  In recent studies, moving target defense (MTD) has been applied to detect
false data injection (FDI) attacks using distributed flexible AC transmission
system (D-FACTS) devices. However, the inherent conflict between the security
goals of MTD (i.e., detecting FDI attacks) and the economic goals of D-FACTS
devices (i.e., reducing power losses) would impede the application of MTD in
real systems. Moreover, the detection capabilities of existing MTDs are often
insufficient. This paper proposes a multi-stage MTD (MMTD) approach to resolve
these two issues by adding a group of designed security-oriented schemes before
D-FACTS' economic-oriented scheme to detect FDI attacks. We keep these
security-oriented schemes for a very short time interval and then revert to the
economic-oriented scheme for the remaining time to ensure the economic
requirements. We prove that a designed MMTD can significantly improve the
detection capability compared to existing one-stage MTDs. We find the supremum
of MMTD's detection capability and study its relationship with system topology
and D-FACTS deployment. Meanwhile, a greedy algorithm is proposed to search the
MMTD strategy to reach this supremum. Simulation results show that the proposed
MMTD can achieve the supremum against FDI attacks while outperforming current
MTD strategies on economic indicators.
