Investigation of load side power conversion for high frequency AC distribution systems

Abstract

Nowadays, power systems have been going through a revolution due to the development of renewable energy and modern electronic systems. The existing power architecture is no longer effective in meeting the competing requirements in the aspects of performance, efficiency and cost. A high frequency alternating current distributed system (HFAC-DS), developed by NASA as an alternative power delivery for space crafts in the 1980s, has recently attracted much attention based on rapid developments in semiconductor technologies. By operating with a high frequency link, the system can be made to be compact and flexible, in order to meet the individual needs of loads/source in the system, speed up response, and reduce noise. It offers an alternative method for high frequency power conversion to variable renewable energy and modern power electronics systems. The high frequency has been embedded on the high frequency transformer link in all the DC-Dc power converters. The proposed work is to examine high frequency AC link for distribution. The objective of this research is to provide a solution to the load side power conversion through investigations of new topologies for the revolutionary HFAC distribution system. Firstly, a topology of resonant step up switched-capacitor-based ac-ac converter is introduced to convert the ac input voltage level to a double ac voltage level. Zero current switching can be achieved; high current stress can be relieved. The topology also extends the switched-capacitor converter family to another ac-ac application and provides an alternative electronic conversion method to the ac transformer. A resonant switched-capacitor based step up/down ac-dc power converter with high frequency switching is explored. Step down voltage is achieved in the circuit by simply introducing cascaded stages, which will be much more convenient for integration. Corresponding analysis is derived to verify the performance of the converter, which provides an ac-dc power transfer method. Then an improved version of resonant switched capacitor step up/down with high frequency switching is proposed. This circuit provides cascaded step up and step down voltage in one circuit. It is easy to have parallel configuration and easy to change the output voltage by inserting or replacing a cascaded step up or step down module. A voltage gain of integer ratio in the style of 2n/m is achieved, with n and m being the cascade stage of step up and step down respectively. The proposed circuit provides a solution of voltage step up/ down for the HFAC distribution system. For current source conversion, switched-inductor power converters with current conversions 2, 1/2 and -1 have been developed. To reduce the power loss, resonant soft-switching technique is introduced to improve the power conversion efficiency. Small resonant capacitors are paralleled with the switches to achieve zero voltage switching. Two families of zero-voltage switching step down switched inductor power converters are presented which can improve the voltage spike issue. They are able to extend to high order step down of 1/2 1/3, 1/4 {21203d}.1/n and -1, -1/2, -1/3 {21203d} -1/n conversion ratios by using only two switches. The proposed new concept of switched-inductor current source power converter provides an alternative method to power conversion and is a new concept in topology and resonant technique. The boundary of maximum storage energy is analyzed to be an alternative to study the instability of the system by bifurcation and chaos of the storage energy. Zero energy is obtained in stable period one and the storage energy with the same value and opposite direction is obtained in period two. These results can provide a new guideline to design a stable system and provide a new control algorithm for power electronic system. To sum up, this research has accomplished comprehensive analysis and in-depth studies in various aspects, including topological investigation, mathematical modeling, and practical applications of load side power conversion. The research outcomes provide meaningful theoretical findings as well as the feasible application of solutions of power transferring for HFAC distribution system.