Research On High Frequency Isolated Three-level Inverter Based On Forword Mode Converter

This paper attempts to extend the multilevel technique to traditional bidirectional voltage source high frequency link inverter proposes the circuit structure of high frequency isolation type three-level inverter.Based on the depth research of forward three-level DC converter, the paper proposes a topology of high frequency isolation type of three-level inverter based on forward converter. The circuit topology has been applied for the Chinese invention patent (application no:CN201310189221.3). The circuit structure joins three-level inverter unit to traditional two-level type of high-frequency link inverter. Without increasing the complexity of the previous circuit topology, the circuit topology has all advantages of two-level type of high-frequency link inverter, such as high frequency electrical isolation, single stage power conversion (DC/HFAC/LFAC) and bidirectional power flow. At the same time, three-level inverter unit reduces the voltage stress of main power switches in the circuit topology,and reduces the size of the output filter inductance. So the kind of inverter is suitable for high-voltage and high-power fields.At first, the paper studies the theoretical basis of high frequency isolation type of three-level inverter based on forward converter (The principle, principle analysis of working steady state and relevant output of forward three-level DC converter.). The paper deduces the circuit topology of high frequency isolation type of three-level inverter based on forward converter, and designs the control method and control circuit. Through introducing the work status of modes and four working modes of inverters, the paper obtains some necessary conditions to make the inverters can work normally, deduces the external characteristic formula of inverters, draws the external characteristic curves of it, and harmonic analyzes the former output voltage of the filter. At last compares it to traditional two-level type high-frequency link inverter, the theory of the main power switches’voltage stress can be reduced by import the three-level inverter is obtained.Through the lkVA200VDC/220V50HzAC saber simulation experiment of high frequency isolation type of three-level inverter based on forward converter, the paper fully proves the correctness and feasibility of the inverter. At last, I produced a prototype and experimental verification.