A magnetic lead screw (MLS), that not only has enough maximum thrust force but also has good controllable performance, is a perfect linear actuator that can convert low-speed linear motion into high-speed rotary motion and apply for wave energy conversion system. In this paper, an improved transient sub-domain analytical model (SDAM) is proposed to analyze the performance of a novel proposed hybrid excitation magnetic lead screw (HEMLS) for the WEC system. The proposed HEMLS not only can have enough maximum thrust through the PM is arranged on both sides of the rotor and mover, but also can be controllable through two-phase windings that carry opposite DC and placed in slots on the mover. The proposed SDAM gives the analytical expressions of trust and torque. The hybrid exciting source and slot effect can be considered in the proposed SDAM. The proposed SDAM is validated by the finite element analysis method under both load and no-load conditions. Finally, a laboratory prototype and the corresponding test platform are developed to verify the effectiveness of the proposed HEMLS and its SDAM.

The magnetic lead screw (MLS) applied to the point-absorbing wave energy converter (WEC) can convert the low-speed linear motion of the buoy into a high-speed rotational motion that can drive a rotating motor to generate electrical power. Aiming at the high permanent magnet (PM) consumption of the traditional MLS, a novel type of consequent-pole MLS is proposed in this paper, a consequent-pole type is adopted on the translator to save the PM consumption. At the same time, the traditional bipolar type is adopted on the rotor to increase the maximum thrust force. To analysis the performance of the proposed MLS, a three-dimensional (3-D) analytical method (AM) model is proposed. Two different materials that are non-ferromagnetic and ferromagnetic, for teeth between the helical PMs on the translator can be considered in the proposed model. To verify the model, a prototype of the proposed MLS and its test platform is developed. To ensure that the manufactured prototype is closer to the design one, a new helical PM installation method through the bolts is introduced in this paper. And a corresponding improved thrust force and torque equations are proposed for the prototypes which the installation method used. Finally, the comparative results of 3-D AM, 3-D finite element method (FEM) model and experiment are given.

Providing stable and reliable power supply for offshore equipment with special power requirements, such as marine data platforms and marine buoys far away from the coast is currently topical research issue. At present, most of these devices use photovoltaic power generation or install high-capacity batteries and carry out regular replacement of electricity supply schemes. Due to the high dependence of photovoltaic power generation on solar radiation and the high cost arising from frequent battery replacements, wave energy is considered as a solution. Wave energy converters (WECs) are devices that convert the energy stored in waves into electrical energy, and its main advantage is the sustainable supply of electricity. In this article, a new built-in wave energy converter with high reliability and low maintenance costs is proposed and investigated for marine data buoys. Its core is a direct-drive energy conversion unit based on a magnetic lead screw design. The device can passively follow the pitching state of the buoy under the impact of waves to maximize its power generation. The proposed WEC is introduced and investigated through model analysis and prototype experiments. The experimental results confirm the power generation performance of a 50 kg power generation prototype and show the advantages of the proposed device.

Direct-driven generation is considered one of the most reliable selections in wave energy conversion systems. Therefore, a direct-driven linear-rotary wave generator (LRWG), which can transfer the low-speed linear wave motion to the high-speed rotating motion of the rotor and then generate electrical power simultaneously, is proposed in this paper. The proposed LRWG comprises three parts: translator, common rotor, and stator. From the energy view, the proposed LRWG can be divided into two sections: the energy transmission section to increase the velocity of the wave and the energy conversion section to generate power. The initial design method is given to determine the main dimensions of the proposed LRWG. To meet the maximum power tracking control requirements, a multi-mode and multi-objective optimization method, which can consider both generator and motor mode, is proposed to improve the performance of the proposed LRWG by sensitivity analysis, response surface methodology, and non-dominated sorting genetic algorithm II method. Finally, a prototype and its experimental platform are developed based on one of the optimization schemes from the possible solutions to verify the proposed approach and the performance of the proposed LRWG.

In order to predict the performance of designed electric machines, and also based on which the high efficiency of the drive systems can be obtained, the accurate calculation of the iron loss is necessary. Taking modeling accuracy versus modeling complexity into account, this paper proposes a general and accurate iron loss calculation method considering harmonics based on the Loss Surface(LS) hysteresis model and Finite Element Method(FEM). Compared with the previous triangular wave excitation, this paper uses the data under sinusoidal wave excitation to establish the LS model, which is more convenient for engineering application. A specimen is tested for different flux density with harmonics, the extensive results verify the modeling method. Due to a powerful hysteresis model, iron loss calculation can be realized by directly integration of hysteresis loops. A separated iron loss calculation package is developed, and it is combined with the commercial finite element software to compute the iron loss distribution. The method that combines the LS model and FEM is proved feasible by comparing the calculated iron loss with the measured one for the Epstein frame.