Electronic system modelling of UT pulser-receiver and the electron beam welding power source

This thesis was submitted for the degree of Doctor of Engineering and awarded by Brunel University.Continuous improvements to industrial equipment used in essential industrial applications are a key for the commercial success to the equipment manufacturers. Industrial applications always demand optimum performance and reliability and almost all equipment used in industrial applications is complex and are very expensive to replace. Often modifications to hardware and retrofitting additional hardware are encouraged by most equipment manufacturers and operators. The complexity of these systems however, makes assessment of modifications and design change difficult. This research implemented system modelling techniques to overcome this issue, by developing virtual test platforms of two distinctive industrial systems for enhancement assessment. The two distinctive systems were the electronic equipment called pulser-receiver used in ultrasonic non-destructive testing of safety critical oil & gas pipelines and a high voltage power supply used in high energy electron beam welding. Optimisation with emphasis on portability of the pulser-receiver and rapid weld recovery after a flashover fault condition in the electron beam welding application required assessment before design changes were made to hardware. SPICE based simulators LTSpice and PSpice were used to model and simulate the pulser-receiver and the welding power supply respectively. All the models were evaluated appropriately against theoretical data and published datasheets. However, validation of low level component models developed in the research against measurement data at a component level suffered due to system complexity and resource constraints. Close mapping of simulation results to measurement data at a system level were obtained. The research helped build up a wealth of knowledge in the development of circuit simulation models that can be analysed in the time domain with no non-convergent issues. Simulation settings were relaxed without compromising accuracy of model performance.The Engineering and Physical Sciences Research Board (EPSRC) and TWI Ltd

Topological issues in single phase power factor correction

The equipment connected to an electricity distribution network usually needs some kind of power conditioning, typically rectification, which produces a non-sinusoidal line current due to the nonlinear input characteristic. With the steadily increasing use of such equipment, line current harmonics have become a significant problem. Their adverse effects on the power system are well recognized. They include increased magnitudes of neutral currents in three- phase systems, overheating in transformers and induction motors, as well as the degradation of system voltage waveforms. Several international standards now exist, which limit the harmonic content due to line currents of equipment connected to electricity distribution networks. As a result, there is the need for a reduction in line current harmonics, or Power Factor Correction - PFC. There are two types of PFC’s. 1) Passive PFC, 2) Active PFC. The active PFC is further classified into low-frequency and high-frequency active PFC depending on the switching frequency. Different techniques in passive PFC and active PFC are presented here. Among these PFC’s we will get better power factor by using high-frequency active PFC circuit. Any DC-DC converters can be used for this purpose, if a suitable control method is used to shape its input current or if it has inherent PFC properties. The DC-DC converters can operate in Continuous Inductor Current Mode – CICM, where the inductor current never reaches zero during one switching cycle or Discontinuous Inductor Current Mode - DICM, where the inductor current is zero during intervals of the switching cycle. In DICM, the input inductor is no longer a state variable since its state in a given switching cycle is independent on the value in the previous switching cycle. The peak of the inductor current is sampling the line voltage automatically. This property of DICM input circuit can be called “self power factor correction” because no control loop is required from its input side. In CICM, different control techniques are used to control the inductor current. Some of them are (1) peak current control (2) average current control (3) Hysteresis control (4) borderline control. These control techniques specifically developed for PFC boost converters are analyzed. For each control strategy advantages and drawbacks are highlighted and information on available commercial IC's is given. This high frequency switching PFC stage also has drawbacks, such as: it introduces additional losses, thus reducing the overall efficiency; it increases the EMI, due to the highfrequency content of the input current. Some of the EMI requirements are discussed. But the level of high-frequency EMI is much higher with a considerable amount of conduction and switching losses. This highfrequency EMI will be eliminated by introducing an EMI filter in between AC supply and the diode bridge rectifier. The efficiency will be improved by reducing the losses using soft switching techniques such as ‘Zero Voltage Switching’- (ZVS), ‘Zero Voltage Transition’ (ZVT), and ‘Zero Current Switching’- (ZCS). We study circuit techniques to improve the efficiency of the PFC stage by lowering the conduction losses and/or the switching losses. Operation of a ZVT converter will be discussed, in which the switching losses of the auxiliary switch are minimized by using an additional circuit applied to the auxiliary switch. Besides the main switch ZVS turned- on and turned-off, and the auxiliary switch ZCS turned-on and turned-off near ZVS. Since the active switch is turned- on and turned-off softly, the switching losses are reduced and the higher efficiency of the system is achieved

10kHz Pulse Repetition Frequency CO2 Laser for Processing High Damage Threshold Materials

Power intensities generated at the workpiece by continuous wave carbon dioxide lasers at 10.6 mum are insufficient to induce the non-conduction limited processes necessary for machining many of the refractory metals and ceramics employed in the manufacture of engineering components. Operated in a pulsed mode, analogous to solid state laser operation, the CO2:N2 laser can be designed to overcome these power intensity limitations. Nitrogen Carbon-dioxide mixtures can be pulse excited to give high output pulse intensities combined with a relatively low mean output power, thus, minimising thermal degradation of the optical system. Flat topped pulses with plateau powers controlled and matched to the processing requirements of metals and ceramics can be generated by proper choice of the input electrical pumping pulse, gas composition and design parameters of the optical resonator. Continuous machining is possible provided pulse repetition frequencies of up to 10 kHz can be achieved, since, at this frequency, a constantly evaporating liquid phase can be sustained

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 04)

For abstract, see N74-20609

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 05)

For abstract, see N75-13677

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 06)

For abstract, see N75-20149

Investigation of Power Factor Correction in Single Phase AC-DC Converters

An ac to dc converter is an integral part of any power supply unit used in the all electronic equipments. These electronic equipments form a major part of load on the utility. Generally, to convert line frequency ac to dc, a line frequency diode bridge rectifier is used. To reduce the ripple in the dc output voltage, a large capacitor is used at the rectifier output. But due to this large capacitor, the current drawn by this converter is peaky in nature. This input current is rich in low order harmonics. Also, as power electronics equipments are increasingly being used in power conversion, they inject low order harmonics into the utility. Due to the presence of these harmonics, the total harmonic distortion is high and the input power factor is poor. Because of the problems associated with low power factor and harmonics, utilities will enforce harmonic standards and guidelines, which will limit the amount of current distortion allowed into the utility, and thus the simple diode rectifier may not be in use. So, there is a need to achieve rectification at close to unity power factor and low input current distortion. Initially, power factor correction schemes have been implemented mainly for heavy industrial loads like induction motors, induction heating furnaces etc., which forms a major part of lagging power factor load. Hence, PFC is becoming an important aspect even for low power application electronic equipments. There are two types of PFC‟s. 1) Passive PFC, 2) Active PFC. The active PFC is further classified into low-frequency and high-frequency active PFC depending on the switching frequency. Different techniques in passive PFC and active PFC are presented here. Among these PFC‟s, we will get better power factor by using high-frequency active PFC circuit. Any DC-DC converters can be used for this purpose, if a suitable control method is used to shape its input current or if it has inherent PFC properties. The DC-DC converters can operate in Continuous Inductor Current Mode – CICM, where the inductor current never reaches zero during one switching cycle or Discontinuous Inductor Current Mode - DICM, where the inductor current is zero during intervals of the switching cycle

Satellite Power Systems (SPS) concept definition study, exhibit C. Volume 2, part 1: System engineering

Volume 2, Part 1, of a seven volume report is presented. Part 1 encompasses Satellite Power Systems (SPS) systems engineering aspects and is divided into three sections. The first section presents descriptions of the various candidate concepts considered and conclusions and recommendations for a preferred concept. The second section presents a summary of results of the various trade studies and analysis conducted during the course of the study. The third section describes the Photovoltaic Satellite Based Satellite Power System (SPS) Point Design as it was defined through studies performed during the period January 1977 through March 1979