Satoshi Ogasawara

The theory of instantaneous power in three-phase four-wire systems: a comprehensive approach

This paper describes a holistic approach to the theory of instantaneous power in three-phase four-wire systems, focusing on the original theory created in 1983 and a modified theory presented in 1994. The two theories are perfectly identical if no zero-sequence voltage is included in a three-phase three-wire system. However, they are different in the instantaneous active and reactive power in each phase if a zero-sequence voltage and current are included in a three-phase four-wire system. Theory and computer simulations in this paper lead to the following conclusions: an active filter without energy storage components can fully compensate for the neutral current even in a three-phase four-wire system including a zero-sequence voltage and current, when a proposed control strategy based on the original theory is applied. However, the active filter cannot compensate for the neutral current fully, when an already-proposed control strategy based on the modified theory is applied.

Operating area of a Switched Reluctance Motor with continuous current operation

This paper shows an operation area consideration of a torque and speed region of a 50kW Switched Reluctance Motor (SRM) for Hybrid Electric Vehicle (HEV) applications. Increasing a number of turns in stator windings is effective to reduce phase current of SRM at low rotational speed, however, motor output power falls significantly at high speed because of an increased back emf. A continuous current operation can enhance output power at high rotational speed. The continuous current operation can be realized by expanding excitation angle of applied voltage. In this operation, phase current is increased, thus, motor output power is maintained at high rotational speed, which is strongly required in HEV applications. An effectiveness of the continuous current operation is shown for a 50kW SRM aimed for HEV application. The SRM is designed with competitive dimensions, efficiency, weight, voltage and current with respect to HEV IPM motors.

Multimedia based e-learning tools for dynamic modeling of DC-DC converters

Exploiting the recent achievements of the information and communication technologies, a new e-learning initiation entitled Yoto project was launched in 2004. On longer run its most important objective is to build up and maintain an electrical engineering knowledge base, on shorter run it helps giving more and more publicity to some relevant fields, especially power electronics, drives and motion control. The multimedia rich content can be utilized in the high level academic education, in the industrial vocational trainings and also in supporting the circuit and system design specialists by fast interactive tools. This paper presents a new e-module attached to the Yoto project about the dynamic operation and modeling of dc-dc converters.

New e-learning tools for DC-DC converters

The paper gives an overview of the Yoto project, a novel e-learning initiative to build up an electrical engineering knowledge base. It also presents a new e-module of the project relating to the steady-state operation of DC-DC converters. The multimedia rich module contains numerous interactive tools promoting the high level education in the academy sector and the vocational trainings in the industry. The interactive tools also highly support the circuit design process by enabling fast calculation and access to relevant circuit quantities and waveforms (voltages and currents) in steady-state without long simulations

Stability analysis of power circuit comprising virtual inductance

The concept of a variable active-passive reactance (VAPAR), which can generate a virtual variable inductance in power circuits, including negative values, has already been proposed. Since it has found application in the power flow control of power systems, where the power flow is essentially restricted by a line inductance, the aim of the paper is to report on the stability of this virtual inductance in an RL circuit. The periodic steady-state operation of the variable-structure, piecewise-linear, nonlinear system is modeled by its Poincare map. The stability criterion employs the position of the eigenvalues of the Jacobian matrix of the Poincare map, evaluated at its fixed point. Bifurcation behaviour when varying the virtual inductance is revealed. Such an analysis allows accurate prediction of stability boundaries and facilitates the selection of parameter values to guarantee stable operation.

Investigating stability of power configuration including virtual negative inductance

Since power circuits are significantly influenced by inductances, a variable active-passive reactance (VAPAR) has previously been introduced in order to generate a virtual negative inductance, which has found applications in the rapid power flow control of power systems. It is used to cancel an existing undesired inductance, since the power flow through a simple power system of two voltage buses connected by an inductive power line is essentially restricted by the line inductance. These studies also indicated that the stability of the system could be compromised by the presence of stray capacitances. The present paper aims to offer a more accurate stability assessment of this RLC configuration, estimated so far by linear approximation, by essentially ignoring the switching process within VAPAR. The normal periodic steady-state regime leads to a fixed point in the stroboscopic map used to model the variable-structure piecewise-linear nonlinear system. The stability is indicated by the eigenvalues of the Jacobian matrix of the stroboscopic map, evaluated at this fixed point. The analysis reveals bifurcation behaviour and allows accurate and convenient prediction of the stability boundary in the parameter space of the virtual negative inductance required by the application and the stray capacitance present in the power circuit.

A Parallel Matrix Converter System

This paper proposes a large-scale matrix converter system which connects two main circuits in parallel and in which the carriers operating each main circuit have a phase difference of 180 degrees. A matrix converter needs an LC filter, not only because it acts as a conventional filter which reduces high frequency ripples caused by the converter switching, but also because the capacitor of the LC filter acts as a virtual voltage source. Therefore, this filter must be connected at the input side. The proposed system can miniaturize the LC filter because the harmonics of the current flowing into the LC filter contain only the even number harmonics of the carrier and the cut-off frequency of the LC filter can be raised. For example, when the cut-off frequency is doubled, the inductor or the capacitor of the LC filter can be reduced to 1/4. The principle of raising the filter currents frequency is verified theoretically using simulation. Furthermore, in the proposed system, the input current waveforms become similar to those of a 3-level converter and the output voltage waveforms become similar to those of a 5-level converter. Therefore, the distortions of the input currents and the output voltages become less than with a conventional single matrix converter, and the common mode voltage, which causes electromagnetic interference (EMI), can also be decreased. On the other hand, the proposed system needs an additional inductance to reduce a cross current that flows between the parallel main circuits. However, it is shown that the peak value of the cross current can be kept low by applying a control to reduce it, if a large motor is used and the motor current increases.

Virtual Power Electronics: Novel Software Tools for Design, Modeling and Education

The current paper is dedicated to present browser-based multimedia-rich software tools and e-learning curriculum to support the design and modeling process of power electronics circuits and to explain sometimes rather sophisticated phenomena. Two projects will be discussed. The so-called Inetele project is financed by the Leonardo da Vinci program of the European Union(EU). It is a collaborative project between numerous EU universities and institutes to develop state-of-the art curriculum in electrical engineering. Another cooperative project with participation of Japanese, European and Australian institutes focuses especially on developing e-learning curriculum, interactive design and modeling tools, furthermore on development of a virtual laboratory. Snapshots from these two projects will be presented.

Proposal of Switching Power Amplifier Using Small Capacity Linear Amplifier and LC Filter

The higher efficiency and the low noise in output voltage and current has been required in some applications, i.e. audio-video equipment, medical equipment and so on. This paper proposes a power amplifier in which a PWM inverter is used as a main circuit. In the proposed power amplifier, a hybrid filter composed of a simple and general LC filter and a small capacity linear amplifier is connected to the output of the inverter. The linear amplifier is inserted in series to the filter capacitor to improve the filtering effect of the LC filter. Switching ripples and LC resonances are considerably suppressed by controlling the amplifier using the proposed method and a low distortion switching power amplifier is realized. The effects of the proposal circuit are verified by simulations and experiments. As a result, the proposed circuit achieves low noise about THD=0.68% in simulation and THD=1.7% in experiment.

Noise-less inverter with novel hybrid output filter

The higher precision and low noise in output voltage and current has been required in some applications i.e. audio-video equipment, medical equipment and so on. In this paper, a new power converter which realizes low noise output with high efficiency is proposed. In the proposed converter, a hybrid filter is inserted to the output of a PWM inverter. The hybrid filter is composed of LC filter and a power amplifier. The amplifier is inserted in series to the filter capacitor to improve the LC filter. Noise suppression effects of the proposal circuit are verified by simulations and experiments.