A maximum power point tracking (MPPT) converter of a renewable energy storage system for tracking and extracting a maximum power from a renewable energy source to provide the maximum power to a DC link. The MPPT converter includes an MPPT controller changing a controlled variable for maximum power point extraction in proportion to a current slope of the renewable energy source, and an MPPT extractor extracting a maximum power from the renewable energy source and converting the extracted maximum power in response to a control of the MPPT controller. The controlled variable variation is set to a large value if the current slope is out of a predetermined current slope range, and the controlled variable variation is set to a small value if the current slope is within the predetermined current slope range.