Research On Novel Single-Phase Three-Level Grid-connected Inverter

With the increasing energy crisis and environmental pollution problems,distributed power generation technology based on clean energy has developed rapidly.And the grid-connected inverter is an important way to connect the distributed generation system with the distribution network.The performance of the inverter structure is directly related to the level of power quality incorporated into the grid.The traditional two-level inverter structure is single which suitable for various low-voltage and low-power applications.The three-level inverter can adapt to higher power and higher voltage applications,which is a hot spot in the development of inverter technology in recent years.Domestic and foreign scholars have done a lot of research on the improvement of traditional three-level topology and the creation of new topologies.New single-phase three-level grid-connected inverter is taken as the research object in this paper and six new inverter topologies are proposed.Three of them are analyzed in detail,and the model is built for simulation verification.Firstly,backgrounds and significance of grid-connected inverter technology are summarized in this paper.In this paper,the domestic and international research status of three-level inverter research in recent years is analyzed and summarized.Most three-level inverter topologies only consider how to output three levels and improve the quality of the output waveform,without considering the hardware cost of the circuit and the size of the system.In response to these problem,this paper conducts in-depth research for the purpose of constructing a new single-phase three-level grid-connected inverter.Secondly,staggered parallel technique is used in this paper to connect a pair of small-sized inductors of equal size between the two bridge arms of a traditional two-level full-bridge inverter structure,which construct a new single-phase inductor interleaved three-level half-bridge inverter topology.When discussing the working principle of this half-bridge inverter and conducting the path current discussion,it is found that current flows only through the freewheeling diode of the power switching device at some modal.Furthermore,the circuit is further simplified,and another semi-controlled single-phase three-level half-bridge inverter topology with a simpler structure is obtained.Then,the two half-bridge structures are extended to the three-phase structures.If the half-bridge is directly extended to the full-bridge,the structure is more complicated.Power switching devices are used more.In this paper,those two new half-bridge structures are combined with the traditional two-level half-bridge structure to construct two new single-phase three-level full-bridge inverter topology with interleaved inductance.The simplest structure of the semi-controlled inductor-interleaved full-bridge inverter is selected and analysised deeply.Finally,combined with the double closed-loop control theory,the grid-connected simulation of the simplest single-phase three-level half-bridge and hybrid full-bridge inverter proposed in the paper is carried out,which verify the correctness of these two circuits.