Islanded microgrids with output distributed delay: Sampled-data based observer design. Issue 12 (2022) - Ammeh, L.
Abstract: In this paper, two majors islanded microgrid issues are addressed: i) the voltage amplitude and frequency control and ii) the time delay introduced by the use of communication networks leading to instability. The studied system is composed of a distributed generator (DG), a voltage source inverter (VSI), an LC filter and local loads. After the system modeling, a voltage controller by means of the backstepping method is proposed. Then, the distributed time delay that comes in the VSI output current is dealt with supposing that it is the only measured signal and the measurements are available only in sampling periods. Two observers are designed to give online estimation of the state signals; the first one involves an intersample predictor and the second one uses a ZOH predictor. The predictors compensate the time delay and the sampling effects. The observers are designed on the base of the high gain principle to deal with the system nonlinearity. From simulations and formal analysis, the following results are assumed: the output voltage tracks its reference and it remains stable, the online estimated signals, given by both observers, converge exponentially to their real values with large time delay and sampling interval. It is worth noting that it is the first time that distributed time delay in islanded microgrids is addressed.