CN103414193A - Global sliding mode variable structure control method applied to active power filter - Google Patents

Abstract

The invention discloses a three-phase active power filter controller based on global sliding mode variable structure control. Firstly, a three-phase parallel-connection active power filter main circuit model is established under a rectangular coordinate system to obtain a math model with three-phase current as a state variable; then, the three-phase current is tracked and compensated by constructing a global sliding mode face to define a corresponding control law, a system motion curve always keeps on the switch hyperplane, a reaching stage is removed, and a time variant factor item related to the state is introduced into the control law to improve transient performance of a system, eliminate effects of unknown parameter perturbation and enhance the robustness of the system; finally, a switch state function is constructed to obtain PWM signals for driving a switch tube. The three-phase active power filter controller uses a global sliding mode variable structure control method, so that the three-phase active power filter controller is simple in design, easy to achieve and good in robustness on the internal parameter perturbation and external interference of the system.

Description

A kind of variable structure control method of global sliding mode for Active Power Filter-APF

Technical field

The present invention relates to the control method of Active Power Filter-APF (APF), specifically adopt the global sliding mode variable structure control method to control the current tracking of Active Power Filter-APF, belong to quality of power supply technical field.

Background technology

Along with the extensive use of power electronic equipment, harmonic wave and reactive current that all kinds of nonlinear loads produce have caused and have had a strong impact on electrical network.Active Power Filter-APF is widely studied and applied as a kind of effective measures that suppress harmonic wave.The principle of Shunt is to make current transformer produce real-time tracking instruction current i _c ^*Offset current i _c, both equal and opposite in directions, opposite direction, thus make the grid side current i _sIn do not contain harmonic wave and idle composition.

The control method of common current tracking has stagnant ring control, triangular carrier control etc.Stagnant ring control has flexibly, response is fast, precision is than advantages of higher, but it is for the having relatively high expectations of switching frequency, and switching frequency is fixing.The characteristics that triangular carrier is controlled are that switching frequency is fixed, circuit is realized simply, but triangular carrier is while being applied in the high fdrequency component in instruction current, and control performance descends to some extent.In addition, also have the methods such as Cycle Control, dead beat control, space vector control, but all be not used widely.

At present; there is reported in literature to study the permanent Sliding mode variable structure control of Active Power Filter-APF; Active Power Filter-APF is being set up on the basis of Mathematical Modeling, drawn the general control rule of Sliding mode variable structure control, thereby make system have insensibility to variation and the external disturbance of parameter.In addition, response is quick, dynamic quality is also well the outstanding advantages that permanent sliding formwork is controlled.But, system only just has robustness and parameter insensibility in sliding phase, therefore there is reported in literature to become structure control to global sliding mode and study in aero-engine system and PMSM Speed, and there is not yet reported in literature in Active Power Filter-APF.The advantage that this control method is the most outstanding is to make the movement locus of system drop at the very start on sliding-mode surface; shortening system effectively enters the time of sliding formwork motion state; avoided permanent Sliding Mode Variable Structure System in the arrival stage characteristic sensitive to disturbance, and the design of its control rate can improve system mapping, overcome the impact of unknown parameter perturbation.

Based on this, the present invention becomes the structure control technology by global sliding mode and is applied in parallel connection type active electric filter, realizes the tracking of three-phase current is controlled.

Summary of the invention

Some common curren tracing control methods of parallel connection type active electric filter (APF) have corresponding speed slow, be subject to the shortcomings such as self parameter and external interference impact.The present invention is directed to the existing weak point of above-mentioned prior art, proposed a kind of Control Method of Active Power Filter that becomes structure control based on global sliding mode, be applied to Active Power Filter-APF, to improve dynamic performance and robustness.

Concrete technical scheme is as follows:

A kind of variable structure control method of global sliding mode for Active Power Filter-APF, comprise the steps:

(1), by being based upon the space mathematical model of Shunt under rectangular coordinate system, obtain take the Mathematical Modeling of three-phase offset current as state variable;

(2) the design global sliding mode becomes structure controller, make the movement locus of state point just drop at the beginning on the sliding-mode surface designed, comprising global sliding mode, become the design of structure switching hyperplane and the design that Global Sliding Mode becomes the structure control rule, the design of control law is stably to remain on system mode on sliding mode; When the sliding-mode surface value is 0, mean that tracking error is 0, the three-phase offset current is followed the tracks of by entirely accurate;

(3) by the structure switch function, obtain the pwm signal of driving switch pipe, make offset current trace command electric current rapidly, make power network current be compensated for as stable equilibrium's sinusoidal current.

The sliding formwork function that described step (2) global sliding mode becomes structure controller is S (x, t)=Cx-CE (t) x (0), wherein defining the omnidistance sliding mode factor is W (t)=CE (t) x (0), this is a time dependent amount, this amount occurs in the sliding formwork function, can effectively shorten the time that state point arrives the sliding formwork state, here, S (x, t) is the sliding formwork switching function; C is the sliding mode parameter; E (t) is exponential function; X is state variable.

In described step (2), in order to eliminate the high frequency chatter, adopt following formula to disappear and quiver:

$M_i\left(S\right)=\frac{s_i}{\left|\right|S_i\left|\right|+{\mathrm{\δ}}_i},i=\mathrm{1,2},\·\·\·,m$

Wherein, M _i(S) be in sliding mode control law one; δ _iBe a little normal number, get 0.1, S _iMean the sliding formwork function; ‖ S _i‖ for matrix for inducing norm; M is the dimension of control law, and value is 3 here.

Control algolithm of the present invention adopts the TMS320F2812 chip to realize.

Compared with the prior art, beneficial effect of the present invention is embodied in:

1) changed the conventional current tracking and controlling method of Active Power Filter-APF, the global sliding mode variable structure control method has been proposed, making current deviation is state variable, controlled device effect remains at sliding-mode surface and slides, make the variation of current tracking and APF self parameter and external interference irrelevant, directly meet the consistency requirement of APF;

2) the global sliding mode face of the present invention's design is compared with traditional sliding-mode surface, introduced the omnidistance sliding mode factor W (t) of a time to time change, thereby making sliding-mode surface S is not only the explicit function of state variable, it is also the explicit function of time variable, be that sliding-mode surface becomes while being, realized global sliding mode, avoided permanent Sliding Mode Variable Structure System in the arrival stage characteristic to the disturbance sensitivity;

3) design of control law of the present invention can improve systematic function, overcome unknown parameter perturbation impact, strengthened system robustness.

4) the present invention adopts the method for quivering of rationally disappearing to eliminate the high frequency chatter.

The accompanying drawing explanation

Fig. 1 is the general frame that the APF system is controlled.

Fig. 2 is software main program flow chart of the present invention.

Fig. 3 is ADC interruption subroutine flow chart of the present invention.

Fig. 4 is that global sliding mode becomes the structure controller design.

Embodiment

Below in conjunction with accompanying drawing, the APF current tracking is described in further detail, this embodiment only, be used to explaining the present invention, does not form the restriction to protection range of the present invention.

Global sliding mode is take in the present invention, and to become the structure control theory be basis, with other curren tracing control methods, compare, the method is except having the rapidity of permanent sliding-mode control, good stability and to Parameter Perturbation and the advantage such as external disturbance is insensitive, especially outstanding is, the control law of the method design remains at system mode on sliding-mode surface, eliminated the arrival stage, and by becoming the structure control rule, introducing variable factor item when relevant with state, improved the mapping of system, overcome the impact of unknown parameter perturbation, thereby greatly strengthened the robustness of system.The software link is realized by the TMS320F2812 chip.

Specific implementation comprises the following steps:

1) state-space model that is based upon the Shunt under ' abc ' coordinate system is:

$\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_{\mathrm{ca}}\\ i_{\mathrm{cb}}\\ i_{\mathrm{cc}}\end{array}\right]=\left[\begin{array}{ccc}-\frac{R_c}{L_c}& 0& 0\\ 0& -\frac{R_c}{L_c}& 0\\ 0& 0& -\frac{R_c}{L_c}\end{array}\right]\left[\begin{array}{c}{i}_{\mathrm{ca}}\\ i_{\mathrm{cb}}\\ i_{\mathrm{cc}}\end{array}\right]+\frac{u_{\mathrm{dc}}}{3L_c}\left[\begin{array}{ccc}-2& 1& 1\\ 1& -2& 1\\ 1& 1& -2\end{array}\right]\left[\begin{array}{c}{d}_1\\ d_2\\ d_3\end{array}\right]+\frac{1}{L_c}\left[\begin{array}{c}{u}_{\mathrm{sa}}\\ u_{\mathrm{sb}}\\ u_{\mathrm{sc}}\end{array}\right]---\left(1\right)$

In formula: i _Ca, i _Cb, i _CcFor the three-phase offset current; d ₁, d ₂, d ₃Be the on off state of three brachium pontis, d=1 means on brachium pontis to manage conducting, lower pipe turn-offs, and d=0 means on brachium pontis that pipe turn-offs, lower pipe conducting; u _Sa, u _Sb, u _ScFor supply voltage; u _DcFor DC voltage; R _c, L _cFor main circuit input resistance and inductance.

Being write as matrix form is:

$\stackrel{\·}{i}=\mathrm{Ai}+\mathrm{Bu}+G---\left(2\right)$

In formula: i=[i _Ca, i _Cb, i _Cc] ^TU=[d ₁, d ₂, d ₃] ^TG=1/L _c[u _Sa, u _Sb, u _Sc] ^T

$A=-\frac{R_c}{L_c}\left[\begin{array}{ccc}1& 0& 0\\ 0& 1& 0\\ 0& 0& 1\end{array}\right];$ $B=\frac{u_{\mathrm{dc}}}{3L_c}\left[\begin{array}{ccc}-2& 1& 1\\ 1& -2& 1\\ 1& 1& -2\end{array}\right]---\left(3\right)$

2) by error i _Ca-i _Ca ^*, i _Cb-i _Cb ^*And i _Cc-i _Cc ^*As the input state variable of sliding mode controller, determine simultaneously omnidistance sliding mode factor W (t), construct accordingly sliding-mode surface to three-phase current i _Ca, i _CbAnd i _CcControl, obtain sliding-mode surface S _a, S _bAnd S _cFor:

$S=\left[\begin{array}{c}{S}_a\\ S_b\\ S_c\end{array}\right]=\mathrm{Cx}-\mathrm{CE}\left(t\right)x\left(0\right)---\left(4\right)$

X=[i in formula _Ca-i _Ca ^*, i _Cb-i _Cb ^*, i _Cc-i _Cc ^*] ^T, C=[C ₁, C ₂] ^TFor the sliding mode parameter matrix.

3) when S=0, tracking error is 0, i _Ca ^*, i _Cb ^*And i _Cc ^*By entirely accurate, followed the tracks of definition control law u _a, u _bAnd u _cFor:

$U=\left[\begin{array}{c}{u}_a\\ u_b\\ u_c\end{array}\right]=-g\left(t\right){\left(\mathrm{CB}\right)}^{-1}\mathrm{sgn}\left(S\right)---\left(5\right)$

G in formula (t) is for needing the change structure control coefficient of design, g (t)=(1-a ₄) ^-1[a ₁‖ x ‖+a ₂+ a ₃Exp (β _minT)]+ε, sgn (S) is the sign function of [1,1].

4) judgement control law controlling party to, obtain u _a ^*, u _b ^*And u _c ^*For:

$u_a^{*}=\mathrm{ksgn}\left(u_a\right)$

$u_b^{*}=\mathrm{ksgn}\left(u_b\right)---\left(6\right)$

$u_c^{*}=\mathrm{ksgn}\left(u_c\right)$

K=2.9 in formula.

5) in order to eliminate the high frequency chatter, adopt the method for quivering that disappears, with following formula, replace becoming the sgn (S) in the structure control rule

$M_i\left(S\right)=\frac{s_i}{\left|\right|s_i\left|\right|+{\mathrm{\δ}}_i},i=\mathrm{1,2},\·\·\·,m---\left(7\right)$

δ in formula _i(i=a, b, c) is a little normal number, gets 0.1.

6) pwm signal of acquisition driving switch pipe is:

$d_{s1}=0.5(1+u_a^{*}/k_0),$ d _s4=1-d _s1

$d_{s3}=0.5(1+u_b^{*}/k_0),$ d _s6=1-d _s3 （8）

$d_{s5}=0.5(1+u_c^{*}/k_0),$ d _s2=1-d _s5

K in formula ₀=2.47.

By design, in the convergence stage of having eliminated traditional sliding mode, shortening system effectively arrives the time of sliding mode, has avoided permanent sliding state variable structure control system can reach the sensitivity of stage to disturbance.Because system mode is on designed switching surface at the very start, so the design objective of control law is that system mode is remained on sliding mode reliably.The design of this control law can effectively improve system mapping, overcome the impact of unknown parameter perturbation; When in the APF system, having Parameter Perturbation, to Parameter Perturbation and the characteristics such as external disturbance is insensitive, now the compensation performance of APF system can not be affected, and has greatly strengthened the robustness of system due to the global sliding mode variable structure control method;

As shown in Figure 1, the full-controlled rectifier bridge is adopted in load, the DC side of rectifier is the resistance sense load, harmonic current detection circuit is that the effect of instruction current computing circuit is to calculate the offset current command signal, the current tracking control circuit adopts the global sliding mode variable structure control method, guarantees that offset current tracking harmonic wave command signal changes.Active Power Filter-APF adopts the full-digital control conceptual design, the TI company's T MS320F2812DSP chip of take is core, be aided with corresponding external sampling modulate circuit, three-phase inverter and drive circuit etc., realize collection, the conditioning of current signal, harmonic wave and reactive current are calculated, the functions such as current tracking control.

Control system mainly completes following functions:

1) adopt i _p-i _qHarmonic current detecting method, utilize the TMS320F2812 software programming to calculate harmonic wave and referenced reactive current value, by data/address bus, result of calculation sent, and utilized the DA conversion chip that the reference current digital signal transition is to analog signal;

2) according to the difference design global sliding mode controller of instruction current and actual offset current, produce basic pwm signal, and this pwm signal is produced to the control signal of control switch break-make through overdrive circuit, thereby realize current tracking control.

As shown in Figure 2, at first main program starts, close all external interrupt, system peripheral and variable are carried out to initialization, and enable external interrupt EXINT1, open global interrupt, wait for and interrupting, the definition of the main completion system control module of Control System Software, peripheral module initialization and some global variables in the present invention.

As shown in Figure 3, at first enter the ADC_ISR entrance, read the ADCRESULT value and be converted to actual current value, the analog-to-digital conversion module of TMS320F2812 is with 12 bit pads of a built-in sampling and maintenance, and have 16 analog-converted passages, system signal accesses the analog input channel of ADC after signal conditioner, after completing analog-to-digital conversion, and access ADC memory register.Then call successively and calculate harmonic wave instruction current subprogram and Sliding mode variable structure control subprogram, thereby obtain pwm signal.

As shown in Figure 4, in the design of global sliding mode change structure controller, utilize the error component △ i under rectangular coordinate system _Ca, △ i _Cb, △ i _CcThe structure sliding-mode surface, definition control law u _a, u _b, u _c, then obtain new control law u through symbol decision _a ^*, u _b ^*, u _c ^*, last, the pwm signal of tectonic forcing switching tube.

Claims (4)

1. the variable structure control method of the global sliding mode for Active Power Filter-APF, is characterized in that, comprises the steps:

(1), by being based upon the space mathematical model of Shunt under rectangular coordinate system, obtain take the Mathematical Modeling of three-phase offset current as state variable;

(2) the design global sliding mode becomes structure controller, make the movement locus of state point just drop at the beginning on the sliding-mode surface designed, comprising global sliding mode, become the design of structure switching hyperplane and the design that Global Sliding Mode becomes the structure control rule, the design of control law is stably to remain on system mode on sliding mode; When the sliding-mode surface value is 0, mean that tracking error is 0, the three-phase offset current is followed the tracks of by entirely accurate;

(3) by the structure switch function, obtain the pwm signal of driving switch pipe, make offset current trace command electric current rapidly, make power network current be compensated for as stable equilibrium's sinusoidal current.

2. a kind of variable structure control method of global sliding mode for Active Power Filter-APF according to claim 1, it is characterized in that, the sliding formwork function that described step (2) global sliding mode becomes structure controller is S (x, t)=Cx-CE (t) x (0), wherein defining the omnidistance sliding mode factor is W (t)=CE (t) x (0), here, S (x, t) is the sliding formwork switching function; C is the sliding mode parameter; E (t) is exponential function; X is state variable.

3. a kind of variable structure control method of global sliding mode for Active Power Filter-APF according to claim 1 and 2, is characterized in that, in order to eliminate the high frequency chatter, adopts following formula to disappear and quiver in described step (2):

$M_i\left(S\right)=\frac{s_i}{\left|\right|s_i\left|\right|+{\mathrm{\δ}}_i},i=\mathrm{1,2},\·\·\·,m$

Wherein, M _i(S) be in sliding mode control law; δ _iBe a little normal number, get 0.1; S _iMean the sliding formwork function; ‖ S _i‖ for matrix for inducing norm; M is the dimension of control law, m=3.

4. a kind of variable structure control method of global sliding mode for Active Power Filter-APF according to claim 1, is characterized in that, described control method adopts the TMS320F2812 chip to realize.

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