Yung-Deug Son

Maintaining precise liquid levels in interconnected tank systems is a critical requirement in many industrial processes; however, achieving reliable control remains challenging due to inherent nonlinearities and external disturbances. This paper presents a comparative analysis of three control strategies—sliding mode control (SMC), feedback linearization (FL), and proportional–integral–derivative (PID) control—applied to a nonlinear two-tank system. To address the practical limitation of unmeasured system states, a high-gain observer (HGO) is integrated into the control architecture to reconstruct unmeasured water levels. In addition, the controller and observer parameters are optimized using a hybrid genetic algorithm to balance tracking precision and control effort. Simulation results demonstrate that, although all three methods achieve acceptable setpoint tracking performance, the SMC-HGO configuration exhibits superior robustness. Specifically, it outperforms FL and PID in rejecting external disturbances and maintaining stability under significant parameter variations, such as changes in discharge coefficients.

Comparison of the feedback linearization plus LQR controller and the PID controller for greenhouse indoor climate

This paper proposes a method for minimizing the inductor current ripple of a DC–DC converter in a two-stage power conversion system consisting of a grid-connected PWM converter and an interleaved multiphase three-level DC–DC converter. To reduce the output voltage ripple, the three-level DC–DC converter is configured in parallel and operated interleaved. However, a circulating current generated by the interleaved operation increases the inductor current ripple of each DC–DC converter and causes system loss and inductor saturation. In this paper, the inductor and output current ripple of the interleaved three-phase three-level DC–DC converter is mathematically analyzed and the effect of the DC–DC converter’s duty ratio and output voltage on each current ripple is described. Based on this analysis, a method is proposed for controlling the optimal DC link voltage through the PWM converter, so that the DC–DC converter is controlled with the duty ratio that minimizes the inductor current ripple. The simulation and experimental results under various operating conditions are presented to verify the feasibility of the proposed control method.