CN105226676A - A kind of STATCOM controls the compensation method of time delay - Google Patents

Abstract

The invention discloses the compensation method that a kind of STATCOM controls time delay, comprise the following steps: the fundamental active component detecting load-side electric current, electrical network current operating conditions is judged, compensation of delay is carried out according to the fundamental active component of result of determination to electric current, obtain the instruction current signal of STATCOM, and it can be used as Setting signal, calculate the difference of Setting signal and power network current signal, adoption rate resonance controls to regulate difference, is then obtained the actuating signal of switching tube by modulation.Control, after compensation of delay, the impact of delay on system performance can be effectively reduced through this STATCOM, ensure the compensation precision of system and quick tracking performance.

Description

A kind of STATCOM controls the compensation method of time delay

Technical field

The invention belongs to STATCOM technical field, particularly relate to the compensation method that a kind of STATCOM controls time delay.

Background technology

Inductive load and the impact loads such as arc furnace, electric welding machine such as a large amount of transformers, motor is there is in coal mining enterprise's power distribution network, the frequent movement that is dissatisfied and impact load of reactive power demand can cause fluctuation and the flickering of line voltage, affect the normal production of enterprise and the normal life of the people, cause line loss to increase and power factor reduction simultaneously.Reactive power compensation can Appropriate application power system capacity, improves power factor, reduces line loss, stable access point system voltage.Compare traditional reactive-load compensation methods such as fixed capacitor, synchronous compensator, Static Var Compensator SVC, STATCOM STATCOM has had the advantages such as high controllability and fast-response, floor space be little and the focus and emphasis of reactive power compensation area research since becoming in recent years due to it.

Along with the deep discovery to STATCOM investigation and application, following two parts can be there are in running and control time delay: detect sampling element and inevitably there is system delay; The intrinsic control signal discretization of numerical control system can produce time delay.The existence controlling time delay makes the compensation performance of STATCOM be subject to larger impact.

The existence controlling time delay makes system command current signal lag behind actual instruction current signal, to greatly affect the compensation precision of STATCOM, and along with delay duration increase impact also larger, not only compensating action is not had under serious conditions, even can introduce extra reactive current for electrical network, power grid quality is worsened more.

Summary of the invention

Controlling time delay to the impact of bucking-out system for solving, the invention provides the compensation method that a kind of STATCOM controls time delay.This compensation method by judging electric network state, and then is revised instruction current signal according to different states, the precision of instruction current signal is improved, improves the control precision of STATCOM.

The technical solution used in the present invention comprises following step:

(1). detect threephase load current i _la, i _lb, i _lc, to i _la, i _lb, i _lccarry out 3/2 conversion and rotation transformation obtains active current and reactive current component i _p, i _q, by i _pits DC component is obtained by low pass filter LPF will the fundamental active component i of system power can be obtained after rotation transformation and 2/3 converts _saF, i _sbF, i _scF;

(2). be the feature of zero according to the power network current sampled point mathematic expectaion in ideally each primitive period, adopt t inspection to judge electric network state: first to pass through calculate the size of t, wherein n is the number of sampled point in a first-harmonic, be the sample average of sampled point in the primitive period, S is the sample variance of sampled point in the primitive period; Then t is drawn by tabling look-up _1-α/2(n-1) value, wherein makes confidence level be α=80%, then to statistical value t and t _1-α/2(n-1) compare, if t > is t _1-α/2(n-1) then think that electrical network is now transient process, if t≤t _1-α/2(n-1) then think that electrical network is steady operation;

(3). according to above-mentioned judged result to i _saF, i _sbF, i _scFcarry out compensation of delay, obtain the instruction current signal i of STATCOM _saF*, i _sbF*, i _scF*.Concrete implementation method is as follows: 1. the compensation method of a, b, c three-phase is identical, is described for a phase at this; 2. the usual duration using a sampling period as control time delay compensates, even control time delay τ to equal sampling period Δ T.When thinking that electrical network is in transient process: a phase instruction current signal i _saF ^*(k)=2i _saF(k)-i _saF(k-1); When thinking that electrical network is in stable state: a phase instruction current signal wherein, T is a primitive period duration, and Δ T is system sampling period duration, and τ is for controlling delay duration, i _saF* (k) is etching system a phase current command signal during kth, i _saF* (k-1) is etching system a phase current command signal during kth-1, be time etching system a phase current command signal.In like manner, the instruction current signal i of b, c two-phase can be obtained _sbF*, i _scF*;

(4). by instruction current i _saF* i _sbF*, i _scF* as Setting signal, power network current i _sa, i _sb, i _scthe control of ratio resonance current is carried out as feedback signal;

(5). by ratio resonance current controlling unit output voltage vector U ^*carry out Realization of pulse width modulation based on voltage space vector, export modulation signal to six switching tubes.

Compared with prior art, the invention has the beneficial effects as follows: the present invention is summing up during STATCOM is run on the basis producing and control delay duration.By judging operation of power networks state, result is reliable rapidly, on this basis by revising instruction current for Power System Steady-state and transient state different situations, improves the precision of instruction current signal.Make the STATCOM adopting this method, control precision is improved, and reduces the existence of control time delay to the harmful effect of system.

Accompanying drawing explanation

Fig. 1 is based on i _p-i _qmethod obtains the principle schematic of system fundamental active current component.

Fig. 2 is the evaluation algorithm schematic flow sheet of power network current transient state of the present invention and stable state.

Fig. 3 is the principle schematic of delay compensation method of the present invention.

Fig. 4 is the general system set-up schematic diagram of delay compensation method of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further illustrated.

Fig. 1 is based on i _p-i _qmethod obtains the principle schematic of system fundamental active current component.

Three-phase mains voltage is symmetrical, i _la, i _lb, i _lcbe respectively threephase load electric current, usually comprise fundamental active current, fundamental reactive current and harmonic current.Can obtain according to instantaneous reactive power theory: by threephase load current i _la, i _lb, i _lcby obtaining biphase current i after 3/2 conversion _α, i _β, by i _α, i _βactive current and reactive current component i is obtained by two-phase rotation transformation _p, i _q, the synchronizing signal source wherein in transformation matrix C is to system a phase voltage e _aphase-locked, by i _pactive current DC component can be obtained by low pass filter LPF will system fundamental active current component i can be obtained after inverse transformation _saF, i _sbF, i _scF.

Fig. 2 is the evaluation algorithm schematic flow sheet of power network current transient state and stable state.

Its three-phase fundamental active current component i when system is in stable state _sFbe the sinusoidal quantity of one-period, the sampled point mathematic expectaion in so each primitive period is zero, in order to accurately judge that power network current is in stable state or transient state actually, adopts the method for hypothesis testing at this.Its general principle is: supposing the system is in stable situation, so selected sample mathematic expectaion μ and overall mathematic expectaion μ ₀equal, be denoted as H ₀; Then sample data is added up, and test according to given confidence level, according to statistics, make refusal or accept hypothesis H ₀judgement.This algorithm makes confidence level be α=80%, can obtain null hypothesis and alternative hvpothesis is respectively:

$\left\{\begin{array}{c}{H}_0:\mathrm{\μ}={\mathrm{\μ}}_0=0\\ H_1:\mathrm{\μ}\≠0\end{array}\right.---\left(1\right)$

The measured value of test statistics meets t distribution, is calculated by following formula:

$t=\sqrt{n}\frac{\stackrel{\‾}{X}-{\mathrm{\μ}}_0}{S}~t(n-1)---\left(2\right)$

Wherein, n is the number of sampled point in a first-harmonic, be the sample average of sampled point in the primitive period, S is the sample variance of sampled point in the primitive period, and computing formula is as follows:

$\stackrel{\‾}{X}=\frac{1}{n}\underset{k=i+1}{\overset{i+n}{\Σ}}{x}_k---\left(3\right)$

$S^2=\frac{1}{n-1}(\underset{k=i+1}{\overset{i+n}{\Σ}}{x}_k^2-n{\stackrel{\‾}{X}}^2)---\left(4\right)$

Wherein, x _kfor k moment current sampling data i _sFk (), i is the starting point of iterative computation, namely current sampled point.

Electric network state basis for estimation and result as shown in the table:

Wherein, t _1-α/2(n-1) obtaining by looking into t distribution table, when evaluation algorithm initialization, making its last cycle be transient state.

Fig. 3 is the principle schematic of carrying out compensation of delay.

When static synchronous compensator system runs, the control system of its current detecting link and discretization is inevitably for system introduces time delay.So, the system fundamental active current component i that we obtain _saF, i _sbF, i _scFbe inaccurate, there is a delay duration is the error of τ.In order to improve the precision of STATCOM, need to compensate control time delay.The compensation method of a, b, c three-phase is identical, is described for a phase at this; By theory analysis and field condition, think using a sampling period and compensate best results as controlling the duration of time delay, even control time delay τ to equal sampling period Δ T.When thinking that electrical network is in transient process, be such as interfered or load variations time: make a phase instruction current signal i _saF ^*(k)=2i _saF(k)-i _saF(k-1); When thinking that electrical network is in stable state: make a phase instruction current signal wherein, T is a primitive period duration, and Δ T is system sampling period duration, and τ is for controlling delay duration, i _saF* (k) is etching system a phase current command signal during kth, i _saF* (k-1) is etching system a phase current command signal during kth-1, be time etching system a phase current command signal.In like manner, the instruction current signal i of b, c two-phase can be obtained _sbF*, i _scF*.

Fig. 4 is the general system set-up schematic diagram of described delay compensation method.

Current detecting link: threephase load current i _la, i _lb, i _lcsystem fundamental active current component i is obtained by the electric current detecting method described in Fig. 1 _saF, i _sbF, i _scF.

Compensation of delay link: comprise two steps: judge electric network state, adopts method described in Fig. 2; To current signal just compensation of delay, adopt method described in Fig. 3, so obtain instruction current i _saF*, i _sbF*, i _scF*.

Current Control link: by i _saF*, i _sbF*, i _scF* as Setting signal, power network current i _sa, i _sb, i _scthe control of ratio resonance current is carried out as feedback signal.

Modulation algorithm link: by ratio resonance current controlling unit output voltage vector U ^*carry out Realization of pulse width modulation based on voltage space vector, export modulation signal to six switching tubes.

Be that system injects reactive current accurately eventually through inverter circuit, realize reactive power compensation.

Aforementioned proportion resonance current controls and Realization of pulse width modulation based on voltage space vector is the art known technology, is not described in detail.

More than show general principle of the present invention, principal character etc., it is only the preferred embodiments of the present invention, be not limited to the present invention, obviously, those skilled in the art can carry out various change and modification to the present invention and not depart from the spirit and scope of the present invention.Like this, if these amendments of the present invention and modification belong within the scope of the claims in the present invention and equivalent technologies thereof, then the present invention is also intended to comprise these change and modification.

Claims (1)

1. STATCOM controls a compensation method for time delay, it is characterized in that, comprises following steps:

(1). detect threephase load current i _la, i _lb, i _lc, to i _la, i _lb, i _lccarry out 3/2 conversion and rotation transformation obtains active current and reactive current component i _p, i _q, by i _pits DC component is obtained by low pass filter LPF will the fundamental active component i of system power can be obtained after rotation transformation and 2/3 converts _saF, i _sbF, i _scF;

(2). be the feature of zero according to the power network current sampled point mathematic expectaion in ideally each primitive period, adopt t inspection to judge electric network state: first to pass through calculate the size of t, wherein n is the number of sampled point in a first-harmonic, be the sample average of sampled point in the primitive period, S is the sample variance of sampled point in the primitive period; Then t is drawn by tabling look-up _1-α/2(n-1) value, wherein makes confidence level be α=80%; Then to statistical value t and t _1-α/2(n-1) compare, if t > is t _1-α/2(n-1) then think that electrical network is now transient process, if t≤t _1-α/2(n-1) then think that electrical network is steady operation;

(3). according to above-mentioned judged result to i _saF, i _sbF, i _scFcarry out compensation of delay, obtain the instruction current signal i of STATCOM _saF ^*, i _sbF ^*, i _scF ^*;

Concrete implementation method is as follows: 1. the compensation method of a, b, c three-phase is identical, is described for a phase at this; 2. the usual duration using a sampling period as control time delay compensates, even control time delay τ to equal sampling period Δ T; When showing that electrical network is in transient process by above-mentioned judgement: a phase instruction current signal i _saF ^*(k)=2i _saF(k)-i _saF(k-1); When electrical network is in stable state: a phase instruction current signal wherein, T is a primitive period duration, and Δ T is system sampling period duration, and τ is for controlling delay duration, i _saF ^*k () is etching system a phase current command signal during kth, i _saF ^*(k-1) be etching system a phase current command signal during kth-1, be time etching system a phase current command signal; In like manner, the instruction current signal i of b, c two-phase can be obtained _sbF ^*, i _scF ^*;

(4). by instruction current i _saF ^*, i _sbF ^*, i _scF ^*as Setting signal, power network current i _sa, i _sb, i _scthe control of ratio resonance current is carried out as feedback signal;

(5). by ratio resonance current controlling unit output voltage vector U ^*carry out Realization of pulse width modulation based on voltage space vector, export modulation signal to six switching tubes.