I-Hsien Lin

Development of a Wave Energy Converter Using a Two Chamber Oscillating Water Column

This paper presents the development and system analysis of segmented oscillating water columns (OWC) for wave energy conversion based on the wave conditions around Taiwan. The OWC chambers are designed for a target site and the power converted by each component (i.e., the chambers, turbine and generator) in the power chain is analyzed so that the overall power output and efficiency can be calculated. The characteristic match between the turbine and the generator is also discussed. The developed OWC is side-mounted and this allows the waves to penetrate and continue propagating after transferring power to the chambers. The OWC consists of two adjacent chambers which are aligned in the direction of the wave propagation. Each chamber has one Savonius turbine on top to convert the chamber power into mechanical shaft power. The two turbines are connected in-line and the individual chambers transfer power to the turbines with a phase difference, so that the power output can be smoothed. A brushless permanent-magnet generator is used to convert the turbine output power into electricity. Experiments are conducted on a scaled-down model in a wave tank to evaluate the performance and the results verify the design. It is also found that the successive chamber should have a different design to the first one as it suffers slight wave attenuation.

Magnetic Circuit Modeling of Brushless Doubly-Fed Machines With Induction and Reluctance Rotors

This paper presents a magnetic circuit modeling (MCM) technique for analysis of the brushless doubly-fed machine (BDFM). Two rotor types are considered: the induction type and the reluctance type. The flux density in both the stator and rotor can be calculated by the developed MCM. This is particularly beneficial to the BDFM with the induction rotor since the generated rotor currents may saturate the rotor or stator and this is difficult to foresee at the design stage due to the complex flux patterns in the machine. A coupling factor is proposed to determine the flux coupling between the stator and rotor teeth of the induction type of BDFM. Saturation is also considered in the MCM. Finite element analysis is used to verify the analytical results.

Design of Brushless Doubly-Fed Machines Based on Magnetic Circuit Modeling

This paper proposes a magnetic circuit model (MCM) for the design of a brushless doubly-fed machine (BDFM). The BDFM possesses advantages in terms of high reliability and reduced gearbox stages, and it requires a fractionally-rated power converter. This makes it suitable for utilization in offshore wind turbines. It is difficult for conventional design methods to calculate the flux in the stator because the two sets of stator windings, which have different pole number, form a complex flux pattern which is not easily determined using common analytical approaches. However, it is advantageous to predict the flux density in the teeth and air-gap at the initial design stage for sizing purposes without recourse finite element analysis. Therefore a magnetic circuit model is developed in this paper to calculate the flux density. A BDFM is used as a case study with FEA validation.

Design and Analysis of High Temperature Superconducting Generator for Offshore Wind Turbines

This paper presents the magnetic analysis and design of a high temperature superconducting generator (HTSG) for offshore wind turbines. High temperature superconducting (HTS) tapes form the rotor winding to produce a strong magnetic field when excited. This allows the generator to achieve high torque density with a compact size and light weight. Gearboxes can be removed for direct-drive operation to improve the reliability and efficiency of the offshore wind turbine. The lightweight and compact generator also helps reduce the construction cost. However, the high cost of HTS tapes should be considered and the reduction of the amount HTS material used should be carefully assessed. An HTSG is designed and analyzed for a 5 MW offshore wind turbine. The analysis involves several factors that affect the amount of HTS material utilized. The weight and volume of the HTSG is also considered in the design and analysis. Finite element analysis is employed for simulation of the HTSGs.

An Analytical Method Combining Equivalent Circuit and Magnetic Circuit for BDFRG

This paper presents an analytical method that integrates the equivalent circuit (EC) and magnetic circuit (MC) in order to analyze and design a brushless doubly fed reluctance generator (BDFRG). The proposed method is capable of evaluating the BDFRG performance at the design stage because the terminal voltage can be predicted through the MC and the torque can be calculated from the EC. The MC is used to calculate the air gap flux density so that the flux linkage can be further obtained for the calculation of the machine performance using the EC and a set of particular operating conditions. The integration of the EC and MC provides a rapid analysis for a direct connection between the physical dimensions and the machine performances, including torque, mechanical power, electric power, and efficiency. The proposed analytical method is applied to two BDFRG designs. One is a manufactured prototype. Finite element analysis and experiments are used to verify the analytical results.

Improved Accuracy for Performance Evaluation of Synchronous Reluctance Motor

This paper develops an approach that is capable of accurately predicting the performance of synchronous reluctance motors (SynRMs). The SynRMs receive increasing attention and have been used in many industrial applications. The 2-D finite element analysis (FEA) is usually considered to be competent for design and analysis of SynRMs. However, the power factor of SynRMs is likely to be considerably overestimated. This would then lead to an underestimation of current required and cause problems for the design of electronic drivers. Compensation should be made to improve the accuracy of the analysis for SynRMs although there does not seem to be a solution put forward so far. The research in this paper shows that the exclusion of end turn leakage inductances in 2-D analysis is a key factor to cause such a significant difference. To resolve this problem, this paper analytically calculates the end turn leakage inductance, which is then incorporated into the 2-D FEA. The developed method is found to agree well with the experimental results, and it significantly improves the design accuracy and efficiency using only the 2-D FEA.

Improved accuracy for performance prediction of synchronous reluctance motor by incorporating end turn inductance in 2-D FEM

This paper proposes an analysis to include end turn inductance in the 2-D FEA for synchronous reluctance motor (SynRM). The developed method can rapidly obtain accurate results without the need of 3-D simulation. It is also concluded that for distributed winding machines, end turns should be considered in the design stage to avoid overestimating the motor performance. In the full paper, a complete study with different inductance calculations and two ratings of SynRM will be presented as the guideline of accurate analysis of SynRM. This would be beneficial to machine designers .

Comparison of brushless induction and reluctance doubly-fed machines

This paper compares alternative rotor designs for the brushless doubly-fed machine (BDFM) using finite element analysis to estimate their operating ranges and characteristics. Two types of rotors are considered: induction (with cage, nested layer, double layer and isolated layer) and reluctance rotors, so a total of five rotors are investigated. Grid-connected converters are connected to the control windings to give a variable voltage and frequency control, with the power windings connected to the grid for constant voltage and frequency connection. The machine then can operate to in a similar manner to the doubly fed induction machine as used in many wind turbines. The results show that the induction rotors benefit from simpler converter topology and smoother power output. The isolated layer of induction rotor gives smallest torque ripple.

Dimension effect on a grid-connected brushless doubly-fed reluctance generator

The brushless doubly-fed reluctance generator (BDFRG) is an excellent candidate for renewable energy applications such as wind turbine generators. It requires a converter with only a fractional rating to operate over a designated speed range and thus the cost of the power electronics can be reduced. This paper discusses a grid-connected BDFRG and the effects of varying the machine dimensions on the performance. If the machine is too small then it may suffer from saturation problems leading to low efficiency and also the reluctance ratio in the rotor may be poor. This means that the BDFRG may not be suitable for generating systems under a certain power rating. A power generation estimation process (PEP) for the control and power windings of the BDFRG is introduced. The proposed PEP is capable of calculating and determining: (a) the grid voltage; (b) the alignment between the rotor position and current excitation and (c) the appropriate voltage phase difference between the control and grid windings. Two scaled designs are compared and dimensioning effects are demonstrated. Finally, an experimental study is carried out to verify the simulation.

A design approach integrating the magnetic circuit and electric circuit models for BDFIM

A design process for brushless doubly-fed induction machine (BDFIM) is presented in this paper. The approach employs the magnetic circuit model (MCM) combining an equivalent circuit model (ECM). The MCM is first accurately constructed for the BDFIM. Through this model, the dimension of the BDFIM can be rapidly calculated. The machine saturation is taken into account in the MCM, and the machine parameters, such as flux density are calculated without time-consuming finite element analysis (FEA). A graphical user interface is developed for the MCM for better user friendliness. The flux linkage obtained in the MCM is further used to determine the magnetizing inductance, which can be passed to the ECM for calculation of machine characteristics. The developed method is validated experimentally.