  Existing methods of non-intrusive load monitoring (NILM) in literatures
generally suffer from high computational complexity and/or low accuracy in
identifying working household appliances. This paper proposes an event-driven
Factorial Hidden Markov model (eFHMM) for multiple appliances with multiple
states in a household, aiming for low computational complexity and high load
disaggregation accuracy. The proposed eFHMM decreases the computational
complexity to be linear to the event number, which ensures online load
disaggregation. Furthermore, the eFHMM is solved in two stages, where the first
stage identifies state-changing appliance using transient signatures and the
second stage confirms the inferred states using steady-state signatures. The
combination of transient and steady-state signatures, which are extracted from
transient and steady periods segmented by detected events, enhances the
uniqueness of each state transition and associated appliances, which ensures
accurate load disaggregation. The event-driven two-stage NILM solution, termed
as eFHMM-TS, is naturally fit into an edge-cloud framework, which makes
possible the real-world application of NILM. The proposed eFHMM-TS method is
validated on the LIFTED and synD datasets. Results demonstrate that the
eFHMM-TS method outperforms other methods and can be applied in practice.
