For heaving wave-energy converters like the CorPower device phase control is crucial in order to harvest energy from waves of different lengths efficiently. The WaveSpring technology provides phase control by a negative spring arrangement that makes the wave energy converter responsive throughout the range of normal ocean waves. It works without the need for real-time wave information or prediction algorithms. The negative spring module acts directly on the buoy hull and eliminates the need of cycling large energy flows through the PTO system, a challenge that has limited the practical use of phase control methods known as reactive control.