JPH0530219B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention provides a method for estimating the equivalent voltage and equivalent reactance of a power system to which a generator is connected, in particular, it is possible to obtain these only from operating information of the generator. This paper relates to methods for estimating voltage and reactance of power systems.

[Conventional technology]

Figure 4 is a system diagram showing a general power system, Figure 5
The figure is a vector diagram showing the relationship between voltage and current in FIG. 4. In addition, in FIG. 4, 1, G is a generator, 2, X _e is a system reactor, and 3 is an infinite bus.

That is, when looking at the power system side from the generator 1 side, it can be expressed by the infinite bus 3 and the system reactor 2 as shown in FIG. At this time,
The stability of the generator 1 is affected by its degree of coupling with the power system. In other words, assuming that the power system is sufficiently large and stable, if the generator 1 is tightly coupled to this power system, that is, if the reactance X _e is small, the stability will be good; That is, the reactance X _e
The larger the value, the worse the stability. Therefore, in each power plant, the equivalent voltage (system voltage) V _B of infinite bus 3 and the equivalent reactance _X e of reactor 2
By estimating this and adaptively controlling the stability of generators in response to system changes, it is possible to improve the stability of individual generators and, ultimately, the stability of the entire power system. Note that such adaptive control is performed by a so-called generator multivariable adaptive control device (TAGEC).

In this way, in order to control stability,
Although it is necessary to know the voltage and reactance of the power system, it is not always easy to obtain these values because in actual power systems, many generators are connected to a complex power grid network.

For example, since the state of an electric power system is uniquely determined by the power flow of each system, the voltage output of each power plant, the load flow, etc., it is possible to use this, but it is possible to Gathering information is quite difficult to realize due to equipment, cost, and technical issues such as delays in information transmission.

On the other hand, in Fig. 4, the generator internal voltage is V _I ,
Assuming that the generator terminal voltage is V _G , the generator current is I, the equivalent voltage of the system is V _B , and the reactance of the system is X _e , the relationship between these voltages and currents can be expressed as shown in FIG. In addition, in FIG. 5, δ is the phase difference angle between voltages V _I and V _B , ω _i is the angular frequency of voltage V _I ,
ω _b is the angular frequency of voltage V _B.

[Problem that the invention seeks to solve]

As is clear from Figure 5, the triangle
OAB and OAC are uniquely determined, but point D is on the line AB
Since it may exist anywhere on the line including the extension line above, it is not uniquely defined. For this reason, a method of determining the phase difference angle δ may be considered, such as by integrating the difference between the angular frequencies ω _i and ω _b , but ω _i is measurable, whereas ω _b is not. Since the integrating circuit is affected by drift, etc., it is not possible to accurately determine point D.

[Means for solving problems]

To provide an estimation method capable of estimating the voltage and reactor of a power system to which a generator is connected using a simple method and with high accuracy from various quantities (operating information) that can be detected on the generator side. .

[Effect]

In estimating the equivalent voltage of the infinite bus and the equivalent reactance of the reactor when the power system to which the generator is connected is expressed by an infinite bus and a reactor, the generator operated under the first condition is After intentionally changing the conditions and moving to the second operating condition, the operation is performed to return to the first condition again,
When it can be considered that the second state has returned to the first state, the equivalent voltage and equivalent reactance are determined from the operating information regarding the generator such as the generator terminal voltage, current, generator output, and reactive power obtained during that time. Estimate.

[Embodiments of the invention]

FIG. 1 is a vector diagram showing changes in the operating state of a generator for explaining an embodiment of the present invention.

In this embodiment, a generator operating in one state is intentionally moved to another state for a short period of time, and then returned to its original operating state. FIG. 1 shows the state of change at this time, where A shows the case where the original operating state has returned, and B shows the case where the original operating state has not returned. In other words, returning to the original operating state as shown in A of the same figure means that there is no change in the grid, and therefore the equivalent voltage and equivalent reactance have not changed either, as shown in B of the same figure. The fact that it did not return to its original state can be considered to be due to a change in the system. Therefore, in the present invention, the operating conditions are changed as described above, it is confirmed that the original state has been returned again, and the voltage and reactance are estimated based on this confirmation. Strictly speaking, even if the generator side returns to its original state, it cannot necessarily be said that there has been no change in the grid side.In other words, as point D shown in Figure 5 above is on line AB and its extension Although it is possible for the system to change in this way, it is highly unlikely that the system will change in this way in a short period of time, so in reality it can be said that there is almost no problem. Furthermore, the condition for determining whether the original operating state has returned is, for example, when I ₁ I ₃ or Q ₁ Q ₃ is satisfied with V _G1 = V _G3 P ₁ = P ₃ as the operating condition. In addition, V _G is the generator terminal voltage, P is the generator output (active power), I is the generator current, and Q is the reactive power. Operating conditions (P, V _G )
"3" represents a state in which the operating conditions have been changed, and "3" represents a state in which the operating conditions have been returned to their original state, and the meanings of these symbols are the same in FIG.

In this way, if it is confirmed that the original state has been returned, as is clear from Figure 2A, two pieces of information regarding the generator operating status have been obtained, and in this invention, based on these pieces of information, By performing the following calculations, the system voltage V _B and the system reactance X _e are determined. Incidentally, in explaining this calculation process, reference is made to FIG. 2. This Figure 2 is a vector diagram that is a modification of Figure 1 A, and the generator voltage ends A ₁ and A ₂ in the figure are made to coincide, and the line segments A ₁ B ₁ and A ₂ B ₂ are drawn on the same line. It is something that However, the magnitude and position of each voltage and current in FIG. 2 are drawn completely unrelated to those in FIG. 1A.

When transformed in this way, the line segment O ₁ D ₁ in Figure 2 and
Since O ₂ D ₂ is expressed by the reciprocal ratio of each current, (V _G1 /I ₁ ) ² − (Q ₁ /I ₁ ² ) ² + (X _e −Q ₁ /I ₁ ² ) ² = ( V _B /I ₁ ) ² ...(1) (V _G2 /I ₂ ) ² − (Q ₂ /I ₂ ² ) ² + (Q ₂ /I ₂ ² −X _e ) ² = (V _B /I ₂ ) ² ……(2) The following relationship holds true. Here, α=(I ₂ /I ₁ ) ² , a=1−α b=Q ₁ /I ₁ ² −αQ ₂ /I ₂ ² c=(V _G1 /I ₁ ² −α V _G2 / I ₂ ) ² , we get aX _e ² + 2bX _e + C=0 ...(3) from equations (1) and (2), so in the end, X _e becomes X _e = b±√ ² −/a ...(4) can be obtained as follows. In other words, becomes. On the other hand, from equation (1), V _B is It is required as follows. Note that since the power system is usually inductive, the reactance X _e needs to satisfy X _e >0. Therefore, the value in the square root symbol expressed as in equation (5) is positive, and (5)
The relationship between the reactive powers Q ₁ , Q ₂ and the generator currents I ₁ , I ₂ will be chosen such that the entire equation is positive.

By the way, if the grid characteristics are estimated continuously as described above, it will cause a disturbance to the generator operation, so in this invention, the above method is carried out only when a change in the grid side is confirmed, thereby eliminating the disturbance. shall be kept to a minimum. In addition, the presence or absence of systematic changes is
The determination is made based on whether the operating information on the generator side has changed while the operation on the generator side has not changed. For example, when operating with constant voltage V _G and output P, that is, when the relationship V _G1 = V _G2 P ₁ = P ₂ is established, when reactive power Q or generator current I changes, that is, when When Q ₁ /Q ₂ I ₁ /I ₂ holds true, it is determined that a systematic change has occurred. The operating situation at this time is, for example, as shown in Figure 3, and when the currents I ₁ , I ₂ or the reactive powers Q ₁ , Q ₂ shown here satisfy the relationships described above, a change has occurred on the grid side. As such, X _e and V _B are estimated.

〔Effect of the invention〕

According to this invention, it is possible to relatively easily and accurately grasp the voltage and reactance of the complex power system to which the generator is connected from information (operating information) only about the generator. This provides the advantage of being able to improve the stability of the power system.

Note that the present invention can be used not only for generator stability control as described above, but also for general control of equipment (for example, a reactive power control device) connected to an electric power system.

[Brief explanation of the drawing]

FIG. 1 is for explaining an embodiment of this invention.
A vector diagram showing changes in the operating status of the generator,
Figure 2 is a modified vector diagram of Figure 1 A, Figure 3 is a vector diagram showing the relationship between voltage and current when the generator voltage and generator output are constant, and Figure 4 is a general power system. The system diagram shown in FIG. 5 is a vector diagram showing the relationship between voltage and current in FIG. 4. Symbol explanation, 1, G... Generator, 2, X _e ... Equivalent reactor, 3... Infinite bus, V _G , V _G1 ~
V _G3 ... Generator terminal voltage, I, I ₁ - _{I 3} ... Generator current, P ₁ , P ₂ ... Generator output, Q ₁ , Q ₂ ... Reactive power, V _B ... Infinite bus Voltage.

Claims (1)

[Scope of Claims] 1. An estimation method for estimating the equivalent voltage of the infinite bus and the equivalent reactance of the reactor when a power system to which a generator is connected is represented by an infinite bus and a reactor, comprising: After a generator that is being operated under the first condition is intentionally changed for a predetermined period of time and transferred to the second operating condition, the generator is operated to return to the first condition again, and the generator is returned from the second condition. When it can be considered that the first state has returned, the equivalent voltage and the equivalent reactance are estimated from operating information regarding the generator such as the generator terminal voltage, current, generator output, and reactive power obtained during that time. Features a method for estimating voltage and reactance of power systems. 2. In the method for estimating the voltage and reactance of a power system according to claim 1, it is determined whether or not there is a change in operating information regarding the generator within a time period in which the operating state of the generator can be considered constant. A method for estimating voltage and reactance of a power system, comprising monitoring and estimating the equivalent voltage and equivalent reactance only when a change is deemed to have occurred.