This paper analyzes the mechanical model of direct-drive wave energy converters under the effect of regular sea waves. With the electromagnetic force of the linear generator equivalent to the linear combination of velocity and displacement as the control method

the characteristic curve of the average output power of the system under the control variables is obtained. The mountain-climbing method can achieve maximum power point-tracking(MPPT)control. For the key issue average power measurement

an average power measuring method based on period judgment is proposed. To avoid errors in estimation in the transient process

a method for judging whether the system is in a steady state is included. Experimental results have verified the validity of the proposed method that has improved its adaptability to the wave period variation and the tracking speed of the MPPT control. This work is supported by National Natural Science Foundation of China(No. 51177084).