西藏藏中电网处于发展初期，系统非常薄弱，青海—西藏直流接入后形成“大直流小系统”的局面，常规直流10%功率解锁的方式无法适应系统运行要求。为了满足系统安全稳定运行要求，对青藏联网直流系统的最小启停功率和启停方法进行了研究，提出了单极和双极启停方法，以及为实现该启停功率对直流平波电抗器和换流阀等设备的特殊要求。提出的10%额定电流、25%额定电压解锁/闭锁的直流系统启停方法，能够实现单极2.5%额定功率的启动和闭锁，降低了直流启停过程对交流系统的频率冲击，保证了系统的安全稳定运行。该启停功率和启停方法在青藏直流联网工程中应用效果良好。

Because of the Tibet power grid is in the early stage of development and its AC system is very weak, the connection of Qinghai-Tibet DC transmission line will cause the situation of weak system with big DC power and the unblock mode with 10 % rated power not satisfying the systems operation requirement. This paper studied the minimum start-stop power and method for the Qinghai-Tibet DC project in order to make system operation safe and stable, and proposed monopole and bipolar start-stop methods. The special requirements of AC smoothing reactor and converter valve were also put forward for the minimum start-stop power. The DC start-stop method of unlock/block with 10% rated current and 25% rated voltage can implement monopole unlock/block with 2.5% rated power and reduce the impact of DC start-stop on the AC systems frequency. This start-stop method can ensure the system operation safe and stable, which has been successfully applied in the Qinghai-Tibet DC interconnection project.