Research On The Key Technologies Of Power Quality Comprehensive Compensation Device In Three-phase Four-wire System

With the development of modern industry and the proposal of the “carbon peaking and carbon neutral”,a large number of nonlinear loads and green energy are connected to the power system,causing more and more serious power quality problems.As an electrical device that can compensate harmonic current,reactive current and unbalanced current efficiently,actively and flexibly,power quality comprehensive compensation device has become one of the important ways to solve power quality problems.This thesis aims to research the key technologies that affect the compensation effect:phase-locked loop technology,command current acquisition method and current loop control strategy.This thesis firstly introduces the research background and a brief overview of the key technologies that affect the compensation effect.The working principle of the power quality comprehensive compensation device is analyzed,mathematical modeling is carried out in the abc static coordinate system and the d-q-0 rotating coordinate system,which lays the foundation for the subsequent analysis.Phase-locked loop technology is one of the core points that affect the compensation effect.Therefore,this thesis firstly proposes an improved second-order generalized integrator in view of the error characteristic of the traditional second-order generalized integrator when facing the grid voltage with DC component.Then based on the improved second-order generalized integrator,the working principle diagram of the improved phase-locked loop is given.The command current is the bridge between the load current and the compensation current,and the command current acquisition method is one of the key technologies.Therefore,this thesis introduces the detection principles and the characteristics of the p-q method,the ip-iq method and the d-q-0 transformation method based on the theory of instantaneous reactive power.Three detection schemes based on the d-q-0transformation method are given: detect harmonic current,reactive current and unbalanced current,detect harmonic current and reactive current,detect specified harmonic current.Whether the current loop controller can track the command current accurately and quickly is one of the most important indicators to measure the performance.Therefore,this thesis aims at the characteristics of poor accuracy of PI control in the face of high-frequency signals and poor dynamic response of repetitive control,the system block diagram of the compound control strategy combining PI control and repetitive control is given.The PI and repetitive controllers in the compound control strategy are analyzed,and the parameters of the controller are designed.Finally,the voltage stabilization control strategy and the neutral potential balance control strategy of the voltage loop are given and analyzed.Finally,for the three key technologies of phase-locked loop technology,command current acquisition method and current loop control strategy mentioned above,modeling and simulation are performed in MATLAB.Through the simulation results,it is verified that the phase-locked loop based on the improved second-order generalized integrator has the improvement of phase-locking performance,the command current detection scheme is correct,the voltage loop control strategy is feasible,and the current loop compound control strategy has the characteristics of high compensation precision and fast dynamic response.