A developed single-phase cascaded multilevel inverter with reduced number of circuit devices

In this paper, an advanced configuration for multilevel voltage source inverters is proposed. The proposed topology can be used as symmetric and asymmetric inverter. In asymmetric mode, DC sources’ magnitudes are defined in a way that the number of output voltage levels gets more than the case when the symmetrical DC sources are applied. In this regard, to calculate the magnitudes of required DC voltage sources, several different solutions are proposed. In multilevel inverters, the overall cost, circuit size and so installation area, complexity of control scheme and reliability are directly dependent on the number of circuit devices needed. The provided comparison study among suggested inverter in all defined solutions, CHB and recently proposed converters validates that the proposed modular inverter uses reduced number of circuit devices. The provided simulation and experimental results confirm the feasibility of the proposed structure and show that the obtained results are in good agreements.     

Improved configuration for symmetric and asymmetric multilevel inverters with reduced number of circuit devices

In this paper, a topology developed for multilevel voltage source inverters is proposed. The suggested modular configuration consists of several series-connected units, which can be applied as symmetric and asymmetric inverters. In the asymmetric mode, different solutions are suggested to generate an increased number of output voltage levels. In multilevel inverters, the number of required circuit elements determines the total cost, circuit size, installation area, complexity of control scheme and reliability of the inverters. The comparison study among the proposed inverter by considering all the presented algorithms for it, cascaded H-bridge (CHB) inverter and recently proposed converters, confirms that the proposed inverter uses a reduced number of circuit elements. In order to show the practicability of the proposed converter, a prototype of the proposed structure is implemented and tested. The simulation and experimental results are in good agreement with each other, indicating the effectiveness of the proposed inverter.     

高效非逆变光伏技术理论基础

关于光伏应用形式的主要争论之一,是光伏电力的逆变应用与非逆变应用之争。其实"逆变"只是电力技术中一种直流变交流的方法,逆变与非逆变的本质区别,并不在于采用该方法与否。在逆变应用中也有直流线路,非逆变应用中也有逆变装置。关键问题是,被统称为"逆变并网"的逆变应用,是推崇用光伏电力取代市电的一种思潮,并长期以来作为主流观点在光伏应用领域占统治地位。而非逆变应用就不赞成这种应用形式,并且有针对性地提出了许多不同意见,归结起来有3条:第一,不必要,因为直流电、交流电都可以应用,将直流低压的光伏电力变成高压交流电去适应普通电气应用是多余而又降低效率的环节;第二,问题复杂化,因为光伏电力的输出功率不稳定,又不采用储能装置,依附电网上的负载卸载,势必给网电造成影响,从而发生一系列技术问题和与电力部门的协调问题,人为增加了光伏电力应用的困难;第三,经济上不合算,无论如何,光伏电力成本的价格还是远高于市电。而逆变应用反驳得不太有说服力,除了第一条所说的应用方便之外,其余2条对于实际问题的解决,至今没有实质性的进展。     

Novel cascaded H-bridge sub-multilevel inverter with reduced switches towards low total harmonic distortion for photovoltaic application

The main objective of this paper is to develop a novel inverter to produce multilevel output voltage. This paper proposes the cascaded H-bridge with sub-multilevel inverter (CHBSMLI) using three unequal DC sources in order to get 15-level output voltage. The unequal DC sources can be obtained from photovoltaic cell. The proposed CHBSMLI reduces the number of switches which in turn reduces the switching losses. The multicarrier sine Pulse Width Modulation (PWM) technique is proposed to obtain pure sinusoidal signal with reduced total harmonic distortion (THD). The performance analysis of the proposed three-phase CHBSMLI carried out using MATLAB/simulink with minimised THD and switching loss. The gating signals are generated using a Spartan-3E FPGA processor. The single-phase 15-level CHBSMLI with PWM developed to validate the simulation result.     

Total harmonic distortion minimisation in multilevel inverters using the teaching–learning-based optimisation algorithm

In this article, the minimisation of total harmonic distortion (THD) of the output voltage of a multilevel inverter is studied. The harmonic component of output voltage in the inverter is reduced in THD minimisation. The output voltage THD in multilevel inverters is minimised by proper selection of switching angles. The teaching–learning-based optimisation algorithm is used to find the optimum switching angles in order to generate the desired voltage value in the possible minimum THD. Experimental and simulation results depict advantages of this approach compared to published papers which discus this concept using genetic algorithm. The experiments conducted on a seven-level inverter confirm the feasibility of this approach.     

针对高次谐波引起的电磁干扰的解决方案

本文叙述了电磁兼容性和电力系统谐波的产生,变频器谐波及其电磁干扰问题,并通过一个电磁兼容实例来进行论述,最后提出对由高次谐波引起的电磁兼容问题的解决办法。由于电力系统中非线性负载的数量越来越多,而作为其中主要一大类的变频器的应用日益广泛,电子电气设备对电磁兼容性的要求越来越高,特别是高次谐波所带来的电磁兼容问题。     

变频器输出产生的负面效应以及抑制对策

指出变频器输出会产生电磁干扰、电动机损耗增加．漏电流增大、电动机轴承损坏．电动机端过电压等负面效应。提出采用电动机侧滤波器和变频器侧滤波器的设计方案,以抑制这些变频器输出产生的负面效应。     

Z源逆变器光伏发电系统变量调制范围随动的两级控制研究

Z源逆变器光伏发电系统是一种具有升/降压功能的单级系统,可以通过调节直通占空比实现前级光伏电池的最大功率跟踪(MPPT)控制,然后由逆变器调制因子m实现并网控制.提出了一种直通占空比调制范围上限随动的两级控制策略.该策略兼顾了两级控制和单级控制的优点:充分利用了直通零矢量,使逆变器的调制因子m增大,直流电压利用率高,相应的有源器件的电压应力和逆变器输出电流谐波得到很大地改善;消除了光伏电池和电网之间的影响.仿真和实验结果验证了理论分析的正确性与实用性.     

三相逆变电源设计与实现

设计一款三相逆变交流电源,输出正弦信号频率为50Hz,负载Y型连接时线电压有效值可达24V,负载线电流有效值最大为2A。系统由三相逆变驱动主电路、滤波电路、STM32最小系统、信号隔离电路、SPWM(正弦脉宽调制)信号发生器、电压和电流测量电路和LCD显示等功能电路组成。测试结果表明,室温下输入直流电压为36V,负载线电流有效值Io在0~2A间变化时,各相负载调整率不大于0.3%,电能转换效率可达88%。     

谈自动扶梯驱动主机交流拖动线路的设计

叙述了电动机Y-△降压起动和变频器驱动的通用拖动线路,分析了GB16899—2011对自动扶梯主机直接供电和由静态元件供电的要求,列出了既满足标准又符合Y-△降压起动或变频器驱动要求的几种拖动线路,最后各推荐出一种性价比较好的自动扶梯驱动主机的拖动线路。     

IGBT逆变点焊电源主回路的研制及计算机仿真

随着电子技术的发展和大功率快速开关等电子元件的应用,逆变技术开始被逐步引入焊接领域。简要介绍逆变技术的点焊逆变电源主回路,利用目前流行的通用电路仿真软件PSPICE,对IGBT逆变点焊电源的主回路进行仿真分析,实践证明应用此方法可以降低成本和提高工作效率。     

采用UPS或电池进行电梯停电应急救援供电的设计

介绍一种采用UPS或电池直接连接变频器直流母线供电进行电梯停电应急救援的设计,重点通过一个实例分析计算UPS的选配。     

空冷配电间降温通风设备选型优化

简要介绍了空冷配电间的特点。结合工程实例,利用CFD技术对采用蒸发冷却降温机组时空冷配电间的室内环境进行了模拟分析,认为其完全满足室内运行要求。通过与常规方案进行技术经济比较,认为在今后空冷配电间设计中,应依据具体工程实际采用适合的蒸发冷却降温机组,以达到节能、经济的目的。     

电力工程中直流微型断路器应用分析

针对电力系统中直流微型断路器的使用场所,从电力系统中直流配电系统各类保护要求(包括基本要求、直流电源柜的短路保护、负荷电流、基本保护要求、继电保护系统的故障电流与保护要求)出发,介绍了直流微型断路器的结构,以及相关使用标准和产品标准,分析了直流微型断路器的选型(包括工作电压与短路电流分断能力、额定电流与最大工作电流等参数的选择),以及微型断路器与其它保护电器的配合等几方面问题。     

直流型变频空调器的智能模糊控制

从直流型智能变频空调器的特点及控制要求出发，提出了智能模糊控制系统的结构，重点讨论了压缩机和电子膨胀阀的模糊控制算法，并对一些特殊功能和控制方法进行了分析。     

50kWp屋顶分布式光伏并网发电系统的研究

结合天津地区某小区屋顶分布式光伏发电系统,对其运行状态进行实时测试和分析。从发电效率、累计发电量、逆变器效率等指标评价实际工程的运行效果。针对分布式发电的特点,比较售楼处4个发电单元的运行情况,验证了发电单元朝向正南、倾角为当地纬度安装才有最佳的运行效果。并网逆变器能在阵列输出功率较小时达到较高的效率,且能量损失小。     

基于逼近理想解排序法的基坑风险模糊识别方法

随着基坑工程深度与规模的增加,建设中的风险源也逐渐增加。为解决风险源无法采用确定数字定量评估的问题,利用三角模糊数与逼近理想解排序法(TOPSIS)相耦合的算法对基坑风险源进行识别,以实现对风险源识别的定量化表达。针对工程特征、周边环境和施工管理三方面的安全风险,结合基坑施工实际与专家工程经验,建立了影响基坑安全的风险源指标体系,提出了基于TOPSIS法的三角模糊风险源识别耦合模型。该模型可有效融合专家风险判别意见,使得结果更合理。对广州市天河路车站基坑风险源识别结果表明,该模型具有较好的适用性和有效性,对类似车站基坑的风险源识别、安全管控具有一定的指导意义。     

智能型氧化锌电阻片直流参数测试仪的研制

研制了基于 89C5 1单片机的 Zn O电阻片直流参数测试仪 ,该仪表能测量 U1m A及0 .75 U1m A下的漏电流 ,测量范围为 0 k V～ 6 k V,具有 RS2 3 2 C串行通信口 ,并能将测量结果分类输出。同时 ,介绍了设计原理 ,程控升、降压电路 ,恒流、恒压控制电路及软件流程。     

微电子交流计数电码化轨道电路的维修探讨

从调整、测试和故障处理等方面探讨了微电子交流计数电码化轨道电路的维修，并对维修中出现的问题提出了解决办法，以使设备正确使用，准确维修，正常运行。     

Using multivariate statistical methods to detect fires

Fire detectors must accurately detect fires, but they should not respond to false alarms. Contemporary smoke detectors sometimes cannot discriminate between smoke and odor sources. These detectors can also be slow in responding to smoldering fire sources. In this paper, a statistical approach for detecting fires based on fusing sensor signals from multiple sensors is presented. The multivariate statistical approach, called principal component analysis, is used to compress the sensor information down to a small number of variables that can be interpreted more easily than the raw sensor signals themselves. Experimental results presented here show that the proposed approach is more accurate than a conventional smoke alarm, particularly for early detection of smoldering fires. However, this new approach does not overcome the problem of false alarms. In spite of this current limitation, the method discussed holds great promise for future fire detection applications.