Ultracapacitor Based Voltage Lift Converter with PID Controller as a Function of Current

Ultracapacitor' s steep droop discharging characteristics require a converter maintaining constant output voltage at various loading conditions. An ultracapacitor based Basic Self-Voltage Lift DC-DC converter has been adopted in this article. The Mathematical modeling and design procedure of the ultracapacitor and the converter with resistive load has been discussed. A conventional single loop PID controller tends to be unstable as the load current shifts from the operating current. This work proposes a current-dependent PID controller formed by considering the integral and differential constants as a function of load current. These functions are represented as first-order polynomial equations obtained through the linear regression technique. The system is validated by constant, increasing, decreasing and random loading patterns in MATLAB environment. The Voltage Lift converter provides an extra utilization of ultracapacitor around 39% compared to Boost converter.