JP4664113B2 - System and method for monitoring natural frequency of power system - Google Patents

Description

  The present invention relates to a system and method for monitoring the state of a power system, and more particularly to a technique for monitoring a natural frequency of a power system online.

  In the power transmission business, it is necessary to always keep the quality (frequency, voltage) of electricity transmitted (see Patent Documents 1 and 2). For this reason, the electric power company grasps and controls the state of the electric power system and the stability margin. Conventionally, the operation state and stability of an electric power system have been grasped by analysis using an offline computer. That is, the power system is modeled, and a predetermined parameter is given off-line and analyzed by a computer.

  However, it is difficult to accurately model an actual power system, and in an actual power system, the operating state changes from moment to moment, so that offline analysis provides sufficient information in terms of accuracy or immediacy. The fact is that it is not possible. For this reason, the operation of the power system is performed with a certain margin, and it is difficult to say that the system facilities are used efficiently.

  In addition, with the recent liberalization of electric power business in Japan, many power sources that are not fully understood by power system operators are connected. These uncertain factors cannot be sufficiently reflected in the off-line computer analysis, which causes a problem in accurately grasping the system state.

In addition, it is important to grasp the natural frequency of the eigenvalue of the power system as an element for grasping the state of the power system.
JP-A-5-336666 JP-A-3-256533

  In view of the situation as described above, a monitoring system capable of accurately and quickly grasping a system state that changes every moment in a power system to which various power sources are interconnected will be demanded.

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an on-line monitoring system for a power system capable of accurately monitoring a natural frequency of the power system as an element indicating the power system state in real time and accurately. It is to provide a monitoring method.

The first monitoring system of the present invention is a system that monitors the natural frequency of the power system. The disturbance adding means injects minute power of a specific frequency into the power system. The filter inputs the response power, which is the response from the power system after the minute power injection, removes the original frequency component of the power transmitted through the power system from the response power, and the fluctuation due to the micro power in the response power To extract. The phase difference detection means detects the phase difference between the specific frequency component in the extracted fluctuation of the response power and the minute power output from the disturbance addition means. The control unit controls the specific frequency of the disturbance adding unit based on the detected phase difference so that the detected phase difference becomes a predetermined value . The controlled specific frequency is detected as a natural frequency of the power system or a frequency shifted from the natural frequency .

The second monitoring system of the present invention is a system for monitoring the natural frequency of the power system. The disturbance adding means injects minute power of a specific frequency into the power system. The filter inputs the response power, which is the response from the power system after the minute power injection, removes the original frequency component of the power transmitted through the power system from the response power, and the fluctuation due to the micro power in the response power To extract. The natural frequency detecting means detects the frequency of fluctuation when the amplitude of fluctuation of the extracted response power becomes a predetermined value. The control means controls the specific frequency so that the specific frequency of the disturbance adding means coincides with the detected frequency. The controlled specific frequency is detected as a natural frequency of the power system or a frequency shifted from the natural frequency.

  According to the present invention, since it is possible to control the frequency of the minute power injected into the power system so as to be locked to the detected natural frequency of the power system, it is possible to accurately monitor the natural frequency of the power system online. Is possible. Conventionally, the state of the power system cannot be accurately grasped, and uncertain factors increase with the liberalization of the power business, so it was necessary to operate the power system with a certain margin. Thus, since the natural frequency of the power system, that is, the state of the power system can be accurately grasped, the margin can be reduced and the operating efficiency of the power equipment can be improved.

  Preferred embodiments of a power system monitoring system according to the present invention will be described below with reference to the accompanying drawings. The power system monitoring system described below monitors the natural frequency of the natural value of the power system as an element that governs the state of the power system.

First Embodiment FIG. 1 is a diagram showing a configuration of a natural frequency monitoring system for a power system in a first embodiment of the present invention. The monitoring system 1 monitors the natural frequency of the natural value of the power system 100. As an example, the power system 100 uses an eight-machine infinite bus system, and a total of about 1000 MW of power is supplied from eight generators G1 to G8.

The monitoring system 1 includes a SMES (Superconducting Magnetic Energy Storage System) 11 that gives a minute power as disturbance to the power system 100, a frequency controller 13 that controls the frequency f _sm of the minute power P _sm output from the SMES 11, A filter 15 that extracts a variation ΔP _line due to disturbance in the power transmitted in the power system 100 and a lock-in amplifier 17 that measures the amplitude and phase of a constant frequency component from the output signal of the filter 15 are provided.

The monitoring system 1 injects minute electric power _Psm into the electric power system 100, and measures the electric power fluctuation of the electric power system with respect to this, for example, transmission line electric power. In general, when the frequency f _sm of the injected micro power P _sm is close to the natural frequency of the eigen value that controls the stability of the power system, the amplitude of the response power P _line from the power system 100 becomes maximum, and the response power P The phase difference Δθ between the _line and the applied minute power P _sm is a predetermined value (for example, 90 degrees). Therefore, in the monitoring system 1 of this embodiment, the phase difference of the response power is used as a feedback amount, and control is performed so that the frequency f _sm of the minute power P _sm to be applied is locked to the natural frequency of the power system. As a result, when the natural frequency changes due to a change in the state of the power system, the frequency f _{sm of the} minute power to be applied follows this, so that the natural frequency of the power system can be monitored online.

  FIG. 2 is a diagram illustrating a change example of the natural frequency of the power system when the output of the generator is changed in the power system 100. In FIG. 2, the unit (p.u.) on the horizontal axis indicates the ratio of the output power to the maximum output power of the generator. For example, 0.8 p.u. indicates that 80% of the maximum output power is output. From the figure, it can be seen that the natural frequency of the power system decreases as the generator output increases. From this, it can be seen that by monitoring the natural frequency, it is possible to know whether or not the generator output has approached the stability limit.

3, while the frequency f _sm of the minute power P _sm varied between 0.5～2.5Hz, injecting minute power P _sm as disturbances in the power system, fluctuation in the response power P _line by the minute power when measured minute [Delta] P _line, the amplitude of the variation [Delta] P _line, and is a diagram showing a variation of the phase difference variation [Delta] P _line and minute power P _sm. As shown in FIG. 3A, the amplitude of the variation ΔP _line shows a maximum value at a certain frequency (1.01 Hz). The frequency indicating the maximum value is the natural frequency of the power system. Further, as shown in FIG. 3B, the phase difference between the minute power P _sm given to the power system and the fluctuation component ΔP _line due to the minute power changes from 180 degrees to 0 degrees as the frequency changes. In particular, it is 90 degrees at the natural frequency (1.01 Hz). In the present embodiment, by paying attention to this characteristic, the phase difference of the minute power P _sm and fluctuation component [Delta] P _line controls the frequency of the minute power P _sm so that 90 degrees, the power frequency of the minute power P _sm Try to follow the natural frequency of the system.

The control of the frequency of the minute power P _sm will be described more specifically. When the state of the power system changes due to fluctuations in the generator output, the natural frequency of the power system changes accordingly. FIG. 4 is a diagram showing changes in the phase difference Δθ for the states of the two power systems. Consider a case where the state of the power system has changed from the first state indicated by “x” in FIG. 4 to the second state indicated by “▲”. In this case, since the natural frequency changes from 1.1 Hz to 0.86 Hz, the frequency f _{sm of the} minute power needs to be reduced. At this time, when the phase difference of the second state is measured near 1.1 Hz, which is the natural frequency of the first state, a value smaller than 90 degrees is observed. Therefore, when a value smaller than 90 degrees is observed as the phase difference, it can be understood that the frequency f _{sm of the} minute power may be decreased. Conversely, when the state changes from the second state to the first state, that is, when the natural frequency of the power system increases, the frequency f _{sm of the} minute power may be increased. Thus, by increasing / decreasing the frequency f _{sm of the} minute power based on the phase difference, the frequency f _sm can be made to follow the natural frequency of the power system.

  Although there may be a plurality of natural frequencies depending on the configuration of the power system, it is generally sufficient to monitor only the minimum natural frequency for the stability of the power system.

  Based on the above points, the operation of the monitoring system 1 shown in FIG. 1 will be described in detail below.

The SMES 11 gives a minute power P _sm to the power system 100 as a disturbance. In the present embodiment, sinusoidal power expressed by the following equation is given.
P _sm = P ₀ sin (2πf _sm t) (1)
P ₀ is the amplitude, and _{0. 0} of the electric power transmitted to the electric power system 100. The value is about several percent (for example, 2 to 3 MW). Further, f _sm takes a value of 0.5 to 2.5 Hz, for example. FIG. 5A shows the waveform of the minute power _Psm injected into the power system.

The filter 15 inputs the response power P _line from one line of the power system 100 after the minute power injection, removes the frequency component of the power originally transmitted to the power system 100 from the input power P _line , Only the variation ΔP _line due to the disturbance by the SMES 11 is taken out. FIG. 5B shows a waveform of the response power fluctuation ΔP _line .

The lock-in amplifier 17 receives the variation ΔP _line from the filter 15 as a measurement signal, receives the minute power P _sm as a reference signal from the SMES 11, and has the same frequency as the frequency f _sm of the minute power P _sm in the variation ΔP _line . The phase difference Δθ between the component and the minute power P _sm is output.

Based on the phase difference Δθ from the lock-in amplifier 17, the frequency controller 13 outputs a control signal to the SMES 11 so that the frequency f _sm of the minute power P _sm output from the SMES 11 matches the natural frequency of the power system 100. To do. Specifically, the frequency controller 13 compares the phase difference Δθ with a predetermined value (here, the predetermined value is 90 degrees that is a phase difference that gives the natural frequency of the power system 100). Frequency controller 13, larger than the phase difference Δθ is 90 degrees, so as to increase the frequency f _sm, if the phase difference Δθ is smaller than 90 degrees, so as to decrease the frequency f _sm, for changing the frequency f _sm The control signal is output.

The SMES 11 receives a control signal from the frequency controller 13 and controls the frequency f _sm of the minute power P _sm . Thereby, the frequency f _{sm of} P _sm that gives disturbance to the power system 100 is controlled to follow the natural frequency of the power system. That is, since the value of the frequency f _sm controlled by the frequency controller 13 is substantially equal to the natural frequency of the power system 100, the natural frequency of the power system 100 can be accurately recognized in real time if the frequency f _sm is monitored. become. As a result, the state of the power system can also be accurately grasped in real time.

  In the above description, SMES is used as a device that does not have a great influence on the power system and gives minute power disturbance. However, instead of SMES, active power and reactive power can be controlled independently and at high speed. Other power supply devices (for example, SVG (Static Var Generator)) can be used as long as their output is not affected by the disturbance.

Second Embodiment In the first embodiment, the frequency controller 13 controls the frequency f _{sm of the} minute power to follow the natural frequency of the power system. However, during the tracking, the excitation of the SMES 11 becomes a power fluctuation near the natural frequency of the power system, and there is a possibility that the stability of the power system may be adversely affected as it is. Therefore, stabilization control is applied to the power system 100 from the SMES 11 simultaneously with the application of the minute power. That is, the minute electric power _Psm given by the following equation is injected into the electric power system.
P _sm = P ₀ sin (2πf _sm t) + k _sm P _stab (2)
Here, k _sm is a control gain, and P _stab is a signal obtained by advancing the phase by 90 degrees for the variation ΔP _line of the response power P _line . The braking coefficient of the power system is increased by the term of k _sm P _stab , and the system can be stabilized by damping the fluctuations quickly.

FIG. 6 is a diagram illustrating a configuration of a monitoring system in consideration of the above-described stabilization control. The monitoring system 1b of the present embodiment is different from that of the first embodiment in that the frequency controller 13 inputs the variation ΔP _line of the response power P _line in addition to the phase difference Δθ. The frequency controller 13 outputs a control signal to the SMES 11 so that the minute electric power P _sm satisfying the above equation (2) is output.

FIG. 7 is a diagram showing an experimental result by the monitoring system of the present embodiment. In the figure, a curve X shows a change in the output of the generator. In the figure, the generator output is increased almost in proportion to the passage of time. “●” indicates the natural frequency measured when the output of the generator is kept constant at a certain value without changing with time. A curve Y represents a change in the natural frequency of the power system (that is, the frequency f _{sm of the} minute power) measured by the monitoring system of the present embodiment. When the curve Y is compared with “●”, they are almost the same, and it can be seen that the measurement system of the natural frequency with high accuracy is obtained by the monitoring system of this embodiment. Further, the curve Z shows the change in the phase difference Δθ, and it can be seen that the curve Z is controlled to approximately 90 degrees.

Third Embodiment In the first and second embodiments, the frequency fsm of the minute power injected into the system is controlled based on the phase difference Δθ output from the lock-in amplifier 17. In the present embodiment, an example will be described in which the frequency fsm is controlled based on the maximum value of the amplitude of the response power fluctuation ΔP _line instead of the phase difference Δθ.

FIG. 8 is a diagram illustrating a configuration of a power system monitoring system according to the present embodiment. In the monitoring system 1c of the present embodiment, the frequency controller 13 outputs the reference signal P (f _r ) to the lock-in amplifier 17 while changing the frequency (f _r ) in the range of 0.5 Hz to 2.5 Hz. To do. The lock-in amplifier 17 receives the reference signal P (f _r ) from the frequency controller 13 and changes the amplitude (| ΔP _line (f _r ) |) of the frequency (f _r ) component in the variation ΔP _line to the frequency (f _r ) Is output in response to changes in The frequency controller 13 obtains the frequency with the maximum amplitude (that is, the frequency that gives the natural frequency), and controls the frequency of the minute power of the SMES 11 to be the obtained frequency. Thus, even if the amplitude of the variation ΔP _line is used instead of the phase difference Δθ, the frequency f _sm of the minute power P _sm can be locked to the natural frequency of the system.

As described above, according to the monitoring systems of the first to third embodiments, the minute electric power _Psm is injected into the electric power system 100 as a disturbance, and the electric power fluctuation of the electric power system is measured as the response electric power. The phase difference or amplitude of fluctuation due to disturbance is used as a feedback amount, and control is performed so that the frequency f _sm of the applied minute power P _sm is locked to the natural frequency of the power system. As a result, when the natural frequency changes due to a change in the state of the power system, the frequency f _{sm of the} minute power to be applied follows this, so that the natural frequency of the power system can be monitored online.

In each of the above embodiments, the frequency f _sm of the minute power P _sm injected into the power system is controlled to be the natural frequency of the system. In this case, the power system is disturbed at the resonance point, and the operation of the power system may become unstable. Therefore, rather than the natural frequency of the frequency f _sm of the fine power P _sm, it may be caused to lock to a value shifted by a predetermined value from the natural frequency. As a result, the power system can be disturbed by avoiding the resonance point, and the stability of the power system can be further improved. That is, in the first and second embodiments, the phase difference Δθ is controlled frequency f _sm of the minute power P _sm so as to be 90 degrees, but instead, as the phase difference Δθ is 100 degrees and 110 degrees The frequency f _sm may be controlled. In the case of the third embodiment, instead of the frequency that gives the maximum value of the amplitude, it may be controlled to lock to a frequency that gives a value that deviates from the maximum value by a predetermined value.

Configuration diagram of a power system natural frequency monitoring system in the first embodiment of the present invention The figure which showed the change of the natural frequency of an electric power system when changing the output of the generator in an electric power system While changing the frequency f _sm of the fine power P _sm, upon introducing the minute power P _sm as disturbances in the power system, (a) the amplitude of the variation due to disturbances in the response power, and variations and (b) small power Diagram showing change in phase difference of minute The figure which showed the change of phase difference (DELTA) ( _theta) between minute electric power _Psm and the variation _{| change_quantity (DELTA)} P _line of response power by it about the state of two electric power _grids (A) shows a micro-power waveform diagram showing (b) the waveform of the variation [Delta] P _line of the response power The figure which showed the structure of the monitoring system which considered the stabilization control in the 2nd Embodiment of this invention. The figure which showed the experimental result by the monitoring system of embodiment The figure which showed the structure of the monitoring system which considered the stabilization control in the 3rd Embodiment of this invention.

Explanation of symbols

1, 1b, 1c Power system natural frequency monitoring system 11 SMES (superconducting power storage device)
13 Frequency controller 15 Filter 17 Lock-in amplifier 100 Power system (8 infinite bus system)

Claims (17)

A system for monitoring the natural frequency of a power system,
Disturbance adding means for injecting minute power at a specific frequency into the power system,
Inputs response power, which is the response from the power system after the micro power injection, removes the original frequency component of the power transmitted in the power system from the response power, and extracts the fluctuation due to the micro power in the response power Filters,
Phase difference detection means for detecting a phase difference between the specific frequency component in the extracted response power fluctuation and the minute power output from the disturbance adding means;
Control means for controlling a specific frequency of the disturbance adding means based on the detected phase difference so that the detected phase difference becomes a predetermined value ;
Detecting the controlled specific frequency as a natural frequency of the power system or a frequency shifted from the natural frequency;
A system for monitoring a natural frequency of a power system. 2. The power system natural frequency monitoring system according to claim 1, wherein the predetermined value is 90 degrees . The system according to claim 1, wherein the predetermined value is a value shifted by a predetermined amount from 90 degrees. A system for monitoring the natural frequency of a power system,
Disturbance adding means for injecting minute power at a specific frequency into the power system,
Inputs response power, which is the response from the power system after the micro power injection, removes the original frequency component of the power transmitted in the power system from the response power, and extracts the fluctuation due to the micro power in the response power Filters,
Natural frequency detection means for detecting the frequency of fluctuation when the amplitude of fluctuation of the extracted response power becomes a predetermined value;
Control means for controlling the specific frequency so that the specific frequency of the minute power injected by the disturbance adding means matches the detected frequency ,
Detecting the controlled specific frequency as a natural frequency of the power system or a frequency shifted from the natural frequency;
A system for monitoring a natural frequency of a power system. The system for monitoring a natural frequency of a power system according to claim 4 , wherein the predetermined value is a maximum value of an amplitude of the fluctuation. 5. The system for monitoring a natural frequency of a power system according to claim 4, wherein the predetermined value is a value shifted by a predetermined amount from a maximum value of the amplitude of the fluctuation. The system for monitoring a natural frequency of a power system according to any one of claims 1 to 6 , wherein the disturbance adding means is SMES (Superconducting Magnetic Energy Storage System) or SVG (Static Var Generator). The system for monitoring a natural frequency of an electric power system according to any one of claims 1 to 6 , wherein the minute electric power is sinusoidal electric power. The system for monitoring a natural frequency of a power system according to any one of claims 1 to 6 , wherein the minute power includes a signal component obtained by advancing the phase of the specific frequency component of the response power by 90 degrees. A method for monitoring the natural frequency of a power system,
Inject minute power of a specific frequency into the power system,
Enter the response power, which is the response from the power system after minute power injection,
From the response power, remove the original frequency component of the power transmitted in the power system, extract the fluctuation due to minute power in the response power,
Detecting the phase difference between the specific frequency component in the extracted response power fluctuation and the injected micro power;
Based on the detected phase difference , the specific frequency of the minute power to be injected is controlled so that the phase difference becomes a predetermined value ,
The method for monitoring a natural frequency of a power system, wherein the controlled specific frequency is detected as a natural frequency of the power system or a frequency shifted from a natural frequency. The method for monitoring a natural frequency of a power system according to claim 10, wherein the predetermined value is 90 degrees . The method for monitoring a natural frequency of a power system according to claim 10, wherein the predetermined value is a value shifted by a predetermined amount from 90 degrees. A method for monitoring the natural frequency of a power system,
Inject minute power of a specific frequency into the power system,
Enter the response power, which is the response from the power system after minute power injection,
From the response power, remove the original frequency component of the power transmitted in the power system, extract the fluctuation due to minute power in the response power,
Detecting the frequency of fluctuation when the amplitude of fluctuation of the extracted response power becomes a predetermined value;
Controlling the specific frequency of the micro power to be injected so that the specific frequency matches the detected frequency ;
The method for monitoring a natural frequency of a power system, wherein the controlled specific frequency is detected as a natural frequency of the power system or a frequency shifted from a natural frequency. The method for monitoring a natural frequency of a power system according to claim 13 , wherein the predetermined value is a maximum value of an amplitude of the fluctuation. 14. The method for monitoring a natural frequency of a power system according to claim 13, wherein the predetermined value is a value shifted by a predetermined amount from a maximum amplitude value of the fluctuation. 16. The method for monitoring a natural frequency of a power system according to claim 10, wherein the minute power is sinusoidal power. The method for monitoring a natural frequency of a power system according to any one of claims 10 to 15 , wherein the minute power includes a signal component obtained by advancing the phase of the specific frequency component of the response power by 90 degrees.

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