Advanced Modulation Techniques for Neutral-Point Clamped Three-Level Inverters in Automotive Applications

The Neutral-Point Clamped (NPC) three-level inverter is a promising multilevel topology in the application of Electric Vehicle (EV). However, the growing requirements by the EV initiate the thermal unbalance problem for this inverter topology. The present thesis highlights the performance of the NPC three-level inverter supplying a Permanent Magnet Synchronous Motor (PMSM) in the application of EV. The PMSM is considered to operate in the region below the base speed. In this condition, there is an unbalance of conduction power loss among the semiconductors of the inverter. The project deals with the conduction power losses of the semiconductors in a NPC three-level inverter controlled with special Space Vector Modulation (SVM) methods. In order to find an appropriate method for balancing the conduction power loss of devices, three SVM methods, “Normal”, “O2” and “O3” are compared. By implementing these three techniques, primarily, the “conduction duty cycle” of the devices is calculated to demonstrate the duration of conducting for each device. Afterwards, the conduction power loss of devices is computed in MATLAB/Simulink. In addition, the impact of two parameters, modulation index and power factor, on conduction duty cycle and conduction power loss is investigated. Furthermore, Comparison of the total harmonic distortion of the line-to-line current for different modulation indices is presented for all three modulation techniques. According to the detailed comparisons of methods, O2 Space Vector Modulation technique stands out as a better candidate for thermal redistribution among semiconductors

Delta STATCOM with partially rated energy storage for intended provision of ancillary services

This thesis presents research on two distinct areas, where the work carried out in the first half highlights the challenges posed by the declining system inertia in the future power systems and the potential capability of the energy storage systems in bridging the gap, supporting a safe and reliable operation. A comparison of various energy storage technologies based on their specific energy, specific power, response time, life-cycle, efficiency, cost and further correlating these characteristics to the timescale requirements of frequency and RoCoF services showed that supercapacitors (SC) and Li-ion batteries present the most suitable candidates. Results of a network stability study showed that for a power system rated at 2940 MVA with a high RES contribution of 1688 MVA, equating to 57% of the energy mix, during a power imbalance of 200 MW, an ESS designed to provide emulated inertia response (EIR) in isolation required a power and energy rating of 39.54 MW and 0.0365 MWh respectively. Similarly, providing primary frequency response (PFR) on its own required a power and energy rating of 114.52 MW and 2.14 MWh respectively. ESS providing these services in isolation was not able to maintain all the frequency operating limits and similar results were also seen in the case of the recently introduced Dynamic Containment service. However, with the introduction of a combined response capability, a significantly improved performance, comparable to that of the synchronous generators was observed. In order to maintain the RoCoF and the statutory frequency limit of 0.5 Hz/s and ±0.5 Hz respectively, an ESS must be able to respond with a delay time of no more than 0.2 seconds and be able to ramp up to full response within 0.3 seconds (0.5 seconds from the start of contingency) for a frequency deviation of ±0.5 Hz. The second half of the thesis focused on investigating the current state-of-the-art power conversion system topologies, with the objective of identifying a suitable topology for interfacing ESSs to the grid at MV level. A delta-connected Modular Multilevel STATCOM with partially rated storage (PRS-STATCOM) is proposed, capable of providing both reactive and active power support. The purpose is to provide short-term energy storage enabled grid support services such as inertial and frequency response, either alongside or temporarily instead of standard STATCOM voltage support. The topology proposed here contains two types of sub-modules (SM) in each phase-leg: standard sub-modules (STD-SMs) and energy storage element sub-modules (ESE-SMs) with a DC-DC interface converter between the SM capacitor and the ESE. A control structure has been developed that allows energy transfer between the SM capacitor and the ESE, resulting in an active power exchange between the converter and the grid. A 3rd harmonic current injection into the converter waveforms was used to increase the amount of power that can be extracted from the ESE-SMs and so reduce the required ESE-SMs fraction in each phase-leg. Simulation results demonstrate that for three selected active power ratings, 1 pu, 2/3 pu, & 1/3 pu, the fraction of SMs that need to be converted to ESE-SMs are only 69%, 59% & 38%. Thus, the proposed topology is effective in adding real power capability to a STATCOM without a large increase in equipment cost. Furthermore, modifying the initially proposed topology with the use of Silicon Carbide (SiC) switching devices and interleaved DC-DC interface converter with inverse coupled inductors resulted in similar efficiencies when operated in STATCOM mode.Open Acces

Active thermal control of power electronic modules in smart transformer applications

The Smart Transformer (ST) is a possible solution to obtain intelligent nodes in the electrical grid, which can be used for the grid management and increase the capacity for the integration of renewable energy sources. A problem for the application of the ST in the distribution grid is the expected lower reliability in comparison with the traditional transformer. To address this problem, the knowledge of power system, power electronics and reliability is combined in this work. Following the "Physics of failure" approach, the most frequently failing components are identified, their load profile in the electrical distribution grid is analyzed and finally solutions are developed to improve the reliability. The power semiconductors are found to be the most prone to fail components and most of their failure mechanisms are found to be affected by thermal cycling. For this reason, thermal stress analysis is performed for the three-stage ST. As an opportunity to increase the reliability, active thermal control is introduced, which is a software based solution for the reduction of the thermal stress during operation. The existing approaches from literature are reviewed and categorized into control of the power converter losses and the control of the device loading. For increasing the reliability by control of the power converter losses, one algorithm is introduced and validated for hard switching power converters and one algorithm is introduced for soft switching power semiconductors. Controlling the thermal stress of modular building blocks in a modular power converter, referring to power routing, is proposed. The capability of the algorithm is investigated analytically for series connected and parallel connected modular building blocks. For the validation, the influence of the power routing on the loading of the single cell is demonstrated experimentally for series connected, parallel connected and medium frequency transformer coupled cells in modular power converters

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion