A Cascaded Distributed Control Framework in DC Microgrids

The conventional distributed secondary controller, consisting of a voltage controller and a power controller, is based on the parallel framework by exchanging two state variables and requires a voltage observer to regulate the voltage. In this article, a cascaded control framework is proposed to achieve the voltage regulation and power sharing, in which only the power state variable is exchanged without the voltage observer. The secondary power controller is designed to adjust the reference value of the secondary voltage controller. And the output of the voltage controller is used to modify the input of the droop controller. Then a resilient cascaded controller is further proposed to enhance the controller resilience against time delays and disturbances. An extra information exchange block between the power controller and the voltage controller is introduced in the resilient cascaded controller. Moreover, the steady-state analysis is carried out to prove the effectiveness of proposed controllers. A small-signal model is also established to investigate the impact of controller parameter variation on the system dynamics. Finally, several case studies are conducted by simulations to demonstrate the performance of proposed controllers.