Abstract
The development of Multiple Input/Multiple Output (MIMO) sliding mode control setups for a fuel cell/supercapacitor module is presented in this paper. The main objective of the proposed controllers consists in simultaneously satisfying the demand and regulating the DC bus voltage, even in the presence of model uncertainties and strongly varying operating conditions. Two design approaches are utilized to synthetise different control setups, each one capable to robustly deal with such control challenges: on one hand, variable-gains first-order sliding mode and, on the other, supert-wisting second-order sliding mode control. The stability of the nonlinear controlled system is formally analysed. Extensive simulations are conducted, to comparatively assess the performance of the proposed MIMO sliding mode controllers. Both control setups exhibited highly satisfactory results, demonstrating robustness to external disturbances and parameter variations, proving to be more suitable than classic linear PID controllers.
Highlights
During the last years, hybrid electric power generation systems based on renewable sources have been strongly studied and developed all over the world
Summarizing, this paper addresses the development of two different MIMO control setups for the Fuel Cell (FC)/SC module, which is assumed to be part of an already existent Hybrid System (HS) that comprises renewable power sources and an electrolyzer
A sinusoidal load variation was applied to the system. Both First-Order Sliding Mode (FOSM) and Second-Order Sliding Mode (SOSM) are able to reject this perturbation, while the PID controllers are not able of regulate the DC bus voltage. Both sliding mode techniques are able to enforce the DC bus voltage, it is important to mention that with FOSM, voltage shows a small modulation around the reference voltage, while this effect is not present with the SOSM algorithm
Summary
Hybrid electric power generation systems based on renewable sources have been strongly studied and developed all over the world. It can be concluded that, given the local stability of the equilibrium point and the existence of an invariant region, where the divergence of the vector field never changes sign, the zero dynamics results stable and converges to the references, within the operating region. From the latter, it can be appreciated that the current rate limitation imposed to the reference by the control strategy makes the system to slowly reach the different operation points and accurately supply the required power, in accordance with the load power demand variations. In this case, the SC are smoothly recharged to its reference voltage (i.e., 40 V), while the current quickly responds to abrupt load power demands, showing the excellent behaviour of the developed controllers. It can be appreciated that, mainly due to the chattering, the FOSM controller produces more power
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