Distributed control subject to constraints on control inputs: A case study on secondary control of droop-controlled inverter-based microgrids

Through a case study in the secondary control of the droop-controlled inverter-based microgrid (MG), we illustrate the problem of distributed control subject to constraints on the control inputs. In order to eliminate the frequency deviation caused by the primary control while keeping the real and reactive power sharing property, the designed distributed controllers need to meet the requirement that the secondary frequency control inputs should be in proportion in the steady state. To address such a constraint, we propose a scheme to design distributed secondary controllers, which are implemented on the local distributed generations (DGs). By allowing these controllers to communicate with their neighboring controllers, the proposed control strategy can achieve satisfactory real and reactive power sharing accuracy while restoring the frequency to the nominal values. A tested MG system simulation validates our proposed control strategy.