Distributed secondary control with ocean thermal energy generation for the frequency stability improvement of island microgrids

Island microgrids (MGs) are characterized by a high proportion of intermittent renewable energy resources. Generally, these units operate in maximum power point tracking mode to maximize the economic benefits of MGs. However, this will lead to insufficient regulation reserves for maintaining frequency stability, especially when traditional generation units are gradually being phased out. Ocean thermal energy generation can provide additional frequency regulation reserves due to its vast and persistent performance. This paper proposes a secondary frequency control strategy with ocean thermal energy generators (OTEGs) participation for island MGs. OTEGs can convert ocean thermal energy into electric power to compensate for the power shortage of MGs when regulation reserves are insufficient. Therefore, the frequency stability of island MGs is improved. Besides, a leader-follower-based distributed control strategy is proposed for OTEGs to achieve frequency restoration and accurate power sharing through a sparse communication network. In the proposed control strategy, global power collected by distribution-level phasor measurement units contributes to the improved dynamic performance of secondary frequency regulation. Furthermore, the Lyapunov stability theorem proves the proposed controller's stability. Finally, numerical simulations on the IEEE 34-bus system validate the effectiveness of the proposed control strategy.