Firstly

the overall structure of the control system in multi-operation modes is analyzed. It is found that the control system design is similar to the conventional HVDC system because of its similar structure at DC side. While there are still some differences in the inverter station

the control functions in bipolar level need to be implemented in the DC station control and the function for the operation mode transform is configured in the AC station control. Nevertheless

the stability control function shall be carried out according to each pole to adapt to its different operation modes. Secondly

the coupling between the two AC systems during the transition period before the asynchronous interconnection finally achieved was also analyzed. Owing to the weak coupling of the two AC systems

the AC filters arrangement and reactive power control can be done independently. Finally

the complete control equipment was installed for the Guanyinyan HVDC transmission project

and some results on the real-time digital simulator(RTDS)verify the rationality and validity of the control system.