the PPFs, certain reactive power is compensated, and APF branches dynamically suppress the remaining harmonics in real time.

Description

Mixed active electric power filter

Technical field

The utility model relates to a kind of mixed active electric power filter, belongs to electric and electronic technical field.

Background technology

Electric energy be modern society produce with people's lives in main and requisite important energy source, more and more serious harmonic pollution and the requirement of the increasingly high quality of power supply have formed a pair of contradiction that is becoming increasingly acute.In recent years; Because mains by harmonics problem; And mend capacitor and can not put into operation because of often tripping, serious even explosion caused, microcomputer protecting device malfunction even tripping also usually occur and accidents caused; The existence of the harmonic wave supplementary load loss of electric line, motor etc. and useful life shorten, and have caused enormous economic loss for power supply and electricity consumption enterprise.

The energy-saving and cost-reducing of industries such as electric power, metallurgy, chemical industry, building materials can be realized in enterprise's electric energy-saving new technology and the new equipment market that has a wide range of applications.In order to reduce the electric energy loss of enterprise, prevent the various harm of harmonic wave, must administer and realize the global collaborative optimal compensating of reactive power to the harmonic wave in the distribution system.Several years ago, harmonic wave dynamic managing equipment in high-pressure side is also abroad being monopolized for a long time, all also basic dependence on import of domestic relevant apparatus, however overseas equipment costs an arm and a leg.

Active Power Filter-APF APF is extensively paid close attention to as a kind of power electronic equipment that can dynamically suppress harmonic wave.The APF development various topological structures occurred so far: independent type, many current transformers mixed type and APF and PPF mixed type.Though the active filter that uses separately has good filtering performance, cost is higher, particularly in the high-power occasion, is difficult to be applied.The control system of many current transformers mixed type APF is quite complicated and loaded down with trivial details, and cost is higher, is in theoretical research stage basically, and practicality is not strong.Therefore, the hybrid active filter that the low capacity active filter combines with big capacity passive filter becomes the focus and the inevitable choice of current practical application, also is the developing direction of following active power filtering technology.It both can overcome the shortcoming that the APF capacity requirement is big, cost is high, can remedy the deficiency of PPF again, made whole filtering system obtain good performance.APF and PPF mixed type mainly contain parallel connection mixed type Active Power Filter-APF and Hybrid Type Series Active Power Filter.

Active Power Filter-APF in the Hybrid Type Series Active Power Filter can suppress the influence of electrical network background harmonics voltage to electric voltage, also can suppress contingent series parallel resonance between electrical network and the passive filter.But when having the harmonic wave that passive filter can not filtering in the load current, because active filter forces this part harmonic wave to flow into passive filter, this will produce harmonic voltage at load end.Therefore, this frame mode inhibition load harmonic current is irreconcilable (promptly can't take into account) with suppressing the load end harmonic voltage.In addition, because active filter is connected in the system, insulation is difficulty, repairs also very inconvenient.And when operate as normal, injection transformer flows through all load currents, and particularly at the secondary side of coupling transformer, the circuit heat waste increases, and filter construction also can be very huge.

The parallel connection mixed type Active Power Filter-APF adopts the injecting circuit structure usually: series resonance is pouring-in pouring-in with parallel resonance.Parallel resonance injection type APF does not possess the reactive power compensation ability; The capacity requirement of serial resonant injection type APF active filter is little; But there is the harmonic wave passage in it between Active Power Filter-APF and passive filter; The offset current that causes Active Power Filter-APF to inject possibly flow into passive filter and system again; Increase the burden of passive filter meaninglessly, and can influence the effect that harmonic wave suppresses.

The utility model content

The utility model technical problem to be solved provides a kind of novel mixed active electric power filter, and this mixed active electric power filter, this filter not only can be administered the harmonic wave in the electrical network preferably, can compensate jumbo reactive power simultaneously.

The technical solution of utility model is following:

A kind of mixed active electric power filter includes source filter, passive filter and isolating transformer, the secondary of the output side joint isolating transformer of active filter, and the former limit of isolating transformer is connected to the grid through passive filter; Electrical network and load are joined; Active filter is the passive filter to N1 characteristic harmonics; N1 is the odd number more than or equal to 5;

The inverter of active filter is a three-phase four switch inversion device, adopts 4 IGBT and 2 electric capacity; These 4 IGBT are one group of two phase brachium pontis that constitute inverter in twos, and these 2 capacitance series constitute the brachium pontis of third phase.

Described mixed active electric power filter also is provided with first-harmonic shunted resistively inductance (L), and first-harmonic shunted resistively inductance (L) is parallelly connected with the secondary of isolating transformer.

Load-side at electrical network also is provided with at least one group of auxiliary passive filter; Described auxiliary passive filter is the passive filter to N characteristic harmonics, and N is the odd number more than or equal to 5, assists passive filter and passive filter to handle the characteristic harmonics of different number of times respectively.

The no-load voltage ratio of isolating transformer is M, and M is the integer greater than 1.[ratio of integers helps calculating like this.】

Described mixed active electric power filter also comprises and is used to detect A phase load current i _La, B phase load current i _LbWith A phase voltage u mutually _a, A phase offset current i _Ca, B phase offset current i _CbTesting circuit, two PI controllers and a SVPWM modulator;

The brachium pontis that described 2 electric capacity are formed is a C phase brachium pontis;

Reference A-phase harmonic currents

and the reference B-phase harmonic currents

, respectively:

$i_{\mathrm{Ca}}^{*}=i_{\mathrm{La}}-i_{\mathrm{fa}};$

$i_{\mathrm{Cb}}^{*}=i_{\mathrm{Lb}}-i_{\mathrm{fb}};$

Wherein, i _FaAnd i _FbBe respectively A phase and B fundamental current mutually, i _Fa=u _a/ k _a,

$i_{\mathrm{Fb}}=(-\frac{1}{2}{u}_a+\frac{\sqrt{3}}{2}{u}_a\mathrm{Ctg\&omega;\; t})/k_b,$ And, $k_a=\frac{<u_a,i_{\mathrm{La}}>}{\left|\right|u_a\left|\right|},$

$k_b=\frac{-1/2<u_a,i_{\mathrm{La}}>+\sqrt{3}/2<u_a\mathrm{ctg\&omega;t},i_{\mathrm{Lb}}>}{\left|\right|u_b\left|\right|};$

Two PI controllers are a PI controller and the 2nd PI controller;

With reference to A phase harmonic current

With A offset current i mutually _CaDifference as the input signal of a PI controller;

With reference to B phase harmonic current

With B offset current i mutually _CbDifference as the input signal of the 2nd PI controller;

The output signal of 2 PI controllers is input to respectively in the SVPWM modulator, the break-make of 4 IGBT of SVPWM modulator output control signal control.

Between the input of PI controller and SVPWM modulator, also be provided with amplitude limiter.

A kind of SVPWM method based on mixed active electric power filter adopts aforesaid mixed active electric power filter; The modulator approach of described SVPWM modulator is as shown in the table:

Wherein, u _AcAnd u _BcBe respectively line voltage and B between mutually of A, C, the C line voltage between mutually; V ₀, V ₁, V ₂And V ₃Be the basic output voltage vector of three-phase four switch inversion device; Three-phase four switch inversion device fundamental space voltage vector and on off state corresponding relation are following: in the table 1 expression open-minded, 0 expression is turn-offed; u _DcThe expression dc voltage;

S _aAnd S _bThe switching signal that is respectively A phase IGBT and B be the switching signal of IGBT mutually; $\left(\begin{array}{c}{u}_{\mathrm{\&alpha;}}\\ u_{\mathrm{\&beta;}}\end{array}\right)=\sqrt{\frac{2}{3}}\left(\begin{array}{cc}-\frac{1}{2}& -\frac{1}{2}\\ \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right)\left(\begin{array}{c}{u}_a\\ u_b\end{array}\right),$ u _αAnd u _βBe corresponding u _aAnd u _bSpace voltage vector α β coordinate components; u _sBe the inverter synthesized voltage vector;

T ₁, T ₂, T ₃, T ₄, T ₅Be respectively five corresponding periods of basic voltage vectors sequence of operation of SVPWM modulator approach, have:

T ₁=mT _S/ 2, T ₂=(1-m+n) T _S/ 4, T ₃=(1-m-n) T _S/ 2, T ₄=T ₂, T ₅=T ₁T wherein _SSwitch periods for IGBT; $m=\frac{|u_{\mathrm{Ac}}+u_{\mathrm{Bc}}|}{u_{\mathrm{Dc}}}{T}_S,$ $n=\frac{|u_{\mathrm{Ac}}-u_{\mathrm{Bc}}|}{u_{\mathrm{Dc}}}{T}_S;$

8. the SVPWM method based on mixed active electric power filter according to claim 7; It is characterized in that; The transfer function of PI controller k=6, T=0.01.

Beneficial effect:

The utility model discloses a kind of mixed active electric power filter of three-phase four switches, comprise Active Power Filter-APF APF, passive filter group PPFs and isolating transformer.The inverter of Active Power Filter-APF adopts three-phase four constructions of switch, constitutes two brachium pontis by 4 IGBT devices, and the electric capacity of DC side constitutes the 3rd brachium pontis.The secondary of the output termination isolating transformer of Active Power Filter-APF, the secondary of isolating transformer is parallelly connected with the first-harmonic shunted resistively inductance, and the former limit of isolating transformer is connected in series with 7 single tuning passive filter PPF, receives in the electrical network again with after nonlinear load is parallelly connected.

5 times, 7 times and 11 inferior principal character harmonic waves that the utility model adopts passive filter group filtering nonlinear load to cause compensate certain reactive power simultaneously, and the Active Power Filter-APF branch road carries out dynamic real-time to remaining harmonic wave and administers.

The outstanding advantage of the utility model is following:

1) inverter in the mixed active electric power filter of three-phase four switches has reduced the use of switching device and respective detection device, power model heat-sink unit and control performer etc.; Cost and loss are reduced greatly, improve the reliability and stability of system.

2) mixed active electric power filter of three-phase four switches combines Active Power Filter-APF and passive filter; The advantage of comprehensive these two kinds of active filters; Remedy shortcoming separately again mutually, had the reactive static complementary energy power of larger capacity and less inverter capacity concurrently.Electric capacity through in the design passive filter when making passive filter can suppress the characteristic subharmonic, can compensate jumbo idle.Active filter is connected with a passive filter wherein, makes active filter need not bear fundamental voltage, has significantly reduced the capacity of inverter.

3) the required detection means of single-phase harmonic current detecting method is few, and computing time is few.

4) avoid complicated irrational number and trigonometric function operation based on the space vector of voltage modulator approach of three-phase four switch active electric-power filters, make it have that the link of detection is few, operand is few and advantage of high precision.

Description of drawings

Fig. 1 is the system global structure figure of the mixed active electric power filter of the utility model.[c5 among the figure, L5, c7, L11 etc. are ground connection all]

Fig. 2 is the switching circuit of the mixed active electric power filter of three-phase four switches;

Fig. 3 is the integral body control block diagram of the mixed active electric power filter of three-phase four switches;

Fig. 4 is the system global structure figure of the mixed active electric power filter of embodiment 1;

Fig. 5 is a simulation waveform; Wherein, (a) be the device preceding power network current that puts into operation; (b) for device put into operation before the frequency spectrum of power network current, (c) be the put into operation frequency spectrum of back power network current of device, (d) be the put into operation frequency spectrum of back power network current of device.

Embodiment

Below will combine accompanying drawing and specific embodiment that the utility model is explained further details:

Embodiment 1:

As shown in Figure 1, the inverter of Active Power Filter-APF adopts three-phase four constructions of switch, and 4 IGBT devices constitute two phases, and dc bus capacitor constitutes third phase.Said passive filter composes in series single tuned filter by electric capacity and inductance; 7 single tuned filters be connected to the grid after connecting in the former limit of isolating transformer; Active Power Filter-APF connects the isolating transformer secondary, and small inductor is parallelly connected with the isolating transformer secondary with the shunting fundamental current.

Above-mentioned passive filter group is tuned at respectively 5 times, 7 times and 11 subfrequency places.

The equiva lent impedance resonance of above-mentioned secondary at 7 single tuned filters and isolating transformer produces resonance at 9 subfrequency places in order to avoid this branch road.

A kind of single-phase harmonic current detecting method that is applied to the mixed active electric power filter of three-phase four switches may further comprise the steps:

1) each phase momentary load electric current can be expressed as before the compensation: i _L=i _f+ i _C(1)

I wherein _fThe expression basic current, i _CThe expression harmonic current.

There is fundamental current to be after the compensation: i _f=ku (2)

Wherein k is the parameter of impedance property.

K can adopt the form of inner product and norm to represent: $k=\frac{<u,i_L>}{\left|\right|u\left|\right|}---\left(3\right)$

[u, iL are vector forms]

Then a is respectively with b k mutually mutually:

$k_a=\frac{<u_a,i_{\mathrm{La}}>}{\left|\right|u_a\left|\right|}---\left(4\right)$

$k_b=\frac{-1/2<u_a,i_{\mathrm{La}}>+\sqrt{3}/2<u_a\mathrm{ctg\&omega;t},i_{\mathrm{Lb}}>}{\left|\right|u_b\left|\right|}---\left(5\right)$

Definition by norm can know || u _a||=|| u _b||=|| u _c||.

2) compensation back a is respectively with b fundamental current mutually mutually

i _fa＝u _a/k _a (6)

$i_{\mathrm{fb}}=(-\frac{1}{2}{u}_a+\frac{\sqrt{3}}{2}{u}_a\mathrm{ctg\&omega;t})/k_b---\left(7\right)$

The reference a that then need compensate mutually with b mutually harmonic current do

$i_{\mathrm{Ca}}^{*}=i_{\mathrm{La}}-i_{\mathrm{fa}}---\left(8\right)$

$i_{\mathrm{Cb}}^{*}=i_{\mathrm{Lb}}-i_{\mathrm{fb}}---\left(9\right)$

A kind ofly be applied to the mixed active electric power filter of three-phase four switches, based on the space vector of voltage modulator approach (SVPWM) of three-phase four switch inversion device structure, may further comprise the steps:

1) seeks new coordinate system, basic output voltage space vector is transferred on the reference axis in the α β coordinate system;

The coordinate transform formula is: $C=\sqrt{\frac{2}{3}}\left(\begin{array}{cc}-\frac{1}{2}& -\frac{1}{2}\\ \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right)---\left(10\right)$

2) in α β coordinate system, two voltages are carried out simple arithmetic, obtain space voltage vector α β coordinate components;

The expression formula of space voltage vector: $\left(\begin{array}{c}{u}_{\mathrm{\&alpha;}}\\ u_{\mathrm{\&beta;}}\end{array}\right)=\sqrt{\frac{2}{3}}\left(\begin{array}{cc}-\frac{1}{2}& -\frac{1}{2}\\ \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right)\left(\begin{array}{c}{u}_a\\ u_b\end{array}\right)---\left(11\right)$

3) the space voltage vector sector distributes corresponding with the rest frame quadrant; Make the judgement of sector can be directly judge like this, and need not carry out asking in the conventional method the required trigonometric function operation of voltage vector phase angle according to the symbol of the α β coordinate components of reference voltage vector; The basic output voltage vector of three-phase four switch inversion device is V ₀, V ₁, V ₂And V ₃, V wherein ₀And V ₃, V ₁And V ₂Be respectively amplitude and equate two pairs of vectors that phase place is opposite.

When S1, S2, S3, S4 represent the break-make of four switches of inverter, when these four switches are in different on off operating modes, inverter synthesized voltage vector u _s=u _α+ ju _βObtain four basic output voltage vector V ₀, V ₁, V ₂And V ₃The corresponding relation of three-phase four switch inversion device fundamental space voltage vector and on off state is as shown in table 2.Sa is 1 o'clock, the S2 conducting, and S4 turn-offs; Sa is 0 o'clock, the S4 conducting, and S2 turn-offs.Sb is 1 o'clock, the S1 conducting, and S3 turn-offs; Sb is 0 o'clock, the S3 conducting, and S1 turn-offs.

Table 1 three-phase four switch inversion device fundamental space voltage vector and on off state correspondence table [u _DcBeing dc voltage, is not Us]

Current Detection Algorithm obtains the harmonic current that will compensate, harmonic current is carried out PI control after, if the output signal is too big, carry out amplitude limit, the amplitude of amplitude limit is confirmed according to practical experience or is made emulation experiment and confirm.Just as the input signal of SVPWM module, the SVPWM algorithm is modulated them in the output of amplitude limit, the result of modulation be exactly the value of S1, S2, S3, S4 be 0 or 1, be used for the break-make of four switching tubes of control inverter.

Table 2 space voltage vector sector determination methods

The sector	I	II	?III	IV
					Determination methods	u β≥0	u β≥0	?u β＜0	u β≥0

4) owing to do not contain zero vector in the basic output voltage vector of three-phase four switch inversion device, consider V ₀And V ₃, V ₁And V ₂Be respectively amplitude and equate, therefore two pairs of vectors that phase place is opposite select a pair of synthetic zero vector of identical time that acts on simultaneously by wherein.In order to simplify control logic, select V ₁And V ₂It is synthetic to carry out zero vector, forms a kind of " five-part form " SVPWM modulation algorithm.As shown in table 3.[basic voltage vectors sequence of operation V for example ₀V ₂V ₁V ₂V ₀Implication be: V ₀And V ₂Be the voltage vector that to export, with V ₂Split into two parts output, a part wherein and V ₁Synthetic zero vector.】

The basic voltage vectors sequence of operation time corresponding of " five-part form " SVPWM modulation algorithm is respectively T ₁T ₂T ₃T ₄T ₅，

T ₁＝m/2，T ₂＝(1-m+n)/4，T ₃＝(1-m-n)/2，T ₄＝T ₂，T ₅＝T ₁。T wherein _SBe switch periods.

Table 3 " five-part form " space voltage vector modulation algorithm

As shown in Figure 1; The mixed active electric power filter of three-phase four switches comprises Active Power Filter-APF, passive filter and isolating transformer; Injection branch composes in series single tuned filter by capacitor C 7, inductance L 7; Active Power Filter-APF APF and small inductor [inductance value of each small inductor is 8mH.] are connected in parallel through isolating transformer T, (are C7, L7) insert electrical network through 7 single tuned filters again.7 times single tuned filter provides a low-impedance passage to harmonic wave, intercepts certain idle of line voltage and compensation.The utility model can be that (N single tuned filter can be 5 times, 7 times, 11 times, 13 inferior for N single tuned filter according to the situation selection injection branch of output of actual harmonic wave and compensating reactive power.Be to choose according to loading condition.If load comprises 5 times, 7 times, 11 times, 13 times and high order harmonic component, and 11 times, 13 times content are heavy, and 5 times, 7 times and higher harmonic content are light, and the passive filter that the harmonic number that then content is the lightest is corresponding is connected with APF.)。Because the impedance of small inductor is very little, is equivalent to the short-channel of fundamental current, all will flow into this network so flow through the fundamental current of injection branch, and can not flow into inverter.The effect of active filter mainly contains: the filtering performance and the filter effect that improve whole filtering system; Suppress of the influence of electrical network background harmonics voltage to electric voltage; Suppress passive filter and the series parallel resonance that the electrical network inductance forms, remedy defective and the deficiency of passive power filter existence etc.The mixed active electric power filter operation characteristic of three-phase four switches is: only by the passive part compensating power, active part and passive part suppress harmonic wave jointly.

The switching circuit of the mixed active electric power filter of three-phase four switches is as shown in Figure 2.Among Fig. 2, Z0 is the impedance of output filter.S _A, S _BThe on off state of expression switching device.e _a, e _bAnd e _cUnified being expressed as:

$e=(Z_S//Z_P)//(Z_7+Z_L)\&CenterDot;(\frac{U_S}{Z_S}+I_L)\&CenterDot;\frac{Z_L}{Z_L+Z_7}=\frac{Z_S{Z}_P{Z}_L(\frac{U_S}{Z_S}+I_L)}{Z_S{Z}_P+Z_S{Z}_7+Z_7{Z}_P+Z_S{Z}_L+Z_L{Z}_P}---\left(13\right)$

Wherein, Z _S, Z _P, Z ₇And Z _LThe equiva lent impedance of representing the parallelly connected equiva lent impedance of system's equiva lent impedance, 5 times and 11 times single tuned filters, 7 single tuned filter equiva lent impedances and small inductor respectively.[equiva lent impedance is to utilize Thevenin's theorem to obtain, and is prior art] I _LIt is load current.

Like e _a, e _bAnd e _cBe expressed as respectively:

$e_a=(Z_{\mathrm{Sa}}//Z_{\mathrm{Pa}})//(Z_{7a}+Z_{\mathrm{La}})\&CenterDot;(\frac{U_{\mathrm{Sa}}}{Z_{\mathrm{Sa}}}+I_{\mathrm{La}})\&CenterDot;\frac{Z_{\mathrm{La}}}{Z_{\mathrm{La}}+Z_{7a}}=\frac{Z_{\mathrm{Sa}}{Z}_{\mathrm{Pa}}{Z}_{\mathrm{La}}(\frac{U_{\mathrm{Sa}}}{Z_{\mathrm{Sa}}}+I_{\mathrm{La}})}{Z_{\mathrm{Sa}}{Z}_{\mathrm{Pa}}+Z_{\mathrm{Sa}}{Z}_{7a}+Z_{7a}{Z}_{\mathrm{Pa}}+Z_{\mathrm{Sa}}{Z}_{\mathrm{La}}+Z_{\mathrm{La}}{Z}_{\mathrm{Pa}}}$

$e_b=(Z_{\mathrm{Sb}}//Z_{\mathrm{Pb}})//(Z_{7b}+Z_{\mathrm{Lb}})\&CenterDot;(\frac{U_{\mathrm{Sb}}}{Z_{\mathrm{Sb}}}+I_{\mathrm{Lb}})\&CenterDot;\frac{Z_{\mathrm{Lb}}}{Z_{\mathrm{Lb}}+Z_{7b}}=\frac{Z_{\mathrm{Sb}}{Z}_{\mathrm{Pb}}{Z}_{\mathrm{Lb}}(\frac{U_{\mathrm{Sb}}}{Z_{\mathrm{Sb}}}+I_{\mathrm{Lb}})}{Z_{\mathrm{Sb}}{Z}_{\mathrm{Pb}}+Z_{\mathrm{Sb}}{Z}_{7b}+Z_{7b}{Z}_{\mathrm{Pb}}+Z_{\mathrm{Sb}}{Z}_{\mathrm{Lb}}+Z_{\mathrm{Lb}}{Z}_{\mathrm{Pb}}}$

$e_c=(Z_{\mathrm{Sc}}//Z_{\mathrm{Pc}})//(Z_{7c}+Z_{\mathrm{Lc}})\&CenterDot;(\frac{U_{\mathrm{Sc}}}{Z_{\mathrm{Sc}}}+I_{\mathrm{Lc}})\&CenterDot;\frac{Z_{\mathrm{Lc}}}{Z_{\mathrm{Lc}}+Z_{7c}}=\frac{Z_{\mathrm{Sc}}{Z}_{\mathrm{Pc}}{Z}_{\mathrm{Lc}}(\frac{U_{\mathrm{Sc}}}{Z_{\mathrm{Sc}}}+I_{\mathrm{Lc}})}{Z_{\mathrm{Sc}}{Z}_{\mathrm{Pc}}+Z_{\mathrm{Sc}}{Z}_{7c}+Z_{7c}{Z}_{\mathrm{Pc}}+Z_{\mathrm{Sc}}{Z}_{\mathrm{Lc}}+Z_{\mathrm{Lc}}{Z}_{\mathrm{Pc}}}$

Likewise, Z _a, Z _bAnd Z _cUnified being expressed as

$Z=((Z_S//Z_P)+Z_7)//Z_L=\frac{Z_S{Z}_P{Z}_L+Z_S{Z}_7{Z}_L+Z_7{Z}_P{Z}_L}{Z_S+Z_P+Z_S{Z}_7+Z_7{Z}_P+Z_S{Z}_L+Z_L{Z}_P}$

(14) [symbol in the formula // expression parallel connection.】

Based on Kirchhoff's law, can obtain equation group from Fig. 2

$\left\{\begin{array}{c}{e}_a=e_{\mathrm{ac}}+e_{\mathrm{cN}}\\ e_b=e_{\mathrm{bc}}+U_{\mathrm{cN}}\\ e_c=e_{\mathrm{cN}}\end{array}\right.---\left(15\right)$

Three-phase system to balance has

e _a+e _b+e _c＝0 (16)

Then $e_c=-\frac{e_a+e_b}{3}---\left(17\right)$

The voltage equation of three-phase four switch APF is:

$\left\{\begin{array}{c}{e}_a=U_{C1}{S}_A\\ e_b=U_{C2}{S}_B\\ e_c=-\frac{e_a+e_b}{3}\end{array}\right.---\left(18\right)$

Wherein $S_i=\left\{\begin{array}{c}0\\ 1\end{array}\right.i=A,B.$

Can find out that by voltage equation as long as control A, B two phase voltages, the C phase voltage is with regard to indirect control.

In like manner, as long as control A, B biphase current, the C phase current is with regard to indirect control.

Fig. 3 is the integral body control block diagram of the mixed active electric power filter of three-phase four switches.Utilize a voltage transformer and two current transformers to obtain A points of common connection voltage u mutually _a[being the phase voltage of A phase] and A mutually, B phase load current i _La, i _Lb, utilize single-phase harmonic current detecting method to obtain A phase, B with reference to harmonic compensation current

[promptly adopt aforesaid formula

Try to achieve with reference to offset current]; Utilize two current transformers to obtain the offset current i of A phase, B phase _Ca, i _Cb, reference harmonic offset current and actual measurement offset current are subtracted each other the input signal that obtains the PI controller, [when the value of PI controller output exceeds error range, utilize amplitude limiter to make error in the scope of regulation through PI control back amplitude limit.], the signal that obtains is carried out the SVPWM modulation, obtain four triggering signal S1, S2, S3 and S4 of three-phase four switch inversion device.[among Fig. 3,

Want and i _CaSubtract each other, at this moment

Should get effective value.】

The control of Active Power Filter-APF APF is the control to the PWM inverter in essence, finally sums up in the point that the switching mode of asking for inverter.Through control, make inverter export the reference voltage or the electric current of corresponding harmonic voltage or current tracking expectation, thereby realize the purpose of harmonic wave control switching mode.Adopting the final purpose of PI controller and whole Fig. 3 system is the triggering signal that obtains switching device in the inverter.The PI controller can make the control system output current will As time goes on level off to 0 to the tracking error of reference current.Fig. 3 is exactly a control procedure.

Embodiment 1:

System configuration is as shown in Figure 5, and in this instance, load is a nonlinear load: resistance value is 37.3 Ω, and inductance value is 66.5mH, and harmonic content is as shown in table 1.

Table 1 harmonic content

The value of various electric capacity and inductance is as shown in table 2.

Table 2

The data substitution formula (14) of table 2 just can be obtained equiva lent impedance.

The transfer function of PI is

k=6, and the parameter of T=0.01 amplitude limiter is-50～+ 50.

All programming realizations in dsp controller of control block diagram shown in Figure 3.

Before compensation equipment put into operation, the power network current distortion was serious.Power factor is lower, is merely about 0.87. and can be found out that by Fig. 5 after passive filter and active filter put into operation, the power network current aberration rate reduced, each main subharmonic current content all reduces greatly, all satisfies the GB requirement.Power factor of electric network brings up to 0.952 from 0.87.

Harmonic content

The three-phase four switch mixed active electric power filters that the utility model proposes have universality.This compensation arrangement can suppress harmonic wave and compensating reactive power.When practical application, at first analyze loading condition, if nonlinear load just contains harmonic wave certainly, utilize measuring instrument to analyze the size of each harmonic content and the size of reactive power.Can calculate the value of electric capacity according to the size that records reactive power; The harmonic number that contains according to load designs passive filter; The capacitance of passive filter is to be confirmed by reactive power, then obtains each passive filter corresponding inductance value and resistance value according to the series resonance principle.Be the capacitance compensation of reactive power by passive filter, main harmonic wave is suppressed by passive filter, and high order harmonic component is suppressed by active filter.Because passive filter has been born most voltage, makes that the capacity requirement of active filter is little, be easy to realize.

Claims (6)

1. a mixed active electric power filter is characterized in that, includes source filter, passive filter and isolating transformer, the secondary of the output side joint isolating transformer of active filter, and the former limit of isolating transformer is connected to the grid through passive filter; Electrical network and load are joined; Active filter is the passive filter to N1 characteristic harmonics; N1 is the odd number more than or equal to 5;

The inverter of active filter is a three-phase four switch inversion device, adopts 4 IGBT and 2 electric capacity; These 4 IGBT are one group of two phase brachium pontis that constitute inverter in twos, and these 2 capacitance series constitute the brachium pontis of third phase.

2. mixed active electric power filter according to claim 1 is characterized in that, also is provided with first-harmonic shunted resistively inductance (L), and first-harmonic shunted resistively inductance (L) is parallelly connected with the secondary of isolating transformer.

3. mixed active electric power filter according to claim 1 is characterized in that, also is provided with at least one group of auxiliary passive filter in the load-side of electrical network; Described auxiliary passive filter is the passive filter to N characteristic harmonics, and N is the odd number more than or equal to 5, assists passive filter and passive filter to handle the characteristic harmonics of different number of times respectively.

4. mixed active electric power filter according to claim 1 is characterized in that, the no-load voltage ratio of isolating transformer is M, and M is the integer greater than 1.

5. according to each described mixed active electric power filter of claim 1-4, it is characterized in that, also comprise being used to detect A phase load current i _La, B phase load current i _LbWith A phase voltage u mutually _a, A phase offset current i _Ca, B phase offset current i _CbTesting circuit, two PI controllers and a SVPWM modulator;

The brachium pontis that described 2 electric capacity are formed is a C phase brachium pontis;

Two PI controllers are a PI controller and the 2nd PI controller;

With reference to A phase harmonic current With A offset current i mutually _CaDifference as the input signal of a PI controller;

With reference to B phase harmonic current

With B offset current i mutually _CbDifference as the input signal of the 2nd PI controller;

The output signal of 2 PI controllers is input to respectively in the SVPWM modulator, the break-make of 4 IGBT of SVPWM modulator output control signal control;

Where the reference phase A harmonic current

and the reference B-phase harmonic currents

, respectively:

$i_{\mathrm{Ca}}^{*}=i_{\mathrm{La}}-i_{\mathrm{fa}};$

$i_{\mathrm{Cb}}^{*}=i_{\mathrm{Lb}}-i_{\mathrm{fb}};$

Wherein, i _FaAnd i _FbBe respectively A phase and B fundamental current mutually, i _Fa=u _a/ k _a,

$i_{\mathrm{Fb}}=(-\frac{1}{2}{u}_a+\frac{\sqrt{3}}{2}{u}_a\mathrm{Ctg\&omega;\; t})/k_b,$ And, $k_a=\frac{<u_a,i_{\mathrm{La}}>}{\left|\right|u_a\left|\right|},$

$k_b=\frac{-1/2<u_a,i_{\mathrm{La}}>+\sqrt{3}/2<u_a\mathrm{ctg\&omega;t},i_{\mathrm{Lb}}>}{\left|\right|u_b\left|\right|}.$

6. mixed active electric power filter according to claim 5 is characterized in that, between the input of PI controller and SVPWM modulator, also is provided with amplitude limiter.

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