Research On Topologies And Control Of Virtual Quadrature Source Baded Direct AC-AC Power Conversion

AC power conversion is the key technology in power electronics researches. Widely used inverter-type and the rectifier-type converters have several drawbacks such as high price, short lifetime and low power density due to the usage of large storage elements. As a result, the development of direct AC-AC converter which requires no storage elements is always one of research hotspots in this field. In this dissertation, a comprehensive review is taken to summarize the topology technologies and their applications in AC power conversion research field. Aimed to the crucial technical constraint of the direct AC-AC chopper that stops it to output arbitrary AC voltages, an Advanced Virtual Quadrature Sources (AVQS) voltage synthesis theory is proposed. It realizes AC voltage outputs with arbitrary frequency, phase and amplitude. With the help of this, The AC chopper topology can now be applied to most AC power application areas, a series of novel power electronics converters with high reliability are developed.Firstly, based on the simple Buck-type AC chopper topology, the method of how to generate fundamental positive sequence voltage, harmonic frequency positive sequence voltages and negative sequence voltages on chopper topologies are derived. Following this, the AVQS theory, which can synthesis AC voltage outputs with arbitrary frequency, phase and amplitude are proposed. At the same time, the byproduct harmonic voltages, which are generated following the modulation, are also effectively eliminated. Thus the single-phase based chopper topologies can theoretically be applied to most AC power application areas without the constraint. At the same time, the new constraint of the simple Buck-type AC chopper topology when applying the AVQS theory is addressed. Therefore, the basic characteristics of the direct AC-AC chopper topologies that are suitable for the AVQS are concluded. It offers a guideline for the selection and derivation of new available chopper topologies.Secondly, a series of line frequency isolated direct AC chopper topologies suitable for the AVQS theory is presented. Within these topologies, an improved Push-Pull forward AC chopper is proposed. Commercial bridge-type IGBT module can be implemented and the switching loss of the transformer is minimized. Then, in order to realize the extreme low frequency voltage output in electrical motor drive applications, a series of high frequency isolated direct AC chopper topologies suitable for the AVQS theory is presented. The magnetizing condition of the high frequency transformer applying the proposed control scheme is fully analyzed to guide the transformer design. After that, the precise large-signal circuit models for the above-mentioned topologies are derived to facilitate the system level simulation. Then, a nonlinear coordinate transformation is implemented to the circuit model to derive the mathematical model of the AVQS theory. At the same time, by employing an additional operator, the control of the AVQS-applied AC chopper can be equated to ones of traditional inverter circuit. Thus the well-developed closed-loop control strategy for inverter-type converter can be seamlessly transferred to the new technology to normalize the researches of control strategies for both technologies.Then, a series of novel high reliability power electronic converters based on the proposed technology for different application areas are developed. At first, a direct AC-AC based dynamic voltage restorer (DVR) is developed for the power distribution system. The algorithm for harmonics detection and compensation voltage generation is derived. The function of harmonic voltage compensation is realized by the direct AC-AC based DVR. Then, the new technology is employed as variable frequency ac supply and electrical AC motor drive. Closed-loop control schemes are developed for different types of load. The capability of the proposed solutions is verified. Again, a direct AC-AC based power flow controller (PFC) is proposed in the power transmission system. A minimum apparent power transfer control strategy is developed for the converter to realize maximum power flow control range while using the minimum volume of the converter. Finally, a direct AC-AC based series active power filter (SAPF) is proposed. The closed-loop control strategy is seamlessly transferred from the classic strategy for inverter-type converter, which shows the correctness of the developed model. Following further explorations, more potential application areas can be found for the new technology.In this dissertation, the AVQS voltage synthesis theory is proposed to enable the arbitrary AC voltage output on the AC chopper topologies. Thus the technical constraint of the AC chopper is overcome, which facilitate its applications to most AC power conversion areas. This piece of works extends a new research direction in power electronics technology, develops its theory system and provides new ideas for the topology researches. Based on a series of new AC chopper topologies applying the AVQS voltage synthesis theory, several novel power electronic converters are proposed. It offers alternative solutions with high reliability for many important AC power conversion areas.Finally, a development of FPGA+DSP based general purpose power electronics digital control platform is introduced. The platform has a robust hardware design, a high portability software design and a touch panel based human friendly user interface design. Two experimental prototypes for novel direct AC-AC power conversion technology based on the platform are designed. Due to the generality, this platform can also be implemented to the researches and products development for most types of power electronic converters.