Research On The Cascaded Multilevel Converter With High-frequency Link

In recent years,power electronics technology has matured in the field of low-voltage and low-power.At present,the requirements for large-capacity converters are getting higher and higher.However,the traditional two-level converter can not meet the needs of these occasions.Multilevel converter is one of the solutions to these problems.It can achieve step-up voltage growth by using a variety of power electronics topology,and thus meets the high voltage requirements.H-bridge multilevel converter is commonly used.However,it requires multiple independent DC power supply.In order to solve this problem,this paper proposed a new topology: the cascaded multilevel converter with high-frequency link,which uses only one DC power supply to provide independent DC bus voltage for multiple H-bridges by controlling the high-frequency transformer.On this basis,casecaed H-bridge multilevel inverter can generate the multilevel voltage needed,and provides energy for three-phase loads.The H-bridge unit is easy to modularize,so the number of H-bridge units can be increased or decreased according to the required voltage level which makes the circuit conversion more convenient and flexible to adapt to different work situations.The use of high-frequency isolation transformer eliminates the DC / DC converter and the number of DC power supply,so that saves the design cost and decreases the volume of entire control topology.The design is more feasible.This paper first describes the characteristics,applications and development status of multilevel converter,and also its control strategies.The advantages of high-frequency transformer are also introduced compared with traditional power frequency transformer.This paper mainly introduces the proposed topology of the cascaded multilevel converter with high-frequency link: The working principle of cascaded H-bridge multilevel inverter and its hierarchical control algorithm are introduced;The power flow of high-frequency link is analyzed,and the phase shift control strategy is proposed which the power flow is controlled by changing the phase difference between a secondary side voltage with the primary side voltage.According to the proposed topology and control stategy,a PSIM simulation circuit with DLL module is built to verify the correctness and feasibility of the whole system.On the basis of the simulation,the hardware circuit platform is designed and built.The programs of DSP and CPLD are written,and experiments are conducted on the hardware circuit platform.According to the expriments result,the correctness and effectiveness of the proposed topology and control algorithm are further verified.