Research On Current Ripple Suppression Of Voltage Source Three-level Inverter

As a widely used topology,the neutral point clamped(NPC)3L-NPC inverter,has low voltage stress,which can effectively reduce the harmonic distortion rate of current and voltage.It is widely used in medium and high voltage industrial applications.However,the amplitude of the current ripple generated by it needs to be limited within a certain range to ensure the safety and reliability of the system.In this paper,3L-NPC inverter,is used as the research carrier to analyze the reliability of DC bus capacitance and the output current ripple of DC side and AC side respectively,and the corresponding control strategy is adopted to suppress the output current ripple.The main body of the thesis is as follows:1.This paper introduces the topology and working principle of several common 3L-NPC inverter,and introduces several common modulation methods such as carrier pulse width modulation(CBPWM),space vector pulse width modulation(SVPWM)and specific harmonic elimination pulse width modulation(SHEPWM)2.This paper introduces three kinds of common mathematical modeling of current ripple,summarizes the time-domain analysis method of current ripple,and lays the foundation for restraining current ripple.3.In this paper,the main body and life estimation of DC bus electrolytic capacitor of 3L-NPC inverter are studied,and the reliability of aluminum electrolytic capacitor is studied.4.In this paper,a novel modulation method of zero sequence component injected into carrier wave is used to calculate the optimal compensation value and suppress the neutral point current ripple,which provides a reference for improving the reliability of bus capacitor.5.Aiming at the disadvantage of large amplitude fluctuation of output current ripple in the AC side of 3L-NPC inverter,a novel control strategy is adopted in this paper,which takes the amplitude of output current ripple vector as the evaluation index,and improves the distribution of switch state by calculating the amplitude of current ripple and the optimal time distribution coefficient under different switch states.6.The experimental prototype system of 3L-NPC inverter is built,including the debugging and design of driving circuit,main power circuit,power circuit and sampling circuit.The software of the system is designed based on 28335 DSP chip,and the experimental verification of the research content is carried out to verify the feasibility and effectiveness of the control algorithm.