A Time-Varying Virtual Resistance Control for Ultracapacitor Based DC–DC Converters

Ultracapacitor (UC) based dc-dc power supplies are widely used for addressing surge power demands and to provide energy backup to critical loads. The conventional control techniques, such as unified control strategy, though ensure seamless mode transition, do not offer complete flexibility in charging and discharging controls which is crucial in UC-based backup systems. On the other hand, controls, such as independent switch control, though allow great flexibility in control, do not ensure seamless mode transition without appropriate mode-switch logic. This paper proposes a time-varying virtual resistance based mode transition control for independent switch control which not only ensures smooth, seamless transition between charging and discharging control modes but also ensures complete control over the mode transition durations. The proposed control is found to be robust to error mode identification as compared to introducing dead band between control modes. The proposed control is verified on a proof of concept experimental setup at a power level of P
_o
= 65 W, voltage level of V
_g
= 26 V with the dc-dc converter switching at f
_sw
= 100 kHz. The performance comparison with PWM blocking method is also evaluated where the proposed control is found to work well.