| Nowadays,energy conservation and environmental protection of renewable energy are strongly advocated.Due to its increasing proportion in the power system,the composition of the traditional power grid is different from the original one.In this context,the concept of microgrid(MG)is proposed.As an energy exchange device between renewable energy and MG,power electronic converter is an important part of power system.Due to large amounts of renewable energy bring in the grid,the former control mode to a certain extent,can meet the power system now existing in the complex condition of inverter power quality requirements.Therefore,the method of control needs to be improved.This paper is based on the project support of the electric power re search institute of "modeling and simulation research of virtual synchronous motor for multi-scene applications of different objects",the improved control of three-phase inverter is studied,analyzed and simulated.First of all,aiming at the shortcoming of lacking inertia and so on,an adaptive feature subspace approach was proposed: VSG inverter control.According to the output characteristics of synchronous generator(SG),the virtual inertia value is added to the power system to improve the overall stability of the system.Under ideal symmetric conditions,the VSG control model and voltage and current control are analyzed to ensure stable operation of the system under symmetric conditions.Next,based on the above VSG control analysis,the concept of as ymmetric conditions is introduced.The phenomena and causes of voltage and current distortion and power fluctuation caused by power system unbalanced complex working conditions are analyzed.For different output power quality requirements,on the basis of the positive and negative sequence separation of output current,active power and reactive power control,ensure that the grid asymmetric conditions the output of the inverter power quality.In the case of isolated island mode,the stability of the output voltage of the system is not only considered,but also the influence of negative sequence circulation when multiple inverters are connected in parallel.Under the combined control of the negative sequence voltage and the negative sequence virtual impedance,the negative sequence circulation value can also be suppressed if the output voltage is not balanced.Since MG can operate in two modes of grid-connected network and isolated island,it needs to switch between two modes during operation.In this paper,o ther stability problems such as shock current caused by traditional switching mode are analyzed and studied.Finally,the improved control under various complex working conditions is simulated and verified in plecs software. |
