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This paper proposes a voltage control method in cooperation with a tap changer, such as a step voltage regulator, for power distribution lines using power conditioning systems. Generally, a town which plays a role of a virtual power plant has an energy management system and consists of a lot of power conditioning systems in houses. In this paper, it is clarifies that the method is able to control the voltage at the connecting point of the distribution system properly cooperating with the step voltage regulator under several voltage fluctuation conditions. Furthermore, it is shown that a communication between the energy management system and power conditioning systems enables the system to resolve unevenness output of reactive power of the power conditioners.

This paper aims at proposing novel methods for multi-terminal VSC HVDC system design and operation with large-scale wind farms. The paper is based on the hierarchical optimal power flow with small-signal stability constraint. Multi-terminal VSC HVDC (MTDC) system reinforcements are designed in the first step. The reinforcement capacities of the HVDC systems are designed by optimization process. Economic load dispatch in the reinforced system with MTDC is carried out in the next step. By the proposed method, multi-terminal VSC HVDC systems can be utilized more effectively even when wind production is not high. Several multi-terminal configurations are designed. Wind power hosting capacities, net present value, and profitability index of the systems are analyzed.

This paper proposes a decentralized charging control method of a battery energy storage system (BESS) that can prevent the over-capacity of a pole transformer in low-voltage (LV) distribution systems due to reverse power flow from the photovoltaic generation system. The distribution system operator provides the charging parameters defined as the relationship between the state-of-charge (SoC) and the charging threshold determined by using only the LV-distribution system configuration and the demand-side information to customers. Each BESS charges the power according to the provided parameters. A high charging amount can be maintained by automatically changing the charging mode based on the change in SoC. Results of the numerical simulation demonstrate that the proposed method can prevent the over-capacity of PTr and maintain the high charging amount of a BESS in LV-distribution systems. Further, the maximum power flow at the distribution substation and the distribution losses in MV-distribution system can be reduced.

This paper reports simple and effective control logic for connecting abrupt, steep and short-term power sources (for example, regenerative power from electric railway vehicles) to distribution lines with renewable energy units connected. With conventional centralized control systems, power conditioner units were unable to keep voltage of the distribution line within an acceptable range when extremely steep regenerative power flowed backward in the line, due to control delay. This new logic has power conditioner units exchange calculated control amounts between themselves repeatedly in fixed intervals. When voltage of the distribution line rises relatively slowly from renewable energy generators such as PV, the power conditioner unit can suppress the voltage rise immediately with no control delay, if regenerative power flows backward to the lines and voltage departure from an acceptable range is foreseen. This logic needs no central control unit in particular, as its power conditioner units can effectively execute and coordinate control between themselves. We verified the effectiveness of this logic through an experiment at our demonstration facility.

This paper investigates the economic benefits of multi-terminal VSC HVDC systems where large scale wind farms are installed. The comparison between multi-terminal VSC HVDC systems and point-to-point VSC HVDC systems in economic aspects is the main topic. Security-constrained optimal power flow analysis is carried out considering the N-1 criterion in mixed AC / VSC HVDC power system models in Japan. Payback period index is adopted for the economic evaluations. A new idea of both wind power and AC grid power transmission through multi-terminal systems is suggested. The initial investment costs of the multi-terminal VSC HVDC systems can be paid back earlier than those of the point-to-point VSC HVDC systems due to higher system capacity factor.

There are a lot of potentials to install photovoltaic panels along the railroad track and some systems have been already realized in Japanese railway network. If a lot of PV systems have installed along the railway premises in the future, the generated power has to be transmitted to the station for the self-consumption because the electric loads along the railroad track between the stations are, in many cases, small. To be cost effective, simple cooperative reactive power control of power conditioner for distribution line voltage control to realize inverse backflow from PV panels to station is required, proposed and tested in the practical trackside solar system. The results of the cooperative reactive power control by two PV-PCSs are shown in this paper.

This paper proposes a generalized admittance based method for fault location analysis of distribution systems. Based on the measurements collected from the feeder breakers and intelligent switches during a fault, the fault type and faulted feeder section are first determined by examining the over-voltages and over-currents on the breakers/switches. The load demands, faulted line segment and fault location are then determined sequentially by finding a set of loads, a line segment and a fault location that has minimal distance between the currents measured at the boundaries of the feeder section, and the estimated currents determined by multiplying the measured voltages by an equivalent admittance matrix determined for the feeder section when applying the given load and fault conditions to the feeder section. The proposed approach determines the equivalent admittance matrix for a feeder section with one or two measuring ports through topology and circuit analysis, and for a feeder section with more than two measuring ports through Kron reduction on nodal admittance matrix. Numerical examples are given to demonstrate the effectiveness of the proposed approach.

For future power outage management of a power distribution system, a smart meter is expected to be used. Disconnection of a high-voltage power distribution line during a power outage runs the risk of a major disaster, so it needs to be detected quickly. In this paper, we describe a power outage management system developed as a part of an in-house smart grid demonstration test for detecting disconnections of highvoltage power distribution lines. Then we propose and validate a disconnection detection method that does not need information of connection phases of pole transformers.

This paper proposes a hybrid current profile based fault location algorithm for double-line-to-ground (DLG) faults in a distribution system. The method uses both short-circuit fault current profile (average of fault currents recorded for the faulted phases) and during-fault load current profile (corresponding to the un-faulted phase) to estimate an accurate fault location. The method is extended to include the effects of fault resistance in determining the fault location. Both fault current profiles and load current profiles are simulated for different values of fault resistances. The profiles are also extrapolated for those fault resistances corresponding to which the simulated profiles are not available. Numerical examples on a sample distribution feeder with multiple laterals and load taps are provided to validate the proposed algorithm for its robustness.