Resumo:
The centralized secondary control strategies for microgrids (MG) are widely used due to
their ease of control and coordination with distributed resources. However, the reliability of
these strategies is extensively influenced by the communication system. To address the reliability
issues associated with centralized control, this work proposes a novel Unified Secondary
Control Structure (USCS). The USCS ensures regulation of the MG’s voltage and frequency
even during communication or control failures. During normal operation, the USCS operates
solely using the centralized control strategy, ensuring coordination with distributed resources.
In case of communication system or centralized control failure, the USCS switches to the decentralized
control strategy as a backup, ensuring voltage and frequency regulation. To facilitate
the USCS voltage regulation, a novel decentralized voltage regulation strategy is proposed.
This voltage control strategy is based on state estimation and equivalent systems. The proposed
USCS and decentralized voltage strategy are implemented and tested on a benchmarkMGbased
on the CIGRE residential European grid in Matlab/Simulink. The results demonstrate that the
decentralized voltage strategy can effectively regulate MG voltage, and the USCS ensures voltage
and frequency regulation even during failures, with a smooth transition between control
modes even during communication delays. Additionally, a hardware-in-the-loop environment
is employed to test the proposed USCS, where the centralized control is built in a real-time
digital controller, and the MG system, converter controls, and decentralized controls are implemented
in the Real Time Digital Simulator (RTDS) simulation environment. The results show
that the proposed control structure can guarantee regulation even during failures and restore
regular operation after failure. While the results are satisfactory, further development of a new
gain-adjust strategy is necessary for the strategies operating in the USCS.
