The WaveSpring technology provides phase control by a negative spring arrangement that inherently widens the response bandwidth of point absorbers without the need for real-time wave information or prediction algorithms. The negative spring module acts directly on the linear mechanism of the buoy. This avoids the losses associated with transmitting large reciprocating energy flows through the PTO system, a challenge that has limited the practical use of phase control methods known as reactive control.
Compared to other phase control methods such as latching, the WaveSpring principle offers similar amplification of power capture, but requires less than half the machinery force and therefore enables a smaller and less costly PTO. The device motion is continuous, avoiding the fatigue and wear challenges associated with more abrupt motion resulting from latching control. Combined with tribological advantages this improves reliability and component lifetime. Since no real-time information on the incident waves is required for making the buoy resonant, the number of sensors and active control loops can be reduced, making the system less complex.
Extensive testing and benchmarking with alternative control methods conducted within the HiWave project shows that the annual average power output of a point abosrber can be increased by more than 300% using WaveSpring. The Annual Energy Production per PTO force is also increased by approximately 300%. The results represent a breakthrough for wave power. The step-change improvement in performance is provided by a low-cost spring arrangement using proven components adding a minimum of cost and complexity compared to the same system without phase control. Moreover, WaveSpring provides the critical function for detuning the device in storms – making it move out of phase with the waves, thereby making it more transparent to large energy flux. The detuning feature has been shown to significantly reduce the loading of the equipment during the test campaign.