Research On Capacitor Voltage Balancing Control Strategy For Hybrid Nine-level Inverter

With the gradual exhaustion of petrochemical energy and increasingly severe environmental problem,the development and utilization of new energy,represented by wind energy,hydropower and solar energy,is an important measure to realize the sustainable development of human society.As a key equipment of new energy power generation system,the multilevel inverter is directly related to the safety,reliability,energy-saving and high efficiency of the entire system.However,traditional high-order multilevel inverters have several disadvantages,including a large number of switching devices,unbalanced capacitor voltages,and complex control algorithm.Therefore,this paper studies the capacitor voltage balancing control strategy for a hybrid nine-level inverter,which has fewer switching devices.The main contents of this paper are listed as follows.1.The research background and significance of multilevel inverter is introduced.And the research status of multilevel inverter topology and modulation method is analyzed in detail.Then the existing problems of the current high-order multilevel inverter is discussed.2.To provide an experimental verification platform for the subsequent research on the topology of the adopted hybrid nine-level inverter and its control strategies,the experimental prototype of a scaled-down inverter based on DSP+CPLD is introduced.3.The basic operation principle of the adopted hybrid nine-level inverter is analyzed in detail,and a voltage balancing control method is presented to realized the balancing of the floating capacitor voltage and neutral-point capacitor voltages.4.On the basis of the proposed capacitor voltage balancing control method,the characteristic and implementation of SPWM and one dimensional SVM are analyzed.Simulation and experimental tests are implemented to compare the performance of these two modulation algorithm.The simulation and experiment results show that the one dimensional SVM has smaller capacitor voltage ripples compared with SPWM.5.To cancel the floating capacitor voltage sensor and related sampling circuit,an improved floating-capacitor-voltage-sensorless voltage control strategy is proposed in this paper.The proposed method can effectively reduce the volume and cost of the hardware circuit while achieving the balancing control of capacitor voltages.