Energy regeneration and control in vehicle suspensions

• Main Author: Pires, Luisa Maria Barradas Pereira Martins
• Published: University of Cambridge 2014
• Subjects: 620
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648496

In this dissertation we propose a regenerative system that can efficiently extract energy from the suspension while improving the overall dynamical performance of the vehicle. It is shown that typical regenerative devices comprising of a linear-to-rotational element driving a permanent-magnet generator can be simply modelled as a dissipative admittance in parallel with an inerter. This configuration allows the performance benefits of inerters in vehicle suspensions to be exploited. The energy recovery circuitry is modelled as an electrical load at the generator's terminals. We propose the novel idea of designing this electrical load with the dual purpose of extracting energy from the suspension as well as acting as a passive controller designed to enhance vehicle performance. It is shown that the losses in the generator are negligible if the real-part of the electrical load is made considerably larger than the internal resistance of the permanent-magnet generator for a given frequency range. We demonstrate that the inertance, damping coefficient and energy efficiency are fundamentally related for typical regenerative devices. 'vVe then investigate how to optimise the passive electrical load at the generator's terminals for vehicle performance. 'vVe show that although the real-part constraint decreases the optimum achievable performance values for vibration isolation and grip, the added dynamical complexity leads to performance benefits when compared to typical parallel spring-damper struts. We propose to have a single dissipative element and provide the controller dynamics through a lossless transformerless coupling. Transformerless conditions are investigated for lossless two-ports. 'vVe show that paramountcy is a sufficient but not necessary condition for transformerless synthesis. We also consider the design of ladder structures when the real-part constraint is imposed in the electrical load. In this dissertation we demonstrate the feasibility of the design methodology through the design of a regenerative device for a passenger vehicle. A prototype of the device is built and tested and the deviations from ideal behaviour are found to be due to nonlinear effects such as friction and backlash. Overall a good overall agreement between the ideal and experimental admittances is obtained. Finally, we show that brushless DC motors can be used as generators, thus benefiting from their topological advantages, if they are supplied with additional power-electronics. We also propose a design of the power electronics for energy recovery.