Current-limiting droop control design of paralleled AC/DC and DC/DC converters in DC micro-grids

In this paper, we propose two nonlinear controllers for a three-phase rectifier, and a bidirectional DC/DC boost converter respectively, to ensure voltage regulation, reactive power control and load power sharing with an inherent current-limiting capability, independently from system parameters. In contrast to the traditional approaches that use small-signal modelling, this approach takes into account the nonlinear model of the rectifier by considering the generic dq transformation, and the accurate nonlinear model of the dc/dc bidirectional converter, to demonstrate the boundedness and the current-limiting capability using Lyapunov methods and the input-to-state stability theory. This new method is based on the concept of introducing a bounded dynamic virtual resistance at the input of the rectifier, and a constant virtual resistance with a bounded dynamic virtual controllable voltage for the bidirectional converter that can be both positive and negative leading to a bidirectional power flow. Simulation results of a DC micro-grid consisting of a three-phase rectifier in parallel with a bidirectional dc/dc boost converter feeding a common load are presented to verify the effectiveness of the proposed control strategy.