Research On Integrated Control Strategy For Islanded Microgrid Based On Droop Characteristics

Microgrid is a power network that utilizes advanced monitoring,control,and communication technologies to provide efficient and secure energy supply.It is considered a new paradigm for intelligent integrated energy supply and has received widespread attention from the engineering and academic communities.Distributed generator in microgrids generally need to be connected through power electronic interfaces.This interface technology not only increases system flexibility and reduces inertia,but also facilitates power management and control.However,the power electronic interface also brings many control difficulties,especially when the microgrid is in islanded operation mode,the internal voltage,frequency and other parameters of the system lose support from the large grid.At this point,the system needs to operate independently,and reliable control strategies are needed to achieve power decoupling,power distribution,and stability of parameters such as voltage and frequency between various DGs after the system is disturbed.This thesis adopts a hierarchical control strategy to control the islanded microgrid system.In order to solve the problem of traditional droop control being unable to achieve approximate power decoupling and difficult power allocation in the system,this thesis first introduces virtual impedance in the primary control system.Although introducing virtual impedance can achieve power decoupling to a certain extent and improve the efficiency of power allocation,there are still some problems with virtual impedance control in practical applications.The most significant issue is that the accuracy of power allocation is not very ideal,which may lead to a significant drop in the system output voltage.Therefore,further research and optimization of virtual impedance control are needed in practical applications.This thesis proposes an adaptive virtual impedance control strategy based on fuzzy PID control to address the issue of insufficient power allocation accuracy in virtual impedance control in microgrids.This control strategy combines fuzzy controller and PID controller,effectively integrating their advantages of strong adaptability,high flexibility,and high accuracy.Afterwards,a fuzzy PID controller is used to adaptively adjust the virtual impedance of a specific circuit,overcoming the problem of insufficient power distribution accuracy caused by the introduction of virtual impedance.Finally,a MATLAB/Simulink simulation model was established to verify that the improved primary control proposed in this thesis can effectively overcome the problem of uneven reactive power distribution caused by inconsistent equivalent impedance of the transmission line,and has higher accuracy and better dynamic performance.Although the improved adaptive virtual impedance one-time control can achieve inverter reactive power decoupling and power allocation,the original voltage and frequency offset issues still exist in the system.To solve the above problems,this thesis analyzes the limitations of traditional PI hierarchical control on voltage and frequency compensation based on the improvement of adaptive virtual impedance primary control,and then introduces a distributed hierarchical control strategy based on multi-agent system consensus algorithm.Calculate the deviation value of voltage frequency using consistency-based algorithms and compensate for it.The distributed hierarchical control strategy based on multi-agent system consensus algorithm can effectively solve the limitations of traditional PI hierarchical control methods in voltage and frequency compensation,while improving the efficiency,stability,and robustness of the system.This strategy has broad application prospects and can be applied to various microgrid systems to achieve distributed intelligent control.Finally,a MATLAB/Simulink simulation model was built to verify the effectiveness of the improved hierarchical control proposed in this thesis in improving system voltage and frequency offset issues.