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

Abstract

The invention discloses a transient stability emergent switch-off control method based on sectional connection line energy forecast, and belonging to the technical field of safety and stability control of a power system. The transient stability emergent switch-off control method comprises the following steps of 1, evaluating emergent control energy, forecasting complete transient energy of the system according to measurement data of a connection line where a vibration center is located after the transient instability of the system is judged, and calculating adjustment power of the connection line; 2, acquiring rotational speed measurement data of a power generator of each place in a power grid, calculating a transient-state kinetic energy change index of the power generator on time, and refreshing a switch-off sequence table; and 3, making a transient stability control strategy based on minimum switch-off quantity according to a power generator-connection line power transfer distribution factor acquired through off-line calculation. By the transient stability emergent switch-off control method, the defects of dependence on full-grid measurement data, poor timeliness and low engineering feasibility existing in the conventional transient stability control method based on the measurement data of the power generator are overcome, and the transient stability emergent switch-off control method has the characteristics of low measurement required, high computational efficiency and strong targeted implementation.

Description

Transient stability emergency tripping control method based on interval tie line energy prediction

Technical Field

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

Background

Reasonable and effective transient stability control is the core content of the safety and stability defense line of the power system. Existing power system emergency control typically employs event-driven control techniques: the operation track and the stability characteristics of the object power grid under the expected fault are obtained through an off-line simulation or on-line budget mode, so that a targeted control measure is formulated, and after the actual disturbance occurs, a corresponding control strategy is triggered through event matching. The method has the characteristics of simplicity, rapidness and strong pertinence, but the reliability of control depends on the accuracy of numerical simulation, and accidents except expected faults cannot be dealt with.

With the widespread application of wide-area metrology technology, response-driven transient stability control techniques have become possible. The literature, "motion stability quantification theory" (Jiangsu scientific and technical publishing, 1999) proposes an extended equal-area rule, and performs system transient instability discrimination and control based on power angle measurement of a generator. The method has the advantages of strong rationality and good applicability, but the method is seriously dependent on the wide area response of the whole network generator, and the timeliness of transient stability control is seriously influenced because the uncertain time lag exists in the acquisition and processing of wide area information.

Due to the imbalance between economic development and energy distribution, large interconnected power grids are generally characterized by long-distance and large-capacity power transmission. Document two "disturbed voltage trajectory-based power system transient instability determination: (II) analysis of the sample (power system automation, 2013, vol 37, No. 17, p 58) indicated: the connection between regional power grids is relatively weak, and the disturbed characteristic of the interval connection line in the transient process of the system is obvious and is easy to become an oscillation center. The research of the document three "transient stability quantitative analysis based on network information-branch potential energy method" (the Chinese electro-mechanical engineering journal, 2004, vol 24, page 1 of 5 th period) shows that: as the transient stability decreases, 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" at that branch. On the basis of this, the fourth document, "a transient power angle instability real-time determination method using actually measured response information" (the chinese electro-mechanical engineering, 2013, volume 33, No. 34, page 171) proposes an instability determination method: and establishing a power and phase angle difference phase plane of a connecting line where the oscillation center is located, and identifying the transient stability of the system by a track characteristic analysis method. The method mainly aims at transient instability characteristics of the interconnected power grid interval, and the required measurement is less. However, this method only performs the instability discrimination and does not involve the transient stability control.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a transient stability emergency tripping control method based on interval tie line energy prediction, which has the characteristics of less required measurement, high calculation efficiency and strong pertinence.

The invention adopts the following technical scheme for solving the technical problems:

the invention provides a transient stability emergency tripping control method based on interval tie line energy prediction, which comprises the following steps of:

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.

As a further optimization scheme of the transient stability emergency tripping control method based on the interval tie line energy prediction, in the step a, the tie line regulation power is calculated, and the specific implementation method is as follows:

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:

$\mathrm{\Δ}\mathrm{\ω}\left(t\right)=\frac{\mathrm{\θ}(t+T)-\mathrm{\θ}\left(t\right)}{T},$

in the actual operation of the system, whether the system is instable or not is judged in real time, and if t, the transient instability is judged_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:

$V_k\left(t_c\right)=\frac{1}{2}{\mathrm{\Δ\ω}}^2\left(t_c\right),$

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

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

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：

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

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

$S_d={\∫}_{{\mathrm{\θ}}_c}^{{\mathrm{\θ}}_b}\left(P_m-\tilde{P}\left(\mathrm{\θ}\right)\right)d\mathrm{\θ},$

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:

$\mathrm{\Δ}P=\frac{S_c}{{\mathrm{\θ}}_b-{\mathrm{\θ}}_d}.$

as a further optimization scheme of the transient stability emergency tripping control method based on interval tie line energy prediction, t_delayTake 0.1 s.

As a further optimization scheme of the transient stability emergency tripping control method based on the energy prediction of the interval tie line, in the step B, the tripping sequence table is refreshed, and the specific steps are as follows:

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.

As one of the inventionTransient stability emergency tripping control method further optimization scheme based on interval tie line energy prediction, T_oTake 0.2 s.

Compared with the prior art, the invention adopting the technical scheme has the following technical effects:

(1) the method is different from the conventional transient stability control method, the generator does not need to be subjected to rapid clustering and equivalent aggregation, only a small amount of data is needed to be interacted and communicated, and the calculation efficiency is relatively high;

(2) aiming at transient instability of an interconnected power grid interval, the method needs less measurement and has engineering feasibility;

(3) the tie line obtained by calculation of the invention adjusts the power and can also be used for generating other emergency control strategies such as load shedding and the like;

(4) based on the existing phasor measurement unit and wide-area measurement system in the power grid, when the regional interconnected power grid generates large disturbance and causes transient instability of the system, the transient energy of the system is evaluated according to the interval measurement information, and a targeted emergency tripping control strategy is executed to maintain the transient stability of the system;

(5) the generator tripping control method overcomes the defects of dependence on whole-network measurement data, poor timeliness and low engineering feasibility of the conventional transient stability control method based on the generator measurement data, provides a generator tripping control method aiming at transient instability of the interconnected network interval, and has the characteristics of less measurement, high calculation efficiency and strong pertinence.

Drawings

FIG. 1 is a general flow diagram of the method of the present invention.

Fig. 2 is a graph of interconnected grid area oscillation patterns.

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

FIG. 4 is a perturbed power angular trajectory diagram of an IEEE-39 node system generator at fault.

FIG. 5 is a diagram of a disturbed power angle trajectory of an IEEE-39 node system generator after emergency tripping control.

Detailed Description

The technical scheme of the invention is further explained in detail by combining the attached drawings:

the specific steps implemented by the present invention are described in detail below with reference to the general method flow diagram shown in fig. 1.

For the regional interconnected power grid, when the power oscillation phenomenon of the system is observed, the system can be divided into two regional systems according to the connection section of the oscillation center, as shown in fig. 2. The subsystem A is a transmitting-end power grid, and the subsystem B is a receiving-end power grid. At this time, the active power of the interval tie a-B can be expressed as:

$P=\frac{U_A{U}_B}{X_L}sin\mathrm{\θ}$

in the formula: p is the active power of the tie line. U shape_AAnd U_BThe voltage amplitudes, X, of the transmitting and receiving terminals, respectively_LFor tie line reactance, θ is the tie line phase angle difference.

Suppose the system has strong voltage regulation capability, i.e. the voltage amplitudes U of the sending end and the receiving end_AAnd U_BAre all constants. The link line of the oscillation center is the main oscillation branch of the system. Its active power P can be approximately characterized as a sinusoidally varying function with respect to the link phase angle difference θ.

When the grid is disturbed, there is unbalanced power in system a. If the disturbance causes the loss of synchronization between the subsystems A and B, the relative power angle of the regional generator group is increased progressively, so that the interval phase angle difference theta is increased, and the power P of the connecting line fluctuates severely. If the power of the connecting line can tend to be stable after being disturbed, the subsystems run synchronously; otherwise, the system will be transient unstable. If the transient instability of the system can be judged as early as possible, the active power of the interval connecting line can be rapidly adjusted through the control of the switching machine, and the energy change between the oscillation systems is controlled, so that the synchronous operation of the whole network unit is maintained. Based on the above reasons, the present invention provides a transient stability emergency tripping control method based on transient energy prediction of an interval tie line, which mainly comprises 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 adjusting power is calculated, as shown in fig. 3.

Firstly, according to a phasor measurement unit, the active power P (t) and the phase angle difference theta (t) of a connecting line t moment where an oscillation center is located are obtained 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)

in the formula: t is t_sFor the system stabilization time, P (t)_s) Is t_sThe active power of the moment tie-line. P_mMechanical power is a constant value.

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:

$\mathrm{\Δ}\mathrm{\ω}\left(t\right)=\frac{\mathrm{\θ}(t+T)-\mathrm{\θ}\left(t\right)}{T}$

in the actual operation of the system, the method is based on the literatureJudging transient instability of the power system on the disturbed voltage track: and (II) performing example analysis (automation of power system, 2013, volume 37, page 58 of No. 17) to judge whether the system is in transient instability or not in real time. 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:

$V_k\left(t_c\right)=\frac{1}{2}{\mathrm{\Δ\ω}}^2\left(t_c\right)$

the active power of the future moment is rapidly predicted by using a curve fitting extrapolation method of five researches on transient stability real-time emergency control of a power system (the Chinese electro-mechanical engineering journal, 2003, volume 23, page 64 of phase 1):

$\tilde{P}\left(\mathrm{\θ}\right)=A+Bsin(\mathrm{\θ}+C)$

in the formula:and (4) performing parameter identification on the A, B and C by a least square method, wherein the A, B and C are fitting parameters for the active power predicted value of the phase angle difference theta.

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

$\tilde{P}\left({\mathrm{\θ}}_b\right)=A+Bsin({\mathrm{\θ}}_b+C)=0$

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

$S_d={\∫}_{{\mathrm{\θ}}_c}^{{\mathrm{\θ}}_b}(P_m-\tilde{P})d\mathrm{\θ}$

In the formula, theta_cFor the phase angle difference at the stable equilibrium point of the system,and the active power predicted value is corresponding to the system phase angle difference theta.

Then calculating to obtain a control compensation area S_c：

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

In the formula: t is t_delayFor the time delay existing between the instability determination and the control execution, it is preferable to take 0.1 s.

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

$\mathrm{\Δ}P=\frac{S_c}{{\mathrm{\θ}}_b-{\mathrm{\θ}}_d}$

step 2: the method comprises the steps of collecting rotating speed measurement of generators in each region in a power grid, calculating transient kinetic energy change indexes of the generators in a timing mode, and refreshing a generator tripping sequence table.

Setting disturbed observation time window T_o. In the actual power grid operation process, the rotating speed value w of the generator i in the area is sampled in real time_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:

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

in the formula: s_iFor the local generator i to T + T at time T_oSeverity of disturbance between moments, w_iAnd (t) is the rotating speed value of the regional generator i at the time t, and the larger the numerical value is, the more serious the disturbance is. Disturbed observation time window T_oPreferably 0.2 s.

And sequencing the disturbance severity of the whole network generator obtained by each calculation, and establishing a generator tripping sequence table based on the response of the generator 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.

And step 3: and according to the power transfer distribution factor of the generator-tie line obtained by off-line calculation, a transient stability control strategy based on the minimum cut amount is formulated.

And obtaining the power transfer distribution factor between each generator and the connecting line of the whole network through off-line calculation. The specific calculation method is shown in the six advanced power network analysis (Qinghua university Press, 2004). Selecting the generator tripping objects according to the sequence of the generator tripping sequence table obtained in the step 2, and estimating how many generators to be tripped according to the power transfer distribution factor to meet the requirement of the tie line regulation power calculated in the step 1, wherein the requirement is as follows:

D₁P₁+D₂P₂+…+D_nP_n＞ΔP

in the formula: 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 connecting lines in the generator tripping sequence tables 1-n. n is the total number of generators cut.

The minimum tripping mode satisfying this formula is the optimal control strategy for maintaining the transient stability of the system.

And (5) result verification: in order to test the effectiveness of the method, the method is applied to carry out simulation verification on the fault condition of the IEEE-39 node system.

Calculation example: and at the time 0, three-phase short circuit occurs after the 4-side switch of the bus of the line 4-14, the main protection of the line is refused for 0.2s, and the backup protection action for 0.3s removes the fault.

At this time, the 39-node unit loses synchronization with other units, the main oscillation branch of the system is branch 2-1, and the disturbed power angle locus of the full-network generator is shown in fig. 4. The transient instability judgment of the power system based on the disturbed voltage track is adopted in the document II: second, an analysis of the case (automation of power system, 2013, volume 37, stage 17, page 58) method judges transient instability of the system 0.54s after disturbance.

At this time, the transient state energy of the prediction interval is measured according to two ends of the connecting line, and the adjusting power of the branch 2-1 is calculated to be 43.7 MW. In the process, the unit disturbed severity is evaluated by using the rotating speed of the generator, and two times of refreshing work of the generator tripping sequence table is completed within 0-0.2s and 0.2-0.4s, wherein the most disturbed generator in the latest generator tripping sequence table is a 32-node unit. According to the offline calculation, the power transfer distribution factor of the 32-node generator and the branch 2-1 is 0.183, and the minimum machine cutting amount is 238.8 MW. If the node is composed of 5 identical units and the total active power output is 650MW, 2 of the units can be cut off, and the total power output is 260MW, so that the requirement of minimum cutting amount is met.

Considering the time delay of 0.1s between the instability judgment and the control execution, the transient stability control is executed in 0.64s, the 260MW generator under the 32-node is cut off, and the disturbed power angle locus of the generator after the control is shown in fig. 5. By the transient stability measure calculated by the invention, the system can recover the transient stability.

The results show that the method has strong pertinence, good effect and engineering feasibility. The method can be used for a dispatching control center of the large-scale regional interconnected power grid, and the interconnected power grid transient stability control based on the interval transient energy prediction is realized based on the wide-area measurement system, so that the safe and stable operation of the power system is guaranteed.

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:

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

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：

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

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

$S_d={\∫}_{{\mathrm{\θ}}_c}^{{\mathrm{\θ}}_b}(P_m-\tilde{P}(\mathrm{\θ}\left)\right)d\mathrm{\θ},$

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:

$\mathrm{\Δ}P=\frac{S_c}{{\mathrm{\θ}}_b-{\mathrm{\θ}}_d}.$

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.