Generalized Techniques of Harmonic Elimination and Voltage Control in Thyristor Inverters: Part II?Voltage Control Techniques

Theoretical techniques of voltage control for the half-bridge and full-bridge inverters are derived based on the results in [1]. Detailed analytical results for the symmetrical pulsewidth modulation method of voltage control are also presented. Voltage control techniques are derived whereby harmonic elimination is possible in variable-frequency variable-voltage three-phase inverter circuits. The technique for the half-bridge inverter is optimized subject to the constraint of switching frequency of the SCR's, using the concepts of modern control theory. Variable-frequency variable-voltage sinusoidal output in three-phase inverters is possible by employing the techniques developed. The methods show great promise in application to variable-speed ac motor drive systems.     

A modified cascade transformer-based multilevel inverter and its efficient switching function

A modified multilevel PWM inverter is proposed to increase the number of output voltage levels and to improve the system characteristic of a prior 11-level shaped PWM inverter scheme. In appearance, it consists of three full-bridge modules and a cascade transformer; therefore, the configuration of the proposed multilevel PWM inverter is equal to that of the prior one. Only the turn-ratio of one transformer and its corresponding switching function are different from each other. Based on the difference, the proposed multilevel PWM inverter has two promising advantages. First, output voltage levels increase almost two-fold. Consequently, it can generate more sinusoidal output voltage waves. Second, due to a suitable switching pattern, it lightens power imposed on the transformer, which is used for compensating output voltages with chopped pulses between step levels. Operational principle of the proposed 19-level shaped PWM inverter is analysed with comparisons of the prior 11-level shaped PWM inverter. The validity of the proposed inverter system is verified by computer-aided simulations and experimental results based on a 1 kW prototype.     

大容量多重化逆变器的输出电压谐波分析

针对目前缺乏对大容量多重化逆变器的输出电压谐波进行全面分析和比较的现状,根据多重化变压器的不同结构,将现有的典型多重化逆变器分为3类并从理论上推导出了它们的输出电压及谐波电压幅值表达式;给出了电压谐波畸变系数与重数和脉冲控制参数间的变化关系;对比分析了它们的电压谐波畸变率。理论和仿真分析结果的一致性表明由三电平逆变桥构成的多重化逆变器不仅能以较低的重数实现高压大容量输出,还可获得满意的电压谐波畸变率,且可有效减小变压器体积、重量和损耗,因而更适用于高压大容量电力电子装置。     

光伏高效软开关DC-DC变换器的数字化控制与实现

为满足三相光伏并网逆变器高输入电压的需求,克服其工频升压隔离变压器耗材严重的不足,本文提出了一种新型的高频变压器隔离升压软开关变换器,它通过两个升压绕组串联整流提高输出电压,一个降压绕组串联换流电感实现了全功率范围内变换器的软开关。文中首先分析了其工作原理,然后给出了一种非对称数字移相脉冲宽度调制控制策略和实现方法,最后设计并制作了工程样机。实验结果表明,该变换器控制方案合理,工作效率高。     

光伏发电双分裂变压器分布电容对逆变器直流电压的影响

兆瓦级光伏电站发电单元通常是由2台500 k W并网逆变器和1台1 MVA三相辐向双分裂升压变压器构成,而辐向升压变压器低压绕组间存在较大的分布电容,常发生2台光伏并网逆变器共同运行困难的问题。针对上述问题,对采用三相辐向升压变压器的光伏发电单元进行了等效建模,分析了变压器低压绕组间分布电容对双逆变器共同运行的影响机理。分析结果表明,并联在变压器两低压侧的2台逆变器之间存在漏电流回路,光伏发电单元中延后并网的逆变器直流母线电压升高导致双逆变器共同运行困难。通过仿真验证了机理分析的正确性。最后,提出了2种解决办法,并进行了仿真和实验验证。     

A New PV Converter for Grid Connection Through a High‐Leg Delta Transformer Using Cooperative Control of Boost Converters and Inverters

This paper proposes a new high‐efficiency photovoltaic (PV) converter for grid connection through a high‐leg delta transformer, which is composed of a symmetrically connected boost converter and three half‐bridge inverters. One of the three half‐bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. This circuit configuration enables to reduce the power losses in both boost converter and inverter. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in switching power loss. Experimental results show that the proposed circuit improves its European efficiency from 91.6% to 94.5%.     

直流电压含二次纹波条件下并网逆变器输出谐波抑制

单相并网逆变器及电网电压不对称情况下的三相并网逆变器,直流母线电压均含有明显的二倍工频纹波分量。受该纹波分量影响,逆变器交流侧输出含有明显的三次谐波,影响逆变器输出电能质量。针对上述问题,利用双重傅里叶变换和开关函数法对并网逆变器的输出谐波特性进行了分析,在此基础上提出了抑制单相和三相逆变器输出三次谐波的改进脉宽调制方法。该方法根据直流母线电压修正调制波,无需提取直流母线电压纹波分量信息,算法复杂度低,易于实现。通过开关函数法详细证明了新型调制方法的可行性,给出了基于该调制方法的单相及三相光伏逆变器的控制策略。仿真验证了所提调制方法可显著降低直流母线电压含二次纹波条件下并网逆变器的输出三次谐波成分。     

新型单相光伏并网逆变器共模电流抑制研究

针对现有非隔离单相光伏并网逆变器拓扑共模电流大、效率低等问题,提出一种新型非隔离单相光伏并网逆变器拓扑,该拓扑在单相全桥逆变器的基础上增加2个续流二极管,并将交流侧滤波电感移至逆变器下桥臂,使得开关周期内共模电压保持恒定,有效抑制了共模电流;同时高频开关管使用MOSFET,工频开关管使用IGBT,且避免引入额外的开关管...     

双降压式全桥逆变器

为避免桥臂功率管直通问题和提高输入直流电压利用率,在全桥逆变器和双降压式半桥逆变器的基础上,提出了双降压式全桥逆变器(dual buck full-bridge inverter,DBFBI),该逆变器具有无桥臂直通、输入直流电压利用率高、效率高、续流二极管可优化选取等优点。半周期调制方式减小了功率管的开关损耗及导通损耗,分析了半周期调制方式下电路的工作模态,给出了电感电流连续与断续时输入输出电压关系。设计了采用滞环电流控制的双降压式全桥逆变器系统,通过控制逻辑设计使之实现了半周期运行模式。仿真和实验结果证明该逆变器具有高质量的输出电压波形和良好的动态响应特性。     

Characteristics comparison of high‐frequency multilevel inverter connected with filter inverters

This paper presents a characteristics comparison of a high‐frequency multilevel inverter connected with small‐ capacity filter inverters. In general, PWM inverters require a low‐pass filter in order to reduce switching harmonics. However, in the high‐frequency systems such as class D power amplifiers, the cutoff frequency of the low‐pass filter must be set at high frequency. Thus, harmonic distortion of the output voltage is enlarged to a harmful level. Increasing the number of output voltage levels is effective in reducing the harmonic distortion of the output voltage and the low‐pass filter size. The proposed systems consist of a five‐level inverter and several cascade‐connected low‐voltage full bridge inverters without any external DC power sources for filtering the output voltage. The five‐level inverter generates a stepwise waveform with five‐level voltage, and the low‐voltage filter inverter superimposes harmonic components to compensate for the voltage waveform distortion. Therefore, the proposed system can reduce its total switching loss and can increase the number of the output voltage levels. In this paper, the effectiveness of the proposed systems is verified through several experiments. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 58–65, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20373     

Zero-current Switching Series Resonant High-voltage DC-DC Converter with Series-connected Primary Windings of Center-tapped Transformer

Abstract—This article proposes a novel zero-current switching series resonant inverter-fed voltage multiplier based high-voltage DC-DC converter. The series resonant inverter in the proposed topology has two power switches (insulated-gate bipolar transistors), two resonant capacitors, and only one high-voltage transformer with center-tapped primary windings. The power switches are connected in the form of a half-bridge network. The leakage inductances of the transformer's primary windings together with resonant capacitors form two series resonant circuits. The series resonant circuits are fed alternately by operating power switches with an interleaved half-switching cycle. The secondary winding of the high-voltage transformer is connected to a voltage multiplier circuit to rectify and boost the voltage. The converter operates in discontinuous conduction mode, and its output voltage is regulated by pulse-frequency modulation. Therefore, all the power switches turn ON and OFF at the zero-current switching condition. The main features of the proposed converter are lower power loss, less cost, and smaller size compared to previously proposed series resonant high-voltage DC-DC converters. The experimental results of a 130-W prototype of the proposed converter are presented both for dynamic and steady-state operation. The results confirm the excellent operation and performance of the converter.     

两种典型的三相SPWM逆变器电路比较

将三相桥逆变器等效变换成形似三个三角形?联结的单相全桥组合而成的三相逆变器,等效而成的单相全桥互相共用一个桥臂。进而在变换后的拓扑基础上提出了一种新的三相桥逆变器数学模型,比较三相桥拓扑和三个三角形联结的单相全桥通过组合而成的三相逆变器拓扑在控制方法、功率容量和输出特性的区别,界定两种三相逆变器的应用领域。     

单相非隔离光伏并网逆变器拓扑推演与分析

针对单相非隔离光伏并网逆变器具有的漏电流问题,对单相非隔离半桥型和全桥型两大类拓扑进行拓扑演化推导,建立了一个桥式拓扑演化网络,研究分析了单相非隔离光伏并网逆变器拓扑的特点,明确了拓扑之间的相互联系,总结出各种桥式拓扑之间的演化规律。并利用总结出的演化规律推导出一种新型拓扑,进一步证明了所提出的演化规律。最后通过PSIM仿真软件进行验证,证明了所提出新型拓扑所具有的漏电流抑制功能的有效性和演化规律的正确性。     

独立/并网双工模式光伏逆变系统的设计

针对目前光伏逆变系统工作模式的单一性,提出一种独立/并网双工模式逆变系统。主电路采用隔离型全桥DC/DC变换器构建前级,使用移相PWM零电压转换(ZVS)控制;采用全桥逆变器构建后级,使用单极性倍频SPWM。在主电路拓扑基础上,研究了各部分的控制方法,给出逆变时不同工作模式下的控制框图,并采用前馈控制方法对其进行改进。提出了一种基于芯片UTC4053的电路切换方法来实现并网和独立两种工作模式的转换。最后研制出一个1 kW的实验样机来验证方案的可行性。     

基于DSP控制的多输出并网逆变器

针对世界各国电网电压规格种类较多的情况,提出一种基于DSP控制的可输出多个国家电网电压规格的并网逆变器。通过DSP控制和2台逆变器的串联和并联,实现了多种规格电网电压的输出,且串联和并联2种运行模式不影响系统的稳定性。详细阐述了逆变器的工作原理,分析了2台逆变器在串联模式下的均压和在并联模式下的均流效果,及串联和并联2种运行模式对系统稳定性及相对稳定性的影响,并以一台1 000 VA基于DSP控制的串并联双降压式半桥逆变器进行了实验验证。实验结果表明在串联和并联2种运行模式下2台逆变器具有很好的功率均分度。     

单相高可靠并网逆变器电路拓扑

针对传统桥式并网逆变器存在桥臂功率开关管的直通问题,提出了一族单相高可靠并网逆变器电路拓扑。所提并网逆变器是由高可靠性单元相互组合而成。分析了双极性和单极性调制高可靠并网逆变器的工作原理,归纳出了高可靠并网逆变器的构成原则。以单极性双降压全桥并网逆变器为例进行了仿真验证。比较分析了传统并网逆变器和所提高可靠并网逆变器。分析结果表明：双降压半桥并网逆变器适合110~120 V电网电压场合,而全桥型高可靠并网逆变器适合220~240 V电网电压场合。     

光伏发电并/离网切换控制策略研究*

对于具有并网及离网双模式运行功能的光伏发电系统,实现两种模式之间的平滑切换一直是控制上的难点。建立了三相光伏发电系统仿真模型,分析研究光伏逆变器的并网、离网两种模式的切换控制策略。提出了一种实现并/离网平滑切换的方法,采用分相并网开关,检测电网电压每相过零实施开关合断并合理配合控制策略的切换时序,离网时则采取PI调节器重载初始值的方式保持逆变器稳定电压输出。仿真结果表明,逆变器输出波形有效地得到改善,证明了该控制方案的可行性。     

半桥变换器与多变压器次级串联的超级电容均压

针对于超级电容串联储能系统中单体电压不均衡的问题,介绍了一种基于半桥变换器和多变压器次级串联的均压电路,可利用多次级绕组减小因变压器单元漏感误差而引起的超级电容单体电压不均衡。该电路结构简单,还可以均衡超级电容器的电压,恒定开关频率和占空比时不需要反馈控制环节。通过分析半桥变换器每个工作模态,建立了输出电压方程,推导了串联超级电容电压均衡方程。根据电路特性,分析了变压器匝比设计方程及实现软开关变压器原边漏感要求。仿真及实验结果表明此均压电路具有均压速度快且均压效果好的特点。     

一种新型单相不对称五电平逆变器

该文对一种新型单相不对称五电平逆变器进行研究，这种新型逆变器是通过将半桥二极管钳位逆变器和传统两电平半桥逆变器共享同一直流母线而获得的。针对这种新型拓扑结构该文分析了一种方波合成与消谐波三角载波PWM相结合的控制方法，在这种控制方法下，新型逆变器允许开关速度较快的器件和耐压值较高的器件工作在一起。文中将这种逆变器与其它三种单相五电平逆变器进行了比较。最后本文对一个单相五电平不对称逆变器电路进行了实验验证，并给出相关结论。     

含扶贫式光伏农村配电网电能质量综合控制技术研究

针对含扶贫式光伏的农村配电网运行特点,提出在逆变器功率控制的基础上,光储联合发电分时协调控制技术。分析了扶贫式光伏电源接入农网后逆变器电压/无功控制原理,在某低压台区建立了光储联合发电系统。其中对逆变器设置死区控制环节保证无功调节优先性,同时分时对光伏电源和储能进行协调控制,平滑功率输出。最后结合Opendss软件对某低压台区进行验证,仿真结果表明所提控制策略能够有效提升农网电能质量运行水平。