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Natural energy sources such as wind turbines and photovoltaic power generators cause instability of the power grid due to their output fluctuations. Battery energy storage systems (BESSs) are being considered as a countermeasure for this issue. A Modular Multilevel Cascade Convertor (MMCC) is one suitable circuit topology for BESSs, because each cell can control each battery's state-of-charge independently, and the level of generated harmonics is low enough to eliminate the AC filter normally installed in conventional two level converters. This paper describes the development of a real-scale (500 kW) H-bridge MMCC for BESSs and reports successful test results of the control functions with a scale down grid model and a 6.6-kV real-scale distribution line.

Natural energy generators such as wind turbines and photovoltaics cause instability of the power grid due to their output fluctuations. Battery energy storage systems are being considered as a countermeasure for this issue. This paper gives an overview of battery energy storage systems used for stabilizing the output fluctuations of natural energy generators in Japan. Some verification test results are also shown.

Wind turbines (WTs) are considered to be one of effective approach to solve global warming and energy issues. However, the output of WTs depends on the weather conditions and the natural environment, which cause large fluctuations in the output power, leading to insufficient of frequency adjustment capacity of the power grid. Several methods have been examined to compensate for such large fluctuations using batteries. In this paper, we describe the development of the world's largest constant output stabilization system using 34 MW sodium sulfur (NAS) batteries for a 51 MW wind farm at Futamata in the Tohoku district of Japan, as well as our field experiences indicating excellent operating performance.

The paper introduces the very high-capacity, megawatt-rated (MW-rated), power electronics (PE) technology trends for the renewable energy (RE) and for the energy greening in industrial area. The PE is indispensable for energy conversion from the RE to the AC power network. In order to expand RE supply capacity, RE generation facilities are now scaled up above megawatt (MW) range. The paper introduces the power conditioning system (PCS) for photo-voltaic (PV) generation, the back to back (BTB) converter for wind power (WP) and PCS for the battery energy storage system (BESS) developed to catch up such demands. Owing to the recent development of the power semiconductor and control devices, even in the high power range, the conversion efficiency and the operation flexibility have been remarkably improved compared with the old generation. The paper also introduces the high efficiency uninterruptible power systems (UPS) technology contributing to the Green IT facilities. The extra large PE technology rated at several tens of MW is also introduced for the Green Factory.

Wind Turbine Generator Systems (WTGSs) are considered to be one of effective approach to solve global warming and energy issues. However, the stability of the output power generated from WTGSs depends on the weather conditions and the natural environment, and any instability in the power causes frequency fluctuations in the power grid. Several methods have been examined to stabilize such fluctuations using batteries. In this paper, we describe the development of an inverter using sodium sulfur (NAS) batteries to stabilize the power from a wind farm and our field experiences indicating excellent operating performance. This system is the world's largest constant-output stabilization system using 34 MW NAS batteries for a 51 MW wind farm at Futamata in the Tohoku district of Japan.

In recent years, the renewable energy sites are installed increasingly in the world. These sites sometimes cause the voltage fluctuation in the power system. Especially the wind turbine systems may cause the voltage fluctuation in the power system by the wind power variation. The STATCOM can reduce this voltage fluctuation by canceling the reactive power. The STATCOM is suitable to compensate several MVar of reactive power and covers the capacity range up to 3MVA by 500kVA step. This STATCOM is also installed for the suppression of the voltage fluctuation by the large capacity fan. This paper describes the STATCOM systems and some field performances of the STATCOMs which have been installed more than 10 sites.