Research On Multilevel Inverter Based On Switched Capacitor And Space Vector Modulation

With the rapid development of renewable energy system like photovoltaic power generation and wind power generation,it is very important to have a set of boost inverter systems with high efficiency and high power density in these low-voltage applications.Traditional multilevel inverter mainly includes neutral-point-clamped,flying capacitor and cascaded H-bridge.However,these types of inverters are complex in structure and without boosting capability.In addition,although a new type of multilevel inverters based on switched capacitor have boosting capability,it still suffer the drawback of higher charging current stress of capacitor,lower power density and more complicated in the extension for three-phase configurations.Hence,a new switched-capacitor basic unit is proposed firstly in this paper.Based on this basic unit,a single-phase seven-level inverter with double-wing structure and a step-up three-phase seven-level inverter are also proposed in this paper.For the seven-level inverter,the voltage ripples of capacitors can be optimized and the current stress can be reduced by using hybrid modulation strategy.As for three-phase four-level inverter,the voltage ripple of capacitors can also be optimized by using space vector modulation or phase disposition pulse width modulation strategy.Finally,the simulation and experimental results demonstrate the correctness of the theoretical analysis and the feasibility of the topology.And therefore it shows that these proposed inverters have practical engineering application value.The main contents of this paper are as follows:(1)The research background and significance are introduced,and the current development of switched capacitor technology is briefly described,which leads to the research content of this paper.(2)A new type of switched-capacitor basic unit and a seven-level inverter with double-wing structure are proposed.Firstly,the topology and operating principle are introduced.Then,the proposed hybrid modulation strategy is used to optimize the capacitor voltage ripple.According to the modulation strategy,the parameters of the topology are also analyzed.Finally,simulations and experiments verify the feasibility of the topology and the correctness of the theoretical analysis.(3)A step-up three-phase four-level inverter is proposed.It introduces the topology,working principle,and modulation strategy and topology parameters in detail.Finally,simulations and experiments verify the feasibility of the topology and the correctness of the theoretical analysis.(4)An improved space vector modulation strategy is introduced based on a three-phase four-level inverter.This chapter analyzes the principle of this modulation strategy in detail,which includes sector judgment,region judgment,on-time calculation,and vector order of seven-step operation.In addition,based on the three-phase four-level inverter and the improved space vector modulation strategy,the frequency-conversion speed-regulation control system is also introduced,which includes mathematical model of permanent magnet synchronous motor,parameter calculation of current closed-loop and speed closed-loop.Finally,the simulation verifies the feasibility of the control system.