| Offshore platform has become a commonly used and effective means in the process of energetically developing Marine resources,especially in the development and construction of the deep sea,because it can "settle down" in the ocean for a long time and assist production nearby.Among them,the DC microgrid with excellent absorption capacity of renewable energy and relatively simple structure has a great prospect in the application of offshore platform power system.However,offshore platforms that lack the support of large power grids and stable power(such as diesel generators)are prone to instability problems,especially those that rely solely on optical storage and power supply.Although the power supply stability of these platforms is poor,due to their advantages in implementation technology and cost,a large number of platforms exist in reality.This paper takes the DC microgrid of offshore platform as the object to explore the static load capacity.In this study,the characteristics and changes of the small signal stability of the power supply system under different modes are analyzed,and the secondary control is used to try to improve the load-bearing performance of the platform DC microgrid.In this paper,according to the common structure of offshore DC microgrid,the simulation platform of single bus isolated island DC microgrid is introduced.It includes multiple groups of photovoltaic cells,battery cells and constant power loads that are more likely to impact the stability of the microgrid,and their control modes under different working conditions are integrated.According to the common working condition of DC microgrid,the simulation of working condition mode is designed,and the availability of simulation platform is verified through the simulation.Then,based on the small-signal impedance model,the influence of the typical droop control improvement method on the system stability is analyzed.The state space averaging method was used to model the small signals of the converters connecting each unit to the DC bus.The output/input impedances of the converters of photovoltaic interface,battery interface and load interface under different control modes were obtained.The influence of relevant parameters on the impedance characteristics of the converters was studied respectively.According to three operating modes of the system,the output/input impedance expressions of the system in different modes are derived,and the influence of the adjustment of relevant parameters on the stability of the system’s small signal is analyzed.Finally,considering the communication reliability and the stability of the system’s small signal,the distributed secondary control based on the consistency algorithm is used to compensate the adverse effects of droop control and line impedance on the system only by adjusting the reference voltage in the control link of the battery.By comparing the system stability before and after adding the secondary control,it is found that the secondary control based on the consistency algorithm has no adverse effect on the system stability,and even can improve the function.The simulation results show that the control can effectively reduce the bus voltage deviation and realize the optimal power distribution of the battery. |
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