| With the developmental diversification of new energy exploitation,requirement of power electronic technology is becoming higher and higher.In the situations of distributed generation and high power supply,it is difficult for a single inverter to work in power rating.So,power supply by several inverters in parallel way is used more and more.Parallel systems have two main developmental stages which is line and wireless,and wireless way has become hot research area because of no communication line.Firstly,the structure of parallel system was studied in this paper.Analyzed the parallel system based on droop method and some deficiencies were discovered.The virtual oscillator control has caused many attentions from the day it was came up with for the new thought compared with droop control method.We studied a lot in this control method,and found the control thought is to make the output of an inverter follows the modulation reference value,which given by the sine wave of a physical model when is oscillating.The inverters with virtual oscillator control in parallel are equal to the virtual oscillator models in parallel themselves,and the models is given by digital controllers.Inverters do not need to sample and calculate the active power and reactive power as control variables in parallel system.Synchronous could be realized automatically under the case of parameter matching,and circumfluence would be reduced gradually.The structure and characteristic of virtual oscillator was researched in this paper,and got the transfer functions.Some defects of original virtual oscillator control method were found,which is that the control system has not been designed clearly between resonant state and oscillatory state so that the quality of output voltage became terrible,and changes of load impedance will affect the output voltage of parallel inverters through sampling load current.To deal with them,control function of virtual oscillator has been optimized in this paper under the circumstance of global asymptotic synchronization condition was suit for.Otherwise,adaptive virtual oscillator control theory based on load current compensation has been put forward,and it can maintain the amplitude and frequency of terminal voltage when load change.Finally,the feasibility of control method was confirmed by simulation. |
