Hiroumi Saitoh

A new index extracted from line flow fluctuation to evaluate power system damping

The authors propose an index to evaluate the damping effect of a power system on a dominant mode of electromechanical oscillation. The index is obtained from numbers of line flow fluctuations in which the dominant mode is strongly observed even in the normal state of the system. To extract the index from the fluctuations, a combined technique is developed which is based on FFT (fast Fourier transform) processing and principal component analysis. The technique is applied to the field data which have been acquired at a single tie-line of a power system in Japan. The regression analysis with respect to the index and the total generation of the system shows that the damping effect of the system becomes strong with an increase of the total generation. This property, which is called a droop characteristic, could be used to determine the steady-state stability region and to identify whether the system is in the normal or alert state. >

An autonomous decentralized control mechanism for power flow in an open electric energy network

This paper discusses a power flow control mechanism for the “open electric energy network” (OEEN), which has been studied by the authors as a demand-side network suitable for a free market of electricity. The important concept of OEEN is that electric energy is treated like a packet of mail, with information about the sender (power producer) and the receiver (consumer). The control mechanism discussed in this paper is called the electric energy router and includes an energy storage device. The electric energy router controls the storage device in such a way that the “electricity packet” reaches a specified consumer from a specified power producer autonomously and in the distributed manner. This paper shows that optimal control theory can be applied to determine the control action of the electric energy router. The obtained optimal control action minimizes the difference between the load pattern of the consumer and the supply pattern of the router under the inequality constraints of energy storage capacity. A numerical example is given in order to check the validity of optimal control theory application. In order to manufacture a small-scale electric energy router for experiments, its basic structure and power control performance are studied through simulation studies.

On-Line Security Monitoring by Detecting of Specified Modes Through Power Flow Observation

Abstract A transmission line selection algorithm is developed for the security monitoring by detecting of a specified mode through the power flow observation. The algorithm is based on the coherent grouping approach by Chows group. The combination of the synchronizing coefficients and grouping matrices, is used for the selection of the appropriate line for the monitoring. The concept of the flow monitoring is reasonable for the security check, which is confirmed through the field data. The proposed approach has been tested by 19-generator, 28-bus and 39-line model. Application of FFT is also discussed.

Improvement of frequency stability by using battery to compensate rate shortage of LFC reserve

AbstractBy introducing large amount of renewable energy sources and electricity deregulation, procuring sufficient reserve power for Load Frequency Control (LFC) becomes difficult for system operator. In this paper, at first, impact of ramp rate shortage on frequency stability is shown by simulation study. Next, a novel battery utilization method is proposed to compensate the rate shortage. In the method, a battery is driven by the component of LFC signal which cannot be responded by existing LFC units. Through comparison study with conventional battery control method, it is clarified that the proposed method can efficiently improve LFC performance under the large amount of renewable energy sources interconnection.

Security Enhancement of Multiple Distributed Generation by the Harmonized Grouping

By social and technical reasons, the amount of the distribution generation will considerably increase in the future power supply system. For the secure supply and the safe operation of the distributed generation (DG) power, the harmonized grouping of DG plants and the careful interconnection of the DG micro grid to the existing power grid are required. This paper discusses the DG grouping in order to harmonize the investment of assets, the quality of power supply and the cooperation with the existing power grid. Model analysis shows there are several schemes of the DG plants and the storage device related to the combination of economical parameters. Recently, the demonstration research projects of DG grouping have been performed in Japan. Brief description of these projects is also included

Dominant mode filter for enhancing power system stability

Abstract This paper proposes a new type of filter, that is, a dominant mode filter (DMF) which uses the rotor speed fluctuations for dynamic security assessment and stability enhancement of power systems. The proposed filter can be used in detecting the degradation of damping power of the system and in improving the stabilizing ability of a control device such as PSS. The basic concept of the DMF design is based on the inherent characteristics of the power system network and the application of principal component analysis to a covariance matrix of the rotor speed fluctuations. The coefficients of the DMF are easily computed from the eigenvector of the covariance matrix. The weak damping modes which are useful for generating the control signals of the stabilizing devices, are satisfactorily estimated from the rotor speed fluctuations by means of the DMF. In the computing process of the DMF coefficients the ‘mode energy’ and ‘mode profile’ are also obtained from the eigenvalue and the eigenvector of the covariance matrix respectively. The mode energy is the strength of each mode contained in the fluctuations. The mode profile expresses the distribution of the mode oscillation with the rotor speed responses of all machines. Since, in the DMF design, the on-line fluctuation data are used, the weak damping modes, the mode energy and the mode profile can be estimated adaptively according to the system situation. In this paper, applications of the DMF are also discussed. One application is to use the mode energy as an on-line stability index. If the damping power of the system becomes weak, a system operator can detect signs of an unstable condition by observing the time variation of the mode energy. Another is a disturbance identifier to find the location and severity of a disturbance. This identifier utilizes the mode profile and mode energy. The third application of the DMF is to supply the slower mode component as a global control signal for HPSS (Hybrid PSS)11. The mode energy can be also utilized for adapting the parameters of the HPSS.

Neural network based preventive control support system for power system stability enhancement

The authors propose an application of a newly developed neural network to the preventive control of a power system. The purpose of the proposed control is to improve the damping effect of the system on electromechanical modes by reallocating load to generators. Since the neural network has flexible learning capability the authors apply it to identify the complex and nonlinear relation between the damping effect and the distribution of generating power. The trained neural network acts as the support system which aids an operator in performing the generating reallocation for enhancing the system stability. Furthermore, the authors develop a new type of neural network which can deal with the equal constraints about the output layer in the error-back-propagation type of neural network because it is important for the generating reallocation to satisfy the equal constraint about the energy balance between generation and load.<<ETX>>

Corrective Generation Rescheduling Based on Neural Network for Preventive Control

Abstract This paper proposes a corrective generation rescheduling method based on a neural network for the purpose of reducing the risk of post-outage overloading. The neural network evaluates the severity of line contingency and its weighting factors are utilized for the generation rescheduling. The simulation study on the IEEE 30-bus system shows that the proposed method can become an useful decision support tool for system operators in the alert state of power systems.

Security Diagnosis by Means of Tie-Line Flow Fluctuation Monitoring

Abstract This paper proposes that the line flow fluctuation can be used as a new security factor to assess the total system damping of the slow natural mode. The line flow fluctuation is evaluated by partitioning Its power spectrum into two major oscillatory modes. The 24 data points observed at the tie line In the central-east area of Japan, are used to extract the features of the fluctuations. A significant result is a droop characteristic of the fluctuation spectrum with respect to the system demand. The system status can be separated Into the SECURE and ALERT state by using the above characteristic. The statistical investigation has been done for identifying the local damping effect.

Evaluation of battery capacity required for assist of balancing control

AbstractThe growth of Renewable Energy Sources (RES) requires more reserve for generation-demand balancing. In recently, energy storage system such as battery is focused on as additional reserve power source. The authors have proposed Battery-Assisted LFC (BALFC) in which the battery is driven by the excess component of LFC signal over the ramp rate limits of LFC unit. In this paper, the required battery power and energy capacity for the BALFC is evaluated by simulation study. As a result, it is clarified that additional reserve can be decreased by using BALFC compared with the case using additional LFC units. Also, the required energy capacity is smaller than required power capacity and it is found that large energy capacity is not needed to utilize the battery for the assist of LFC.