We established a model for the stability analysis of hybrid UHV half-wavelength and DC transmission system based on the quasi-steady model of half-wavelength transmission system.Moreover

we studied the stable operation range of the half wavelength transmission line

and discussed the power angle stability of the hybrid system during DC commutation failure and DC blocking.Meanwhile

we studied the power fluctuation mechanism of half-wavelength system caused by DC commutation failure and DC blocking based on shock response model and step response model of the two-order system

respectively

and studied the feasibility of emergency power support for the system to improve the transient stability of the half wavelength interconnected system by taking the advantage of fast power response of DC transmission system.The electromechanical transient simulation of UHV half wavelength and DC hybrid system proves the correctness of the methodology for the analysis of system power fluctuation caused by DC commutation failure and DC blocking

and also verifies the effectiveness of emergency power support of DC to half-wavelength transmission lines.The study shows that the peak of the power fluctuation of the half-wavelength line is related to the oscillation frequency during DC commutation failure.It also comes to the conclusion that the less the DC locking power is

the greater the damping and the smaller the peak value of the wave.And the DC power modulation can improve the transient stability of the asynchronous network system.