A current source type converter can easily generate a sinusoidal current in the ac side by employing a PWM strategy. In the converter system for a single-phase supply, however, the dc current is pulsated because the dc output voltage of the converter contains the ac component with twice the ac supply frequency. The dc current pulsation causes the ac current waveform to be distorted. Although the use of the dc reactor with large inductance allows the dc current pulsation to decrease, the size and the weight of the converter equipment including the dc reactor become larger. A two-phase rectification by using two full-bridge converters and a converter system with ac chopper circuit have been proposed for the purpose of elimination of the dc pulsation. In these converters, the number of the switching devices which consist of the circuit can not avoid increasing.
To solve such a problem, this paper proposes a novel single-phase current source type converter coupling with ac chopper circuit and the PWM method. In this circuit, two switching devices in the main bridge are used to form the ac chopper bridge with two added devices and a capacitor. This paper gives the experimental and the theoretical waveforms and the steady-state characteristics. The results prove that the smoothing dc current and the sinusoidal ac current are obtained, and the great reduction of the dc inductance can be achieved in the proposed converter.

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Attention has been paid to practical applications of series active filters and series active capacitors into power systems. These consist of both voltage-source PWM inverters and matching transformers (MTs) for series-connection to power systems. The purpose of the matching transformer is not only to isolate the PWM inverter from the source, but also to match the voltage and current ratings of the PWM inverter with those of the source. The output terminals on the ac side of the PWM inverter exhibit a high impedance because the impedance on the source side of the matching transformer is multiplied by N² where the MT's turns ratio is 1: N. The PWM inverter consists of semiconductor switching devices such as MOSFETs or IGBTs. It is therefore essential to connect a small-rated LC passive filter for suppressing switching ripples appearing in the output voltage of the PWM inverter. Oscillation between a small-rated inductor and capacitor may occur because of the high impedance on the ac side of the PWM inverter, causing undesirable high frequency currents to flow into the power system.
This paper proposes a new control scheme for the series active filter, aiming at suppressing the voltage oscillation between the small-rated inductor and capacitor. It is shown theoretically that the proposed simple current feedback can suppress the oscillation so that no undesirable current flows into the source. The proposed scheme is actually applied to a hybrid series active/shunt passive filter, and then a design example is shown. Digital simulation confirms that the proposed scheme can damp the oscillation effectively. In addition, experimental results demonstrate the effectiveness and practicability of the proposed control scheme.

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In attempt to improve the constant power operation properties of the induction motor (hereafter, IM) for electric vehicles, we have developed a six- phase pole change IM (hereafter, six-phase PCIM). The six- phase PCIM can expand the constant power operation range without increasing the volume and current of IM. This advantage is realized by making use of the difference of the IM's maximum torque in the dissimilarity in the number of poles.
This paper can be summarized as follows:
A six- phase PCIM which can be operated as 4-pole and 8-pole is smaller than a 4-pole IM with the same rating.
The method of vector control based on the six- phase to two pairs of rotational d- q axis transformation is established.
When a six-phase PCIM is operated with a six-phase inverter, a mechanical contactor to change the number of poles is not necessary and the pole change is carried out automatically at the proper speed.
The pole change can be done smoothly without the large torque variation by the technique of controlling the flux levels of both modes independently.
The characteristics of the proposed control method are shown through the simulations and experimental results, and the usefulness of this control method for the electric vehicle drive system is made clear.

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It is well known that magnetic field linearities of the conventional quadrupole magnet and the skew-quadrupole magnet are improved by the end shaping of the pole. We found that small iron plates which were attached to the end shaping changed field distributions and radial and azimuthal multipole error components were cancelled by selecting the optimum mass of iron plates. The optimum mass was determined from a few field measurements easily. In addition, we found that the transverse distribution of the field gradient of the quadrupole magnet changed concavely according to increasing iron plates and the that distribution of the skew-quadrupole magnet changed convexly in reverse. This difference of the change of the field is due to the difference of the sign of the dodecapole error component between the quadrupole magnet and the skew-quadrupole magnet

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Under the speed-up on electric railways, overhead catenary systems on narrow-gauge lines have been improved with an increase of messenger wire tension. However, contact loss ratio of pantograph is comparatively high under the heavy simple catenary or feeder messenger wire type overhead catenary. These catenary has higher tension of messenger wire. In order to investigate into the causes and to work out effective improvement methods, laboratory and field tests have been carried out. From the results thereof, it is confirmed that contact force fluctuation comes under the influence of wave reflection factor at hanger, and a hanger which has spring mechanism is found effective to improve it. It is expected that rubber damping hanger or friction damping hanger contributes to reducing the contact loss of pantograph and the wear of contact wire.

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It is possible to estimate the starting performance of a squirrel-cage induction motor by the actual loading method, circle diagram method, equivalent circle method, and so on.
However, since these methods employ a commercial three-phase power supply, the testing equipment used becomes large-scaled with the increase in capacity of the tested equipment.
The set tester used at the testing factory can be sized down if the starting performance can be estimated by standstill tests using small-capacity devices.
In this paper we propose a new method which can estimate the starting performance by standstill tests using a small-capacity D. C. power supply. In this method, a D. C. current is first made to flow through the armature winding (two terminals with the third one open) of an induction motor.
Then the current decay, caused by short-circuiting between the two phases, is recorded.
The operational impedance on the induction motor per phase is determined by Fourier transformation of the current decay.
The starting performance is obtained using the two-reaction theory.
This paper shows that this method is clearly useful as an estimation method for the startig performance.

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The Dalton-Cameron method is well-known as a method for determining direct and quadrature axis subtransient reactance (x_d" and x_q") by standstill response testing. This method entails calculating x_d" and x_q" from the voltage and current measured when a rated-frequency single-phase voltage is applied to each armature winding (U-V, V-W and W-U) in turn. The authors have developed a new method to calculate x_d", x_q" and the impedance loci by means of applying a D. C. voltage instead of a single-phase voltage, and named it the expanded Dalton-Cameron method. This method is a small-capacity standstill test, and is carried out by the following three steps. The first is to short-circuit the U and V terminals while a D. C. current flows between these terminals, to measure the voltage and current (V_DC and I_DC) when the D. C. current flows between these terminals, and to record the D. C. decay current (i(t)) after these terminals are short-circuited. This same procedure is also performed for the V-W and W-U terminals in turn. The second is to draw the impedance loci from the measured V_DC, I_DC and i(t) by means of Fourier transformation, and to divide it into the directand quadrature-axis impedance loci (Z_d(js), Z_q(js)). The third is to calculate from Z_d(js) and Z_q(js) values of x_d" and x_q" and the starting performance on the basis of two-reaction theory. Experimental and calculation results on starting performance as well as a comparison with calculation results of x_d" and x_q" by Dalton-Cameron method clearly show that this method is very useful.

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A method to solve the trajectory generation problem in redundant degree of freedom manipulators has been proposed, in which the variational approach and the B-Spline curve are introduced for minimization of the consumed electrical energy of a robot manipulator system. In the proposed method, the inverse matrix of Jacobian calculation is not required, and the minimal trajectory error is guaranteed while minimizing the consumed electrical energy. The theory, simulation, and experiments are presented in this paper.

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For EDS-type magnetically levitated trains, magnetic shielding of stray fields produced by superconducting magnets is an important task. We seek the ‘optimal’ thickness distribution (configuration) of magnetic material, which is the lightest and keeps the magnetic field at tolerable levels in the vehicle. In many cases, trial and error metohds have been adopted for this purpose. In this paper, we propose a new method for a preliminary design of the magnetic shielding. In this method, we simplify the magnetic shielding problem, assuming the infinite permeability of the magnetic material, and calculate the magnetic flux going into or out of the shield surface. In this case, we can design an optimal magnetic shield (distribution and configuration of the magnetic material) and know the minimum weight of the magnetic shielding. We finally show an example of the magnetic shielding designed by this method and investigate its characteristics in a magnetically levitated train.

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In hybrid type (HB type) stepping motors, 2 phase motors have been used widely, and 4 phase or 5 phase motors have also used for a high resolution purpose. It is generally said that, the motor performance is improved as the number of phase is increased. However, increased number of phase results in the increase of stator poles, complicated manufacturing process and driving circuit accompanied by higher manufacturing cost. In case of 3 phase stepping motors, however, the number of poles less than 8 poles which are widely used in 2 phase motors can be available. Furthermore, number of driving transistors can be reduced, because number of winding terminals for power supply can be reduced to 3. From these considerations, HB type 3 phase stepping motors look possible to be an actuator superior in the point of cost-performance. In spite of such possibility, little review of 3 phase HB type stepping motors has been found.
In this paper, 3 phase HB type stepping motor is reviewed in the following points. They are, (1) It is shown that HB type 3 phase stepping motor has 2 types of construction which are different in magnetic path, and the features of both types are discussed. (2) Equations for static torque characteristics are derived, and the effects of rotor harmonic flux on the torque-angle characteristics are clarified. (3) Step response characteristics and (4) Pull-out torque characteristics are analysed for various excitation modes, and the results are compared and discussed.

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Permanent magnet synchronous motor (PM motor) is widely used for several industrial applications. Some applications such as an electric vehicle and a compressor drive require a constant power operation. The available maximum power considering the voltage and current constraints can be obtained by the optimal current vector control such as the maximum torque control and the flux-weakening control. The operating limits, however, deeply depend on the machine parameters. This paper examine the relationships between the machine parameters and the output characteristics, and it is clarified that the speed versus power characteristics depend only on the difference between the magnet flux-linkage and the maximum d-axis armature reaction flux-linkage. The maximum torque, the constant power operating range are given as a function of this difference value. The optimal machine parameters and the design of PM motor for the constant power operation are discussed based on the generally analyzed results and the examinations considering both copper loss and core loss in the light load operation.

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The side wall electrodynamic suspension (EDS) system has the advantage of not requiring gap control, and the magnetic drag is smaller than for the repulsive arrangement. This levitation system is applied in the JR magnetically levitated (Maglev) transportation system. From the experimental results in the Miyazaki test line, this system has large damping. However calculation results shows this system has little damping, and reason of large damping in the test line is not clearly shown. So running characteristics and improved design can be investigated using numerical analysis to improve riding comfort and reduce loss of the superconducting magnet. As this is non-linear system, complicated analysis is needed. Usually running characteristics of this EDS system is given from the numerical analysis which combines electromagnetic phenomena with mechanical movement equation. However this method requires very large calculation times. So more simple suspension model of this EDS system is needed. This paper shows levitation and guidance characteristics of this system, and develops the equivalent suspension system model from the electric circuit characteristics of this system. The approximation is developed by a simple function of the velocity and position of the bogie. The dynamic movement of the bogie was calculated using this model easily, and the results corresponds to the results given by the electric circuit model.

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The authors had proposed the revolving permanent magnet type magnetic wheel called the “magnet wheel”, which have both functions of induction repulsive type magnetic levitation and thrust. In this paper, the relation between magnetic poles and lift force or thrust characteristics is examined to grasp the performance. Five types of magnet wheels are discussed in the experimental study and four more types are used in the theoretical study with the three-dimensional numerical analysis. The following parameters are considered, they are magnetomotive force (mmf) of permanent magnet, thickness of magnet in magnetizing direction and the total volume of magnets, fundamental factor and distortion factor of the space mmf distribution of poles, pole pitch, diameter of magnet wheel, mechanical clearance, thickness and resistivity of conducting plate, etc. The result cleared the following. 1. The lift force per magnet volume is nearly proportional to the fundamental factor of space mmf distribution of pole. The low degree space harmonic mmf is effective to increase lift force. 2. The driving power per lift force is almost independent of configuration of the primary member including pole arrangement and position against the secondary conducting plate respectively, and only depends on the resistance of conducting plate. 3. In both the “partial overlap type” and “tilt type” magnet wheels, many number of poles with the sufficiently large pole pitch is useful. In the tilt type the use with a small tilt angle is desirable.

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A stepping motor is frequently used as an actuator of position control mainly in a low-cost system. In such case, the motor is usually driven by open loop control. For requirement of more accurate performance in positioning, closed loop control may be adopted. However, a position sensor is needed for feedback and the advantage of simple and low-cost construction is reduced by existence of the sensor. To realize a closed loop system without spoilage of this advantage, a technique for sensorless detection of position must be employed.
The authors developed a new method for sensorless detection of angular displacement of a stepping motor. In this method, relationship between waveforms of angular displacement of the rotor and the current of the stator winding in a step response is previously learned by feedforward neural network, and a waveform of angular displacement is estimated at each step by the neural network using the information of the electrical current data only.
Applying this method to an actual system by using the neural network which has learned previously using the step response data with various inertial loads, waveforms of angular displacement are estimated sufficiently in the cases driving condition is not different from that of the learned data. However, in the case with different condition, accuracy of estimation is not kept. This shows that the data for learning must be obtained in many cases of different step responses with a wide range of driving condition.

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