Research On Key Technologies Of Three-phase Unbalance Compensation Device Based On Multi-inverters Paralleled Sequence-decomposition Strategy

With the rapid development of the economy,a large number of power electronic equipment and unbalanced loads have been widely applied in electrical engineering field,and heavily increase the threephase unbalance on load side of the grid.Moreover,modern power electronic equipment has higher requirements on the grid power quality.Since the three-phase unbalance problem will seriously affect safe and stable operation of the power grid,effective measures must be taken for the power quality governance.Active power filter(APF),as a compensation device,can effectively improve power quality and has been widely applied in power quality governance.The research of this thesis is focused on three-pahse-twocapacitor APF(3P4L-2C-APF),the main contents are as follows:1.In order to decouple the positive and negative sequence currents in second harmonic form,a SOGIbased three-phase unbalanced component detection method,combined with the average filter,is proposed.The method has fast dynamic response and small steady-state error,as well as application value.Further more,an average filter is designed with no phase offset,high filtering precision and good dynamic performance,so as to improve detection accuracy.The simulation comparison results show that the average filter is superior to the traditional LPF and Butterworth filters in filtering performance and response speed.2.The voltage and current control strategies of single-inverter APF and the coordinated control strategy of multi-inverter parallelled APF are studied.Aiming at the problem that the traditional PI controller can not track the AC signal without static difference,a quasi-PR controller is designed to expand the system bandwidth and improve the response ability of grid frequency fluctuation,which could realize the static tracking to the command current,by maintaining the high system gain at the resonant frequency of PR controller.Meantime,in order to control the DC side voltage of APF,a double-loop voltage control strategy based on PI controller is proposed to contral DC side total voltage and capacitor equalization voltage.Moreover,since the modular multi-inverter parallelled APF requires coordinated control smong sub-modules,a sequence-decomposition APF coordinated control strategy,based on hierarchical control as well as equalization and current limiting strategy,is proposed,which can not only improve system redundancy and operational efficiency and reduce the data transmission error,but also ensure the security and stability of submodule operation.3.The simulation research on three-phase unbalance compensation system,based on multi-inverter sequence-decomposition contral strategy,are completed.The hardware parameters of the APF are designed,and the simulation model is built up.The three-phase unbalanced component compensation under unbalanced,harmonic and comprehensive loads are carried out,the results prove the feasibility and accuracy of the proposed control startegy.Moreover,the sub-module switching and hot-plugging of multi-inverter parallelled APF system are simulated,the results further show that the proposed three-phase unbalance compensation system based on the proposed control strategy has excellent compensation effect and operational stability.