JPH06153397A - Voltage stability monitor - Google Patents

Abstract

PURPOSE:To allow quick and easy generation of PV curve or voltage control strategy by employing such voltage value as the sign of power flow Jacobian matrix is different from that of voltage increasing solution as an initial value for determining a voltage decreasing solution. CONSTITUTION:When a PV curve section generates a PV curve, power flow calculation is carried out while designating effective and reactive powers such that total demand increases starting from current state for the curve on the increasing side where the solution of previous power flow calculation is employed as an initial value. Demand is then increased and if power flow calculation does not converge even if demand is increased by increasing magnification finely, a transition is made to the curve on the decreasing side with that point as a stability limit point. Power flow calculation is carried out by setting demand in decreasing direction from the stability limit point. At first, a decreasing solution is determined at the stability limit point using a preserved voltage value as an initial value. This constitution allows quick and easy generation of PV curve because the sign of ¦J¦ is different from that of an increasing solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage stability monitoring device for creating a PV curve and monitoring the voltage stability, and more particularly to creating a PV curve and determining a voltage control strategy in online monitoring quickly and easily. The present invention relates to a voltage stability monitoring device suitable for

[0002]

2. Description of the Related Art In order to monitor the voltage stability of an electric power system, it is important to create a PV curve showing how the bus voltage changes in response to an increase in electric power demand and obtain a stability limit point. Is. As a method of creating a PV curve, for example, as described in JP-A-3-21524, a voltage increase solution and a voltage decrease solution are calculated by power flow calculation while virtually increasing the total power demand from the current state. There is a way to go. In addition, there is a method of setting the initial value of the power flow calculation for obtaining the lower voltage solution by reducing the magnitude of the voltage and the phase angle based on the higher voltage solution.

The initial value for obtaining the lower voltage solution is, as discussed in PE-88-114 of the Institute of Electrical Engineers of Japan, Technical Report of the Institute of Electrical Engineers of Japan, the sign of the determinant of the Jacobian tidal current is the higher voltage solution and the lower voltage solution There is also a method of focusing on the difference and finding a voltage value having a sign different from that of the higher voltage solution and using it as an initial value.

[0004]

In the above-mentioned prior art, there has been a method of, for example, reducing the magnitude of the voltage and the phase angle as the initial value for obtaining the lower voltage solution. It was not clear whether a lower voltage solution could be obtained, and trial and error was sometimes repeated. The method that focuses on the sign of the tidal current Jacobian determinant can almost certainly obtain a lower voltage solution, but it requires special processing to obtain a voltage value that has a different sign from the higher voltage solution, which requires calculation time. was there.

Further, even when obtaining a high voltage solution, it takes an extra calculation time because there is no effective method for quickly determining that the power flow calculation does not converge when the power demand exceeding the stability limit point is specified. There was a problem.

An object of the present invention is to provide a method for obtaining an initial value that can reliably obtain a low voltage solution in a short calculation time, and a method for quickly determining that the power flow calculation does not converge.
An object of the present invention is to provide a voltage stability monitoring device capable of easily creating a V curve and a voltage control measure at high speed.

[0007]

In order to achieve the above object, the present invention provides an initial value for obtaining a lower voltage solution,
Focusing on the sign of the determinant of the Jacobian tidal current, the voltage value that has a different sign from the higher voltage solution is used as the initial value. Since such a voltage value is obtained in the process of power flow calculation when the power demand exceeding the stability limit point is specified, the value at that time is saved and used as it is.

Also, when calculating the power flow solution for increasing the voltage, pay attention to the sign of the determinant of the Jacobian power flow, and if the sign is reversed during the calculation, immediately determine that the power flow calculation does not converge. did.

Further, by providing a means for setting the operation policy of the voltage control device and creating a PV curve according to the setting, it is possible to evaluate how much the voltage stability is improved. The operation policy is set based on the PV curve in the current state or the predicted state.

[0010]

The lower voltage solution can be almost certainly obtained by using as the initial value a voltage value whose sign of the determinant of the higher current solution and that of the Jacobian of the power flow are different. Therefore, the calculation time can be shortened without repeating trial and error. In addition, such a voltage value is often obtained in the middle of the power flow calculation when the power demand that exceeds the stability limit is specified, and by using it as it is, the initial value can be easily set without any special processing. Can be obtained. Since the power flow calculation that specifies the power demand exceeding the stability limit point should be performed at least once to obtain the stability limit point, the voltage value obtained at that time may be used.

When obtaining a higher voltage solution, the sign of the determinant of the power flow Jacobian usually does not change if the power flow calculation converges. On the contrary, if the sign changes, it can be determined that the convergence does not occur immediately. When the power demand exceeding the stability limit is specified, the power flow calculation does not converge, but by determining it immediately by the change of the sign of the determinant of the Jacobian of the power flow, it is possible to avoid unnecessary repeated calculations. You can save time.

When the voltage stability needs to be improved, the operating strategy of the voltage control device is set and a PV curve is created to examine how much the voltage stability is improved. Since the PV curve can be created at high speed by this method, it becomes possible to examine the voltage stability of a large number of operating measures prepared in advance. The control policy is P in the present state or the predicted state.
An effective control strategy can be obtained by finding a portion having weak voltage stability based on the V curve and controlling the portion.

[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 a block diagram when the present invention is applied to an online monitoring system of a power system.

First, the data input unit 11 takes in values of voltage, active power, reactive power, etc., which are sent from a power plant, a substation or the like in the power system, every moment. The state estimation unit 12 determines the most probable state quantity at the present time point based on these data. A weighted least squares method, for example, is used as the state estimation method. The PV curve creation unit 13 creates a PV curve by performing power flow calculation while appropriately setting the power demand, starting from the current state quantity, and displaying the PV curve on the monitoring display 15. The voltage stability index calculation unit 14 calculates a stability index such as an active power margin based on the PV curve, and similarly, the monitoring display 1
5 Display on top. Here, the active power margin is the difference between the power demand in the present state and the power demand at the stability limit point.

Of the above, the method by which the PV curve creating unit 13 creates a PV curve will be described in detail below.

The PV curve is basically created by calculating the power flow and calculating the voltage value of the bus while setting various power demands. Here, the power flow calculation is to obtain a voltage that satisfies the power flow equation shown in Formula 1.

[0018]

F (x) = 0 where x is a variable vector in which bus voltage at each point of the system is arranged, and f (x) is active power, reactive power at each point of the system, or a mismatch of voltage magnitudes. It is a function to be expressed, and specifically consists of the following three.

[0019]

[Number 2] _{P i (x) -P i =} 0

[0020]

[Number 3] _{Q i (x) -Q i =} 0

[0021]

V _i (x) −V _i = 0 where P _i (x) is the active power at the load bus or generator bus, Q _i (x) is the reactive power at the load bus, and V _i ( x) is a function that represents the magnitude of the voltage at the generator bus. These functions are quadratic algebraic equations when the complex voltage values are expressed in rectangular coordinates. P _i , Q _i , and V _i are designated values of active power, reactive power, and voltage magnitude, respectively.

The Newton method is generally used as the solution. The Newton method is a method for solving a non-linear algebraic equation, and the solution is obtained by solving a linear equation using the Jacobian matrix J as shown in Equation 5.

[0023]

X (k + 1) = x (k) −J ⁻¹ (x (k)) f (x (k)) where x (k) is the value of the variable vector x at step k. is there. The Jacobian matrix is a matrix in which partial differentiation of f (x) with elements of x is arranged. Hereinafter, the Jacobian matrix of the power flow equation is called the power flow Jacobian.

FIG. 2 shows an example of a PV curve, in which the horizontal axis represents the total power demand P and the vertical axis represents the voltage magnitude V of a certain bus. The procedure is as follows. First, the upper curve (point a → b →
c, hereinafter referred to as a high-side curve), and then a lower curve (points d → e → f, hereinafter referred to as a low-side curve).

The details of the procedure will be described below with reference to the flow of FIG.

In the high-side curve, starting from point a in the current state, P _i and Q _i of equations 2 and 3 are designated so as to increase the total power demand P (step 101), and the power flow is calculated. (Step 103). The method of designating P _i and Q _i is, for example,
Increase all at the same rate. Similarly, the reactive power and the power generated by each generator are also uniform. As a method of increasing the total power demand, for example, assuming that the current state is 1, 1.1 times,
1.2 times, and so on.

The solution of the previous power flow calculation is used as the initial value of the power flow calculation. For example, the value of the current state is used as the initial value for the 1.1 times calculation, and the calculation result at the 1.1 times is used as the initial value for the 1.2 times calculation. In this way, by using the solution of the previous calculation as the initial value, the calculation can be started at a point close to the solution, so compared to the case of starting from the flat start value (one in which all voltages are 1), for example, There is an effect that the number of iterations of the Newton method is small. In particular, the effect is remarkable near the stability limit point.

As the power demand increases, the stability limit is exceeded at some point. When the stability limit is exceeded, there is no solution for the power flow equation and the power flow calculation does not converge. In that case, decrease the increment of the magnification and perform the calculation again. For example,
If it converges at 1.5 times and does not converge at 1.6 times, then it increases to 1.51 times, 1.52 times, and so on. If the power flow does not converge even if the power factor is increased further (for example, in increments of 0.001) and the power demand is further increased (step 102), that point is set as the stability limit point c and set to the lower curve. move on.

In the power flow calculation (step 103), first,
After updating x according to equation 5 (step 104), the sign | J | of the current Jacobian is obtained (step 105). If | J | is reversed, it is immediately determined that the power flow calculation does not converge (step 106). When the power flow calculation does not converge, a predetermined number of times of repetition such as 10 times or 20 times is usually calculated, but if this method is used, the number of times of repetition can be reduced and the calculation time can be shortened. Note that the calculation of | J | can be easily obtained by using the result of LU decomposition when solving the linear equation of Equation 5 and calculating the product of the diagonal elements of the LU decomposed matrix. Therefore, the calculation time required for calculating | J | is very short.

When the mismatch in equations (2) to (4) becomes smaller than a specified value, it is determined that the convergence has occurred (step 10
7) Go to the next point. If it does not converge, step 104
Return to. If the sign of | J | is reversed, the power flow calculation is aborted, and the voltage value at that time is saved for use later in obtaining the lower curve (step 10).
8). Next, the lower curve is calculated. The lower curve sets the power demand in the direction of decreasing the power demand from the stability limit point.
(Step 111), the power flow is calculated (Step 113).
First, a lower solution at the stability limit point d is obtained. At the strict stability limit point, the solution of the tidal current equation becomes a root, so there is no lower solution, but since the point c obtained by this method is an approximate stability limit point, there is usually a lower solution. As the initial value, the voltage value saved in step 108 is used. This voltage value has a higher sign of | J | and a sign different from that of the solution, and thus tends to converge to a lower solution. In this way, by using the voltage value generated in the previous calculation process as it is as the initial value for the lower solution, it is not necessary to perform special processing for obtaining the initial value for the lower solution, which shortens the calculation time. Is effective. Further, since it is possible to almost certainly obtain a lower solution, it is not necessary to repeat trial and error.

When a lower solution is obtained at the point d, the power demand is reduced contrary to the high side curve (step 111).
As the initial value, the solution of the previous power flow calculation is used.
Once a lower solution is obtained, then this method can be used to obtain a lower solution. The procedure of the power flow calculation (step 113) is almost the same as the case of the high side curve, but when obtaining a lower solution
Even if the sign of | J | is inverted, it may converge, so the procedure corresponding to step 106 is omitted. The calculation ends when the power demand returns to the current state (step 11).
2).

In the example described above, the operation of the voltage control device was not considered before obtaining the PV curve, but if it is taken into consideration, the power demand and the magnitude of the voltage, the value of the phase adjusting equipment, etc. Basically, the above method can be applied as it is by changing the above. Further, even in the case of an accident case such as one line stoppage of the transmission line, the present invention can be applied in exactly the same way only by changing the impedance of the system.

Next, an example in which the present invention is applied to the selection of voltage control measures will be described with reference to FIG. When the voltage stability is not sufficient in the present state or the future predicted state, it is necessary to improve the stability by voltage control. Voltage control measures include turning on a power capacitor, changing the SVC set value, changing the set value of the transformer LTC, and changing the set value of the generator voltage. The voltage control policy setting unit 16 sets an operation policy of the voltage control device for that purpose. The PV curve creation unit 13 creates a PV curve based on the set conditions, and the voltage stability index calculation unit 14 calculates the voltage stability index to check how effective the set control strategy is. it can. For example, if a large number of control measures are prepared in advance and one by one is selected and investigated, the most effective control measure can be selected. In particular, since the PV curve can be created at high speed by using the method of the present invention, the optimum one can be easily selected from a large number of measures.

If a sufficient improvement in voltage stability cannot be obtained by the set control policy, it is possible to increase the capacity of the power capacitor to be turned on, the amount of change in the SVC set value, or the like. If the voltage control policy setting unit 16 changes the setting of the operation amount of the voltage control device based on the calculation result of the voltage stability index calculation unit 14, the optimum control policy can be automatically set.

Further, it is generally effective to apply the voltage control to a portion of the power system where the voltage stability is low. For the portion with low voltage stability, for example, a bus bar having a low voltage on the lower curve of the PV curve may be selected. Voltage control policy setting unit 1
If 6 sets a control policy by selecting a portion with low voltage stability based on the PV curve created by the PV curve creation unit 13, an effective control policy can be automatically selected.

The method for automatically setting the voltage control policy has been described above. However, of course, a method in which an operator interactively designates and a PV curve or a voltage stability index is calculated according to the method may be used. On the contrary, an automatic control method in which all control measures are automatically set and the optimum one is executed is also conceivable. Since the PV curve can be created at high speed in the method of the present invention, it can be sufficiently applied to automatic control online.

[0037]

According to the present invention, when a PV curve required for voltage stability monitoring is created, an initial value for surely obtaining a low voltage solution can be obtained easily and at high speed. In addition, because it is easy to determine when the power flow calculation does not converge,
The calculation time can be shortened. Further, by applying it to the selection of the voltage control measure, an effective voltage control measure can be obtained quickly and easily.

[Brief description of drawings]

FIG. 1 is a block diagram when the present invention is applied to an online monitoring system of a power system.

FIG. 2 is a characteristic diagram showing an example of a PV curve.

FIG. 3 is a flowchart showing a procedure for creating a PV curve.

FIG. 4 is a block diagram when the present invention is applied to selection of a voltage control measure.

[Explanation of symbols]

13 ... PV curve creation unit, 14 ... Voltage stability index calculation unit,
16 ... Voltage control policy setting unit.

Claims (5)

[Claims] 1. A PV curve creating means for creating a PV curve representing the relationship between active power and voltage magnitude while obtaining a voltage-increasing solution and a voltage-lowering solution by power flow calculation, and voltage stability based on the PV curve. Voltage stability index calculating means for calculating a power index, and the PV curve creating means uses the determinant of the flow current Jacobian of the determinant of the power flow Jacobian as an initial value when obtaining a lower voltage solution. A voltage stability monitoring device characterized in that a voltage value different from a sign is used, and the voltage value obtained in the past process of power flow calculation is used as it is. 2. The voltage stability monitoring device according to claim 1, wherein a voltage value obtained in a process of power flow calculation in which a power demand exceeding a voltage stability limit is designated is used as an initial value for obtaining the lower voltage solution. . 3. A PV curve creating means for creating a PV curve representing the relationship between active power and voltage magnitude while obtaining a voltage-increasing solution and a voltage-lowering solution by power flow calculation, and voltage stability based on the PV curve. Voltage stability index calculating means for calculating a power index, and the PV curve creating means determines that the power flow calculation does not converge on the basis of a change in the sign of the determinant of the flow Jacobian. Stability monitoring device. 4. A voltage control policy setting means for setting an operation policy of a voltage control device according to claim 1 or 3, wherein the PV curve creation means creates a PV curve in accordance with the conditions set by the voltage control policy setting means. Voltage stability monitoring device. 5. The voltage stability monitoring device according to claim 4, wherein the voltage control policy setting means sets an operation policy of the voltage control device based on a PV curve.