Research On Stability Control Strategy Of Converter In Dc Microgrid

With the shortage of fossil energy and the increasing environmental pollution,distributed power generation based on new energy has gradually become an effective supplement and support for the large power grid.However,when the distributed power supply is directly connected to the power grid on a large scale,the phenomenon of voltage fluctuation may occur,affecting the power quality of the power grid and even disturbing its stable operation.In order to solve this problem,people use the DC microgrid as a bridge to integrate various types of distributed power sources,energy storage devices and loads through the DC/DC converter to the bus of DC microgrid,then connect the bus to the grid.It realizes the efficient utilization of the distributed power supply,thus becoming an effective form of renewable energy access to the grid.The DC/DC converter is used as a conversion device between various devices,and its reliability lays a solid foundation for the stable operation of the DC microgrid.This paper mainly studies the control strategy of DC/DC converter in DC microgrid,the problems caused by the negative impedance characteristics of constant power load,the parallel circulating current,the DC bus voltage fluctuation and the like are effectively improved,and improved the stability of the DC microgridThere are a large number of constant power loads in the dc microgrid.Due to its negative impedance characteristics,it will affect the output voltage stability of the source side converter,causing instability of the system.In this paper,the Boost converter with constant power load is modeled,and the passive-based control theory is used to inject virtual damping into the system to obtain the passive control law of the system.At the same time,the PI regulator was added to the feedback loop as the parameter correction part,and the closedloop feedback is used to realize the stable control of the system,eliminating the steady-state error caused by the load variation.Simulation results show that the improved passive-based controller can respond quickly and keep the system running stably when the load changes.At the same time,in order to improve the influence of bus voltage fluctuation on the load,this paper designs the input filter circuit suitable for the load converter through Middlebrook impedance matching criterion,and then performs impedance analysis on the power subsystem and the load subsystem through small signal modeling.The whole system is equivalent to a one-port network,and the influence of adding input filter circuit on system stability is obtained through bus impedance analysis.In addition,each distributed power supply is connected in parallel on the bus of DC microgrid,while the output voltage of the distributed generation unit may be different under the influence of the environment.The line impedance between the converter and the bus are not exactly the same,so there may be differences in the output current of the converter,thus generating circulation.In this paper,the parallel connection of two Boost converters is analyzed.The passive-based control is used to keep the output voltage of each converter near the expected value.Then,proposes a control strategy to actively compensate the line impedance for the line impedance difference,and compensates the measured line impedance to the controller,so that the current of the two converters are nearly equal.The simulation results show that the circuit impedance compensation can effectively improve the circulation problem and reduce the deviation between the bus voltage and the set value.Finally,a semiphysical simulation platform based on RT-LAB is built to verify the effectiveness of the control strategy based on passive control theory.