Modelling And Analysis Of Matiari To Lahore HVDC Transmission Line In Pakistan

HVDC transmission has the advantages of low line cost,long transmission distance,and large transmission capacity.After many years of development,the technology has become very mature and is one of the most important transmission technologies at present.Pakistan has built a ± 660 kV HVDC transmission project from Matiari to Lahore.This is Pakistan’s first HVDC transmission project and it is of great significance to alleviate the power shortage problem in some areas.However,the high-voltage DC transmission system uses grid commutation converters.Its normal commutation relies on the AC system to provide commutation voltage support.It is easy to cause commutation failure during a fault.In addition,once the DC system power is interrupted momentarily,the reversal of work power is likely to cause transient over-voltage,which will endanger the safety of power grid operation.Therefore,it is necessary to study the commutation failures and transient over-voltage problems of HVDC transmission systems to improve the theoretical support for practical projects in Pakistan.First,based on the actual engineering,an electromagnetic transient model of the bipolar HVDC transmission system was built in PSCAD/EMTDC,the control strategy and parameter design of the HVDC transmission system were studied,and the validity of the model was tested through a transient steady state simulation study..Then,the dynamic characteristics of the rectifier-side AC bus voltage under different rectifier-side AC system strengths are compared,and the effect of the rectifier-side AC system strength on the rectifier-side TOV value under two different operating conditions is studied.Finally,the dynamic characteristics of the HVDC transmission system after inverter commutation failure are simulated and analyzed.The mechanism of the commutation failure of the HVDC transmission system is analyzed.Based on the characteristics of the DC current and the off angle after the failure,a new method is proposed.The control strategy to suppress the commutation failure,the simulation proves the effectiveness of the proposed control strategy under different fault levels under single-phase grounding and three-phase faults on the inverter side.