CUK Converter Controller Design, Modelling and Tuning for Solar Battery Charger System

This paper aims at designing, modelling and tuning of the controller for a DC-DC converter employed in a solar aided battery charging system and thus constructing a simple yet efficient working solar battery charger which focuses on long battery life. CUK single stage DC-DC converter topology is chosen for the application as it enables minimum ripple current at both the solar photo voltaic (PV) cell and battery, with low component count. A detailed analyses of the control scheme employed, which is maximum power point tracking & battery charge control convoluted with proportional-integral-derivative (PID) control followed by pulse width modulation scheme for generation of the gate pulse, is provided. The controller uses the system model of the CUK converter to find the ratio between the proportionality constants of the PID controller (Kp, Ki, Kd) given the specifications of the solar PV array and the battery. Tuning of a PID controller is often done using hit and trial method for finding three values which is cumbersome and time consuming. In this paper the controller requires tuning of just one parameter which has a direct linear relation with the bandwidth and the settling time of step response. Thus the proposed battery charger system is efficient yet simple. Bode plot is used for stability analysis. Verification of system working is done by thorough simulations of the CUK DC-DC converter with the controller, for charging a 48V lead acid battery on MATLAB/Simulink and results are presented in the paper.