Mgl Maurice Roes

Acoustic Energy Transfer: A Review

Acoustic energy transfer (AET) is a relatively new form of contactless energy transmission that uses sound waves to wirelessly convey energy. In contrast to inductive coupling, it is suited for energy transmission over distances that are large in comparison to the transmitter and receiver dimensions. The frequencies that are used are low, minimizing losses and keeping the electronics simple. This review summarizes the work done on AET by various researchers.

Contactless energy transfer through air by means of ultrasound

An alternative approach to the wireless transfer of energy is proposed, employing acoustic waves in air. Unlike conventional methods, acoustic energy transfer is able to achieve energy transfer at high efficiencies over distances that are large in comparison to the dimensions of the transmitter and the receiver. This paper gives an overview of the principle and explains the different loss mechanisms that come into play. A theoretically limit on the achievable efficiency is calculated. It exceeds that of a comparable inductively coupled system by an order of magnitude. First preliminary measurements indicate that AET is feasible, although the measured efficiency is lower than the predicted theoretical limit.

Disturbance observer-based control of a dual output LLC converter for solid state lighting applications

Feedback sensor isolation is often an expensive necessity in power converters, for reasons of safety and electromagnetic compatibility. A disturbance observer-based control strategy for a dual-output resonant converter is proposed to overcome this problem. Current control of two LED loads is achieved through estimation rather than measurement. Robustness against temperature changes, which have significant impact on the behavior of the LEDs, is achieved through estimation of offsets in the forward voltages of the LED strings. The power converter and LEDs are modeled accurately to obtain a good estimation accuracy. The whole implementation is steered toward a low-cost solution.

The effect of reflections on the performance of an acoustic energy transfer system

The performance of an acoustic energy transfer (AET) system, defined as the ratio of electrical output to input power, is affected to a large extent by reflections. Their effect is examined in this paper. A finite element model is created to model reflections in a typical AET system, of which the simulation results are compared to measurements. The results show that modelling reflections is possible, but the transducer model is extremely critical for accurate prediction. The effect of the addition of horns to the transducers was examined by means of both experiments and finite element modelling. Although the experiments showed that the horns did not reduce the reflections, it was found that the decline in performance as a function of distance is significantly lower. Moreover, the energy transfer efficiency was found to be much higher than in the experiments with the hornless transducers.

Continuous control set space vector modulation for the 3x3 direct matrix converter

In this paper, a new method for Space Vector Modulation (SVM) for the 3×3 direct matrix converter is proposed. This method is based on a combination of Model Predictive Control (MPC) and SVM, also denoted as Continuous Control Set MPC. The proposed method uses all available vectors, and allows the converter to produce waveforms of high quality at both power ports, also when subjected to unbalanced or distorted waveforms. The mathematical derivation of the proposed method is explained, and the operation illustrated by means of simulation experiments in open loop. The paper finishes with conclusions and prospects for further development and application of the method.

Design of stepped exponential horns for acoustic energy transfer systems

Stepped exponential horns are proposed as a measure of acoustic impedance adaptation in an acoustic energy transfer (AET) system. Resonances due to impedance mismatches in the horn are used to obtain a maximal power throughput at a single frequency. Finite element (FE) models are used for optimisation of the horn parameters. Although experimental results do not match particularly well with simulations, the results still look promising. The horns boost the power transfer and efficiency for greater distances, which was one of the major problems in prior AET systems. The measured output power increased by a factor 3.1 and the efficiency by a factor 7.5 at a distance of 10cm between the transmitter and the receiver. Discrepancies between the model and the measurements are expected to be largely due to variations in transducer parameters. The transducer losses were measured separately by means of impedance measurements in vacuum for improvement of the FE model.

Grid-connected converters with voltage support using only local measurements

This paper considers a single-phase grid-connected converter in the presence of non-linear loads. A local voltage support strategy is proposed to compensate the harmonics caused by the loads. This is an added feature implemented in parallel with a conventional current control method, and distinctively, it does not need measurements of the grid or load current. The converter output current consists of two components: a part at the fundamental frequency for power injection, and a part to compensate the harmonics introduced by the non-linear loads. As a result, the grid current harmonic distortion is minimized and the local voltage quality is enhanced. Simulation and experiments validate the effectiveness of the proposed voltage support strategy.

Contactless energy transfer: Magnetics and acoustics

Introduction Contactless energy transfer (CET) is used in many applications where a physical connection between a device and a power source is impractical or even impossible.

Phased transducer array for acoustic energy harvesting inside an MRI machine

In this study, an array of piezoelectric speakers is used to focus acoustic energy on a single transducer that acts as a harvester. The transmitting transducers are located along a curve that fits inside the magnetic resonance interferometer (MRI) torus interior. The numerical results for the pressure fields generated by circular-shaped and parabolic-shaped phased transducer arrays are compared, and the optimal locations for the acoustic energy harvester are determined for both shapes. In a series of experiments, the pressure on the axis of a single standalone speaker and on the axis of the non-phased parabolic array was measured to verify the numerical model. The experimentally determined location of the pressure peak in front of the parabolic-shaped array is predicted numerically with 4% accuracy. An acoustic energy harvester is placed at the location of the pressure peak, and the optimal resistive load value is determined experimentally for maximum output power. Approximately 1 μW of electric power is dissipated on the load when 10 mW is consumed by the source array at its second resonant frequency of 16 kHz, resulting in the electric input-to-output efficiency of 10-4.