In a superconductive linear synchronous motor for magnetically suspended trains, on-board superconducting coils experience space harmonic magnetic field generated by armature coils installed along the guideway. Current in a superconducting coil varies to keep total linkage magnetic flux constant when the coil is exposed in an external magnetic field.
In the conventional analysis, current in a superconducting coil was treated as constant, because the electromagnetic forces can be estimated easily and in sufficient accuracy compared to that obtained by constant flux mode analysis. However, it is important to know the behaviour of the persistent current to make reliable and tough superconducting magnets.
This paper proposed a simple method to analyze fluctuating persistent current in a superconducting coil, and discuss its characteristics through the typical calculation models.
Calculations for the normal running condition showed that the fluctuation of persistent current is less than one percent of the initial magnetomotive force. Then, the fluctuating magnetic field generated by armature coils will never affect stability for superconducting magnets, and the constant current mode analysis will predict accurate electromagnetic forces.

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In this paper the architecture of a dependable multi-processor system for an advanced train control system is discussed. The multi-processor system is composed of a fail-safe computer and some peripheral interface computers. Dependability of the system calls for complete safety as well as high system reliability. It is for this reason that we developed a bus-level synchronous fail-safe computer and 32 bit type LSI comparator which is used as a self-checking element for the fail-safe computer. For the purpose of system reliability, a duplex architecture of multi-processors which consists of two connected independent system buses, i.e. VME-buses, with dual-port memory is developed. This method, called a mirror-memory scheme, assures continuous processing during exchanging interval.

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Material Handing System (MHS) is regarded as important as a mother machine in Factory Automation (FA) or Computer Integrated Manufacturing (CIM). Accurate description of specifications and control actions is one of basic techniques to construct a MHS. Sequential Function Chart (SFC) is such a kind of graphic representation included in IEC standard for sequential control systems. SFC surpasses Ladder Diagram which has been widely used until now, because of its simplicity of graphic representations and the clarity of relations of sequences. However, it is hard to represent extraordinary or emergency processes, and interlocks, which frequently occur in MHS. In this paper, we propose a new method called Total-SFC (T-SFC) which consists of three parts, i.e., SFC describing sequential processes, Random Function Chart (RFC) describing extraordinary or emergency processing, and Interlock Tables describing interlocks.

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A 2-mass system connected by a non ideal shaft has resonance modes and it is difficult to design a controller suppressing the vibration in the face of parameter variation.
In this paper, we propose a method of μ-Synthesis based on the descriptor form representation to deal with parameter uncertainties independently. We first consider a class of parameter uncertainty given in the descriptor form and show how to achieve robust stability and robust performance for this class of perturbed systems. Then we apply this method to the 2-mass spring system with parameter uncertainties of the torsional constant and the load inertia. By using this method these two physical uncertainties are treated independently and a controller is designed to achieve not only robust stability but also robust disturbance suppression. In addition, we also use two-degree freedom control scheme to achieve a good transient response.
Simulation results are presented to demonstrate the control effects.

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The AC magnetic characteristics of an iron core vary depending on the magnetization conditions. As power semiconductor devices come to be used in control system a knowledge of the magnetic properties of the equipment using a distorted input is required. This paper described the effect of high harmonic flux distortion on the magnetic properties of silicon steel plate.
In performing the analysis, the magnetization characteristics is approximated by Fourie-series. And the assumption in which eddy current factor is proportional to the rate of change of the flux is adopted. From the result of numerical analysis, relation between distortion factor and iron loss, exciting apparent power and high harmonics of exciting current are clarified. The results of the analysis were confirmed by experiments.

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This paper describes relationships between characteristics of a magnetically anisotropic slot wedge and voltage higher harmonics in an AC exciting synchronous generator terminal due to permeance ripple caused by an open slot type rotor. From the relationships obtained, practical guide lines were formulated for machine designs applying the magnetically anisotropic slot wedge. The results were as follows.
(1) Equivalent permeability of the magnetically anisotropic slot wedge became isotropic wedge permeability for air-gap flux ripple.
(2) Two ways were identified to reduce voltage higher harmonics by using the slot wedges.
(3) The level of leakage flux passing through the anisotropic slot wedge was determined only by its permeability in the width direction.
(4) Effectiveness of the magnetic anisotropic slot wedges inserted into the stator slots was verified from experimental results using a model machine of the open slot type rotor.

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The oscillatory behavior and the maximum slewing pulse rate of the hybrid stepping motor depends to a large extent on the type of drive circuit which is used. In this paper, four types of drive circuits are discussed, that is, (a) a diode in series connection with the winding (b) the diode in parallel with the winding (c) the diode and the zener diode in series and in parallel with the winding (d) a capacitor connection between two windings. The step response is calculated with connection (b) and compared with test data. It is shown that the step response has a close relation with the performance characteristics such as the oscillatory frequency and it's amplitude. Considering this relationship, effects of the drive circuit on the oscillatory characteristics and the maximum slewing pulse rate are investigated.

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We already developed a conventional SMR (Switch Mode Rectifier) converter using bilateral switch. A conventional SMR converter has a weak point that is to be need of AC snubber circuit and the complicated circuit for regeneration of snubber energy.
This paper discribes a novel three-phase SMR converter which was named DC-Clamped type SMR ( DCC-SMR ) using direct frequency changing technology for industrial use power supply. DCC-SMR consists of frequency changer, HF (High Frequency) transformer and HF rectifier. Frequency changer of DCC-SMR doesn't use bilateral switch. Then, we can use DC snubber for switch. Furthermore, DCC-SMR doesn't-need regenerative circuit and discharge resistance, because snubber circuit is only capaciter and snubber energy is regenerated to primary winding of HF transformer by main switch.
We verified usefulness in experimentation. Moreover, we refer to efficiency of 100kw prototype system.

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This paper describes the computational method of the transient performance for permanent magnet synchronous motors using the finite element method. The new method is proposed, where the mechanical, electromagnetic and electric circuit equations for the permanent magnet machines are transformed into the discrete equations by using a time-stepping finite element technique. First, the position of the rotor at a certain time is determined by solving the mechanical equation. Next, the electromagnetic and electric circuit equations are solved directly by using the finite element method. In this paper, no load current is obtained from this analysis. An agreement between calculated and measured values for no load current is good. Therefore, it is clear that this method is reasonable.

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With remarkable progress of switching devices, the switching frequency of a voltage-source PWM inverter has been higher and higher. A high frequency PWM inverter gives great benefits in reduction of current ripples and acoustic noises. However, high frequency hard switching causes the increase of switching losses and EMI to be solved.
The authors propose a zero-current-switching based three-phase PWM inverter which has small resonant circuits on the ac side. The current flowing in a switching device is a sum of the resonant current and the load current. Since the switching device is turned on and off at zero current, the switching losses and electromagnetic noises are greatly reduced. This paper describes the principle of the zero current switching operation, the design of the resonant circuits and the control scheme for the new soft switching inverter. Moreover, it shows interesting experimental results obtained by the zero-current-switching PWM inverter which drives an induction motor of 2.2kW.

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This paper describes which is better, a single bridge or multi bridges, what switching frequency is best, at a bulk power converter system for static var compensation from the viewpoint of power loss, utilization rate of power devices, distortion factor of current and voltage waveforms, control response and reliability. Our study shows that multiple connection of single-phase bridges with one pulse PWM and that of three-phase bridges with three pulse PWM are superior to a three-phase single bridge with multiple pulse PWM. These results are quite different from general thoughts in UPS or general purpose motor drive systems, where higher switching frequency has resulted in less harmonics, better response and smaller size.
At a bulk power converter system many power devices are required, thus multiple connection can be easily applied without the sacrifice of economy. In addition, it is very important, our newly adopted control strategy provides very quick transient response at the lowest (fundamental) switching frequency.

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For modeling DC-DC converter circuits, the state space averaging method is the representative method. However, its application field is restricted to operation of small fluctuation and rather narrow. For operation of large fluctuation, a novel approach which composes the equations by taking the initial values of the circuit at the starting point of each switching period as the state variables is proposed. All instantaneous values of the current and the voltage at each switching period can be represented by a linear combination of these initial values. So, the discrete space state equations can be formulated; all kinds of the information about circuit operation such as average values, waveform envelopes and instantaneous value at an arbitrary instant are given. The solution can be calculated with accuracy as high as one desires, without excessive work

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PWM rectifiers which can realize unity power factor and sinusoidal input current have been widely investigated to overcome problems of reactive power and harmonic current in electric power systems. However, in such PWM rectifiers, an LC filter which is necessary for absorption of carrier harmonics and for reduction of commutation spike voltage may cause waveform distortion and transient oscillation of the ac input current. As a solution to these problems, a new control method introducing state feedback control of the LC filter was proposed in our previous paper. To achieve stable operation in this method, the control frequency or carrier frequency of the PWM rectifier must be higher than 5 times the resonant frequency of the LC filter. So, a method to reduce the required carrier frequency is necessary to implement high power PWM rectifiers.
In this paper, a parallel connection of two bridge circuits is introduced to reduce the required carrier frequency. A new control method for the parallel connected PWM rectifiers is proposed. The main circuit configuration and inter-bridge current between the two component bridge circuits are investigated. To achieve the reduction of the required carrier frequency without affecting the controllability, a new method of generating PWM pattern is developed. The effectiveness of the proposed control method is confirmed by some experimental results employing a test system.

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