Kikuo Takagi

System study of direct current power transmission system connected to wind farm

This paper discusses the DC transmission from a large-scale wind farm. The useful controls are proposed and studied by the digital simulation. Many advantages of the system are reported, and the robustness of this system is shown. This system enables usage of simple squirrel-cage induction generator. The rating capacity of 12 MW with the voltage source converter for the DC system is assumed in this study.

Development of PCS for battery system installed in megawatt photovoltaic system

Population growth, global warming, depletion of fossil fuels, and ensuring nuclear power safety are serious energy issues, and solutions to these issues have been becoming increasingly important globally. One solution that has been focused on is the use of renewable energy. The introduction of photovoltaic (PV) and wind turbine (WT) systems has been accelerating around the word. However, the power generation efficiency of these renewable energy systems is low, and the power generation level is unstable. At present, therefore, the ratio occupied by renewable energy in the overall power generation system cannot be considerably increased from the viewpoint of grid stability. Nevertheless, renewable energy is one of the most important energy sources for the future, and various studies and field demonstrations are underway. This paper gives an overview of a MW PV plant equipped with a large-capacity battery system (NAS battery), together with the results of grid stability enhancement achieved with the battery system, in trials conducted by Okinawa Electric Power Company Co., at a research facility on Miyako Island. In particular, this paper reports on power stability control and frequency compensation using a power conditioning system (PCS) for energy storage. This MW PV plant and power storage system were installed in an independent power grid on Miyako Island. The total grid capacity is about 50,000 kW. The MW PV system and an existing WT system make up about 16% of the total system capacity, and the battery system makes up about 8%. Power supply instability and frequency fluctuations become larger with an increasing proportion of power generated by renewable energy. The developed PCS using the battery system showed good performance in solving this problem.

Demonstration results using Miyako Island Mega-Solar Demonstration Research Facility

The Miyako lsland Mega Solar Demonstration Research Facility has two objectives. The first objective is to examine the impact on the power system from installing large scale renewable energy such as photovoltaic power. The second objective is to study measures for power system stabilization by analyze data from PV and rechargeable battery. This pilot project will be conducted for three years (until March 2013) by the Okinawa Electric Power Company, Inc. This paper will explain the overview of the Miyako Island Mega Solar Demonstration Research Facility, then explain in detail about each device such as photovoltaic system and storage battery and end with the report of favorable demonstration results recorded from the execution of the research.

A Voltage Control Method of Static Var Compensator for the Remote System Interconnected by Long Distance AC Cables

The voltage variation in the remote system is large when the system is connected by long distance AC cables due to the cable capacitance. In Japan, the longest 54km 66kV AC submarine cable interconnection between Kyushyu mainland and Goto-islands was commissioned in 2005. It is requested to mitigate the voltage variation caused by switching off and on of one circuit of AC cables out of two circuits when a fault occurs. Since the conventional voltage control methods such as transformer tap changer or shunt capacitor and reactor banks are not sufficient because of their slow response time, therefore an SVC (Static Var Compensator) was installed in Goto-islands. In such application, SVC control method should be developed not to override the existing voltage control systems. This paper describes the SVC control method developed for Goto-islands AC interconnection project, which can be applied to similar applications. The effectiveness of the control method was verified by effective-value-based simulation results and field test results of which implemented before SVC commissioning in 2007.