Research On Parallel Control Method Of Converter In Microgrid Based On V/f Control

In recent years,with the construction of ecological civilization,the development of microgrid is accelerating,which puts forward higher requirements on the capacity and expansion ability of converter.As the core of the micro grid system,the development trend of the converter gradually changes from increasing the capacity of a single converter to running multiple converters in parallel.The parallel operation of multiple converters determines the stability of the whole microgrid system.The parallel operation of the converter can distribute the load power to each converter,make the power electronic devices bear less current stress and improve the reliability of the system.In addition,reducing the capacity can reduce the volume and weight of the converter,thus reducing the production and maintenance costs of the system.Therefore,the study of parallel operation of converter is of great significance.Firstly,the control methods of current converters are summarized and the parallel control methods are compared.Subsequently,the decoupling process of three-phase bridge converter topology is discussed,and the circulation current of parallel system is analyzed,then,a parallel control method for converter based on V/f control is proposed.All converters use constant voltage constant frequency(V/f)control,all output voltage with rated amplitude and frequency,only the phase Angle is different.The relationship between phase Angle difference of output voltage and load voltage is analyzed,according to different application environments,three strategies of adjusting phase Angle are proposed.By adjusting the phase Angle of the output voltage,the amplitude,frequency and phase Angle of the output voltage of each converter are the same,the converters run in parallel stably,the system circulation current is small,and the load power is evenly divided.Secondly,the large inductance and line inductance are analyzed,which have been mentioned in the parallel strategy.The distance from the converter to the load is not the same,it is proposed to add a large inductance L at the converter end to weaken the influence of line inductance difference.The terminal voltage of each converter is approximately equal to the load voltage,so each converter has a common voltage reference.Then,the influence of large inductance and line inductance on the steady state circulation current of the system is discussed.The influence of large inductance on the parameters of parallel system is also analyzed and the design process of large inductance is described.The feasibility of replacing real inductors with virtual inductors is also discussed.Finally,based on the PSIM(Power Simulation)platform,a simulation model of the parallel system was established,and the proposed parallel operation strategy of the converter was simulated and verified.At the same time,a three-phase converter parallel operation experimental platform was built based on TMS320F28335,and the proposed parallel operation strategy of the converter was experimentally verified on the experimental platform.The simulation and experimental results show that the parallel control method of converter based on V/f control proposed in this paper can make the converter in the system achieve current sharing and load power sharing.The effectiveness and feasibility of the proposed parallel control strategy are verified.