CN105896571A - Transient stability emergent switch-off control method based on sectional connection line energy forecast - Google Patents

Abstract

The invention discloses a transient stable emergency cut-off control method based on interval tie line energy prediction, and belongs to the technical field of power system safety and stability control. It includes the following steps: Step 1: Emergency control energy evaluation. When the transient instability of the system is determined, the complete transient energy of the system is estimated according to the measurement data of the tie line where the oscillation center is located, and the adjustment power of the tie line is calculated; Step 2: Collect the speed measurement data of generators in various regions in the power grid, regularly calculate the transient kinetic energy change indicators of the generators, and refresh the machine cut-off sequence table; Step 3: According to the generator-tie line power transfer distribution factor obtained by offline calculation, Formulate a transient stability control strategy based on the minimum shedding amount. The invention overcomes the disadvantages of the conventional transient stability control method based on generator measurement data, such as relying on the measurement data of the entire network, poor timeliness, and low engineering feasibility, and has the advantages of less required measurement, high calculation efficiency, and strong pertinence features.

Description

Transient Stability Emergency Shutdown Control Method Based on Interval Tie Line Energy Prediction

technical field

The invention relates to the technical field of power system safety and stability control, in particular to a transient stability emergency cut-off control method based on interval tie line energy prediction.

Background technique

Reasonable and effective transient stability control is the core content of power system security and stability defense. Existing power system emergency control usually adopts event-driven control technology: the operation trajectory and stability characteristics of the target power grid under expected faults are obtained through offline simulation or online budgeting, so as to formulate targeted control measures. When the actual disturbance occurs , and trigger the corresponding control strategy through event matching. This type of method has the characteristics of simplicity, speed, and strong pertinence, but the reliability of control depends on the accuracy of numerical simulation, and it cannot deal with accidents other than expected failures.

With the wide application of wide-area measurement technology, response-driven transient stability control technology has become possible. Document 1 "Motion Stability Quantification Theory" (Jiangsu Science and Technology Press, 1999) proposed the extended equal-area law, based on the measurement of the power angle of the generator to identify and control the transient instability of the system. This method has the advantages of strong rationality and good applicability, but it is heavily dependent on the wide-area response of the whole network generator. Due to the uncertain time-lag in the collection and processing of wide-area information, this will seriously affect the transient stability control. Timeliness.

Due to the imbalance of economic development and energy distribution, large-scale interconnected power grids are usually characterized by long-distance and large-capacity power transmission. Document 2 "Discrimination of Power System Transient Instability Based on Disturbed Voltage Trajectories: (2) Case Analysis" (Automation of Electric Power Systems, 2013, Vol. 37, No. 17, Page 58) points out that the connection between regional power grids is relatively weak , in the transient process of the system, the interval tie line has obvious disturbance characteristics, and it is easy to become the oscillation center. Literature 3 "Quantitative Analysis of Transient Stability Based on Network Information - Branch Potential Energy Method" (Proceedings of the Chinese Society for Electrical Engineering, 2004, Vol. 24, No. 5, Page 1) shows that: as the transient , the transient potential energy of the system will concentrate on the main oscillation branch where the oscillation center is located, causing the synchronous operation of the system to "tear apart" in this branch. On this basis, Document 4 "Real-time Judgment Method for Transient Power Angle Instability Using Measured Response Information" (Proceedings of the Chinese Society for Electrical Engineering, 2013, Vol. 33, No. 34, Page 171) proposes a method for judging instability: The power of the tie line where the oscillation center is located and the phase angle difference phase plane are used to identify the transient stability of the system with the method of trajectory characteristic analysis. This method is mainly aimed at the transient instability characteristics of the interconnected grid interval, and requires few measurements. However, this method only conducts instability discrimination, and does not involve transient stability control.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a transient stable emergency cut-off control method based on the energy prediction of the interval tie line, which has the characteristics of less required measurements, high calculation efficiency and strong pertinence.

The present invention adopts the following technical solutions for solving the problems of the technologies described above:

According to the present invention, a transient stability emergency cut-off control method based on interval tie line energy prediction comprises the following steps:

Step A, emergency control energy evaluation, when the transient instability of the system is determined, the complete transient energy of the system is estimated according to the measurement data of the tie line where the oscillation center is located, and the adjustment power of the tie line is calculated;

Step B. Collect the speed measurement data of generators in various regions in the power grid, regularly calculate the transient kinetic energy change indicators of the generators, and refresh the machine cut-off sequence table;

Step C, according to the power transfer distribution factors between the generators and the tie lines in the whole network obtained by off-line calculation, formulate a transient stability control strategy based on the minimum cut-off amount; the details are as follows:

Select the cut-off objects sequentially from the cut-off sequence table obtained in step B, and estimate how many generators to cut off according to the power transfer distribution factor can meet the adjustment power demand of the tie line calculated in step A, and satisfy the minimum cut-off mode of the following formula, namely The optimal control strategy to maintain the transient stability of the system;

D ₁ P ₁ +D ₂ P ₂ +…+D _n P _n >ΔP,

Among them, P ₁ ~ P _n is the active power of the generators in the sequence table 1 ~ n of the machine, D ₁ ~ D _n is the power transfer distribution factor between the generator and the tie line in the table 1 ~ n of the machine sequence, and n is The total number of generators removed, ΔP is the tie-line regulation power.

As a further optimization scheme of the transient stability emergency cut-off control method based on the energy prediction of the interval tie line in the present invention, in the step A, the adjustment power of the tie line is calculated, and the specific implementation method is as follows:

According to the active power P(t) and phase angle difference θ(t) of the tie line where the oscillation center is located at time t obtained by the phasor measurement unit in real time, t is any sampling time; when the system is stable, the active power of the tie line is the mechanical power:

P _m =P(t _s ),

Among them, t _s is the stable moment of the system, P(t _s ) is the active power of the tie line at the time t _s , P _m is the mechanical power and is a constant value;

According to the sampling period T, calculate the discrete value of the interval speed deviation Δω(t) at time t:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span>$

In the actual operation of the system, it is judged in real time whether the system is transiently unstable. If the system is judged to be transiently unstable at time t _c , the kinetic energy V _k (t _c ) of the oscillating system at this time is calculated as:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;\&omega;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

Use the curve fitting extrapolation method to quickly predict the active power in the future:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

in, is the predicted value of active power with respect to the phase angle difference θ, A, B, and C are fitting parameters, and the parameters of A, B, and C are identified by the least square method;

According to the predicted value of active power Calculate the phase angle difference θ _b of the unstable equilibrium point of the system:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>$

Then predict the remaining deceleration area S _d of the system without transient stability control:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}^{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; ,</span>$

Among them, θ _c is the phase angle difference of the stable equilibrium point of the system;

Then calculate the control compensation area _Sc as:

S _c =V _k (t _c )-S _d ,

Use the rotational speed deviation Δω(t _c ) at the instability discrimination time t _c to approximate the phase angle difference θ _{d at the control execution time t d :}

θ _d = θ _c -Δω(t _c )t _delay ,

Among them, t _delay is the time delay between the instability judgment and the control execution;

Therefore, the adjustment power ΔP of tie line is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; .</span>$

As a further optimization scheme of the transient stability emergency cut-off control method based on the energy prediction of the section tie line in the present invention, t _delay is set to 0.1s.

As a further optimization scheme of the transient stability emergency cut-off control method based on the energy prediction of the interval tie line in the present invention, in the step B, refresh the cut-off sequence table, the specific steps are as follows:

Step B1: Set the disturbed observation time window T _o , during the actual power grid operation, sample the speed value w _i of the generator i in the area in real time, and regularly evaluate the kinetic energy of each generator in the whole network within the disturbed observation time window, Calculate the disturbance severity of the generator by this:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

Among them, S _i is the disturbance severity of regional generator i from time t to time t+T _o , and w _i (t) is the speed value of regional generator i at time t;

Step B2: Sort the disturbance severity of generators in the whole network obtained by each calculation, and formulate a machine cut-off sequence table based on the generator response from the numerical value in descending order; when the system is unstable, use the latest cut-off sequence The bit table sequentially selects the cut-off objects.

As a further optimization scheme of the transient stability emergency cut-off control method based on the energy prediction of the interval tie line in the present invention, T _o is set to 0.2s.

Compared with the prior art, the present invention adopts the above technical scheme and has the following technical effects:

(1) The present invention is different from the conventional transient stability control method. It does not need to perform fast grouping and equivalent aggregation of generators, and only needs a small amount of data interaction and communication, and the calculation efficiency is relatively high;

(2) The present invention is aimed at the transient instability of the interconnected power grid, requires less measurement, and has engineering feasibility;

(3) The tie line regulation power calculated by the present invention can also be used to generate other emergency control strategies such as load shedding;

(4) The present invention is based on the existing phasor measurement unit and wide-area measurement system in the power grid. When a large disturbance occurs in the regional interconnected power grid and causes the transient instability of the system, the transient energy of the system is evaluated according to the interval measurement information, and Implement targeted emergency shutdown control strategies to maintain system transient stability;

(5) To overcome the shortcomings of the conventional transient stability control method based on the measurement data of the generator, such as relying on the measurement data of the whole network, poor timeliness, and low engineering feasibility, and provide a solution for the transient instability of the interconnected grid interval The computer control method has the characteristics of less measurement required, high calculation efficiency and strong pertinence.

Description of drawings

Fig. 1 is the general flowchart of the method of the present invention.

Figure 2 is a diagram of the regional oscillation mode of the interconnected grid.

Fig. 3 is a schematic diagram of power regulation based on interval transient energy prediction.

Fig. 4 is a diagram of the disturbed power angle trajectory of the IEEE-39 node system generator when it is faulty.

Fig. 5 is the disturbed power angle trajectory diagram of the IEEE-39 node system generator after emergency shutdown control.

detailed description

Below in conjunction with accompanying drawing, technical scheme of the present invention is described in further detail:

The specific steps for realizing the present invention will be described in detail below according to the overall method flow chart shown in FIG. 1 .

For the regional interconnection grid, when power oscillation is observed in the system, the system can be divided into two regional systems according to the contact section where the oscillation center is located, as shown in Figure 2. Among them, subsystem A is the sending end power grid, and subsystem B is the receiving end power grid. At this time, the active power of the section tie line A-B can be expressed as:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}$

Where: P is the active power of the tie line. U _A and U _B are the voltage amplitudes of the sending end and the receiving end respectively, X _L is the reactance of the tie line, and θ is the phase angle difference of the tie line.

Assume that the system has a strong voltage regulation capability, that is, the voltage amplitudes U _A and U _B of the sending end and the receiving end are constant. Then the connecting line where the oscillation center is located is the main oscillation branch of the system. Its active power P can be approximately characterized as a sinusoidal change function with respect to the phase angle difference θ of the tie line.

When the power grid is disturbed, system A has unbalanced power. If the disturbance causes the loss of synchronization between subsystems A and B, the relative power angle of the regional generator group will increase, resulting in an increase in the phase angle difference θ between the intervals, and the power P of the tie line will fluctuate violently. If the tie-line power can tend to be stable after being disturbed, the subsystems will run synchronously; otherwise, the system will be transiently unstable. If the transient instability of the system can be determined as early as possible, the active power of the inter-section tie line can be quickly adjusted through the cut-off control, and the energy change between the oscillation systems can be controlled to maintain the synchronous operation of the whole network unit. Based on the above reasons, the present invention proposes a transient stability emergency cut-off control method based on the transient energy prediction of the section tie line, which mainly includes the following steps.

Step 1: When the transient instability of the system is determined, the complete transient energy of the system is predicted according to the measurement of the tie line where the oscillation center is located, and the tie line regulation power is calculated, as shown in Figure 3.

First, according to the phasor measurement unit, the active power P(t) and the phase angle difference θ(t) of the tie line where the oscillation center is located at time t are obtained in real time, where t is any sampling time. When the system is stable, the active power of the tie line is the mechanical power:

P _m =P(t _s )

In the formula: t _s is the stable moment of the system, and P(t _s ) is the active power of the tie line at the time t _s . P _m is the mechanical power, which is a constant value.

According to the sampling period T, calculate the discrete value of the interval speed deviation Δω(t) at time t:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}$

In the actual operation of the system, according to Literature 2 "Discrimination of Power System Transient Instability Based on Disturbed Voltage Trajectories: (2) Case Analysis" (Automation of Power Systems, 2013, Vol. 37, No. 17, Page 58) real-time Determine whether the system is transiently unstable. If the transient instability of the system is determined at time t _c , the kinetic energy V _k (t _c ) of the oscillating system at this time is calculated as:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;\&omega;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>$

Use the curve fitting extrapolation method of Document 5 "Research on Real-time Emergency Control of Power System Transient Stability" (Proceedings of the Chinese Society for Electrical Engineering, 2003, Vol. 23, No. 1, Page 64) to quickly predict the active power in the future:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; )</span>$

In the formula: is the predicted value of the active power with respect to the phase angle difference θ, A, B, and C are the fitting parameters, and the parameters of A, B, and C are identified by the least square method.

According to the predicted value of active power Calculate the phase angle difference θ _b of the unstable equilibrium point of the system:

$\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; B</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}$

Then predict the remaining deceleration area S _d of the system without transient stability control:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}^{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}$

In the formula, θ _c is the phase angle difference of the stable equilibrium point of the system, is the predicted value of active power corresponding to the system phase angle difference θ.

Then calculate the control compensation area S _c :

S _c ＝V _k (t _c )-S _d

Use the rotational speed deviation Δω(t _c ) at the instability discrimination time t _c to approximate the phase angle difference θ _{d at the control execution time t d :}

θ _d ＝θ _c -Δω(t _c )t _delay

In the formula: t _delay is the time delay between the instability judgment and the control execution, preferably 0.1s.

Therefore, the adjustment power ΔP of tie line is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}$

Step 2: Collect the speed measurement of generators in various regions in the power grid, regularly calculate the transient kinetic energy change indicators of the generators, and refresh the machine cut-off sequence table.

Set the disturbed observation time window T _o . In the actual power grid operation process, the speed value w _i of generator i in the area is sampled in real time, and the kinetic energy of each generator in the whole network is regularly evaluated within the disturbance observation time window, so as to calculate the severity of generator disturbance:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

In the formula: S _i is the disturbance severity of regional generator i from time t to time t+T _o , w _i (t) is the speed value of regional generator i at time t, and the larger the value, the disturbed more serious. The disturbed observation time window T _o is preferably 0.2s.

Sorting the disturbance severity of generators in the whole network obtained by each calculation, and formulating a generator cut-off sequence table based on the generator response from the largest value to the smallest value. When the system is unstable, select the cut-off objects in the order of the latest cut-off sequence table.

Step 3: According to the generator-tie line power transfer distribution factor obtained by off-line calculation, formulate a transient stability control strategy based on the minimum shedding amount.

The power transfer distribution factor between each generator and tie line in the whole network is obtained through off-line calculation. For specific calculation methods, see Document 6 "Advanced Power Network Analysis" (Tsinghua University Press, 2004). Select the cut-off objects sequentially from the cut-off sequence table obtained in step 2, and estimate how many generators to cut off can meet the tie-line regulation power demand calculated in step 1 according to the power transfer distribution factor, as shown below:

D ₁ P ₁ +D ₂ P ₂ +…+D _n P _n >ΔP

In the formula: P ₁ ~ P _n is the active power of the generator in the cut-off sequence table 1 ~ n, and D ₁ ~ D _n is the power transfer distribution factor between the generator and the tie line in the cut-off sequence table 1 ~ n. n is the total number of generators removed.

The minimum cut-off mode that satisfies this formula is the best control strategy to maintain the transient stability of the system.

Result verification: In order to test the validity of the method of the present invention, the method of the present invention is applied to carry out simulation verification on the failure situation of the IEEE-39 node system.

Calculation example: At time 0, a three-phase short circuit occurs after the switch on bus 4 side of line 4-14, the main protection of the line refuses to operate in 0.2s, and the backup protection operates to remove the fault in 0.3s.

At this time, the unit at node 39 will lose synchronization with other units, and the main oscillation branch of the system is branch 2-1. The disturbed power angle trajectory of the generators in the whole network is shown in Figure 4. Using the method of Document 2 "Discrimination of Power System Transient Instability Based on Disturbed Voltage Trajectory: (2) Case Analysis" (Automation of Electric Power Systems, 2013, Vol. 37, No. 17, Page 58) to judge 0.54s after the disturbance The system is transiently unstable.

At this time, according to the transient energy in the prediction interval measured at both ends of the tie line, the adjusted power of branch 2-1 is calculated to be 43.7MW. During this process, the generator speed is used to assess the severity of the unit disturbance, and two refreshes of the cut-off sequence table are completed at 0-0.2s and 0.2-0.4s, among which the most seriously disturbed power generation in the latest cut-off sequence table The machine is a 32-node unit. According to the off-line calculation, the distribution factor of the power transfer between the 32-node generators and the branch 2-1 is 0.183, and the calculated minimum cut-off capacity is 238.8MW. Assuming that the node is composed of 5 identical units with a total active output of 650MW, two of the units can be removed, totaling 260MW, to meet the minimum cut-off requirement.

Taking into account the time delay of 0.1s between the instability judgment and the control execution, the above transient stability control is executed at 0.64s, and the 260MW generator under 32 nodes is cut off. After the control, the disturbed power angle trajectory of the generator is shown in Figure 5 . Through the transient stability measures calculated and obtained by the present invention, the system will restore transient stability.

From the above results, it can be found that the method of the present invention has strong pertinence, good effect and engineering feasibility. The invention can be used in a dispatching control center of a large-scale regional interconnection grid, realizes transient stability control of the interconnection grid based on interval transient energy prediction based on a wide-area measurement system, and ensures safe and stable operation of the power system.

Claims (5)

1. A transient stability emergency tripping control method based on interval tie line energy prediction is characterized by comprising the following steps:

step A, emergency control energy evaluation, namely after transient instability of the system is judged, estimating complete transient energy of the system according to link measurement data of an oscillation center, and calculating link adjusting power;

b, collecting rotating speed measurement data of generators in each region in the power grid, calculating transient kinetic energy change indexes of the generators at regular time, and refreshing a generator tripping sequence table;

step C, according to power transfer distribution factors between all generators of the whole network and contact lines obtained through off-line calculation, a transient stability control strategy based on the minimum machine switching amount is formulated; the method comprises the following specific steps:

b, selecting the generator tripping objects according to the sequence of the generator tripping sequence table obtained in the step B, estimating how many generators to be tripped according to the power transfer distribution factor to meet the requirement of the tie line regulation power obtained by calculation in the step A, and meeting the following minimum generator tripping mode, namely the optimal control strategy for maintaining the transient stability of the system;

D₁P₁+D₂P₂+…+D_nP_n＞ΔP，

wherein, P₁～P_nFor generator active power of generator 1-n of the generator tripping sequence table, D₁～D_nThe power transfer distribution factors of the generators and the tie lines in the generator tripping sequence tables 1-n are shown, n is the total number of the generators to be cut off, and delta P is the adjusting power of the tie lines.

2. The method for controlling the transient stability emergency tripping based on the energy prediction of the interval tie line according to claim 1, wherein in the step a, the tie line adjusting power is calculated by:

according to the active power P (t) and the phase angle difference theta (t) of a connecting line t moment where the oscillation center is located, which are obtained by a phasor measurement unit in real time, wherein t is any sampling moment; when the system is stable, the active power of the tie line is the mechanical power:

P_m＝P(t_s)，

wherein, t_sFor the system stabilization time, P (t)_s) Is t_sActive power of the time-of-day line, P_mIs mechanical power and is constant;

calculating a discrete value of the rotating speed deviation delta omega (T) in the interval at the time T according to the sampling period T:

in the actual operation of the system, it isJudging whether the system is in transient state instability, if t_cThe transient instability of the system is judged at any moment, and the kinetic energy V of the oscillating system at the moment is calculated_k(t_c) Comprises the following steps:

and (3) carrying out active power rapid prediction at a future moment by utilizing a curve fitting extrapolation method:

$\tilde{P}\left(\mathrm{\&theta;}\right)=A+Bsin(\mathrm{\&theta;}+C),$

wherein,the active power prediction value about the phase angle difference theta is obtained, A, B and C are fitting parameters, and parameter identification is carried out on the A, B and C through a least square method;

according to the active power predicted valueCalculating the phase angle difference theta of the unstable equilibrium point of the system_b：

$\tilde{P}\left({\mathrm{\&theta;}}_b\right)=A+Bsin({\mathrm{\&theta;}}_b+C)=0,$

Further predicting the remaining deceleration area S of the system when transient stability control is not performed_d：

$S_d={\&Integral;}_{{\mathrm{\&theta;}}_c}^{{\mathrm{\&theta;}}_b}(P_m-\tilde{P}(\mathrm{\&theta;}\left)\right)d\mathrm{\&theta;},$

Wherein, theta_cPhase angle difference of stable balance point of system;

then calculating to obtain a control compensation area S_cComprises the following steps:

S_c＝V_k(t_c)-S_d，

discrimination of time t by means of instability_cRotational speed deviation Δ ω (t)_c) Approximate estimation control execution time t_dPhase angle difference of theta_d：

θ_d＝θ_c-Δω(t_c)t_delay，

Wherein, t_delayDetermining the time delay existing between instability and control execution;

thus, the tie-line regulated power Δ P is:

$\mathrm{\&Delta;}P=\frac{S_c}{{\mathrm{\&theta;}}_b-{\mathrm{\&theta;}}_d}.$

3. the method as claimed in claim 2, wherein t is the time of transient stability emergency tripping control method based on energy prediction of the interval tie line_delayTake 0.1 s.

4. The method for controlling the emergency shutdown of the transient stability based on the energy prediction of the inter-zone link line according to claim 1, wherein in the step B, the shutdown sequence table is refreshed, and the method specifically comprises the following steps:

step B1: setting disturbed observation time window T_oSampling the rotating speed value w of the generator i in the area in real time in the actual power grid operation process_iAnd periodically evaluating the dynamic energy of each generator in the whole network in the disturbed observation time window so as to calculate the disturbed severity of the generator:

$S_i=\frac{1}{2}{w_i}^2(t+T_o)-\frac{1}{2}{w}_i\left(t\right),$

wherein S is_iFor the local generator i to T + T at time T_oSeverity of disturbance between moments, w_i(t) is the rotating speed value of the regional generator i at the moment t;

step B2: sequencing the disturbance severity of the whole network generator obtained by each calculation, and making a generator tripping sequence table based on generator response from large to small according to numerical values; and when the system is unstable, selecting the cutting machine object according to the latest cutting machine sequence table sequence.

5. The method as claimed in claim 4, wherein T is the time-series energy of the interval tie line, and T is the time-series energy of the interval tie line_oTake 0.2 s.