Research On Current Zero Crossing Distortion Control Methods For Three Phase Dual Buck Grid-Connected Inverter

With the worsening of environmental problems,new energy sources have been continuously exploited and utilized to replace the existing fossil fuels and become the main source of power generation systems.The traditional three-phase full-bridge grid-connected inverter is the most widely used topology in the new energy power supply system at present.However,the existence of dead zones of the topology results in low harmonics.Thus,various compensation strategies are introduced to eliminate dead zones which make the control more complicated and reduce the reliability of the whole system.In recent years,no dead zone topologies such as Z-source grid-connected inverter,switched boost grid-connected inverter and dual Buck grid-connected inverter have attracted more and more research and three phase dual Buck grid-connected inverter becomes one of the hot spots.However,due to its unique half-cycle control,the topology has the problem of zero-crossing distortion of grid-connected current.To meet the harmonics requirement of grid-connected current,the control method of suppressing zero-crossing distortion has become the key issue which needs to be studied.This paper first introduces the application field of three-phase grid-connected inverter and the methods of suppressing current zero-crossing distortion in dual Buck inverter.Then it briefly introduces the basic principle of three-phase dual Buck grid-connected inverter in two working modes.And the loss of the main power devices in two working modes is given,which proves the superiority of the half cycle control.The reasons for the occurrence of current zero-crossing distortion are explained,and the zero-distortion range is determined.Taking the influence of the phase lead and the digital delay into account,the symmetric half-cycle control is proposed,which lays the foundation for suppression of the current distortion in the following.In order to better suppress current zero-crossing distortion,this paper improves the hybrid control of full cycle and half cycle control.Based on predecessors,it specificly optimizes the interval of full cycle control in order to minimize the additional losses,and zero-crossing distortion is suppressed to a certain extent.However,this method is contrary to the design intent and optimal working characteristics of dual Buck topology and the distortion cannot be completely eliminated.Thus,the duty cycle compensation method is adopt.Based on the theoretical analysis,the ideal duty ratio function and its linearization expression are calculated and the control block diagram of the system is given.In the following,the repetitive control is introduced into the three-phase dual Buck grid-connected inverter.Due to the high harmonics in the distortion current of the topology,the parameters of the repetitive controller with PI control in series are specifically designed.And it analyzes the stability of the whole system in the z domain.Thus,the current zero-crossing distortion is solved.At the same time,the size of filter can be reduced under premise of meeting the requirement of the grid current.In order to verify the above analysis,a 3kW three-phase dual Buck grid-connected inverter experimental platform is set up.And the design of LCL filter and the software design of the system are introduced.Finally,the simulation and experiment are carried out under this platform.And the results are given which verify the correctness of theoretical analysis.