Development and Practical Operation of Micro-grid with Seamless Transition from Grid-connecting to Islanding Operation by use of several types of distributed power generation Systems.

System configuration of the micro-grid.

Fig.1 System configuration of the micro-grid.

Bode diagram of distributed generators.

Fig.2 Bode diagram of distributed generators.

Block diagram of the load following controller.

Fig.3 Block diagram of the load following controller.

Micro-grids are expected to promote the introduction of distributed generators, which contribute the reduction of CO2 emission. A micro-grid of 600 kW output has been operating at Institute of Technology of Shimizu corporation since July, 2006. The photovoltaic of 10 kW is installed. Main generators are two gas engine CHP systems which rated power are 350 kW and 90 kW, respectively. Two power storages: nickel metal hydride battery (described as NiMH) and electric double layer capacitor (described as EDLC) are also installed to keep high power quality. These power storages are allotted roles to compensate fast component of power fluctuations.

We have developed a load following control technique of the different types of distributed generation systems so as to keep incoming power flow constant at the incoming point in the grid-connecting operation. The load following control technique have applied to continue the islanding operation stably so as to balance the quantities between the load demand and power generation in the micro-grid. Consequently, the micro-grid is possible to transfer seamlessly from the grid-connecting to the islanding operation. The power quality in the transient and during the islanding operation is maintained similarly to the grade of existing grid.

We have evaluated the power quality in the islanding operation from results of 50 times transition experiments. The frequency fluctuation has been evaluated to stay within 50 ± 0.2Hz by probability of 99.9%. The voltage fluctuation has been evaluated to satisfy completely ITIC (Information Technology Industry Council; formally CBEMA) curve which is the power supply standard for the IT equipment of U.S.A.


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[2] S. Numata, K. Morino, E. Shimoda, T. Ito, T. Tanabe and N. Sasaki、Development of micro-grid control system、2006、Meiden-jiho, Vol.309, No.4, pp.9-12 (in Japanese)
[3] S. Numata, K. Morino, E. Shimoda, S. Suzuki, Y. Ueda, T. Ito and N. Sasaki、Development of Power system stabilizer with a EDLC、2006、Meiden-jiho, Vol.309, No.4, pp.13-17 (in Japanese)
[4] S. Numata, E. Shimoda, K. Morino, J. Baba, T. Nitta and E. Masada、Development of a Micro-grid and Islanding Operation Control Methods、2008、The 2008 Annual Meeting Record IEEJ, Vol.6, 6-S6-4 (in Japanese)
[5] E. Shimoda, S. Numata, J. Baba, T. Nitta and E. Masada、Capacity Evaluation of Several Types of DG Systems in Micro-grid using Load Demand Analysis and Frequency Response of DG Systems、2009、IEEJ Transactions on Power and Energy, Vol.129, No.12, pp.1553-1559 (in Japanese)
[6] Y. Shindo and K. Ishikawa、Development and Application of Nickel Metal Hydride Battery、2006、Electric Review, Vol.91, No.12, pp.22-25 (in Japanese)
[7] T. Koga, M. Kawamura, K. Sugimoto and Y. Shindo、Control of Power Converter using virtual generator model for Micro Grid、2006、The 2006 Annual Meeting Record IEEJ, pp.122-123 (in Japanese)

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