CN105162127A - Calculation method of nonlinear model of capacitor switching bus voltage increment - Google Patents

Abstract

The invention discloses a calculation method of a nonlinear model of capacitor switching bus voltage increment, and aims at solving the technical problems of inaccurate calculation result, frequency action of a capacitor and reactive power fluctuation of voltage due to the fact that the capacitor switching bus voltage increment is calculated by a sensitivity method in the prior art. According to the method disclosed by the invention, the bus voltage increment after the switching action of the capacitor can be conveniently calculated by combining measurement which is only collected from power plant and station under the conditions of known rate voltage and rated capacity of the capacitor and comprehensive impedance of the system on the basis of three basic assumptions according to the basic principle of a power system. Whether the bus voltage exceeds the limit or not after the capacitor acts is judged by the bus voltage increment calculated by the method disclosed by the invention; the judgment result is reliable; the capacitor can be effectively prevented from frequently acting; and reactive power fluctuation is reduced.

Description

The computational methods of capacitor switching busbar voltage Incremental Nonlinear Models

Technical field

The present invention relates to a kind of nonlinear model and its computational methods of capacitor switching busbar voltage increment, belong to operation and control of electric power system technical field.

Background technology

Capacitor is the capital equipment regulated in automatic voltage control system (hereinafter referred to as AVC system), but all there is mediating effect+6 to voltage and reactive power in its action, when the adjustment direction of voltage and reactive power is contrary time, such as voltage is higher, but reactive power owes to mend, once the inappropriate capacitor of the capacity of input, reactive power can be caused normal, voltage but gets over the situation of the upper limit, this phenomenon is adjusted more general on the ground that voltage bandwidth is narrower, so AVC needs to determine whether capacitor actions can cause busbar voltage out-of-limit before decision-making.

Traditional determination methods is as a reactive power source using capacitor, bus is as PQ node, first calculate the sensitivity of busbar voltage and reactive power injection, the rated capacity of electricity container is multiplied by the increment that this sensitivity just can draw voltage reality, and then after can judging capacitor actions, whether busbar voltage is out-of-limit.Sensitivity method principle is simple, but it exists following problem:

1: sensitivity method uses the whole network to measure, and much county adjust measure arrange and measuring quality still very weak;

2: sensitivity method have employed a lot of hypothesis, such as think that original paper two ends phase place is 0, voltage is perunit value, and these hypothesis are irrational mostly;

3: sensitivity method is very large to dependences such as the structural parameters (impedance, rated capacitor capacity) of whole electrical network and operational factors (meritorious, reactive power), if the parameter of other plant stands is wrong, then can bring very large error to the calculating of other plant stands;

4: sensitivity method think capacitor all the time to electrical network inject rated reactive power, but its to electrical network inject reactive power be with drop into after voltage become quadratic relationship, the characteristic of reflection capacitor that cannot be appropriate.

If be in bound edge at voltage, capacitor actions voltage is not out-of-limit to utilize sensitivity method to judge, so AVC can say the word make capacitor actions, but owing to being subject to the impact of four factors above, this judged result is insecure.So voltage out-of-limit after capacitor actual act, so send out another order to capacitor again, frequent movement, voltage and reactive power is caused to fluctuate.

Summary of the invention

The object of the invention is to overcome deficiency of the prior art, there is provided a kind of nonlinear model and computational methods of capacitor switching busbar voltage increment, result of calculation is inaccurate, the technical problem of capacitor frequent movement, voltage power-less fluctuation to adopt sensitivity method calculable capacitor switching busbar voltage increment to cause in solution prior art.

The method only needs to measure in plant stand, and bound fraction operational factor can calculate bus voltage increment after capacitor switching action.

For achieving the above object, the technical solution adopted in the present invention is: the computational methods of capacitor switching busbar voltage Incremental Nonlinear Models, comprise the steps:

Step one: record following parameter before capacitor switching:

Upper level plant stand main transformer high side bus voltage U ₀, current plant stand main transformer high side bus voltage U ₁, current plant stand main transformer low-pressure side bus voltage U ₂, main transformer no-load voltage ratio K in upper level plant stand ₀: 1, the impedance R of main transformer no-load voltage ratio K:1, the capacity C needing switching action capacitor, upper level plant stand main transformer in current plant stand _t0+ jX _t0, current plant stand main transformer impedance R _t1+ jX _t1and the impedance R+jX of transmission line;

Step 2: do following three hypothesis:

1, upper level plant stand main transformer high side bus voltage U ₀approximate constant before and after capacitor switching;

2, resistance is much smaller than reactance, can the cross stream component of simultaneously negligible resistance and voltage drop;

3, active loss and the reactive loss of main transformer in plant stand is ignored;

Step 3: based on three hypothesis of step 2, equivalent transformation is carried out to main transformer equivalent circuit in plant stand, specific as follows:

Upper level plant stand main transformer high side bus voltage is converted low-pressure side, as the input voltage of equivalent electric circuit, then upper level plant stand main transformer low-pressure side bus voltage

By the impedance R of upper level plant stand main transformer _t0+ jX _t0, current plant stand main transformer impedance R _t1+ jX _t1reactance jX is equivalent to the impedance R+jX of transmission line _s(suppose 2, negligible resistance, X _s=X _t0+ X _t1+ X);

By current plant stand main transformer low-pressure side bus voltage U ₂conversion is to high-pressure side, and as the output voltage of equivalent electric circuit, current plant stand main transformer high side bus voltage is KU ₂;

Step 4: before capacitor drops into, according to the equivalent electric circuit that step 3 exports, in conjunction with line voltage landing principle, obtains following formula:

${\mathrm{KU}}_2+\frac{Q_L{X}_S}{{\mathrm{KU}}_2}=U_0^{\′}---\left(1\right)$

In formula: Q _lit is total reactive power of the load on low-pressure side bus;

Step 5: will the capacitor of switching action be needed to drop into, if the stable state busbar voltage increment that current plant stand main transformer low-pressure side produces is Δ U, the variable quantity simultaneously produced reactive load power is Δ Q, and the angular frequency of busbar voltage is ω; After capacitor drops into, the reactive power injected to system is: Q=ω C (U ₂+ Δ U) ²so, have:

$K(U_2+\mathrm{\Δ}U)+\frac{\[Q_L+\mathrm{\Δ}Q-\mathrm{\ω}C{(U_2+\mathrm{\Δ}U)}^2\]X_S}{K(U_2+\mathrm{\Δ}U)}=U_0^{\′}---\left(2\right)$

Do first approximation to formula (2) to obtain:

${\mathrm{KU}}_2+\frac{Q_L{X}_S}{{\mathrm{KU}}_2}+(K-\frac{Q_L{X}_S}{{\mathrm{KU}}_2^2})\mathrm{\Δ}U+\frac{X_S\mathrm{\Δ}Q}{{\mathrm{KU}}_2}=U_0^{\′}+\frac{{\mathrm{\ωCX}}_S(U_2+\mathrm{\Δ}U)}{K}---\left(3\right)$

Formula (1) is substituted into after formula (3) simplifies and obtains:

$\mathrm{\Δ}U=\frac{\frac{{\mathrm{\ωCX}}_S{U}_2}{K}-\frac{X_S\mathrm{\Δ}Q}{{\mathrm{KU}}_2}}{\left(K-\frac{Q_L{X}_S}{{\mathrm{KU}}_2^2}-\frac{{\mathrm{\ωCX}}_S}{K}\right)}---\left(4\right)$

As ignored the variation delta Q that reactive load power produces, even Δ Q=0, if the rated voltage of switched capacitor is U _n, rated capacity is Q _n, then after substitution formula (4) simplifies:

$\mathrm{\Δ}U=\frac{Q_N{X}_S{U}_2^3}{\left(K^2{U}_N^2{U}_2^2-U_N^2{Q}_L{X}_S-U_2^2{Q}_N{X}_S\right)}---\left(5\right)$

Step 6: calculate X _s=X _t0+ X _t1+ X, and substitute into formula (5) and calculate, Δ U is bus voltage increment after capacitor switching.

Compared with prior art, the beneficial effect that the present invention reaches is: no longer need the whole network to measure, only need to measure in plant stand, when known capacitor rated voltage, rated capacity and system synthesis impedance, in conjunction with operational factor, just can calculate bus voltage increment after capacitor switching action exactly, after the busbar voltage increment adopting the inventive method to calculate judges capacitor actions, whether busbar voltage is out-of-limit, judged result is reliable, can effectively avoid capacitor frequent movement, reduce reactive power fluctuation.

Accompanying drawing explanation

Fig. 1 is transformer station's equivalent circuit diagram in the present invention.

Fig. 2 is the transformer station equivalent circuit diagram of Fig. 1 based on hypothesis.

Embodiment

Below in conjunction with accompanying drawing, the invention will be further described.Following examples only for technical scheme of the present invention is clearly described, and can not limit the scope of the invention with this.

The computational methods of capacitor switching busbar voltage Incremental Nonlinear Models, comprise the steps:

Step one: record following parameter before capacitor switching:

Upper level plant stand main transformer high side bus voltage U ₀, current plant stand main transformer high side bus voltage U ₁, current plant stand main transformer low-pressure side bus voltage U ₂, main transformer no-load voltage ratio K in upper level plant stand ₀: 1, the impedance R of main transformer no-load voltage ratio K:1, the capacity C needing switching action capacitor, upper level plant stand main transformer in current plant stand _t0+ jX _t0, current plant stand main transformer impedance R _t1+ jX _t1and the impedance R+jX of transmission line;

Step 2: do following three hypothesis:

1, upper level plant stand main transformer high side bus voltage U ₀approximate constant before and after capacitor switching;

2, resistance is much smaller than reactance, can the cross stream component of simultaneously negligible resistance and voltage drop;

3, active loss and the reactive loss of main transformer in plant stand is ignored;

Step 3: based on three hypothesis of step 2, carry out equivalent transformation to main transformer equivalent circuit in plant stand, as shown in Figure 1, be the circuit diagram of transformer station, concrete equivalent transformation step is as follows:

Upper level plant stand main transformer high side bus voltage is converted low-pressure side, as the input voltage of equivalent electric circuit, then upper level plant stand main transformer low-pressure side bus voltage

By the impedance R of upper level plant stand main transformer _t0+ jX _t0, current plant stand main transformer impedance R _t1+ jX _t1reactance jX is equivalent to the impedance R+jX of transmission line _s(suppose 2, negligible resistance, X _s=X _t0+ X _t1+ X);

By current plant stand main transformer low-pressure side bus voltage U ₂conversion is to high-pressure side, and as the output voltage of equivalent electric circuit, current plant stand main transformer high side bus voltage is KU ₂;

As shown in Figure 2, be that Fig. 1 is based on the circuit diagram after three hypothesis equivalent transformations of step 2.

Step 4: before capacitor drops into, according to the equivalent electric circuit that step 3 exports, in conjunction with line voltage landing principle, obtains following formula:

${\mathrm{KU}}_2+\frac{Q_L{X}_S}{{\mathrm{KU}}_2}=U_0^{\′}---\left(1\right)$

In formula: Q _lit is the reactive power that transformer station's low-voltage bus bar flows;

Step 5: will the capacitor of switching action be needed to drop into, if the stable state busbar voltage increment that current plant stand main transformer low-pressure side produces is Δ U, the variable quantity simultaneously produced reactive load power is Δ Q, and the angular frequency of busbar voltage is ω; After capacitor drops into, the reactive power injected to system is: Q=ω C (U ₂+ Δ U) ²so, have:

$K(U_2+\mathrm{\Δ}U)+\frac{\[Q_L+\mathrm{\Δ}Q-\mathrm{\ω}C{(U_2+\mathrm{\Δ}U)}^2\]X_S}{K(U_2+\mathrm{\Δ}U)}=U_0^{\′}---\left(2\right)$

First approximation is done to formula (2):

${\mathrm{KU}}_2+\frac{Q_L{X}_S}{{\mathrm{KU}}_2}+(K-\frac{Q_L{X}_S}{{\mathrm{KU}}_2^2})\mathrm{\Δ}U+\frac{X_S\mathrm{\Δ}Q}{{\mathrm{KU}}_2}=U_0^{\′}+\frac{{\mathrm{\ωCX}}_S(U_2+\mathrm{\Δ}U)}{K}---\left(3\right)$

Formula (1) is substituted into after formula (3) simplifies and obtains:

$\mathrm{\Δ}U=\frac{\frac{{\mathrm{\ωCX}}_S{U}_2}{K}-\frac{X_S\mathrm{\Δ}Q}{{\mathrm{KU}}_2}}{\left(K-\frac{Q_L{X}_S}{{\mathrm{KU}}_2^2}-\frac{{\mathrm{\ωCX}}_S}{K}\right)}---\left(4\right)$

Ignore the variation delta Q that reactive load power produces, even Δ Q=0, if the rated voltage of switched capacitor is U _n, rated capacity is Q _n, then after substitution formula (4) simplifies:

$\mathrm{\Δ}U=\frac{Q_N{X}_S{U}_2^3}{\left(K^2{U}_N^2{U}_2^2-U_N^2{Q}_L{X}_S-U_2^2{Q}_N{X}_S\right)}---\left(5\right)$

Step 6: calculate X _s=X _t0+ X _t1+ X, and substitute into formula (5) and calculate, Δ U is bus voltage increment, wherein X after capacitor switching _t0, X _t1, X can read from EMS system.

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the prerequisite not departing from the technology of the present invention principle; can also make some improvement and distortion, these improve and distortion also should be considered as protection scope of the present invention.

Claims (1)

1. the nonlinear model of capacitor switching busbar voltage increment and computational methods, is characterized in that comprising the steps:

Step one: record following parameter before capacitor switching:

Upper level plant stand main transformer high side bus voltage U ₀, current plant stand main transformer high side bus voltage U ₁, current plant stand main transformer low-pressure side bus voltage U ₂, main transformer no-load voltage ratio K in upper level plant stand ₀: 1, the impedance R of main transformer no-load voltage ratio K:1, the capacity C needing switching action capacitor, upper level plant stand main transformer in current plant stand _t0+ jX _t0, current plant stand main transformer impedance R _t1+ jX _t1and the impedance R+jX of transmission line;

Step 2: do following three hypothesis:

1, upper level plant stand main transformer high side bus voltage U ₀approximate constant before and after capacitor switching;

2, resistance is much smaller than reactance, can the cross stream component of simultaneously negligible resistance and voltage drop;

3, active loss and the reactive loss of main transformer in plant stand is ignored;

Step 3: based on three hypothesis of step 2, equivalent transformation is carried out to main transformer equivalent circuit in plant stand, specific as follows:

Upper level plant stand main transformer high side bus voltage is converted low-pressure side, as the input voltage of equivalent electric circuit, then upper level plant stand main transformer low-pressure side bus voltage

By the impedance R of upper level plant stand main transformer _t0+ jX _t0, current plant stand main transformer impedance R _t1+ jX _t1reactance jX is equivalent to the impedance R+jX of transmission line _s;

By current plant stand main transformer low-pressure side bus voltage U ₂conversion is to high-pressure side, and as the output voltage of equivalent electric circuit, current plant stand main transformer high side bus voltage is KU ₂;

Step 4: before capacitor drops into, according to the equivalent electric circuit that step 3 exports, in conjunction with line voltage landing principle, obtains following formula:

${\mathrm{KU}}_2+\frac{Q_L{X}_S}{{\mathrm{KU}}_2}=U_0^{\′}---\left(1\right)$

In formula: Q _lit is total reactive power of the load on low-pressure side bus;

Step 5: the capacitor that AVC decision-premaking is gone out, its input impact on busbar voltage of anticipation, if the stable state busbar voltage increment that current plant stand main transformer low-pressure side produces is Δ U, the change in voltage simultaneously caused due to change in voltage is Δ Q to the variable quantity that reactive load power produces, and the angular frequency of busbar voltage is ω; After capacitor drops into, the reactive power injected to system is: Q=ω C (U ₂+ Δ U) ²so, have:

$K(U_2+\mathrm{\Δ}U)+\frac{\[Q_L+\mathrm{\Δ}Q-\mathrm{\ω}C{(U_2+\mathrm{\Δ}U)}^2\]X_S}{K(U_2+\mathrm{\Δ}U)}=U_0^{\′}---\left(2\right)$

Formula (2) first approximation is obtained:

${\mathrm{KU}}_2+\frac{Q_L{X}_S}{{\mathrm{KU}}_2}+(K-\frac{Q_L{X}_S}{{\mathrm{KU}}_2^2})\mathrm{\Δ}U+\frac{X_S\mathrm{\Δ}Q}{{\mathrm{KU}}_2}=U_0^{\′}+\frac{{\mathrm{\ωCX}}_S(U_2+\mathrm{\Δ}U)}{K}---\left(3\right)$

Formula (1) is substituted into after formula (3) simplifies and obtains:

$\mathrm{\Δ}U=\frac{\frac{{\mathrm{\ωCX}}_S{U}_2}{K}-\frac{X_S\mathrm{\Δ}Q}{{\mathrm{KU}}_2}}{\left(K-\frac{Q_L{X}_S}{{\mathrm{KU}}_2^2}-\frac{{\mathrm{\ωCX}}_S}{K}\right)}---\left(4\right)$

If ignore the variation delta Q that reactive load power produces, even Δ Q=0, if the rated voltage of switched capacitor is U _n, rated capacity is Q _n, then after substitution formula (4) simplifies:

$\mathrm{\Δ}U=\frac{Q_N{X}_S{U}_2^3}{(K^2{U}_N^2{U}_2^2-U_N^2{Q}_L{X}_S-U_2^2{Q}_N{X}_S)}---\left(5\right)$

Step 6: calculate X _s=X _t0+ X _t1+ X, and substitute into formula (5) and calculate, Δ U is bus voltage increment after capacitor switching.