Research On Electromagnetic Energy Conversion Of The High Power AC-DC-AC PWM Converter

With the development of industry, power electronics converters are more and more implemented in the industry fields. On one hand, people hope that the capacity of power electronics converters becomes greater. On the other hand, people demand high power density and high reliability of converters. Therefore, this thesis analyzes the electromagnetic energy conversion process of the converters, and carries out in-depth research on the DC storage energy exchange laws in converters through theoretical analysis, simulation and experimental research methods with the high power AC-DC-AC PWM converters as the research object.First, based on the analysis of the steady-state energy transform process in two-level PWM voltage source inverter and diode rectifier to discuss the energy flow of grid and load, summarize the DC storage energy fluctuation laws. Analyzed the quantitative relationship between system operating parameters and the DC storage energy fluctuation in cases of inverter with pure reactive load and diode rectifier under DCM mode, the quantitative relationship between capacitance of DC side and system operating parameters in two-level voltage source inverter and two-level diode rectifier AC-DC-AC converter are studied so that constrains of DC capacitor are confirmed for parameters design.Secondly, under steady-state, after studying the DC storage energy fluctuation law, and the quantitative relationship between system operating parameters and the DC storage energy fluctuation in three-level neutral point clamped (NPC) inverter, the influence of the relationship between the frequency of two AC sides, the phase difference between the input and output power of DC side on the DC storage energy fluctuation in three-level NPC back-to-back (BTB) converter have been further studied. Then, analyzed the dynamic energy balance process, and proposed the theoretical minimum DC storage energy fluctuation, by establishing the instantaneous energy balance mode of the three-level NPC BTB converter. In addition, the DC storage energy fluctuation law and the quantitative relationship between system operating parameters and the DC storage energy fluctuation in steady-state of three-level cascaded H-bridge converter have been studied so as to propose the design criteria of DC energy storage capacitor. The DC energy storage capacitor design of cascaded H-bridge topology and NPC topology was compared.Finally, the quantitative relationship between system operating parameters and the DC storage energy fluctuation in steady-state of Five-level NPC/H-bridge converter were deduced. The influences of power factor, output frequency, amplitude of output current on energy conversion were proved by simulation. The design criteria of DC energy storage capacitor in Five-level NPC/H-bridge converter was proposed to guide the DC capacitor selection of 20MW super power converter prototype, and verified the correctness of the theoretical analysis and design through prototype experiment.