CN104092378A - Control method of robust high order sliding mode for Flyback convertor - Google Patents

Abstract

The invention provides a control method of a robust high order sliding mode for a Flyback convertor. Output voltage of a Flyback power supply convertor is subjected to digital sampling; an output voltage sampling value and a corresponding target value are calculated to obtain a sliding mode variable; converter control input is subjected to Super-Twisting sliding mode control; and on-and-off of a power converter switch tube is controlled according to the converter control input, so that a sliding mode track of the output voltage is restrained in the sliding mode variable, and finally, the output voltage tracks the target value always. The control method of the robust high order sliding mode for the Flyback convertor is free from the influence of input and output disturbance, the control accuracy is high, the dynamic response is rapid, and the control method is particularly suitable for new energy power generation.

Description

Robust High-Order Sliding Mode control method for a kind of Flyback converter

Technical field

The present invention relates to a kind of robust control method of converter.

Background technology

Day by day under deficient background, taking wind, light, hydrogen as the new forms of energy of representative are developing just at a terrific speed, become the focus of research field in fossil energy.And in the grid-connected power generation system of input, exist the features such as unpredictability, intermittence and discrete type using solar energy, wind energy etc. as energy, and this output to supply convertor makes a big impact, and output accuracy and stability are difficult to reach requirement.Therefore, exist under disturbance and condition of uncertainty, designing a kind of robust controller is a task very with realistic meaning.Sliding formwork control is simple in structure with it, to inner parameter and external disturbance all insensitive strong robustness be widely applied.But traditional sliding formwork control is because the discrete type of self control law exists the problem of inevitably shivering, will there is the higher-order of oscillation in controlled system, affected the effect of sliding formwork control, even damage control system when serious.Specifically; the control of tradition sliding formwork is used analog control circuit more; circuit parameter regulates very difficult; and application is the control of low order sliding formwork; there is the problem of shivering in system output; under the condition of large input disturbance or output disturbance, often there will be the problem of output voltage distortion, this has all obtained checking in various experimental studies.When serious, output voltage distortion can be damaged electrical device, even makes whole system quit work, and causes larger economic loss.

Summary of the invention

In order to overcome the deficiencies in the prior art, the present invention is based on the experimental study of Super-Twisting control algolithm in intermittent power supply, for the intermittent perturbed problem existing in generation of electricity by new energy, design a kind of Flyback converter robust High-Order Sliding Mode control method, the impact of the large disturbance that can solve energy input in generation of electricity by new energy on power converter, realizes the level and smooth output of power.

The technical solution adopted for the present invention to solve the technical problems comprises the following steps:

Step 1, Flyback converter modeling: at one-period T _sthe direct current mean value of middle output voltage wherein, n is the turn ratio of converter, and D is convertor controls input duty cycle, and U1 is input voltage; With inductive current i _lwith capacitance voltage V _cfor state variable, the state space equation that obtains Flyback converter is:

$\left[\begin{array}{c}\frac{{\mathrm{di}}_L}{\mathrm{dt}}\\ \frac{{\mathrm{dv}}_c}{\mathrm{dt}}\end{array}\right]=\left[\begin{array}{cc}0& -\frac{1}{\mathrm{nL}}\\ \frac{1}{\mathrm{nC}}& -\frac{1}{\mathrm{CR}}\end{array}\right]\left[\begin{array}{c}{i}_L\\ v_c\end{array}\right]+\left[\begin{array}{c}\frac{E-v_c/n}{L}\\ -\frac{i_L}{C}\end{array}\right]u$

Wherein, C, L represent respectively electric capacity, inductance, and R is load resistance, and u is convertor controls input, and t is converter running time;

Step 2, carries out digital sample to the output voltage of Flyback supply convertor;

Step 3, by reference value corresponding with it the output voltage sampled value of Flyback supply convertor (desired value) by calculating sliding variable s;

Step 4, to convertor controls input, u carries out the control of Super-Twisting sliding formwork:

u＝u ₁+u ₂

${\stackrel{.}{u}}_1=\left\{\begin{array}{cc}-u& \left|u\right|>u_{\max }\\ -\mathrm{Wsign}\left(s\right)& \left|u\right|\≤u_{\max }\end{array}\right.$

$u_2=\left\{\begin{array}{cc}-\mathrm{\λ}{\left|s_0\right|}^{\mathrm{\ρ}}\mathrm{sign}\left(s\right)& \left|s\right|>s_0\\ -\mathrm{\λ}{\left|s\right|}^{\mathrm{\ρ}}\mathrm{sign}\left(s\right)& \left|s\right|\≤s_0\end{array}\right.$

Wherein, W, ρ, λ and s ₀be normal number, u _maxit is convertor controls input maximum;

Step 5, according to the break-make of convertor controls input u power ratio control converter switches pipe, repeating step two, to step 4, makes the sliding formwork track of Flyback converter output voltage converge on sliding variable, finally makes the output voltage tracking target value all the time of Flyback converter.

The invention has the beneficial effects as follows: for realizing the strong robustness of power system, and the impact of not shivered, controller has been applied the thought of High-Order Sliding Mode control.High-Order Sliding Mode is the popularization of traditional sliding formwork, and it had both eliminated the defect of traditional sliding formwork, had kept again traditional sliding formwork advantage.High-Order Sliding Mode is placed on discontinuous term in the higher derivative of sliding-mode surface, buffets from having eliminated in essence low order sliding-mode surface, finally realizes the robust of system and smoothly exports.

The present invention is based on High-Order Sliding Mode control, and adopt digital signal processor, so the debugging of parameter of the present invention is very convenient, be more suitable for being controlled at applying in generation of electricity by new energy in High-Order Sliding Mode.

In new energy resources system, apply less situation for High-Order Sliding Mode, the present invention is based on Super-Twisting control algolithm, designed a kind of High-Order Sliding Mode Flyback converter.This High-Order Sliding Mode power converter is not subject to the impact of input and output disturbance, and control precision is high, and dynamic response is fast, is particularly suitable for using in generation of electricity by new energy impact electric power system being caused to solve large input disturbance.

Brief description of the drawings

Fig. 1 is Flyback changer system modeling block diagram;

Fig. 2 is Flyback inverter main circuit design drawing;

Fig. 3 is High-Order Sliding Mode Super-Twisting program flow diagram;

Fig. 4 is Super-Twisting algorithm sliding-mode surface s phase path convergence curve figure;

Fig. 5 is that under twice load variations, PI controls design sketch;

Fig. 6 is that under twice load variations, Super-Twisting controls design sketch;

Fig. 7 is that under three times of load variations, PI controls design sketch;

Fig. 8 is that under three times of load variations, Super-Twisting controls design sketch;

Fig. 9 is that under four times of load variations, PI controls design sketch;

Figure 10 is that under four times of load variations, Super-Twisting controls design sketch;

Figure 11 is that twice input voltage changes lower PI control design sketch;

Figure 12 is that twice input voltage changes lower Super-Twisting control design sketch.

Embodiment

Below in conjunction with drawings and Examples, the present invention is further described, the present invention includes but be not limited only to following embodiment.

The present invention includes the following aspects:

One, Flyback converter modeling

Flyback converter is direct current buck-boost converter, and it is that a kind of conventional Switching Power Supply is opened up benefit structure, has typical nonlinear characteristic.

Fig. 1 is the topology theory figure of Flyback converter, and Vg is input direct voltage, and Q is switching tube, is responsible for the break-make of whole circuit.D is diode, and C, L represent respectively electric capacity, inductance, and R is load resistance, and V represents output voltage.

Converter is operated in two operating states of switching under the control of the driving signal c of switching tube Q, at T _onc>0 during this time, switching tube conducting.At T _offc=0 during this time, switching tube turn-offs.

In the time of c>0, i.e., during the Ton of switching tube conducting, transformer primary side inductive current starts to rise, and now, due to the relation of secondary Same Name of Ends, output diode D ends, transformer storage power, and load provides energy by output capacitance C.

Magnetic core is saturated when preventing that load current is larger, and the transformer magnetic core of anti exciting converter will add air gap, has reduced the permeability of magnetic core, and the design of this transformer is more complicated.

In the time of c=0, the T blocking at switching tube _offduring this time, transformer primary side inductance induced voltage is reverse, now output diode conducting, and the energy in transformer powers to the load via output diode, simultaneously to capacitor charging, supplements the energy just having lost, and schematic diagram is as shown in Figure 2.

In the time that switching tube turn-offs, the transformer energy storage of anti exciting converter discharges to load, and magnetic core resets naturally, and therefore anti exciting converter is without separately adding magnetic reset measure.The condition that magnetic core resets is naturally: switch conduction and during the turn-off time, the voltage-second product of a voltage that winding bears of transformer equates.

This converter is the buck-boost converter of isolated form, can reach the effect of buck by changing duty ratio.Can release at one-period T _sthe direct current mean value U of middle output voltage _ofor:

$U_0=\frac{{\mathrm{nDU}}_1}{1-D}---\left(1\right)$

Assumed load is resistive load, with inductive current i _lwith capacitance voltage V _cfor state variable, ignore the dead resistance of inductance and electric capacity, the state space equation that can obtain Flyback converter is:

$\left[\begin{array}{c}\frac{{\mathrm{di}}_L}{\mathrm{dt}}\\ \frac{{\mathrm{dv}}_c}{\mathrm{dt}}\end{array}\right]=\left[\begin{array}{cc}0& -\frac{1}{\mathrm{nL}}\\ \frac{1}{\mathrm{nC}}& -\frac{1}{\mathrm{CR}}\end{array}\right]\left[\begin{array}{c}{i}_L\\ v_c\end{array}\right]+\left[\begin{array}{c}\frac{E-v_c/n}{L}\\ -\frac{i_L}{C}\end{array}\right]u---\left(2\right)$

Two, Super-Twisting sliding mode control algorithm

Super-Twisting sliding Mode Algorithm is the Second Order Sliding Mode Control algorithm that is applied to variable structure control system, and owing to discrete control law being transferred to the more sliding-mode surface of high-order, it has eliminated the buffeting problem existing in traditional sliding formwork control.Super-Twisting control algolithm is made up of two parts, and Part I is sliding-mode surface integration in time, the continuous function that Part II is sliding-mode surface.

u(t)＝u ₁(t)+u ₂(t) (3)

${\stackrel{.}{u}}_1=\left\{\begin{array}{cc}-u& \left|u\right|>u_{\max }\\ -\mathrm{Wsign}\left(s\right)& \left|u\right|\≤u_{\max }\end{array}\right.---\left(4\right)$

$u_2=\left\{\begin{array}{cc}-\mathrm{\λ}{\left|s_0\right|}^{\mathrm{\ρ}}\mathrm{sign}\left(s\right)& \left|s\right|>s_0\\ -\mathrm{\λ}{\left|s\right|}^{\mathrm{\ρ}}\mathrm{sign}\left(s\right)& \left|s\right|\≤s_0\end{array}\right.---\left(5\right)$

Ensure that the adequate condition that converges on sliding-mode surface initial point in finite time is:

$\left\{\begin{array}{c}W>\frac{\mathrm{\&phi;}}{{\mathrm{\&Gamma;}}_M}\\ {\mathrm{\&lambda;}}^2\&GreaterEqual;\frac{4\mathrm{\&phi;}{\mathrm{\&Gamma;}}_M(W+\mathrm{\&phi;})}{{{\mathrm{\&Gamma;}}^3}_m(W-\mathrm{\&phi;})}\\ 0<\mathrm{\&rho;}\&le;0.5\end{array}\right.---\left(6\right)$

Wherein: W, ρ, λ and s ₀be constant.

In the time of the system and control rule u degree of correlation >=1, controller can be reduced to:

$\begin{array}{c}u=u_1+u_2\\ \&CenterDot;\\ u_1=-\mathrm{Wsign}\left(s\right)\\ u_1=-\&Integral;\mathrm{Wsign}\left(s\right)\mathrm{dt}\\ u_2=-\mathrm{\&lambda;}{\left|s\right|}^{\mathrm{\&rho;}}\mathrm{sign}\left(s\right)\end{array}---\left(7\right)$

Super-Twisting algorithm without any need for the information about sliding-mode surface differential in time.If ρ gets 1 in formula (7), system will reach an exponentially stable second order sliding mode, if ρ gets 0.5, maximum possible is realized second order sliding mode by system.

Three, High-Order Sliding Mode controller design

Select herein with TMS320F28035 as control core, 32 float-point DSP that Ta Shi TI company releases, support floating-point operation, dominant frequency 60MHZ, the highest can frequency multiplication to 240MHZ; The AD converter of 12; Adopt Harvard's bus structures, there is interrupt response and interrupt handling capacity fast; In sheet, there is voltage regulator, need 3.3V single power supply.

Sliding mode control algorithm design

For Flyback converter, adopt Second Order Sliding Mode Super-Twisting algorithm to control, design respectively switching function s (x) and the sliding mode control rate u (x) [12,13] of Flyback converter.

Its sliding-mode surface switching function can be taken as: s=x-c (x is output voltage, and c is given voltage).For its control rate: u (t)=u ₁(t)+u ₂(t), be

$u=\&Integral;-\mathrm{Wsign}\left(s\right)\mathrm{dt}-\mathrm{\&lambda;}{\left|s\right|}^{\mathrm{\&rho;}}\mathrm{sign}\left(s\right)$

So control algolithm is:

$u=\left\{\begin{array}{cc}-\&Integral;\mathrm{Wdt}-\mathrm{\&lambda;}{\left|s\right|}^{\mathrm{\&rho;}}& s>0\\ \&Integral;\mathrm{Wdt}+\mathrm{\&lambda;}{\left|s\right|}^{\mathrm{\&rho;}}& s<0\end{array}\right.---\left(8\right)$

Write above control algolithm as discrete form:

$u=\left\{\begin{array}{c}-\mathrm{\&lambda;}\&CenterDot;s^{\mathrm{\&rho;}}+W\&CenterDot;\mathrm{\&Delta;t}+W_0,s>0\\ \mathrm{\&lambda;}\&CenterDot;{(-s)}^{\mathrm{\&rho;}}-W\&CenterDot;\mathrm{\&Delta;t}+W_0,s<0\end{array}\right.---\left(9\right)$

In order to prove convergence, according to Liapunov's stability criterion, structure positive definite integral form

$V=\frac{1}{2}{s}^2>0---\left(10\right)$

To this function differentiate, can obtain

$\begin{array}{c}\stackrel{.}{V}=s\stackrel{.}{s}=(v_c-c)({\stackrel{.}{v}}_c-0)\\ =(v_c-c)(\frac{1}{\mathrm{nC}}{i}_L-\frac{1}{\mathrm{CR}}{v}_c-\frac{i_L}{\mathrm{nC}}u)\\ =-\frac{1}{\mathrm{CR}}{v}_c^2-\frac{c}{\mathrm{CR}}{v}_c+\frac{i_L}{\mathrm{nC}}(v_c-c)(1-u)\end{array}---\left(11\right)$

According to the known v of the output characteristic of Flyback converter _c>0; | v _c– c|< δ, wherein δ is minimum normal number, the duty ratio that is in the nature driving switch pipe signal of known control input u, therefore meets u≤1.Can obtain by analysis, the function in formula (11) meets

$\stackrel{.}{V}<0---\left(12\right)$

Therefore demonstrate,prove thus to such an extent that Super-Twisting algorithm is restrained in finite time, i.e. the output of converter meets the requirement of stability.

Four, according to the algorithm of above discrete form, can design flow chart is shown in Fig. 3, and the source code design procedure in DSP is:

Step 1, the modeling of Flyback converter;

Step 2, carries out digital sample to the output voltage of Flyback supply convertor;

Step 3, by set-point corresponding with it output voltage sampled value by calculating sliding-mode surface (sliding variable);

Step 4, sends sliding-mode surface into System with Sliding Mode Controller, and System with Sliding Mode Controller calculates output controlling value according to Super-Twisting sliding Mode Algorithm.

Step 5, according to the break-make of the controlling value power ratio control converter switches pipe of sliding mode controller, repeating step two to four, makes the sliding formwork track of output voltage converge on sliding-mode surface, finally makes the output voltage tracing preset value all the time of Flyback supply convertor.

Claims (1)

1. a robust High-Order Sliding Mode control method for Flyback converter, is characterized in that comprising the steps:

Step 1, Flyback converter modeling: at one-period T _sthe direct current mean value of middle output voltage wherein, n is the turn ratio of converter, and D is convertor controls input duty cycle, U ₁for input voltage; With inductive current i _lwith capacitance voltage V _cfor state variable, the state space equation that obtains Flyback converter is:

$\left[\begin{array}{c}\frac{{\mathrm{di}}_L}{\mathrm{dt}}\\ \frac{{\mathrm{dv}}_c}{\mathrm{dt}}\end{array}\right]=\left[\begin{array}{cc}0& -\frac{1}{\mathrm{nL}}\\ \frac{1}{\mathrm{nC}}& -\frac{1}{\mathrm{CR}}\end{array}\right]\left[\begin{array}{c}{i}_L\\ v_c\end{array}\right]+\left[\begin{array}{c}\frac{E-v_c/n}{L}\\ -\frac{i_L}{C}\end{array}\right]u$

Wherein, C, L represent respectively electric capacity, inductance, and R is load resistance, and u is convertor controls input, and t is converter running time;

Step 2, carries out digital sample to the output voltage of Flyback supply convertor;

Step 3, by desired value corresponding with it the output voltage sampled value of Flyback supply convertor by calculating sliding variable s;

Step 4, to convertor controls input, u carries out the control of Super-Twisting sliding formwork:

u＝u ₁+u ₂

${\stackrel{.}{u}}_1=\left\{\begin{array}{cc}-u& \left|u\right|>u_{\max }\\ -\mathrm{Wsign}\left(s\right)& \left|u\right|\&le;u_{\max }\end{array}\right.$

$u_2=\left\{\begin{array}{cc}-\mathrm{\&lambda;}{\left|s_0\right|}^{\mathrm{\&rho;}}\mathrm{sign}\left(s\right)& \left|s\right|>s_0\\ -\mathrm{\&lambda;}{\left|s\right|}^{\mathrm{\&rho;}}\mathrm{sign}\left(s\right)& \left|s\right|\&le;s_0\end{array}\right.$

Wherein, W, ρ, λ and s ₀be normal number, u _maxit is convertor controls input maximum;

Step 5, according to the break-make of convertor controls input u power ratio control converter switches pipe, repeating step two, to step 4, makes the sliding formwork track of Flyback converter output voltage converge on sliding variable, finally makes the output voltage tracking target value all the time of Flyback converter.