Research On Inertia Control And Stability Analysis Of DC Micro-grid

With the problems of energy shortage and environmental pollution becoming increasingly serious,the distributed generation technologies attract more and more concerns.DC micro-grid has a broad development prospect in the growing situation of utilization of both DC micro-sources and DC loads,in view of its internal use of DC transmission which shows a series of outstanding advantages.However,in the event of such as photovoltaic,wind power and other intermittent energy power fluctuations,frequent load switching and other common disturbances,a large number of power electronic converters of very fast response speed in DC micro-grid will cause sharp DC bus voltage fluctuations,directly threatening the safe and stable operation of the DC micro-grid.Therefore,the low inertia DC micro-grid will be a rather fragile system.The virtual inertia control of DC micro-grid is proposed in this thesis considering the potential inertial support of rotating equipment and storage equipment in DC micro-grid.And the stability analysis will be used as an important reference for the design of controller parameter,so as to ensure that the system can operate stably under inertial control.The main work and achieved results are shown as follows:(1)The working principle and mathematical model of each DC micro-grid component unit are analyzed detailedly.And the model of DC micro-grid,which includes wind power generation unit,photovoltaic power generation unit,battery energy storage unit,grid connected converter unit and AC/DC load unit,is established in MATLAB/SIMULINK.(2)The virtual inertia control strategy based on voltage variation is proposed.The control strategy takes full account of the potential inertial support of rotating equipment and storage equipment in DC micro-grid.The additional inertial power is directly determined by the DC bus voltage variation and the virtual inertia control coefficient.Finally,the selection range of virtual inertial control coefficient is given through the stability analysis,so as to ensure that the system can operate stably under inertial control.(3)In view of the superior performance of the traditional virtual synchronous generator control in primary frequency modulation,inertia and damping characteristics,a DC micro-grid analogous virtual synchronous generator control strategy based on voltage-current relationship is proposed by analogy and is applied to DC/DC converter of battery energy storage unit.The control strategy has good dynamic characteristics,static characteristics and starting characteristics.It can be seen from the stability analysis that as long as the virtual inertia time constant is not less than zero,the system can be guaranteed to operate stably under the analogous virtual synchronous generator control.(4)The control strategies proposed above are validated in the simulation system established in step one.The results show that,the proposed control strategies are able to improve the transient response of DC bus voltage and the inertial capability of DC micro-grid.