| As an important part of microgrid,energy storage system is actually a special type of micro power supply in microgrid.The energy storage system can provide certain power to the microgrid through converter,and realize the power adjustment function of peak load and valley filling and short time power support.But the capacity of the energy storage system has a certain amount of capacity in the stable working condition,and may even be idle in a certain time.Considering the similarity of APF and STATCOM in the structure topology with the energy storage system,a new type of combination device will be adopted in this thesis to realize"multi function".This thesis focuses on the feasibility and control method of multi-objective energy storage device.Firstly,the mathematical model of the energy storage inverter system and the P/Q control during decoupling under the grid-connected microgrid is analyzed.Secondly,i_p-i_q current-detection method is based on the instantaneous reactive power theory,and it is used to synthesize the compensation currents of harmonics,reactive power,and three-phase unbalance and then perform comprehensive compensation in order to solve the problem of nonlinear inductive load and unbalanced load in microgrid.Therefore,the energy-storage-conversion system has the function of compensating the power quality at the same time as the output power stabilizes the power fluctuation,thereby achieving multi-objective control.The measurement error of traditional phase-locked loop caused by three-phase voltage imbalance and distortion is analyzed.The software phase-locked loop of decoupled double synchronous reference coordinate transformation is introduced and analyzed theoretically.The principle of multi-objective control of energy storage system is analyzed,and the overall structure diagram of multifunctional energy storage and conversion system is given.Finally,a small microgrid platform and Multi-Objective control simulation is built by the PSCAD/EMTDC software.The simulation results show that the feasibility of the control method of multi-function energy storage and conversion system and the correctness of its operation result.This device can not only achieve the function of grid-connected regulation of microgrid power,but also improve the affect the problem of power quality between microgrid and distribution network,it save the costs and ensure the safe and reliable operation of the microgrid. |
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