Thermodynamic process control of ocean thermal energy conversion

Abstract

The small temperature difference in ocean thermal energy conversion (OTEC) causes the high sensitivity of thermodynamic process to perturbations such as temperature and power load, which requires an efficient control strategy of thermodynamic process for OTEC. To this aim, an integral dynamic model is established to study the dynamic response of thermodynamic process in an OTEC system. To ensure the system efficiency and operating safety of power cycle, a multi-objective active-disturbance rejection control (ADRC) strategy is proposed and compared with corresponding single-objective ADRC and PI controller. Multi-objective ADRC includes a load-following control loop and two auxiliary control loops (evaporator control loop and condenser control loop). The results indicate that the multi-objective ADRC is most efficient to track the change of power load, in which the overshoot and integration absolute error (IAE) of load-following are reduced by 50% and 16% when compared with the single-objective ADRC. In addition, the multi-objective control strategy can maintain the stability of superheat degree and condensation pressure, and hence improves the system efficiency by 8.64% for the output power of 35 kW. Especially, the feedback-feedforward controller and feedback controller are attractive candidates to maintain the stable superheat degree and condensation pressure.