Novel Utility-interactive Electrical Energy Storage System by Electrical Double Layer Capacitors and an Error Tracking Mode PWM Converter

A novel electrical energy storage system interacting to a commercial ac network was designed and evaluated by experiments, which consists of an ac/dc converter with a constantly-sampled PWM scheme termed Error Tracking Mode and electrical double layer capacitors paralleled by monitor circuits. The ac ratings are 100V, 500W and 1.0 power factor. The storage capacity is designed to be 500Wh. Since the voltage of the capacitor bank decreases to one-fourth with discharge, a reversible boost-down chopper is inserted between the bank and the ac/dc converter. 95.6% and 95.8% were obtained for the ac/dc converter efficiency in rectifier operation and inverter operation respectively. The average switching frequency was settled between 10.4_??_11.2 kHz for any operating conditions. For the chopper, efficiency values of 94.6% and 93.1% were measured in charge and discharge modes respectively. The storage efficiency of the capacitor bank was 89.8 %. This novel utility-interactive energy storage system has demonstrated good and quick performance.