CN103414193B - 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 global sliding mode variable structure control method for Active Power Filter-APF

Technical field

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

Background technology

Along with the extensive use of power electronic equipment, the harmonic and reactive currents that all kinds of nonlinear load produces causes electrical network and has a strong impact on.Active Power Filter-APF is widely studied and applied as a kind of effective measures of harmonic inhabitation.The principle of Shunt makes current transformer produce real-time tracking instruction current i _c ^*offset current i _c, both equal and opposite in directions, direction is contrary, thus makes grid side current i _sin not containing harmonic wave and idle composition.

The control method of common current tracking has Hysteresis control, triangular carrier control etc.Hysteresis control has flexibly, response fast, precision comparatively advantages of higher, but it is higher for the requirement of switching frequency, and switching frequency is not fixed.The feature of triangular carrier control is that switching frequency is fixed, circuit realiration simple, but when triangular carrier is applied in the high fdrequency component in instruction current, control performance declines to some extent.In addition, also have the methods such as Cycle Control, track with zero error, Frequency conversion control, but be not all used widely.

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

Based on this, global sliding mode variable-structure control technology is applied in parallel connection type active electric filter by the present invention, realizes the tracing control to three-phase current.

Summary of the invention

Common some curren tracing control methods of parallel connection type active electric filter (APF) have corresponding speed slow, be subject to the shortcoming such as inherent parameters and external interference impact.The present invention is directed to the weak point existing for above-mentioned prior art, propose a kind of Control Method of Active Power Filter based on global sliding mode variable-structure control, be applied to Active Power Filter-APF, to improve dynamic performance and robustness.

Concrete technical scheme is as follows:

For a global sliding mode variable structure control method for Active Power Filter-APF, comprise the steps:

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

(2) global sliding mode variable-structure controller is designed, on the sliding-mode surface movement locus of state point initially being dropped on design, comprising the design of global sliding mode structure changes tangential-hoop method and the design of global sliding-mode variable structure regulator rule, the design of control law is stably remained on sliding mode system mode; When sliding-mode surface value is 0, represent that tracking error is 0, three-phase offset current is followed the tracks of by entirely accurate;

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

The sliding formwork function of described step (2) global sliding mode variable-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 sliding formwork function, effectively can shorten the time that state point arrives sliding formwork state, here, S (x, t) is sliding formwork switching function; C is sliding mode parameter; E (t) is exponential function; X is state variable.

In order to eliminate high frequency chatter in described step (2), adopting following formula to disappear and quivering:

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

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

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

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

1) the conventional current tracking and controlling method of Active Power Filter-APF is changed, propose global sliding mode variable structure control method, current deviation is made to be state variable, controlled device effect remains at sliding-mode surface and slides, current tracking and APF inherent parameters are changed and external interference has nothing to do, 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, introduce omnidistance sliding mode factor W (t) of a time to time change, thus make sliding-mode surface S be not only the explicit function of state variable, also be the explicit function of time variable, namely become when sliding-mode surface is, achieve global sliding mode, avoid the characteristic of permanent Sliding Mode Variable Structure System in the arrival stage to disturbance sensitivity;

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

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

Accompanying drawing explanation

Fig. 1 is the general frame of APF Systematical control.

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 the design of global sliding mode variable-structure controller.

Embodiment

Be described in further detail APF current tracking below in conjunction with accompanying drawing, this embodiment only for explaining the present invention, does not form limiting the scope of the present invention.

The present invention is based on global sliding mode variable structure control theory, compared with other curren tracing control methods, 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, system mode remains on sliding-mode surface by the control law of the method design, eliminate the arrival stage, and variable factor item during by introducing relevant with state in variable-structure control rule, improve the mapping of system, overcome the impact of unknown parameter perturbation, thus greatly strengthen the robustness of system.Software link is realized by TMS320F2812 chip.

Specific implementation comprises the following steps:

1) state-space model being 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 three-phase offset current; d ₁, d ₂, d ₃be the on off state of three brachium pontis, d=1 represents pipe conducting on brachium pontis, the shutoff of lower pipe, and d=0 represents that on brachium pontis, pipe turns off, 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] ^t; U=[d ₁, d ₂, d ₃] ^t; G=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 omnidistance sliding mode factor W (t) simultaneously, construct sliding-mode surface accordingly 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 sliding mode parameter matrix.

3) as S=0, tracking error is 0, i _ca ^*, i _cb ^*and i _cc ^*followed the tracks of by entirely accurate, definition control law u _a, u _band u _cfor:

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

In formula, g (t) is the variable-structure control coefficient that need design, g (t)=(1-a ₄) ^-1[a ₁‖ x ‖+a ₂+ a ₃exp (-β _mint)]+ε, sgn (S) are the sign function of [-1,1].

4) judge the controlling party of control law 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 high frequency chatter, adopting the method for quivering that disappears, replacing the sgn (S) in variable-structure control rule with following formula

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

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

6) pwm signal obtaining 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, eliminate the convergence stage of conventional slip mode, effectively can shorten the time that system arrives sliding mode, avoid permanent sliding state variable structure control system and can reach the sensitivity of stage to disturbance.Because system mode is on designed switching surface at the very start, therefore the design objective of control law is reliably remained on sliding mode system mode.The design of this control law effectively can improve the mapping of system, overcome the impact of unknown parameter perturbation; When there is Parameter Perturbation in APF system, because global sliding mode variable structure control method is to Parameter Perturbation and the feature such as external disturbance is insensitive, now the compensation performance of APF system can not be affected, and greatly strengthen the robustness of system;

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

Control system mainly completes following functions:

1) i is adopted _p-i _qharmonic current detecting method, is utilized TMS320F2812 software programming to calculate harmonic and reactive currents command value, result of calculation is sent by data/address bus, and utilizes DA conversion chip to be analog signal by reference current digital signal transition;

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

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

As shown in Figure 3, first ADC_ISR entrance is entered, read 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 there are 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, thus obtain pwm signal.

As shown in Figure 4, the error component △ i under rectangular coordinate system is utilized in the design of global sliding mode variable-structure controller _ca, △ i _cb, △ i _ccstructure 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 ^*, finally, the pwm signal of tectonic forcing switching tube.

Claims (3)

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

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

(2) global sliding mode variable-structure controller is designed, on the sliding-mode surface movement locus of state point initially being dropped on design, comprising the design of global sliding mode structure changes tangential-hoop method and the design of global sliding-mode variable structure regulator rule, the design of control law is stably remained on sliding mode system mode; The sliding formwork function of described global sliding mode variable-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) be sliding formwork switching function, C is sliding mode parameter, E (t) is exponential function, x is state variable, x (0) represents the value at state variable x corresponding to t=0 moment, the deviation namely between three-phase offset current and offset current command signal; When sliding-mode surface value is 0, represent that tracking error is 0, three-phase offset current is followed the tracks of by entirely accurate;

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

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

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

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

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