CN101944741A - Load security domain researching method based on voltage level restraint - Google Patents

Abstract

In fact, a system runs normally for most of the time, only when the security level of the system is reduced to enter the alert condition, the re-appeared accident can enable the equipment to be overloaded and enable the system to enter the emergency state; therefore, before entering the voltage alert state, judging the load power safety margin of the current operation is more meaningful. From the thought, according to a load security domain researching method based on voltage level restraint of the invention, the load impedance range is computed according to a Thevenin equivalent model and an online equivalent parameter under a given voltage level restraint so as to obtain a load apparent power security domain under the current operation state and give the most dangerous growth manner of the apparent power in the security domain. The method is simple, practical, clear in physical significance, and convenient to perform online voltage/load control by the operator and maintain the favorable operation state of the system.

Description

Load security domain research method based on the voltage levvl constraint

Technical field

Power system voltage, load safe operation and control.

Background technology

Because nonlinear characteristic, the coupling between the quantity of state and the part throttle characteristics etc. of system, it is online definite to make steady state stability limit voltage be difficult to.P-V curve method and Q-V curve method are based on the thinking of P, Q decoupling zero, and the burning voltage limit point that obtains is also inequality; The trend method depends on system's accurate model, and near the ill trend the limit point is found the solution difficulty, and can't differentiate the unstability type; Based on circuit local message voltage stability index L _P, L _q, F _VSI, I _PN, L _QN, L _PPAnd L _QPDeng, all be after power equation is carried out the conversion of various ways, there is the condition of separating to obtain based on the quadratic form equation.Analyze to find that state variable and coefficient intercouple in the quadratic form power equation, so the derivation of the mathematical theory of these indexs is tight inadequately, and the actual effect of online application is unsatisfactory.

From safety perspective, operation states of electric power system can be divided into 5 kinds, promptly normal, warning, urgent, extreme and return to form.The real system most of the time operates in normal condition, generally can bear contingent and does not exceed constraints; Just under the situation of adverse circumstances or the increase of operation constraints, system security level just reduces step by step.After entering the state of alert, the possibility that the voltage unstability takes place under contingent is just bigger.During the electric power system actual motion, should adjust running status in real time, the maintenance system operates on the lsafety level.Therefore, the border of asking for the load power zone of corresponding voltage normal condition has more practical significance.

Summary of the invention

By measurement to the online local message of the current running status of electric power system, analyze the border, load safety zone of voltage state of alert correspondence, obtain the load power nargin of current operation, and the most dangerous growth pattern of apparent power that obtains loading is for the operations staff carries out the on-Line Voltage security control and load to control foundation is provided.

Description of drawings

Fig. 1 Dai Weinan Equivalent Model

Fig. 2 impedance phase spirogram

Z under the constraint of Fig. 3 voltage levvl _∑Z _L

Under Fig. 4 voltage levvl constraints | Z _L| extreme value

Fig. 5 apparent power security domain diagram

The most dangerous growth pattern of Fig. 6 apparent power

The apparent power minimum value of Fig. 7 under the voltage levvl constraint

Security control of Fig. 8 on-Line Voltage and load control flow chart

Embodiment

1. the resistance value under voltage levvl retrains

Employing Fig. 1 simplifies two node system models, establishes equivalent source and is

The Dai Weinan equiva lent impedance is Z _f, load bus voltage is

Load impedance is Z _L=R _L+ jX _L

Dai Weinan Equivalent Model total impedance

Z _∑＝Z _f+Z _L (1)

In the R-X coordinate system, establish Z _f: { (0,0), (R _f, X _f), the impedance Z of then drawing _L, Z _∑Phasor diagram be Fig. 2.

Suppose R _LAnd X _LAll be freely to change, according to the constraint of load bus voltage levvl, calculated load impedance span.The equivalent electromotive force E of Ruo Daiweinan is known, and establishing load bus voltage levvl binding occurrence is U ₂

Can get by Fig. 1

$\left\{\begin{array}{c}\stackrel{\·}{U}=\stackrel{\·}{I}{Z}_L\\ \stackrel{\·}{E}={\stackrel{\·}{U}}_f+\stackrel{\·}{U}=\stackrel{\·}{I}{Z}_f+\stackrel{\·}{I}{Z}_L\end{array}\right.---\left(2\right)$

After the delivery value, have

$\frac{\left|U\right|}{\left|E\right|}=\frac{\left|Z_L\right|}{|Z_f+Z_L|}---\left(3\right)$

According to formula (3), have

$\frac{{(R_{\mathrm{\Σ}}-R_f)}^2+{(X_{\mathrm{\Σ}}-X_f)}^2}{R_{\mathrm{\Σ}}^2+X_{\mathrm{\Σ}}^2}={\left(\frac{U}{E}\right)}^2---\left(4\right)$

Abbreviation is

(R _∑-a) ²+(X _∑-b) ²＝r ² (5)

Wherein: $a=\frac{R_f}{1-{(U/E)}^2},$ $b=\frac{X_f}{1-{(U/E)}^2},$ $r^2=[{\left(\frac{1}{1-{\left(\frac{U}{E}\right)}^2}\right)}^2-\frac{1}{1-{\left(\frac{U}{E}\right)}^2}](R_{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HSA00000215860900023.png,HSA00000215860900031.png"\; state="\{\{state\}\}">f</figure-callout>}}^2+X_f^2).$

Because resistance R＞0 according to formula (5) as can be known, keeps U at the horizontal U of a certain confinement voltage ₂The time, impedance Z _∑Actual value be one section circular arc, as Fig. 3.

As seen from Figure 2, Z _LBe starting point (R _f, X _f), terminal point is (R _∑, X _∑) phasor.So with the phasor translation, Z under the Dai Weinan impedance model when obtaining loading the voltage levvl that limits _LThe value set:

(R _L-a′) ²+(X _L-b′) ²＝r ² (6)

Wherein: $a^{\&prime;}=\frac{R_f}{1-{({\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="HSA00000215860900023.png,HSA00000215860900031.png"\; state="\{\{state\}\}">U</figure-callout>}}_2/E)}^2}-R_f,$ $b^{\&prime;}=\frac{X_f}{1-{({\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="HSA00000215860900023.png,HSA00000215860900031.png"\; state="\{\{state\}\}">U</figure-callout>}}_2/E)}^2}-X_f,$ ${\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HSA00000215860900023.png,HSA00000215860900031.png"\; state="\{\{state\}\}">r</figure-callout>}}^2=[{\left(\frac{1}{1-{\left(\frac{U_2}{E}\right)}^2}\right)}^2-\frac{1}{1-{\left(\frac{U_2}{E}\right)}^2}](R_{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HSA00000215860900023.png,HSA00000215860900031.png"\; state="\{\{state\}\}">f</figure-callout>}}^2+X_f^2)$

The programming Z that draws according to formula (5) and formula (6) _∑, Z _LAs Fig. 3.

Among Fig. 3 center of circle A coordinate be (a, b), radius

Center of circle B coordinate is: (a ', b '), radius

Z _∑Curve representation is: keep U at voltage levvl ₂Condition under, Z _∑Value be starting point at initial point, terminal point is at center of circle A, radius is the phasor of circle on the circular arc of first quartile of r.Z _LCurve representation is for to keep U at voltage levvl ₂Condition under, Z _LValue be starting point at initial point, terminal point is B in the center of circle, radius is

The phasor of circle on the circular arc of first quartile.If load impedance is on circular arc, load bus voltage is bound level; If when load impedance was positioned at the circular arc outside, load voltage was higher than bound level; If when load impedance was positioned at the circular arc inboard, the load voltage level was lower than bound level.

Z among Fig. 4 _LmaxBe illustrated in load bus voltage and keep identical U ₂Under the constraints, work as Z _∑Z _LZ _fDuring the same direction of three phasors, Z _LMaximum is arranged.Easily observing to draw has this moment

Both under the constraint of same voltage levvl, when the impedance angle of load and the impedance angle of circuit equate, the mould value maximum of load impedance.

2. load apparent power security domain

The essence of electrical network steady stability nargin research is from physically being the power delivery ability of research electrical network, voltage instability be derived from the power that obtains of load surpass transmission and electricity generation system the trend of energy transmitted power.And said power in the general document refers to active power.In fact, maximum active power is transmitted the derivation result of theorem: when the plural number of load impedance equals the conjugate complex number of transfer impedance, load power obtains maximum, application that can not fine adaptation electric power system, and in the actual motion system, the active power value of not reaching capacity is following, and load bus also may the voltage unstability take place because of idle disappearance.Many electrical equipments are considered as the design limit value of power with the product of the effective value of its voltage and current on the engineering, and promptly the maximum of electrical equipment is utilized capacity.For this reason, the consideration load capacity should adopt with the apparent power of load and weigh.

According to above-mentioned conclusion, the equivalent electromotive force of Dai Weinan in the calculation system

Equiva lent impedance Z _f, if system specialization node voltage level can not be lower than certain value U ₂The time, obtain Z _LSpan, then the apparent power value is

$S_L={\stackrel{\&CenterDot;}{U}}_2{\stackrel{\&CenterDot;}{I}}^{*}={\stackrel{\&CenterDot;}{U}}_2\frac{{\stackrel{\&CenterDot;}{U}}_2^{*}}{Z_L^{*}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="HSA00000215860900023.png,HSA00000215860900031.png"\; state="\{\{state\}\}">U</figure-callout>}}_2^2}{Z_L^{*}}---\left(7\right)$

Can find out very intuitively from formula (7): at known voltage horizontal restraint U ₂Under the situation, Z _LSize and Orientation has determined the apparent power scope that can allow.According to formula (7), on the P-Q state space, construct the security domain S of reflection node running status _L, as Fig. 5.

Dash area is illustrated in the load apparent power safety zone under the sustaining voltage horizontal restraint among Fig. 5.When the load power in this zone, the voltage of load bus is greater than the U of binding occurrence ₂, the power curve of ionization voltage horizontal restraint correspondence is far away more, and voltage levvl is high more; When load power outside this zone, the voltage of load bus is then less than the U that limits ₂Value, the power curve of ionization voltage horizontal restraint correspondence is far away more, and voltage levvl is low more.

Provided the most dangerous growth pattern of apparent power among Fig. 6.Suppose that current load operation state is illustrated in figure 6 as S ₀, S ₀The phasor lower end is at initial point, and is terminal in interval, static security territory, connects S ₀End and center of circle C, the direction of line is to S thus _LThe intersection point of curve is a curve S _LNormal direction, obtain

Be to load under present running status, apparent power flash-up mode causes the fastest mode of voltage decline, is called the most dangerous load growth mode.

Among Fig. 7, curve S _LPower value when being illustrated in the sustaining voltage horizontal restraint, phasor S _MinBe illustrated in the apparent power of same electrical voltage levels constraints counterdie value minimum.

In real system,, each node load is all organized anti-circle accordingly calculate, and then obtain the apparent power security domain of all load buses in the system all given node voltage constraints of loading.

3. on-Line Voltage security control and load control

For all load bus voltages in the maintenance system on lsafety level, all loads are all operated in separately the apparent power security domain.Near more from the security domain border when actual load, load bus voltage is just low more, and more near the safe voltage binding occurrence.So on-Line Voltage/load control makes the load of dynamic change remain in the load security domain exactly.

The running status of discontinuity surface is calculated the Dai Weinan equivalent parameters in the time of can be by nearest two; According to formula (3), obtain impedance circle; According to formula (7), can obtain the apparent power security domain border of load bus under the voltage levvl constraint.Specific algorithm program flow diagram such as Fig. 8:

The program flow diagram explanation:

Step1:, obtain the running status of load bus according to real-time measurement.

Step2: calculate equivalent electromotive force E of Dai Weinan and equivalent impedance Z _f

Step3: given voltage levvl constraint U ₂, according to

Equation obtains Z _∑Impedance circle.

Step4: by Z _L=Z _∑-Z _f, calculate Z _LImpedance circle.

Step5: because resistance one be decided to be on the occasion of, so judge Z _LReal part R _LWhether greater than zero, if enter Step6; If not, enter Step4.

Step6: according to formula

The border of the apparent power security domain of calculated load.

Step7: on-Line Voltage security control and load control:

(1) monitors load in real time; Whether performance number is in apparent power security domain scope;

(2) according to the trend and the security domain of load variations, make corresponding decision-making.If can increase how many loads, or whether current state can drop into certain bar load circuit; During cutting load, should cut what or that circuit, not only keep voltage levvl but also make the load loss minimum.

The real system most of the time operates in normal condition, and just under the situation of adverse circumstances or the increase of operation constraints, system security level just reduces step by step.Under normal condition, system can bear contingent and not exceed any constraints.Have only when system security level and reduce, enter the state of alert after, the contingent of Chu Xianing just may make the equipment overload once more, thereby makes system enter the state of emergency.If fault is serious or cause the system equipment chain reaction, then may make system directly enter extremity.

Therefore, say that the security domain border of the current operation of judgement system has more practical significance than unstability border from practical standpoint.Load apparent power security domain border has been arranged, can be the operations staff and carry out the control of on-Line Voltage/load decision-making foundation is provided.

Claims (2)

1. under given voltage levvl constraint,, equal modulus of impedance value ratio according to the voltage magnitude ratio based on Dai Weinan Equivalent Model and online equivalent parameters, promptly | U|/| E|=|Z _L|/| Z _L+ Z _f|, obtained the minimum impedance mould value of loading earlier; By confinement voltage value and load minimum impedance mould value, obtain corresponding apparent power security domain border then, and then obtained the load power security domain under the given safe voltage level constraint.

2. the load security domain that above method is obtained is used for on-Line Voltage security control and load control.

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