Motor load detection for voltage transient based non-intrusive load monitoring

Del Mar, Paul
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University of Delaware
Investment in smart grid technology by the electric utilities is continually growing. Demand peak shifting, motivated by time-of-use pricing, is a way to reduce electric capacity requirements, as well as align loads with variable alternate sources such as wind or solar. These methods require feedback from the customers via a smart meter to see real time power usage and other data such as individual load usage. Smart meters allow the end-user to take advantage of the time-of-use pricing schemes to intelligently use their highest power loads during the low point of pricing, as well as gaining a better understanding of how the loads in their household use electricity. Individual appliance monitoring can be by a distributed sensing network, where each appliance or device has its own direct communication line with the smart meter. A much less costly alternative is non-intrusive load monitoring (NILM), which uses information seen in the power consumption profiles or actual current and voltage signals, to determine appliance usage. NILM does not require professional installation and voltage signal acquisition and can be measured right at a typical household outlet. Devices impart voltage transients or noise on the power line of the house when they are switched that can be used for NILM. The transients of particular loads can provide signatures specific to them. However, the load itself can introduce transients independent of switching, and these need to be distinguished. Particularly, we show here that motors having commutating switches introduce repetitive transients that resemble load switching. Time-frequency analysis provides insight into these short-time non-stationary signals. An experimental setup was implemented in order to record voltage transients of a few different common household loads. It is shown that universal motor loads with a commutating switch can be detected separately than transients created by a single switching action typical of most devices.