借助实时数字仿真器研究了特高压直流工程一极中单换流单元运行时在线投入另一个换流单元，或当一极中双换流单元运行时在线退出其中一个单换流单元的控制策略。研究结果表明：零功率解锁方式及小触发角解锁方式均可行，且零功率解锁方式下触发角约85，而小触发角解锁方式下触发角不得低于70；在线投入一组换流单元时，只要配合得当，整流侧先解锁、逆变侧后解锁和逆变侧先解锁、整流侧后解锁2种方式均可实现目标；从安全可靠、交直流系统扰动小等方面考虑，在线投入一组换流单元时可采用零功率解锁方式、整流侧先解锁，而在线退出一组换流单元时，逆变侧应先进行退出控制，以有利于整组换流单元的退出。

By means of real time digital simulator (RTDS), the control strategies for two conditions are researched, i.e., another commutation unit is deblocked in on-line way while one single commutation unit in a pole of UHVDC project is running or one of two single commutation units is blocked in on-line way while two single commutation units in a pole of UHVDC project are running. Research results show that both zero power deblocking mode and small firing angle mode are feasible, the firing angle under zero power deblocking mode is about 85° and the firing angle should be not less than about 70°; When a set of commutation units are deblocked by on-line way, so long as the coordination is appropriate, both deblocking modes are available, i.e., the deblocking is firstly implemented at rectifier side then at inverter side or adopting the contrary operating order. Considering security and reliability as well as smaller disturbances in DC and AC system, when a set of commutation units is deblocked in on-line way, the zero power deblocking mode can be used while the deblocking is firstly executed at rectifier side; when a set of commutation units are blocked in on-line way, in order to be favorable to the deblocking of whole commutation set, the inverter should be firstly seceded from the commutation unit.