Capacitor Pattern H-Bridge Multilevel Inverter (CPHMLI) Using Phase Diposition Pulse Width Modulation for Grid Applications

This work presents an implementation of an innovative single phase multilevel inverter using capacitors with reduced switches. The proposed Capacitor pattern H-bridge Multilevel Inverter (CPHMLI) topology consists of a proper number of Capacitor connected with switches and power sources. The advanced switching control supplied by Pulse Width Modulation (PDPWM) to attain mixed staircase switching state. The charging and discharging mode are achieved by calculating the voltage error at the load. Furthermore, to accomplish the higher voltage levels at the output with less number of semiconductors switches and simple commutation designed using CPHMLI topology. To prove the performance and effectiveness of the proposed approach, a set of experiments performed under various load conditions using MATLAB tool.

Study and Design of a DC/AC Energy Converter for PV System Connected to the Grid Using Harmonic Selected Eliminated (HSE) Approach

Nowadays, distributing network-connected photovoltaic (PV) systems are expanded by merging a PV system and a Direct Current (DC)/Alternating Current (AC) energy converter. DC/AC conversion of PV energy is in great demand for AC applications. The supply of electrical machines and transfer energy to the distribution network is a typical case. In this work, we study and design a DC/AC energy converter using harmonic selective eliminated (HSE) method. To this end, we have combined two power stages connected in derivation. Each power stage is constituted of transistors and transformers. The connection by switching of the two rectangular waves, delivered by each of the stages, makes it possible to create a quasi-sinusoidal output voltage of the inverter. Mathematical equations based on the current-voltage characteristics of the inverter have been developed. The simulation model was validated using experimental data from a 25.2 kWp grid-coupled (PV) system, connected to Gridfit type inverters. The data were exported and implemented in programming software. A good agreement was observed and this shows all the robustness and the technical performances of the energy converter device. It emerges from this analysis that the inverter output voltage and the phase angle thus simulated are very important to control in order to orientate the transfer of the power flow from the continuous cell to cell to the alternating part. Simulated and field-testing results also show that increases in the value of the modulation factor (m) for low power output are highly significant. This study is an important tool for DC/AC inverter designers during initial planning stages. A short presentation of the design model of the inverter has been proposed in this article.

Genetic Algorithm Based 7-Level Step-Up Inverter with Reduced Harmonics and Switching Devices

This paper presents a unique voltage-raising topology for a single-phase seven-level inverter with triple output voltage gain using single input source and two switched capacitors.The output voltage has been boosted up to three times the value of input voltage by configuring the switched capacitors in series and parallel combinations which eliminates the use of additional step-up converters and transformers.The selective harmonic elimination(SHE)approach is used to remove the lower-order harmonics.The optimal switching angles for SHE is determined using the genetic algorithm.These switching angles are com-bined with a level-shifted pulse width modulation(PWM)technique for pulse generation,resulting in reduced total harmonic distortion(THD).A detailed com-parison has been made against other relevant seven-level inverter topologies in terms of the number of switches,drivers,diodes,capacitors,and boosting facil-ities to emphasize the benefits of the proposed model.The proposed topology is simulated using MATLAB/SIMULINK and an experimental prototype has been developed to validate the results.The Digital Signal Processing(DSP)TMS320F2812 board is used to generate the switching pulses for the proposed technique and the experimental results concur with the simulated model outputs.

Modulation Index Effect on the 5-Level SHE-PWM Voltage Source Inverter

Harmonic content of the voltage source inverters is important and must be in the allowed ranges. Different method are proposed to decrease the Total Harmonic Distortion (THD) and caused to be sinusoidal the output voltage of inverters. One of these methods is using multilevel structure. In this structure many important parameters which are effective on voltage source inverter operation that among them we can mention to modulation index (MI). Variation of modulation index can change the THD. One of the harmonic reduction methods is using multilevel structure. In this paper, a sample 5-level SHE-PWM voltage source inverter is presented and all equation and choosing switching angles for elimination desired harmonics from different order. To investigate the effective parameters on the inverter operation, a typical 5-level inverter is simulated in PSPICE software. The simulation has been done for different values of modulation and its effect on the inverter operation is evaluated.

A type of inverter power supply based on harmonic elimination PWM control

In order to output sine wave with small degree of distortion and improve stability,a type of inverter power supply is designed based on harmonic elimination pulse-width modulation(PWM)control.The rectifier and filter are added to input circuit of the inverter.Single-phrase full-bridge inverter performs the function of converting direct current into alternating current(DC/AC).In the control circuit,single chip micyoco(SCM)AT89C2051 is used for main control chip to accomplish the hardware design of the control system.A given value of output frequency of the inverter is input in the way of coding.According to the output frequency code which is read,SCM AT89C2051 defined harmonic elimination PWM control data which will be selected.Through internal timing control,the switches are switched under this provision of PWM control data.Then the driving signals of the switches in the inverter are output from I/O of SCM AT89C2051 to realize harmonic elimination PWM control.The results show that adding Newton homotopic algorithm of harmonic elimination PWM control to corresponding software of the control system can make the quality of output voltage of the inverter higher and it will have broad application prospects.

改进蛇算法的七电平逆变器SHEPWM研究

多电平逆变器控制策略中的特定谐波消除脉宽调制(SHEPWM)能够以较低的开关频率得到较好的电压输出波形,重点在于开关角的求取。在多电平逆变器SHEPWM调制的开关角求解算法上提出改进蛇优化算法,对传统蛇优化算法采用Tend混沌映射初始种群,使初始种群分布更加均匀;引入Levy飞行策略增强算法的全局搜素能力,能够更加精准快速得到全局开关角的最优解。仿真结果表明,改进蛇优化算法所求的开关角相较于传统算法更好地消除低次谐波,并降低了输出线电压的畸变率,充分验证了该方法的可行性。

基于SHEPWM的三电平三相逆变器中点电位主动平衡控制策略

在大功率系统中,常采用特定次谐波消除脉宽调制(SHEPWM)以降低系统的开关损耗。针对三电平中点钳位(NPC)型三相逆变器在SHEPWM下的中点电位偏移问题,分析SHEPWM下逆变器输出相电压基波与3次谐波在不同电压相位范围内对中点电位的影响,设计两种在基波周期内对中点电位总充放电效果相反的开关角组合方案,并提出一种通过测量中点电位偏移值及中点电位滞环控制,选择不同的开关角组合方案进行调制的中点电位主动平衡控制策略。实验结果验证了所提出方法的实用性及有效性。

适用于三电平逆变器的电流谐波最小脉宽调制策略

受限于散热条件,大功率牵引传动系统中逆变器开关频率通常很低,三电平逆变器由于在低开关频率下具有较小的输出谐波、较低的dv/dt等特点在中高压大功率领域中被广泛应用。以三电平中点钳位型逆变器为研究对象,提出一种电流谐波最小脉宽调制策略(CHMPWM),基于加权总谐波畸变最小的优化目标求解不同开关角个数下的开关角曲线,与目前应用较为广泛的特定次谐波消除脉宽调制进行谐波性能对比。该方法不会完全消除特定次数的谐波成分,但是总体电流谐波可以达到最小。针对电流谐波最小脉宽调制策略在实现过程中存在的困难,设计全速度范围基于电流谐波最小脉宽调制的多模式调制策略。仿真和实验结果表明,提出的调制策略具有良好的谐波性能,与理论分析结果一致。

基于混合谐波注入的潜水感应电机电磁噪声削弱

针对感应电机在变频供电时会在绕组中产生时间谐波而导致电机的电磁振动和噪声增大的问题,提出了一种采用混合谐波注入的改进型正弦脉宽调制控制策略。以一台1120 kW的潜水感应电机为研究对象,通过对电机进行3、9次混合谐波注入,削弱了电压的调制波和载波谐波及其边带谐波分量,从而降低了电机的振动和噪声。对3、9次混合谐波注入方法中的谐波占比系数进行优化,进一步强化了对边带谐波的削弱效果,整体降低了电机噪声。最后通过对采用混合谐波注入方法的电机与优化前的常规电机进行铁耗、铜耗等方面的性能对比,验证了所提策略在不影响电机的基本性能的前提下,有效削弱了电机的电磁噪声。

高温气冷堆吸收球停堆驱动机构机柜的抗干扰设计研究

步进电机驱动器是高温气冷堆核电站吸收球停堆驱动机构机柜的主要设备,采用脉冲宽度调制(Pulse Width Modulation,PWM)技术,脉冲宽度调制过程产生的高次谐波分量又反向影响驱动器的工作稳定性和精度,严重时可能引发吸收球误落或拒落而影响反应堆运行安全。本研究旨在制定合理的抗干扰方案,降低PWM脉宽调制机理带来的危害及其影响。在充分掌握PWM产生干扰的传输路径、作用机理和影响程度的基础上,定制适用于高温堆吸收球停堆驱动装置工作环境的光电隔离器、电抗器和滤波器布置在干扰传输路径上阻断干扰传播,降低干扰影响。经过优化设计研究,可使得步进电机每运行20圈,角度偏差在1°之内,满足了控制精度要求,防止了吸收球误落或拒落风险,提升了吸收球停堆驱动机构的运行可靠性。

改进的单相三电平PWM整流器中点电位平衡模型预测控制

针对单相三电平脉冲整流器存在中点电位不平衡问题,提出一种评价函数,在模型预测算法的基础上增加了一个评价因子,在无需额外的中点电位平衡模块条件下实现了单相三电平脉冲整流器中点电位平衡。为降低硬件设计成本,提高电路可靠性,采用无网压传感器算法,但传统的无网压传感器会因引入一阶低通滤波器而产生相位偏移和幅值衰减的问题;为解决相位和幅值问题,提出一种改进的无网压传感器算法,利用α-β的垂直关系进行幅值和相位补偿,得到无相位偏移和幅值衰减的网侧交流电压。通过实验验证了所提控制方法的正确性和有效性。

基于钳位方式切换的Vienna整流器载波断续脉冲宽度调制策略

当Vienna整流器工作在直流电压不平衡条件下时,传统载波断续脉宽调制(carried-based discontinuous pulse-width modulation,CB-DPWM)会增加输入电流谐波和中点电压波动。为解决上述问题,提出一种基于钳位方式切换的CB-DPWM策略。为了减小输入电流谐波,根据变化的电压矢量对子区域和零序分量进行重新划分和计算。据此,建立统一的CB-DPWM调制波,分析可运行区域,得到直流电压不平衡度和可运行区域成反比的结论。结合中点电流分析不同钳位方式对中点电压大小的影响,并根据直流电压不平衡度的大小实时切换钳位方式,从而有效地减小中点电压波动。通过钳位区域判断和优化开关序列,减少切换钳位方式引入的开关动作,提高了Vienna整流器效率。最后,在Vienna整流器实验平台上验证所提策略的有效性。

一种抑制高速电机低次电流谐波的调制方法

针对高速永磁同步电机低载波比、数字控制延时所引起的电流谐波较大的问题,提出一种抑制低次电流谐波的改进型特定次谐波消除调制方法。首先,对该调制方法的调制波形原理和数字实现特点进行分析,建立新的电压谐波方程和开关角求解方程;其次,以电流总谐波失真为目标优化函数,研究了调制比和载波比对开关角分布、电流谐波含量的影响;最后,以三相高速永磁同步电机为研究对象,搭建系统仿真模型对所提调制方法进行验证。验证结果表明,通过与特定次谐波消除调制方式相比,所提调制方法计算量更少,可以提高输出脉宽调制波形的对称性,具有更优的低次电流谐波抑制能力。

变量施药系统压力波动特性及其消除方法研究进展

变量施药系统具有提高农药利用率、降低农药残留、减轻环境污染等优点,根据控制方式可分为药液浓度调节式、压力调节式和流量调节式。基于脉宽调制技术的变流量式施药系统因流量调节范围广、雾滴特性稳定等优点成为国内外研究热点,但在变量施药过程中因部分喷头启闭、泵源脉动、阀体开关动作等会造成管路压力波动,导致雾化质量差,药量不精准等亟待解决的问题。从变量施药系统类型、系统压力波动特性研究、系统压力波动抑制方法与装备方面综述国内外研究现状,分析总结药液浓度调节式、压力调节式、流量调节式变量施药系统的构成、优势和缺陷,重点阐述和归纳国内外施药系统中管路和喷头附近压力波动特性,主要介绍回流稳压、空气阀、稳压喷嘴等压力冲击抑制方法和装备,指出我国在变量施药系统精确性、变量施药系统压力稳定产品开发等方面的不足并提出展望,为实现变量施药系统的进一步精准化、智能化提供思路。

表贴式永磁电机在PWM激励下永磁体涡流损耗计算模型

针对现有模型难以计算PWM激励下表贴式永磁电机永磁体涡流损耗问题,提出了一种计算由PWM谐波引起的永磁体内涡流损耗计算模型。该模型通过磁导率分布函数获取气隙径向磁密,能够考虑定子开槽及谐波电流影响。首先,在忽略涡流反作用情况下解析计算了永磁体内磁密变化率;然后,应用有限差分法数值计算了永磁体内电位,综合得到了涡流损耗;最后,用有限元法验证了模型的准确性。研究结果表明:随着永磁体分段数的增大,涡流损耗减小,涡流反作用也随之减弱;永磁体涡流损耗主要由1倍、2倍开关频率附近电流谐波引起。

Carrier dynamic overlapping switching frequency optimal pulse width modulation method for modular multilevel converters

Modular multilevel converters(MMCs) operate in the low modulation index region in many applications.However, when utilized at the low modulation index region, large harmonics appear in the output voltage, which degrade the performance of the MMC. To improve the harmonic characteristic in the low modulation index, the carrier dynamic overlapping switching frequency optimal pulse width modulation(CDOSFOPWM) method is proposed for the MMC here. The whole modulation index region is divided into three regions: high modulation index region, middle modulation index region, and low modulation index region. The carrier amplitude, carrier overlap ratio, and frequency of triangular carriers are chosen dynamically according to the modulation index region of the modulation signals, to achieve the optimal harmonic characteristic in the whole modulation index region and maintain the switching loss. The number of on-state submodules(SMs) can be calculated by CDOSFOPWM, and the selection of SMs is performed by a reducing switching frequency voltage balancing algorithm. Finally, the proposed method is verified by simulation and experimental results.

三电平牵引逆变器电流谐波最小调制策略

使用三电平变流器拓扑结构,可有效降低单个开关器件所承受的电压等级,为碳化硅(SiC)器件在高压大功率牵引变流器领域的应用提供解决方案。文章根据牵引逆变器的应用需求,针对三电平二极管中点箝位(Neutral-Point-Clamped,NPC)型逆变器拓扑的电流谐波最小脉宽调制(Current harmonic minimum pulse width modulation,CHMPWM)策略开展了研究,通过求解不同开关角个数下开关角度随调制比的变化曲线,实现了三电平逆变器脉冲数较低情况下的电流谐波的总体优化,理论分析了CHMPWM不同开关角个数下的各次电流谐波和加权总谐波畸变(weighted total harmonic distortion,WTHD)特征,介绍了CHMPWM的脉冲产生方式及基于定子磁链偏差矢量的调制模式切换方法。最后,利用小功率试验平台对三电平逆变器CHMPWM及调制模式切换策略进行了试验研究,结果表明,三电平逆变器CHMPWM策略具有较好的动态和稳态性能,能满足牵引逆变器的技术应用需求。

Global synchronous discontinuous pulse width modulation method with fast calculation capability for distributed three-phase inverters

When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling(PCC). This paper proposes a new fast global synchronous discontinuous pulse width modulation(GSDPWM) method of threephase inverters to effectively attenuate the high frequency current harmonics at PCC. Firstly, the basic principle and the realization method of GSDPWM for three-phase inverters are explained, which can be employed for different modulation types. Then a fast calculation method,which can equally derive the minimized total harmonic distortion(THD) of total current, is proposed to release the calculation burden. Finally, MATLAB simulations and experimental results are presented to verify the performance of GSDPWM.

准Z源逆变器的低谐波含量梯形调制优化策略

针对准Z源逆变器谐波污染和功率器件电压应力高的问题,提出一种基于梯形波的优化策略。该调制策略通过选取合适的梯形化率,在保证直流电压利用率的同时大幅降低准Z源逆变器输出电流的总谐波畸变率,从而提高电能质量。此外,选取梯形波作为调制波能有效降低准Z源网络中电容及功率器件的电压应力。采用MATLAB/Simulink软件对所提出的调制策略进行仿真分析,以确保其正确性和有效性。最后,通过RT-LAB实验平台对基于梯形波的调制策略进行进一步验证。

基于牛顿-蚁群算法与选择性谐波调制的电网功率放大器宽频控制策略

选择性谐波消除/生成脉宽调制技术能与多电平电力电子变换器相结合,实现低开关频率下的高频电网谐波功率复现。然而,为生成特定次谐波,需要求解非线性开关角方程,其求解精度受开关角初值选取约束,且实时性随着谐波次数的增加而降低。因此提出一种基于牛顿-蚁群算法的实时选择性谐波生成脉宽调制技术。通过建立开关角方程,利用蚁群算法求解初值,进一步结合牛顿算法获得不同开关频率及计算步长对应的最多谐波数目,并分析得到调制比-开关角对应关系。通过查找表获得初始开关角,并前馈至电压控制环路,实现对特定次谐波的无静差跟踪。最后以级联H桥多电平变换器为例,搭建仿真与实验平台,验证了理论分析的正确性与所提策略的可行性。