A method and system for early warning and suppression of wind power subsynchronous oscillation

Abstract

The present invention belongs to the technical field of power systems, and particularly relates to a method and system for early warning and suppression of wind power sub-synchronous oscillation risks, including: obtaining the operating state of a power system containing wind power; identifying the weak links in the obtained operating state of the power system, and constructing an impedance model of power equipment in the identified weak links; monitoring and warning whether a sub-synchronous oscillation event occurs according to the obtained operating state of the power system and the constructed impedance model; when a sub-synchronous oscillation risk event occurs, optimizing the primary side parameters of the power system and disconnecting grid-connected wind turbines to suppress the sub-synchronous oscillation event.

Description

Technical Field

[0001] The invention belongs to the technical field of power systems, and particularly relates to a method and system for early warning and suppression of wind power subsynchronous oscillation risks. Background Art

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] In recent years, new energy represented by wind power has developed rapidly. Different from traditional rotating generators, new energy units mostly use power electronic converters to connect to the power grid. The interaction between the converter and the power grid may cause resonance or oscillation problems, resulting in unit tripping and even equipment damage, endangering the safe and stable operation of the power grid. With the large-scale grid connection of new energy and the wide application of other large-capacity power electronic devices, especially the highly concentrated connection in the western and northern regions of China, the oscillation stability problem is becoming an increasingly huge potential risk. If effective strategies and solutions cannot be studied and implemented in a timely and comprehensive manner, it may cause huge economic losses to equipment manufacturers, power generation enterprises and power grid companies, and even cause large-scale stability accidents, endangering the safe and reliable operation of the power grid and affecting the smooth implementation of the national energy strategy.

[0004] With the development of new energy, there are more and more oscillation stability problems in various forms related to new energy units. For example, a certain wind farm has experienced hundreds of times of subsynchronous resonance caused by the interaction between wind turbine groups and series-compensated power grids, with its frequency varying within 3 - 10 Hz, which has caused abnormal vibration of transformers and disconnection of a large number of wind turbines; in a certain area, subsynchronous oscillations involving wind turbine groups frequently occur, with the frequency varying within 20 - 40 Hz. The subsynchronous oscillation power penetrates multiple levels of power grids such as 35 / 110 / 220 / 500 / 750 kV, and even excites the torsional vibration of the shafting of steam turbine units, resulting in the total tripping of units in a power plant 300 km away and a sharp drop in the power of UHV DC.

[0005] The phenomenon of subsynchronous oscillation seriously threatens the equipment safety, system stability and power quality of the power grid, and restricts the large-scale access and consumption of new energy such as wind and light.

[0006] At the sending end of the DC transmission system, a high proportion of wind power access is likely to have frequency dynamic interactions with the power grid, DC converter stations, reactive power compensation equipment, etc., resulting in the risk of subsynchronous oscillation. Therefore, it is necessary to provide a method for early warning and suppression of subsynchronous oscillation risks in the near area of the DC sending end. Summary of the Invention

[0007] To solve the above problems, the present invention proposes a method and system for early warning and suppression of wind power subsynchronous oscillation risks, which solves the problem that in the sending end of the DC transmission system, a high proportion of wind power access is prone to frequency dynamic interaction with the power grid, DC converter stations, reactive power compensation equipment, etc., resulting in the risk of subsynchronous oscillation, and can quickly and accurately analyze the risk of subsynchronous oscillation, and improve the early warning and defense capabilities against the risk of subsynchronous oscillation during the operation of the power grid.

[0008] According to some embodiments, the first solution of the present invention provides a method for early warning and suppression of wind power subsynchronous oscillation risks, adopting the following technical solutions:

[0009] A method for early warning and suppression of wind power subsynchronous oscillation risks includes:

[0010] Obtain the operating state of the power system with wind power;

[0011] Identify the weak links in the operating state of the obtained power system, and construct the impedance model of the power equipment in the identified weak links;

[0012] According to the operating state of the obtained power system and the constructed impedance model, monitor and early warn whether a subsynchronous oscillation event occurs;

[0013] When a subsynchronous oscillation risk event occurs, optimize the primary side parameters of the power system, cut off the grid-connected wind turbines, and suppress the subsynchronous oscillation event.

[0014] As a further technical limitation, during the process of identifying the weak links in the operating state of the obtained power system, according to the subsynchronous oscillation recording data, analyze and restore the typical subsynchronous oscillation events, restore the system frequency change situation, equipment operating state, and relay protection device action situation in chronological order, and identify the weak links in the system operation according to the analysis results.

[0015] As a further technical limitation, the key power equipment causing subsynchronous oscillation includes wind turbines, converter stations, and series compensators.

[0016] As a further technical limitation, according to the obtained operating state and the constructed component impedance model, pre-analyze and judge the location and frequency characteristics of subsynchronous oscillation occurrence through impedance analysis method, combine the monitored active power waveform and frequency information, and based on the oscillation early warning threshold set according to the identified weak links, monitor in real time whether a subsynchronous oscillation event occurs. When a subsynchronous oscillation event occurs, send out an early warning signal.

[0017] As a further technical limitation, when optimizing the primary side parameters, before a subsynchronous oscillation event occurs, combine historical fault information and accident disposal plans to formulate a disposal plan for gradually withdrawing wind turbines and series compensators after the occurrence of a subsynchronous oscillation event.

[0018] Further, when a sub-synchronous oscillation event occurs and a warning is issued, according to the formulated accident handling plan and in combination with the constructed impedance model, the control system parameters of the wind turbine and the converter are optimized offline, and the grid-connected wind turbines and series compensators are cut off in rounds.

[0019] Further, the Nyquist criterion is used to adjust the control system parameters of the wind turbine and the converter, so as to realize the offline optimization of the control system parameters of the wind turbine and the converter.

[0020] According to some embodiments, the second solution of the present invention provides a risk warning and suppression system for wind power sub-synchronous oscillation, and adopts the following technical solution:

[0021] A risk warning and suppression system for wind power sub-synchronous oscillation, comprising:

[0022] An acquisition module, configured to acquire the operating state of a power system containing wind power;

[0023] A construction module, configured to identify the weak links in the acquired operating state of the power system and construct an impedance model of the power equipment in the identified weak links;

[0024] A warning module, configured to monitor and warn whether a sub-synchronous oscillation event occurs according to the acquired operating state of the power system and the constructed impedance model;

[0025] A suppression module, configured to optimize the primary side parameters of the power system, cut off the grid-connected wind turbines, and suppress the sub-synchronous oscillation event when a sub-synchronous oscillation risk event occurs.

[0026] According to some embodiments, the third solution of the present invention provides a computer-readable storage medium, and adopts the following technical solution:

[0027] A computer-readable storage medium, on which a program is stored, and when the program is executed by a processor, the steps in the risk warning and suppression method for wind power sub-synchronous oscillation described in the first solution of the present invention are implemented.

[0028] According to some embodiments, the fourth solution of the present invention provides an electronic device, and adopts the following technical solution:

[0029] An electronic device, comprising a memory, a processor, and a program stored on the memory and executable on the processor, and when the processor executes the program, the steps in the risk warning and suppression method for wind power sub-synchronous oscillation described in the first solution of the present invention are implemented.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] The present invention traces and analyzes grid subsynchronous oscillation events, forms a scientific evaluation system for subsynchronous oscillation events, identifies weak links in system operation, and provides a basis for the construction of a monitoring and control system for subsynchronous oscillation.

[0032] Based on the identified weak links in the system, the present invention constructs a complete impedance model of grid components considering control links, and clearly reveals the time-varying mechanism of the system subsynchronous oscillation frequency based on the physical meaning of the model, identifies the characteristics of subsynchronous oscillation events, and adopts a subsynchronous oscillation risk early warning method based on impedance analysis and online monitoring technology, which can quickly and accurately analyze the subsynchronous oscillation risk, thereby enhancing the early warning and defense capabilities against subsynchronous oscillation risk during the operation of the power grid.

[0033] For the detected subsynchronous oscillation risk events, the present invention optimizes the primary side parameters, cuts off grid-connected wind turbines in rounds, effectively prevents the shafting torsional vibration and tripping of thermal power units caused by continuous subsynchronous oscillation, and solves practical on-site problems; on the other hand, adjusts the control system parameters of wind turbines and converters according to the Nyquist criterion, optimizes the parameters, fully excavates the potential of the wind turbines themselves, improves the impedance characteristics of the wind turbines, and fundamentally solves the subsynchronous oscillation problem, thereby suppressing the huge problems brought by the subsynchronous oscillation problem to the equipment safety, system stability and power quality of the power grid. Brief Description of the Drawings

[0034] The schematic diagrams in the specification forming a part of this embodiment are used to provide a further understanding of this embodiment. The illustrative embodiments and descriptions thereof are used to explain this embodiment and do not constitute an improper limitation to this embodiment.

[0035] Figure 1 It is a flow chart of the risk early warning and suppression method for wind power subsynchronous oscillation in Embodiment 1 of the present invention;

[0036] Figure 2 It is a schematic diagram of a typical direct-drive wind power control system in Embodiment 1 of the present invention;

[0037] Figure 3 It is a schematic diagram of a converter grid-connected system in Embodiment 1 of the present invention;

[0038] Figure 4 It is a structural block diagram of the risk early warning and suppression system for wind power subsynchronous oscillation in Embodiment 2 of the present invention. Detailed Embodiments

[0039] The present invention will be further described below in conjunction with the drawings and embodiments.

[0040] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0041] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] In the case of no conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0043] Embodiment 1

[0044] Embodiment 1 of the present invention introduces a method for early warning and suppression of wind power subsynchronous oscillation risks.

[0045] As Figure 1 shown, a method for early warning and suppression of wind power subsynchronous oscillation risks includes:

[0046] Step 1: Identification of grid subsynchronous oscillation risk points;

[0047] According to the historical recording data of subsynchronous oscillation occurrence, analyze and restore typical subsynchronous oscillation events, restore the system frequency change situation, equipment operation status, and relay protection device action situation in chronological order. According to the analysis results, identify the weak links in the system operation, and set the oscillation warning threshold of the corresponding equipment monitoring device according to the external characteristics of the event, such as the changes in active power and frequency, etc., to provide a basis for system status monitoring and subsynchronous oscillation risk assessment and prevention and control.

[0048] Step 2: Construction of impedance models for key grid components;

[0049] Based on the weak links identified in Step 1, establish impedance models for the key power equipment that causes subsynchronous oscillation. The key power equipment that causes subsynchronous oscillation includes wind turbine generators, converter stations, and series capacitors. When modeling, fully consider the secondary side control systems included in the key power equipment that causes subsynchronous oscillation and establish control system impedance models. After the impedance models are established, use Simulink simulation software to verify the effectiveness of the established impedance models of each component based on the frequency scanning method.

[0050] In this embodiment, for a typical direct-drive wind power control system, such as Figure 2As shown, a typical direct-drive wind power control system needs to consider the combined effects of active power, reactive power, voltage, current, and phase-locked loop control. An impedance analysis method combining circuit theory and Nyquist criterion is adopted. For example, Figure 3 As shown, the converter grid-connected system is divided into two parts: the converter side and the grid side. The frequency-domain impedance or its frequency response characteristics of the two-side systems are obtained respectively, and then the stability of the grid-connected system is judged. For Figure 3 For the new energy grid-connected system based on the equivalent impedance model shown, the grid side is equivalent to the series connection of an ideal voltage source and an impedance, and the new energy access converter is equivalent to the parallel connection of an ideal current and an impedance. Then the relationship between the grid current and the converter current source is

[0051]

[0052] In the above formula, I g (s) is the grid-side current, I in (s) is the converter-side current, Z g (s) is the grid-side impedance, Z in (s) is the converter-side impedance.

[0053] Let G0(s) = Z g (s) / Z in (s). Then the stability of the converter grid-connected system is equivalent to the stability of the closed-loop system with the open-loop transfer function G0(s). Thus, the stability of this new energy grid-connected equivalent circuit can be determined according to the stability criterion of the classical negative feedback system.

[0054] Step 3: Sub-synchronous oscillation risk warning;

[0055] Based on the impedance analysis method and on-line monitoring technology, sub-synchronous oscillation events are warned; the two risk warning methods confirm each other and complement each other, effectively improving the accuracy of system sub-synchronous oscillation risk identification. According to the operating conditions of the system and the established component impedance model, the impedance analysis method is used to pre-analyze and judge the location and frequency characteristics of sub-synchronous oscillation occurrence, providing a reference for further on-line monitoring. In the actual operation stage of the system, based on the measured active power waveform and frequency information, combined with the oscillation warning threshold set by the equipment monitoring device, sub-synchronous oscillation events are warned.

[0056] For the impedance analysis method, the transfer function of the system can be obtained through theoretical solution to carry out detailed theoretical analysis. Specifically for the direct-drive wind turbine grid-connected system in this embodiment, the transfer function G0(s) is obtained through the above formula, and then the characteristic equation of the obtained transfer function is solved, and the eigenvalues are solved for discrimination to judge the stability of the system. The specific discrimination method is:

[0057] (1) If the real parts of all eigenvalues are negative, that is, the eigenvalues are located in the left half-plane region of the complex plane, then the system is stable to a certain extent.

[0058] (2) If there are positive real parts among the eigenvalues, that is, there are eigenvalues located in the right half-plane region of the complex plane, then the system is unstable.

[0059] (3) If 0 is included in the eigenvalues, but the real parts of the remaining eigenvalues are all negative, then no conclusion can be drawn on whether the system is stable.

[0060] As the basic theory for judging the stability of the system, the impedance analysis method should be combined with on-line monitoring technology when used in engineering. The on-line monitoring technology monitors the subsynchronous oscillation amplitude and duration of the system. For the actual subsynchronous oscillation event, according to the oscillation early warning threshold set in step 1, when the subsynchronous oscillation amplitude and duration reach the critical value, a warning is given to the dispatching operator.

[0061] Step 4, suppression of subsynchronous oscillation risk.

[0062] Optimize the parameters of the primary side and secondary side of the system respectively. For the optimization of the primary side parameters, before the occurrence of the subsynchronous oscillation event, combined with the historical fault information and accident disposal plan, formulate a disposal plan for gradually withdrawing the wind turbine and series compensation after the occurrence of the subsynchronous oscillation event, and conduct simulation verification on the effectiveness of the disposal plan; when the subsynchronous oscillation event occurs and a warning is given, according to the corresponding disposal plan formulated, cut off the grid-connected wind turbines and series compensation in rounds. For the optimization of the secondary side parameters, according to the impedance model of the key components established in step 2, optimize the parameters of the wind turbine and converter control system offline, adjust the parameters of the wind turbine and converter control system according to the Nyquist criterion, and verify its effectiveness through simulation.

[0063] In this embodiment, in terms of the analysis of subsynchronous oscillation characteristics, through the analysis of historical subsynchronous oscillation data, the weak links where subsynchronous oscillation occurs frequently can be identified. On the one hand, through tracing and analyzing the subsynchronous oscillation, determine the oscillation early warning threshold of the corresponding equipment monitoring device. During the actual operation stage of the system, according to the measured active power waveform and frequency information, combined with the set oscillation early warning threshold of the equipment monitoring device, give a warning of the subsynchronous oscillation event. On the other hand, according to the identified weak links, establish a detailed impedance model for the key power equipment such as wind turbines, converter stations, and series compensations that cause subsynchronous oscillation. Use the impedance analysis method to pre-analyze and judge the location and frequency characteristics of the occurrence of subsynchronous oscillation, providing a reference for further on-line monitoring.

[0064] In terms of the measures to suppress subsynchronous oscillation, on the one hand, formulate a disposal plan for gradually withdrawing wind turbines and series capacitors after a subsynchronous oscillation event occurs. When a subsynchronous oscillation event occurs, according to the risk warning information, orderly implement the established plan online to prevent the spread of the subsynchronous oscillation event. On the other hand, based on the impedance model and Nyquist criterion, offline study the adjustment strategy of the control system parameters of wind turbines and converters to fundamentally solve the problem of subsynchronous oscillation.

[0065] The method for early warning and suppression of wind power subsynchronous oscillation risks proposed in this embodiment has been practically applied in a certain area and achieved good results. Before adopting the method for early warning and suppression of wind power subsynchronous oscillation risks in this embodiment, subsynchronous oscillations involving wind turbine groups frequently occurred in this area. By adopting the method for early warning and suppression of wind power subsynchronous oscillation risks in this embodiment, based on the historical oscillogram data of subsynchronous oscillation events, analyze and restore typical subsynchronous oscillation events. According to the analysis results, identify the weak links in the system operation, and set the oscillation warning threshold of the corresponding equipment monitoring device according to the external characteristics of the event, so that the monitoring system can effectively warn and record the subsequent subsynchronous oscillation phenomena. And combined with historical fault information and accident disposal plans, before a subsynchronous oscillation event occurs, formulate a disposal plan for gradually withdrawing wind turbines and series capacitors after the subsynchronous oscillation event occurs. The online monitoring system can online monitor the subsynchronous oscillation signals of key nodes. When the amplitude and duration of the subsynchronous oscillation reach the critical value of the oscillation warning threshold, give a warning to the dispatching operators. According to the corresponding disposal plan formulated, cut off the grid-connected wind turbines and series capacitors in rounds, effectively preventing the continuous subsynchronous oscillation from causing the shaft torsional vibration and tripping of thermal power units, which affects the safe and stable operation of the power grid. On the other hand, according to the impedance model of key components, offline optimize the control system parameters of wind turbines and converters, and adjust the control system parameters of wind turbines and converters according to the Nyquist criterion. After testing in the actual system, it began to be promoted and applied, and good results have been achieved. After the fan parameters were rectified, the overall number of subsynchronous oscillations monitored in this area showed a downward trend.

[0066] Embodiment 2

[0067] Embodiment 2 of the present invention introduces a system for early warning and suppression of wind power subsynchronous oscillation risks.

[0068] As Figure 4 shown, a system for early warning and suppression of wind power subsynchronous oscillation risks includes:

[0069] An acquisition module, which is configured to acquire the operation state of a power system containing wind power;

[0070] A construction module, which is configured to identify the weak links in the operation state of the acquired power system and construct an impedance model of the power equipment in the identified weak links;

[0071] An early warning module, which is configured to monitor and give an early warning of whether a subsynchronous oscillation event occurs according to the obtained operating state of the power system and the constructed impedance model;

[0072] A suppression module, which is configured to optimize the primary side parameters of the power system, cut off the grid-connected wind turbines, and suppress the subsynchronous oscillation event when a subsynchronous oscillation risk event occurs.

[0073] The detailed steps are the same as those of the wind power subsynchronous oscillation risk early warning and suppression method provided in Embodiment 1, and will not be elaborated here.

[0074] Embodiment 3

[0075] Embodiment 3 of the present invention provides a computer-readable storage medium.

[0076] A computer-readable storage medium, on which a program is stored, and when the program is executed by a processor, the steps in the wind power subsynchronous oscillation risk early warning and suppression method described in Embodiment 1 of the present invention are implemented.

[0077] The detailed steps are the same as those of the wind power subsynchronous oscillation risk early warning and suppression method provided in Embodiment 1, and will not be elaborated here.

[0078] Embodiment 4

[0079] Embodiment 4 of the present invention provides an electronic device.

[0080] An electronic device, including a memory, a processor, and a program stored on the memory and executable on the processor, and when the processor executes the program, the steps in the wind power subsynchronous oscillation risk early warning and suppression method described in Embodiment 1 of the present invention are implemented.

[0081] The detailed steps are the same as those of the wind power subsynchronous oscillation risk early warning and suppression method provided in Embodiment 1, and will not be elaborated here.

[0082] The above are only the preferred embodiments of this embodiment, and are not used to limit this embodiment. For those skilled in the art, this embodiment can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this embodiment shall be included within the protection scope of this embodiment.

Claims

1. A method for early warning and suppression of wind power subsynchronous oscillation risks, characterized in that, Including: Obtain the operating state of a power system with wind power; Identify the weak links in the obtained operating state of the power system and construct the impedance models of the power equipment in the identified weak links; specifically, according to the sub-synchronous oscillation recording data, analyze and restore typical sub-synchronous oscillation events, restore the system frequency change situation, equipment operating state and relay protection device action situation in chronological order, and identify the weak links in the system operation according to the analysis results; based on the weak links, establish impedance models for the key power equipment causing sub-synchronous oscillation, and the key power equipment includes wind turbine generators, converter stations and series compensators; establish a control system impedance model for the secondary side control system included in the key power equipment causing sub-synchronous oscillation; According to the operating state of the obtained power system and the constructed impedance models, monitor and give early warning of whether a sub-synchronous oscillation event occurs; According to the obtained operating state and the constructed impedance models, pre-analyze and judge the location and frequency characteristics of the occurrence of sub-synchronous oscillation by impedance analysis method, combine the monitored active power waveform and frequency information, and based on the oscillation early warning threshold set according to the identified weak links, monitor in real time whether a sub-synchronous oscillation event occurs, and when a sub-synchronous oscillation event occurs, send out an early warning signal; When a sub-synchronous oscillation risk event occurs, optimize the primary side parameters of the power system, cut off the grid-connected wind turbine generators, and suppress the sub-synchronous oscillation event.

2. The method for early warning and suppression of wind power subsynchronous oscillation as described in claim 1, characterized in that When optimizing the primary side parameters, before the occurrence of a sub-synchronous oscillation event, combine the historical fault information and the accident handling plan to formulate a handling plan for gradually withdrawing the wind turbine generators and series compensators after the occurrence of a sub-synchronous oscillation event.

3. A method for early warning and suppression of wind power subsynchronous oscillation risks as described in claim 2, characterized in that, When a sub-synchronous oscillation event occurs and a warning is issued, according to the formulated accident handling plan and combined with the constructed impedance models, offline optimize the control system parameters of the wind turbine generators and converters, and cut off the grid-connected wind turbines and series compensators in rounds.

4. A method for risk warning and suppression of wind power sub-synchronous oscillation as described in claim 3, characterized in that, Adopt the Nyquist criterion to adjust the control system parameters of the wind turbine generators and converters to realize offline optimization of the control system parameters of the wind turbine generators and converters.

5. A risk warning and suppression system for wind power subsynchronous oscillation, characterized in that, Including: An acquisition module configured to obtain the operating state of a power system with wind power; A construction module configured to identify the weak links in the obtained operating state of the power system and construct the impedance models of the power equipment in the identified weak links; in the process of identifying the weak links in the obtained operating state of the power system, according to the sub-synchronous oscillation recording data, analyze and restore typical sub-synchronous oscillation events, restore the system frequency change situation, equipment operating state and relay protection device action situation in chronological order, and identify the weak links in the system operation according to the analysis results; based on the weak links, establish impedance models for the key power equipment causing sub-synchronous oscillation, and the key power equipment includes wind turbine generators, converter stations and series compensators; establish a control system impedance model for the secondary side control system included in the key power equipment causing sub-synchronous oscillation; An early warning module configured to monitor and give early warning of whether a sub-synchronous oscillation event occurs according to the operating state of the obtained power system and the constructed impedance models; According to the obtained operating status and the constructed impedance model, the location and frequency characteristics of the occurrence of subsynchronous oscillation are pre-analyzed and judged through impedance analysis method. Combining the monitored active power waveform and frequency information, and based on the oscillation warning threshold set according to the identified weak links, it is monitored in real time whether a subsynchronous oscillation event occurs. When a subsynchronous oscillation event occurs, a warning signal is issued; A suppression module, which is configured to optimize the primary side parameters of the power system and cut off the grid-connected wind turbines to suppress the subsynchronous oscillation event when a subsynchronous oscillation risk event occurs.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, the steps of the method for early warning and suppression of wind power subsynchronous oscillation risk described in any one of claims 1-4 are implemented.

7. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, the steps of the method for early warning and suppression of wind power subsynchronous oscillation risk described in any one of claims 1-4 are implemented.

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