  Transactive or market-based coordination strategies have recently been
proposed for controlling the aggregate demand of a large number of electric
loads. Such schemes offer operational benefits such as enforcing distribution
feeder capacity limits and providing users with flexibility to consume energy
based on the price they are willing to pay. However, this paper demonstrates
that they are also prone to load synchronization and power oscillations. A
transactive energy framework has been adopted and applied to a population of
thermostatically controlled loads (TCLs). A modified TCL switching logic takes
into account market coordination signals, alongside the natural
hysteresis-based switching conditions. Studies of this market-based
coordination scheme suggest that several factors may contribute to load
synchronism, including sharp changes in the market prices that are broadcast to
loads, lack of diversity in user specified bid curves, low feeder limits that
are encountered periodically, and the form of user bid curves. Case studies
illustrate challenges associated with market-based coordination strategies and
provide insights into modifications that address those issues.
