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According to the characteristics of the linear generator for direct drive wave energy converters, a novel primary permanent magnet transverse flux linear generator (TFLG) is studied. The structure has the advantages of simple structure, easy maintenance, and high mechanical strength, which is especially suitable for the harsh marine climate environment. Firstly, the operating principle of the generator is described, and the three-dimensional equivalent model of the generator is established by magnetic circuit method. The mathematical expressions of back electromotive force (EMF) and cogging force are derived. Secondly, the EMF, waveform distortion rate and cogging force are taken as optimization objectives, the key structural parameters of the generator are selected as the influence factors. The local multi-objective optimization of the primary permanent magnet TFLG is carried out by the Taguchi method, and a group of parameters with suitable comprehensive performance are obtained. Finally, the effectiveness of the method is verified by three-dimensional finite element simulation.

A variable exponential approaching law is designed, which shortens the approaching time of the traditional approaching law sliding surface and improves the speed of the system. On the basis of variable exponential approaching law, aiming at the shortcomings of traditional PID control, a sliding mode switching function with a given speed as a variable is proposed. A simulation model of a permanent magnet synchronous linear motor was built through theoretical analysis, and the model was verified. Through verification, an improved sliding mode switching function is obtained, whether there is overshoot when following given speeds, and the rapidity is good. When following a dynamic given speed, the following rapidity is good and the error is small. When there is system disturbance and load disturbance, the system has better robustness.

Tubular linear vernier generator keeps the advantages of high efficiency and low cost of primary permanent magnet linear generator, but it has more flux leakage. First of all, a new type of tubular linear vernier generator is proposed in this paper. The permanent magnet is embedded in the primary teeth by horizontal and vertical magnetization, which effectively solves the problem of more magnetic leakage at the end of the generator and puts forward the concept of modularization, which greatly reduces the cogging force by modularization. Secondly, taking no-load back EMF, waveform distortion rate and cogging force as the optimization objectives, the sensitivity analysis of the optimization variables of the generator is carried out, and the optimization variables with significant sensitivity are selected to build the model based on box Behnken. Thirdly, particle swarm optimization algorithm is used to solve the response surface model and generate a set of Pareto solutions, so as to obtain the optimal structural parameters of the generator. Finally, the cogging force, output voltage quality and other performance of the optimized generator are calculated and analyzed based on the two-dimensional finite element method, and the multi-objective optimization based on the response surface model and particle swarm optimization algorithm is verified the effectiveness of the design method based on modularization.