Space Vector PWM Strategy For NPC Three-Level Inverter With Comprehensive Performance Optimization

Neutral-point-clamped three-level inverter has advantages with high output voltage and current quality,low dv/dt and high conversion efficiency,it's more and more widely used in traction,naval propulsion and other medium-voltage high-power applications.Due to its wide modulation range,high output quality and easy digitization,space vector pulse width modulation has the outstanding advantages of reducing switching loss which improve conversion efficiency and reducing output current harmonic which improve output characteristics.Thus,how to achieve the optimization both in switching loss and output current harmonic is a research hotspot of modulation strategy for NPC three-level inverter.A space vector modulation strategy with the optimization of comprehensive performance by considering switching loss and output current harmonic for three-level inverter is proposed.The basic principle of space vector pulse width modulation is described specifically,which include synthesis of the reference vector and calculation and distribution of the dwell time for basic vector,etc.On this basis,the inverter switching loss and output current harmonic performance are studied,the relationship between the comprehensive performance index FswR and modulation index m,reference vector angle ? and power factor angle(p is derived out by quantifying the switching loss and output current harmonic calculation.In addition to the switching sequences of the conventional "+" and "-" clamping states,the switching sequence of "0" clamping state is applied as an alternative sequence,which is extend to the switching sequence set,the further distribution of each region is based on the minimum FSWR principle to determine optimal sub region of the "+","-" and "0" three clamping states.Thus,the proposed method of switching sequence selection is helpful for improving the switching loss and output current harmonic performance of the inverter.In order to verify the effectiveness of the proposed strategy of comprehensive performance optimization,a NPC three-level inverter simulation system based on Matlab/Simulink and an experiment system of middle high power NPC inverter are established.Compared with the traditional modulation strategies,the simulation and experimental results show that the proposed modulation strategy has the overall optimization effect on the switching loss and output current harmonic performance of inverter system.