To overcome the drawback of the conventional master-slave control as shown in DC voltage becoming uncontrollable when the master station gets lost or reaches its power limit and the drawback of conventional droop control shown in the inability of each station to control its active power to its reference value during normal operation

a dual-limiting power balance controller is proposed. The dual-limiting controller is composed of an upper limit loop and a lower limit loop

the former will play a part only when the DC terminal voltage of a converter is higher than a certain upper limit value and reducing the rectified power of a converter. The lower limit loop will play a part only when the DC voltage is lower than the lower limit and reduces the inverted power of a converter. In normal operation

the DC terminal voltage of a converter is somewhere between the upper limit and the lower limit and the dual-limiting controller will not be activated. The power balance controller for voltage source converters interfaced to wind farm is also proposed. Simulations on a 4-terminal multi-terminal direct current(MTDC)system under unbalanced power orders

tripping of the master station and wind power variations have verified the effectiveness of the proposed dual-limiting controller. The dual-limiting controller combines the advantage of master-slave control shown in the active power of each power terminal precisely controlled in normal operation and the advantage of droop control showing the system stability retained in case of unbalanced power orders or fault

the drawbacks of the two conventional controllers overcome. This work is supported by National Natural Science Foundation of China(No. 51261130484)and National Basic Research Program of China(973 Program)(No. 2014CB247400).