Research On Wide-Voltage Input Doubly Grounded Single-Phase Transformer-Less Photovoltaic Grid-Connected Inverter

Solar energy has become the object of future human development and utilization due to its clean and renewable advantages.Photovoltaic grid-connected inverter is an important part of solar power generation.Compared with traditional isolated photovoltaic grid-connected inverters,transformer-less photovoltaic grid-connected inverters have the advantages of small size,light weight,and high efficiency.However,there is an electrical connection between the photovoltaic cell of the non-isolated photovoltaic grid-connected inverter and the power grid,which easily generates a large leakage current to the ground.In recent years,the topology of double-grounded transformer-less grid-connected inverters have become one of the research hotspots because it can solve the leakage current problem.However,most doubly grounded photovoltaic topologies have problems that the inverter input voltage is less than the grid voltage and cannot operate normally under the shading conditions of photovoltaic.The traditional solution is to add an additional Boost unit in the front stage of the inverter to ensure that the input inverter voltage is higher than the grid voltage.But the traditional scheme has the following problems: the boost unit runs for so long time that the current stress is large;the device voltage stress is high;the number of high-frequency switching tubes is too large that the loss is high.In order to solve these problems,the double-grounded transformer-less photovoltaic grid-connected inverter with the shortest operating time of the boost unit,low voltage stress,high efficiency,and wide input voltage range has become the key to research.Firstly,in order to solve the problems of the traditional solution,a new single-phase doubly grounded transformer-less photovoltaic grid-connected inverter with wide input range is proposed.The boost unit only needs to work when the input voltage is less than the output during the positive half cycle of the grid voltage,and the working time is reduced.In addition,multi-mode cooperative control is adopted to reduce the voltage stress of each power device and decrease the cost of the inverter.There is only one high-frequency switch of the power tube at the same time,which improves the efficiency of the inverter.The article introduces the inverter’s working principle and control method in detail,analyzes the inverter’s loss,and compares it with the traditional method,which reflects the advantages of this inverter’s such as Short operating time of booster unit,low loss and electrical stress.The working principle is verified through simulations.Secondly,in order to solve the problem of the straight-through that may exist in the half-bridge topology,a dual-buck type highly reliable wide-input doubly grounded transformer-less photovoltaic grid-connected inverter is proposed.The half-bridge topology is replaced of with Double Buck structure in this topology.The double Buck structure uses the series inductance between the power tubes on the inverter side to prevent the bridge arm from passing through and improve the reliability of the inverter.The working principle,control method and loss model of the inverter are introduced detailly,and the correctness of the principle is verified through simulations.Additionally,a booster unit cascaded high-reliability wide-input duale-ground transformer-less photovoltaic grid-connected inverter is proposed because the increasing cost and volume caused by dual-buck topology.This step-up unit is cascaded with the positive half-cycle circuit of the gridconnected inverter,and the inductance of the step-up unit is used to prevent the bridge arm from passing through and causing overcurrent.This paper introduces the topology of the inverter and the two control methods in detail,compares the efficiency of the two control methods,and finally verifies the correctness of the principle through simulation.Finally,the parameters of the proposed topology are designed in this paper combining the principle analysis.The principle prototype is built,and the topology and control scheme proposed in this paper are experimentally verified.The experimental results and data are given to prove the correctness of the proposed topology scheme.