With the complex hybrid AC-DC power system in China coming into being, the HVDC faults, such as DC block faults, have an enormous effect on the frequency stability of the AC side. To improve the frequency stability of the receiving-end system, this paper proposes an emergency DC power support (EDCPS) strategy, which is based on a designed droop characteristic between the active power of LCC-HVDC lines and the receiving-end system frequency. Then, a coordinated optimal method is proposed to determine the droop coefficients of the multi-infeed HVDC lines, which considers the inertia of the sending-end systems and the operation constraints of the whole AC-DC system. To test the proposed EDCPS method, a hybrid AC-DC system electromagnetic transient (EMT) model containing four CIGRE HVDC systems is built on the CloudPSS platform, and the test results verify the effectiveness of the proposed EDCPS strategy.

coordinated droop control,emergency DC power support,hybrid AC-DC system,frequency control