Jumpei Baba

Autonomous Distributed V2G (Vehicle-to-Grid) Satisfying Scheduled Charging

To integrate large scale renewable energy sources in the power grid, the battery energy storage performs an important role for smoothing their natural intermittency and ensuring grid-wide frequency stability. Electric vehicles have not only large introduction potential but also much available time for control because they are almost plugged in the home outlets as distributed battery energy storages. Therefore, vehicle-to-grid (V2G) is expected to be one of the key technologies in smart grid strategies. This paper proposes an autonomous distributed V2G control scheme. A grid-connected electric vehicle supplies a distributed spinning reserve according to the frequency deviation at the plug-in terminal, which is a signal of supply and demand imbalance in the power grid. As a style of EV utilization, it is assumed that vehicle use set next plug-out timing in advance. In such assumption, user convenience is satisfied by performing a scheduled charging for the plug-out, and plug-in idle time is available for the V2G control. Therefore a smart charging control is considered in the proposed scheme. Satisfaction of vehicle user convenience and effect to the load frequency control is evaluated through a simulation by using a typical two area interconnected power grid model and an automotive lithium-ion battery model.

Autonomous distributed V2G (vehicle-to-grid) considering charging request and battery condition

Integration of large scale renewable energy sources into power grid, battery energy storage performs an important role for smoothing their natural intermittency and ensuring grid-wide frequency stability. Plug-in hybrid electric vehicle and electric vehicle have potential of alternative of the battery because of its high performance lithiumion battery and longer plug-in time than driving time. Therefore, vehicle-to-grid is expected to be one of the key technologies for smart grids integrating renewable energy sources. In this paper, an autonomous distributed vehicle-to-grid control scheme is proposed. Grid-connected electric vehicles contribute frequency regulation and spinning reserve triggered by self-terminal frequency, which is a signal of supply and demand balance in the power grid. Proposed scheme also consider charging request for the next drive and battery condition during the vehicle-to-grid. Satisfaction of vehicle user convenience and effect load frequency control is evaluated through coupled analysis of vehicle-to-grid model and typical power grid model.

Effective application of superconducting magnetic energy storage (SMES) to load leveling for high speed transportation system

The consecutive pulse power demand of the high speed transportation systems like Shinkansen, gives deteriorative influences to the power supply system and increases its operational costs. To cope with this problem, it has been studied to install the superconducting magnetic energy storage system (SMES) in railway substations. However, the scale of installation becomes too large because of low space factor of SMES, and hampers its realization. Then, it is considered to use SMES only for suppression of the high frequency component of load fluctuation, and to combine with a large capacity battery storage (BEMS), which can not follow fast fluctuation and covers its low frequency component. A novel control scheme of this combined energy storage system is proposed. The fluctuation of power demand caused by high speed train operations in a railway substation is measured separately in the frequency range and used to regulate both SMES and BEMS to suppress fluctuation. With simulation studies based on the load model of high speed train operation at a certain substation, this hybrid approach and its control scheme are verified effective. The system configuration is compact enough to be installed at a substation.

Superconducting Fault Current Limiter Design Using Parallel-Connected YBCO Thin Films

Superconducting fault current limiters (SFCLs) are able to reduce fault currents to an acceptable value, reducing potential mechanical and thermal damage to power system apparatus and allowing more flexibility in power system design and operation. The device can also help avoid replacing circuit breakers whose capacity has been exceeded. Due to limitations in current YBCO thin film manufacturing processes, it is not easy to obtain one large thin film that satisfies the specifications for high voltage and large current applications. The combination of standardized thin films has merit to reduce costs and maintain device quality, and it is necessary to connect these thin films in different series and parallel configurations in order to meet these specifications. In this paper, the design of a resistive type SFCL using parallel-connected YBCO thin films is discussed, including the role of a parallel resistor and the influence of individual thin film characteristics, based on both theory and experimental results.

Autonomous Distributed Vehicle-to-Grid for Ubiquitous Power Grid and its Effect as a Spinning Reserve

This paper propose an autonomous distributed vehicle-to-grid control scheme of grid-connected (plug-in hybrid) electric vehicle. Grid-friendly charge and discharge maintaining user convenience for plug-out and battery state-of-charge is realized based on frequency measurement at the plug-in terminal. Implementing proposed scheme to automotive power electronics circuit, (plug-in hybrid) electric vehicle works as a smart storage which is an alternative to stationary battery. The smart storage is expected to be a spinning reserve because of its high-speed response without information exchange to a central load dispatch center. An effect of the autonomous distributed vehicle-to-grid and cooperation with centralized speed governor control and load frequency control of conventional thermal power generator is evaluated.

Design and Basic Test of SFCL of Transformer Type by Use of Ag Sheathed BSCCO Wire

Superconducting fault current limiters (SFCLs) are promising devices to reduce the fault current constraint when designing and operating power systems. SFCLs must meet requirements for precise operation, operating impedance, recovery time, and so on. SFCLs using YBCO thin film or bulk BSCCO meet some of these requirements. However, it is quite difficult to satisfy the requirements for precise operation and recovery time. A transformer type SFCL with an adjustable trigger current level can enhance the precision of operation and fulfill the requirements for SFCLs. It needs long wire; however, long high temperature superconducting (HTS) wire like Ag sheathed BSCCO, is not considered suitable for SFCL because its resistance in its normal state is very low. This paper describes the design of an SFCL of transformer type by use of wire of very low normal resistance and basic testing of a trial SFCL using this design.

Combined power supply method for micro grid by use of several types of distributed power generation systems

A power control method to compensate power fluctuation of the load in the microgrid systems is proposed and discussed. Active power responses of several kinds of distributed power generation systems (DGs) such as gas engine, micro gas turbine, etc., energy storage system, and load fluctuation of a site have been measured. Based on the measurements, combination control method for several kinds of DGs and an energy storage system has been made and experiments have been carried out by use of small scale micro grid model system. It is shown that the load fluctuation has been compensated by the proposed method

Implementation of grid-friendly charging scheme to electric vehicle off-board charger for V2G

Integrating large-scale renewable energy sources and electric vehicles into the power grid, Smart Charging and Vehicle-to-Grid of the electric vehicles play an important role for supply and demand matching in the power grid. Many control schemes have been proposed, and implementation of the smart charging and V2G to the electric vehicle charger is also an important issue. This paper proposes an off-board charger that realizes seamless charge and discharge control via the DC connector on the existing electric vehicle. A grid-friendly charging scheme is implemented to the V2G test system consisting of the off-board charger, an electric vehicle battery test-bed, and a smart interface controller with flexibility in software installation. Communication and control functions of each component are confirmed through fundamental experiments. A load frequency control function for the real-time digital power system simulator is tested on the proposed V2G test system.

Tests for Conceptual Design of 6.6 kV Class Superconducting Fault Current Limiter With YBCO Thin Film Elements

A superconducting fault current limiter (SFCL) for 6.6 kV and 400 A installed in a cubicle for a distribution network substation was conceptually designed. The SFCL consists of parallel- and series-connected superconducting YBCO elements and a limiting resistor. Before designing the SFCL, some tests were carried out. The width and length of each element used in the tests are 30 mm and 210 mm, respectively. The element consists of YBCO thin film of about 200 nm in thickness on cerium dioxide (CeO2) as a cap-layer on a sapphire substrate by metal-organic deposition with a protective metal coat. In the tests, characteristics of each element, such as over-current, withstand-voltage, and so on, were obtained. From these characteristics, series and parallel connections of the elements, called units, were considered. The characteristics of the units were obtained by tests. From the test results, a single phase prototype SFCL was manufactured and tested. Thus, an SFCL rated at 6.6 kV and 400 A can be designed.

Design methods and integrated control for microgrid

The authors have been carrying out a preliminary study on the design of microgrid. Designing microgrid includes selection and capacity determination of power supply devices according to their response characteristics, efficiency and initial cost, and development of methods for integrated control to maintain power quality and efficiency. Both design and control methods depend on conditions of loads, for which microgrid is installed. In this paper, design methods of microgrid, such as power demand analysis, response characteristics measurement of power sources and fuel efficiency measurement of engine-generators, and integrated control methods for power sources are proposed, along with experimental results for a prototype of microgrid.