CN102778840B - IST control system based on sliding mode variable structure and control method of IST control system - Google Patents

Abstract

The invention relates to an IST control system based on a sliding mode variable structure and a control method of the IST control system. The method comprises the following steps: firstly, collecting voltage and current of a system circuit, comparing the voltage and the current with target voltage and current, and determining the active power and the reactive power to be input by the IST according to the calculation of a calculation module (DSP (digital signal processor)); secondly, calculating a position where an ST to be put through a sliding mode variable control module compared to a position where the ST is currently located, and controlling a switching tap of the ST to switch to the target position; and finally, after the ST is switched to the target position, calculating the residual capacity to be switched by a UPFC (unified power flow controller) and controlling the UPFC with a PI (proportional integral) controller to trace the switching in real time. The system and the method realize the closed-loop control of the IST, the ST in discrete variation can reach a compensation point more quickly and more accurately under the sliding mode variable control, and then, the UPFC controlled by the PI can trace and control in real time. The system and the method can not only make full use of the advantages of large capacity and low price of the ST, but also can quickly and accurately control the power flow.

Description

A kind of IST control system and control method thereof based on sliding moding structure

Technical field

The present invention relates to a kind of control system and control method thereof based on sliding moding structure, especially relate to a kind of IST control system and control method thereof based on sliding moding structure.

Background technology

Sliding mode variable structure control be last century early sixties proposed by scholars such as USSR (Union of Soviet Socialist Republics) Emelyanov, Utkin and Itkin, it is a kind of nonlinear control method.

Sliding mode variable structure control is the special nonlinear Control of a class in essence, and non-linear behavior is the uncontinuity of controlling. the difference of this control strategy and other controls is that " structure " of system is unfixing, but can be in dynamic process, the state (as deviation and all-order derivative thereof etc.) current according to system on purpose constantly changes, and forces system according to the state trajectory motion of predetermined " sliding mode ".Because sliding mode can design and irrelevant with image parameter and disturbance, this just makes, and sliding formwork control has quick response, corresponding parameter changes and disturbance is insensitive, without advantages such as system on-line identification, physics realization are simple.

In system control procedure, controller, according to system state at that time, with the on purpose constantly conversion of transition mode, forces system by the state trajectory motion of predetermined " sliding mode ".Become structure and realize by switching function, it is to be noted especially, conventionally require to have sliding mode district on diverter surface, be often called as again sliding mode control therefore become structure control.Design variable structure control system can be divided into two steps substantially:

(1) determine switching function S (x), i.e. switching surface, makes its determined sliding mode Asymptotic Stability and has good quality, and switching surface has represented the desirable dynamic perfromance of system.

(2) design sliding mode controller, is met arrival condition, thereby makes convergence motion (non-sliding mode) arrive switching surface in finite time, and in the process of convergence fast, buffet little.

Sliding mode variable structure control has that range of stability is wide, dynamic response is fast, parameter is changed and the advantage such as disturbance is insensitive.Research object relates to the numerous complicated systems such as discrete system, distributed parameter system, nonlinear large system.

Sliding formwork control also has its shortcoming, as arrived after sliding mode face when state trajectory, is difficult to strictly slide towards equilibrium point along sliding mode, but passes through back and forth ground convergence equilibrium point in its both sides, buffets thereby produce.

Sliding mode variable structure control is to adopt a switching function to realize the switching of closed-loop system structure as decision rule, utilize variable control, in finite time, system state is driven and maintained on the determined lineoid of switching function, as Fig. 1 represents the motion of system on sliding-mode surface.

Up to now, existing multiple control system have adopted Sliding mode variable structure control strategy, have obtained good effect.Here list the typical application of part.

1, the application of motor

This is a sliding moding structure topmost application all the time, due to direct current generator, synchronous motor and induction motor all exist serious non-linear, the application of very applicable sliding moding structure.

2, the application of switch converters

Switch converters is a strongly non-linear system, the application of sliding moding structure can solve switch converters be difficult for stable, to problems such as Disturbance Rejection ability.According to the switch cycle, dynamically sliding formwork error is revised, compensate the size of controlled quentity controlled variable, be conducive to ensure approx that system moves along diverter surface, and can reduce systematic steady state error, reach and weaken the object of buffeting.

3, the application of robot control

Robot becomes one of main application aspect of sliding moding structure in recent years.Robot is typical nonlinear system, has various unpredictalbe external disturbance, has in a large number the research about in this respect.Can side pass through two sliding-mode surfaces of design, realize the research with the doublejointed robot of the elasticity arm of force.

4, the application of aircraft control

The premium properties of Sliding mode variable structure control itself, is applicable to the motion control of aircraft.And develop rapidly in missile guidance.

At present the control based on ST is mainly open loop, rarely has it is carried out to closed-loop control.This control mode response speed is slower, likely causes the switching pin vibration of ST tap in tap switching process, does not reach the target of normal compensation.The present invention adopts sliding formwork to become the object that the ST controlling is aided with UPFC and reaches closed-loop control, can obtain fabulous compensation to system load flow.

Summary of the invention

Above-mentioned technical matters of the present invention is mainly solved by following technical proposals:

A kind of IST control system based on sliding moding structure, it is characterized in that, comprise that the SEN transformer being connected between system sending end and receiving end becomes control module and is connected the PI controller for controlling THE UPFC with DSP and expansion module with THE UPFC, two groups of the PT harvesters for measuring voltage and electric current and CT harvester, the DSP being connected with two groups of PT harvesters and CT harvester and expansion modules being separately positioned on system sending end and receiving end, the sliding formwork being connected with DSP and expansion module for controlling SEN transformer.

Here SEN transformer is hereinafter to be referred as ST, and THE UPFC is hereinafter to be referred as UPFC; The IST here refers to adopt SEN transformer to add the hybrid control method of THE UPFC, is called modified SEN transformer.

In above-mentioned a kind of IST control method based on sliding moding structure, it is characterized in that, comprise the following steps:

Step 1, the electric current and voltage of two groups of PT harvesters and CT harvester acquisition system circuit, contrast target voltage electric current, calculates through DSP and expansion module, determines active power and the reactive power of the required input of IST;

Step 2, becomes control module by sliding formwork, and the contrast current residing position of ST, calculates the required position of putting into of ST, and controls the switching tap of ST, throws into target location;

Step 3, ST switching is behind target location, and sliding formwork becomes control module and calculates the capacity of remaining required UPFC switching, and adopts PI controller control UPFC real-time follow-up to drop into.

Therefore, tool of the present invention has the following advantages: 1. closed-loop control, can bring into play greatly ST and the UPFC effect in system load flow compensation; 2. fast response time, what can be exceedingly fast obtains ST and the UPFC required impact point compensating to put into fast target location separately; 3. the large good economy performance of compensation capacity, can bring into play the large but cheap economic advantages of ST compensation capacity greatly; 4. control is effective, and to the ST of Discrete Change, sliding formwork becomes can better meet its variation tendency, and gives accurate control.

Brief description of the drawings

Fig. 1 is the schematic diagram of the motion of load system on sliding-mode surface.

Fig. 2 is a kind of structure of the present invention and controller principle schematic diagram.

Fig. 3 is the motion schematic diagram of the ST-UPFC control system that adopts of the present invention on sliding-mode surface.

Fig. 4 is hardware configuration schematic diagram of the present invention.

Fig. 5 is the control principle schematic diagram corresponding with Fig. 4.

Embodiment

Below by embodiment, and by reference to the accompanying drawings, technical scheme of the present invention is described in further detail.

Embodiment:

First be necessary to introduce definition and the existence of Sliding mode variable structure control.

An if nonlinear system

$\stackrel{\·}{x}=f(x,u,t)$ (formula 1)

Wherein, x ∈ R ⁿ, u ∈ R ^m, t ∈ R

Need to determine sliding formwork functional vector S (x), S ∈ R ^m, and seek to become structure control

$u_i\left(x\right)=\left\{\begin{array}{c}{u}_i^{+}\left(x\right)S_i\left(x\right)>0\\ u_i^{-}\left(x\right)S_i\left(x\right)<0\end{array}\right.$ (formula 2)

Here (i=1,2 ..., m), make diverter surface S _i(x) phase path beyond=0 enters diverter surface in finite time, and such control system is called Sliding Mode Variable Structure System.

System mainly contains two design objects: select sliding-mode surface S _i(x), ask for control the condition that Sliding mode variable structure control exists:

$\underset{{S\&RightArrow;0}^{+}}{\lim }\stackrel{\&CenterDot;}{S}<0$ $\underset{S\&RightArrow;0^{-}}{\lim }\stackrel{\&CenterDot;}{S}>0$ (formula 3)

Or

$\underset{S\&RightArrow;0}{\lim }\stackrel{\&CenterDot;}{S}S<0$ (formula 4)

Be switching function to meet can be micro-and cross initial point requirement.At this moment, Sliding mode variable structure control exists and convergence.

Then introduce hybrid IST controlling party ratio juris of the present invention.

As shown in Figure 2, for system sending end voltage, for system is subject to terminal voltage, X _s, X _l, X _rbe followed successively by the reactance of system sending end, line reactance and the reactance of system receiving end, with for system equivalence sending end voltage and equivalence are subject to terminal voltage, for the voltage of ST series connection partial-compensation system, for the voltage of UPFC series connection partial-compensation system.Control section is by the voltage and current of acquisition system circuit, and then comparison object voltage and current, determines ST and UPFC active power and the reactive power of required input compensation separately.ST and UPFC are the devices of regulating system trend, but, because ST and UPFC have respectively merits and demerits separately, herein both in conjunction with composition IST(Improved ST) trend of the control system deficiency that can make up both reaches optimum regulating effect, as fast response time, pondage is large, cost is low, regulate more accurately, suppress tap action vibration etc.

It should be noted that both have different principle of work and the method for operation, can not control by same control method simultaneously, must find a kind of effective control device and realize both collaborative works.

Next introduce control method flow process of the present invention:

1. select sliding-mode surface.

Because the control target of ST has two, one is the meritorious P of circuit transmission, and one is idle Q, when working control, is also the substep control of P, Q, and in this system, sliding-mode surface has two:

$\left\{\begin{array}{c}{S}_P\left(x\right)=P\left(x\right)-P_{\mathrm{ref}}\\ S_Q\left(x\right)=Q\left(x\right)-Q_{\mathrm{ref}}\end{array}\right.$ (formula 5)

Wherein P (x) is instant meritorious in circuit, and Q (x) is immediately idle in circuit, P _refand Q _refbe respectively object transmission power.

2. judge convergence.

To S _p(x)=P (x)-P _refhave

${\stackrel{\&CenterDot;}{S}}_P\left(x\right)=\stackrel{\&CenterDot;}{P}\left(x\right)$

Work as S _p(x) when > 0,

P(x)-P _ref＞0,P(x)＞P _ref

Be that P (x) has exceeded predetermined target value, control system can make P (x) reduce in next moment,

$\stackrel{\&CenterDot;}{P}\left(x\right)<0,$

Therefore

${\stackrel{\&CenterDot;}{S}}_P\left(x\right)<0$

And meet

$\underset{S\&RightArrow;0^{+}}{\lim }{\stackrel{\&CenterDot;}{S}}_P<0$ (formula 6)

Work as S _p(x) when < 0,

P(x)-P _ref＜0,P(x)＜P _ref

Be that P (x) is less than predetermined target value, control system can make P (x) increase in next moment,

$\stackrel{\&CenterDot;}{P}\left(x\right)>0,$

Therefore

${\stackrel{\&CenterDot;}{S}}_P\left(x\right)>0$

And meet

$\underset{S\&RightArrow;0^{+}}{\lim }{\stackrel{\&CenterDot;}{S}}_P>0$ (formula 7)

By formula (6), (7) known S _p(x) meet the condition of convergence, in like manner, S _q(x) also meet the condition of convergence.

3.ST becomes the discretize of structure control.

Because the control of ST is discrete, can not ensure sliding-mode surface S _p(x), S _q(x) be substantially equal to zero, and in actual control, also can not ensure that control device arrives zero error, therefore actual target area is a neighborhood δ along diverter surface, and δ > 0, works as S _p(k), S _q(k) when ∈ (δ ,+δ), can think that target is to predetermined value, system arrives steady state (SS).

Therefore the change structure control of ST reality into:

$u_P\left(k\right)=\left\{\begin{array}{c}{u}_P^{+}\left(k\right)S_P\left(k\right)>+\mathrm{\&delta;}\\ u_P^{-}\left(k\right)S_P\left(k\right)<-\mathrm{\&delta;}\end{array}\right.$ (formula 8)

$u_Q\left(k\right)=\left\{\begin{array}{c}{u}_Q^{+}\left(k\right)S_Q\left(k\right)>+\mathrm{\&delta;}\\ u_Q^{-}\left(k\right)S_Q\left(k\right)<-\mathrm{\&delta;}\end{array}\right.$ (formula 9)

Wherein,

$\left\{\begin{array}{c}{S}_P\left(k\right)=P\left(k\right)-P_{\mathrm{ref}}\\ S_Q\left(k\right)=Q\left(k\right)-Q_{\mathrm{ref}}\end{array}\right.$

Concrete control structure is as follows:

be switched to the compensation point that the P nearest with current compensation point reduces

be switched to the compensation point that the P nearest with current compensation point increases

be switched to the compensation point that the Q nearest with current compensation point reduces

be switched to the compensation point that the Q nearest with current compensation point increases

In working control, each compensation point has switched, all precedence parse S _p(k), secondly analyze S _q(k), only have and be introduced into sliding-mode surface S when system _p(k) after, just can be again to sliding-mode surface S _q(k) motion, in the time that two diverter surfaces all arrive, represents that compensation is stable.

The control of 4.UPFC and ST

Become at ST on the basis of structure control, UPFC adopts PI to control, in ST action simultaneously, UPFC exports the target voltage vector of a head for target power all the time, this vector is taking ST output voltage and terminal as initial point, taking circuit sending end voltage vector terminal corresponding to target power as terminal, this target voltage vector changes fast along with the variation of ST output voltage.

Control in conjunction with UPFC, IST control strategy can be expressed as:

U (k, x)=u _p,Q(k)+u _upfc(x) (formula 10)

Wherein u _upfc(x) be the control of UPFC, belong to continuous control system, and not with sliding-mode surface S _i(x) situation changes but adopts PI control mode.

Be illustrated in figure 3 the motion schematic diagram of ST-UPFC control system on sliding-mode surface, in figure, two dotted lines represent respectively diverter surface S _p(x)=0 and S _q(x)=0, four straight lines that are parallel to respectively two dotted lines have represented the neighborhood border along diverter surface.ST control system is moved in diverter surface neighborhood sliding-mode surface, and first arrives with S _p(x) centered by=0 in the neighborhood of line, then to S _q(x) in=0 neighborhood, approach.And the control of UPFC coordinates the output of ST all the time, make target power approach desired value most.

Specific embodiment described herein is only to the explanation for example of the present invention's spirit.Those skilled in the art can make various amendments or supplement or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.

Claims (1)

1. the IST control method based on sliding moding structure, it is characterized in that, based on a kind of IST control system based on sliding moding structure, comprise the SEN transformer and the THE UPFC that are connected between system sending end and receiving end, be arranged on PT harvester and the CT harvester of system sending end for measuring voltage and electric current, be arranged on PT harvester and the CT harvester of system receiving end for measuring voltage and electric current, the DSP and the expansion module that are connected with two groups of PT harvesters and CT harvester, the sliding formwork being connected with DSP and expansion module for controlling SEN transformer becomes control module, and be connected with DSP and expansion module for controlling the PI controller of THE UPFC,

Comprise the following steps:

Step 1, the electric current and voltage of two groups of PT harvesters and CT harvester acquisition system circuit, contrast target voltage electric current, calculate through DSP and expansion module, determine active power and the reactive power of the required input of IST transformer, here IST transformer refers to adopt SEN transformer to add the hybrid control method of THE UPFC, is called modified SEN transformer;

Step 2, becomes control module by sliding formwork, and the contrast current residing position of IST transformer, calculates the required position of putting into of IST transformer, and controls the switching tap of IST transformer, throws into target location;

Step 3, IST transformer switching is behind target location, and sliding formwork becomes control module and calculates the capacity of remaining required THE UPFC switching, and adopts PI controller control THE UPFC real-time follow-up to drop into.