Effects of Nonlinear Efficiency Characteristics on the Power-tracking Control: a Case Study of Hydrokinetic Energy Conversion System

Maximum power point tracking (MPPT) for many alternative energy conversion systems implies the application of control methods where the operation of the primary energy conversion process is optimized through a nonlinear control arrangement. This assumes the presence of constant efficiency values for the subsystems in cascade to the front-end process. In case, efficiency of the subsequent stages are not constant and are dependent on diverse operating conditions, it becomes important to identify the success of power tracking as seen by the load unit. In this work hydrokinetic energy conversion systems are studied in this regard. A repetitive approach that matches nonlinear efficiency information to the overall performance of the system is presented. With specific focus on 'power curve' and 'performance/efficiency curve' two figures of merit are introduced to identify issues such as success of power tracking and divergence from optimum operating point. A comprehensive simulation study and a experimental test example are also presented. This method can also be used for identifying the effects on efficiency nonlinearity in other alternative energy systems.