Distributed cooperative current-sharing control of coupled parallel charging systems with super-capacitor loads

In order to address the output current imbalanced problem of parallel chargers for energy storage type light rail vehicles, a distributed cooperative current-sharing scheme is proposed in this paper. Considering each charger as an agent, the current-sharing control design can be modeled as the output current consensus-tracking problem of nonlinear and non-identical multi-agent systems with the bounded control input. The communication topology between each parallel charger is modeled a directed graph, which only needs a spanning tree. In order to guarantee the boundedness of the control input, a general saturation function is introduced into the control law. One distributed cooperative PID current-sharing controller is designed based on the nearest neighborhood rule. The system stability and dynamic performance of the proposed cooperative control scheme is evaluated by analyzing the transfer function matrix from the input duty ratio to the output current. When the physical parameters and communication topology of the parallel chargers are given in advance, the system stability can be maintained by choosing the proportional, integral and derivative control gains. The output current of parallel chargers can be balanced by adopting the proposed approach, which is verified by simulating a parallel charging test system.