±800 kV ultra-high voltage direct current(UHVDC)transmission project from Ximeng to Taizhou is hierarchically connected to 1 000 kV and 500 kV AC grid in Taizhou converter station. As for this new circuit structure

it is very important how to ensure the DC voltage balance of two series valve groups connected to different voltage level AC grid in one pole for the safe and stable operation of HVDC transmission system. Combined with the UHVDC project from Ximeng to Taizhou

on the basis of the analysis of the control strategy of the DC transmission system

the voltage balance control of the series valve groups is studied

and the control strategy of voltage balance and the fault tolerance method of middle point divider are put forward. The RTDS modeling test verifies the correctness of the control strategy and achieves good application results in the HVDC project from Ximeng to Taizhou.