Thesis (M.S.)--University of Wisconsin--Madison, 1980. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 86).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 99-101). Also available via the Internet.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2006. / Thesis Advisor(s): Alexander Julian. "March 2006." Includes bibliographical references (p. 103-104). Also available online.

This paper investigates the voltage and phase dynamics of a low inertia inverter based Microgrid in islanded operation. In such case, the network is less robust to disturbances due to the lack of associated inertia within an inverter. In islanded operation, the assumption of a stiff grid is no longer valid due to the voltage and phase adjustment based on conventional droop control have a resulting effect on the power flows throughout the network where voltage and frequency stability of the network may be compromised. Other approaches neglect the network dynamics when there are power imbalances in the system and how each node is affected and if the resulting increase in demand can be met with the available power generation. This paper uses the fact that the phase dynamics of coupled inverters that employ droop control closely resemble the phase dynamics proposed by the Kuramoto model. Using this model allows the network stability to be analyzed under the true nonlinear operation. It Is observed through the strong coupling impedance of the secondary distribution transmission lines and the implementation of proportional droop control will provide an appropriate means for rural and suburban neighborhoods to operate independently, given the proportional droop gain is tuned appropriately.

No description available.

This paper treats the theory and basic design of a DC-AC inverter. The output voltage, a periodic wave form, is derived from a low level DC source. The inverter's operation is described in detail for two different classes of switching device: SCR and transistor. A new design configuration which achieves higher efficiency than most commercial inverters on the market is discussed. Laboratory measurements for the design are tabulated in order to give an estimate of its performance.

Several space vector modulation schemes have been analyzed for three-leg and four-leg voltage source inverters. The analysis is performed with respect to a) switching losses, b) total harmonic distortion, c) peak-to-peak ripple in the line current and d) the ease of digital implementation. The analysis is performed over the entire range of modulation index and for varying load power factors (leading and lagging) under both balanced and unbalanced load conditions. The analysis shows that the performance of four-leg inverters is similar to three-leg inverters for various space vector modulation schemes. The analysis also verifies the fact that a modulation scheme with good harmonic performance usually has high switching losses and vice-versa. The analysis is verified using simulation and experiments. A novel algorithm for the calculation of total harmonic distortion of PWM signals has been proposed. / Master of Science

With the introduction of high speed semiconductor power devices and the increased application of adjustable speed drives (ASDs) for efficient speed control of ac motors, there has been a growing number of costly motor-drive related process failures. It has been found that the high dv/dt and high switching frequency have caused premature motor insulation failures due to motor terminal over-voltages (exacerbated by longer cable lengths). It is also acknowledged that high dv/dt and high frequency common-mode voltages generated by pulse-width modulated (PWM) inverters contribute significantly to electromagnetic interference (EMI) and may also cause damaging bearing and leakage currents. In response to these problems, a variety of mitigation techniques have been proposed in the past. However, the known solutions usually address these problems one at a time and some of the mitigation techniques are not highly effective. The major objective of this research is to search for solutions to these ASD application issues with an emphasis on solving all of the problems at the source. Therefore, theoretical analysis of all the above adverse effects are presented and the existing mitigation techniques are evaluated in this dissertation. It is found that common-mode voltage is the major cause of both bearing currents and the conducted EMI, thus the research is focused on new inverter topologies and control strategies in order to eliminate the common-mode voltage. To achieve the goal of common-mode voltage cancellation, a novel dual-bridge inverter (DBI) is proposed and studied. The DBI employs an additional inverter output stage to drive a standard three-phase dual-voltage induction motor and is controlled to generate balanced excitation of the motor resulting in a zero common-mode voltage. It is shown through experimental results that the motor bearing current is eliminated and the conducted EMI is significantly reduced. In addition to the DBI, multilevel inverter topologies have also been studied. It has been found in this research that with proper selections of the switching states, certain multilevel PWM inverters will not generate common-mode voltages. This new control method is verified in simulation by using both sine-triangle intersection PWM (SPWM) and voltage space-vector modulation (SVM). / Graduation date: 1999

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