In order to solve the difficulty of steady voltage regulation of AC power grid due to the surplus reactive power at operation of DC project with smaller power

the common way is to add inductive low voltage reactor or static reactive power compensator in the substation to absorb the surplus reactive power

or to change the reactive power consumed by the converter by way of adjusting the operation mode of both AC and DC system so as to achieve the balance of the reactive exchange between AC and DC power grids.On the basis of detailed analysis of the adopted auxiliary reactive power control strategy of converter（the reactive power control of converter and the reactive optimization function of low load） on the DC protection system of the line with different technology

the correlation among the reactive power consumption

ignition angle/arc extinguishing angle and the converted DC current is deducted by way of experimental method

which shows that improvement of the minimum turn-off angle can absorb surplus reactive power and can solve the problem of rise of AC grid voltage of the DC system which is operated with smaller power. At the same time

the coordination of the reactive control strategy and reactive power balance of the converter involved by the low voltage reactive which is widely used in DC project and the static reactive power compensator which is adopted in the weak AC system is discussed and studied in detail. It is proved by the experiment that the method proposed can solve the issue of surplus of reactive power effectively of DC operated at small power and

at the same time

the reactive power allocation of converter station is simplified. This method can be used as reference in the DC project and has good applicability.