This paper presents a PWM strategy for matrix converters for reducing switching losses and the output voltage harmonics. The authors have previously proposed a PWM strategy, in which the number of commutations in all three phases during one control period can be four. In this study, using detected output currents for the calculation of the duty cycles, seven PWM patterns are proposed for reducing the number of commutations to three during one control period. It is found that two out of the seven patterns are satisfactory in each control period. The pattern with smaller harmonic voltages is selected on the basis of the instantaneous effective value of the output voltage during each control period. The effectiveness of the proposed PWM strategy is verified by performing experiments.
This paper proposes a new method for designing feedforward inputs for Galvano scanners in laser drilling machines. The heat generated by current amplifiers becomes a problem as the positioning speed of the Galvano scanner is increased. The proposed method involves the use of a final-state control that considers the voltage constraint of a current amplifier. By constraining the applied voltage to the motor, the power supply voltage of the current amplifier is reduced. Therefore, the electricity consumed and the heat generated by the current amplifier can be reduced. The effectiveness of the proposed method is shown through simulation and experimental results.
This paper describes an improved strategy for the total harmonic distortion of an input current of a simplified indirect matrix converter. The control of the current-source rectifier on the input side is based on space vector modulation, and a two-phase triangular carrier modulation technique is applied to the input and the output to prevent interference due to zero-vector collision between both the sides. In addition, this paper describes that the simplified indirect matrix converter cannot achieve a unity input power factor operation and harmonics reduction in the low-load range because it has a real DC bus. Therefore, leading current compensation is applied to solve the problem, focusing on the low-load range. The improved operation characteristics are confirmed through computer simulations and experimental tests. The total harmonic distortion improved by 31 points, whereas the total input power factor degraded slightly by 14 points.
This paper presents line loss minimization control using shunt and series converters of a UPFC (Unified Power Flow Controller) in a loop distribution system. Line loss in a loop distribution system is caused by the circulating current flowing in the loop and the mesh currents flowing to the loads. The authors have previously proposed a compensation method for circulating current using a series converter. In this paper, the authors propose a suppression method for reactive currents using a shunt converter. In the prototype model of a loop distribution system, a theoretical loss reduction ratio of 92% without line loss caused by active currents is obtained. Similar line loss reduction characteristics are obtained by experiments using the prototype distribution system.
A prototype of the flux-modulated type magnetic gear is manufactured and tested to evaluate its efficiency and torque transmission characteristics. According to the test results, the maximum torque transmission is proportional to the gear's size and the flux density of each rotor. The efficiency of the gear is dependent upon core material and core shape. As for the gear made for trial purposes, the efficiency of 99% was obtained in the maximum. The prototype gear obtained comparative advantages over mechanical gears with respect to efficiency and noise.
The authors achieved the restraint of the heating irregularity in the heating equipment of beverage cans by the high-frequency induction heating method and determined the resulting improvement in the heating efficiency. The heating irregularity between the top and bottom of the can was reduced to less than 3°C by improving the arrangement of the heating coil for the beverage can by the thinning of the winding, and by circuit configuration. Furthermore, the efficiency of the power conversion was improved from 93.0% to 97.4%. Here, the configuration of the equipment and the experimental results are reported.
The circulating current in parallel-connected armature windings of synchronous machines causes losses in parallel circuits due to voltage unbalance. This paper describes a study on the effect of mutual inductances on the circulating current using the finite element electromagnetic analysis on a large synchronous machine with parallel-connected armature windings with a missing turn. The analysis results indicate that the mutual inductances between the parallel circuits affect the circulating current. The magnetic flux distribution due to the circulating current in each circuit can be evaluated individually using the magnetic permeability distribution of the circulating current in each circuit.
When distributed generators such as photovoltaic (PV) systems spread widely in distribution networks, it is important to detect islanding caused by power system fault for ensuring electrical safety. We developed a model of the nonlinear magnetizing characteristics of a pole transformer for analyzing islanding-prevention of PV systems. Basic experiments of islanding detection were performed for verification of the developed model. The analytical results obtained using the proposed model agreed well with the experimental results.
Recently, industrial machines and electrical equipment with multi-degree-of-freedom (multi-DOF) mechanisms have become complicated because many single-degree-of-freedom motors are used. A multi-DOF actuator is expected to solve this problem. We have proposed various multi-DOF actuators. However, they have some problems such as low torque and narrow rotation angle. This paper describes a new 2-DOF actuator with an outer rotor, which rotates widely. The operating principle is described, and the torque characteristics are clarified through the 3-D finite element analysis.
Iron loss in two kinds of electrical steel, which have the same iron loss in case of conventional linear amplifier excitation but different thickness, is found to have a difference of 10%-20% in case of PWM inverter excitation, which is often used in a motor drive control system. The PWM inverter has many time harmonics in the output voltage, whereas the linear amplifier does not. The difference in iron loss is not always ignored while considering the electrical steel grade in commercial catalogs and the JIS (Japanese Industrial Standards). Since the iron loss also increases by about 10%-60% in PWM inverter excitation, a material evaluation system and a method for reducing iron loss are considered to be important.
In the Tokaido Shinkansen, rolling stock types have been unified with an inverter controlled type, which was introduced after Series 300. As a result, the input power factor of the main converter of the rolling stock has been controlled to 1. In accordance with this change, the role of reactive compensation of SVC has shifted from the load power of trains to the power consumed by the reactance in an electrical power system. Therefore, considering the aging of power converters, it is time to reassess their layout and the configuration for the future of the Tokaido Shinkansen. We reassessed the equipment configuration, capacity, and layout of power converters as well as verified the impact on the stabilization of power supply when introducing self-commutated power converters.
Because of the improved performance of power devices, the volume of the AC filter inductors used in the high-frequency PWM inverters has reduced. However, the temperature rise in the filter inductor due to the miniaturization has become more pronounced. Therefore, the authors have proposed the iron loss calculation method for the AC filter inductor. However, the accuracy of the value calculated via the loss map method cannot be verified, because the iron loss arising during each switching duration cannot be measured using the conventional power measuring instruments. In order to solve this problem, we developed an inductor loss analyzer (ILA), which enables the measurement of the iron loss of the inductor precisely during each switching period. The accuracy of the iron loss of the filter inductor calculated by the loss map method is verified using the ILA. It is found that the value calculated via the loss map method differs slightly from the value measured using the ILA. However, these differences can be reduced if we take into the accurate flux density calculation and the loss effect of the duty ratio of the PWM pulse. Finally, it is verified that the loss map method can provide accurate iron loss calculation.
The purpose of our study is to achieve the dynamic model-based control of a nonlinear robot arm, while taking joint-elasticity into consideration. We previously proposed a multi-input multi-output system identification method, called the decoupling identification method, for a planar two-link robot arm with elastic-joints due to the Harmonic-drive reduction gears. The robot arm is treated herein as a serial two-link two-inertia system with nonlinearity. Physical parameters such as motor inertias, link inertias, joint-friction coefficients, and joint-spring coefficients of the robot dynamic model are accurately estimated by the decoupling identification method. This paper describes a simple method for achieving the vibration suppression control of a serial two-link two-inertia system based on physical-parameter estimation. We propose a torsional angular velocity feedback scheme, which can be “plugged-in” to an existing PI velocity controller, using a nonlinear state observer based on the accurately estimated dynamic model. In addition, we propose a gain-scheduling control scheme that involves switching inertia parameters to compensate for payload variation. Through several experiments, we demonstrate the effectiveness of the proposed control method by using the elastic-joint robot arm.
The world's first electric vehicle is discussed. It is said that the first experiment on an electric vehicle was performed in the mid of 1830s, just after the discovery of Faraday's law. Therefore, this era is called the age of invention of the application of electric motor, with one of applications being an electric vehicle. There are numerous theories, rumors and opinions about the first electric vehicle. Here, the author will clarify as to which experiment should be called as the first experiment on the electric vehicle.