Analysis Of Resonant Coupling Mechanism Of Multi-parallel Inverters And Optimization Method Of Active Damping In Micro Grid

The distributed power generation technology is the effective form to connect new energy into grid. The micro grid is a small autonomous power distribution system, which is connected with parallelled distributed generations and energy storage units, which has the advantages of flexible installation, reliable power supply, high efficiency, clean energy and so on. Distributed generations are connected into the micro grid through power electronic equipments. Multi-parallel inverter system will cause resonance coupling, which leads to the amplification of specific harmonics, arid also leads to the poor energy quality of micro grid. It is an urgent problem to solve the analysis of the resonance coupling mechanism of multi-parallel inverter system and improve the power quality in micro grid.In this paper, we use multi-parallel grid-connected single phase photovoltaic inverters based on LCL type filter as the research object, details are as follows:(1) The modeling of single phase photovoltaic inverter based on LCL type filter is carried out, and the structure parameters is designed, and control strategy of the single phase photovoltaic inverter is chosen after analyzing and comparing two different types of active damping method. The Norton equivalent circuit model is established to analyse the resonance coupling mechanism of the multi-paralled grid-connected inverter system.(2)In order to analyse multi-paralled grid-connected inverter system’s resonant coupling mechanism in case of non-active damping, we establish the mathematical model of the multi-paralled grid-connected inverter system, which bases on theNorton equivalent circuit model that contains controlled current source and shunt admittance. By using this model, the resonance phenomena can be explained in a qualitative and quantitative way. Firstly, the inverter’s resonances are categorized into three types:internal resonance,parallel resonance and series resonance.Then,according to the difference of control scheme, the inverter’s resonances are categorized into two types:controller resonance and filter resonance. According to whether the resonant points change with the change of the inverter’s number, the inverter’s resonancesare categorized into two types:fixed resonance and unfixed resonance.(3)The most salient of this model is to very intuitively determine optimal range of active damping feedback coefficient. And the correctness and feasibility of the generalized model and of the analysis approach are investigated by simulation and experiment.(4)This paper designs a micro grid experiment platform which three sets of single phase photovoltaic inverter which are connected in parallel. This paper introduces the design of hardware circuit, the selection of main electronic components and the function of the main circuit module. We also give the details of the experimental platform of software algorithms, including the main program of the software and the main subroutines. The experiment verifies the analysis of multi-parallel grid-connected inverter system resonance coupling mechanism theory and the validity of active damping method.