Dara L. O'Sullivan

Power-Factor-Corrected Single-Stage Inductive Charger for Electric Vehicle Batteries

A novel power-factor-corrected single-stage alternating current/direct current converter for inductive charging of electric vehicle batteries is introduced. The resonant converter uses the current-source characteristic of the series-parallel topology to provide power-factor correction over a wide output power range from zero to full load. Some design guidelines for this converter are outlined. An approximate small-signal model of the converter is also presented. Experimental results verify the operation of the new converter

Microfabricated inductors for 20 MHz Dc-Dc converters

This paper presents the design and measured results for micro-fabricated inductors suitable for use in high frequency (> 10 MHz), low power (1 -2 W) dc-dc converters. The design has focused on maximizing inductor efficiency for a given converter specification. Inductors in the range of 100 nH to 300 nH have been fabricated and tested. The small signal measurements show a relatively flat inductance profile, with a 10% drop in inductance at 30 MHz. Inductance vs. dc bias current measurements show less than 15% decrease in inductance at 500 mA current. The performance of the micro-inductors have also been compared to a conventional wire-wound inductor in a 20 MHz dc-dc converter. The converter efficiency is shown to be approximately 4% lower when the micro-inductor is used compared to the when the wire- wound inductor is used. The peak efficiency of the micro-inductor in the converter is estimated to be approximately 93%.

A Family of Single-Stage Resonant AC/DC Converters With PFC

A family of novel, single-stage, isolated, resonant-based AC/DC power supply circuits with inherently high power factor is presented in this paper. The three topologies in the family are transformer isolated; they contain a bulk energy storage capacitor to enable output voltage holdup, and they also contain a resonant circuit in which a resonant capacitor is connected directly across the mains input rectifier. The presence of this resonant circuit results in AC line current being drawn over much of the line cycle, as well as in soft switching of the power devices. The rectifier-compensated fundamental-mode approximation (RCFMA) method is used to provide an accurate yet simple analysis of the circuit. Experimental results for closed-loop operation of two of the topologies are also presented. This family of single-stage, high-power-factor converters provides for simple control and high-frequency operation, due to the resonant configuration of the power circuit, without the excessive conduction loss of fully resonant techniques.

Parasitic inductance effect on switching losses for a high frequency Dc-Dc converter

This work examines the impact of packaging parasitics on the efficiency of a synchronous DC-DC buck converter. An analytical model of the losses in the converter is developed and this is compared to practical results at switching frequencies in the range of 1-2 MHz. The effect that the packaging parasitic inductance has on efficiency is highlighted by predicting the expected losses from a converter with optimised packaging parasitics.

Generator Selection and Comparative Performance in Offshore Oscillating Water Column Ocean Wave Energy Converters

In the field of wind energy, electrical generator solutions have converged on a small number of technologies for specific technical and economic reasons. This paper investigates whether a similar rationale exists within the field of oscillating water column, wave energy converters. The suitability or otherwise of the various generator options in the offshore marine environment is examined in detail. Each generator configuration is then modeled and the annual energy output for a typical wave climate assessed with consideration being given to the impact of speed control on the energy output. Finally, some conclusions are drawn regarding the relative suitability of the different generator options.

Impact of a Medium-Size Wave Farm on Grids of Different Strength Levels

Power fluctuations generated by most oscillating wave energy converters may have a negative impact on the power quality of the local grid to which the wave farms will be connected. Hence, assessing their impact is an important step in the selection process of a suitable deployment location. However, site-specific grid impact assessment studies are relatively time-consuming and require a high level of detail on the local network. Both of these constraints mean that grid impact studies are usually not performed in the preliminary stages of the site selection process, despite the extremely negative consequences resulting from poor power quality. This paper details a comprehensive study based on a relatively typical wave farm design connected to networks of different strength levels. The study was performed using experimental electrical power time series of an oscillating water column (OWC) device generated under the framework of the European FP7 project “CORES”. Simulations were performed using DIgSILENT power system simulator “PowerFactory”.

Supercapacitor Testing for Power Smoothing in a Variable Speed Offshore Wave Energy Converter

This paper investigates power smoothing in a full-scale offshore oscillating water column (OWC) wave energy converter (WEC) by integrating supercapacitors (SCs) with the inertia of a Wells turbine controlled at variable speed. With the simulation package Simulink developed by MathWorks, a model is developed for the WEC system utilizing sea-state data and an SC system is sized to smooth and reduce the grid peak power for a 570-kW (peak) system. Long component lifetime is a requirement for offshore WECs. Hence, a computer-controlled test rig has been built to validate SC lifetimes to manufacturers specifications and determine application lifetime. Cycle testing is carried out on individual SCs at room temperature and also at rated temperature utilizing a thermal chamber and equipment interconnected by the general purpose interface bus (GPIB) and programmed by the MathWorks developed computing environment Matlab. Application testing is carried out using time-compressed scaled-power profiles from the model to allow a comparison of lifetime degradation. The SCs under standard testing at ambient and rated temperature, and application testing at ambient temperature, have undergone approximately 4 000 000, 700 000, and 500 000 cycles, respectively. The results demonstrate cycle lifetimes in excess of manufacturer specifications.

Efficiency Optimization in Low Inertia Wells Turbine-Oscillating Water Column Devices

The Wells turbine is a bidirectional air turbine which operates efficiently over a restricted range of air flow. The optimization of its efficiency requires control of rotational velocity in order to maintain the ratio between airflow and tip speed within the high efficiency range. This paper introduces two generator control strategies that optimize the power take-off efficiency for low inertia turbine systems in which instantaneous control of the turbine air flow to tip speed ratio is a realistic goal. The first control strategy requires measurement of turbine rotational speed and air chamber pressure, and the second strategy removes the requirement for air pressure measurement. The implementation issues associated with this level of control are examined and the simulation results are validated in an experimental test rig.

A 20 MHz 200-500 mA Monolithic Buck Converter for RF Applications

In an RF system power amplifiers (PAs) typically consume the most power. This paper presents a buck converter design optimised for a wideband code division multiple access (WCDMA) PA. The design approach taken focuses on the optimization of switch sizing based on the overall power losses of the system including the output inductor losses. The converter is optimised for 20 MHz switching and output currents in the range of 200-500 mA. Experimented results are presented on the fabricated converter, with a maximum measured efficiency of 82%.

Dimensioning the equipment of a wave farm: Energy storage and cables

Still largely untapped, wave energy is particularly abundant and may represent an important share in the energy mix of many countries in the future. However, the power fluctuations generated by most wave energy converters with little to no storage means or without suitable control strategies may deteriorate the power quality of the local network to which wave farms will be connected. They may in particular generate an excessive level of flicker. The minimum amount of storage required for a wave farm to be grid compliant with respect to typical flicker requirements was investigated and is presented in the first part of this study. Besides giving rise to power quality issues, the rapid and high amplitude power peaks generated by wave devices may also render more complex the optimal dimensioning of the wave farm electrical components, whose cost is highly dependent on their power rating. This statement applies also to submarine cables, as the maximum current flowing potentially through them seems to be no longer a relevant criterion for determining their optimal current rating. Hence, the second part of the presented study focuses on the minimum current rating required from a submarine cable to avoid its thermal overloading.