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The interconnection of distributed generators (DGs) in a power system increases the difficulty of managing the system. The minimization of the voltage deviation by network reconfiguration is an important requirement for dealing with the issue. We had previously developed a reconfiguration technique, named the intelligent flow algorithm (IFA), for determining the optimum or suboptimum network configuration within a short computation time. In the present paper, we propose an extension of IFA, named the extended flow algorithm (EFA), for more effective determination of the optimal network configuration of a distribution system containing massive installations of DGs. EFA is a two-stage method in which the configuration that produces uniform power supply, referred to as the balanced configuration, is first generated, and then used to seek the optimal configuration using an improved branch exchange approach. Accordingly, EFA is more simplified to improve its computation speed on large-scale systems. The algorithm was tested by case studies of different test distribution systems in the MATLAB environment, and was confirmed to have high performance to cope with DG installations and large-scale systems. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Reactive power supply plays an important role in active power supply with adequate system voltages. Various pricing mechanisms for reactive power supply have been developed and some of them have been adopted in some power systems, but they are in a trial stage. The authors also focus on development of a pricing method for reactive power ancillary services. This problem involves two technical issues: rational estimation of the cost associated with reactive power supply, and fair and transparent allocation of the estimated cost among the market participants. This paper proposes methods for evaluating the contribution of generators and demands. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 36-45, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21016 [ABSTRACT FROM AUTHOR]

The authors have proposed Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS) as a future power distribution system. In the FRIENDS, new facilities called quality control centers (QCCs), which consist of power electronics devices, distributed generators (DGs), energy storage systems (ESSs), etc., are installed between distribution substations and customers. By controlling and operating those devices in QCCs adequately, various functions can be realized. Particularly, when a power supply from the transmission network is interrupted, isolated local networks which consist of some QCCs are composed in order to realize uninterruptible power supply. In the isolated local network, the DG and ESS in QCCs are employed as backup generators. This paper proposes a novel distributed and autonomous method for balancing the supply and demand during isolated operation. This paper also investigates the effectiveness of the proposed method through some computational simulations using PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

The authors have proposed the Flexible, Reliable and Intelligent ENergy Delivery System (called “FRIENDS”), which is a new concept for future power distribution systems. Also, a “micro grid” which is a similar concept to FRIENDS has been developed. In a micro grid, an independent distribution system can be constituted by a number of distributed generators. In this paper, FRIENDS, Micro grid, and conventional distribution systems are compared quantitatively in supply reliability and system cost through time sequential Monte Carlo simulations. In addition, for cost evaluation, interruption costs are included to show risk incurred by unsupplied energy. Finally, the authors search for preferable form with install and operation of distributed generators and network composition according to social cost including interruption cost and system cost. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 28–37, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20659 [ABSTRACT FROM AUTHOR]

Recently, the basic framework of electric power systems has been changed significantly by deregulation of electric power industry. Also, distributed generators (DGs) such as renewable energy generations, co-generations, and energy storage systems have been introduced into the demand sides not only for saving energy and the global environment, but also for compensating voltage drops and supply interruption. In the future power systems, a lot of small-sized DGs will supply the electricity with existing large-scale generators under a competitive environment. In this context, it is desirable that DGs contribute to stable, reliable and economic operations by coordinating with existing large-scale generators. For example, power from large-scale generators could be leveled if DGs are operated during the peak period. Also, ancillary services such as frequency control, voltage control, and supply of reserve capacity could be executed by controlling DGs directly or indirectly. Under these circumstances, the authors have proposed a new power distribution system: Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS). This paper investigates some kinds of power supply systems which coordinate DGs with existing large-scale generators including the concept of FRIENDS and considering how DGs are managed. The effects of DGs which contribute to supply the energy and/or the reserve in every power system are evaluated. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 48–56, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20358 [ABSTRACT FROM AUTHOR]

This paper proposes a new dynamic preventive control strategy to maintain power system security, in terms of both transient and midterm stabilities. While the authors have already presented preventive control strategies for transient stability, a new problem has arisen in midterm instability in which some generators lose synchronism after 10 seconds or more from a fault clearance. It is clear that the cause of the instability is mainly post-contingency dynamic steady-state instability. This paper first shows a preventive control strategy for improving midterm stability using a dominant eigenvalue of post-contingency equilibrium point. This paper also presents a unified dynamic preventive control algorithm that can maintain both stabilities together. In this algorithm, the time domain for each stability problem is considered appropriately and the difference between the classical model and the detailed model is analyzed in detail. The effectiveness of the proposed method is examined with numerical examples for a model system. [ABSTRACT FROM AUTHOR]