Research On Stability Control Technology Of DC/DC Converter Based On Virtual DC Machine

In recent years,distributed energy,such as wind power and photovoltaic,has occupied an increasing proportion in the process of electricity production.These sources are built on the user side and have the flexibility of running independently or interconnection.However,it also has randomness and volatility,which will undoubtedly bring many unstable factors to the DC microgrid system.In DC micro grid system,Though DC/DC converter acts as the medium of distributed energy flowing into the DC bus,it will reduce the damping,so that the stability of the whole system will be greatly reduced.Therefore,it’s very important to use effective control strategy to improve the stability of the DC/DC converter.Based on the experience of introducing VSM control strategy into AC/DC grid system to improve its stability,we introduce virtual DC Machine(VDM)control technology into DC microgrid.VDM control technology adjusts the balance between damping and inertia in the DC system by virtue of the external mechanical characteristics of DC motor,so as to suppress the fluctuation of DC bus voltage.The operation object is the DC/DC converter in the DC microgrid.The VDM control technology can make it have the external characteristics of the DC motor,which can effectively improve the voltage fluctuation of the bus caused by new energy power generation,so that the voltage of the input side of the bus remains stable.First of all,this paper introduces the research background and significance,and understands that the construction of microgrid is the way for distributed energy to access the power grid,while the DC microgrid has become a hot research topic because it does not need to consider frequency and harmonics.DC/DC converter is an indispensable part of DC microgrid,and its stability control is very important.And because the DC/DC converter system itself is a nonlinear system with low inertia,and VDM control technology can improve the inertia and damping of the system by simulating the mechanical and electrical characteristics of the DC motor,so VDM control of DC/DC converter is feasible.Then carries out systematic research on the DC/DC converter system controlled by VDM technology.Starting from the small signal model of the system,the VDM to stabilizing mechanism of control technology based on the form of zero pole control system transfer function of the small signal model of VDM control structure,use the bandwidth of the control system and the phase margin of VDM inertia and damping parameters on the effect on the stability of the control system,and the two parameters were determined and the control system of open loop gain and the correspondence across the frequency general conclusions are obtained.Furthermore,the mathematical relationship between the parameters of the virtual DC motor and the control system is obtained by analyzing the Buck converter as the control object.However,the linear method can only analyze the stability near a single steady-state point.Therefore,the large-signal average model is established based on the closed-loop controlled DC/DC converter with the mixed potential function as the carrier,and the mixed potential function of the VDM controlled DC/DC converter system is listed to obtain the sufficient conditions for large-signal stability.Furthermore,the parameters of the system are designed by using this condition,and the asymptotic stability region is obtained.By constructing energy function,Lyapunov stability criterion is used to verify the existence of stability region.Finally,the results are verified by simulation and experiment.Matlab is used for preliminary simulation and the results not only prove the influence of VDM parameters on the stability under the condition of small signal,but also fully verify the rationality of the large-signal stable operation condition obtained by using the method of mixed potential function.The hardware design is completed and the software design of VDM control algorithm programming is completed,which is based on TMS320F28335 software development environment CCS6.0.Finally,an experimental prototype of VDM technology control DC/DC converter based on F28335 core development board is built,and the proposed stability comparison test is completed.The experimental results verify the correctness of the theoretical analysis.