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## Graduate School of Science and Engineering Electrical and Electronic Engineering

### Laboratory for Electric Circuits and Systems

We apply circuit and control theories to elucidate the “operation” of ever more complex circuit systems with a goal of creating “high-efficiency” systems.

#### Staff

Toshiji KATO
[Professor]

Telephone : +81-774-65-6322

Office : YE-312
Database of Researchers

Kaoru INOUE
[Professor]

Telephone : +81-774-65-6296

Office : YE-216
Database of Researchers

#### Research Topics

• Developing computer-aided circuit analysis methods and automated circuit design methods
• Developing wave analysis systems and failure diagnostic methods
• Operation analysis and control methods for power electronic circuits
• Investigating drive methods for rotating electric machines
• Slip control in electric vehicles

#### Research Contents

Electric circuits are indispensable to modern life. In the course of ordinary life, however, we do not think much about where electric circuits are in use. Electric circuits are found in all sorts of everyday products, including cars, home appliances, computers and mobile phones, where they perform very important functions. In cars, for example, an amount of injection fuel is determined to run engine efficiently based on information such as the air mass flow and the throttle valve opening. Moreover, head lights, power windows, wipers, air conditioners and so on… which require electric circuits. The hybrid car is a recent development that uses fuel efficiently by combining inverters and motors. The importance of electric circuits is further increasing. At the Laboratory for Electric Circuits and Systems, we are conducting both computer simulations and experimental research that focus on developing operation analysis methods that investigate system behavior, treating the entirety of the electric circuits and their surrounding devices as a system, and control methods to make these systems function as desired. For example, we have following themes.
<1> Computer-aided circuit analysis and automated circuit design methods
1. Formulation of a General Circuit Equation
A method of formulating a general circuit equation incorporating digital and control elements is under development through the extension of the Modified Nodal Method.

2. Optimizing Circuit Parameter Design
Optimal circuit parameters are computed for a given circuit design by determining the minimum of a selected index function. For this process, efficient computation of parameter sensitivity is under development using the direct method.

3. Parallel Processing of Circuit Analysis Methods
Fast circuit analysis algorithms which are suitable for parallel computing are under development. We are also researching algorithms for parallel processing using two or more computers to speed up analysis of ever more complex circuits.

4. Automatic circuit design based on Generic Programming
PC cluster system has sixteen computers are used to generate active filter circuits. Generic Algorithm (GA) and Genetic Programming (GP) are adopted to design circuits automatically.

PC cluster

<2> Waveform analysis and diagnostic analysis in electric instruments
1. Transfer Function Method for Power Transformer Analysis
The transfer function method, based on convolution and deconvolution operations by FFTs is under development in the application of power transformer and AC motor design and testing.

2. Digital Signal Processing of High-Voltage Measuring Systems
Computer software which provides automatic and objective quantification of lightning impulses is also under development.

Transformer failure diagnosis

<3>
Operation analysis and control methods
for power electronic circuits
1. Operation Mode Analysis of Power Converters
As converter circuits become more complex (adding clamp circuits, for example), it becomes necessary to use computer-aided numerical methods to analyze their operation modes. We are developing programs that automatically analyze operation modes.

2. Control of Inverters and Converters
Stable and fast converter control methods such as optimal control and sliding-mode control are being developed for efficient power conversion.

3-level inverter system

<4> Drive methods for rotating electric machines
1. Efficient Drive of AC motor
We research high-efficient drive methods for electric motors and generators. Optimum regenerative torque to convert rotational energy into electrical power is under study when reducing rotation speed.

2. Analysis and Control of Vibration Caused between Motor and Resonant Mechanical rotor
The vibration is caused in the situation that the mechanical resonant frequency is less than the motor's maximum operating frequency or the fluctuation's frequency of the load. We analyze the problem and propose appropriate control methods both by simulation and experiment.

Experiment of high-efficient drive methods for induction motors

<5>
Slip control in electric vehicles
This research gives an analytical result of the rapid variation of slips between wheels and road surfaces, and proposes a novel Traction Control System(TCS) of EVs to suppress the rapid variation of slips.

Slip control experiment using scaled electric vehicle model

#### Keywords

• Computer-aided circuit analysis methods
• Simulation algorithms and methods of power electronic systems
• Digital processing methods of high-voltage measuring system
• High-efficiency control methods of power electronic systems
• Vibration suppression methods of motor drive system
• Efficient motor drive methods

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