Improved performance in a supercapacitor-based energy storage control system with bidirectional DC-DC converter for elevator motor drives

A supercapacitor-based energy storage control scheme for elevator motor drives that exhibits improved performance and maximum exploitation of the storage device is proposed. The suggested energy storage system is connected to the DC-link of an elevator motor drive through a bidirectional DC-DC converter, and the braking energy is stored at the supercapacitor bank. The aim of the control scheme is to ensure the power supply to the elevator motor as far as possible from the temporary stored energy of the supercapacitors, in order to minimize the power consumption from the grid. Also, since the capacitance of the supercapacitor and consequently the energy storage capability reduces with increasing frequency, the proposed control scheme aims to provide smooth charging and discharging performance. This is attained by optimally controlling the DC-DC power converter through a new control technique that takes into account any variations of the AC supply voltage to the elevator motor drive and also on-line adjustment of the DC-link voltage proportional-integral (PI) controller parameters according to the elevator operating conditions. Several simulation results are presented to demonstrate the resulting improvements of the suggested control scheme.