| Medium-Voltage DC (MVDC) distribution and power conversion systems have become more attractive in recent years due to advances in power electronic technology. It can be used in a range of high power applications such as shipboard, electric propulsion in large multi-motor drives, and so on.;In this dissertation, first, the concept of a MVDC amplifier system for shipboard application is proposed. The dc amplifier system must provide a medium-voltage dc bus with the possibility of superposing a high bandwidth time-varying signal and should be capable of producing voltage excursions at a high slew-rate. This is intended to facilitate the development of new technologies, i.e., new high power non-linear loads based on power electronics, in all electric ships as part of the newly proposed MVDC ship power system. To achieve the required system characteristics, a specific 'hybrid front-end' is proposed in which a high-power, line-commutated multi-pulse thyristor-based front-end, which serves as the main AC-to-DC converter, is integrated with an IGBT-based DC active power filter (SDAF) connected in series on DC-bus. The system parameters and specifications for the MVDC amplifier system are set forth, and the proposed system solution is validated through both simulations and experimental results based on a 12-kVA, 400-V laboratory-scale DC amplifier test-bed.;Second, hybrid front-ends have also shown great promise in increasing the existing state-of-the-art AC-to-DC power conversion in large mobile mining equipment such as shovels and draglines. Hybrid front-end (HFE) converters based on hybrid topology of mature diode/thyristor-bridge technology and IGBT-based, AC active power filters have shown a path towards a simpler, more efficient and more reliable system. In this hybrid circuit topology, a 12-pulse thyristor-based AC-to-DC rectifier supports the main active power flow and an IGBT-based active power filter, which shares the same DC-link, is connected to point of connection to power grid for reducing total harmonic distortion (THD) and for providing partial VAR support. The system performance and control are validated through both steady-state and dynamic simulations. The modeling, design and digital control of active power filter in a 12-kVA, 208-VAC, 450-VDC laboratory-scale test-bed are presented. Comprehensive experimental results are presented which prove the feasibility, demonstrate different functionality, and show promising performance of the system in term of total efficiency, THD and reactive power compensation.;Third, size and weight are critical constraints in any application where space is limited such as in shipboard power system, mobile mining and so on. Thus, high switching frequency and high power density operation is required. Power semiconductor devices with high-voltage, high frequency and high-temperature operating capabilities are the enabling technology for more efficient and compact power conversion. A comparative design study of a high power medium-voltage converter with a 6.5 kV Si-IGBT/Si-PiN diode, a 6.5 kV Si- IGBT/SiC-JBS diode and a 10 kV SiC-MOSFET/SiC-JBS diode is presented. It is shown that the 6.5 kV Si-IGBT incorporating an anti-parallel SiC-JBS diode, with its high efficiency performance up to 5 kHz switching frequency, is a strong candidate for MW-range power converters. The 10 kV SiC-MOSFET/SiC-JBS diode remains an option for higher switching frequency (5-10 kHz) high power converters. |
