Research On Optimized PWM Methods In Three-level Neutral Point Clamped Inverter

Optimized PWM methods in three-level NPC inverter are researched in this thesis, including three-level NPC SHEPWM method and three-level ANPC optimized SPWM method. The main work of this thesis includes:1. Three-level PWM methods are discussed, including SPWM, SVPWM, and SHEPWM. SHEPWM method is mainly researched. Switching angles are calculated by means of multi-objective particle swarm optimization algorithm. In order to realize real-time control of SHEPWM technique, polynomial interpolation and BP neural network fitting are adopted to obtain curves of switching angles in whole range of modulation depth. Harmonic characteristics of SHEPWM method are analyzed.2. For the problem of unbalanced loss of power devices in three-level NPC inverter, operating principle of three-level ANPC inverter is analyzed. Current path can be reasonably selected by means of PWM technique according to power devices’ losses in practical operation, so as to obtain the purpose of loss balance in power devices. Losses of power devices in three-level ANPC inverter under different PWM methods are calculated and compared by means of numerical method. An optimized SPWM method is realized, which can adjust the ratio of different PWM methods under different currents, and realize loss balance in power devices to some extent.3. Simulations of theoretical analyses are carried out by means of Matlab/Simulink software. An experimental test bench based on DSP and FPGA is set up. Three-level NPC SHEPWM method and three-level ANPC optimized SPWM method are experimented by means of this test bench. Simulation and experimental results verify the validity of these methods.The work in this thesis is supported by the National Natural Science Foundation of China (No.51307002), Natural Science Foundation of Anhui Province (No. 1308085ME81), and Natural science foundation of colleges and universities of Anhui Province (No. KJ2013A011).