© The Institution of Engineering and Technology
The hierarchical control structure is widely investigated for a microgrid. Conventionally, the tertiary control layer and the primary and secondary control layers are studied independently since they are separated in time scale. It is difficult for distributed generation (DG) units to directly track the optimal power references provided by the tertiary control because they are controlled to behave as voltage sources by the primary and secondary controls. Moreover, even if the DG unit can realise power tracking, improper coordination among the primary, secondary and tertiary controls may still lead to instability of the microgrid. To fill the gap among the three control layers, this study proposes a method for realising their distributed joint operation. With the proposed method, DG units can track the optimal power references in a distributed manner. Regarding the stability issues, this study also presents (i) a detailed stability analysis of the system based on the constructed smallsignal dynamic model and (ii) an adaptive regulation strategy of control parameters for enhancing the system stability. Finally, numerical studies and timedomain simulation results are provided to validate the proposed method's ability to realise a distributed optimal and stable operation for a hierarchically controlled microgrid.
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