Okinawa Enetech

Okinawa, Japan

Okinawa Enetech

Okinawa, Japan

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Sasamoto H.,University of Tokyo | Imanaka M.,University of Tokyo | Baba J.,University of Tokyo | Higa N.,Okinawa Enetech | And 2 more authors.
2013 4th IEEE/PES Innovative Smart Grid Technologies Europe, ISGT Europe 2013 | Year: 2013

The use of a pump system for water supplies as the controllable load is proposed in order to compensate power fluctuations caused by renewable energy sources (RES) in an isolated island, and a control method of pump system power consumption is discussed. The dynamic model of the pump system is proposed taking into account the two step response of the power consumption caused by the pressure surge. Then, as the way to compensate the short cycle power fluctuations of RES by use of the pump system, deadbeat control with consideration of the pressure surge is proposed. Experimental results with deadbeat control show that power consumption can be settled more quickly compared with the case without deadbeat control. This shows that by use of deadbeat control, it is possible to compensate more rapid power fluctuations of RES. © 2013 IEEE.


Yoshihara T.,University of Tokyo | Yokoyama A.,University of Tokyo | Imanaka M.,University of Tokyo | Onda Y.,University of Tokyo | And 4 more authors.
2010 International Conference on Power System Technology: Technological Innovations Making Power Grid Smarter, POWERCON2010 | Year: 2010

In this paper, a novel control method using seawater desalination plant instead of battery energy storage system as a controllable load, to suppress the frequency fluctuation is proposed. A high pressure pump is usually installed for reverse osmosis method in the desalination plant. In this research, it is assumed that the power consumption of the high pressure pump can be changed continuously and rapidly through the control of inverter. Since every seawater desalination plant has a storage tank of the produced fresh water, the power consumption of motor can be changed without affecting its daily production. The new method is proposed in this paper for securing regulating capacity while taking into account customer's convenience. A linearized power system model was used to calculate the system frequency or regulating capacity. The results of the study indicate that the fluctuation of the system frequency can be suppressed by the control of power consumed by seawater desalination plant. ©2010 IEEE.


Imanaka M.,University of Tokyo | Sasamoto H.,University of Tokyo | Shimada N.,University of Tokyo | Baba J.,University of Tokyo | And 3 more authors.
IEEJ Transactions on Industry Applications | Year: 2016

Okinawa has many islands, and the installation of photovoltaics (PVs) is accelerating. This paper focuses on the compensation of power fluctuation in PVs by the use of variable speed control of waterworks pumps for weak island grids. A simple model of a waterworks pump system is proposed to calculate power consumption, water flow and pressure from the power converter input frequency, and the efficacy of the model is verified by field tests. The model is based on hydraulics, and its constants fit the test results. Ramp response tests and PV power fluctuation compensation tests are conducted to evaluate the transient characteristics of power consumption control. The ramp response test results show that power consumption differs from its command value by a few seconds because of the pressure surge caused by the pipes. The latter tests show that control of power consumption compensates for most of the PV power fluctuation under the test conditions. © 2016 The Institute of Electrical Engineers of Japan.


Yoshihara T.,University of Tokyo | Yokoyama A.,University of Tokyo | Imanaka M.,University of Tokyo | Onda Y.,University of Tokyo | And 4 more authors.
17th Power Systems Computation Conference, PSCC 2011 | Year: 2011

This paper presents a new coordinated control scheme of a seawater desalination plant as a controllable load and diesel engine generators for operation of a small island power system. Recently, more renewable energy based generations have been installed into small islands. However, their intermittent outputs may cause large system frequency fluctuation because of the shortage of regulating capacity. In this paper, the power consumption of the seawater desalination plant is controlled for improving the economy of the power system operation and securing more regulating capacity.


Yoshihara T.,University of Tokyo | Yokoyama A.,University of Tokyo | Imanaka M.,University of Tokyo | Onda Y.,University of Tokyo | And 4 more authors.
IEEJ Transactions on Power and Energy | Year: 2012

Recently, more and more unstable renewable energy based generations such as photovoltaic generations and wind turbine generations have been installed into power systems. This paper focuses a small island power system operation and proposes a novel control method of power consumption of a seawater desalination plant as a controllable load in order to secure more regulating capacity of the power system considering the customer's convenience of the desalination plant. Through a frequency analysis simulation, fuel cost can be reduced and system frequency fluctuation can be suppressed for the proposed control method of seawater desalination plant. © 2012 The Institute of Electrical Engineers of Japan.


Imanaka M.,University of Tokyo | Baba J.,University of Tokyo | Kuniba Y.,Okinawa Electric Power Co. | Higa N.,Okinawa Enetech
IEEJ Transactions on Power and Energy | Year: 2015

Installation of renewable energy sources in island grids is focused on as large expense of island power generation and their power fluctuations should be conpensated. Desalination system is being focused on as a controllable load. This paper proposes a model for the desalination system, estimates controllable ranges under restrictions and evaluates the ability to suppress the power fluctuations. The model calculates the pressure, flow and power consumption. Parameters of the model are fitted by tests with an experimental system. Next, controllable ranges of power consumption under restrictions of the membrane etc. are estimated both by tests and by the model. Controllable ranges with fixed valve openness are estimated as 27 to 43 percent of its rated power. Finally, to evaluate transient response, step and ramp response tests and photovoltaic (PV) output suppression tests are conducted. Most of the fluctuations of PV output are suppressed when PV output is within the controllable range. © 2015 The Institute of Electrical Engineers of Japan.


Onda Y.,University of Tokyo | Imanaka M.,University of Tokyo | Yoshihara T.,University of Tokyo | Baba J.,University of Tokyo | And 4 more authors.
3rd International Conference on Clean Electrical Power: Renewable Energy Resources Impact, ICCEP 2011 | Year: 2011

It is proposed that the seawater desalination system as a controllable load for compensating the power fluctuation caused by renewable energy in small island power system. For controlling the power consumption of the system, the system modeling is needed. In this paper, the high pressure pump and the RO membrane are modeled, and the accuracy of that model is discussed. In addition, it is necessary to make it clear the boundary condition of the upper and lower limitation of the power consumption of the system. The boundary condition derived from the mechanical restriction of using RO membranes is discussed through modeling and experiment. © 2011 IEEE.


Kaneko N.,National Museum of Nature and Science | Kaneko N.,Okinawa Enetech | Kubodera T.,National Museum of Nature and Science | Iguchis A.,University of Ryukyus
Malacologia | Year: 2011

A recent study revised the generic level taxonomy of the family Octopodidae, and several species groups that were previously included in Octopus are now recognized as independent genera. However, knowledge regarding phylogenetic relationships among taxa in the family Octopodidae is still poor. The phylogenetic relationships of shallow-water benthic octopus species in Japan and adjacent waters were examined in the present study using mitochondrial DNA cytochrome c oxidase subunits I and III (COI and COIII, respectively) sequence data, and the taxonomic statuses of the octopus species were compared to those derived by morphological identification. We obtained COI (657 bp) and COIII (464 bp) sequences from 45 taxa assigned to 34 species of seven genera. Samples used were voucher specimens stored in the National Museum of Nature and Science, Tokyo. Sequences of the genes of both Haliphron atlanticus and Tremoctopus violaceus from GenBank were included as outgroup taxa. Additionally, sequences of the genes of Octopus vulgaris obtained from Mediterranean coast of France, which is type locality of this species, was also included from GenBank in order to discuss about status of Japanese O. vulgaris. Through phylogenetic analyses, we recognized Callistoctopus and a distinct group including four Octopus species and an Enteroctopus species, which was designated the "Enteroctopus group" in the present study, with high bootstrap support. Amphioctopus was not completely distinguished because it sometimes formed a clade together with Hapalochlaena, which shows morphological affinities with Amphioctopus. Abdopus + O. laqueus + O. cyanea and O. vulgaris + O. oliveri were recognized as distinct groups, but the phylogenetic support for these groups was weak. For identifying species using short DNA sequences, sequence divergences were calculated using COI sequences. Sequences within and among species were generally divergent enough to discriminate the species, but several overlaps with intra- and interspecific divergence caused by poor taxonomic resolution were also observed. Although performing species identification using DNA sequences from shallow-water benthic octopus species is premature, the results in this study indicated the possible application of COI sequences in octopus species identification, thereby providing a preliminary dataset for future DNA barcoding of octopus.


Imanaka M.,University of Tokyo | Sasamoto H.,University of Tokyo | Baba J.,University of Tokyo | Higa N.,Okinawa Enetech | And 2 more authors.
Journal of Electrical Engineering and Technology | Year: 2015

In remote islands, due to expense of existing generation systems, installation of photovoltaic cells (PVs) and wind turbines has a chance of reducing generation costs. However, in island power systems, even short-term power fluctuations change the frequency of grids because of their small inertia constant. In order to compensate power fluctuations, the authors proposed the power consumption control of pumps which send water to tanks. The power control doesn’t affect water users’ convenience as long as tanks hold water. Based on experimental characteristics of a pump system, this paper shows methods to determine reference power consumption of the system with compensation for short-term PV fluctuations while satisfying water demand. One method uses a PI controller and the other method calculates reference power consumption from water flow reference. Simulations with a PV and a pump system are carried out to find optimum parameters and to compare the methods. Results show that both PI control method and water flow calculation method are useful for satisfying the water demand constraint. The water demand constraint has a little impact to suppression of the short-term power fluctuation in this condition. © The Korean Institute of Electrical Engineers.


Imanaka M.,University of Tokyo | Baba J.,University of Tokyo | Shimabuku M.,Okinawa Enetech | Tobaru C.,Okinawa Enetech | Uezu Y.,Okinawa Enetech
2015 IEEE Power and Energy Society Innovative Smart Grid Technologies Conference, ISGT 2015 | Year: 2015

Demand response of waterworks has a big possibility because waterworks consume 2 ∼ 3 % of world electricity and water is easy to store. This paper proposes a control method called 'simple dead-beat control' to suppress the two-step power consumption of pumps of waterworks occurred in the step response. Though a dead-beat control method have been proposed, the method needs a lot of parameters to determine. The simple dead-beat control needs only step-response tests to determine the parameters. In tests of this method by use of actual waterworks site, the amplitude of two-step responses is modelled as bivariate quadratic function of the present and next target of pump power consumption. The effectiveness of the suppression is evaluated by the RMS value of the difference between the target and the actual pump power of the test data. © 2015 IEEE.

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