Research On Power Quality Management Of Micro Electrical Grid Based On Multifunctional Grid-tied Inverter

With the aggravation of global energy crisis,the development and utilization of new clean energy has been stimulated,and new energy power generation technology has emerged.As the main application mode of distributed generation technology,micro electrical grid system has attracted the attention of scholars.Micro electrical grid can effectively restrain the impact of new energy power generation on the grid and ensure reliable power supply quality.However,the load current harmonics,reactive power components and unbalanced components are the key factors affecting the power quality of micro electrical grid.Using active power filter in micro electrical grid can meet the demand of improving power quality.Its structure is similar to grid connected inverter in micro electrical grid,so it can achieve more efficient power quality governance by designing control scheme.Aiming at the problem of harmonic components in grid connected inverter’s active power output under unbalanced grid voltage,a Multi-functional Grid tied Inverter is proposed,which combines grid connected power generation and micro electrical grid power quality optimization under unbalanced grid voltage.This paper focuses on the comprehensive compensation control strategy of MFGTI under unbalanced grid voltage.Firstly,this paper summarizes the background and research status of MFGTI,and expounds the research significance of the subject.Then,MFGTI and active power quality control device are compared and analyzed.Three phase full bridge voltage source inverter is selected as the main circuit topology.On this basis,the mathematical model of three-phase full bridge inverter circuit under unbalanced grid voltage is constructed.Then,the command current of three-phase MFGTI is studied.Aiming at the harmonic and reactive command current,an improved algorithm based on FBD power theory is used to detect the harmonic and reactive current under unbalanced grid voltage.Aiming at the problem that the grid connected tracking command current is difficult to detect in micro electrical grid,an effective calculation method is designed,which can accurately extract the grid connected tracking command current and make MFGTI realize stable output of active current under unbalanced grid voltage.In order to realize the fast and accurate phase locking when the grid voltage is unbalanced,the decoupling multi synchronous reference frame synchronous signal detection method is used to detect the phase,amplitude,frequency and other signals of the grid voltage in real time and accurately.On this basis,a comprehensive compensation control strategy of MFGTI is proposed.Firstly,a combined positive and negative sequence control method is adopted to control the DC flow in the positive sequence component and the secondary AC flow in the negative sequence component in a closed-loop manner,which improves the calculation accuracy and the utilization rate of the control system.Then,a multi quasi proportional resonance controller for MFGTI is proposed,which makes MFGTI realize active power output and compensate the harmonic and reactive components caused by load current in micro electrical grid.Under the condition of ensuring the maximum output power of MFGTI,aiming at the problem of limited power quality compensation capacity of single MFGTI,a power quality evaluation model based on analytic hierarchy process is established to realize the coordinated control of harmonic and reactive current compensation and realize the optimal governance.Finally,the key hardware and software of MFGTI are designed.Through MATLAB/Simulink simulation analysis and 10 k W MFGTI experimental verification,MFGTI meets the demand of micro electrical grid for high quality power.