Graham E. Town

Impedance-source networks for electric power conversion Part I: A topological review

Impedance networks cover the entire of electric power conversion from dc (converter, rectifier), ac (inverter), to phase and frequency conversion (ac-ac) in a wide range of applications. Various converter topologies have been reported in the literature to overcome the limitations and problems of the traditional voltage source, current source as well as various classical buck-boost, unidirectional, and bidirectional converter topologies. Proper implementation of the impedance-source network with appropriate switching configurations and topologies reduces the number of power conversion stages in the system power chain, which may improve the reliability and performance of the power system. The first part of this paper provides a comprehensive review of the various impedance-source-networks-based power converters and discusses the main topologies from an application point of view. This review paper is the first of its kind with the aim of providing a “one-stop” information source and a selection guide on impedance-source networks for power conversion for researchers, designers, and application engineers. A comprehensive review of various modeling, control, and modulation techniques for the impedance-source converters/inverters will be presented in Part II.

Impedance-Source Networks for Electric Power Conversion Part II: Review of Control and Modulation Techniques

Impedance-source networks cover the entire spectrum of electric power conversion applications (dc-dc, dc-ac, ac-dc, ac-ac) controlled and modulated by different modulation strategies to generate the desired dc or ac voltage and current at the output. A comprehensive review of various impedance-source-network-based power converters has been covered in a previous paper and main topologies were discussed from an application point of view. Now Part II provides a comprehensive review of the most popular control and modulation strategies for impedance-source network-based power converters/inverters. These methods are compared in terms of theoretical complexity and performance, when applied to the respective switching topologies. Further, this paper provides as a guide and quick reference for researchers and practicing engineers in deciding which control and modulation method to consider for an application in a given topology at a certain power level, switching frequency and demanded dynamic response.

Label-free biosensing with high sensitivity in dual-core microstructured polymer optical fibers.

We present experimentally feasible designs of a dual-core microstructured polymer optical fiber (mPOF), which can act as a highly sensitive, label-free, and selective biosensor. An immobilized antigen sensing layer on the walls of the holes in the mPOF provides the ability to selectively capture antibody biomolecules. The change of the layer thickness of biomolecules can then be detected as a change in the coupling length between the two cores. We compare mPOF structures with 1, 2, and 3 air-holes between the solid cores and show that the sensitivity increases with increasing distance between the cores. Numerical calculations indicate a record sensitivity up to 20 nm/nm (defined as the shift in the resonance wavelength per nm biolayer) at visible wavelengths, where the mPOF has low loss.

Refractive Index Sensing in an All-Solid Twin-Core Photonic Bandgap Fiber

We describe a highly sensitive refractive index sensor based on a twin-core coupler in an all-solid photonic bandgap guiding optical fiber. A single hole acts as a microfluidic channel for the analyte, which modifies the coupling between the cores, and avoids the need for selective filling. By operating in the bandgap guiding regime the proposed sensor is capable of measuring refractive indices around that of water, and because the analyte varies the coupling coefficient (i.e., instead of phase matching condition) the device is capable of both high sensitivity and a relatively large dynamic range.

Microstructured optical fiber refractive index sensor

We describe a dual-core microstructured optical fiber designed for refractive index sensing of fluids. We show that by using the exponential dependence of intercore coupling on analyte refractive index, both large range and high sensitivity can be achieved in the one device. We also show that selective filling of the microstructure with analyte can increase the device sensitivity by approximately 1 order of magnitude.

Y-Source Boost DC/DC Converter for Distributed Generation

This paper introduces a versatile Y-source boost dc/dc converter intended for distributed power generation, where high gain is often demanded. The proposed converter uses a Y-source impedance network realized with a tightly coupled three-winding inductor for high voltage boosting that is presently unmatched by existing impedance networks. The proposed converter also has more variables for tuning the required gain and, hence, more degrees of freedom for meeting design constraints. These capabilities have been demonstrated by mathematical derivation and experimental testing. For the experiments, a 300-W prototype has been built in the laboratory using silicon carbide devices for better efficiency. The prototype has been tested with a regulated power supply, before operating it with a high-temperature proton-exchange-membrane fuel cell. Results obtained confirm the practicality and performance of the proposed converter.

Direct Writing of Fiber Bragg Grating in Microstructured Polymer Optical Fiber

We report point-by-point laser direct writing of a 1520-nm fiber Bragg grating in a microstructured polymer optical fiber (mPOF). The mPOF is specially designed such that the microstructure does not obstruct the writing beam when properly aligned. A fourth-order grating is inscribed in the mPOF with only a 2.5-s writing time.

Simplification of millimeter-wave radio-over-fiber system employing heterodyning of uncorrelated optical carriers and self-homodyning of RF signal at the receiver

A simplified millimeter-wave (mm-wave) radio-over-fiber (RoF) system employing a combination of optical heterodyning in signal generation and radio frequency (RF) self-homodyning in data recovery process is proposed and demonstrated. Three variants of the system are considered in which two independent uncorrelated lasers with a frequency offset equal to the desired mm-wave carrier frequency are used to generate the transmitted signal. Uncorrelated phase noise in the resulting mm-wave signal after photodetection was overcome by using RF self-homodyning in the data recovery process. Theoretical analyses followed by experimental results and simulated characterizations confirm the systems performance. A key advantage of the system is that it avoids the need for high-speed electro-optic and electronic devices operating at the RF carrier frequency at both the central station and base stations.

Dual-wavelength DBR fiber laser

Stable continuous-wave lasing of two longitudinal modes of a distributed Bragg reflector fiber laser is reported. Intensity noise and coupling between the modes was characterized for both 0.8- and 0.2-nm mode separations

Improved modulation Technique for voltage fed quasi-Z-source DC/DC converter

A new shoot-through pulse width modulation (PWM) technique for voltage fed quasi-Z-source DC/DC converters is presented. One advantage of the technique is it minimizes switching losses in the converter by minimizing the number of switching commutations of the active devices in the intermediate H-bridge. The duration of the active and shoot-through states are independently controllable, allowing the shoot-through duty cycle to reach its maximum limit (Dst, max = 0.5), thus enabling a high voltage gain suitable for applications with renewable energy sources (fuel cells, photovoltaics) and other applications requiring a large voltage boost. In addition, the switches achieve zero voltage switching (ZVS) which reduce EMI and improves efficiency of the converter. A 500W prototype converter was implemented demonstrating improved performance with the new modulation technique.