It is very useful for UYS parallel operation using digital load current-sharing control technique.After detailed analysis of the circulation power model in a UYS parallel system with N modules,a series of equations are built,which describe the relationship between the circulation current active power and reactive power and the amplitude and phase of UYS output voltage.Further more,two-level phase-locked technique and re-modulation technique for DSY frequency control is introduced to realize the precise and effective regulation on output voltage amplitude and phase for a UYS module.Thus a good load-sharing effect is achieved accordingly.In the end,a parallel UYS system with two 4kVA modules is built,which uses TMS320LF2806 DSY and CAN communication bus as core techniques.The performances of load-sharing using circulation power control method are validated by expenments.