| As energy and environmental issues continue to intensify,distributed generation(DG)technology is becoming more professional and widely used in power systems.When the grid loses power due to faults or maintenance,DGs can be used to supply power to the critical loads in the distribution network to establish a temporary islanded system.It can reduce the power interruption area,improve the resilience of the power system,and increase the consumption of renewable energy.The islanded operation can effectively improve the reliability of the distribution network,which is of great practical significance.A basic feature of islanded operation in distribution networks is that the voltage and frequency fluctuate frequently,and is affected by intermittent power fluctuations and load changes.Due to the lack of support from large power grids,the stability problem will be more aggravated.Therefore,a good control method is indispensable for the islanded operation of the distribution network.The main work of this paper is as follows:Firstly,the traditional islanded control methods of are introduced and analyzed,and the advantages and disadvantages are summarized.The active power sharing problem in angle droop control method is analyzed in detail,and the corresponding supplement control is designed for this problem.The supplement control method can adjust the active power of each DG by angle information measured by the μPMU,realize the accurate sharing of active power.The effectiveness of the control method is illustrated through the simulation results based on the PSCAD/EMTDC platform.In order to improve the dynamic performance of the islanded distribution,a complete small-signal model is established for the whole system,and the variations of the system eigenvalues under the changes of active supplement control parameters are analyzed.The optimization model of control parameters for distribution network is proposed.Based on the eigenvalues calculated by the small-signal model,the key control parameters are optimized to ensure the stability of the system.Finally,a switching control method based on angle droop control is proposed for the switching process of islanded distribution.Because the switching method has a similar structure in the islanded and grid-connected operation modes,the controller has less impact on the system when switching.Through the designed switching method,the voltages on both sides of the grid-connected point can be adjusted synchronously,which can effectively reduce the impact current caused by switching. |
