In this paper, proposed is the state-of-the art auxiliary high-frequency transformer-assisted quasi-resonant DC link (Transformer-assisted Quasi-Resonant DC Link; TQRDCL) with and active voltage-clamping function, which is able to exclude a predictive load current feedback control scheme for maintaining a zero-voltage soft-switching operation in the DC bus line. This new conceptional advanced quasi-resonant circuit topology operated under the principle of zero-voltage soft-switching is actually demonstrated in order to achieve the minimized switching losses of all the power semiconductor devices incorporated into the three-phase voltage-fed PWM inverters and/or PWM converters, together with lowered electrical dynamic stresses as well as reduced EMI noise level. The basic operating principle of a novel type of TQRDCL circuit family for ZVS-PWM inverter and converter are presented and its related theoretical and practical considerations of the optimum circuit design procedure are discussed including its promising remarkable and unique features. Its operating characteristics are illustrated and evaluated on the basis of using the computer-aided circuit simulating results. The experimental results of this trially-produced TQRDCL circuit which is more acceptable and suitable for the zero-voltage soft-switching PWM CVCF inverter and active AC/DC converter systems are demonstrated and evaluated from a practical point of view as compared with simulating ones.

抄録全体を表示

Many investigations about the chopper type AC power supply have been reported But, AC line switch suffers from many difficulties due to snubber circuit losses and switching noise because of the AC line inductances.
In this paper, I propose the partial voltage control type AC power supply using AC switches composed of antiparallel connected unidirectional switches. The switching signals for 4 switches are given by the logical output baser on the polarity signals of both the line voltage and the current. The controllable region of the AC output voltage depends on the two tapped-voltages. The most remarkable point of the AC power supply is a snubber less operation which can be realized by avoiding the flowing current interruption. So, it is possible not only to improve the operating efficiency but also to reduce the switching noise generation.
In the paper, the switching actions of the proposed AC power supply is investigated in detail. And the feasibility of the control system is verified by simulation and experimental results.

抄録全体を表示

This paper proposes a novel quick-response torque control strategy of an induction motor, which is robust against variations of primary and secondary resistances. Conventional field oriented control is originally robust against the variation of the primary resistance, but has very high parameter sensitivity of the secondary resistance. To compensate the effect of it, many researches have been done by using a stator voltage model, a low sensitivity flux observer, an adaptive system and so on. It is supposed that successful results have not been made it practice because each method needs not only complicated configurations but also motor parameters. Therefore its compensation has to be carried out having no relation with the motor parameter, especially the primary resistance. In this paper, a robust parameter-identification technique is applied to the field oriented control system with a flux simulator as a solution of the problem. The technique is based on instantaneous reactive power which is never affected by the primary resistance. The authors describe the above control theory and practical implementation. Excellent performance was confirmed by some computer simulations and experimental tests as a result.

抄録全体を表示

Recently, the V/F control drive system of the induction motor is widely applied to the drive of compressors, pumps, and so on, because it is very simple and basically requires no speed sensors. However, in the case that the V/F controlled induction motor drives a pulsating load such as the compressors, the rotational speed of the motors is considerably fluctuated and the motor frame is vibrated due to the pulsating load torque. When frequency of the torque pulsation is especially close to the resonant frequency of the mechanical system, large vibration and acoustic noise are produced.
In this paper, authors propose a method to reduce the vibration of the V/F controlled induction motor with a fluctuated load by repetitive control utilizing an acceleration sensor. It is easy to install the acceleration sensor on the motor or load frame. The repetitive control is considered effective for reduction of the vibration, as the load torque varies periodically. Effectiveness of the proposed method is confirmed by approximate analysis and experiments.

抄録全体を表示

Super high speed and high power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high power drives can be achieved with bearingless motors. In this paper, a bearingless motor with principles of permanent magnet type synchronous motors is proposed. High power factor and high efficiency can be expected in permanent magnet type bearingless motors. The proposed bearingless motor is a 4-pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. The relationships between radial forces and the permanent magnet thickness were derived. From these relationships, the optimal permanent magnet thickness to produce radial forces efficiently is found. A test machine was built to confirm relationships of radial forces, currents and voltages.

抄録全体を表示

This paper describes large turbine generator electromagnetic characteristics, considering harmonic components of the armature current, for a static frequency converter (SFC) start. Namely, the magnetomotive force for an SFC start is calculated, and frequency characteristics of higher harmonic magnetic flux and currents in a field circuit and a damper circuit are considered. Then the pulsating torque is analyzed, and the effects of the damper circuit toward the pulsating torque are considered. The results are as follows.
(1) When the fundamental frequency is more than about one hertz, the higher harmonic magnetic flux decrease, and vibration due to the electromagnetic force is insignificant.
(2) The eddy currents in each damper bar differ with each slot position and each angle between the armature fundamental magnetomotive force and the field fundamental magnetomotive force.
(3) The torque waveforms differ for each fundamental frequency.

抄録全体を表示

This paper proposes a method of analyzing three dimensional magnetic field of a system containing coil currents and magnetic substances using virtual currents. Various methods have been presented for analysis of three-dimensional static field of open boundary space, but, in a large-scale problem, the size of computation easily exceeds the acceptable limit of computing time and the capacity of a machine. The basic idea of the proposed method is to divide the whole region into interior and exterior region with an artificial boundary and to substitute virtual currents for source currents and magnetic substances within the boundary. The use of virtual currents reduces the number of elements for the analysis and shortens computing time while maintaining accuracy of analysis. In this paper, a method of determining virtual current is proposed and principal parameters of virtual currents which affect accuracy of analysis are examined. The conditions under which the virtual current method can be applied are examined through analysis of errors introduced by virtual current method. This method has been applied to analyze magnetic shielding of a magnet for magnetic resonance imaging. This example proves that the proposed method is effective in reducing scale of analysis and computing time.

抄録全体を表示

In the field of rolling mill large motors, we have usually adopted DC machines, since they have both high responsibility and over-load endurance.
Recently AC machines become more popular, since maintaining and controlling AC machines becomes easier in progress of power electronics and control theories. However, many old DC machines are still in operation at steel works, so we have to make precise diagnosis of isolation deterioration.
In this report we have theoretically studied how isolation resistance is affected by humidity, and correlation between isolation resistance and humidity has been made clear by our experiment.
Analysis of the maintenance data on DC machines that have been observed for more than twenty years at Nagoya works, proves that isolation deterioration depends on humidity.
So we propose the chart “%Mg-m value” as the diagnosis method of isolation deterioration. We have tested the breakdown voltage of DC machines when they were renewed after twenty-nine years operation and observed that breakdown voltage is the same to the %Mg-m value. These results proved that this method is effective for estimation of isolation deterioration for large DC machines.

抄録全体を表示

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 this purpose we have examined the combined propulsion, levitation and guidance system (PLG system) which can generate levitation, guidance and propulsion forces by the same coil. This paper describes the test run of the PLG system, whose ground coils (PLG coil) are constructed in one part of the Miyazaki test track. In designing the PLG coil, we make clear the magnitudes of the force acting both under normal and unusual conditions because the electromagnetic force, which levitates, guides, and propels the vehicle, directly acts on the magnet winding of the PLG coil. In the experiment, we examine both the performance of the vehicle and the force of a PLG coil. The measurement of the force at the PLG coil gives not only propulsion force and levitation force directly, but also guidance stiffness by shifting the measured coil. Good correlation recognized between the calculation and the experiment in the propulsion force, levitation force, and guidance stiffness proves that the required characteristics can be expected from the PLG system even under combination of propulsion, levitation and guidance.

抄録全体を表示

In this paper, the load leveling of the power pulsation of an induction motor with a pump load by a phase angle regulator is described. The power flow is controlled by varying the phase angle of the voltage vector. The phase angle control enables us to level the input power to reduce the power pulsation. In this case, the energy required to level the input power is stored in the flywheel effect of the motor and pump system. A novel phase angle regulator, Solid State Phase Shifter (SSPS) is also presented, for which the PWM switch schemes are employed between +30° and -30° phase voltage to yield the voltage within ±30° under continuous and rapid control. We carried out a simulation study and an experiment using a vacuum pump load and the induction motor. They were in good agreement on the reduction rate of the power pulsation, which was reduced from 63% to 10% of the average level.

抄録全体を表示

For the purpose of light-weight and compact implementation of generation set, many attempts have been made by some researchers in a development of brushless self-excited synchronous generator without ac exciter. We proposed, in a previous paper, a “novel self-excitation scheme” by which the 2nd-space harmonic component of armature mmf is used for exciting the rotor field system. This excitation scheme has a positive feature that the effect of series excitation characteristic, as well as a self-excited and brushless inplementation without ac exciter, is automatically obtained. However, in case of the system configuration of the generator reported previously, there was a problem that the voltage regulation in the inductive load condition was very large. To remove the above disadvantage this paper presents a new system configuration of the generator with self-regulating feature that can compensate the voltage regulation automatically. The new generator consists of a stator installing two three-phase windings, externally connected to a load and a capacitor bank respectively, and a rotor with field and harmonic windings.
In this paper the system configuration and theoretical concepts of the presented generator are described, and detailed experimental investigations with a laboratory machine are also shown.

抄録全体を表示

Two dimensional (2D) drive system is needed in many aspects of factory automation (FA) and office automation (OA) machines, such as pen drivers in X-Y plotters, X-Y stage for machining, 2D moving robots, etc. Conventional 2D drive systems are consisted from two sets of rotational motor drive and several types of rotary-to-linear transform mechanisms. Linear motors, in these days, have become to be effective as the requirement for high speed increases. We have been studying about Surface Motor which enables 2D drive on a surface by single mover, and the characteristics are measured. Main difficulty of the actuator is that it is short of thrust forces. Also the feasibility is limited because of its locational uncertainty caused by the open loop control.
Our interest is to introduce the closed loop digital control, to obtain required thrust force at any point on the stator. Since open loop control is used, that is, stability point where the thrust force is zero is moved one after another, generated thrust force within the range of synchronization is small. We have been studying about the peculiar expression of exciting currents to generate required direction at all the stator. On the basis of results, two dimensional positional feedback system is assembled, which detect the two dimensional location of the mover by optical sensors and direct current instructions are generated for all the four phases of the mover.

抄録全体を表示