Dual loop controllers using PI, sliding mode and flatness controls applied to low voltage converters for fuel cell applications

This paper treats the design, control and implementation of a non-isolated low voltage DC/DC converter with a high voltage ratio coupled a fuel cell stack and a DC bus which can be used in transport applications. The proposed converter consists of two cascade stages non-isolated DC/DC converters. The first stage is an interleaved boost converter and the second is a double dual-interleaving boost converter. The selection of each stage is based on the efficiency of the converter with a high output voltage, a small input current ripple, and an output voltage ripple. The control of the converters is ensured by a dual loop control that contains for the first step a voltage loop with a linear PI controller and a fast current loop using a non-linear sliding controller for both converters. After that, the voltage loop of the first stage is replaced by an energy loop based on a differential flatness control approach. The simulation of the proposed control is performed under Matlab-Simulink environment and validated by experimental results using small-scale test bench with dSPACE-1104 card. This paper presents and comments the introduced device and discusses the obtained results.