Research On Topological Design And Common Mode Current Attenuation Of Single-phase Photovoltaic Inverter

As the world economy on growth in energy demand,solar energy as a renewable energy,is obtaining the growing concern of countries in the world.Photovoltaic power generation is an important form to utilize the solar energy.Photovoltaic inverter is the key component of the grid-connected photovoltaic(PV)systems.It is significant to reduce the cost,improve the efficiency,the security and the reliability of the PV inverter.The topology structure selected by the inverter is closely related to the multiple performances of the inverter,which is an important factor affecting the performance of photovoltaic gridconnected system.Therefore,the reasonable selection or design of the topology structure can effectively optimize multiple performances before using complex control strategies.Non-isolated photovoltaic inverter has been developed rapidly because of its high efficiency,small size,low cost and simple structure.However,due to the lack of transformer isolation,common mode current will be generated.In order to solve the problem of common mode current caused by non-isolated photovoltaic grid-connected inverters,this paper establishes the research topic of topological design and common mode current attenuation of single-phase photovoltaic inverter,The main contents include:The classification of photovoltaic inverters and the research status of multilevel inverters are reviewed.This paper introduces the cause and harms of common mode current in non-isolated single-phase photovoltaic inverter system.The equivalent model of common mode circuit and the common mode voltage expression are deduced in detail.According to the matching properties of the two-phase filter inductors,the paper summarizes the typical topologies proposed in the existing research to suppress common mode current and their corresponding working principles.The power loss,efficiency,ability to suppress common-mode current,advantages and disadvantages of different types of inverters are compared and analyzed,and then,the key research topology of this paper is determined: ANPC three-level half-bridge singlephase photovoltaic inverter topology.A single-phase non-common mode current photovoltaic inverter adapted to a 400 V input voltage level is proposed based on the charge transfer auxiliary circuit.The proposed inverter realizes charge transfer by constructing a charge transfer auxiliary circuit with its idle switching devices.The design idea,modulation mode,working principle and performances of the inverter are analyzed in detail.The proposed inverter is compared with the H5 inverter,which is widely used in the full-bridge topology,in terms of switching stress,switching loss,conduction loss,and ability to suppress common mode current.The structure of the new inverter is simplified according to the method of indirect transfer to direct transfer.Finally,the correctness and effectiveness of the theoretical analysis are verified by simulation and experiments.The proposed inverter can be developed into a non-common mode current inverter with voltage balancing capacity of dc bus capacitance through symmetrical expansion auxiliary circuit,and can adapt to the input voltage of 800 V voltage grade.The simplified inverter also achieves this function by expanding the entire circuit symmetrically.The modulation methods and working process of the two inverters are given in detail.The extended singlephase non-common mode current inverter with DC bus capacitor voltage balancing capability is simulated and experimentally verified.Finally,other applications of the two extended inverters are described.