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In tandem with the penetration of Renewable Energy Sources (RES) such as photovoltaic and wind power generation to reduce CO₂ emissions and conserve energy, development of advanced smart grid technologies is needed to secure a stable power supply of grid with RES by controlling power quality (voltage and frequency) within each secure range. This paper describes Japanese trend of the advanced smart grid technologies to harmonize RES and conventional bulk power system. Furthermore, several ongoing field tests to try to realize Japanese version of smart grid are briefly introduced.

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The line voltage control in a distribution network is one of the most important issues for a penetration of Renewable Energy Sources (RES). A loop distribution network configuration is an effective solution to resolve voltage and distribution loss issues concerned about a penetration of RES. In this paper, for a loop distribution network, the authors propose a voltage control method based on tap change control of LRT and active/reactive power control of RES. The tap change control of LRT takes a major role of the proposed voltage control. Additionally the active/reactive power control of RES supports the voltage control when voltage deviation from the upper or lower voltage limit is unavoidable. The proposed method adopts SCADA system based on measured data from IT switches, which are sectionalizing switch with sensor installed in distribution feeder. In order to check the validity of the proposed voltage control method, experimental simulations using a distribution system analog simulator “ANSWER” are carried out. In the simulations, the voltage maintenance capability in the normal and the emergency is evaluated.

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It is of prime importance to introduce distributed generators which can utilize renewable energy in order to improve the energy and environmental issue. When a distribution network has a large amount of distributed generators, voltage profile management becomes one of serious problems. To solve this problem, the authors have proposed “voltage profile control method” using power factor control of distributed generators in the previous works. Especially, the reactive power control of system connection inverter is utilized for voltage control in the method. On the other hand, the reduction of distribution power loss is also important issue because the resistance of distribution line is larger than that is utilized in the upper system. It is expected the distribution power loss is reduced by the flexible control of reactive power based on the reserve capacity of inverter. Hence, we improved the voltage profile control method in order to reduce distribution power loss. The proposed method is tested in 24-node model system and its effectiveness is shown.

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This paper proposes the optimal operation of power generation by waste. Refuse is taken as a new energy resource of biomass. Although some fossil fuel origin refuse like plastic may be mixed in, CO₂ emission is not counted up except for above fossil fuel origin refuse for the Kyoto Protocol. Incineration is indispensable for refuse disposal and power generation by waste is environment-friendly and power system-friendly using synchronous generators. Optimal planning is a key point to make much of this merit.
The optimal plan includes refuse incinerator operation plan with refuse collection and maintenance scheduling of refuse incinerator plant. In this paper, it has been made clear that the former plan increases generation energy through numerical simulations. Concerning the latter plan, a method to determine the maintenance schedule using genetic algorithm has been established. In addition, taking environmental load of CO₂ emission into account, this is expected larger merits from environment and energy resource points of view.

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In recent years, the number of connection of distributed generators (DGs) such as the photovoltaic generation (PV) and wind power generation is increasing, and there is in danger of changing the voltages in a distribution system by the precipitous output variation of DGs. In this study, the authors propose one voltage control method of a distribution system by the static var compensator (SVC) in consideration of cooperation with the load ratio control transformer (LRT) of laggard control response installed beforehand in the distribution system. The proposed method may be able to make the rated capacity of SVC small and may be able to reduce the aggravation of power factor of the distribution system, by setting up the dead band of voltage control appropriately. And the authors propose one determination method of the necessary minimum rated capacity and optimum control parameters of SVC in view of the cost of equipment and high-speed controllability. In order to verify the validity of the proposed method, the numerical calculations are carried out by using a distribution system model.

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In recent years, distributed generation (DG) and renewable energy source (RES) are attracting special attention to distribution systems. Renewable energy such as photovoltaic (PV) system and wind turbine generator are used as a source of clean energy. However, the large amount of distributed generation causes voltage deviation beyond a statutory range in distribution systems. This paper proposes a methodology for voltage control by using inverters interfaced with DG and tap changing transformers. In the proposed method a one-day schedule of voltage references for the control devices are determined by an optimization technique based on predicted values of load demand and PV power generation. Furthermore, decided reactive power output according to the locally measurable voltage based on droop characteristic. Slope and base value on droop characteristic are selected by fuzzy control. The proposed method accomplishes improvement against voltage distribution considered the reactive power output sharing and reduction of distribution loss. The effectiveness of the proposed method is verified by using MATLAB^®.

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When large amounts of photovoltaic power generation systems (PV systems) are integrated into power distribution systems, voltage rise due to reverse power flow will be a great concern. Because the PV systems must restrict their output power in case of the voltage rise beyond the statutory upper limit. In order to improve this problem, the cooperative control of reactive power by the PV systems was proposed and the reduction of output suppression loss was estimated for a model distribution system. The result indicated that the output suppression loss is reduced to about 15% while line loss is increased a little, and the sum of the two losses is decreased by half.

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Penetrating large amount of renewable energy sources into power system, battery energy storage performs an important role for smoothing their natural intermittency, ensuring grid-wide frequency stability, and suppressing voltage rise caused by reverse power flow. The ubiquitous power grid concept has been proposed as a smart grid in Japanese context, where the total battery capacity can be optimized by coordinating renewable energy sources, controllable distributed generators, and controllable loads on demand side, for example, heat pump based water heater with heat storage, and plug-in hybrid vehicle or electric vehicle with onboard battery, and so on. In this paper, we propose an autonomous distributed vehicle-to-grid (V2G) control scheme. The proposed V2G control has droop characteristics against power system frequency measurement at 200/100V plug-in terminal, and battery state-of-charge (SOC) is balanced within designable range by restraining V2G gain according to estimated SOC. Of course, the convenience for vehicle user is considered by V1G charge, which is one-way charging control for plug-out. Self terminal frequency measurement algorithm, model based battery SOC estimation method, and the proposed autonomous distributed V2G control are implemented to automotive power electronics circuit and electric control unit. These concepts are summarized as Smart Storage in ubiquitous power grid applications.

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Recently, the various political movements, which reduce CO2-emission, have been proposed against global warming. Therefore, battery energy storage systems (BESSs) such as NAS (sodium and sulfur) battery are attracting attention around the world. The first purpose of BESS was the improvement of load factors. The second purpose is the improvement of power quality, especially against voltage-sag. The recent interest is oriented to utilize BESS to mitigate the intermittency of renewable energy.
NAS battery has two operation modes. The first one is a fixed pattern operation, which is time-schedule in advance. The second mode is the load following operation. Although this mode can perform more the flexible operation by adjusting the change of load, it has the risks of shortage/surplus of battery energy. In this paper, an accurate demand forecasting method, which is based on multiple regression models, is proposed. Using this load forecasting, the more advanced control of load following operation for NAS battery is proposed.

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This paper presents a robust control approach to enhance the participation of Variable Speed Wind Turbines (VSWTs) in the primary frequency regulation during network disturbances. The proposed control system utilizes an H_∞ Linear Matrix Inequality (H_∞ LMI) based scheme to improve the closed-loop performance. In order to demonstrate the effectiveness of the proposed control scheme, it is compared with two classical control systems: the Inertial Control (IC) and the Modified Inertial Control (MIC). Several simulations on a multi-machine test system were performed in Matlab/Simulink environment. The H_∞ LMI controller optimizes the trade-off between frequency deviation smoothing and wind turbine (WT) speed deviation after the disturbance. Results show a considerable improvement in frequency deviation smoothing, optimal speed recovery and power injection, during a sudden variation in the system load, compared with the two traditional approaches. A desirable robust performance was also obtained with the proposed scheme after variations in the system parameters.

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This paper aims at development of a new emergency control scheme that can minimize interrupted power even under a severe fault condition by effectively using advanced power control devices available in the future power system. As the available equipment in the future grid, unified power flow controllers (UPFCs), one of the FACTS devices, and battery energy storage systems (BESSs) are considered in addition to generators and controllable loads. In order to overcome a transmission overload problem caused by a route fault, a new control method based on multiple optimal power flow (OPF) calculations is proposed and applied to the available equipment. Numerical simulations are carried out with a route fault in a meshed test power system. Several simulation cases, with and without UPFCs and BESSs, are compared to verify the effect of UPFCs and BESSs on the reduction of interrupted power. The results show that the UPFCs and the BESSs can work well in the expected operating mode by using the proposed control scheme, and that they make it possible to reduce the PNS.

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In recent years, many wind turbine generation systems (WTGSs) have been installed in many countries from a point of view of grobal environment due to CO₂ emission. But wind turbine generator output and annual energy production are dependent on wind characteristic of each area and a kind of WTGS. Authors' previous paper presented the analyses about annual electrical energy production and capacity facotor of WTGS for each area with different wind data. This paper presents a method to calculate each cost of WTGS component such as drive train system, generator and other equipments, and also to evaluate generation cost obtained from WTGS cost and annual electrical energy production. Based on these results, the optimal kind of WTGS can be determined for each installation area from an economical point of view.

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