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.

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.

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.

This paper presents an identification algorithm of the scalar Preisach model by using a set of symmetric minor hysteresis loops and suggests an improved vector Preisach model to describe the vector and anisotropic hysteresis behavior of a non-oriented (NO) electrical steel sheet (ESS) under rotating magnetic fields. Symmetric minor hysteresis loop is quite easy measured, so an identification algorithm based on symmetric minor hysteresis loop instead of first-order reverse curve is presented in this paper. The vector Preisach model employs a nonlinear coefficient, which is a function of magnitude and a direction of magnetic flux density, to describe the anisotropic property of the NO ESS and increases the numerical accuracy. The validity of the suggested vector Preisach model is investigated through comparisons with the experimental results under various magnetic field conditions.

For PWM-fed motors, many harmonics are induced in the magnetic field by excitations, which makes accurate iron loss calculation more difficult. This paper presents a general iron loss calculation method based on a dynamic hysteresis model and finite element analysis. The dynamic hysteresis model is developed by introducing the derivative of the magnetic field induction, which can precisely describe the dynamic hysteresis effects of frequency and harmonics. The measured fundamental magnetization curve is introduced to improve the accuracy. To examine the suitability of the hysteresis model, an Epstein frame and a ring core are both utilized to build the hysteresis model and calculate the iron loss. The results based on the ring core show better performance in this paper. An iron loss calculation package based on the built hysteresis model is developed and can be directly applied in the post-processing of finite element analysis. The proposed iron loss calculation method is applied to a PWM-fed IPMSM. The hysteresis distortion and iron loss distribution inside the PWM-fed motor can be analyzed in detail. The comparison of measured and calculated iron loss over a wide range of operating frequencies proves the feasibility and accuracy of the proposed method.