Effects Of Clock Deviations On The Performance Of Microgrids Based On Virtual Synchronous Generators

An inverter-based microgrid is a small-scale power network governed by a distributed control system. In this system, the nodes are the digital controllers of the power inverters, normally located at separate points within the microgrid. A relevant issue is that these controllers operate at different frequencies due to inherent clock deviations in the local hardware oscillators. This paper evaluates the effects of these clock deviations on the performance of microgrids equipped with inverters that emulate the operation of synchronous machines. A systematic procedure is presented to derive steady-state expressions of the inverter active power and microgrid frequency as a function of clock drift rates. This procedure is applied to swing and governor equations of the virtual synchronous generators, revealing the mechanism that allows clock drifts to be absorbed, making their presence negligible. In addition, it allows recognising the controllers that should never be implemented in a distributed control system, since they cause an unsatisfactory behaviour that can even lead to a blackout in the microgrid. Therefore, the relevance of this study is the identification of the control schemes that are most sensitive to clock drifts, which makes it easier to choose the most suitable control implementation for a particular application. Furthermore, technical guidelines are reported to help researchers on developing control solutions more robust to clock drifts. In this study, the theoretical results are validated by experimental tests in a laboratory microgrid.