Research On Output Impedance Optimization Technology Of Distributed DC-DC Converter

In the DC microgrid system,distributed generation and load are usually connected to the common DC bus by the power electronic circuit.The intermittent nature of distributed generation and the randomness of load will cause disturbance or impact to the common DC bus.The stability of the common DC bus voltage is an important indicator to evaluate the stability of the whole system.This article selects PV-storage DC microgrid system for the study,analyzes the disturbance types and its characteristics in the common DC bus.From the perspective of optimizing the equivalent output impedance of the energy storage system,the methods to suppress the fluctuation of bus voltage and to improve the anti-interference ability of the system is improved.Firstly,the mathematical model of a typical bidirectional DC-DC converter for energy storage is analyzed,study the influence that system discretization and sampling delay bring on system stability.On this basis,a discrete mathematical model of the energy storage control system is established,and its equivalent output impedance model is derived,furthermore,the coupling relationship between the time delay and the system bandwidth and the equivalent output impedance is quantitatively analyzed.What’s more,a delay compensation applied to the inner loop control of the inductor current is studied,which optimizes the equivalent output impedance characteristics of the system.Secondly,the disturbance current feedforward control is introduced to further reduce the high-band output impedance,and a high-pass filter is added to the current feedforward to maintain the low-band droop characteristics.In addition,the quantitative relations between the output impedance of the distributed energy storage system,the system parameters and the parameter selection range are obtained by impedance analysis.Moreover,the optimization method of the system equivalent output impedance of under the condition of capacitive current feedback is studied.The quantitative relations between the equivalent output impedance of the system,the system parameters and the range of parameter selection are obtained.Finally,simulation analysis and verification are carried out and builds an experimental platform to test in this article.The analysis conclusion and the impedance optimization strategy are verified by experiments.The simulation and experimental results show that the analysis method and the impedance optimization strategy is effective.