Data converters for communication systems

Data converters are playing an ever increasingly important role in digital communication channels. As VLSI technologies scale, more of the signal processing is performed in the digital domain, making superior converter design critical. Attributes of various modern analog-to-digital converters such as flash and ΣΔ are described     

Recent research on photovoltaic solar energy converters

This paper contains a review of recent work on photovoltaic cells fabricated from semiconductors other than silicon; the effects of radiation on silicon n/p and p/n cells, and gallium arsenide p/n cells; and thin film photovoltaic cells.     

High-speed data converters for communication systems

Discusses the ever increasing demands on IC specifications, namely speed and resolution, We will see that often more than 14 bits and several hundreds of MHz are required, In addition, many applications impose continuous reductions in power consumption. As a result, market challenges favor research on high speed data converters, In turn, the results achieved lead to new architectural solutions which create new needs, This paper analyses this process and discusses recent circuit solutions suitable for meeting key system specifications     

刍动化测试解决之道——构建以软件为核心的模块化系统

如今,伴随着测试需求的多样化和复杂化,软件定义的仪器系统成为测试测量行业最重要的发展趋势和主流技术。软件定义的模块化系统不仅可以帮助用户在提高效率的同时降低测试成本,还能满足未来不断升级扩展的需要。     

通用光伏系统测试平台的设计

为了统一光伏系统测试方案,避免项目管理混乱和不必要的重复设计等问题,提出了一种通用光伏系统测试平台,制定了光伏系统与PC软件端数据交互协议,实现了用来获取常用光伏系统测试参数及具有良好扩张性的通用用户监控界面。测试结果表明,该测试平台很好地解决了上述问题,从而缩短了系统设计周期。     

The influence of monolithic series connection on the efficiency ofGaAs photovoltaic converters for monochromatic illumination

This paper presents a theoretical study of the performance and optimization of monolithically series connected GaAs photovoltaic converters under homogeneous monochromatic illumination. The effects of base resistance, perimeter recombination, and isolation trench optical losses on device efficiency are especially highlighted. All the calculations are made for values of the number of individual photovoltaic converters connected in series, n, of 1 (such is the case of a conventional GaAs photovoltaic converter without monolithic connection) 2, 3, and 6. The results show that the losses in monolithic connection can be minimized by means of an increase in device area together with the inclusion of a highly doped lateral conduction layer, and that monolithic connection does not lead to a greater immunity from high series resistance relative to a conventional photovoltaic converter (as stated in literature). The maximum efficiencies predicted are 60.2, 58.9, 58.5, and 57.5% for n=1, 2, 3, and 6, respectively, for an illumination power density of between 10 and 20 W/cm² and a wavelength of 830 nm. Nevertheless, if a dc-dc converter is considered to boost the voltage of an n=1 GaAs photovoltaic converter (with losses associated to this circuit usually of 20%), its maximum efficiency drops to 48.2%     

SPICE macromodeling of photovoltaic systems

SPICE piecewise linear resistor (PWLR) and piecewise current‐controlled (PWCC) current source models are applied to represent conventional loads of PV systems, namely, a washing machine, a refrigerator, lights and a d.c.–a.c. converter. The parameter extraction for these models has been performed by experimental measurements. A complete system of 440 Wp has been simulated and the results compared to experimental measurements. Future application advanced dispatching strategies and intelligent load management are indicated as possible uses of these models. Copyright © 2000 John Wiley & Sons, Ltd.     

Heterostructures of metamorphic GaInAs photovoltaic converters fabricated by MOCVD on GaAs substrates

Heterostructures of metamorphic GaInAs photovoltaic converters (PVCs) are on GaAs substrates by the metal-organic chemical vapor deposition (MOCVD) method. It is shown that using a multilayer metamorphic buffer with a step of 2.5% in indium content and layer thicknesses of 120 nm provides the high quality of bulk layers subsequently grown on the buffer up to an indium content of 24%. PVCs with a long-wavelength photosensitivity edge up to 1300 nm and a quantum efficiency of ~80% in the spectral range 1050–1100 nm are fabricated. Analysis of the open-circuit voltage of the PVCs and diffusion lengths of minority carriers in the layers demonstrates that the density of misfit dislocations penetrating into the bulk layers increases at an indium content exceeding 10%.     

Simulation of the ohmic loss in photovoltaic laser-power converters for wavelengths of 809 and 1064 nm

The method of mathematical simulation is used to examine the influence exerted by the characteristics of the epitaxial structure and contact grid of photovoltaic laser-power converters on their ohmic loss. The maximum attainable photoconverter efficiency at a Gaussian distribution of the laser-beam intensity on the surface of a photovoltaic converter and at dark-current densities of p–n junctions typical of structures grown by the metal-organic vapor-phase epitaxy (MOVPE) technique are determined. An approach to finding the optimal parameters of GaAs and In_0.24Ga_0.76As/GaAs photovoltaic converters in relation to the optical power being converted is suggested, and the structural parameters for incident-power values of 5, 20, and 50 W at wavelengths of 809 and 1064 nm are determined. It is found that, at laser-light intensities of up to 5 W, >60% efficiency can be achieved in laser-light conversion at a wavelength of 809 nm and >55% efficiency, at a wavelength of 1064 nm.     

Impact of power electronics packaging on the reliability of grid connected photovoltaic converters for outdoor applications

This paper deals with thermal and reliability aspects of converters for grid connected photovoltaic applications (rate power approximately 100 W) which can be integrated into solar modules. The use of these Module Integrated Converters (MIC) promises a reduction of costs due to mass production. It improves behaviour of the whole photovoltaic system, as there is no voltage mismatch caused by shading effects. The electronic components of the MIC are exposed to extreme environmental conditions. Lifetime limiting factors are described. Methods to increase the lifetime of the most crucial components in the MIC, electrolytic capacitors, are described. The presented 1st generation Low Profile MIC with “optimised design” is capable of running in very high ambient temperatures. This design maximises availability of the photovoltaic system, which consequently leads to a cost reduction of the electrical energy delivered to the grid. Different realisations of how to integrate the designed Low Profile MIC into the solar module are discussed. A detailed thermal simulation is used to optimise the MIC design according to temperature and reliability issues. The models used for thermal simulation are described.     

Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

Metamorphic Ga_0.76In_0.24As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In_0.24Al_0.76As/p-In_0.24Ga_0.76As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 10¹⁸ cm^–3 and completely remove the potential barrier, thereby reducing the series resistance of the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.     

Theoretical and experimental investigation on the stability of matrix converters

Matrix converters perform a direct coupling between two ac sources without the need for energy storage components. This characteristic, together with the presence of L-C input filters and the feedforward compensation of the input voltage variations, may determine unstable operation as the power delivered to the load exceeds a limit value. In this paper, a theoretical analysis of the stability of matrix converters is presented with the aim of predicting possible critical operating conditions. It is verified that all of the system parameters affect more or less the stability, including the delay introduced by the digital controller and the power losses. The theoretical analysis is supported by numerical simulations and experimental results carried out on a matrix converter prototype.     

Electronic controlled device for the analysis and design of photovoltaic systems

The characterization and design of photovoltaic systems is a difficult issue due to the variable operation atmospheric conditions. With this aim, simulators and measurement equipments have been proposed. However, most of them do not deal with real atmospheric conditions. This letter proposes an electronic device that first measures the real evolution of the I-V characteristic curves of photovoltaic modules and generators, and then physically emulates in real time these curves to test photovoltaic inverters. The device consists of a dc-dc converter, a microcontroller and a data storage unit. The two operation modes (emulation and measurement) are digitally driven by the microcontroller. The converter current is controlled by means of a variable-hysteresis control loop, whose reference is provided by the microcontroller. In addition, a digital voltage control loop is designed to find out the complete characteristic curves of the photovoltaic generators. A 15-kW prototype is designed and built that can measure three times per second the characteristic curves of up to seven generators and then emulate their electrical behavior to test photovoltaic inverters. With the proposed device, the optimal configuration and performance of photovoltaic modules and generators, as well as the operation of photovoltaic inverters can be thoroughly analyzed under real atmospheric conditions.     

A decrease in ohmic losses and an increase in power in GaSb photovoltaic converters

The transmission-line model with radial and rectangular geometry of contact pads has been used to study the contact systems Cr-Au, Cr-Au-Ag-Au, Ti-Pt-Au, Pt-Ti-Pt-Au, Pt-Au, Ti-Au, Ti-Pt-Ag, Ti-Pt-Ag-Au, and Pt-Ag deposited on the p-GaSb surface by the methods of magnetron sputtering and resistive evaporation. It is established that the contact systems Ti-Pt-Ag-Au and Ti-Pt-Ag exhibit the smallest values of the specific contact resistance (ρ _c ≤ 10⁻⁶ Ω cm²), which makes it possible to use these systems in fabrication of photovoltaic converters generating photocurrents with densities as high as 15 A/cm².     

高功率密度系统需要大电流转换器

本文介绍了降压型稳压器设计中需要注意的问题及面临的新挑战,并介绍了LTC7150S和LTC7130两款满足特定需求的降压型变压器.     

光伏系统最大功率跟踪技术的研究

基于传统的滑膜控制算法,本文采用一种改进的指数趋近律方法,来实现最大功率跟踪,使得控制输出变量可以为连续变量,再通过调制器得到开关管的控制信号,实现控制,以弥补传统方法的参数灵敏度、适用范围受限制等方面的缺陷。通过对传统算法和改进算法的仿真比较,得出了改进的滑模控制法能够快速地跟踪最大功率点,振荡幅度较小,鲁棒性较好。     

Five-stepped PWM inverter used in photovoltaic systems

A PWM (pulse-width-modulated) inverter that has five-stepped output-voltage levels is introduced. In this inverter, the waveform of the output voltage has a smaller harmonic content than that of a conventional PWM inverter. A novel PWM technique is analyzed. The PWM pulses included in the waveform of the output voltage are formed using a criterion based on the calculation that each area of voltage pulses is equal to the integrated value of each time shared area of a reference sinusoidal waveform. This PWM technique for the five-stepped PWM inverter is superior to the conventional PWM technique, and the experimental results coincided with the calculation obtained using the fast Fourier transform. In addition, the relations between the number of PWM pulses and the harmonic contents of the output voltage are described