Research On Multifunctional Grid-connected Inverter With Reactive And Harmonic Current Compensation

With the growth of energy demand and the aggravation of environmental problems,distributed new energy power generation technology based on photovoltaic and wind power is booming.The grid-connected inverter,as a key device for distributed new energy grid-connected power generation,with its control technology developing continuously,has more controlling freedom.Compared with the traditional gridconnected inverter that can only input the fundamental wave sinusoidal current to the grid,the multifunctional grid-connected inverter(MFGCI)with auxiliary function of energy management has attracted more and more attention from researchers.It provides an innovative solution for power quality management,which achieves local balancing and decentralized management more flexibly with less extra equipment of management.This paper makes a detailed study on the multifunction grid-connected inverters with reactive power and harmonic compensation functions,and in virtue of this,manages the power quality of the point of common coupling(PCC).First,this study explores the controlling method of multifunctional grid-connected inverter.The author of the paper firstly establishes the mathematical model of T-type three-level grid-connected inverter,and obtains its decoupling controlling model based on rotating coordinate system.Then,based on grid-connected control,command current generation and current tracking control,the multi-function grid-connected inverter is researched to obtain its specific implementation method for power quality management.Then,the FBD harmonic current detection algorithm is studied.Since the traditional FBD harmonic current detection has the flaw of time delay and low accuracy,the adaptive algorithm with variable step size is studied.Meanwhile,the adaptive filter is used to replace the low-pass filter to improve the dynamic response and steady-state accuracy of harmonic current detection.Next,the optimal compensation control strategy of a single multi-function gridconnected inverter is studied.In order to solve the problem of limited compensation capacity of a single multi-function grid-connected inverter,a power quality assessment method based on tomographic analysis is studied,and a comprehensive power quality assessment model is established.Also,based on different controlling objectives,the corresponding optimal compensation control strategy is selected.After the reactive power and harmonic current compensation coefficients are obtained,the reactive power and harmonic current are selectively compensated.Finally,the flexible management of the power quality at the PCC is realized.Finally,the power coordination control strategy of the distributed grid-connected power generation system with multi-function grid-connected inverter is researched.In view of the random and intermittent characteristics of photovoltaic power generation,an energy storage unit is introduced to suppress power fluctuations and stabilize the DC bus voltage,and a coordinated control strategy based on the combination of masterslave control and layered control is proposed.The strategy aims to track the maximum output power of the photovoltaic,stabilize the DC bus voltage,and synchronize the power quality management,which gives the priority to ensuring the power requirements for the power quality management of the multi-function grid-connected inverter.