Inverter Modeling And Parallel System Stability Analysis With Droop Control

With the tremendous progress of society and the rapid economic development,there will be many issues such as environmental pollutions and energy exhaustion.Facing the crisis of environmental protection and energy depletion,distributedgeneration technology and micro-grid technology will become the focus of energy development in the future.The micro-grid system is mainly composed of new energy sources,storage equipment and energy transfer devices,which can not only manage itself locally,but also can realize interconnected communication with the outside world.Finally,it completes power balance and energy dispatch of the whole system.As the conversion interface of the high-frequency inverter,whose inertia is small,it may have a serious impact on the stable operation of the micro-grid system.Therefore,it is very necessary to establish a complete mathematical model for the inverter.The model of inverter's was established with small signal method in this paper using the small signal method.Firstly,Output impedance model of inverter without outer loop control was built,the relationship between the output impedance and the control parameters was analyzed from the perspective of the open-loop and voltagecurrent inner loops.After that,introduced the power outer loop,adopting the traditional droop control.Considering voltage and the angular frequency as the little perturbation to this system,the output impedance model was completed with power outer loop and voltage-current inner loop.Thus,the output impedance model of the inverter is complete and clear to analyze.For the whole micro-grid system,this paper applied the impedance criterion and the generalized Nyquist criterion.After "Source and Load Division" reasonably,analyzed the stability of the inverter parallel system under different conditions of single operation,two parallel and three parallel systems.The MATLAB/Simulink simulations of corresponding working conditions were carried out to verify the argument.At last,the experimental platform of three-phase voltage-type inverter(VSI)in parallel based on TMS320F28335 DSP was built.The hardware and software were designed.Experiments were carried out to verify the correctness of the above analysis.Proved the feasibility of the proposed impedance modeling.