  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. In multi-infeed HVDC (MIDC) system, 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 optimization method is proposed to
determine the droop coefficients of the MIDC lines. To test the proposed EDCPS
method, the electromagnetic transient (EMT) model of a MIDC system is built on
the CloudPSS platform, and the test results verify the effectiveness of the
proposed EDCPS strategy.
