CN102638044B - 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 T<K+1> of the next time; T<K+1>=(Us+L1*(Iref-Iinv-Ic1-Ic2)/T +L2*(Iref-I<L>-Ic1)/T)/U<DC1>, or computing by the formula T<K+1>=-(Us+L1*(Iref-Iinv-Ic1-Ic2)/T +L2*(Iref-I<L>-Ic1)/T)/U<DC2>; and step 3: controlling a switching device of each phase in a three-level inverter bridge according to the T<K+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 Active Power Filter 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 subject to serious impact, particularly domestic electric appliance and is widely used the power supply of rectifier unsteady flow, and power distribution network has been brought to a large amount of harmonic pollutions, must be administered.The improvement of harmonic wave is mainly contained to passive filter, active filter and hybrid filter.Parallel passive filter is the simplest harmonic wave management method, but can only have good filter effect to specific subharmonic, and filtered band is very narrow.Passive filter is a kind of power electronic equipment, can compensate optional frequency and big or small harmonic wave, compensation characteristic is not subject to the impact of electric network impedance and frequency change, is a kind of desirable harmonic compensation device, but be limited to the impact of power electronic device capacity, be difficult to be applied directly in 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 is mainly used to improve 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 more to have superiority on cost, there is again better filtering performance simultaneously.

For power distribution network three-phase four-wire active power filter, due to the harmonic band very wide (General Requirements is from 2 subharmonic to 50 subharmonic) of needs improvement, must guarantee controller at wide frequency range have a larger gain, traditional PI controls and is difficult to meet.For this reason, 2 to 50 subharmonic must be detected respectively, then for the independent CONTROLLER DESIGN of every subharmonic, this makes controller will become very complicated, be difficult to the response speed of the system that guarantees, if also will carry out imbalance compensation, must control respectively by three-phase, more increase the weight of the burden of controller.

Summary of the invention

Technical problem to be solved by this invention is to provide 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, fast response time.

The technical solution of invention is as follows:

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 is the series arm of the first electric capacity and the second electric capacity composition; The tie point of the first electric capacity and the second electric capacity connects the center line of three-phase and four-line electrical network; Two electric capacity is in parallel 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 rear class LC output filter;

A, B, C three-phase are adopted to a point phase control, comprise the following steps:

Step 1: collection signal, and computing reference current signal I _ref:

The signal gathering comprises the output voltage U of three-level inverters _inv, line voltage U _s, the electric current I in prime output filter on inductance _inv, electric current I in prime output filter on inductance _l, electric capacity output in prime output filter electric current I _c1, electric capacity output in rear class 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 _hfor load harmonic current, obtain by load current being carried out to synchronous conversion; I _preffor U _cD1+ U _cD2-U _dCrefoutput variable after a PI controller; Wherein U _dCreffor capacitance voltage reference value [U _dCrefget a value between 700-800, can be set to 800V, be made as 700 also passablely, just affect the index of modulation]

ω is line voltage fundamental frequency;

I _dc-preffor the active current for stablizing capacitance voltage, I _dc-preffor U _cD1-U _cD2through the output variable of the 2nd PI controller;

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

$T_{K+1}=(U_s+L_1\frac{I_{\mathrm{ref}}-I_{\mathrm{inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{ref}}-I_L-I_{C1}}{T})/{\mathrm{<figure-callout\; id="1"\; label="U\; DC"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}};$ Wherein T is that [T gets 10 to control cycle ^-4, switching frequency is made as 10kHz]; L ₁, L ₂be respectively the first order of filter, the inductance value of the second level, [value 1.5mH respectively, 0.5fmH].

Judge T _k+1whether < 0 sets up, if set up, upgrades T by following formula _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+1control the switching device of the every phase in three-level inverters.

For the T finally obtaining _k+1if, T _k+1> 0, represents in next cycle, answers control inverter output positive level T _k+1time, output 0 level T-T _k+1time;

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

If T _k+1< 0, represents in next control cycle, the output negative level T of inverter _k+1time, output 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 a control cycle T, the three-level inverter output positive level time is T _on, the output negative level time is T _off, output 0 level time is T ₀(T ₀=T-T _on-T _off), duty ratio can be expressed as T ₀/ T.

, inverter output voltage is:

U _inv＝T _onU _DC1-T _offU _DC2

The state equation of considering output filter, has:

$U_{\mathrm{inv}}-U_S={\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">L</figure-callout>}}_1\frac{{\mathrm{dI}}_{\mathrm{inv}}}{\mathrm{dt}}+L_2\frac{{\mathrm{dI}}_L}{\mathrm{dt}}$

I _L＝I _inv+I _C1

I _Z＝I _L+I _C2

Wherein L ₁two-stage output filter first order inductance, L ₂it is second level inductance.Finally arrangement obtains the model of three-phase four-wire active filter:

$T_{\mathrm{on}}{U}_{\mathrm{DC}1}-T_{\mathrm{off}}{U}_{\mathrm{DC}2}=U_s+L_1\frac{d(I_z-I_{C1}-I_{C2})}{\mathrm{dt}}+L_2\frac{d(I_z-I_{C1})}{\mathrm{dt}}$

In order to reduce inverter switching frequency, in a control cycle, should not there is not positive level in the output voltage of inverter simultaneously, 0, and the situation of negative level can first suppose that inverter only exports positive level and 0 level in next cycle for this reason, now, T _off=0:

$T_{\mathrm{on}}=(U_s+L_1\frac{d(I_z-I_{C1}-I_{C2})}{\mathrm{dt}}+L_2\frac{d(I_z-I_{C1})}{\mathrm{dt}})/{\mathrm{<figure-callout\; id="1"\; label="U\; DC"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}}$

In order to guarantee that current tracking that next cycle is injected into electrical network is to reference current I _ref, that is:

I _Z＝I _ref

Meanwhile, because output filter electric capacity mainly comprises switching frequency harmonic wave, can suppose that electric current and the grid voltage change on next cycle electric capacity is little, and utilize difference form to represent differential, can obtain:

$T_{\mathrm{on}}=(U_s+L_1\frac{(I_{\mathrm{ref}}-I_{C1}-I_{C2})-I_{\mathrm{inv}}}{T}+L_2\frac{(I_{\mathrm{ref}}-I_{C1})-I_L}{T})/{\mathrm{<figure-callout\; id="1"\; label="U\; DC"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}}$

Wherein, I _refreference current signal, by load harmonic wave, stable two active currents of capacitance voltage and the direct current of control capacittance balance of voltage composition.

If T _on> 0, represents in next control cycle, the output portion of time of inverter is at positive level, and portion of time is 0;

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

If T _on< 0, represents in next control cycle, and some time of the output of inverter, at negative level, for this reason, makes the T in filter model _on=0, retain T _off, above calculation procedure again.

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

1) in control cycle initial time, export T _onthe positive level of time, then exports T-T _on0 level of time;

2) in control cycle initial time, export

0 level, then export T _onpositive level, finally export again

0 level;

3) in control cycle initial time, export T-T _on0 level of time, then exports T _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 occurring in 2 control cycles before and after guaranteeing, that is:

1) if upper one the last moment in cycle occur be positive level, select distribution method 1);

2) if upper one the last moment in cycle occur be 0 level, select distribution method 3);

3) if upper one the last moment in cycle occur be negative level, select 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 calculating next cycle should adopt great duty ratio in order to guarantee the current tracking current reference signal that injects electrical network, then adopt the minimum variation strategy of on-off times, determine positive level in next switch periods, the appearance order of 0 level and negative level, finally converter bridge switching parts is carried out to make-break operation according to the control model of setting, not only improve the response speed of filter, guaranteed has enough gains simultaneously in utmost point wide frequency range, especially in the time of compensating three-phase unbalance harmonic current, performance is outstanding.

The invention has the beneficial effects as follows: 1) switching signal PREDICTIVE CONTROL of the present invention can be carried out in phase-splitting energy compensating three-phase unbalance harmonic wave; 2) control object of the present invention is to inject the electric current of electrical network, rather than inverter output current, has suppressed contingent resonance between two-stage output filter and electrical network; 3) the present invention directly calculates the duty ratio of switching device in next cycle by Active Power Filter-APF model, at very wide frequency band range have a larger gain, improve the control precision of system, be directed to common band capacitance-resistance rectifier bridge load, adopt after 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, in the time that harmonic load changes, only needs 2 cycles just can reach new stable state; 5) switch periods is fixed, and is beneficial to design output filter.

Accompanying drawing explanation

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 of the present invention detects schematic diagram;

Fig. 3 is 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 scheming a is application the present invention current on line side before; Figure b is the current on line side adopting after the present invention;

Fig. 6 is dynamic effect picture.Wherein scheming a is application the present invention current on line side before; Figure b is the current on line side waveform adopting after the present invention.

Embodiment

Below with reference to the drawings and specific embodiments, the present invention is described in 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 composition.Its operation principle is, according to reference current signal I _ref, calculate the control switch state of three-level inverters, make to inject the electric current I of electrical network _zcan follow the tracks of I _refvariation, reach the object of harmonic.

Fig. 2 is reference current signal I _refdetect schematic diagram, I _refformed by 3 parts: load harmonic current, for stablizing the active current of capacitance voltage, and for maintaining the direct current of two capacitance voltage balances.Load harmonic wave detects with instantaneous reactive power theory; Voltage sum on two electric capacity for active current, with reference value U _dCrefrelatively, then carry out PI adjusting, be finally multiplied by and synchronize the sin ω t of variation with voltage and detect;

The parameter that the one PI controls 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 on upper and lower two electric capacity for direct current, then carries out PI adjusting, and last mean allocation detects to three-phase.

Fig. 3 is PREDICTIVE CONTROL flow chart.First read inverter output voltage U _inv, line voltage U _s, the electric current I on output filter _inv, I _l, I _c1, I _c2, inverter direct-flow side two capacitance voltage U _cD1, U _cD2, and reference current signal I _ref.The present invention adopts a point phase control, if above-mentioned signal is (except U _cD1, U _cD2in addition) be all taken from A phase, control output needle for A phase, if be taken from B phase or C phase, control export also respective needle for B to or C phase.

Then calculate the switching time in next moment,

$T_{K+1}=(U_s+L_1\frac{I_{\mathrm{ref}}-I_{\mathrm{inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{ref}}-I_L-I_{C1}}{T})/{\mathrm{<figure-callout\; id="1"\; label="U\; DC"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}},$ In reality, T gets 0.0001s.

If T _k+1< 0, changes a model and calculates,

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

The T obtaining _k+1in next cycle of value representation, inverter need to be exported the time of corresponding level:

T _k+1> 0, represents in next cycle, answers control inverter output positive level T _k+1time, output 0 level T-T _k+1time;

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

If T _k+1< 0, represents in next control cycle, the output negative level T of inverter _k+1time, output 0 level T-T _k+1time.

Finally according to Signal level assignment policy control switching device break-make.

Mutually as example, first detect the inverter output voltage U of A phase take the A in Fig. 4 _{inv_A}, line voltage U _{s_A}, the electric current I on output filter _{inv_A}, I _{l_A}, I _{c1_A}, I _{c2_A}, inverter direct-flow side two capacitance voltage U _cD1, U _cD2, and reference current signal I _{ref_A}.If inverter switching frequency is 10kHz, at next control cycle,

$T_{K+1}=(U_{S\_A}+L_1\frac{I_{\mathrm{ref}\_A}-I_{\mathrm{inv}\_A}-{\mathrm{<figure-callout\; id="1"\; label="I\; C"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_C-I_{C2\_A}}{{10}^{-4}}+L_2\frac{I_{\mathrm{ref}\_A}-I_{L\_A}-{\mathrm{<figure-callout\; id="1"\; label="I\; C"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">I</figure-callout>}}_C}{{10}^{-4}})/{\mathrm{<figure-callout\; id="1"\; label="U\; DC"\; filenames="HDA0000154163810000021.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{DC}}$

Suppose by after calculating T _k+1> 0, and when a upper moment finishes, A exports positive level mutually, triggers VT1, VT2 conducting T _k+1time, then turn-off VT1 and trigger VT2, VT3 conducting (0.0001-T _k+1) time.(change to VT2, VT3 conducting from VT1, VT2 conducting, can make inverter output level change to 0 by Udc1, if VT3, VT4 conducting are that change in voltage is large by change to-Udc2 of Udc1, can cause larger du/dt).

Suppose by after calculating T _k+1=0, and upper moment when finishing, A item output positive level, turn-offs VT1, VT4, and triggers the time of VT2, VT3 conducting 0.0001s.

The situation of B phase and C phase is similar.

Then proceed to the calculating of next control cycle.

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

Claims (3)

1. a 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 is the series arm of the first electric capacity and the second electric capacity composition; The tie point of the first electric capacity and the second electric capacity connects the center line of three-phase and four-line electrical network; Two electric capacity is in parallel 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 rear class LC output filter;

It is characterized in that, A, B, C three-phase are adopted to a point phase control, comprise the following steps:

Step 1: collection signal, and computing reference current signal I _ref:

The signal gathering comprises the output voltage U of three-level inverters _inv, line voltage U _s, the electric current I in prime LC output filter on inductance _inv, electric current I in rear class LC output filter on inductance _l, electric capacity output in prime LC output filter electric current I _c1, electric capacity output in rear class LC 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 _hfor load harmonic current, obtain by load current being carried out to synchronous conversion; I _preffor U _cD1+ U _cD2-U _dCrefoutput variable after a PI controller; Wherein U _dCreffor capacitance voltage reference value;

ω is line voltage fundamental frequency;

I _dc-preffor the active current for stablizing capacitance voltage, I _dc-preffor U _cD1-U _cD2through the output variable of the 2nd PI controller;

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

$T_{K+1}=(U_s+L_1\frac{I_{\mathrm{ref}}-I_{\mathrm{inv}}-I_{C1}-I_{C2}}{T}+L_2\frac{I_{\mathrm{ref}}-I_L-I_{C1}}{T})/U_{\mathrm{CD}1};$ Wherein T is control cycle; L ₁, L ₂be respectively the prime of filter, the inductance value of rear class;

Judge T _k+1whether <0 sets up, if set up, upgrades T by following formula _k+1, otherwise keep T _k+1constant:

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

Step 3: according to T _k+1control the switching device of the every phase in 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 finally obtaining _k+1if, T _k+1>0, represents in next cycle, answers control inverter output positive level T _k+1time, output 0 level T-T _k+1time;

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

If T _k+1<0, represents in next control cycle, the output negative level T of inverter _k+1time, output 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 that the 2nd PI controls is: proportionality coefficient gets 0.1, and integral coefficient gets 100.

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