A New Switching Strategy for Improving Efficiency and Thermal Distribution of a Three-Port Converter for Solar DC Stand-Alone System

This brief proposes a new switching scheme for a recently published three-port converter to make it suitable for Photo-Voltaic (PV) fed dc stand-alone system with battery backup. The resulted scheme is capable of Maximum Power Point (MPP) Tracking, charging, and discharging of the battery, and can feed power to the load while maintaining the desired load voltage. This scheme, when operated with a saw-tooth or triangle carrier, leads to improved efficiency and dynamic response as compared to existing similar schemes reported in the literature. This brief also proffers toggling between saw-tooth and triangle carriers periodically for better thermal distribution in the switching devices which is envisaged to enhance the reliability of the overall system. A suitable control strategy is also proposed for the complete stand-alone scheme to facilitate operation in various possible modes along with smooth transition between these modes. Small signal analysis is performed based on the proposed switching scheme, and the controller design during various operating modes is discussed. Validation and performance analysis of the overall system are carried out under various operating conditions utilizing a 400W experimental prototype.