Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

M.Ing. / 50 Hz technology has led the plasma torch converters up to now. This technology was used. The high power levels of plasma torches made it difficult to implement high frequency technology. At this stage it is possible to use high-frequency technology in plasma torch applications. This thesis implements a high frequency converter suitable for plasma applications. The converter used for this application is the Partial Series Resonant Converter. A study launched to get the properties of plasmas showed that the control method used at this stage namely current control is not the ideal control method. Changing the control method of the converter made it possible to see what influence it has on the plasma. A thorough large signal analisis of the Partial Series Resonant Converter was done. From this analisis a transfer function of the converter was developed and the control parameters were calculated. This control parameters made it possible to change the control and to investigate the different control methods. The design of the plasma torch converter was based on the design of a distributed transformer, input and output filter and a non-linear controller. The results of the Partial Series Resonant Converter showed that power control leads to a more stable plasma. This thesis made a positive contribution to the knowledge of plasma torches and the knowledge of plasma torch converters. The thesis forms a summarry of plasmas and plasma-related topics, and futher study fields are defined by this thesis.

Thesis: Elec. E., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1978 / Includes bibliographical references. / Elec. E. / Elec. E. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis deals with three phase inverters and the different control strategies that can be associated with an inverter being used together. The first part of this thesis discusses the present research in the fields of PV panels, motor drive systems and three phase inverters along with their control. This control includes various strategies like MPPT, Volts-Hertz and modulation index compensation. Incorporating these techniques together is the goal of this thesis. A new topology for operating an open end motor drive system has also been discusses, where a boost converter and a flyback converter have been used in cascade to run a three phase motor. The main advantage of this is increasing the number of levels and improving the quality of the output voltage, not to mention a few other benefits of having the proposed circuit. A new algorithm has also been designed for starting and stopping the motor, which controls the current drawn from the power source during starting.

Indiana University-Purdue University Indianapolis (IUPUI) / The inner structural characteristics of non-minimum phase DC-DC converters pose a severe limitation in direct regulation of voltage when addressed from a control perspective. This constraint is reflected by the presence of right half plane zeros or the unstable zero dynamics of the output voltage of these converters. The existing controllers make use of one-to-one correspondence between the voltage and current equilibriums of the non-minimum phase converters and exploit the property that when the average output of these converters is the inductor current, the system dynamics are stable and hence they indirectly regulate the voltage. As a result, the system performance is susceptible to circuit parameter and load variation and require additional controllers, which in turn increase the system complexity. In this thesis, a novel approach to this problem is proposed for second order non-minimum phase converters such as Boost and Buck-Boost Converter. Different solutions have been suggested to the problem based on whether the converter is modeled as a linear system or as a nonlinear system. For the converter modeled as a linear system, the non-minimum phase part of the system is decoupled and its transfer function is converted to minimum phase using a parallel compensator. Then the control action is achieved by using a simple proportional gain controller. This method accelerates the transient response of the converter, reduces the initial undershoot in the response, and considerably reduces the oscillations in the transient response. Simulation results demonstrate the effectiveness of the proposed approach. When the converter is modeled as a bilinear system, it preserves the stabilizing nonlinearities of the system. Hence, a more effective control approach is adopted by using Passivity properties. In this approach, the non-minimum phase converter system is viewed from an energy-based perspective and the property of passivity is used to achieve stable zero dynamics of the output voltage. A system is passive if its rate of energy storage is less than the supply rate i.e. the system dissipates more energy than stores. As a result, the energy storage function of the system is less than the supply rate function. Non-minimum phase systems are not passive, and passivation of non-minimum phase power converters is an attractive solution to the posed problem. Stability of non-minimum phase systems can also be investigated by defining the passivity indices. This research approaches the problem by characterizing the degree of passivity i.e. the amount of damping in the system, from passivity indices. Thus, the problem is viewed from a system level rather than from a circuit level description. This method uses feed-forward passivation to compensate for the shortage of passivity in the non-minimum phase converter and makes use of a parallel interconnection to the open-loop system to attain exponentially stable zero dynamics of the output voltage. Detailed analytical analysis regarding the control structure and passivation process is performed on a buck-boost converter. Simulation and experimental results carried out on the test bed validate the effectiveness of the proposed method.

Simulations of two types of constant-frequency resonant power converters using SPICE-2/I-G SPICE are performed. The first one is a parallel resonant converter (PRC) using a controlled output rectifier. The PRC is operated at a constant frequency and its output voltage is regulated by controlling the firing angle of the output rectifier. The other circuit is the phase-controlled dual resonant converter (DRC) which employs two PRCs with their output (Capacitor voltages) connected in series. In the scheme, again the PRCs are operated at a constant frequency. By controlling the phase delay of the two PRCs, regulation of the output voltage is achieved. The behaviors of these two types of constant frequency resonant converters have been analyzed in details recently by Tsai and documented in his thesis. The objectives of the present work is to verify some of Tsai's key findings via computer simulations. First of all, the DC output characteristics of the parallel resonant converter (PRC) using the conventional acontrol (phase control) scheme and the new a-control scheme are simulated. The a-control scheme is implemented by monitoring the delay angle of the output controlled rectifier and the zero-crossing of the resonant capacitor voltage waveform while the a control is implemented by monitoring the delay angle of the output controlled rectifier with respect to the switching instance of the input inverter. The current and voltage ratings of different circuit components as a function of the control parameter-a angle are shown. The control-to-output characteristics are verified. The advantages of acontrol scheme is demonstrated. Simulation results of the phase-controlled dual resonant converter (DRC) are presented under various operating conditions. A comprehensive understanding of the behavior complex of the DRC are obtained. The ability to regulate the link voltage of the DRC is demonstrated. Boundary conditions of the DRC for natural commutation ( line or load) of the power devices are also verified. Some comments on SPICE-2/I-G SPICE simulation of the resonant circuits are presented. / M.S.

A computer-aided design procedure has been developed to determine the minimum weight design solutions, for singly wound EE- and EI-cored inductors that perform the functions of energy storage and transfer in switching DC–DC power converters. Three converter topologies, namely the Buck, the Boost, and the Buck/Boost have been considered in implementing the closed form Lagrange Multiplier-based solution to the design problem. A notable feature is the interactive use of design graphs to facilitate a trade-off study between the weight of the inductor, the total losses in the inductor and the peak current stress in the switching transistor and diode. Thus useful insight is obtained by bringing aspects of converter design into view. Practical core and magnetic material data from manufacturer's catalogs can be specified and the design optimized for the minimal weight. / Master of Science

The large-signal transient response of duty ratio controlled dc-to-dc converters is investigated using the phase-plane technique. The transition pattern of large-signal trajectories is provided in terms of the circuit parameter and operating conditions. Several transient trajectories of practical interest including start-up, step input voltage change and step-load change are analyzed. The effect of large-signal characteristics of the feedback controller on the transient trajectory is presented. / Master of Science

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