Design Optimization of a Direct-Drive Electrically Excited Synchronous Generator for Tidal Wave Energy

Abstract

In the field of marine renewable energies, the extraction of marine currents by the use of tidal current turbines has led to many studies. In contrast to offshore wind turbines, the mass minimization is not necessarily the most important criterion. In that case, Direct-Drive Electrically Excited Synchronous Generators (EESG) can be an interesting solution in a context where the permanent magnet market is more and more stressed. In the particular case of a tidal turbine, the electric generator operates at variable torque and speed all the time. Its sizing must therefore take into account the control strategy and check that all the constraints are respected during the working cycle, particularly the thermal one because its permanent regime is never reached. There is no solution today that can completely solve such a sizing problem. The paper presents a specific solution. In particular, we will see that the method presented allows an avoidance of an oversizing of the generator compared to conventional methods while finding the optimal control strategy. Thus, the design optimization of an EESG is conducted considering the variable torque and speed profiles related to marine currents. The analytical model used in the paper is presented at first. In a second step, the innovative and original method that allows solving at the same time the design optimization and the control strategy (dq stator currents and rotor current) are presented. It shows how it is possible to minimize both the lost energy during the working cycle and the mass while fulfilling all the constraints (especially the thermal constraint with its transient temperature response) and keeping a reduced computation time. The case of a 2 MW tidal wave turbine is chosen to illustrate this study. Finally, the optimal design selected is validated by a 2D magnetic Finite Element Analysis (FEA).

Design and Optimization of a Five-Phase Permanent Magnet Synchronous Machine Exploiting the Fundamental and Third Harmonic

“…The airgap flux density created by the magnets is represented in Figure 1b. Under each pole, its magnitude is obtained from Ampere's law [22]. It can be written as a Fourier series, where each harmonic component, B h f (θ, θ r ) , of odd rank, h, is expressed as follows:…”

“…We assume here a two-level back-to-back voltage source converter. In this case, the voltage limit must not exceed half the DC bus voltage, U DC [22,26].…”

“…The magnitude of the flux density must be limited in each magnetic part of the machine [17,22]. The flux density in the stator yoke (B sym ), the stator teeth (B stm ), and the rotor yoke (B rym ) is limited to B sat with the choice of B sat = 1.6 T.…”

Optimum design of slot and magnet structure of permanent magnet synchronous generator with teaching‐learning‐studying‐based optimization

“…As a result of the optimization, an improvement was made at about 18% in mass. 19 In another study, magnet pole arc, magnet thickness, air-gap length, slot opening and stator inner radius parameters of the PMSM were determined as optimization parameters. High efficiency, high torque, low cogging torque, and low total harmonic distortion were determined as objective functions.…”

“…Minimum energy loss and minimum mass were determined as objective functions. As a result of the optimization, an improvement was made at about 18% in mass 19 . In another study, magnet pole arc, magnet thickness, air‐gap length, slot opening and stator inner radius parameters of the PMSM were determined as optimization parameters.…”