Former Stage AC-DC Converter Technology Of High Power Three-Level Frequency Converter

Green, energy-saving and high effective is the rhythm of current technology development. In AC drive area, variable frequency speed regulation get a large application for its high efficiency, excellent speed performance, energy saving and environment protection. How to reduce the harmonics current injected by the device is a technical problem. Expecially for large power variable frequency speed regulation device, it is a problem needing solution urgently.An easier method to reduce the harmonics current is using multi pulse rectifier. The more the pluses use, the fewer harmonic current will produce. But the cost, bulk and weight are relatively increasing. So the 500KW frequency converter uses self-coupled 12 pluses rectifier by analyzing many constructs of multi pluses rectifier technology. In this dissertation, the technology of self-coupled 12 pluses rectifier is studied, including the analyzing of current input and voltage output character, energy stock by DC type, the influence of filtering capacitance toward input and output, and the critical parameters design of balance reactor. On these basics, a 3KW experimental machine and a 500KW project machine are designed.Comparing with multi pluses rectifier technology, PWM rectifier has higher input power factor, lower harmonics and it could realize four quadrant operation of frequency converter. So PWM rectifier technology will be a hot-spot of front-end rectify in large power variable frequency research. In this dissertation, a PWM rectifier with three-level NPC inverter is also researched. The research works are following.First, the mathematic PWM rectifier model is analyzed. And a strategy of direct current control is designed according to the mathematic model. By studying the vector control of three voltage level, the controlled switch time and order the reference voltage vector in different sector are proposed.The problem of neutral-point voltage unbalance in three-level PWM rectifier is analyzed in advance. To solve the problem, A control strategy based fuzzy adaptive system (FAS) of neutral-point voltage balance is studied and the Matlab simulink model is also constructed. According to the results, the voltage of neutral-point is well controlled.On the basic of theoretical analyze and simulation, the reason of high starting current is analyzed, and then a solution is proposed. On the basisi, the circuit of three-level PWM rectify is built. The results show that the harmonics currents are low, the input power factor is high, starting current is low, and the voltage of neutral-point could be controlled in a small bias.