In this article, the JST CREST research area entitled “Creation of Fundamental Theory and Technology to Establish a Cooperative Distributed Energy Management System and Integration of Technologies Across Broad Disciplines Toward Social Application“ is introduced and presented. After reviewing its unique features and some backgrounds, new visions and research challenges are discussed.

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This paper presents a simple analysis tool for torsional vibration of the rotor shaft of turbine generator which is interconnected with a power system with self-commutated converters. The evaluation is based on the analysis of measurement data in the field and the instantaneous value based power system simulation. A number of power converters with large capacity are installed in industrial power systems. Especially, interharmonics originated from self-commutated converters cause the torsional vibration at the rotor shaft of rotating machines. The interaction between rotating machine and converters is known as sub-synchronous torsional interaction. The resonance between interharmonics from converters and the natural frequency of the rotor shaft cause the large torsional vibration, which leads to the shaft damage. In this paper, the influence of interharmonics to turbine generators is investigated. If there were air gap torque fluctuations with frequency near the natural frequency caused by interharmonics, which have frequency less than 100 Hz of sideband wave caused by asynchronous pulse width modulation, the rotor shaft might be damaged by the torsional vibration. In this paper, the emerging condition of the torsional vibration and the impact to the generator are investigated.

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Large-scale deployment of electric vehicles adds electric load to the power system. Without control of the temporal distribution of EV charging, steep load peaks could arise in the power system. Therefore, we propose two charging algorithms for the purpose of load leveling. The first algorithm uses off-peak rate period. We test this algorithm in two cases: in the first, all EVs are assigned at the same off-peak rate period; in the second, all EVs are divided into two groups, and each group is assigned at its individual off-peak rate period separately. The second algorithm changes the starting time of charging according to the charging duration required for full charge of EV. We test this algorithm in two cases: in the first, charging start time varies linearly with charging duration; in the second, charging start time varies quadratically with charging duration. The results shows that the algorithm that changes the charging start time based on the quadratic function is the most effective for load leveling.

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The liberalization movement in Japan will be expanded to the residential sector and full liberalization of the retail market will be achieved in near future. Under this background, it is expected that transaction in Distribution Network (DN) which has many consumers of the residential sector is activate. Furthermore, consumers can control their loads depending on selling prices offered by retailers with introducing Demand Response (DR) technology such as Home Energy Management System (HEMS). Due to the variation of load by DR, however, a voltage profile in DN could be changed compared to the present situation. This may make the voltage management difficult and cause several problems such as voltage deviation from an adequate range. In this paper, the impact of DR in a liberalized electricity market on DN is evaluated for efficient voltage management. In order to evaluate the behavior of the retailer and consumers, this paper proposes a bi-level programming approach based on the Stackelberg game model. Solving the bi-level programming problem including the power flow equation for a DN model based on IEEE 13-bus test feeder, we analyze the impact of retailer and consumers on voltage in DN in order to account for transaction between these market players.

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Temperature on a contact surface after a high-current vacuum arc influences on the interruption ability of a vacuum interrupter (VI). This paper shows relation between the interruption ability of the VI with AMF electrodes and the contact temperature after the high-current arc. First, 2D axis-symmetric temperature calculation model was constructed, taking into account with a two-region arc input and melting and evaporating losses. To validate these calculation results, we performed contact surface temperature measurements after high current vacuum arc, using a two-color pyrometer and high-speed flaming video. Assuming 50% of the total arc energy was consumed in the anode region, the calculation gives fairy good result. Next, for several types of AMF electrodes, their temperature variations during and after the high-current arcs were calculated and compared each other. Then these AMF electrodes were built into the prototype vacuum interrupters, and investigated under short-circuit interruption tests. As the result, the interruption ability was found to be related with peak temperature on the contact surface at current zero.

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This paper explains an error involved in well-known formulas of the earth-return impedance of an overhead multi-conductor derived by Pollaczek, Carson and Sunde. It has been said that Pollaczek's infinite integral formula is numerically instable, and Carson's formula cannot deal with displacement currents. This paper has shown an accurate earth-return impedance formula considering the displacement currents, and Carson's formula is modified so as to be able to deal with the displacement currents. Also, an approximate formula considering the displacement currents is derived. The formula is of a simple closed form and is applicable to high frequencies.

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