In a factorial hidden Markov model, there are multiple independent chains of hidden variables, which in this case are the current operating state of each appliance. At each time slice, there is also an observed variable conditional on the states of all of the corresponding hidden variables, which in the case is the premise-level power value. Below is a diagram of a factorial hidden Markov model.
where:
- Z - hidden (latent) variable, subscript - time slice, superscript - variable number
- X - observed variable, subscript, time slice
NIALM solutions are interested in evaluating the state of appliances, and given a look-up table of appliance state power values, can therefore evaluate the power of each appliance at each time slice. We are therefore interested in modelling the probability of an appliance being in a certain state, given the appliance's state in the previous time slice and the observed variable for that time slice:
This is an approach I will be investigating over the following weeks, after reading up on the relevant theory on sequential data and expectation-maximisation.
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