This paper describes a simple and clear approach to analyze harmonic instability of phase controlled thyristor converters with input passive filters. It is shown by analysis and experiment that harmonic instability may occur at the parallel resonant frequency between the passive filter and the ac source even if the ac source impedance is low. A combined system of series active and shunt passive filters has already been proposed as a new approach to harmonic compensation in power systems by the authors. It is confirmed analytically and experimentally that the series active filter used has the capability to suppress the harmonic instability at the parallel resonant frequency. However, it is also shown that the series active filter may cause harmonic instability adversely at lower frequencies. However, harmonic instability at a frequency except for the parallel resonant frequency does not cause any practical problem. The obtained analytical results are confirmed by experiment in detail.
This paper describes a high voltage three-phase monolithic inverter IC using dielectrically isolated power IC technology. This inverter IC has the ability to drive a 50 W brushless motor, and it can be supplied voltage from a commercial voltage source using only a rectifier. This inverter IC includes six insulated gate bipolar transistors (IGBTs) and fast recovery diodes for output stages having a current capability of 1 A for continuous current. The IGBTs and fast recovery diodes realize a reduction in forward voltage drops and fast switching speeds. The IC also provides functions such as drive circuits suitable for pulse width modulation (PWM) control at a switching frequency of 20 kHz, a charge pump type power supply for each upper driver, and unique overcurrent protection circuits on one chip. The drive circuits which prevent the IGBTs from incorrect turning on under the large dV/dt condition, and the overcurrent circuits, provide easy use and enhanced reliability.
The production number of printed circuit boards (PCBs) is increasing very rapidly. To automize the PCB production, a visual inspection system for assembled PCB has been developed. The system inspects many kinds of defects on assembled PCBs, such as parts missing, improper parts on PCBs, polarity error of diodes and capacitors and improper insertion of leads, using image processing techniques. The multi-step similarity vector method has been developed to read various character patterns of IC names from many manufacturers. To inspect polarity marks on movable parts with long leads, the flexible window system has been installed. The slitted light is casted on leads backside of PCB to inspect parts missing and improper insertion of leads. To execute these variety of image processing at high-speed, the inspection system is equipped with a micro-programmable digital signal processor for image processing, the DSP-i. The DSP-i enables the system to inspect the various inspection functions 25 times faster than general purpose 16 bits microcomputers.
A method to simultaneously measure the resistivity and the permeability of a sample conductor from the difference in the complex impedance obtained by measuring the vectors of two identical circular solenoid coils, one surrounding and coaxial with the sample conductor moving at a constant speed and the other without the sample conductor is studied. The sample conductor in the study moved at a constant speed but when the measuring frequency is high enough, the effect of the speed on the complex impedance becomes insignificant. In this paper, the lowest possible measuring frequency which keeps, within 1%, the effect of the speed on the difference in the impedance between a static and a moving sample s shown. The resistivity and initial permeability of an iron sample were measured under such condition. These values were compared with values obtained by conventional methods. The difference in the values for the resistivity of an iron sample was within 8.3%, and for the initial permeability within 3%.
In general, the thyristor controlled rectifier circuit (thyristor converter) generates a large amount of harmonics in the input power supply. Consequently, in the power system, the harmonics become more increased for larger capacity of such converter, so it is important to improve their harmonic characteristics. Among those converters, the double three-phase bridge converter with transformer of star and delta windings is well known. By application of such techniques, Miyairi and his group had proposed the thyristor converter which has excellent harmonic characteristics. On the other hand, the multiple connected inverter circuit without output transformer had been already proposed. However, it contains the lower order harmonics. In this paper, the author proposes a converter which can reduce the harmonics like the above mentioned double bridge converter. This circuit has the center tapped reactor that can control the dc current like the current control of Miyairi's interphase reactor. This novel converter need not use the input three phase transformers that usually make the cost higher. The proposed circuit has a commutation one with capacitor that is analogous to the series diode type thyristor inverter. This circuit keeps the commutation to operate successfully with constant reverse bias time. The whole circuit operation and the commutation circuit operation have been discussed and confirmed experimentally and theoretically.
Preprocessing in a program for a 3-D finite element analysis, subdividing an analysis field into finite elements formed by tetrahedra, is usually much more complex compared with subdivision in 2-D field problems. For encouraging the 3-D finite element analysis to practical use an automatic tetrahedral elements generation method should have the following prerequisites: (1) Inputting data is easy and their amount is small. (2) Mesh density control is easy. (3) The shapes of generated elements are closer to that of regular tetrahedron. (4) It is applicable even if the analysis field includes complicated objects. (5) The processing time for generating elements is short. In this paper, an automatic tetrahedral elements generation method satisfying all the conditions mentioned above is proposed: Manual operations required are only to divide an analysis region into several rectangular regions and a latticed wire frame for each region in consideration of suitable mesh density. Then the frames are mapped on objects, hexahedra generated from the frames are divided into tetrahedra, and then the shapes of tetrahedra are modified to the closer regular ones automatically. The processing time is very short because of using mapping method.
Magnetic frequency triplers have a configuration with star-connected primary windings and opendelta-connected secondary windings of three single-phase saturable reactors. Most devices used in the field of industry have output windings providing for each of the three saturable reactors (called the “separate core type”). The authors have proposed a frequency tripler (called the “T-shaped core type”), which has the cores combined into a T-shape and the output windings tied up into a bundle, and with this have proved that high efficiency comparable to that of large unit can be realized even in small units by reducing the length of the output windings to about 57% of that in the separate core type. However, due to a magnetic circuit imbalance, the T-shaped core type had the disadvantage of causing a two step jumping phenomenon, which limits the operating range of the device. In the present paper, a new frequency tripler (called the “symmetrical core type”), whose cores are combined into a Y-shape, has been tested, analyzed, and reviewed. The operation of the devices were analyzed by the harmonic balance method taking count of the magnetic circuit imbalance and the resistance component of the windings. As a result, it is shown that operating characteristics can be improved by adopting the symmetrical core type. The results obtained from this paper will offer useful data to the design and operation of symmetrical core type frequency triplers.