Research On Optimization Control Of SVPWM Technology Of EMU Three-Level Inverter

China has the world's largest, fastest, most modern and experience-rich, high-speed rail network and currently has the largest number of high speed trains. China proposed the Silk Road Economic Belt and the 21 st century Maritime Silk Road "along the way" strategy for China's railway transportation equipment provides more space to make a difference. High-speed EMU as a technology-intensive products, its rapid development needs the support of technology research in all aspects. Because Neutral-Point-Clamped three-level inverter with switching pressure low, low harmonic distortion, output waveform which tends to sinusoidal and other advantages, so it has been in the high power inverter is widely applications.In this paper, a type of high-speed EMU three-level traction inverter system as the research object. Firstly, analysis of the traction inverter technology of two-level and multilevel converter topologies and their control strategies, then introduced the NPC-type three-level inverter's work mode and control requirements, the space voltage vector, and a mathematical model is established. For traditional space vector pulse width modulation algorithm, in the calculation process determines the reference vector Area and basic vector action time, involves a lot of trigonometric function computation, which require high computing power to controller, and it is not conducive to the rapid adjustment. This paper summarizes the distribution of vectors and its mathematical properties, studies a space voltage vector algorithms which based on 60° coordinate system, here gives the reference voltage vector in which corresponds to the space voltage vector distribution diagram sector and minimum position of the triangle judgment rule. This algorithm can save a large number of trigonometric functions used in the traditional SVPWM algorithm, which can reduce the computational burden of the controller. Simulation results verify the feasibility of the proposed algorithm.Secondly, this paper also researched the harm caused by the voltage unbalance of the DC side capacitor of the three level inverter, reasons and control methods. To solve the inherent problem, this paper from the three-level SVPWM control algorithm to start, using positive and negative redundant small vectors to produce the same line voltage, but the potential impact on the neutral point of the opposite, presented an optimized quasi-bipolar SVPWM modulation algorithm. This algorithm based on quasi-bipolar modulation strategy on adding a real-time control factor k, it can redistribute positive, negative small vectors relative duration of action of the next PWM cycle according to the DC side of the midpoint potential size, as real-time control to the midpoint of the capacitor's charge, reducing the fluctuation of neutral point potential. Matlab simulation results show that this method can effectively restrain the fluctuation and drift of the neutral point potential of the DC side, especially in the depth of modulation. Finally, under laboratory conditions, this paper designed with TMS320F2812 DSP as the control center of the NPC three-level inverter experimental platform. The platform includes hardware circuit design of the main circuit, optical coupling isolation, drive protection, power supply circuit, and the SVPWM algorithm DSP software programming etc. Experimental data and waveforms are analyzed to verify the feasibility of the proposed control algorithm.