Application of linear switched reluctance actuator in active suspension systems

Abstract

Electromagnetic active suspension system is attracting more and more attention due to recent advances in motor design, power electronics and modern control method. Compared to the hydraulic active suspension system, it is more energy-efficient, and has a faster dynamic response. In this thesis, a novel configuration of linear switched reluctance actuator (LSRA) is proposed for the application in active suspension system. The robust construction, low manufacturing and maintenance cost, less thermal problem, good fault tolerance capability and high reliability in harsh environments make LSRA attractive alternative to permanent magnet actuator. In order to determine the requirements on actuator design, the effects of suspension parameters on system characteristics are analyzed by the frequency response Bode plots method. A Linear Quadratic Regulator (LQR) controller is developed and simulated with the quarter-vehicle model to obtain the optimal force requirement on LSRA. By considering the requirements and constraints, a novel configuration of LSRA that comprises of four double-sided modules is proposed. The whole design procedure, ranging from the determination of basic actuator parameters to the calculation of flux linkage and force characteristics, is demonstrated in this thesis. The accuracy of the analytical design is then verified by the finite element method (FEM). Besides, the longitudinal and transversal end effects of double-sided LSRA are evaluated by analyzing the sensitivities of translator position and excitation current. To improve the performance of designed actuator, a multi-objective optimization method to obtain higher average force, reduced force ripple and higher force density is proposed in this thesis. Some practical constraints are taken into consideration in the optimization procedure. The effects of stator and translator pole width on the three optimization criteria and the actuator volume are analyzed. Based on the optimized specification, a prototype of the proposed LSRA was fabricated. The flux linkage and force characteristics were measured to verify the theoretical design. Finally, an improved direct instantaneous force control (DIFC) scheme for four-quadrant operation of the proposed LSRA is developed. The controller incorporates adaptive force distribution function (FDF), instantaneous force estimation, hysteresis force controller and on-line determination of switching positions. By introducing the on-line estimated force of outgoing phase to FDF, the force demand of incoming phase is adaptively adjusted. Hence, the force ripple can be minimized over a wider range of switching positions. On the other hand, the operational efficiency is improved by on-line optimizing the switching positions according to the force demand. The simulation and experimental results demonstrate the effectiveness of the proposed control scheme.