JP2599744B2 - Power system stabilizer - Google Patents

Description

The present invention relates to a power supply for preventing a plurality of generator groups constituting a power supply system from becoming transiently unstable due to a power line accident or the like. The present invention relates to a system stabilizer.

[Conventional technology]

FIG. 5 shows a paper, for example, a presentation paper of the 1983 IEEJ National Convention.
2 is a system model for determining a stabilization control amount of the conventional power system stabilizing device shown in FIG. 2, wherein 1A to 1N are generator groups constituting a power system to be controlled, and 2 is a generator group 1A This is the main system supplied with power from ~ 1N.

Next, the operation will be described. The electrical outputs of the generator groups 1A to 1N are sampled at intervals of Δt from before the occurrence of the accident to after the occurrence, and the angular velocity ω is obtained by integrating them. Angular velocity ω at the present time t ₀ , t ₁ before time ₁ , t ₂ before time ₂
By applying the Lagrange interpolation method to the three data (t ₀ ), ω (t ₁ ), and ω (t ₂ ), the predicted value of the angular velocity ω (t) at the future time point t is given by the following equation.

ω (t) = ω (t ₂ ) + α ₁ (t−t ₂ ) + α ₂ (t−t ₁ )
(T−t ₂ ) (1) where α ₁ = {ω (t ₂ ) −ω (t ₁ )} / (t ₂ −t ₁ ) α ₀ = {ω (t ₁ ) −ω (t ₀ ) ｝ / (T ₁ −t ₀ ) α ₂ = (α ₁ −α ₀ ) / (t ₂ −t ₀ ) The equation for estimating the generator phase angle δ is the following equation by integrating the equation (1).

δ (t) = δ (t ₀ ) + ω (t ₂ ) (t−t ₀ ) + α ₁ ｛(t ²
− ▲ t ² ₀ ▼) / 2−t ₂ (t−t ₀ )｝ + α ₂ ｛(t ³ + ▲ t ² ₀ ▼) / 3− (t ₁ + t ₂ ) (t ² − ▲ t
² ₀ ▼) / 2 + t ₁ t ₂ (t−t ₀ )｝ (2) The generator phase angle δ (t) given by equation (2) shows a divergence tendency during the predicted time of 0.2 to 0.3 s, If it is equal to or more than a preset threshold value δlimit, it is determined that the step-out (unstable) occurs. In this case, the stabilization control amount (generator cutoff amount) is determined by the method described below, and the control for that amount is performed.

The total unit inertia constant of the generator groups 1A to 1N in FIG. 5 is M, and the total mechanical input is Pm. The short-circuit reactance jXs, which is the imaginary part of the short-circuit impedance (drive point impedance) when the main system is viewed from the bus S in FIG. 5, the trans-impedance jXt when viewed from the generator side, and the generator internal impedance j
The sum with Xd ″ is jXg. These quantities are expressed in unit method based on a unified system reference capacity. The capacities of the generators 1A to 1N are assumed to be the same.

Now, assuming that n out of N generator groups are cut off, the inertia constant M 'and the mechanical input Pm' after the cut off are as follows.

Also, by modeling the target power supply system as shown in FIG. 5, the total value P
e 'can be approximated as in the following equation.

Here, Pe is the total value of the electrical output immediately before the interruption is performed.

Let t _{C be} the time of interruption and t _E , ΔT ₂ = t _E -t _C the time of grasping the tendency of oscillation after interruption. Since ΔT ₂ is a short time of about 0.02 to 0.03 s, the change in electrical output during that time can be approximated to be constant. Therefore, the phase angle increase Δδ ′ between ΔT ₂ is obtained by substituting the equations (3) and (4) into the equation of motion of the generator to obtain ΔT ₂
By integrating between Is required. If the cutoff is not performed, the phase angle increase Δδ is Therefore, the improvement amount Δδn of the phase angle by the interruption is Δδn = Δδ−Δδ ′.

By this improvement of Δδn, the predicted phase angle value δ at time t _{E is} calculated.
When (t _E ) is smaller than the threshold value δlimit and δ (t _E ) is larger than δlimet in the case of n-1 blocks, n
Is determined as the stabilization control amount (generator cutoff amount).

[Problems to be solved by the invention]

Since the conventional power system stabilization device is configured as described above, the target system must be modeled in advance using the short-circuit reactance Xs in order to determine the stabilization control amount. If the conditions change significantly from the setting of the short-circuit reactance Xs, the control error is large, and a huge amount of simulation had to be performed in advance in order to determine the threshold δlimit for stability determination. There was a problem that the economic burden was large.

The present invention has been made in order to solve the above-mentioned problems, and the stabilization control amount can be determined without modeling the target system in advance using the short-circuit reactance Xs, and the threshold value of the stability determination is also reduced. An object of the present invention is to provide a power system stabilization device that can be automatically calculated using online data without setting in advance.

[Means for solving the problem]

The power system stabilizing device according to the present invention integrates a group of generators constituting the power system into one equivalent generator, and the integrated generator is virtually infinite via a 2 × 2 node admittance matrix. represent the power supply system connection model to a large bus, is the size product of E ₀ size Eg and infinite bus voltage transfer susceptance component B ₁₂ and aggregate generator internal voltage of the node admittance matrix elements The peak value of the power-phase difference angle curve is estimated using online data of the generator output at a predetermined time immediately after the accident is cleared, and the energy method is applied based on the online estimated value of the peak value of the power-phase difference angle curve. This is to determine the stability and determine the stabilization control amount.

[Action]

The peak value of the power one-phase difference angle curve according to the present invention is obtained by using the on-line
Since it can be estimated only with data, there is no need to model the target system in advance with short-circuit impedance, and the critical energy (potential energy at the unstable equilibrium point), which is the threshold for stability determination, is also the peak of the power-phase difference angle curve. Since the value can be automatically calculated from the estimated value, the stability determination and the stabilization control amount can be determined in accordance with the system condition and the accident condition.

(Example of the invention)

An embodiment of the present invention will be described below with reference to the drawings. First, the basic principle of the present invention will be described with reference to FIG. FIG. 1 shows a model of a power system to be protected by a power system stabilizing device according to the present invention. Reference numeral 21 denotes an integrated generator in which constituent generator groups are integrated into one unit by a parallel impedance method and equivalently expressed. , 22 is a virtual infinity bus representing the main system supplied with power from the power supply system, and 23 is a 2 × 2 node admittance matrix representing the electrical coupling between the integrated generator 21 and the infinite bus 22. It is. In this embodiment, a method of determining stability and determining a stabilization control amount using the energy method will be described.

In the system model shown in FIG. 1, the electric output Pe of the integrated generator 21 is given by the following equation.

In the above equation, G ₁₁ is a node admittance matrix 23
Generator side self conductance component elements, G ₁₂ is also transconductance component, B ₁₂ is also transmitted susceptance component, Eg is the generator internal voltage of a magnitude, [delta] is the generator internal voltage phase angle, E ₀ is infinite bus The magnitude of the voltage. These quantities and the mechanical input P of the integrated generator in FIG.
m and the unit inertia constant M of the generator are all values expressed in a unit method based on a certain unified system reference capacity.
(Pm, Pe, and M are the total values of the constituent generator groups.) Generally, the resistance of the transmission line is smaller than the inductance, and the load in the power supply system is not so large. Therefore, B ₁₂ ≫G ₁₁ , G ₁₂ holds, and the right side of equation (7) can be approximated as follows.

Pe ≒ EgE ₀ B ₁₂ sinδ ... (8) The state after an accident such as a short-circuit or ground fault has occurred on the power supply line in the power supply system to be protected by this stabilization device and the fault has been cleared (8) Assuming that the equation expresses, the critical energy Vc of the transient stability (potential energy at the unstable equilibrium point) after clearing the accident is given by the following equation.

Paying attention to equation (9), it is understood that even if the individual values of Eg, E ₀ , and E ₁₂ are not known, if the product EgE ₀ E ₁₂ is obtained and the value is known, the critical energy Vc can be calculated. That is, And rewriting equation (9), the following equation is obtained.

P in equation (11) can be calculated by the following method using only the electrical output data of the integrated generator 21 after the accident is cleared, that is, only the total value Pe of the electrical outputs of the constituent generator groups. .

If equation (8) is rewritten using P, Pe = Psinδ (12) Differentiating both sides of equation (12) with t gives In equation (13), dδ / dt is the angular velocity deviation Δω, I can write By squaring both sides of equations (12) and (14), Pe ² = P ² sin ² δ (15) Therefore, if the equations (15) and (16) are added together, Therefore, P can be calculated from the following equation.

(17) Δω on the right side of the equation is based on the assumption that the accident occurrence time is t = 0. It is obtained from the integral calculation of. Mechanical input of central generator 21
Since Pm is almost equal to the total electric output value of the constituent generator groups 1A to 1N before the occurrence of the accident, it can be grasped as online data in advance. Also, for several seconds after the accident occurs, Pm
Since it can be regarded as constant, the only online data necessary for calculating Δω is only the electrical output Pe of the centralized generator 21.
Other components on the right side of the equation (17) are also given only by the electric output Pe.

For example, dPe / dt can be obtained from the following approximate expression.

Δt: sampling interval of online data Therefore, P is calculated from equation (17) using only online data of the electrical output Pe of the centralized generator 21 after the accident is cleared, and the estimated values P ^* and (11) From the equation, the critical energy Vc adapted to the accident state and the system condition can be calculated. P ^* is obtained, for example, as an average value of P at each sampling time.

Since the value of P ^* can be grasped almost accurately in 60 to 70 msec after the accident is cleared, the stability determination threshold value Vc, which is the critical energy, is automatically calculated without delaying the stabilization control timing. Therefore, the prediction calculation of the electrical output Pe of the generator group is not required. The stability determination is performed by comparing the magnitude relationship between the stability determination threshold value Vc and the energy energy V during the accident calculated by the following equation using the online data of the electrical output Pe during the accident.

The integral calculation in the equation (19) is executed numerically using trapezoidal approximation or the like. When the accident is cleared by the main protection relay, the potential energy Vp becomes almost negligible.

The stability determination is performed by the following equation by using the during-accident energy Vx and the stability determination threshold value Vc calculated online.

If it is determined in this equation (20) that it is unstable, the stabilization control amount (generator cutoff amount) can be determined as follows using the online estimated value P ^* of P as well.

The system shown in FIG. 1 is further modeled as shown in FIG. In FIG. 2, Xg is the sum of transreactance Xt and generator internal reactance (initial transient reactance) Xd 'as seen from the bus S and the generator side, and Xs ^* is the online short-circuit reactance as seen from the bus S and the main system side. This is an estimated value and can be calculated from the following equation (21). These amounts are also assumed to be Pu values based on the system reference capacity.

The value of Xg can be grasped as prior online data from the generator parallel state before the accident. The short-circuit reactance estimated value Xs ^* is obtained by using the online estimated value P ^* of P, and assuming that the magnitude Eg of the generator internal voltage and the magnitude E ₀ of the infinite bus voltage are both 1.0 Pu. You can ask.

That is, in the model of FIG. 2, the short-circuit impedance Xs is not given as a set value in advance, but a value estimated online is used.

Now, the generator groups 1A to 1N constituting the integrated generator 21 of FIG.
Is cut off, the total capacity (generator cutoff amount) is γ%
Assume that it has decreased. The inertia constant after this interruption is performed is M ',
Assuming that the mechanical inputs are Pm ', these are approximately given by the following equations.

Also, 'When, P ^* value after cutoff embodiment P ^*' and the transformer reactance Xt that varies by interrupting the generator internal reactance Xd "and the sum Xg Xg is as follows.
(Assuming Eg = E ₀ = 1.0 Pu) M ′, Pm ′, P ^* ′ in equations (22) and (23) and (1
From the expressions 1) and (19), the critical energy Vc after the interruption and the reevaluation values Vc ', V' of the energy V during the accident are given by the following expressions.

The minimum stabilization control amount (generator cutoff amount) γ that satisfies V ′ <Vc ′ (26) where Vc ′ and V ′ obtained by Expressions (24) and (25) are determined. In addition, corresponding to the cutoff pattern in advance,
If M ', Pm', and Xg 'are tabulated, the stabilization control amount can be determined efficiently.

Next, an embodiment of a power system stabilizing apparatus based on the above-described stabilization control amount determination method and its operation will be described with reference to FIGS. 3 and 4. FIG.

In FIG. 3, 1A to 1N are generator groups constituting a power supply system to be controlled, 3A to 3N are step-up transformers of the generator groups 1A to 1N, 31 is a substation bus in the power supply system, and 32A and 32B are A power supply line for transmitting the power of the generator groups 1A to 1N to the main system side, 33 is a low-voltage side bus of a substation corresponding to a connection point between the power system and the main system, 34
Is the main transformer of the substation, 35 is the high voltage side bus of the substation, 36A, 36B, 37A, 37B are the main transmission lines in the main system, 4A to 4
N is a circuit breaker for the step-up transformers 3A to 3N, 5 is a system stabilization control device, 51A to 51N are sensors for measuring the electrical output of the generator group 1A to 1N, and 52A to 52N are the measured electrical A control cable for inputting output data to the system stabilization controller 5, 53A to 53N are control cables for outputting a trip signal from the system stabilization controller 5 to the circuit breakers 4A to 4N, and 54 is a substation. A sensor 55 for measuring the voltage of the bus 31 and a control cable 55 for inputting this voltage data to the system stabilization control device 5 are shown.

Next, the operation of the present apparatus will be described. Generator group 1A-1N
The electrical output data is constantly measured by the sensors 51A to 51N, and is controlled and controlled at sampling intervals of about 10 msec.
The signals are input to the system stabilization control device 5 via the cables 52A to 52N. If the electrical output of the generator groups 1A to 1N changes (decreases) by more than a certain set value, it is determined that a short circuit or a ground fault has occurred, and the system stabilization control device 5 enters a startup state. The stabilization control is performed according to the flowchart shown in FIG.

That is, when the device activation step ST1 detects the occurrence of an accident and starts the device, in the processing step ST2, the time is reset once to set the time of occurrence of the accident as a time reference, and in the processing step ST3 following the processing step ST2,
After the accident is cleared, P (t) at each sampling time is calculated by the equation (17) using the online data of the electrical output Pe of the generator groups 1A to 1N. Then, the decision step
At ST4, the time is carried out stability determination, determines whether it is time t ₁ to determine the stability control amount. That is, the calculation of P (t) in the processing step ST3 is repeated until this condition is satisfied, and all the results are stored in the memory. In addition, t ₁ is set to be about after the accident clear 60~70msec. ST5 is time than the value of P was stored in the memory (t) at the time point when t _1, seeking the estimated value in process step ST5 average P ^*. Next, in the processing step ST6, the average value P ^* and the generator output data Pe (t) (t = 0 to tf, tf: accident clear time) sampled during the accident and stored in the memory are used. (11), (1
Calculate the critical energy Vc and the energy V during an accident by using the equation 9). In the determination step ST7, a stability determination is performed using the values of the critical energy Vc and the energy during accident V calculated in the processing step ST6. If it is determined that V <Vc, the stability is determined. Ends. On the other hand, if it is determined that V> Vc and thus unstable, the process proceeds to the stabilization control amount determination processing step ST9, and the minimum cutoff amount γ (generator total % With respect to the capacity), and stores it as a cutoff pattern for the generator groups 1A to 1N. Then, the time in the processing step ST10 to output a generator cutoff signal gamma% fraction at the time of a stabilization control execution time t _2. t ₂ is set to about 90 msec after the accident is cleared. An accident detection element such as a frequency or a frequency change rate obtained from the voltage data of the substation bus 31 measured by the sensor 54 and input to the accident detection relay in the system stabilization control device 5 via the control cable 55 is previously determined. If the accident detection conditions set in step
The interruption signal outputted from reaches the corresponding one of the interruption devices 4A to 4N, and the interruption is executed. After that, in processing step ST11, appropriate parameters such as a frequency and a phase angle and a stability monitoring and correction control processing routine using this method are executed, and after confirming stabilization, a device stopping step is performed.
The process proceeds to ST8 and ends.

In the above embodiment, an application example in which the generator group operates as a generator is shown. However, the present invention is also applicable to a case where the pumping generator operates as a nighttime electric motor.

Further, by applying the above-described embodiment to a plurality of power supply systems and exchanging information between the respective devices, the step-out mode is determined, and the stabilization control amount corresponding to the mode is determined. Therefore, it can be extended to a wide-area stabilizing device.

〔The invention's effect〕

As described above, according to the present invention, the power system stabilizing device is configured so that the stability determination threshold can be determined online by an equation using only the generator output data. It is not necessary to model using, and the value of the peak value of the power one-phase difference angle curve can be grasped almost accurately in the required time, so that prediction calculation is unnecessary, and high accuracy is adapted to system conditions and accident conditions. There is an effect that a power system stabilizing device capable of performing stabilization control can be obtained.

[Brief description of the drawings]

FIG. 1 is a model system diagram of a power supply system for explaining a basic principle in one embodiment of the present invention, FIG. 2 is a model system diagram for stabilization control amount determination for explaining the same basic principle,
FIG. 3 is a block diagram of a power system stabilizing device according to an embodiment of the present invention, FIG. 4 is a processing flowchart of stabilization control, and FIG. 5 is a diagram for determining a stabilization control amount of a conventional power system stabilizing device. It is a model system diagram. In the figure, 1A to 1N, 21 ... generator, 2 ... main system, 22 ... infinite bus, 23 ... node admittance matrix, 5 ... system stabilization control device. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuji Oshida 1-1-2, Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Pref. Mitsubishi Electric Corporation (72) Inventor Tadahiro Goda Wako, Hyogo-ku, Kobe-shi, Hyogo No. 1-2, Tasaki-cho, Mitsubishi Electric Corporation Control Factory (56) References JP-A-63-140627 (JP, A) JP-A-62-110498 (JP, A)

Claims (1)

(57) [Claims] In a power system stabilizing apparatus configured to maintain a transient stability of a power system constituted by a plurality of generator groups, said generator group is equivalently expressed as one equivalent aggregate generator. In addition, the power supply system is represented by a model in which a virtual infinite bus is connected to the centralized generator via a 2 × 2 node admittance matrix, and the transmission susceptance of the node admittance matrix element and the centralized power generation are represented. The peak value of the power one-phase difference angle curve, which is the product of the magnitude of the machine internal voltage and the magnitude of the virtual infinite bus voltage, is calculated using the online data of the required time of the integrated generator output immediately after the accident is cleared, using the following formula. Estimating means for estimating the estimated value of the peak value of the power one-phase difference angle curve, Pe: Central generator electrical output Δω: Central generator angular velocity deviation M: Unitary inertia constant of the centralized generator Pm: Mechanical input of the centralized generator, that is, electrical output immediately before the occurrence of an accident in the centralized generator Pe, M, Pm: Unit method expression based on the same grid reference capacity This estimate Calculating means for calculating the critical energy Vc by the following equation using P ^* ; Stability determination means for performing stability determination based on the magnitude relationship between the critical energy calculated by the calculation means and the online calculation value of energy during an accident; and the online calculation value is more unstable than the critical energy by the stability determination means. If it is determined that the stabilization control further stabilization control processing means to cut off a part of the generator group, the critical energy re-evaluated by this stabilization control processing means and the magnitude of the re-evaluated energy during the accident By comparing the relations, a stabilization control amount calculating means for calculating a minimum stabilization control amount necessary for the re-evaluated critical energy to be larger than the re-evaluated accident energy, and the stabilization control amount calculation means Stability judgment that adapts to changes in accident conditions and system conditions without modeling the target power system in advance with short-circuit impedance And power system stabilizing apparatus which is characterized in that a stabilization control amount determining means for performing determination of stability control amount.