Lifetime estimation for IGBT modules in wind turbine power converter system considering ambient temperature

Power semiconductors in the wind turbine power converter system suffer from two-scale thermal loadings, the fundamental frequency thermal cycling caused by the output frequency of converter and the low frequency thermal cycling due to the variation of long-term wind speed. These two-scale thermal loadings introduce different consumed lifetimes. Accurate lifetime estimation in the wind power application is desired for reliability prediction and health management. This paper adopts the Bayerer lifetime model to evaluate the consumed lifetime of power semiconductors in wind power converter systems based on a numerical junction temperature calculation method. Lifetime estimation can be improved by taking into account the ambient temperature. Studies show that fluctuations of the ambient temperature increase the consumed lifetime due to the low frequency thermal cycling, but have little effect on the consumed lifetime due to the fundamental frequency thermal cycling. Our results also show that the consumed lifetime due to fundamental frequency thermal cycling mainly falls on the high wind speed area, whereas the consumed lifetime due to low frequency thermal cycling is clustered in the area due to large low frequency junction temperature fluctuations. The resulting distribution characteristics can be used in the thermal management for reliability improvement.     

The electrical properties of Hg-sensitized “photox”-oxide layers deposited at 80°C

This paper deals with the electrical properties of low-pressure CVD SiO₂ deposited at 80°C. The deposition rate is enhanced by UV radiation in the presence of Hg vapor. The photo-enhanced low-pressure chemical-vapor-deposited oxide, known also as “photox,” offers a good quality oxide deposited at temperatures as low as 80°C. The films are deposited in a batch-load “photox” barrel reactor and subsequently annealed at 950°C for 30 min in a conventional hot-wall furnace. Cold-sputtered aluminum-gate guard-ring capacitors are fabricated on the oxide films. High-frequency and quasi-static capacitance measurements indicate the interfacial properties of “photox” are comparable to those of thermal oxide. Fast interface states density are less than 2 × 10¹⁰ cm⁻² eV⁻¹ and a light negative interfacial charge could just be detected. The dielectric breakdown field is typically 4–5 MV/cm.Deep-depletion transient-capacitance measurements were performed at temperatures between 20 and 100°C to investigate the possible impact of “photox” processing on the generation lifetime. The Hg in particular might be suspected as a heavy-metal contaminant. Typical recovery times observed at 20°C were in the range of 10–15 min. The generation lifetime derived from such measurements ranges from 140 to 200 μs which is comparable to values for control samples made with standard thermal oxide. The magnitude and temperature dependence of the generation lifetime suggest that the same G-R centers are present in both “photox” and thermal oxide devices. The only apparent electrical effect of the Hg vapors used in the deposition process is a small negative fixed interface charge, 2 × 10¹⁰cm⁻².     

一种基于变速恒频的双馈风力发电MPPT设计

采用双PWM控制型变流器,变速恒频发电技术,变浆距角进行最佳风能追踪(MPPT)控制。分析了如何由绕线式异步电动机参数设计出双馈风力发电最大风能跟踪控制的风力机参数。通过Matlab仿真,分析了风机的切入风速、切出风速、风速过大情况下的变桨距角控制及浆距角随风速减小而自动恢复的最大风能跟踪特性,验证了控制策略的有效性和可行性。     

实验室模拟风力机的研究

为了解决实验室风力机的模拟问题,提出了直流电机模拟风力机的方案。同时分析了风力机的运行特性及最佳风能利用原理,采用简单有效的转速、转矩控制,搭建风力机的Matlab仿真模型。该风力机模拟系统应用于变速恒频风力发电系统中,满足了双馈电机在不同状态下运行以及追踪最大风能的变速恒频发电运行等方面研究的需要。     

Leaf-Like TENGs for Harvesting Gentle Wind Energy at An Air Velocity as Low as 0.2 m s−1

Existing technologies for harvesting electrical energy from gentle wind face an enormous challenge due to the limitations of cut-in and rated wind speed. Here, a leaf-like triboelectric nanogenerator (LL-TENG) is proposed that uses contact electrification caused by the damped forced vibration of topology-optimized structure consisting of flexible leaf, vein bearing plate, and counterweight piece. The effectiveness of the topology-optimized leaf-like structure is studied, which solves the problem of reduced output due to electrostatic adsorption between the leaf surfaces while reducing the cut-in (0.2 m s⁻¹) and rated wind speed (2.5 m s⁻¹). The LL-TENG unit having small dimensions of 40 cm⁻² (mass of 9.7 g) at a gentle wind of 2.5 m s⁻¹ exhibits outstanding electrical performances, which produces an open-circuit voltage of 338 V, a short-circuit current of 7.9 µA and the transferred charge density of 62.5 µC m⁻² with a low resonant frequency of 4 Hz, giving an instantaneous peak power of 2 mW. A distributed power source consists of the five LL-TENGs in parallel is developed by designed self-adaptive structure, for which the peak power output reaches 3.98 mW, and its practicability and durability are successfully demonstrated. This study is a promising distributed power source technology to drive electronics in gentle wind outdoor environments.     

Solid State Voltage and Frequency Controller for a Stand Alone Wind Power Generating System

This paper deals with the voltage and frequency controller of a wind turbine driven isolated asynchronous generator. The proposed voltage and frequency controller consists of an insulated gate bipolar junction transistor based voltage source converter along-with battery energy storage system at its dc link. The proposed controller is having bidirectional active and reactive powers flow capability by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind turbine. It is also having capability of harmonic elimination and load balancing. The proposed electro-mechanical system along with its controller is modeled and simulated in MATLAB using Simulink and power system block-set toolboxes. Performance of the proposed controller is presented to demonstrate voltage and frequency control of a wind turbine driven isolated asynchronous generator along with harmonic elimination and load balancing.     

Variable-band hysteresis current controllers for PWM voltage-sourceinverters

Hysteresis current controllers having fixed bands are used in inverters of high-performance AC drives. The switching frequency of such controllers varies over the fundamental period of the modulating signal. The maximum switching frequency (MSF) of these controllers is high. To limit the MSF within the limit of inverter switches, fixed carrier lockouts are usually incorporated. The incorporation of carrier lockouts causes current distortion, and load currents do not confine within the predetermined band. In this paper, two new controllers are proposed. One is a mixed-mode controller of sinusoidal band added to a fixed band, and the other is an equidistant-band current controller, performances of the proposed controllers are compared with the performances of the conventional fixed-band and sinusoidal-band controllers     

Optimal Variable Switching Frequency Scheme for Reducing Switching Loss in Single-Phase Inverters Based on Time-Domain Ripple Analysis

The choice of switching frequency for pulsewidth modulation single-phase inverters, such as those used in grid-connected photovoltaic application, is usually a tradeoff between reducing the total harmonic distortion (THD) and reducing the switching loss. This paper discusses an approach to minimize the switching loss while meeting a given THD requirement using variable switching frequency schemes (switching schemes with the switching frequency varying within a fundamental period). An optimal switching scheme is proposed based on time-domain current ripple analysis and the calculus of variations. The analysis shows that, to meet the same THD requirement, the optimal scheme has a significant saving on switching loss, compared to the fixed switching frequency scheme and the hysteresis control scheme, in addition to other benefits such as reduced peak switching loss and a spread spectrum of the current harmonics. The optimal scheme has been implemented in a prototype and the experimental results have verified the theoretical analysis. Also, a straightforward design method for designing filter inductors for single-phase converters is provided based on the time-domain current ripple analysis.     

A low power dissipation high-speed CMOS image sensor with column-parallel sigma–delta ADCs

A 60frames/s CMOS image sensor with column-parallel inverter-based sigma–delta (ΣΔ) ADCs is proposed in this paper. In order to improve the robustness of the inverter, instead of constant power supply, two buffers are designed to provide power supply for inverters. Instead of using of an operational amplifier, an inverter-based switch-capacitor (SC) circuit is adopted to low-voltage low-power ΣΔ modulator. Detailed analysis and design optimization are provided. Due to the use of the inverter-based ΣΔ ADCs, the conversion speed is improved while reducing the area and power consumption. The proposed CMOS image sensor has been fabricated with 0.18 μm CMOS process. The measurement results show that the random noise (RN) is 7e_rms⁻, the pixel conversion gain is 100 μV/e⁻. Since the measured full well capacity of the pixel is 25000e⁻, the CMOS image sensor achieves a 71 dB dynamic range (DR). The total power consumption at 60frame/s is 58.2 mW.     

Switching Characterization of Cascaded Multilevel-Inverter-Controlled Systems

In this paper, the method of triangular carrier switching control of two-level inverters is extended to cascaded multilevel inverters using phase-shifted multicarrier unipolar pulsewidth modulation (PWM). The condition for smooth modulation is obtained using the Bessel's function representation of the PWM output and the switching condition of the multilevel-inverter-controlled system. A method is proposed for the determination of the minimum amplitude of the triangular carrier for smooth modulation at fixed switching frequency. It is shown that the multilevel modulation based on the phase-shifted carriers significantly reduces the ripple magnitude in the switching function and allows the use of a smaller carrier amplitude under closed loop. This increases the forward gain and, hence, improves the tracking characteristics. The proposed cascaded multilevel inverter control is implemented for the operation of a distribution static compensator (DSTATCOM) in the voltage control mode. The experimental verification of the theoretical and simulation results is provided through a field-programmable gate array (FPGA) based control of a laboratory model of a single-phase DSTATCOM.     

Digital output compensation for precise frequency transfer over commercial fiber link

An ultra-highly precise and long-term stable frequency transmission system over 120 km commercial fiber link has been proposed and experimentally demonstrated. This system is based on digital output compensation technique to suppress phase fluctuations during the frequency transmission process. A mode-locked erbium-doped fiber laser driven by a hydrogen maser serves as an optical transmitter. Moreover, a dense wavelength division multiplexing system is able to separate forward and backward signals with reflection effect excluded. The ultimate fractional frequency instabilities for the long-distance frequency distributed system are up to 3.14×10^-15 at 1 s and 2.96×10^-19 at 10 000 s, respectively.     

Patterning Liquid Crystalline Organic Semiconductors via Inkjet Printing for High-Performance Transistor Arrays and Circuits

Liquid crystalline (LC) organic semiconductors having long-range-ordered LC phases hold great application potential in organic field-effect transistors (OFETs). However, to meet real device application requirements, it is a prerequisite to precisely pattern the LC film at desired positions. Here, a facile method that combines the technique of inkjet printing and melt processing to fabricate patterned LC film for achieving high-performance organic integrated circuits is demonstrated. Inkjet printing controls the deposition locations of the LC materials, while the melt processing implements phase transition of the LC materials to form high-quality LC films with large grain sizes. This approach enables to achieve patterned growth of high-quality 2,7-dioctyl[1]-benzothieno[3,2-b][1]benzothiophene (C₈-BTBT) LC films. The patterned C₈-BTBT LC film-based 7 × 7 OFET array has 100% die yield and shows high average mobility of 6.31 cm² V⁻¹ s⁻¹, along with maximum mobility up to 9.33 cm² V⁻¹ s⁻¹. As a result, the inverters based on the patterned LC films reach a high gain up to 23.75 as well as an ultrahigh noise margin over 81.3%. Given the good generality of the patterning process and the high quality of the resulting films, the proposed method paves the way for high-performance organic integrated devices.     

A power-efficient 14.8-GHz CMOS programmable frequency divider with quadrature outputs in 40-nm CMOS process

This paper presents a power-efficient CMOS frequency divider (FD) with wide-band programmable division ratio and quadrature outputs for high-speed data transmission applications. The proposed FD consists of a power-efficient programmable divider (PD), a complementary volt-age-to-time converter based duty-cycle correction circuit, and a compact quadrature divider (QD). In the chain of PD, a sense-amplifier based dynamic flip-flop is proposed for 2/3 divider cell to achieve high-speed operation with significantly reduced power consumption. In addition, a simple but effective QD based on two pseudo-differential voltage-controlled tri-state inverters, is beneficial for generating precise quadrature output signals. Measurement results in 40-nm CMOS process show that the proposed FD achieves a wide division range from 16 to 254 and operates up to 14.8 GHz while consuming the power of 540.6 μW at 1.1-V supply, and occupying the active area of 0.00267 mm² (114.6 μm × 23.3 μm).     

Novel field‐effect passivation for nanostructured Si solar cells using interfacial sulfur incorporation

Surface passivation of a nanostructured Si solar cells plays a crucial role in collecting photogenerated carriers by mitigating carrier recombination at surface defect sites. Interface modification by additional sulfur (S) incorporation is proposed to enhance the field‐effect passivation performance. Here, we report that simple annealing in a H₂S ambient induced additional negative fixed charges at the interface between atomic‐layer‐deposited Al₂O₃ and nanostructured Si. Annealing at various temperatures allowed us to control the S concentration and the fixed charge density. The optimized S incorporation at the interface significantly enhanced the negative fixed charge density and the minority carrier lifetime up to ~5.9 × 10¹² cm⁻² and ~780 μs, respectively. As a result, the internal quantum efficiency was nearly two times higher in the blue response region than that of control cells without S incorporation. Copyright © 2017 John Wiley & Sons, Ltd.     

Fast switching gate driver for self resonant inverters applicableto electronic ballasts

A fast switching gate driver suitable for self-oscillating resonant inverters such as electronic ballasts is presented. The proposed gate driver has negligible switching loss and driving loss owing to fast driving and zero voltage switching (ZVS) control capability. Experiments show that the gate transition time is as short as 20 ns and the switching loss is as little as one quarter of that of a conventional gate driver     

A vector control technique for medium-voltage multilevel inverters

This paper presents a switching strategy for multilevel cascade inverters, based on the space-vector theory. The proposed switching strategy generates a voltage vector with very low harmonic distortion and reduced switching frequency. This new control method is an attractive alternative to the classic multilevel pulsewidth modulation techniques considering the following aspects: (1) voltage and current total harmonic distortion; (2) range of linear operation; and (3) number of commutations.     

Wind Speed Estimation Based Sensorless Output Maximization Control for a Wind Turbine Driving a DFIG

This paper proposes a wind speed estimation based sensorless maximum wind power tracking control for variable-speed wind turbine generators (WTGs). A specific design of the proposed control algorithm for a wind turbine equipped with a doubly fed induction generator (DFIG) is presented. The aerodynamic characteristics of the wind turbine are approximated by a Gaussian radial basis function network based nonlinear input-output mapping. Based on this nonlinear mapping, the wind speed is estimated from the measured generator electrical output power while taking into account the power losses in the WTG and the dynamics of the WTG shaft system. The estimated wind speed is then used to determine the optimal DFIG rotor speed command for maximum wind power extraction. The DFIG speed controller is suitably designed to effectively damp the low-frequency torsional oscillations. The resulting WTG system delivers maximum electrical power to the grid with high efficiency and high reliability without mechanical anemometers. The validity of the proposed control algorithm is verified by simulation studies on a 3.6MW WTG system. In addition, the effectiveness of the proposed wind speed estimation algorithm is demonstrated by experimental studies on a small emulational WTG system.     

A low power tunable Gm–C filter based on double CMOS inverters in 0.35?μm

In this article, an inverter based transconductor using double CMOS pair is proposed for implementation of a second order lowpass G_m?CC Filter. The proposed operational transconductance amplifier (OTA) and biquad filter are designed using standard 0.35???m CMOS technology. Simulation results demonstrate the central frequency tunability from 10?kHz to 2.8?MHz which is suitable for the wireless specifications of Bluetooth (650?kHz), CDMA 2000 (700?kHz) and Wideband CDMA (2.2?MHz) applications. The power consumption of the filter is 445?nW and 178???W at 10?kHz and 2.8?MHz from 3.3?V supply voltage, respectively. The active area occupied by the designed filter on the silicon is 215?×?720???m². The proposed approach guarantees the upper bound on THD to be ?40?dB for 300?mVpp signal swing. Employing the double CMOS pair in the inverters causes PSRR to reach 68.6?dB which is higher than similar works.     

变系数降频模型预测直接功率控制

模型预测直接功率控制是三相并网逆变器有效的控制策略之一，但是为了维持稳定快速的功率跟踪，通常需要一个较高的采样频率，造成不必要的开关损耗。定系数降频控制策略可以降低有效地开关动作次数，但是不方便确定合适的开关函数系数，且降低了系统性能。变系数降频控制策略可以同时实现稳定的功率跟踪和开关频率降低。仿真和实验结果显示，与定系数降频控制策略相比，变系数策略具有更优越的特性。     

Controller design for a wind farm, considering both power and load aspects

In this paper, a wind farm controller is developed that distributes power references among wind turbines while it reduces their structural loads. The proposed controller is based on a spatially discrete model of the farm, which delivers an approximation of wind speed in the vicinity of each wind turbine. The control algorithm determines the reference signals for each individual wind turbine controller in two scenarios based on low and high wind speed. In low wind speed, the reference signals for rotor speed are adjusted, taking the trade-off between power maximization and load minimization into account. In high wind speed, the power and pitch reference signals are determined while structural loads are minimized. To the best of authors’ knowledge, the proposed dynamical model is a suitable framework for control, since it provides a dynamic structure for behavior of the flow in wind farms. Moreover, the controller has been proven exceptionally useful in solving the problem of both power and load optimization on the basis of this model.