F.P. Dawson

A comparison of load commutated inverter systems for induction heating and melting applications

A comparative analysis of a current source inverter and a voltage source inverter suitable for induction heating and melting applications is presented. Both power supplies considered operate on the principle of load commutation. The comparison is based on criteria such as input power factor, component ratings, maximum and minimum operating frequencies, operation under varying load conditions, inverter starting capability, and system and control simplicity. The voltage source series resonant inverter is found to offer the best overall performance with respect to converter utilization. >

New synchronization method for thyristor power converters to weak AC-systems

An improved approach to obtaining good zero-voltage-crossing signals is presented. These signals are subsequently used as synchronization signals for a phase-controlled thyristor power converter. Detection of accurate zero crossings is possible even when there are large frequency changes, sudden load changes, or large commutation overlap angles. The improved accuracy in the integrity of the zero crossing is obtained by reconstructing a voltage representing the AC source voltage. This voltage is determined from the distorted thyristor converter input voltage, the converter input current, and an online identification of the source impedance using a microcontroller-based adaptive algorithm. The improvement provided by the new zero crossing detection scheme is verified experimentally. >

Investigation of Printed Wiring Board Testing By Using Planar Coil Type ECT Probe

A new application of eddy current testing techniques for investigating trace defects on printed circuit boards is proposed. A test probe consisting of a meander type exciting coil is used to induce eddy currents. The following three experiments are conducted: measuring the induced signal when a circuit trace is cut; measuring the induced signal for a number of traces placed in parallel and with a cut in the centre trace; measuring the induced signal for two back to back right angle traces. The experimental results reveal that it is possible to clearly detect defects and that the signal response obtained is strongly associated with a particular defect pattern. The signals obtained from a high density patterned board have a complicated signal signature and are therefore difficult to interpret. This complexity can be avoided by comparing the signal signature of a known good board with a defective board. The difference signal gives a clear indication of a trace defect.

Eddy current testing probe composed of planar coils

This paper presents a new eddy-current probe composed of a micro-planar mesh coil and meander coil. The probe can be used to detect the existence and the size of cracks in metallic structures. Experimental results for the sensed output voltage of this device are presented. The output signal is shown to have a discrete nature. Also, the results show that the signal strength is weak and that an offset voltage exists. Improved probe characteristics are obtained by connecting two mesh coils in series, stacking the coils on top of each other and orienting the two coils 180/spl deg/ apart.

Preparation and characterization of polymer-coated magnetic nanoparticles

Composite materials consisting of polystyrene-coated iron nanoparticles were prepared by the thermal decomposition of iron pentacarbonyl in the presence of polystyrene-tetraethylenepentamine dispersants. The nanocomposites contain both simple core-shell particles of 10-20 nm diameter, and more complex particles (20-100 nm) made from the agglomeration of several core-shell particles. Electron diffraction revealed that the core was composed of iron, in contrast to the iron nitride (Fe/sub 3/N) reported for similar conditions with a polyisobutylene-based dispersant. The materials exhibit hysteresis and /spl sigma//sub s/ ranges from 7.6 to 29.3 emu/g. The coercivity goes through a maximum for particles of /spl ap/25 nm diameter. Removal of unbound dispersant from the materials greatly increases the magnetization.

Synchronization system with Zero-Crossing Peak Detection algorithm for power system applications

This paper presents a new synchronization system that can be used to extract real time information such as the amplitude, phase and frequency of the fundamental component from an input power signal. The synchronization system is based on a zero-crossing (ZC) and peak-detection (PD) algorithm. Among its advantages, the Zero-Crossing Peak Detection (ZCPD) system performs well in the presence of input signal distortion with THD values as high as 50%, tracks positive and negative frequency ramps as high as 250Hz/sec and has a transient recovery time of two to four fundamental cycles. The ZCPD system is able to recover and re-synchronize from transient disturbances such as amplitude sags and swells (0.2pu - 1.8pu), positive and negative phase steps (±60°) and signal interruptions spanning from a few cycles to several seconds. This article details the key design features of the synchronization system and experimental results that bring into focus the performance of the ZCPD system.

A comparison of power circuit topologies and control techniques for a high frequency ballast

A comparison of power circuit topologies and fluorescent lamp current control strategies for medium to high power rapid-start high-frequency ballasts is presented. Issues such as output current harmonic content, current crest factor, and starting current are addressed. It is found that the LCC type and the LCLC type power converter satisfy the lamp requirements. The LCLC type converter has the added advantage of having the lowest kVA rating. Experimental results for the LCC type power converter under voltage mode control are provided.<<ETX>>

Defect images by planar ECT probe of meander-mesh coils

This paper presents results pertaining to image data obtained from a planar meander-mesh coupled coil type ECT probe. The image data makes it possible to detect not only the existence of a defect but also to extract detailed information regarding the nature of the defect, such as its position, shape, length, and direction. In order to recognize a defect distinctly, we have fabricated the high sensitive planar coil which can be used to image a 2-D representation of the ECT signal. The relationships between the image pattern and defect shape are discussed.

Systems for induction heating and melting applications: a comparison of load commutated inverter

A comparative analysis of current-source and voltage-source inverters suitable for induction heating and melting applications is presented. The comparison is based on criteria such as input power factor, component ratings, maximum and minimum operating frequencies, operation under varying load conditions, inverter starting capability, and system and control simplicity. Both power supplies considered operated on the principle of load commutation. Coil parameters suitable for specifying the power supply requirements are described. The results of the comparative analysis show that the voltage-source series tuned inverter offers a better converter utilization than the current-source inverter. The voltage-source inverters only shortcoming is the transient flux requirement for the matching transformer. This problem is most severe at frequencies below 400 Hz and does not have much significance above 1 kHz from a practical point of view.<<ETX>>

Phase synchronization using zero crossing sampling digital phase-locked loop

The main objective of this paper is to analyze a zero crossing sampling digital phase-locked loop (PLL) as a building block for a phase synchronization system. To that purpose, the paper deals with modeling, analysis and implementation issues of the PLL. Derived are nonlinear and linear state-space models and a transfer function model. Operation of the PLL is also analyzed using frequency domain methods. An implementation of the PLL using a digital signal processor is described. On the basis of the derived models, two different system controllers are designed and the system transient response for the two cases is compared. The first controller is of a proportional-integral (PI) type and the second controller is minimum response time controller. It is shown how the input signal amplitude variations affect the system transient response. A solution for solving this problem is presented.