Cascaded Common Nodal Point Multi-level Inverter Topology

Recent trends in the multi-level inverter (MLI) technology demand reduced number of switches, driver circuits, isolated DC sources, peak inverse voltage (PIV), appreciable number of voltage level, and lower total harmonic distortion. This paper presents an improved cascaded MLI configuration. Each module comprises ten switches, two isolated DC sources, and two capacitors; it can generate a maximum of 9-level output voltage waveform. Optimized switching sequence is developed that ensures minimum switching transitions and is implemented through single-carrier pulse width modulation for the control of the proposed topology. The classical cascaded H-bridge inverter and some recently developed MLI configurations were compared with the proposed inverter circuit. Results show that the proposed inverter configuration generates high number of output voltage levels with reduced number of power switches and PIV. It also has a lower per-unit power loss profile. Unit capacitor voltage balancing scheme is developed, which ensures proper control of the unit step voltage level in each of the cascaded modules, at extreme loading condition. For two cascaded inverter modules, simulation and experimental verifications are carried out on the proposed inverter for an R–L load. Simulation results of the output voltage waveforms and its harmonic spectrum are in conformity with experimental results.     

基于SPWM控制的级联型五电平逆变器仿真研究

针对三电平逆变器输出电压谐波分量高和IGBT承受回路电压过大的问题,采用SPWM控制的级联型五电平逆变器进行改进,分析了级联型五电平逆变器的拓扑结构及工作原理,对载波SPWM控制策略进行了研究,在不同调制比下通过Mat-lab/Simulink仿真,对该控制技术进行了谐波分析,得出了一种适合于级联型五电平逆变器的调制方法。     

一种电流型三相逆变器PWM调制的数字实现

对一种倍频式电流型三相逆变器PWM调制方法进行分析,并用DSP与CPLD配合的数字方式实现了该调制方法.仿真结果显示,该调制方法与传统方法相比具有更好的开关损耗、THD特性.实验结果表明,提出的方案能够高质量地实现该调制方法,具有一定的实用价值.     

分布式电源并网逆变器谐波抑制方法

为了解决传统的比例-积分(PI)控制器由于自身缺陷引起的电压、电流谐波问题,提出了两相同步旋转坐标系下基于比例-积分-谐振(PIR)控制器的电压、电流双闭环逆变器控制策略;同时引入了简化三电平空间矢量脉宽调制(SVPWM)算法,并在此基础上提出相电压重构方法。仿真实验表明,上述控制策略对指定次谐波具有良好的抑制效果,采用该策略的逆变器具有良好的输出特性,进而验证了该控制策略对并网系统的有效性。     

A new structure of three-phase five-level inverter with nested two-level cells

This paper presents a new structure of three-phase five-level inverter with a single direct current (DC) source for low- and medium-voltage applications. The proposed configuration is built with a cascade connection of two-level cells in a nested form and owns the advantages of a reduced number of passive components, total blocking voltage of the switches, and isolated DC sources. In order to make this topology attractive, a comparison is made with five-level inverter topologies proposed for low- and medium-voltage applications in recent years. The proposed circuit is powered using a single DC source and an auxiliary voltage-balancing circuit (AVBC) to maintain the desired DC-link capacitor voltages. A sinusoidal pulse width modulation (SPWM) scheme is implemented in field-programmable gate array (FPGA), using Xilinx blocks developed in MATLAB/SIMULINK environment, to control the inverter switches. The performance of the proposed topology is verified through MATLAB simulation and prototype model for a step change in load. Finally, the experimental results are presented to validate the effectiveness of the proposed topology.     

基于分子动理论算法的三电平逆变器谐波优化

在许多大功率交流传动场合下,开关损耗大。为了降低开关损耗,提高逆变器效率,开关频率一般限制在1 kHz以下,导致牵引逆变器中含有大量的谐波。以应用于大功率电力机车的三电平逆变器为特定的研究对象,建立了三电平逆变器最小相电流总谐波畸变率谐波优化模型。采用分子动理论优化算法求解模型时施加了消除窄脉冲算法,完成全调制范围、多种脉波条件下优化函数的求解。与传统SPWM和SHEPWM比较,MMTPWM具有良好的谐波优化效果。最后,通过仿真实验和硬件实验结果验证了理论分析的正确性。     

一种改进的单周控制的开关功率放大器

针对单周控制开关功率放大器存在的输出直流偏置问题,从理论上进行了分析,结果表明输出直流偏置电压的大小与复位脉冲宽度成正比.为了消除输出直流偏置电压,提出了电压补偿的解决方案,给出了补偿电压的计算公式.对补偿前和补偿后的系统进行了仿真和实验研究.仿真和实验结果表明,电压补偿方法能有效消除输出直流偏置问题,改善放大器的THD,验证了理论分析的正确性.     

Effect of Weather Conditions on Harmonic Performance of PV Inverters

Abstract

The effect of weather conditions on the generation of harmonics in PV systems is investigated. A PV model, including the inverting stage, is considered. The output of the equivalent PV model is fed to the load via an inverter and transformer. The analysis is conducted by using a dataset of weather conditions in a North American city. Two converter techniques, which form the basis for the majority of converters, are used to validate the proposed approach: a square-wave inverter with 60?Hz switching, and pulse width modulation (PWM). Probability density functions and probability distribution models with best fit are determined as aids for improving the quality of the power generated for different range of converter values and the best is selected in this article. The long-term effects of weather conditions on harmonics produced by PV inverters are considered. The results show the variability in amplitude of each harmonic component, the boundaries of each harmonic component, and which harmonic magnitudes occur more frequently. The classic PV DC-AC conversion system has been modeled using MATLAB. The work is validated by using different ranges of dataset for two different converters and the results improved the importance of the proposed work. Also, the results agree with previous studies that have been carried with a different method which could be considered as another way of validation for the proposed work. Based on the generated harmonic variation cases, the appropriate parameter values for dynamic adaptive circuit switching of the filtering system and determining the capacity of the storage system could be determined.