JPH0715876A - Preventively controlling method for electric power system transient stability - Google Patents

Abstract

PURPOSE:To take into account economy of a system operation and an improvement in active state stability. CONSTITUTION:A method for preventively controlling transient stability of an electric power system has the steps of evaluating assumed disturbance in which the transient stability of the system is previously set, and calculating a regulated amount of a generator output as a preventive control amount by using a mathematical programming method, and comprises the step of adding a sum square of an altered amount from an output command value of the generator obtained by an economic load distributing calculation to an objective function in which an unbalanced amount of generators of acceleration energy during a fault is a minimum as a penalty item.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preventive control method for monitoring and controlling transient stability of a power system online.

[0002]

2. Description of the Related Art As the power system becomes large-scale and complicated, it is more important to grasp and maintain the stability of the power system. Under such circumstances, in order to ensure the stability of the power system in the future as well, in addition to the emergency stabilization control, preventive control during normal times will also be important. Until now, the stability improvement measures that have been applied to actual systems have been mainly emergency control systems that urgently control various stabilizing devices on the condition that disturbance has occurred. On the other hand, the stability during normal times is monitored, and necessary control is performed in advance so that the stability can be maintained against a certain amount of disturbance (for example, adjustment of the generator output).
The so-called preventive control, which is applied to the plant, is still in the research stage, and there are few cases where it is applied to an actual system. The preventive control method for transient stability that has been proposed in the past was mainly to find the output adjustment amount of the generator that maximizes the transient stability by mathematical programming using acceleration energy during an accident. (For example, Japanese Patent Application No. 62-12695).

FIGS. 4 and 5 show the flow of a preventive control method for transient stability that has been conventionally proposed. That is, in the conventional preventive control method, as shown in FIG. 4, first, in step S41, a target expected disturbance is set according to the current supply and demand state of the power system. Next, in step S42, failure calculation is performed for each assumed disturbance, and the output P _fj of each generator at the time of the accident occurs
Ask for. Then, in step S43, the unbalanced AE value between the generators of the acceleration energy for the expected accident is calculated from the equation (1) based on the output P _fj of each generator obtained in step S42 at the time of the accident, and A in step S44
If the E value is larger than the preset reference value AE ^*, it is registered as an unstable case in step S45.

[0004]

[Equation 1] Here, N is the number of generators connected to the power system, and ΔT is the accident duration time of the expected disturbance. Further, M _j and P _INj are the inertia constant of the generator j and the generator output before the accident, respectively.

Next, when the unstable case is registered according to the flow of FIG. 4, the preventive control amount is calculated according to the flow of FIG.
First, in step S51, a failure calculation is performed for each assumed disturbance determined to be unstable. Next, in step S52, by using the output at the time of the accident of each generator for the unstable assumed disturbance obtained in step S51, the equation (2) representing the supply and demand balance of the system by the nonlinear programming method and the output of the generator j The objective function of the equation (4), that is, the output P _INj of each generator that minimizes the AE value with respect to the unstable assumed disturbance is obtained by using the equation (3) representing the upper and lower values as a constraint condition.

[0006]

[Equation 2]

[0007]

[Equation 3]

Here, M is the number of unstable assumed disturbances registered according to the flow of FIG. Further, P _INj is the output of the j-th generator after generator adjustment, P _fij is the in-accident output of the j-th generator for the i-th assumed disturbance, and a _i is a weighting coefficient for the assumed disturbance (for example, The more serious accidents, the larger a _i ). Finally, in step D53, step S52
The output adjustment amount ΔP _INj of each generator is calculated using the output P _INj of each generator and the current value output P _INj (0) of each generator _obtained in
Obtained from equation (5).

[0009]

[ _Formula 4] ΔP _INj = P _INj −P _INJ (0) (5) From the above results, according to the conventional preventive control method of the power system transient stability, the generator of acceleration energy during an accident is generated. Since the objective function is set so that the unbalanced AE value is minimized, the output adjustment amount of the generator that maximizes the transient stability with respect to the assumed disturbance determined to be unstable can be obtained. .

[0010]

As described above, in the conventional preventive control method for the transient stability of the power system, the objective function that minimizes the unbalanced AE value between the generators of the acceleration energy during an accident is set. Set. As a result, the output adjustment amount of the generator that maximizes the transient stability can be obtained. On the other hand, however, it was not possible to take into consideration the economic efficiency in terms of grid operation, that is, the minimization of power generation costs, or dynamic stability, which is a different stability problem.
The present invention has been made to solve the above problems, and an object of the present invention is to provide a preventive control method for transient stability of a power system that can consider the economic efficiency of system operation and dynamic stability.

[0011]

In the preventive control method for transient stability of a power system according to [Claim 1] of the present invention, an object is to minimize an unbalanced AE value between generators of acceleration energy during an accident. Function that is obtained by multiplying the function by the sum of squares of the change from the output command value of the generator obtained from the economic load distribution (ELD) calculation that minimizes the power generation cost by the weighting coefficient that fluctuates according to the total load demand. Is added as a penalty term. In the preventive control method according to [claim 2] of the present invention, in the preventive control method according to claim 1, the penalty term is multiplied by a weighting coefficient so as to be variable according to the total load demand. In the preventive control method according to [claim 3] of the present invention, the constraint condition that the dynamic stability of the power system is stable is added to the preventive control method according to claim 1.

[0012]

According to the preventive control method of the power system transient stability according to [Claim 1] of the present invention, when the unstable stability is found as a result of the transient stability evaluation for a large number of assumed disturbances, the economic load distribution is performed. Since the penalty term calculated from the output command value of the generator obtained from the (ELD) calculation and the total demand of the load is added, the reliability and economical efficiency of the system operation are considered. The preventive control method according to claim 2 of the present invention is
Since the weight of the penalty term is changed, the balance between transient stability and economic efficiency can be adjusted. Further, the preventive control method according to [claim 3] of the present invention does not become unstable because the dynamic stability is taken into consideration.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall flowchart for explaining a preventive control method for transient stability of a power system according to [Claim 1] of the present invention. First, in step S1, the current operating state of the system, that is, the operating state data of the system indicating the generator output, voltage, etc. is collected. Next, in step S2, step S is performed for a large number of assumed disturbances f ₁ , f ₂ , ... F _n prepared in advance.
In 3, the failure calculation is performed and the output of each generator at the time of the accident is obtained. In step S4, based on this result, the unbalanced AE value between the generators of the acceleration energy during the accident for each expected accident is calculated using the equation (1). Then, in step S5, the transient stability is evaluated, and if it is unstable, it is registered as an unstable assumed disturbance in step S6. If the transient stability evaluation of all assumed disturbances is completed (step S7) and there is an unstable case, the output adjustment amount of the generator as the preventive control amount is calculated (step S).
8).

First, in step S9, failure calculation for an unstable presumed disturbance is performed to obtain the output of each generator at the time of the accident. Next, in step S10, the economic load distribution (ELD) calculation result performed by the self-power supply system such as the central power supply command station is input, and the value is set as the command value of the generator output from the economical operation side. Then, in step S11, the weighting factor of the penalty term for considering the economy in the objective function is calculated based on the total load demand, and in step S12, the constraint condition that the dynamic stability is stable is considered. Calculate the power swing eigenvalue and the sensitivity coefficient of the generator output to it.

Further, in step S13, steps S9-S are performed.
Input the generator output at the time of the accident, the generator output command value from the economic point of view, the weighting coefficient of the penalty term of the objective function and the eigenvalue and the sensitivity coefficient of the generator output corresponding to the The generator output that minimizes the objective function is determined by programming. Finally, the difference from the current output is calculated as the preventive control amount from equation (5) (step S14),
This result is presented to the system operator in step S15 and reflected in the operation of the actual system.

The above is the overall flow of the preventive control method. Here, the configuration of the objective function and the constraint condition used in step S13, which is the feature of the present invention, and the weighting factor of the penalty term calculated in step S11. The calculation method and the calculation method of the eigenvalue sensitivity coefficient of the generator output for considering the dynamic stability constraint obtained in step S12 will be specifically described below.

First, the objective function used for obtaining the preventive control amount by using the nonlinear programming method and the constraint condition which is an incidental condition thereof will be described. Now, as the objective function (4)
Equation, that is, the minimization of the unbalanced AE value between the generators of the acceleration energy during the accident against the unstable assumption disturbance,
Also, as a constraint condition, the power supply and demand balance is expressed (2).
Let us consider equation (3), which represents the upper and lower limits of the generator output, as the starting points. The conditions that must be added to this are as follows. Improving transient stability while also considering economic efficiency (ELD calculation plan). Dynamic stability does not become unstable by adjusting the output of the generator to improve transient stability. Can be realized by expressing the trade-off between transient stability and economic efficiency (complying with the ELD calculation plan) by the objective function of Eq. (6).

[0018]

[Equation 5] Here, E: a weighting factor for economic considerations. P _Sj : Output command value of the j-th generator obtained from the ELD calculation plan.

Next, the preventive control method according to claim 2 of the present invention, in which the second term on the right side of the equation (6) is calculated from the output command value of the ELD calculation in order to improve the transient stability. This is a penalty term for changing the actual output of the generator, and by changing the weighting coefficient E, the balance between transient stability and economic efficiency can be adjusted. For example, when the transient stability is severe, the weighting factor E is reduced to give priority to the improvement of the transient stability. On the contrary, when the transient stability is low, E can be increased to give priority to economic efficiency.

Further, the preventive control method according to [Claim 3] of the present invention will be described. In order to consider the dynamic stability condition of, the dynamic stability does not become unstable by adjusting the generator output. That is, it is only necessary to add a constraint condition that the real part of the eigenvalue corresponding to the power fluctuation is always negative. Specifically, the formula becomes (7).

[Equation 6] Here, σ _K (0): a value of the Kth power fluctuation eigenvalue before the generator adjustment. α _Kj : Sensitivity coefficient of the j-th generator with respect to the above eigenvalue. From the above, the problem was formulated into a nonlinear programming problem for finding the generator output P _INj that minimizes Eq. (6) under the constraints of _Eqs . (2), (3), and (7). The solution can be solved by a general-purpose nonlinear programming program.

Next, the weighting factor E for considering the economical efficiency
The calculation method of will be described. In general, the transient stability becomes more severe as the total demand for addition increases. This is because the generator output increases as the load increases, and normally, when the generator output increases, the acceleration energy due to an accident increases and the transient stability deteriorates. Therefore, when the total demand is large, the transient stability is considered to be severe, so that the weighting factor E is reduced to give priority to the transient stability, and conversely, when the total demand is small, the transient stability is easy, and the weighting factor E is considered to be easy. It is effective to increase. This can be realized by expressing the weighting factor E as a function of the total demand D. Consider an example of a function
It becomes formula (8).

[0022]

[Equation 7] Here, D _max : maximum total demand expected in the year. e: a fixed amount of the weighting factor E. C: A constant set in advance. Assuming that n = 3, e = 0.0 and C = 0.1 in the equation (8), the relationship between the total demand D and the weighting coefficient E is shown in FIG. In FIG. 2, the horizontal axis is the total demand value normalized by the expected maximum demand for the year.

Finally, a method of calculating the sensitivity coefficient α _Kj of the eigenvalue real part of the generator output for considering the dynamic stability constraint will be described. The system model for dynamic stability analysis uses a linear model that is linearly approximated near the operating point. The eigenvalue analysis method has been conventionally used as a method for determining the stability of this model. However, the dimension of the system is large,
Further, this method cannot be directly used for online calculation because the calculation time is too long when there are many analysis cases. On the other hand, an eigenvalue sensitivity analysis method has been proposed as a method for analyzing how the eigenvalue of a target system changes when a system parameter such as a generator output changes (for example, J.E. . Van Nees and others
“Sensitivities of Large-Loop contorol Systems”,
IEEE Trans on Automatic c
ontrol, Vol. 10, pages 308-315,
July, 1965).

According to this method, the eigenvalue calculation basically needs to be performed only once for one operating point. The change in eigenvalue with respect to the change in parameter [Δλ] is

[Outer 1] (b) Eigenvector [W] of [A] and transposed matrix [A] ^t
Eigenvector [V] of. Since it can be calculated using, the influence of the parameter can be obtained relatively easily.

FIG. 3 shows the procedure for calculating the sensitivity coefficient for the real part of the eigenvalue of the generator output using this method. In FIG. 3, steps S21 to S24 are preparations for sensitivity calculation.
That is, in step S21, the power flow calculation for determining the current power flow distribution state is performed, and the coefficient matrix [A] _{D of the system} is created in step S22 based on this power flow calculation plan. Next, in step S23, the eigenvalue calculation calculates the eigenvalues [A] _D of eigenvalues λ _Ko and K = 1 to n (n is a dimension) and eigenvectors [W _K ] and K = 1 to n corresponding to each eigenvalue, and the transposed matrix [A]
An eigenvector [V _K ] of ^t , K = 1 to n is obtained. Steps S25 to S31 are a part of the sensitivity analysis which is repeatedly calculated for each generator. That is, in steps S25 and S26, the target generator j is set, and the power flow is calculated to determine the power flow distribution when the output is changed by the unit amount ΔP _j . In step S27, the system matrix [A] ₁ after the generator output is changed is created based on the power flow calculation result in step S26.

Next, in step S28, the change [ΔA] of the coefficient matrix [A] due to the generator output change is calculated. Eigenvalues at step S29 by using the λ _{K, K} = _1~n changes predicted value _{Δλ K (Δσ K + jΔ ωK} ), calculates the K = 1 to n. If this is found, the real part is used to perform step S
At 30, the eigenvalue sensitivity α _Kj of the generator output is obtained. Finally, in step S31, it is determined whether or not the processing of all the generators is completed. If not completed, the processing returns to step S25, and the processing of steps S25 to S30 is repeated. When the processing of all generators is completed, the calculation processing of the eigenvalue sensitivity coefficient of FIG. 3 is completed.

As described above, according to the present embodiment, the electric power generated by the economic load distribution (ELD) calculation is used as the objective function that minimizes the unbalanced AE value between the generators of the acceleration energy during an accident. A function that multiplies the sum of squares of changes from the output command value of the machine by a weighting coefficient that fluctuates according to the total load demand is added as a penalty term, and a constraint condition that the dynamic stability of the power system is stable is added. Since this is added, by solving this with a non-linear programming method, it is possible to calculate the preventive control amount of transient stability in which the reliability and economic efficiency of system operation are well balanced. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.
For example, changing the calculation formula (Formula (8)) of the weighting factor E of the penalty term of the objective function.

[0028]

As described above, according to the present invention, both reliability of system operation (maintaining transient stability and dynamic stability) and economic efficiency (minimization of power generation cost) are adjusted depending on the system state. Thus, it is possible to provide a preventive control method for the transient stability of the power system, which can be considered in good balance.

[Brief description of drawings]

FIG. 1 is an overall flow chart showing an embodiment for explaining a preventive control method of power system transient stability according to the present invention.

FIG. 2 is a diagram showing an example of a method of changing a weighting factor of a penalty term in FIG.

3 is a flow chart of a procedure for calculating a sensitivity coefficient of an eigenvalue in FIG.

FIG. 4 is a flowchart for explaining a conventional preventive control method.

FIG. 5 is a flowchart for explaining a conventional preventive control method.

[Explanation of symbols]

Step S1 System state data collection unit Step S2 Expected disturbance setting unit Step S3 Failure calculation unit Step S4 AE value calculation unit Step S5 Transient stability determination unit Step S6 Unstable expected disturbance registration unit Step S7 Transient stability determination of all assumed disturbances Judgment unit for determining whether or not it has ended Step S8 Judgment unit for determining whether or not there is an unstable case in the assumption disturbance Step S9 Failure calculation section for unstable assumption disturbance Step S10 Economic load distribution (ELD) calculation result input section Step S11 Weighting factor calculation part for penalty term of objective function Step S12 Eigenvalue and eigenvalue sensitivity calculation part Step S13 Generator output calculation part by nonlinear programming Step S14 Output adjustment amount calculation part of generator as preventive control amount Step S15 System operator Control execution section by

Claims (3)

[Claims] 1. The transient stability of a power system is evaluated for preset assumed disturbances, and if there are unstable assumed disturbances, the amount of adjustment of the generator output is used as a preventive control amount using mathematical programming. In the preventive control method of transient stability calculated by the following, the change amount from the output command value of the generator obtained by the economic load distribution calculation to the objective function that minimizes the unbalanced portion of the acceleration energy during the generator between accidents The preventive control method for the transient stability of the power system, wherein the sum of squares of is added as a penalty term. 2. The power system transient stability control method according to claim 1, wherein the penalty term is multiplied by a weighting coefficient to make it variable according to the total load demand. Preventive control method. 3. The preventive control method for power system transient stability according to claim 1, wherein a constraint condition that the dynamic stability of the power system is stable is added. Method.