DC power grid has the characteristics of low inertia and weak damping, and power surplus caused by disturbance may develop quickly and lead to the breakdown of the power system. Firstly, the mechanism of solving power surplus in voltage source converter (VSC)-based DC grid by AC bus independent operation changing from parallel operation is analyzed. When sending-end station monopolar blocks, AC bus independent operation can prevent the normal polar from loading power initially loaded by faulty polar, thus protecting the normal polar. When receiving-end station monopolar blocks, corresponding polar in normal station can be blocked to eliminate power surplus. DC energy consumption device and this scheme are contrasted and their advantages and disadvantages are analyzed. Strategies to reduce voltage vibrating are proposed. PSCAD simulation of a four-terminal VSC-based DC grid model is performed, which verifies the correctness of the theoretic analysis.