Improved Control Strategy of a Supercapacitor-Based Energy Recovery System for Elevator Applications

This paper proposes an improved control strategy for a supercapacitor (SC)-based energy recovery system (ERS) for elevator applications. The ERS is connected to the dc-link of the elevator motor drive through a bidirectional dc-dc converter for storing and then recovering the braking energy. A system of two fuzzy-logic controllers is introduced for online adjusting the dc-link voltage through the dc-dc converter of the ERS, according to the elevator operating conditions and the ac-grid voltage variations. Thus, the reduction in the consumed energy by the grid in an elevator operating cycle and, therefore, increase in the elevator system efficiency is achieved. Also, the developed control system keeps the SCs current ripple low in order to protect the SCs from overheating and, therefore, preserves their energy storage capability and operating lifetime. The proposed control scheme can be easily installed without requiring modifications to the elevator motor drive and, thus, it can be applied to any elevator system, even existing elevator installations. The effectiveness and the resulting operational improvements of the proposed control scheme have been experimentally validated on a real elevator system.