基于三维空间矢量算法的三相四桥臂逆变器的研究

对于传统得三相三桥臂逆变电源,当三相负载不对称时,负载中性点电位将会发生漂移,输出三相相电压不再对称,使得负载不能正常工作。三相四桥臂逆变电源,在三相三桥臂的基础上增加一个桥臂作为三相负载的中性点,通过对四个桥臂上下开关的状态进行控制,实现输出三相对称且稳定的相电压。文章主要分析了三相四桥臂逆变器主电路的拓扑结构,在探讨三维空间矢量算法的基础上实现了仿真。仿真结果表明该方案可获得良好的控制特性。     

级联型有源滤波器均压控制方法的研究

研究了级联型H桥有源滤波器（Active Power Filter,APF）的拓扑结构与控制方法;基于级联有源滤波器直流侧电压失衡问题,提出了一种分层控制思想,顶层主要是实现有功指令电流跟踪和相间电压的均衡,底层控制则是实现相内各H桥模块电压的均衡,从而有效的解决了相间电压和相内电压的均衡问题;使用仿真软件PSCAD/ EMTDC初步实现了该控制策略的仿真验证;最后,搭建以DSP+FPGA为控制核心的实验平台并进行试验验证。     

中小功率三相高频节能型谐振极逆变器

作为中小功率发电系统重要环节的三相逆变器的开关频率增大时,开关损耗也显著增大,不利于节能。为实现中小功率三相逆变器的高频化和节能化,提出了一种三相零电压开关谐振极逆变器拓扑结构.当桥臂上的辅助谐振电路处于工作状态时,开关器件并联的电容的电压能周期性变化到零,使开关器件完成零电压软切换,这有利于高频金属氧化物半导体场效应晶体管（Metal Oxide Semiconductor Field Effect Transistor,MOSFET）作为逆变器的开关器件.分析了电路的工作流程,实验结果表明开关器件处于零电压软切换.因此,该拓扑结构对于研发高性能的中小功率三相逆变器具有参考价值.     

基于改进SPWM的三相四桥臂逆变器控制研究

三相四桥臂逆变器由于加入了第四桥臂,使得其负载不平衡或非线性时,逆变器输出电压三相对称且稳定。但第四桥臂的加入,却使得其控制变得较为复杂。该文比较了国内外文献中各种三相四桥臂逆变器控制方法的优缺点,分析了三相四桥臂逆变器的调制信号与输入直流电压之间的关系,在此基础上研究了一种基于三次谐波注入的新型PWM控制方案。仿真和实验显示谐波的注入不会影响输出电流,且该PWM控制方案使得三相逆变器在任意负载情况下均有较好的输出特性。实验验证了该方案的正确性和有效性。     

中小功率三相高频节能型谐振直流环节逆变器

为使中小功率三相逆变器实现在高开关频率下的节能运行,首次提出了一种新型三相谐振直流环节逆变器拓扑结构.设置在逆变器直流环节的辅助电路参与换流过程时,桥臂输入端的直流环节电压能周期性形成零电压状态,主开关和辅助开关都能完成零电压软切换.在高频金属氧化物半导体场效应晶体管（Metal Oxide Semiconductor Field Effect Transistor,MOSFET）作为该逆变器的开关器件时,实现零电压软切换能消除MOSFET的容性开通损耗,有利于优化逆变器效率.文中分析了电路的工作流程.2.5kW样机上的实验结果表明开关器件都处于零电压软切换.因此,该拓扑结构对于研发高性能的中小功率三相逆变器具有参考价值.     

四开关三相逆变器的空间矢量控制

主要研究四开关的三相逆变器电路,该电路由两组开关桥臂和一组电容桥臂组成。它采用了四个基本矢量构成的空间矢量控制方案,并且引入了双环解耦的控制策略。仿真表明了系统设计的可行性,以及解耦控制对系统性能的优化作用。     

节能型三相桥式零电流开关整流器

为使三相桥式整流器实现节能运行,提出了一种节能型三相桥式零电流开关整流器拓扑结构,在各相桥臂上的辅助谐振电路处于工作状态时,整流器的开关器件能完成零电流软关断.三相桥式整流器通常以绝缘栅双极型晶体管（Insulated Gate Bipolar Transistor,IGBT）作为开关器件,实现零电流软关断能消除IGBT拖尾电流产生的关断损耗.分析了电路工作过程,在三相3kW样机上的实验结果表明开关器件实现了零电流软切换.因此,该拓扑结构可实现以IGBT作为开关器件的三相桥式整流器的节能运行.     

高效率三相谐振极逆变器

为优化三相逆变器的性能,提出了一种高效率三相谐振极逆变器.在各相桥臂上增设的辅助谐振电路参与逆变器的换流过程时,桥臂上的各主开关并联的谐振电容的电压能周期性形成零状态,使主开关能完成零电压软切换,而且辅助谐振电路中的各开关器件也能完成零电流软开通和零电压软关断.开关器件实现软切换能降低开关损耗,从而使逆变器实现高效率运行.文中分析了电路的工作流程.3kW样机上的实验结果表明主开关和辅助开关都处于软切换.因此,该拓扑结构对于研发高性能三相逆变器具有借鉴价值.     

新型三相谐振极软开关逆变器

为提高三相逆变器的转换效率,提出了一种新型三相谐振极软开关逆变器拓扑结构,通过在每相桥臂上增加结构简单的辅助电路,实现了主开关的零电压软开通和零电流软关断.逆变器主开关采用金属氧化物半导体场效应晶体管（Metal Oxide Semiconductor Field Effect Transistor,MOSFET）或者绝缘栅双极型晶体管（Insulated Gate Bipolar Transistor,IGBT）时,都能实现无损耗切换,解决了MOSFET内部结电容造成的容性开通损耗问题和IGBT拖尾电流造成的关断损耗问题.分析了电路的工作过程,实验结果表明开关器件完成了软切换.因此,该拓扑结构对于提高逆变器的性能具有重要意义.     

电容中点式三相四线制APF中直流侧电容的选择

三相四线制APF中,采用电容中点式拓扑,直流侧电容上要流过很大的电流,对直流侧支撑电容的耐流能力要求很高。本文以一台30kVA的三相四线制电容中点式APF为例,通过对比分析,证明了在电容中点式APF中,选择薄膜电容比电解电容要更适合。     

Novel compound PWM strategy of a four-leg shunt active power filter

The currently used hysteresis method is of low control accuracy, and the PWM-based strategy fails to provide a high enough response speed; thus, there is always a trade-off between the performances of control accuracy and response speed for a four-leg shunt active power filter (APF) to cope with the large variation in the load harmonic profile. First, an improved SVPWM strategy is proposed in this paper; with the aim to increase the response speed of a four-leg APF by simplifying the implementation of current 3D-SVPWM methods, the principle and realisation of this strategy are explained in detail. Based on these works, a compound PWM algorithm that effectively integrates the improved SVPWM and a PI-based current hysteresis method is proposed to simultaneously guarantee a higher response speed and a higher control accuracy for a four-leg APF. The realisation and parameter tuning of the compound PWM are elaborated. The correctness and effectiveness of the improved SVPWM and the compound PWM strategy are verified by simulations using Matlab/Simulink software. Finally, experimental results on a four-leg APF implemented in a closed-loop real-time simulation platform are presented.     

Application of a three-level NPC inverter as a three-phase four-wire power quality compensator by generalized 3DSVM

A two-level four-leg inverter has been developed for the three-phase four-wire power quality compensators. When it is applied to medium and large capacity compensators, the voltage stress across each switch is so high that the corresponding dv/dt causes large electromagnetic interference. The multilevel voltage source inverter topologies are good substitutes, since they can reduce voltage stress and improves output harmonic contents. The existing three-level neutral point clamped (NPC) inverter in three-phase three-wire systems can be used in three-phase four-wire systems also, because the split dc capacitors provide a neutral connection. This paper presents a comparison study between the three-level four-leg NPC inverter and the three-level NPC inverter. A fast and generalized applicable three-dimensional space vector modulation (3DSVM) is proposed for controlling a three-level NPC inverter in a three-phase four-wire system. The zero-sequence component of each vector is considered in order to implement the neutral current compensation. Both simulation and experimental results are given to show the effectiveness of the proposed 3DSVM control strategy. Comparisons between the 3DSVM and the 3-D hysteresis control strategy are also achieved.     

并联型有源电力滤波器指定次无静差控制策略

为提高有源电力滤波器的补偿性能和动态响应,本文提出了一种基于同步旋转坐标系下的有源电力滤波器的新型的控制策略,通过与某指定次谐波频率同步旋转的旋转坐标变化,将该次谐波变成直流量进行PI调节,实现指定次谐波的检测和控制,然后反变换到与基波同步旋转的坐标系下进行指令的综合和PI再调节,理论上可以实现对任意指定次谐波的无静差补偿,与传统的电流环控制方法相比,补偿精度显著提高,动态响应好,在负载变化剧烈的场合具有明显的优势,也可以对非线性负载产生的谐波和无功电流进行全部补偿,以达到灵活补偿的目的。在改进的控制算法中可以灵活加入相角补偿,以补偿系统的检测环节和电流控制环引入的固有时延。理论分析和试验结果证明了提出的控制策略的优越性。     

Three-Level Inverter-Based Shunt Active Power Filter in Three-Phase Three-Wire and Four-Wire Systems

This paper presents a direct current-space-vector control of an active power filter (APF) based on a three-level neutral-point-clamped (NPC) voltage-source inverter. The proposed method indirectly generates the compensation current reference by using an equivalent conductance of the fundamental component using APF's dc-link voltage control. The proposed control can selectively choose harmonic current components by real-time fast Fourier transform to generate the compensation current. The compensation current is represented in a rotating coordinate system with chosen switching states from a switching table implemented in a field-programmable gate array. In addition, a three-phase four-wire APF based on a three-level neutral-point-clamped inverter is also presented. The proposed APF eliminates harmonics in all three phases as well as the neutral current. A three-phase three-wire NPC inverter system can be used as a three-phase four-wire system since the split dc capacitors provide a neutral connection. To regulate and balance the split dc-capacitor voltages, a new control method using a sign cubical hysteresis controller is proposed. The characteristics of the APF system with an LCL-ripple filter are investigated and compared with traditional current control strategies to evaluate the inherent advantages. The simulation and experimental results validated the feasibility of the proposed APF.      

基于DSP单周控制有源电力滤波器的研究

针对有源电力滤波器中畸变电流检测的快速实时响应问题,研究有源电力滤波器的单周控制原理与控制策略,提出单相并联型有源电力滤波器的单周控制模型。并在以DSP为核心控制器的基础上,设计单周控制有源电力滤波器,对其进行了实验研究,对试验的结果进行了分析。实验结果表明,该法实时性好、控制电路结构简单、动态特性好。     

A carrier-based PWM method for three-phase four-leg voltage source converters

In this paper a voltage modulation method based on a triangular carrier wave for the three-phase four-leg voltage source converter is described. The four-leg converter can produce three output voltages independently with one additional leg. The proposed modulation method for the four-leg converter can be implemented with a single carrier by a simple but useful "offset voltage" concept. The method is equivalent to the so called three-dimensional space vector PWM method, but its implementation is much easier. The maximum magnitude of the balanced three-phase voltage and the maximum magnitude of zero sequence voltage, which can be synthesized simultaneously, are derived. The feasibility of the proposed modulation technique is verified by computer simulation and experimental results. These results show that a proposed carrier-based pulsewidth modulation (PWM) technique can be easily implemented without conventional computational burden.     

A shunt active filter for compensating harmonics and unbalance in three-phase four-wire systems

ABSTRACT

This paper introduces a split-capacitor shunt Active Power Filter (SC-APF) based on Synchronous Reference Frame (SRF) theory. This topology is used in compensating the currents of 3-Ph unbalanced non-linear loads. The voltage control loop used in SRF which is only suitable in controlling Four-Leg APF (FL-APF) is modified to control Spilt-Capacitor APF (SC-APF). The proposed scheme provides compensating the 3-Ph unbalanced non-linear loads with lower number of switches, passive elements, and sensors. The performance of the SC-APF with the modified calculation algorithm is verified through simulation and experimental studies.     

Modeling of multileg sine-wave inverters: a geometric approach

Three fundamental sine-wave inverter topologies are analyzed: two-leg (one-phase, two-wire); three-leg (three-phase, three-wire); and four-leg (three-phase, four-wire). The topologies are “full-bridge” voltage-source inverters with LC filters suitable for producing sinusoidal output voltages. The switching states and corresponding output voltage vectors produced by each inverter are identified and presented along with an analysis of the geometric arrangement of these voltage vectors. A pattern of characteristics is established whereby the “qd” modeling forms commonly used with three-leg inverters are extended to address the expanded capabilities of the four-leg inverter. A unique 4×4 decoupling transformation matrix is presented for the four-leg inverter that enables direct transformation between the four-degree-of-freedom (DOF) leg-modulation space of the inverter and its corresponding 3-DOF output-voltage space. This is shown to be directly analogous to the well-known “abc-qd” transformation developed for the three-leg inverter. Fully decoupled models for each inverter are presented     

Selective Harmonic Elimination PWM Control Scheme on a Three-Phase Four-Leg Voltage Source Inverter

A selective harmonic elimination (SHE) control strategy on a three-phase four-leg inverter is reported in this paper. The control signals of the four legs are calculated as follows: 1) control signals of three legs are mathematically expressed using Fourier-based equations on line-to-line basis as conventional SHE technology, which eliminates lower order nontriplen harmonics, and 2) the fourth leg produces the harmonics that are equal to the lower triplen harmonics produced by the other legs. The inverter has almost symmetric three-phase output voltage with unbalanced load because the fourth leg provides a low-impedance path for the triplen harmonics. The switching-to-fundamental frequency ratio is only 13 and 27 (per unit) p.u. for the three legs and the fourth leg in the proposed prototype, which is with the total harmonic distortion of output voltage lower than 4%. Selected solutions for the switching angles are presented and verified by simulation and experimentation in order to confirm the effectiveness of the proposed scheme.     

Four-wire dynamic voltage restorer based on a three-dimensional voltage space vector PWM algorithm

A modified voltage space vector pulse-width modulated (PWM) algorithm for a four-wire dynamic voltage restorer (DVR) is described. The switching strategy based on a three-dimensional (3-D) /spl alpha//spl beta/O voltage space is applicable to the control of three-phase four-wire inverter systems such as the split-capacitor PWM inverter and the four-leg PWM inverter. In contrast to the conventional voltage space vector PWM method, it controls positive, negative and zero sequence components of the terminal voltages instantaneously. Three 3-D modulation schemes are analyzed with respect to total harmonic distortion (THD), weighted total harmonic distortion (WTHD), neutral line ripple and switching loss over the whole range of the modulation index when the DVR experiences both balanced and unbalanced sags with phase angle jumps. Experimental results from a 9 kW DVR system using a split-capacitor PWM inverter are presented to validate the simulation results.