Use of electrical devices in automobiles has increased greatly in recent years. For simplification and weight reduction of the electrical wiring system, the negative terminals of the electrical devices are usually connected to common ground lines (chassis) of the automobile. In addition power semiconductor switches called high side switches for driving the electrical devices are connected to the lines on the positive side of a DC power supply (battery).
For the high side switches, it is desirable to use N type MOSFETs (NMOSFETs). Since no inductive element should be contained in the gate drive circuits for the NMOSFETs, it is necessary to adopt voltage boost circuits using switched capacitors to make the gate terminal voltage referred to the ground higher than the DC source voltage while the NMOSFET is in on-state.
This paper presents an approximated analysis of the steady state and transient state characteris-tics of the gate drive circuit with the voltage boost circuit. The obtained results are useful for designing the interface circuits.
Experimental results agree well with the analytical ones and the validity of the approximated analysis is confirmed.

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This paper presents a variable speed synchronous generator system. The system consists of a brushless self-excited type synchronous generator and a bi-directinal voltage source PWM frequency changer. The rotor field windings of the generator are short-circuited with diodes, and the field excitation is obtained through the half-wave rectification of the induced voltages. To induce the AC voltages in the field windings which are rotating at synchronous speed, the stator output currents of the generator are so controlled by the PWM converter coupled to the generator that they can contain DC components. In addition, the rotating fields which are produced by harmonic components included in the stator current, are used effectively to obtain a self-excitation. The system can provide power generation into the power system over a wide speed range at unity power factor.
In this paper, a simulation of the steady state characteristics of the generator is given, which takes account of both the resistance of each winding and the interruption of the rotor field current caused by the insertion of the diode, also the characteristics of the system are clarified through both the simulation and experiments.

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This paper presents the robust control design of a magnetic suspension system for a flexible beam which is a simplified model of an elastic rotor in a magnetic bearing system. To stabilize this magnetic suspension system which is unstable in nature, the H^∞ control theory is applied for a design of the control system.
To apply the H^∞ control theory, a state-space model of an augmented plant with frequency weighting functions is constructed. This augmented plant has two inputs which are the exogenous inputs and the control inputs, and two outputs which are the sensor outputs and the regulated outputs. Here we consider the mixed sensitivity problem. The H^∞ controller is implemented by a digital controller which is able to execute the computations very quickly.
For the evaluation of the control performance, several experiments are made. The robustness of the closed loop system is confirmed by the experimental results. The result of this study is useful for the control design of a magnetic bearing system.

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The model reference adaptive system (MRAS) is generally described in the field of real numbers. Therefore, the MRAS cannot be directly applicable to the system described by complex numbers such as three-phase ac motors.
In order to apply the MRAS to the discrete-time linear time-invariant system whose coefficients and variables are complex numbers, the authors expand the theory of the MRAS into the field of complex numbers. The hyperstability theory in the field of complex numbers is used to give the asymptotic stability of the suggested algorithm.
The effectiveness of the suggested algorithm is proved by simulation results for the parameter identification. The results show that the convergence time of the parameters using the proposed method can be reduced to one tenth compared with that using the MRAS in the field of real numbers.

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As the operating lifetimes of direct current machines depend on their commutation performance, for electrical engineers. The progress of power switching devices expands a range of an abrupt load variation of direct current machines.
Therefore, though overall commutation performance of direct current machines is good, sometimes problems arise.
This paper describes the investigation results on main pole search-coil method for detecting commutation condition. The method can be used in the commutation compensation system which enables to materialize no-spark commutation.
The detecting equipment is possible to judge the commutation condition by detecting the induced voltage on the main pole search-coil during commutation. The equipment for use in a commutation test machine is fabricated and proved effective by performance tests.

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The position of a moving object can be measured with avoiding contact in real time by observing intensity from a gamma-ray source attached to the object. Experimental position measurements are carried out for linear (l-dimensional) and rotary (2-dimensional) motion, and the results obtained are compared with theoretically calculated ones. The position measurements in 3-dimensional motion are also theoretically deduced by the aid of computer simulation. On this occasion, the statistical characteristics of the gamma-ray count rate observed will be varied with time. The dynamic error in the position measurement increases with increasing velocity of the object. The statistical error increases in comparison with the stationary one when the object is closing up to a detector, and decreases in the opposite motion. The system with short time constant permits quick response for change of the object position, but increases statistical error. In the experimental 1-dimensional position measurement, use of a 3.4 MBq ²⁴¹Am gamma-ray source with a time constant of 94ms, an object velocity below 100mm/s and a detector-to-source distance below 500mm gave dynamic and statistical (1σ) errors less than ±10 and ±25mm, respectively.

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A current control system is the most important element for a high-performance adjustable-speed control system. One of current control systems that are used now is control method with average value.
In this paper, the equations of proportional integral control circuits are converted to those of the synchronously rotating frame, to adapt the fundamental equations of a permanent-magnet AC servomotor, and a method of exact numerical analysis by the state variable method is proposed. Nominal induced emf is compensated for a change for the worse of the current control that is problem in high speed operation. The results of the nominal induced emf compensation are comfirmed, and the results are compared with those of analysis. Moreover compensation of internal emf is analyzed, and the results of the analysis are compared with those of analysis that a case of only nominal induced emf compensation.
Consequently, following results are given.
(1) Analytic waveforms coincide with experimental waveforms.
(2) In high-speed operation, current control grow worse by equivalence gain drop of current control loops. Especially light loads make control grow worse remarkablly, but emf feedback can compensate for it.
(3) High gain of current control loops effect equivalent results as emf compensation.
(4) The effects of nominal induced emf compensation are approximately equibalence to that of internal emf compensation.

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To protect products from the dust in the factory automation system, various conveyance systems, which make use of magnetic suspension, have been considered and investigated. We have been investigated an alternative magnetic suspension system by linear induction motor (LIM) and obtained the stable suspension characteristics.
This system has linear induction motor as the primary guide way, and an U-shaped iron core is fixed on the center top of the vehicle. The vehicle is kept near the directed position by changing the repulsed motion and the attracted motion by switching the short-circuit and open circuit of the coil wound on the U-shaped core. To simplify the system structure, the driving magnetic field of linear induction motor, which is excited by three phase voltage, is used for both the suspended force and the driving force. To obtain the stability of the suspended motion of this system, the gap displacement and the calculated velocity of the displacement are used for the switching control. In this paper, we report the details of the stable suspension characteristics of the system and the transient chracteristics.

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