Study On Microgrid Power Quality Conditioner Based On Hybridenergy Storage

With the rapid development of distributed technologies,microgrids have also developed rapidly.The reliability and security of the microgrid itself have become particularly important.The power quality problems such as harmonics,reactive power and voltage dips in the microgrid can seriously affect the stable operation of the microgrid.The power quality regulator based on hybrid energy storage proposed in this thesis is a power quality control device with comprehensive compensation capability.And it is based on the hybrid energy storage of super capacitors and batteries,which has the ability to compensate for harmonic currents,reactive power,and lack of power.It can meet the multiple power quality problems of a microgrid that can be managed with only one device.Firstly,the battery and super capacitor based hybrid energy storage system are studied systematically in this thesis,and the charging and discharging characteristics and mathematical models of the two energy storage technologies are analyzed in detail.Compared the connection topology of several hybrid energy storage systems,finally the topological form that both the battery and super capacitor are connected to the DC bus of the microgrid power quality conditioner through two-way DC/DC converter is adopted.In order to make full use of the respective advantages of the battery and the super capacitor,a low-pass filtering based hybrid energy allocation strategy is proposed to compensates power quality problems through the power converter under the premise of stabilizing the DC bus voltage.In this power allocation strategy,the high-frequency part of the power imbalance caused by the power shortage in the microgrid is borne by the super capacitor,and the low frequency part is borne by the battery output.Secondly,after analyzing several harmonic current detection methods based on instantaneous reactive power theory,a device suitable for detecting power quality problems of a microgrid system is constructed which can accurately provide active,reactive,and harmonic command currents.Thirdly,with the advantages of large capacity and small harmonic distortion of the neutral point clamped(NPC)three-level inverter,it can be directly connected in parallel with the microgrid to compensate for the internal power quality problem of the microgrid.After comparing several traditional control strategies,a fast control set model predictive control with excellent dynamic performance and good steady-state performance is adopted for the NPC converter.This method does not require the modulation module also avoids complex controller parameter tuning and compensates for the large computational inadequacies of the traditional finite control set model predictive control(FCS-MPC)and optimizes system operation.To sum up,the simulation model of microgrid power quality regulator based on hybrid energy storage is built in Matlab/Simulink,and the parameters of the model are set.On thebasis of the simulation of several common power quality problems,the compensation effect of the power quality regulator and the corresponding control strategy are tested.The simulation results show that the hybrid energy storage microgrid power quality regulator of microgrid are active and reactive power shortage,harmonic current and other power quality problems of compensation based on ensuring the stable operation of microgrid,with the value of broad development prospects and practical research.