This paper describes causal sub-optimal control of a direct drive linear generator to extract the maximum power from real sea conditions without wave prediction. The reaction force required to control the buoy to move in phase with the ocean waves is provided by the linear generator. After determining the power take-off force based on the model of a machine, the required currents from the generator can be obtained. These currents have varying amplitudes and frequencies thus presenting a challenge to traditional Pulse Width Modulation control. In this paper, a continuously varying average voltage method is presented where the average voltage for each switching cycle is determined by pre-calculated duty ratio to meet the required voltages before coming into the power converter. Using Matlab/Simulink, simulated results of the power converter current control are presented.