Synchronous Fixed-frequency Microgrid Regional Interconnection Coordination Control Research

With the large-scale development and utilization of new energy sources and the implementation of national energy strategies such as "carbon peaking and carbon neutrality,",the traditional power system is gradually transitioning to a new power system based on new energy sources.Microgrid is an important path to increase the penetration rate of renewable energy and support the development of a new type of power system that is clean,low-carbon,safe,and efficient.In the future,under the background of a high percentage of renewable energy and a high percentage of power electronic equipment",multiple microgrids can be interconnected flexibly to realize energy interchange and mutual assistance between different power supply areas,improve the regional cooperation and fault recovery capability of the grid,and effectively improve the reliability of power supply.This paper improves the control strategy of independent microgrids and proposes the interconnection and coordination control strategy of multiple microgrids based on synchronous and fixedfrequency microgrids,which have natural synchronization conditions.A reliable and effective independent microgrid control strategy is the basis of multinetwork interconnection.Based on the voltage-current(U-I)droop synchronous fixedfrequency control strategy,an improved droop control strategy based on virtual negative impedance is proposed for the problem that the output power of Distributed Generation(DG)cannot be distributed in proportion to its capacity due to the inconsistent line impedance in an islanding mode microgrid.The synchronization information in the synchronous fixedfrequency microgrid is used to synchronize the voltage and current measurements at different measurement points to realize the active identification of line impedance.On this basis,virtual negative impedance is used to fully compensate the line impedance to eliminate the influence of line impedance inconsistency on power distribution,so that each DG can precisely distribute power according to its capacity ratio.In addition,to improve the system stability,the influence of the parameters of the virtual negative impedance on the system stability is analyzed by the Nyquist curve to provide a basis for the parameter design.Based on the two key factors of coordinated control of multi-microgrid interconnection,the study proposes a coordinated control strategy for microgrid interconnection: firstly,to eliminate current shocks and voltage disturbances during the interconnection transient process;secondly,to stabilize the power flow control between different regions in the interconnection mode.To address the problems of voltage disturbance and current impact during the transient interconnection process,a phase-progressive tracking method is proposed to track the satellite synchronous reference phase and control the output voltage phase of each DG to achieve smooth switching of the transient interconnection process.For the control of regional power flow in the stable interconnection state,a power coordination control strategy based on voltage compensation is proposed to use voltage translation compensation to eliminate the influence of contact line impedance on power distribution and further achieve uniform power distribution among DGs in the interconnected microgrid based on uniform power distribution in the independent microgrid.A small-signal model of the microgrid in islanding mode is established,and the influence of the system controller parameters on the system performance is investigated by analyzing its state-space matrix as a means to optimize the design of the controller parameters.Using MATLAB/Simulink simulation software and a synchronous fixed-frequency microgrid test system,the independent microgrid control strategy and multi-grid interconnection coordinated control strategy are simulated and verified.The simulation and experimental results prove the effectiveness of the control strategy proposed in this paper.