Electromagnetic design method for a TLSRG with application in ocean wave energy conversion

Abstract

The tubular linear switched reluctance machine (TLSRM) has shown potential for applications as generator in direct drive conversion of ocean wave energy devices. However, the design of this type of machine is a difficult task and there is no methodology to provide an explicit solution. This work aims to contribute for the solution of this problem with the proposal of a new procedure to design tubular linear switched reluctance generators (TLSRG). With the proposed procedure the TLSRG can be designed to develop a given linear force and to achieve better generation efficiency. The design is defined as a minimization problem where an optimization process is used to find the optimal solution for the dimensional parameters. Finite element method (FEM) analysis is applied to compute the relevant electromagnetic characteristics. The mathematical model of the generator conversion system is formulated to evaluate its dynamic performance. An H-Bridge asymmetric converter is adopted to control the energy flow in the generator. The electric currents in the generator phases are adjusted with a hysteresis controller. A TLSRG with a maximum mean force of 120 kN is designed by applying the proposed procedure, implemented in Matlab® and combined with MagNet® (FEM commercial software) to compute the electromagnetic characteristics of the machine. The system mathematical model is solved in Simulink®. The dynamic simulations are performed for a constant velocity of 1.3 m/s. For these operating conditions, the generator is characterised with an output power of 126.2 kW and an efficiency of 82.1%. The control proposed to drive the TLSRG is experimentally tested on a small-scale prototype. The experimental results show the effectiveness of the controller in keeping the phase current near the reference value.