Design of charging system based on three level structure for ultracapacitor light rail vehicles

Ultracapacitor has been utilized as main power in light rail vehicles due to its characteristic of high energy-efficiency and fast response. In real application, ultracapacitor needs to be charged rapidly by charging systems when the vehicle parks at platform. However, it is typically challenging to design a rapid high power charging system with good dynamic performance. In this paper, a novel topology for ultracapacitor charging system is proposed to replace traditional buck charging system. Firstly, a three-level buck circuit for ultracapacitor charging system is designed, which halves the voltage stress on IGBT, as well as reduces the value of inductor. And the topology is modified in a way that it has a faster dynamic response. Secondly, the charge control design is reformulated as a model predictive control problem considering current peak constraints. To solve such optimization problem, an extended interior point method is used to simplify the iteration process. Simulation and experiment results are presented to verify the effectiveness of the proposed design.