JPH0530221B2 - - 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 3 is a system diagram showing a general power system;
The figure is a vector diagram showing the relationship between voltage and current in FIG. 3. In Fig. 3, 6 is the generator G, and 11 is the system reactance.
X _e ), 12 is an infinite generatrix.

That is, when looking at the power system side from the generator 6 side, it can be expressed by the infinite bus 12 and the system reactor 11 as shown in FIG. At this time, the stability of the generator 6 is affected by its degree of connection with the power system. In other words, assuming that the power system is sufficiently large and stable, the generator 6
If is tightly coupled to this power system, that is, if the reactance X _e is small, the stability will be good;
On the other hand, if they are loosely coupled, that is, if the reactance X _e is large, the stability will be poor. Therefore,
At each power plant, if the equivalent voltage (system voltage) V _B of the infinite bus 12 and the equivalent reactance X _e of the reactor 11 are estimated, and the stability of the generator is adaptively controlled according to system changes, the individual The stability of the generator and, by extension, the stability of the entire power system can be improved. 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,
It is necessary to know the voltage V _B and reactance X _e of the power system, but since the actual power system has many generators connected to a complex power grid,
Determining these values is not always easy. For example, if the relationship between the current and voltage in Figure 3 is expressed as a vector, it will look like Figure 4. In Figure 4, triangles OAB and OAC are uniquely determined, whereas point D is on line AB. Since it may exist anywhere on the line including the extension line, it cannot be determined uniquely. In other words, if quantities that can be easily measured at the generator end are used, the system voltage V _B and the system reactance X _e become indefinite, cannot be uniquely determined, and cannot be estimated. In addition, in Fig. 4,
V _I is the generator internal voltage, V is the generator terminal voltage, I
is the generator current, δ is the phase angle between voltages V _I and V _B , ω _i
represents the angular frequency of the voltage V _I , and ω _b represents the angular frequency of the voltage V _B , respectively.

For this reason, the applicant has proposed the following method. To explain this simply, a generator operating under the first condition is intentionally moved to the second operation state for a predetermined period of time, and a predetermined operation information is obtained from various operating information obtained during the first and second operation. This is a method of calculating and estimating the result.

[Problem that the invention seeks to solve]

However, the above method requires operations to temporarily change the operating voltage and power of the generator.
This method has the problem of being complicated.

[Means for solving problems]

The generator current and voltage are monitored, and operating information regarding the generator, such as generator terminal voltage, current, generator output, and reactive power, is extracted at two points in time during the transient oscillation period of the generator, and a predetermined value is calculated for the generator. By performing the calculations, the equivalent voltage V _B and equivalent reactance X _e can be estimated without the need for special operations.

[Effect]

If the vector diagram of FIG. 4 is rewritten by focusing on the active power P and reactive power Q of the generator, it will become as shown in FIG. 5. The operation will be explained below with reference to FIG.

As is clear from Figure 5, OB ² = OD ² - DB ² = OC ² - CB ² , so OD = V _B I, DB = Q - I ² X _e OC = VI, CB = Q are substituted. Then, V _B ² I ² −(Q−I ² X _e ) ² =V ² I ² −Q ² ……(1) holds true.

Now, let the values of I, V, and Q at different points in time be respectively I ₁ , I ₂ , V ₁ , V ₂ , Q ₁ , and Q ₂ ,
Assuming that V _B and X _e remain unchanged during this period, V _B ² I ₁ ² − (Q ₁ − I ₁ ² X _e ) ² = V ₁ ² I ₁ ^{2 −} Q ₁ ² ……(2) V _B ² I ₂ ² − (Q ₂ − I ₂ ² X _e ) ² = V ₂ ² I ₂ ² − Q ₂ ² ...(3) is derived. Expanding the parentheses of equations (2) and (3) and dividing both sides by I ₁ ² and I ₂ ² , respectively, we get V _B ² + 2Q ₁ X _e −I ₁ ² X _e ² = V ₁ ² ……( ₂ ⁾ _{′ V B} ^{2 + 2Q} ₂ ^X _e ^−I _{2 2} )X _e ² −2(Q ₂ −Q ₁ )X _e +(V ₂ ² −V ₁ ² )=0 (4) A quadratic equation regarding X _e is obtained.

_Therefore ^{, by} _{solving this , X e becomes :} ^_ _{_} ^_ _{_} ^_
)(V ₂ ² −V ₁ ² )/I ₂ ² −I ₁ ² ……(5). If X _e is found, V _B is
From equation (3)′, it can be determined as V _B =√V ₂ ² −2Q ₂ X _e +I ₂ ² X _e ² ……(6).

Here, we will consider the conditions for estimating X _e and V _B from equations (5) and (6).

As is clear from equation (5), when the denominator (I ₂ ² − _{I 1} ² ) is small, (Q ₂ −Q ₁ ), (V ₂ ² −V ₁ ² ) becomes Each quantity is also small, and both the denominator and numerator of equation (5) are small values, and errors due to measurement noise of Q, V, and I cause errors in the estimated values, so the value of I ₂ ² − I ₁ ² , that is, I ₂ The estimation is performed in a region where the difference in −I ₁ is larger than a predetermined value, in other words, in a transient oscillation state rather than in a steady state. This is the first condition. Also, if (I ₂ ² − I ₁ ² ) (V ₂ ² − V ₁ ² )>0, the radical in equation (5) may become a negative value and X _e cannot be calculated. Therefore, only when (I ₂ ² - I ₁ ² ) (V ₂ ² - _{V 1} ² ) < 0, that is, when either current I or voltage V is on a decreasing trend and the other is on an increasing trend. In addition, since the reactance X _e is normally inductive, X _e >0, and therefore the (+) of the (±) negative sign in equation (5)
limited to only. This is the second condition. _In ^this _{way , X e becomes} ^_ _{_ _} ^_ _{_} ^_ _{_} ^_
)(V ₂ ² −V ₁ ² )/I ₂ ² −I ₁ ² ……(5)′.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. In the same figure, 1 is generator current I, voltage V
and a detection unit that detects generator output (active power) P and reactive power Q from these; 2 a sampling unit that samples these quantities; 3 a memory unit that stores these sampling values; 4 a determination unit; 5 is an arithmetic unit, and 6 is a generator.

In other words, in order to eliminate phase errors during each measurement, the detection unit 1 measures the instantaneous currents i _a , i _b , i _c and the instantaneous voltages v _a , v _b , v _c of the three phases, and performs various operations without phase errors. Information (P, Q, V, I) is detected, sampled by the sampling unit 2 at predetermined time intervals τ, and sequentially stored in the memory unit 3. In the determination section 4,
Based on the previous current and voltage values, current values I ₁ and V ₁ , and I ₂ and V ₂ , it is determined whether the first and second conditions described above are satisfied, and |I ₂ −I ₁ | > ε (I ₂ ² − I ₁ ² ) (V ₂ ² − V ₁ ² ) < 0 When the condition is satisfied, the calculation unit 5 calculates the
Compute equations (5)' and (6) to find X _e and V _B. Note that ε is a set value.

By the way, when X _e and V _B are estimated moment by moment, these values usually fluctuate, so it is necessary to smooth them using a predetermined filter or the like. However, for example, the value _{of X e estimated} at a certain time point k
(k) is the value of X _e at the next k+1 time point X _e (k
+1) to estimate X _e (k+1) = X _e (k) + α [V ₂ ² (k) − V ₁ ² (k)
−2(Q ₂ (k)−Q ₁ (k))X _e (k)+(I ₂ ² (k)−
I ₁ ² (k))X _e ² (k)] ...(7) V _B (k+1)=(V ₂ ² (k)−2Q ₂ (k ₎
1 _{) +} ^I ₂ ² ( _k ⁾ in,
X _e and V _B can be found. Note that the value in brackets [ ] in equation (7) is the calculated value on the left side of equation (4) above,
Further, the value in parentheses in equation (8) is the calculated value on the right side of equation (6) above, and α is the filter gain.

FIG. 2 shows an example of a method for estimating the system reactance value based on the above principle.
Here, 7 is a delay device, 8 is a coefficient multiplied by α, and 9 is a
This is an arithmetic unit that performs the calculations in [ ] in equation (7), and with these, the current X _e can be estimated moment by moment from the past X _e . In this way, X _e ,
Since V _B can be determined, there is an advantage that not only a special filter is not required, but also the area limitation as described above is not required. Note that the gain α in equation (7) can also be changed from time to time depending on the operating state.

In the above, the active power P of the generator operation information is not used, but if this is used, for example, instead of the measured current value I, The amount can be used.

〔Effect of the invention〕

According to this invention, it is possible to estimate the equivalent voltage and equivalent reactance of the system as seen from the generator side by using the period of transient oscillation of the generator state that occurs due to system operation including the generator or a system fault. Therefore, by using this, it is possible to adaptively control the generator stability with the optimum gain that suits the system situation in each case.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of this invention.
Fig. 2 is a block diagram showing another embodiment of the system reactance estimation method, Fig. 3 is a system diagram showing a general power system, Fig. 4 is a vector diagram showing the relationship between current and voltage in Fig. 3, FIG. 5 is a vector diagram showing the relationship between power and reactive power at the generator terminals. Description of symbols, 1...detection section, 2...sampling section, 3...memory section, 4...judgment section, 5...calculation section, 6...generator, 7...delay unit, 8...coefficient unit , 9... Arithmetic unit, 11... System reactance,
12...Infinity bus.

Claims (1)

[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 including a generator is represented by an infinite bus and a reactor, which sampled with a period of
When the difference between the current value and the previous value of the current is larger than a predetermined value, and one of the current and voltage values is decreasing and the other is increasing, the generator current and voltage that can be measured on the generator side, A method for estimating voltage and reactance in a power system, comprising performing predetermined calculations from current and previous values of generator output and reactive power to estimate an equivalent voltage of the infinite bus and an equivalent reactance of the reactor.