Research On Forward Multilevel Inverter Based On Switched Capacitors

After years of development of high-frequency multi-level inverters,three-level technology has matured.However,there are few studies on five-level,mainly due to the voltage equalization of its DC capacitors and the difficulty in controlling the number of switching tubes.In this paper,based on the novel forward bidirectional full-bridge five-level DC/AC converter,forward five-level inverter based on the switched capacitors with improved H-bridge is obtained.The main contents are as follows:Comparing the isolated three-level and five-level inverters of the high-frequency chain,a five-level converter of switched capacitors based on the improved H-bridge is proposed.The steady-state working state is introduced,and the switching tube in each state is analyzed.The change of voltage stress,the steady state and dynamic output parameters of the circuit are calculated,and the condition of core reset is determined.The Fourier series expansion of the output voltage is performed,and the calculation process of the fundamental wave is given.Secondly,the overall circuit control including multi-way logic distribution and optimization,voltage-dividing capacitor equalization,inductor current zero-crossing repeated hopping filtering,power circuit small-signal model establishment and control loop corresponding compensation parameter design are introduced in detail.The simulation results are verified,and the advantages of the five-level switching capacitor are also reflected by comparative simulation.Finally,the hardware circuit parameters such as main power circuit,AC voltage sampling,optocoupler isolation drive and current zero-crossing detection are designed and fabricated.A 1000 VA prototype is built.The software is designed based on DSP28335 development board.The function of the circuit and the correctness of the control strategy are verified by power-on experiments.