Control Method Of Parallel Inverters Working In Random Islanded Microgrid

With the development of science and technologies of human society in recent years,energy demand shows a rapid growth trend,but,the traditional power generation mode not only burn lots of fossil fuel but also pollutes the environment.Therefore,in the large-scale development of energy construction also must pay attention to the negative influence of the energy utilization to the society and environment,so in recent years,micro-grid make up by distributed generation units which are clean,flexible and reliable has gradually become a hot research topic in the world widely.Micro-grid can work in two different modes,respectively,grid connected operation mode and islanded operation mode;the islanded micro-grid can look upon as a self-contained system,it can make all the load in the system working in a stable operation without the grid support,this advantage makes it possible for the micro-grid to improve the reliability of the regional power supply and avoiding unpredictability losses of personal and economic losses caused by large scale power outages,at the same time there is an irreplaceable advantage in some remote areas that can not connected to the grid,so it is of great practical value to study the control strategy of islanded micro grid.In order to realize the characteristics of plug and play in the DG unit in the micro-grid,the droop control is usually used in the micro-grid inverters.However,when the micro-grid work in islanded mode,because the system has great randomness,such as the difference of line impedance and load properties inconsistent and bus voltage is not ideal,the micro-grid inverters which lose the support of the grid must have a strong ability to adapt,to maintain safe and reliable operation of the islanded system.So his paper proposed improved droop control based on inverse trigonometric functions to control the system frequency,then the sensitive load can work normally;Secondly,improving the power sharing of parallel system,so it no longer impacted by the line impedance difference,thereby reducing the power circulation;What's more,in order to control the 5~thh and 7~thh harmonic in the three-phase system,the quasi proportional complex(QPCI)regulator is used,it can reduce the content of harmonic current effectively in both parallel inverters system and grid-connected system.Aiming at all kinds of control strategies proposed in this paper,we first use MATLAB to simulate and verify,then build an experimental platform make up by three three-phase inverters,and use DSP2812 as control circuit to realize digitization of control algorithm.Finally,simulation and experimental results verify the effectiveness and feasibility of the proposed control strategy in suppressing frequency shift,improving power sharing accuracy and harmonic circulation suppression.