Koji Kawahara

An interaction problem of distributed generators installed in a MicroGrid

This paper investigates an interaction problem that might be induced from various kinds of distributed generators installed in a MicroGrid. One of the most important features of MicroGrid is islanding operation. MicroGrid does not include large central generators and all distributed small generators have to share all loads existing in the MicroGrid. In this case, undesirable mutual oscillation problem might appear when MicroGrid goes into islanding mode. In this paper, MicroGrid itself and several types of distributed generator are modeled by using Matlab/Simulink. A typical case is simulated and examined by using the developed model.

A proposal of a supporting expert system for outage planning of electric power facilities retaining high power supply reliability

It is necessary for a power system to undertake maintenance works regularly to secure stable power supply, which inevitably cause outage of associated apparatus. This problem, referred to as the outage planning of an electric power system in this paper, has been so far made based on the knowledge and experiences of planning engineers. However, the scheduling made by the engineers is not necessarily optimal since there are no rational criterion to judge the results. Furthermore, this problem belongs to a class of combinatorial optimization problems. Therefore, we propose a supporting expert system for the outage planning retaining high power supply reliability. This paper presents some issues on the outage planning and an outline of the proposed supporting system. The concept of work unit is introduced and three security indices are utilized to properly merge several related outage work into the same group.

A proposal of a supporting expert system for outage planning of electric power facilities retaining high power supply reliability. II. Knowledge processing and simulation results

For pt.I see ibid., vol.13, no.4, p.1453-8 (1998). A prototype system has been constructed to validate the proposed method for assisting outage work scheduling that has been described in part I. The prototype system has the following three functions: (1) to identify outage areas to be caused by requested outage works, (2) to generate a work unit into which as many outage works as possible should be merged, and (3) to schedule work units and to determine a suitable system configuration to assure a high supply reliability. In order to realize these functions, it is necessary to deal with demands of planning engineers for improving power system security as well as some constraints such as the number of available workers and ordering among outage works. Therefore, knowledge processing is mandatory since these factors are difficult to formulate in conventional procedure oriented languages. The proposed system has been successfully applied to test cases with 50 outage work requests taken from a part of the 110 kV transmission line system. Results obtained have made clear the superiority of the proposed method to the current scheduling based on just the experience of the maintenance engineers.

An economic evaluation for an autonomous independent network of distributed generators

This paper proposes a method for economic evaluation of an autonomous independent network of distributed generators. There are some proposals for this kind of networks and microgrid is one of them. Microgrid is a new framework of power delivering system, which is formed by small, modular generation systems connected to each other to realize an autonomous small grid. In this paper, the total cost when the consumers in a microgrid optimally operated their distributed generators (DG) and energy storage systems (ESS) is reasonably estimated. It includes not only installation and operation costs but also the additional expenses to construct the microgrid. The authors try to find out whether it is economical or not for consumers to form this kind of autonomous independent network

Expert system for designing transmission line protection system

This paper presents a powerful expert system (ES) which makes a basic design of an adequate protective relaying system based on the knowledge of skilled protection engineers. Following the basic design, the ES carries out the relay setting and its validation by means of the integrated power flow and fault calculation programs. Furthermore, the ES has a capability of securing coordination among separately set relays. It is very flexible in that it is able to reset the relays according to power system changes. The effectiveness has been demonstrated by using a part of the Chugoku Electric Power Company System.

A study of allocation planning of dispersed electrical and thermal energy systems into distribution networks-optimal operation planning

The authors have so far studied a framework of an optimal placement problem of dispersed type of cogeneration systems and energy storage systems into distribution networks. The framework has included operation planning and installation capacity estimations before deployment planning. However, the procedures of them were very simple and not enough to reflect the actual situations. In this paper, a new framework is presented that includes other thermal energy sources and provides a more practical operation of them. In order to illustrate improved points, some numerical simulations are carried out by using test data.

A study of outage work allocation by means of agent technology

This paper presents an outage work allocation method by means of agent technology, which is used in the planning supporting system for monthly outage work. The agent technology is used for the purpose of minimizing the maximum of the ratio of the power flow of a line to its nominal capacity. Outage works in the agent are optimized using the extended optimal switching power flow (EOSPF). Adjustment of outage works among various agents has been achieved by communicating with each other. The convergence criterion is that no more communication is tenable. In order to confirm the effectiveness of the proposed method, it has been applied to a real power system with successful results.

Construction of automatic drawing system for power system diagram by using GA

In the case of analyzing a power system by numerical calculation for power flow and transient stability, it is very useful to make a power system diagram to ease the modification and the change of data for analysis. Although making a system diagram involves the replacement of nodes and the addition of components such as a generator and a load based on system configuration, it has been so far done by manpower. It not only takes a lot of time to make a drawing for a large scale power system, but also causes a mistake. This paper proposes a supporting system for drawing the system diagram by applying a method for the automatic replacement of nodes by means of a genetic algorithm.