A Practical and Efficient Nonlinear Observer for Supercapacitor Energy Identification

In this paper, a novel nonlinear observer is proposed to accurately identify supercapacitor (SC) energy. With the consideration of dynamic modeling uncertainty, a nonlinear state space model is established based on the SC three branch equivalent circuit model. A piecewise nonlinear feedback function is designed by employing sign function, whose gain is adaptivelyadjusted. By using the nonlinear function apply for correcting SC model uncertainty, the discrete nonlinear observer is designed. With the observer, the corrected internal capacitor voltages is derived and thus the SC energy is identified. With an elaborately designed experimental scheme, a test platform is built. The derived experimental results show that the energy observation error is 0.4% in charging stage and 1% in discharging stage, which verified the practicability and high accuracy of the proposed energy identification method.