The proposed inverter combines two methods which can largely decrease the on-state and switching losses. The first method, by using a current transformer and a single transistor, makes possible to reduce the on-state loss to less than 1/3 of the usual Darlington transistor. The second method, by using the auxiliary commutation IGBT in parallel with the transistor, makes possible the zero voltage switching resulting in no switching loss. To realize the higher inverter efficiency, snubber and its loss recovery circuit are employed. Three three-phase inverters were made experimentally to confirm the idea. Its volume and weight can be decreased to 1/3 than that of conventional three-phase inverter, and obtained the efficiency of 98.0% from 5kW to 20kW at switching frequency of 16kHz.

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A voltage-source PWM inverter produces common-mode and normal-mode currents flowing through stray capacitors inside an ac motor every switching. Therefore, the currents may cause radiational EMI to electronic equipment, e.g., AM radio receivers, because its oscillation frequency ranges from 100kHz to several MHz. However, few technical papers related to the radiational EMI have been reported although attention has paid to the EMI.
This paper discusses relationships between radiational electromagnetic noises and the commom-mode and normal-mode currents. Reduction methods of both the commom-mode and normal-mode currents are also discussed on the basis of a motor model including the stray capacitors. It is shown theoretically and experimentally that both the currents can be damped by the combination of the common-mode transformer which has already been proposed by the authors and normal-mode filters proposed in this paper. Radiational EMI of a vector-controlled induction motor drive system of 3.7kW is measured according to the VDE 0877. Experimental results show not only that the radiational EMI results from the high-frequency oscillatory currents, i.e., the common-mode and normal-mode currents, but also that the combination of the common-mode transformer and the normal-mode filters is an effective, practical way of reducing the EMI.

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To improve energy consumption and to meet quality requirement for slab heating process of reheat furnaces in hot strip mills, a new optimal slab heat pattern calculation simulator has been developed.
The simulator consists of the following functions;
(1) two-dimensional (slab thickness direction and slab length direction) slab temperature calculation function, which is capable of calculating skidmark along the length of a slab,
(2) furnace heat balance calculation function,
(3) optimizing calculation function of slab heat pattern using linear programming method.
The developed simulator has been installed into a furnace computer control system for actual plant.
This paper describes the functions of the simulator and simulation results using the simulator.

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The loop transfer property (LTR) of a full state feedback control system can be recovered by an observer. But the disturbance attenuation property (DAPR), which is characterized by the closed loop transfer function from the disturbance to the controlled output, may not be recovered by the same observer. It is desirable in practical control systems that both properties should be able to be recovered simultaneously.
In this paper, we show that the simultaneous recovery is possible by a proportional integral (PI) observer. Two remarkable results are presented: First, a new design method of PI observer is presented by utilizing the relation between PI observer and another observer which is constructed for a new augmented system. Second, the condition for simultaneous recovery by PI observer is given, and a design method of PI observer for simultaneous recovery is derived based on modified LQG/LTR. Finally, an example demonstrates the effectiveness of the proposed design method.

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The stepping motors are used as the driver for positioning in industry applications. It is well-known that the transient response of stepping motor is generally oscillatory in the case of open-loop operation. The rotor oscillation must be suppressed in quick positioning applications. Accordingly, many researches about rotor positioning and suppression of rotor oscillation of stepping motors have been reported in recent years.
In this paper, multi-step drive for variable reluctance stepping motors are studied. The multi-step drive is achieved by the inverse-phase excitation damping using fuzzy reasoning. The availability of the proposed method is shown by numerical simulations and experiments. As the result, it has been found that the proposed method is carried out by simple excitation sequence in short time. Therefore, the quick positioning control of rotor position is possible. Since the rule-type fuzzy reasoning of the proposed method is made up easily, the system cost of the proposed damping control would be inexpensive.

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Axial Flux Interior PM (AFIPM) synchronous motors, as candidates for small electric city cars drives, are presented in this work. The motor parameters effects on the motor torque performance are examined by the analysis of the stator current trajectories in the (i_d-i_q) plane. The AFIPM motor parameters are designed by this analysis to make the motor power capability matching the torque requirements, considering the inverter current and the DC voltage limits.
Furthermore, the voltage-limited optimum Torque per Ampere trajectory is drawn in the (i_d-i_q) plane. It is shown that the proper choice of the motor parameters is a trade off between the parameters to get the ideal operating characteristic for the optimum control over a wide speed range and the parameters to get the high operating torque at low speed. Finally, some design considerations and the simulation results for a 180V (DC bus voltage), 10kW AFIPM synchronous motor drive for electric vehicles are presented.

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This paper proposes a new measuring method of unsaturated inductances of synchronous machine. The measurements can be carried out at standstill except for normal no-load saturation test and sustained three-phase short-circuit test. The theoretical formula for unsaturated inductances, which can be analyzed easily, are obtained by these standstill tests. The outline of measuring method is as follows.
(1) The simultaneous equations concerning unsaturated inductances of direct-axis equivalent circuit are set up by determining coefficients from the results of following four tests and numerically solved. (a) No-load saturation test. (b) Sustained three-phase short-circuit test. (c) Alternating current excitation test to direct-axis with the field winding open-circuited. (d) Alternating current excitation test to direct-axis with the field winding short-circuited.
(2) Unsaturated inductances of quadrature-axis equivalent circuit are obtained directly from the results of following two tests. (a) Quadrature-axis armature current decay test. (b) Alternating current excitation test to quadrature-axis.
With the above-mentioned method, all unsaturated inductances concerning both direct- and quadrature-axis are obtained.

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A method is given for calculating the characteristics of the series-connected windings capacitor motors by applying the theory of two-phase symmetrical components. This winding connection is effective to decrease the voltages of windings and capacitor. Experimental confirmation of the theory is included. Relation between the characteristics of the series connected windings capacitor motor and that of the parallel-connected windings capacitor motor are clarified. Two methods for speed adjustment of the series connected windings capacitor motor are discussed: (a) capacitor adjust type (b) extra-winding type. The principal characteristics, such as the slip for the maximum torque, and efficiency, are obtained taking into account the symmetric conditions. Characteristics of these two-speed capacitor motor are compared with that of the conventional capacitor motor with tapped auxiliary winding.

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The inverter circuit of dc brushless motor (DCBLM) needs feedback diodes to protect the switching element from counterelectromotive force.
In this paper, we describe the computational method of magnetic field analysis of DCBLM with feedback diodes. The electric circuit equations were formulated based on the theoretical formula of the PN-junction diode. And, solving these equations with the magnetic circuit equation by using the FEM, the electrical characteristic and the magnetic property of DCBLM were calculated. By replacing the switching elements with variable resistor, and transforming electric circuit by using Ho•Thevenin's theorem, the route of current is not necessary to change according to the state of feedback diode and switching elements.
This method for feedback diodes is confirmed by the analysis of the permanent magnet DCBLM.

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Since the rare metal magnets show the high saturation flux density, the ferrite magnets of the magnetic field poles of PM (permanent magnet) motors have been substituted for them in recent years. The feature of the rare metal magnet realize small size or high power BLM (brushless dc motors). However, the ordinary magnetic field poles of the PM motors generate higher harmonic flux and cause torque ripple. They are usually removed by short pitch winding, skew slot method and so on. But these methods show a drawback to lower efficiency. This problem is important especially for high power BLM.
Recently new methods have been proposed to realize zero torque ripple and high efficiency drive at the same time. The methods optimize the reference current waveform which is calculated by motor EMF (electromotive force)in advance, and current are controlled to follow up the optimized one. However, the one method assumes try and error. The other one doesn't prove that it realizes maximum efficiency and zero torque ripple drive at the same time. And they have much room to improvement to apply to BLM.
This paper proposes the simultaneous equations which give the accurate relation among instantaneous torque, EMF and current, and proposes a new index CSR which evaluates the relation between copper loss and current waveform. Then the optimized current waveform to drive BLM with zero torque ripple and maximum efficiency is calculated by using new equations and CSR. For this waveform includes triplex harmonic order, normal three phase full bridge inverter can't be used. This paper proposes four arm full bridge inverter which can apply triplex order current to BLM. Experimental result proves this method is available.

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This paper is concerned with the type of connection in the primary windings in short secondary member linear induction motors (LIMs). Differently from rotating motors, the LIM does not have periodical magnetic circuits, and the characteristics are much different between parallel-connected and series-connected primary windings. In this paper, using the two-dimensional finite element (FE) analysis considering practical conditions such as, constant voltage power sources, series impedance in the primary circuits, we investigate differences of characteristics for each connection. The results are also compared with experiments to confirm the validity of the analysis, resulting follows; (1) For the double-sided LIM, the performance of the parallel-connected machine is superior to that of the series-connected, because it yields an ideal distribution of the primary current such that the linkage flux increases and the leakage flux decreases. (2) For the single-sided LIM, the adoption of series connection, which is not done in ordinary design, improves the performance, because it yields an ideal distribution of the primary voltage such that the linkage flux increases. (3) We propose a novel block feeding method for use in the single sided LIM.

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In commercializing the superconducting maglev system it is important to reduce the cost, especially that of ground coils constructed along the whole length of the guideway. For a system to save the cost, we have examined the combined propulsion, levitation and guidance system (PLG system) which can generate levitation, guidance and propulsion forces by the same ground coils. This system is composed of superconducting coils on board and 8-shaped ground coils on the side wall of the guideway whose unit coils are connected reversely between the upper and lower sides and between the right and left sides to make null flux circuits, and serially between the front and rear sides to make a three phase circuit with the power source. On the contrary, the EDS (Electro-Dynamic Suspension) maglev including the PLG system needs auxiliary wheels at low speed at which the levitation force and the electromagnetic stiffness are insufficient for non-contact running. The take off velocity is desirably made as low as possible for dispensing with the strength design and maintenance of track and wheels. Since the side wall levitation system has a large coupling between guidance and rolling, it is important to improve the stiffness considering this coupling, which restricts the take off velocity. The ground coils in the above-mentioned examination have symmetric figure and same impedance between upper and lower coils. This paper describes the PLG system with asymmetric figure between upper and lower coils which reduce the large coupling between guidance and rolling and increase the guidance stiffness. We present not only the principle but also the characteristics of this system with a numerical example and a test run at Miyazaki test track.

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Power converters have been widely used in many industrial applications. On the ac-side of such converters, the current is distorted because of the nonlinearity of the power devices even when the source voltage is sinusoidal. This leads that the power converter is regarded as a harmonic-current source. The harmonic current is one of the most important factors in the analysis of converters. This paper analyzes power flow of a power converter that behaves synchronously with the line frequency. For example, power-flow analysis in a three-phase diode converter with a resistance on the ac-side is presented; the analysis was compared with the conventional analysis with the assumption that the ratio of the resistance on the ac-side to that on the dc-side is very small. The proposed power flow concept enables electrical engineers and students to discuss rationally the power flow of a converter.

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This paper proposes a simple and practical method for improving performance of DSP-controlled current source active power filters (AF). The transfer function of a DSP-controlled AF has a phase-lag nature because there is a time lag in the control output due to the computation time required by DSP, and the converter used for AF has first order lag characteristic. As AF has to generate high frequency compensation currents, the phase-lag characteristic causes a serious deterioration in the filter performance. In the proposed system, an adaptive digital filter (ADF) is used as a series compensator of AF and it compensates for the phase-lag characteristic of AF. It was confirmed by experimental results that a simple two-tap ADF is very effective to improve AF compensation performance.

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The electric power generated from a photovoltaic array (PVA) is generally utilized by interacting with the utility line through a utility-interactive inverter. This method, however, debases the power quality of the utility line and causes electromagnetic interference without a bulky power filter. On the other hand, the electric power from a PVA is utilized to drive a motor of a heat pump and so on. But the conventional pumping system can not generate a constant mechanical power since the solar power depends on weather conditions.
The authors have proposed a new pumping system which is composed of two coupled induction machines. One induction machine is related to a PVA through a general-purpose inverter and the other is interacted to the utility line. This system can generate a desired mechanical power all day and supply the surplus electric power of the PVA to the utility line. This paper discusses the stability of the proposed two induction machines system in order to get a desired mechanical power from variable power of a PVA. It proves that the stability of this system is assured although the PVA is a non-constant voltage source. In addition, this paper proposes the use of a twin stator induction machine instead of two coupled induction machines construction. This new system can be implemented compactly. It is shown by experiments that the system can easily and stably generate a desired mechanical power under the condition of tracking the maximum power operating point of the PVA without measuring the operating voltage and a mechanical load demand.

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This paper provides complex circuit equations of cylindrical synchronous machine taking damper winding currents into consideration and its analytical solutions. I expressed cross section of synchronous machine as complex plane and named it space complex plane. I named voltages, currents and magnetic fluxes in this complex plane, space voltages, space currents, and space magnetic fluxes respectively.
To distinguish ordinary complex quantities, such as complex currents of single-phase circuit, from space complex quantities, such as space complex currents, I named it time complex quantity temporarily in this paper.
Using these space complex quantities and time complex quantities, I analyzed cylindrical synchronous machise.
For instance, calculated results of transient phenomena of 3-phase sudden short circuits and step change of field voltages of cylindrical synchronous machine are showed in this paper.

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For parallel operating system of two single-phase GTO PWM converters, a coupling effect between two secondary sides due to a common primary leakage inductance of the input transformer is analyzed and solved by cross-compensation. With this strategy, the source current becomes more sinusoidal waveform. In addition, an effective power factor control scheme considering the magnetizing current of the transformer is involved. Experimental results for a laboratory system of 20kVA converter confirm the validity of the proposed algorithm.

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