Ocean wave energy is a renewable energy which remains too costly for large-scale electricity generation. The oscillating water column (OWC) wave energy converter (WEC) is a promising device-type with a rectifying air turbine and generator which convert alternating airflow induced by the water motion into kinetic energy then into electric energy. Applying control at each stage of energy conversion could increase the electric energy output of the device. As researchers overcome the modeling challenges of OWC, such as the nonlinearities due to air compressibility and power take-off (PTO) dynamics, we can integrate specific control algorithms to test their ability to improve the efficiency of the OWC. Herein, we present a state-space model of an array of OWC WECs restricted to heave motion with nonlinear PTO dynamics. We apply second-order sliding mode control (SMC) which commands a smooth torque signal to a direct-drive generator to maintain a reference turbine angular velocity. Because the algorithm can yield high turbine torques, we investigate a simple feed-forward relation for the control of a valve to limit the turbine airflow and discard mechanical power. We find that implementing the SMC algorithm and valve control can improve electric energy conversion most effectively in less energetic sea states.

中文翻译：

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用于提高功率的振荡水柱波能转换器的二阶滑模控制


海浪能是一种可再生能源，但对于大规模发电来说成本仍然过高。振荡水柱（OWC）波浪能转换器（WEC）是一种有前途的装置类型，具有整流空气涡轮机和发电机，可将水运动引起的交变气流转换为动能，然后转换为电能。在能量转换的每个阶段应用控制可以增加设备的电能输出。随着研究人员克服 OWC 的建模挑战，例如空气压缩性和动力输出 (PTO) 动力学造成的非线性，我们可以集成特定的控制算法来测试其提高 OWC 效率的能力。在此，我们提出了一系列 OWC WEC 的状态空间模型，该模型仅限于具有非线性 PTO 动力学的升沉运动。我们应用二阶滑模控制（SMC），它向直接驱动发电机发出平滑的扭矩信号，以维持参考涡轮机角速度。由于该算法可以产生高涡轮扭矩，因此我们研究了一种简单的前馈关系来控制阀门，以限制涡轮气流并丢弃机械功率。我们发现，在能量较低的海况下，实施 SMC 算法和阀门控制可以最有效地改善电能转换。