Akihiko Yokoyama / Professor / Division of Transdisciplinary Sciences
Department of Advanced Energy / / Power Systems Engineering, Ubiquitous Power Grid, Distributed Generations

Career Summary
1979: BEng, Faculty of Engineering, The University of Tokyo
1984: DEng, School of Engineering, The University of Tokyo
1984: Research Associate, The University of Tokyo
1985: Lecturer, The University of Tokyo
1987 - 88: Visiting Scholar, ESRC, University of Texas, Arlington
1988 - 89: Visiting Scholar, Department of EECS, University of California, Berkeley
1989 - 2000: Associate Professor, The University of Tokyo
2000 - present: Professor, The University of Tokyo

Educational Activities
Graduate school: Power System Dynamics, Power System Circuit Analysis, Special Seminar of Power Systems Engineering
Undergraduate school: Power Systems Engineering 1 & 2
Research Activities
1) Installation of Large Capacity Distributed Generations into Power System
A large number of distributed generations are expected to be installed in power systems because of their advantages of reducing environmental loads, maintaining power system reliability, and reducing costs, for example.
However, many problems, such as voltage profile, short circuit capacity, islanding operation detection, and system stability have to be solved to promote the integration of distributed generations into grid.
The researches conducted in this laboratory include the following topics: impacts of distributed generations on system reliability, supply-and-demand control in a micro grid consisting of distributed generations, and frequency control by battery storage technology in a power system with a large number of wind power generations. (Ref. 1)

Ubiquitous Power Grid
Ubiquitous Power Grid

2) Optimal Power Flow Control of Power System using Power Electronics Applied Devices(FACTS Devices)
With recent development of power electronics technology, enhancing power system stability and controlling optimal power flow using FACTS (Flexible AC Transmission System) devices such as UPFC (Unified Power Flow Controller) and STATCOM
or self-commutated BTB, HVDC, and ASG have been proposed. In this research, we consider IPFC (Interline Power Flow Controller), a new generation of FACTS device, an optimal power flow control for controlling power flows on multiple transmission lines. It is being applied to a well-known basic test system as a loop flow controller to cope with overload constraint.
In addition, we also research applying UPFCs for improving ATC (Available Transfer Capability) and maintaining electric supply reliability by controlling optimal power flow with both overload and stability constraints. (Ref. 2)

Interline Power Flow Controller(IPFC)
Interline Power Flow Controller(IPFC)

Optimal Power Flow Control by IPFC
Optimal Power Flow Control by IPFC

3) Power Systems in Deregulated Environment
Because deregulation of the electric power sector has started in the world, a new power market scheme including a supervisory body for fair access to the grid and nationwide wholesale market has just been introduced in Japan. In this deregulated environment,
there are concerns such as electricity price spikes caused by transmission line congestion and decrease in investment in transmission facilities.
These facts may affect the reliability of electric power supplies. To keep this reliability high, we study the following three topics: transmission contracts, power system expansion problems and estimations of an optimal margin in transmission line capability.
For the power system expansion problem, we study three solutions: construction of new transmission lines, reinforcement of transmission line capability, and introduction of FACTS devices.
As for estimating an optimal margin in transmission line capability, we study a calculation method of transient-stability-constrained optimal TTC (Total Tranfer Capability) and CBM (Capacity Benefit Margin) amounts in transmission lines to maintain power supply reliability
at a certain level in the deregulated environment. (Ref. 3)

Total Transfer Capability (TTC), Available Transmission Capacity (ATC), and Margins of Tie Line
Total Transfer Capability (TTC), Available Transmission Capacity (ATC), and Margins of Tie Line

Capacity Benefit Margin (CBM) of Tie Line
Capacity Benefit Margin (CBM) of Tie Line

4) Intelligent Monitoring and Control of Wide-area Power System
In recent years, power systems have become large-scale and complicated and hence should be operated under severe conditions in a deregulated environment. Our study aims to improve the reliability of power supply for modern power systems by researching and developing
intelligent monitoring and control. Research works on automatic generator control and grid monitoring using information technology such as time-stamped measurement of the system states have also been done. (Ref. 4)

Online Adaptive Power System Stabilizer
Online Adaptive Power System Stabilizer

1) H. Irie, A. Yokoyama, Y. Tada: Application of Heat Pump Water Heater for Frequency Stabilization in Power Systems with Large Penetration of Wind Power Generation, Proc. of IEEJ Joint Technical Meeting of Power Technology Committee and Power System Technology Committee, Aug., 2008
2) K. Kawabe, A. Yokoyama: Minimizing Control of PNS by Multiple FACTS Devices in Power Systems, Proc. of ICEE, Okinawa, July, 2008
3) K. Tangpatiphan, A. Yokoyama: Transient Stability Constrained Optimal Power Flow Using Evolutionary Programming, Proc. of PSCC, UK, July, 2008
4) T. Sugihara, A. Yokoyama, A. Izena: Online Parameter Design Method of Adaptive PSS based on Low-order Linear Model in Multi-area Power System, IEEJ Trans. PE, Vol.126, No.12, 2006

Other Activities
Institute of Electrical and Electronics Engineers (IEEE)
Institute of Electrical Engineers of Japan (IEEJ)
Japan Society for Industrial and Applied Mathematics (JSIAM)
The Society of Instrument and Control Engineers (SICE)
1999 - present Vice Chairman of Technical Committee of Protective Relay, IEE of Japan
2004 - present Chairman of Japanese National Committee, IEC TC8
2007 - present Chairman of Membership Development Committee, IEEE Tokyo Chapter
2007 - present Vice Chairman of PES, IEEE Tokyo Chapter
2006 - present Vice Chairman of Japanese National Committee, CIGRE
2005 - 2007 Executive Board Member of Power and Energy Society of IEE of Japan
1995 - 2006 TPC Member of Power System Computation Conference (PSCC)
Future Plan
The main research objectives of our laboratory are to alleviate the global warming problem, to guarantee energy security, and to maintain power supply reliability.
To achieve the above objectives, we are researching the implementation of a gubiquitous power gridh for an innovative and integrated electric energy supply network.
Besides photovoltaic and wind power generations, we would like to investigate controllable loads, such as heat pumps, charge control methods for electric vehicles, local hydrogen supply systems
and even the use of photovoltaic power generated by satellites in outer space, i.e., solar power satellites.
Since power supply interruptions caused by severe faults in supply systems occur around the world, we would like to develop a general method considering economical concerns
to minimize the impact of those interruptions on society.

Messages to Students
Technological innovation has become a must in modern society, so it seems that people tend to develop new technologies and to establish and operate new systems
in a short time by using fundamental technologies such as a "black box".
Though it is quite time consuming to clarify the interior of the black box and develop our own technologies, we make it a policy to do so in our laboratory.
Therefore, I believe that our students will become confident researchers and engineers capable of dealing with any challenges by the time they graduate.
If you are interested in research topics for public interests such as a secure and stable power supply and resolution of global environmental problems,
we are the right place for you.