Design of Hybrid Nonlinear Controller for Dual Active Bridge DC-DC Converter Used for Hydrogen Electrolyzer Load

Dual Active Bridge (DAB) dc-dc converters are mostly preferable for hydrogen electrolyzers (HEs) at grid scale due to inherent galvanic isolation and high voltage ratio conversions. The controllers for this converter can be linear or non-linear. Linear controllers, especially proportional and integral controllers, are easy to implement. However, they are highly affected due to several system disturbances. This paper presents a hybrid nonlinear control strategy for the DAB DC-DC converter operating in buck mode, intended for hydrogen electrolyser load applications. It is named as robust backstepping fast integral terminal sliding mode control (RBFITSMC). It consists of an outer non-linear recursive backstepping controller (BSC) and an inner FITSMC. The dynamics of the DAB converter are derived. BSC is implemented to accurately track the output voltage and generate a virtual reference current simultaneously. FITSMC is implemented to ensure the fast convergence of input current with the help of quick-reaching law. The proposed hybrid controller, along with a 500 KW DAB converter, is modelled using MATLAB/Simulink. The HE load is modelled using its dynamic electrochemical equivalent model. The robustness of the proposed controller is tested against output voltage tracking, input voltage disturbances and changes in switching frequencies. In all the scenarios, the proposed controller provides fast and accurate response.