The paper considers a reference-based control system for heaving wave energy converters. The proposed controller comprises two parts: lower level part (LLP) and higher level part (HLP). The HPL generates the buoy's velocity reference with the objective to maximize the power absorption with the constraints in the maximum control force and the power take-off device's utilization index. The index is determined as the ratio between the maximum electrical power with its average power. The LLP ensuring the actual velocity of the buoy follows reference by utilising the feedback controlled system. The simple robust lead-lag controller is used as the main controller in the LLP. The proposed control method is examined using the irregular and regular sea-states, as so with the perturbations and nominal scenarios.