Real-time coordination of distributed energy resources for frequency control in microgrids with unreliable communication

The management of distributed energy resources (DER) via control strategies mitigates frequency fluctuations stemming from the volatility of renewable resources and fluctuating power demand. Recently, open communication networks are integrated with the traditional control strategies to overcome the ubiquity of DER system and the lack of dedicated communication infrastructures. However, open networks are exposed to communication degradation and can reduce the control performance. This work investigates the reliability of the integrated DER system and open communication networks, i.e. the cyber-physical microgrid system, with reference to the frequency control in the face of communication degradation. Adequate control strategy is provided by a discrete PID controller tuned via multi-objective particle swarm optimization. The integrated system is tested on a real-time platform with different MAC protocols and open-communication-network architectures to investigate how the communication degradation reduces the frequency control performance. Simulation results demonstrate that transmission delays and packet dropouts jeopardize the ability of the integrated system to maintain the system frequency deviation within bounds. In particular, the use of Ethernet ensures higher reliability as compared to 802.11 b/g. Moreover, the impact of interfering traffic and of the percentage of used bandwidth on the PID controller performance reduction is assessed. The optimized PID controller can compensate for communication degradation and uncertainty conditions of the microgrid, and ensures robustness against unknown network configurations.