| As the penetration of distributed renewable energy increases,microgrids can integrate and utilize them sufficiently,which is a research hotspot.One important feature of microgrids is islanded operation mode in which microgrids face serious voltage stability problems while distributed renewable energy takes power electronic devices(inverter)as interface.Droop control method is widely used in inverter control of distributed energy in islanded microgrids because it can stabilize the system voltage and frequency without communication.This paper focuses on the fast calculation method of the boundary of power flow feasible region in parameter injection space,analyzes the properties of the feasible region boundary under static conditions,analyzes the influence of the droop coefficients of inverter control on the power flow feasible region of islanded microgrids,and further puts forward the optimal selection method of droop coefficients.The main works are as follows:1.The continuation power flow calculation model of microgrid with inverter control mode in the islanded operation mode is established.2.A new method to quickly calculate the boundary of power flow feasible region in parameter space is proposed.A mathematical model of the feasible region boundary of the microgrid using droop control is established.By using the state information of the adjacent saddle node bifurcation point in the parameter space,the calculation efficiency is improved by using the idea of pre-estimate and correction.The boundary of feasible region in the high-dimensional space is further expanded.Then the influence of droop coefficient of inverter control on the feasible region boundary of the microgrid is studied.3.Taking fully into account the uncertainty of the capacity of distributed renewable energy,the uncertainty of the load growth direction,and the change of network topology,a method for quickly calculating the power flow feasible region of microgrid under parameter space based on deep learning is proposed to reduce the calculation time of voltage stability margin of the islanding microgrid4.A multi-objective optimization method with adaptive weights is proposed.Static voltage stability and small signal stability of microgrid are comprehensively considered to optimize the droop coefficients based on the power flow feasible region in parameter injection space.5.The methods proposed above is applied for simulation and calculation in actual microgrid test systems.The simulation results show that the speed of solving feasible region is greatly improved and the optimized droop coefficient of inverter control significantly improves the system voltage stability margin,which verifies the effectiveness and applicability of the proposed method. |
