CN102638044A - Control method for predicating switching signal of three-phase four-wire active filter - Google Patents

Abstract

The invention discloses a control method for predicating a switching signal of a three-phase four-wire active filter, comprising the following steps of: step 1: acquiring a signal, and computing a reference current signal Iref, wherein the computing formula of the reference current signal is that Iref=Ipref*sin omega t+Idc-pref/3+Ih; step 2: computing the switching time TK+1 of the next time; or computing by the formula in the specification; and step 3: controlling a switching device of each phase in a three-level inverter bridge according to the TK+1. The control method for predicating the switching signal of the three-phase four-wire active filter is used for predicating the switching state of the next control period according to the single-phase status of the active filter, thereby being easy to implement, and quick in response speed.

Description

Three-phase four-wire active filter switch signal estimation control method

Technical field

The invention belongs to the active power filtering technology, relate to a kind of three-phase four-wire active filter switch signal estimation control method.

Background technology

Along with popularizing of home electronics, distribution network electric energy quality is seriously influenced, and the particularly widely-used rectifier unsteady flow power supply of domestic electric appliance has brought a large amount of harmonic pollutions to power distribution network, must administer.Improvement to harmonic wave mainly contains passive filter, active filter and hybrid filter.The parallel connection passive filter is the simplest harmonic wave management method, but can only filter effect preferably be arranged to specific subharmonic, and filtered band is very narrow.Passive filter is a kind of power electronic equipment; Can compensate the harmonic wave of optional frequency and size, compensation characteristic does not receive the influence of electric network impedance and frequency change, is a kind of desirable harmonic compensation device; But be subject to the influence of power electronic device capacity, be difficult to be applied directly in the high-pressure system.Hybrid filter has been taken into account the advantage of passive filter and active filter, utilize the most of harmonic wave of passive part filtering, and active part mainly is used for improving the filtering performance of passive part.

In power distribution network; Electric pressure is low, electric current is little; Be more suitable for directly adopting Active Power Filter-APF, this is because the price of passive filter just progressively rises, and the power electronic device price of low capacity is in steady decline; Directly use Active Power Filter-APF on cost, more to have superiority, have better filtering performance simultaneously again.

For the power distribution network three-phase four-wire active power filter because the harmonic band of need administering very wide (generally requiring from 2 subharmonic) to 50 subharmonic, must guarantee controller at wide frequency range all to have bigger gain, traditional P I to control very difficult satisfied.For this reason; Must 2 to 50 subharmonic be detected respectively, then to the independent CONTROLLER DESIGN of each harmonic wave, this makes controller will become very complicated; The response speed that is difficult to the system that guarantees; If also will carry out imbalance compensation, then must control respectively by three-phase, increased the weight of the burden of controller more.

Summary of the invention

Technical problem to be solved by this invention provides a kind of three-phase four-wire active filter switch signal estimation control method; This three-phase four-wire active filter switch signal estimation control method is according to the on off state of single-phase next control cycle of status predication of active filter; Easy to implement, response speed is fast.

The technical solution of invention is following:

A kind of three-phase four-wire active filter switch signal estimation control method, described three-phase four-wire active filter is made up of two electric capacity, three-level inverters and two-stage LC output filter; Two electric capacity are the series arm that first electric capacity and second electric capacity are formed; The tie point of first electric capacity and second electric capacity connects the center line of three-phase and four-line electrical network; Two electric capacity are parallelly connected with three brachium pontis of three-level inverters, and the output of three-level inverters is connected with electrical network through two-stage LC output filter; Two-stage LC output filter is prime LC output filter and back level LC output filter;

A, B, C three-phase are adopted phase-splitting control, may further comprise the steps:

Step 1: acquired signal, and calculate reference current signal I _Ref:

The signal of being gathered comprises the output voltage U of three-level inverters _Inv, line voltage U _S, the electric current I in the prime output filter on the inductance _Inv, the electric current I in the prime output filter on the inductance _L, electric capacity output in the prime output filter electric current I _C1, electric capacity output in the back level output filter electric current I _C2, the first capacitance voltage U _CD1With the second capacitance voltage U _CD2

The computing formula of reference current signal is I _Ref=I _Pref* sin ω t+I _Dc-pref/ 3+I _h

Wherein:

I _hBe the load harmonic current, obtain through load current is carried out synchronous conversion; I _PrefBe U _CD1+ U _CD2-U _DCrefOutput variable behind a PI controller; U wherein _DCrefBe capacitance voltage reference value [U _DCrefGet a value between the 700-800, can be set to 800V, be made as 700 also passablely, just influence the index of modulation]

ω is the line voltage fundamental frequency;

I _Dc-prefFor being used for stablizing the active current of capacitance voltage, I _Dc-prefBe U _CD1-U _CD2Output variable through the 2nd PI controller;

Step 2: T switching time that calculates next control cycle _K+1

$T_{K+1}=(U_s+L_1\frac{I_{\mathrm{Ref}}-I_{\mathrm{Inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{Ref}}-I_L-I_{C1}}{T})/U_{\mathrm{DC}1};$ Wherein T is that [T gets 10 to control cycle ^-4, promptly switching frequency is made as 10kHz]; L ₁, L ₂Be respectively the first order of filter, partial inductance value, [difference value 1.5mH, 0.5fmH].

Judge T _K+1Whether＜0 set up, if set up, presses following formula and upgrade T _K+1, otherwise keep T _K+1Constant:

$T_{K+1}=-(U_s+L_1\frac{I_{\mathrm{ref}}-I_{\mathrm{inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{ref}}-I_L-I_{C1}}{T})/{\mathrm{<figure-callout\; id="2"\; label="U\; DC"\; filenames="HDA0000154163810000041.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}};$

Step 3: according to T _K+1The switching device of the every phase in the control three-level inverters.

For the T that finally obtains _K+1If, T _K+1＞0, in the expression next cycle, answer control inverter output positive level T _K+1Time, export 0 level T-T _K+1Time;

If T _K+1=0, represent then in the next control cycle that the output of inverter is 0 entirely;

If T _K+1＜0, then represent in the next control cycle output negative level T of inverter _K+1Time, export 0 level T-T _K+1Time.

The one PI controller parameter is: proportionality coefficient gets 0.01, and the parameter that integral coefficient is got 1, the two PI control is: proportionality coefficient gets 0.1, and integral coefficient gets 100.

Suppose in the control cycle T that the three-level inverter output positive level time is T _On, the output negative level time is T _Off, exporting 0 level time is T ₀(T ₀=T-T _On-T _Off), duty ratio can be expressed as T ₀/ T.

Then, inverter output voltage is:

U _inv＝T _onU _DC1-T _offU _DC2

Consider the state equation of output filter, have:

$U_{\mathrm{inv}}-U_S=L_1\frac{{\mathrm{dI}}_{\mathrm{inv}}}{\mathrm{dt}}+{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000154163810000041.png"\; state="\{\{state\}\}">L</figure-callout>}}_2\frac{{\mathrm{dI}}_L}{\mathrm{dt}}$

I _L＝I _inv+I _C1

I _Z＝I _L+I _C2

L wherein ₁Be two-stage output filter first order inductance, L ₂It is second level inductance.Arrangement at last obtains the model of three-phase four-wire active filter:

$T_{\mathrm{on}}{U}_{\mathrm{DC}1}-T_{\mathrm{off}}{\mathrm{<figure-callout\; id="2"\; label="U\; DC"\; filenames="HDA0000154163810000041.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}}=U_s+L_1\frac{d(I_z-I_{C1}-I_{C2})}{\mathrm{dt}}+L_2\frac{d(I_z-I_{C1})}{\mathrm{dt}}$

In order to reduce inverter switching frequency, in a control cycle, the output voltage of inverter should positive level not occur simultaneously, and 0, the situation of negative level can suppose earlier that for this reason inverter only exports positive level and 0 level in following one-period, at this moment, T _Off=0, then:

$T_{\mathrm{on}}=(U_s+L_1\frac{d(I_z-I_{C1}-I_{C2})}{\mathrm{dt}}+L_2\frac{d(I_z-I_{C1})}{\mathrm{dt}})/U_{\mathrm{DC}1}$

In order to guarantee that current tracking that following one-period is injected into electrical network is to reference current I _Ref, that is:

I _Z＝I _ref

Simultaneously,, can suppose that electric current and the grid voltage change on the electric capacity of following one-period is little, and utilize difference form to represent differential, can get because output filter electric capacity mainly comprises the switching frequency harmonic wave:

$T_{\mathrm{on}}=(U_s+L_1\frac{(I_{\mathrm{ref}}-I_{C1}-I_{C2})-I_{\mathrm{inv}}}{T}+L_2\frac{(I_{\mathrm{ref}}-I_{C1})-I_L}{T})/U_{\mathrm{DC}1}$

Wherein, I _RefBe reference current signal, by the load harmonic wave, the active current of stable two capacitance voltages and the direct current of the control capacittance balance of voltage are formed.

If T _On＞0, represent then in the next control cycle that the output portion of time of inverter is at positive level, portion of time is 0;

If T _On=0, represent then in the next control cycle that the output of inverter is 0 entirely;

If T _On＜0, represent then in the next control cycle that some time of the output of inverter for this reason, makes the T in the filter model at negative level _On=0, keep T _Off, above again calculation procedure.

According to duty ratio, always have distribution method in 3, with T _On＞0 is example,

1) in the control cycle zero-time, exports T _OnThe positive level of time is exported T-T then _On0 level of time;

2) in the control cycle zero-time, export

0 level, export T then _OnPositive level, at last again output

0 level;

3) in the control cycle zero-time, export T-T _On0 level of time is exported T then _OnThe positive level of time.

In order to reduce switch harmonic, allocation strategy is: select suitable distribution method according to the on off state of last last moment in cycle, and the switch change least number of times that occurs in 2 control cycles before and after guaranteeing, that is:

1) if the last moment last one-period occurs is positive level, then selected distribution method 1);

2) if the last moment last one-period occurs is 0 level, then selected distribution method 3);

3) if the last moment last one-period occurs is negative level, then selected distribution method 2).

Beneficial effect:

Three-phase four-wire active filter switch signal estimation control method of the present invention; According to the single-phase state model of active filter, directly calculate following one-period should adopt great duty ratio in order to guarantee the current tracking current reference signal that injects electrical network, adopt the switch least number of times to change strategy then; Confirm the appearance order of positive level in next switch periods, 0 level and negative level; At last converter bridge switching parts is carried out make-break operation according to the control model of setting, not only improved the response speed of filter, having guaranteed simultaneously all has enough gains in utmost point wide frequency range; When the compensating three-phase unbalance harmonic current, performance is outstanding especially.

The invention has the beneficial effects as follows: 1) switching signal PREDICTIVE CONTROL of the present invention can be carried out in phase-splitting, ability compensating three-phase unbalance harmonic wave; 2) controlling object of the present invention is to inject the electric current of electrical network, rather than the inverter output current, has suppressed contingent resonance between two-stage output filter and the electrical network; 3) the present invention directly goes out the duty ratio of switching device in following one-period through the Active Power Filter-APF Model Calculation; At very wide frequency band range bigger gain all arranged; Improve the control precision of system, be directed to common band capacitance-resistance property rectifier bridge load, behind employing the present invention; THD (total harmonic distortion, i.e. power network current aberration rate) drops to below 4% by more than 50%; 4) prediction algorithm is simple, does not need just direct control inverter switch of complicated calculating, has improved system response time, and when harmonic load changed, 2 cycles of need just can reach new stable state; 5) switch periods is fixed, and is beneficial to the design output filter.

Description of drawings

Fig. 1 is three level three-phase four-line active power filter structure figure of the present invention;

Fig. 2 is that reference current signal according to the invention detects schematic diagram;

Fig. 3 is a PREDICTIVE CONTROL flow chart of the present invention;

Fig. 4 is the topology diagram of three-level inverters;

Fig. 5 is steady state effect figure; Wherein scheme a for using the present invention's current on line side before; Figure b is the current on line side behind employing the present invention;

Fig. 6 is a dynamic effect picture.Wherein scheme a for using the present invention's current on line side before; Figure b is the current on line side waveform behind employing the present invention.

Embodiment

Below will combine accompanying drawing and specific embodiment that the present invention is explained further details:

Embodiment 1:

Fig. 1 is three level three-phase four-line active power filter structure figure, by two electric capacity, and three-level inverters, two-stage LC output filter is formed.Its operation principle is, according to reference current signal I _Ref, calculate the control switch state of three-level inverters, make the electric current I of injecting electrical network _zCan follow the tracks of I _RefVariation, reach the purpose of harmonic.

Fig. 2 is reference current signal I _RefDetect schematic diagram, I _RefForm by 3 parts: load harmonic current, the direct current that is used for stablizing the active current of capacitance voltage and is used to keep two capacitance voltage balances.The load harmonic wave detects with instantaneous reactive power theory; Active current is with the voltage sum on two electric capacity, with reference value U _DCrefRelatively, carry out PI then and regulate, multiply by the sin ω t that changes synchronously with voltage at last and detect;

The parameter of the one PI control is: proportionality coefficient gets 0.01, and the parameter that integral coefficient is got 1, the two PI control is: proportionality coefficient gets 0.1, and integral coefficient gets 100.

Voltage difference about direct current is used on two electric capacity is carried out PI then and is regulated, and last mean allocation detects to three-phase.

Fig. 3 is the PREDICTIVE CONTROL flow chart.At first read inverter output voltage U _Inv, line voltage U _S, the electric current I on the output filter _Inv, I _L, I _C1, I _C2, inverter direct-flow side two capacitance voltage U _CD1, U _CD2And reference current signal I _RefThe present invention adopts phase-splitting control, if above-mentioned signal is (except U _CD1, U _CD2In addition) all be taken from the A phase, then control output needle for the A phase, if be taken from B mutually or the C phase, then control export also respective needle for B to or the C phase.

Calculate next switching time constantly then,

$T_{K+1}=(U_s+L_1\frac{I_{\mathrm{Ref}}-I_{\mathrm{Inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{Ref}}-I_L-I_{C1}}{T})/U_{\mathrm{DC}1},$ T gets 0.0001s in the reality.

If T _K+1＜0, then change a Model Calculation,

$T_{K+1}=-(U_s+L_1\frac{I_{\mathrm{ref}}-I_{\mathrm{inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{ref}}-I_L-I_{C1}}{T})/{\mathrm{<figure-callout\; id="2"\; label="U\; DC"\; filenames="HDA0000154163810000041.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}}$

The T that obtains _K+1Value representation following one-period, inverter need be exported the time of corresponding level:

T _K+1＞0, in the expression next cycle, answer control inverter output positive level T _K+1Time, export 0 level T-T _K+1Time;

If T _K+1=0, represent then in the next control cycle that the output of inverter is 0 entirely;

If T _K+1＜0, then represent in the next control cycle output negative level T of inverter _K+1Time, export 0 level T-T _K+1Time.

At last according to level allocation strategy control switch device break-make.

With the A among Fig. 4 is example mutually, at first detects the inverter output voltage U of A phase _{Inv_A}, line voltage U _{S_A}, the electric current I on the output filter _{Inv_A}, I _{L_A}, I _{C1_A}, I _{C2_A}, inverter direct-flow side two capacitance voltage U _CD1, U _CD2And reference current signal I _{Ref_A}If inverter switching frequency is 10kHz, then at next control cycle,

$T_{K+1}=(U_{S\_A}+L_1\frac{I_{\mathrm{ref}\_A}-I_{\mathrm{inv}\_A}-I_{C1\_A}-{\mathrm{<figure-callout\; id="2"\; label="I\; C"\; filenames="HDA0000154163810000041.png"\; state="\{\{state\}\}">I</figure-callout>}}_C}{{10}^{-4}}+L_2\frac{I_{\mathrm{ref}\_A}-I_{L\_A}-I_{C1\_A}}{{10}^{-4}})/U_{\mathrm{DC}1}$

Suppose through after calculating T _K+1＞0, and when last one finished constantly, A exported positive level mutually, then triggers VT1, VT2 conducting T _K+1Time, turn-off VT1 then and trigger VT2, VT3 conducting (0.0001-T _K+1) time.(change to VT2, VT3 conducting from VT1, VT2 conducting, can be so that the inverter output level change to 0 by Udc1, if VT3, VT4 conducting then are to be changed to-Udc2 by Udc1, change in voltage is big, can cause bigger du/dt).

Suppose through after calculating T _K+1=0, and last one when constantly finishing, and A item output positive level then turn-offs VT1, VT4, and triggers the time of VT2, VT3 conducting 0.0001s.

B is similar with C situation mutually mutually.

Change the calculating of next control cycle then over to.

DC side two electric capacity are value 1000 μ F respectively.First order LC filter power taking sense 1.8mH, electric capacity 5.2uF, second level LC filter power taking sense 0.5mH, electric capacity 2.2uF.

Fig. 5 is a static Simulation design sketch of the present invention, and when stable state, the power network current aberration rate drops to 3.84% from 57.02%.Fig. 6 is a dynamic simulation design sketch of the present invention, and during 0.3s, load current increases suddenly, and through about 2 cycles, when 0.34s, system reaches new stable state, and response speed is very fast.

Claims (3)

1. three-phase four-wire active filter switch signal estimation control method, described three-phase four-wire active filter is made up of two electric capacity, three-level inverters and two-stage LC output filter; Two electric capacity are the series arm that first electric capacity and second electric capacity are formed; The tie point of first electric capacity and second electric capacity connects the center line of three-phase and four-line electrical network; Two electric capacity are parallelly connected with three brachium pontis of three-level inverters, and the output of three-level inverters is connected with electrical network through two-stage LC output filter; Two-stage LC output filter is prime LC output filter and back level LC output filter;

It is characterized in that, A, B, C three-phase are adopted phase-splitting control, may further comprise the steps:

Step 1: acquired signal, and calculate reference current signal I _Ref:

The signal of being gathered comprises the output voltage U of three-level inverters _Inv, line voltage U _S, the electric current I in the prime output filter on the inductance _Inv, the electric current I in the prime output filter on the inductance _L, electric capacity output in the prime output filter electric current I _C1, electric capacity output in the back level output filter electric current I _C2, the first capacitance voltage U _CD1With the second capacitance voltage U _CD2

The computing formula of reference current signal is I _Ref=I _Pref* sin ω t+I _Dc-pref/ 3+I _h

Wherein:

I _hBe the load harmonic current, obtain through load current is carried out synchronous conversion; I _PrefBe U _CD1+ U _CD2-U _DCrefOutput variable behind a PI controller; U wherein _DCrefBe the capacitance voltage reference value;

ω is the line voltage fundamental frequency;

I _Dc-prefFor being used for stablizing the active current of capacitance voltage, I _Dc-prefBe U _CD1-U _CD2Output variable through the 2nd PI controller;

Step 2: T switching time that calculates next control cycle _K+1

$T_{K+1}=(U_s+L_1\frac{I_{\mathrm{Ref}}-I_{\mathrm{Inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{Ref}}-I_L-I_{C1}}{T})/U_{\mathrm{DC}1};$ Wherein T is a control cycle; L ₁, L ₂Be respectively the first order of filter, partial inductance value.

Judge T _K+1Whether＜0 set up, if set up, presses following formula and upgrade T _K+1, otherwise keep T _K+1Constant:

$T_{K+1}=-(U_s+L_1\frac{I_{\mathrm{ref}}-I_{\mathrm{inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{ref}}-I_L-I_{C1}}{T})/U_{\mathrm{DC}2};$

Step 3: according to T _K+1The switching device of the every phase in the control three-level inverters.

2. three-phase four-wire active filter switch signal estimation control method according to claim 1 is characterized in that, for the T that finally obtains _K+1If, T _K+1＞0, in the expression next cycle, answer control inverter output positive level T _K+1Time, export 0 level T-T _K+1Time;

If T _K+1=0, represent then in the next control cycle that the output of inverter is 0 entirely;

If T _K+1＜0, then represent in the next control cycle output negative level T of inverter _K+1Time, export 0 level T-T _K+1Time.

3. three-phase four-wire active filter switch signal estimation control method according to claim 1; It is characterized in that a PI controller parameter is: proportionality coefficient gets 0.01, and integral coefficient gets 1; The parameter of the 2nd PI control is: proportionality coefficient gets 0.1, and integral coefficient gets 100.

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