Design and optimisation of constrained electromagnetic energy harvesting devices

This thesis investigates the design and optimisation of constrained electromagnetic energy harvesters. It provides optimal design guidelines for constrained electromagnetic energy harvesters under harmonic and random vibrations. To find the characteristics of the vibration source, for instance vertical motion of a boat, the spectrum of the excitation amplitude should be obtained. Two Kalman filter based methods are proposed to overcome the difficulties of calculating displacement from measured acceleration. Analytical models describing the dynamics of linear and rotational electromagnetic energy harvesters are developed. These models are used to formulate a set of design rules for constrained linear and rotational energy harvesters subjected to a given sinusoidal excitation. For the sake of comparison and based on the electromechanical coupling coefficient of the systems, the maximum output power and the corresponding efficiency of linear and rotational harvesters are derived in a unified form. It is shown that under certain condition, rotational systems have greater capabilities in transferring energy to the load resistance and hence obtaining higher efficiency than linear systems. Also, the performance of a designed rotational harvester in response to broadband and band-limited random vibrations is evaluated and an optimum design process is presented for maximizing the output power under these conditions. It is furthermore shown that the profile of the spectral density of the measured acceleration signal of a typical boat can be approximated by a Cauchy distribution which is used to calculate the extracted power extracted by the proposed energy harvester in real conditions. In order to increase the operational bandwidth of rotational energy harvesters, subjected to time-varying frequency vibrations, a variable moment of inertia mechanism is proposed to adaptively tune the resonance frequency of harvester to match the excitation frequency. Also, the effects of combining the variable moment of inertia mechanism and adjusting the load resistance to increase the operational bandwidth of the system for constrained and unconstrained applications are studied. Finally, a ball screw based prototype is manufactured and the experimental results of its testing are presented which confirm the validity of the design and the derived dynamic equations of the system

An inertial coupled marine power generator for small boats

This paper proposes a device to harvest energy from the vertical motion of small boats and yachts. The device comprises a sprung mass coupled to an electrical generator through a ball screw. The mathematical equations describing the dynamics of the system are derived. The equations are used to determine the optimum device parameters, namely its mass, spring constant, ball screw lead, within practical constraints. Simulation results are presented to determine the maximum power that can be generated and the optimum load resistance as a function of boat vibration frequency

A novel Kalman filter based technique for calculating the time history of vertical displacement of a boat from measured acceleration

This is the final version of the article. Available from Science and Engineering Publishing Company via the link in this record.Accelerometers are used to measure velocity and displacement in many applications such as ship motion, monitoring of civil and mechanical structure, seismology and machine condition monitoring. However, using direct numerical integration to calculate velocity and displacement from the acceleration signal is known to suffer from low frequency noise amplification and wind-up. In this paper, a Kalman filter based method is proposed for calculating displacement from measured acceleration. Integration wind-up is eliminated by incorporating an additional state variable, namely the integral of the displacement whose "measured" value is assumed to be equal to the known average value of the displacement. In many applications, such as those in marine environment, this average value can be assumed to be constant, usually conveniently assigned to be zero if non-linear behaviour and permanent deformations are deemed negligible. The paper describes the technique and investigates its performance under different conditions of amplitude and frequency of vibrations and sampling rate and validates it by conducting two laboratory experiments. In the first experiment the displacement of a small shaker is calculated from a relatively high frequency (tens of Hz) acceleration signal sampled at 1 kHz with a resolution of 1 g. The calculated displacement of the shaker is found to agree well with that measured using a high resolution laser. In the second experiment, the proposed method is applied to the calculation of the vertical displacement of a boat from a low frequency (less than 1 Hz) acceleration signal sampled at 5 Hz and a resolution of 0.01g. An experimental set up designed to mimic typical motion of a boat is used to validate the results. Although the method explained in this paper is used to calculate the vertical displacement of a boat, it can be applied for calculating the displacement in a wide range of applications with reciprocating movement.The authors wish to thank Mr Mike Russell for his financial support and for collecting boat motion data. They also wish to thank Mr L. Auboin for his help with collecting boat motion data and conducting simulated boat motion lab experiments. Thanks are also due to Dr Jamil Renno for facilitating the high-frequency vibration experiments

Probabilistic modelling of a rotational energy harvester

Relatively recently, many researchers in the field of energy harvesting have focused on the concept of harvesting electrical energy from relatively large-amplitude, low-frequency vibrations (such as the movement caused by walking motion or ocean waves). This has led to the development of ‘rotational energy harvesters’ which, through the use of a rackand-pinion or a ball-screw, are able to convert low-frequency translational motion into high-frequency rotational motion. A disadvantage of many rotational energy harvesters is that, as a result of friction effects in the motion transfer mechanism, they can exhibit large parasitic losses. This results in nonlinear behaviour, which can be difficult to predict using physical-law-based models. In the current article a rotational energy harvester is built and, through using experimental data in combination with a Bayesian approach to system identification, is modelled in a probabilistic manner. It is then shown that the model can be used to make predictions which are both accurate and robust against modelling uncertainties

An inertial coupled marine power generator for small boats

This paper proposes a device to harvest energy from the vertical motion of small boats and yachts. The device comprises a sprung mass coupled to an electrical generator through a ball screw. The mathematical equations describing the dynamics of the system are derived. The equations are used to determine the optimum device parameters, namely its mass, spring constant, ball screw lead, within practical constraints. Simulation results are presented to determine the maximum power that can be generated and the optimum load resistance as a function of boat vibration frequency

Design guidelines for optimization of an inertially coupled energy harvesting generator from boat motion

This paper proposes a set of guideline for optimum design of an energy harvester from the vertical motion of small boats and yachts. The device comprises a sprung mass coupled to an electrical generator using a ball screw. The mathematical equations describing the dynamics of the system are derived. The equations are used as a basis for determining the optimum device parameters, namely, its mass, spring stiffness, ball screw lead, and load resistance. The process of design optimization is presented as an integrated part of the design guidelines, to maximize the system output power and efficiency within practical constraints. In addition, the experimental results of testing a ball screw based energy harvester are presented. The main purpose of conducting the experiment is to observe the performance of the system and validate the dynamic equations of the system. The experimental results that investigate the frequency response, relation between base and relative displacements and the output power profile are in reasonable agreement with the theoretical calculations