A Research On HVDC System With Polymorphic Dynamic Phasors Model For AC Asymmetrical Faults

HVDC technology develops very rapidly in our country.Domestic large scale AC/DC hybrid power systems have been established and put into operation in recent years.Further research on the dynamic characteristics of HVDC system is necessary and urgent.In this thesis,problems such as modeling and simulation of AC faults in HVDC system with dynamic phasors are analyzed.HVDC system with dynamic phasors model for AC asymmetrical faults is deeply researched.The non-ideal operating conditions including the asymmetric in three-phase fundamental voltages at the AC side and the fluctuations in direct currents are taken into account.A polymorphic dynamic phasors method is presented.By using this method,HVDC dynamic phasors model is established.Simulation results show that polymorphic dynamic phasors models of HVDC systems are able to solve the problems caused by the traditional models such as the calculation inaccuracy and slow simulation speed for asymmetric faults.An advanced dynamic phasors method based on modified critical damping adjustment to eliminate the oscillation mentioned is presented.Then an HVDC model based on the advanced dynamic phasors is established.Simulation results show that this model is not only able to eliminate numerical oscillations effectively,but also represent the dynamic characteristics of HVDC systems correctly.