Rotating-space-vector-modulated matrix-converter-based advanced drive topologies with enhanced features

Direct-matrix-converters are well known for three-phase ac machine drives, without storage electrolytic capacitors, which lead to a high power density power-conversion-system with high reliability. However, similar to the state-of-the-art voltage-source-based back-to-back converters, the direct-matrix-converter modulated with conventional PWM schemes generate a high-frequency common-mode voltage at the machine terminals. In addition, the converter voltage gain in per-unit is limited to 0.866 in the linear modulation range. At a non-unity grid power factor, when the power-conversion-system supplies reactive power to the grid, which is an important requirement for the grid interconnection of wind turbines, the converter voltage gain reduces (below 0.866) in proportion to the grid power factor. This fact limits the active and reactive power control range of the power-conversion-system.;This dissertation proposes a new direct-matrix-converter-based drive for three-phase ac machines, without storage electrolytic capacitors, with matrix converters connected at each end of open-ended stator windings of the machine. The open-end winding structure can be obtained by opening the star-terminal, or opening the delta terminals, of three-phase stator windings of a conventional machine and hence creating another set of three-phase stator terminals. It is shown how two direct-matrix-converters, one at each side of this open-end-winding machine, are modulated synchronously with the proposed PWM scheme to achieve the following advanced features simultaneously: (1) converter voltage gain up to 1.5 which is independent of the grid power factor in a wide range. This fact enhances the active and reactive power control range of the drive system, (2) peak voltage-stress across the slot-insulation of the machine is limited to the peak of input phase voltage i.e. a factor of at least 1.732 lower as compared to the state-of-the-art back-to-back converters, (3) elimination of the high-frequency common-mode voltage at the machine terminals. Elimination of the high-frequency common-mode voltage leads to significant savings in the common-mode filters which further increase the power density of the converter system. The converter topology used in the proposed drive requires 36 semiconductor switches. However, with the aforementioned capabilities along with the assumption that the cost of semiconductor devices will decrease in the future, the proposed drive offers a more silicon solution to a high performance drive with high power density. A laboratory prototype of the proposed drive system is built. Experimental results verifying the advanced features of the drive are presented.;An improved three-level indirect-matrix-converter based topology, alternative to the use of direct-matrix-converters at each end of three-phase open-end-winding of the machine, with the same switch-count (i.e. 36 semiconductor switches) is described next. This topology has the following advantages in addition to the advanced features described above for the direct-matrix-converter-based open-end-winding drive: (1) reduced switching losses; and (2) reduced protection-clamp-circuit requirement which requires one diode as compared to 18 diodes in the direct-matrix-converter-based topology. With the proposed analysis, it is shown that the modulation strategy of this three-level indirect-matrix-converter topology is same as the modulation strategy of the direct-matrix-converter based topology; however, with a very small modification. Simulation results presented verify the operation of the indirect-matrix-converter based open-end-winding drive.;In many applications, to achieve a high power density power-conversion-system, increasing the power density of the power-electronic-converter may not be sufficient. The use of 60Hz isolation transformers, which are bulky and weighty due to the low frequency excitation, is a major bottleneck. For example in wind power generation applications, these transformers occupy more than 15% of the nacelle volume. To address this problem, a novel power-electronic-transformer-converter is proposed which is a combination of a high-frequency transformer (hence significant reduction in the weight and volume) and a matrix converter (high power density). This topology has an order of magnitude reduced controlled switch requirement on the high-voltage side of the transformer as compared to the prior-art. The modulation strategy of this power-electronic-transformer-converter is derived from the modulation of the direct-matrix-converter-based open-end-winding drive. Simulation results are presented to demonstrate the operation of the power-electronic-transformer-converter.;In summary, in this dissertation, new power-electronic-converter topologies along with new power-electronic-transformer-converter topology are described. The primary objective is to achieve a power-conversion-system with high power density, high efficiency and high reliability. Proposed topologies are derived from the well known concept of direct and indirect-matrix-converter in the literature. However, they are superior to its predecessors due to many aforementioned system-level advantages. Experimental verifications of the main topology are performed. Simulation verifications of other topologies are also performed which defines further research topic to be investigated in the future. (Abstract shortened by UMI.)...