A Modified Sector Based Space Vector PWM Technique for Five-Phase Drives

Space vector PWM (SVPWM) is a popular and well-known technique for standard three-phase drives, which has been extended recently to multi-phase voltage source inverters (VSIs). Several SVPWM techniques, which utilize the principle of vector space decomposition (VSD), have been developed for various operating modes. The VSD approach inherently relies on considerations in two-dimensional (2-D) subspaces, while SVPWM for a multi-phase VSI is in essence a multi-dimensional problem. Hence, an alternative approach to SVPWM, which is based on the direct multi-dimensional space consideration in the space vector selection process rather than on space vector selection in 2-D subspaces obtained by vector space decomposition, has been recently introduced. Good performance has been identified, but the method is complex and difficult for the real-time implementation. This article therefore combines multi-dimensional SVPWM approach with off-line calculations to achieve required output voltage generation under non-sinusoidal and/or unbalanced voltage requirements, which represent the most challenging operating conditions from the point of view of the vector selection for PWM. As a consequence, the implementation becomes rather simple in standard DSPs. The performance of the algorithm is verified by simulation and experimentation. © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

High-voltage autotransformer frequency converters for electric drives

The application of autotransformers in high-voltage ac electric drives with transistor frequency converters is considered. Circuit designs based on independent inverters of lower voltage, which are intended for increasing the power of electric drives, are demonstrated.     

级联式多电平逆变器SPWM控制技术的研究及仿真实现

在高压大功率交流变频调速领域,级联式多电平逆变器目前处于主导地位,而三角载波移相控制技术又是其较适合的控制方略。本文在详细推导级联式多电平逆变器输出波形的基础上,研究分析了其实现的技术方法,并进行了仿真验证,得出了相应的结论。     

Interaction between photovoltaic distributed generation and electricity networks

Electricity power systems worldwide have traditionally been designed to a vertically connected scheme characterised by centralised generation. Over the last few decades, several factors have dictated a gradual shift from the central‐control approach to a more distributed layout where distributed generation (DG) technologies are effectively integrated and not just connected (appended) to the networks; amongst others liberalisation of electricity markets, security and quality of supply and environmental issues. Photovoltaic powered distributed generation (PV‐DG), although still having a much lesser impact than other DG technologies, is increasingly being embedded into electricity distribution networks worldwide within the framework of successful regulatory state and marketing programmes. PV‐DG has added values (benefits) for the electricity systems that extend from peak power and load reduction (when deployed close to electricity consumption points) to participation in grid‐supporting or grid‐forming modes of operation. The question arises as to what the present situation of PV technology is for its optimal integration in distribution networks, whether there are still technical barriers to overcome as well as new opportunities for PV in future renewably supplied electricity systems. This paper presents the current state of knowledge concerning these topics from a European perspective with regard to different grid structures. It also discusses existing standards, new opportunities to provide grid services and research and development needs identified to fully exploit the added‐value—and still developing—benefits of PV‐DG. Copyright © 2008 John Wiley & Sons, Ltd.     

载波交叠特性PWM方法在飞跨电容多电平逆变器中的应用研究

研究了具有载波交叠特性的PWM方法在飞跨电容多电平逆变器中的应用。载波交叠PWM方法具有优化开关利用率，使得开关损耗平均化的特性。经过详细分析，推出在飞跨电容型多电平逆变器中载波交叠特性不能导致飞跨电容的电压平衡。为了应用载波交叠特性，该文提出一种能保证飞跨电容电压平衡的新型PWM方法，并通过实验证明新型PWM方法在三电平飞跨电容型逆变器中的有效性。     

并网光伏逆变器闪变特性测量与分析

辐照度变化和并网光伏逆变器启停机引起的功率波动都可能会引起并网点电压闪变。文章首先分析了闪变与并网点短路容量、阻抗角度及并网功率波动大小的关系,并基于Matlab/Simulink软件搭建了虚拟电网模型和数字闪变测试仪模型。针对目前广泛使用的500k W光伏逆变器开展了不同运行功率和启停机工况下的测试,测量不同工况下该逆变器引起的闪变大小,并对测量结果进行了对比分析。     

一种增强型单相无变压器型逆变器的漏电流抑制拓扑

无变压器型逆变器相比变压器隔离型逆变器,具有更高的效率和更低的成本,已广泛应用于光伏并网系统。由于去除了变压器隔离,其共模漏电流问题会进一步带来严重的EMI和安全问题。针对上述问题,提出了一种增强型单相无变压器型漏电流抑制拓扑。首先,研究了经典交直流解耦方案中仍然存在的漏电流问题;继而提出了新的拓扑和相应的调制策略;最后,搭建了2 k W的实验平台,对提出新拓扑的有效性进行了验证,并与HERIC逆变器进行了对比分析。     

一种共地型低开关纹波光伏微逆变器

提出了一种只包含3个开关的单相非隔离光伏微逆变器拓扑结构。该逆变器为交流侧和直流侧共地的拓扑,从而完全消除了共模漏电流。针对该拓扑还提出了一种调频控制策略,以抑制逆变器直流侧的2倍频功率振荡。此外,在该逆变器的交流侧配置一个小容量的单电感滤波器。将滤波电感与该逆变器的内部电感进行磁集成,以构建纹波转移通道,并通过合理设计耦合系数即可将滤波电感上的开关电流纹波转移至该逆变器的内部电感,进而有效抑制并网电流的纹波。最后,搭建了额定功率为420 W的实验室样机,验证了所提逆变器的有效性。     

并网逆变器LCL接口直接输出电流控制建模及稳定性分析

并网逆变器LCL接口直接输出电流控制存在不稳定的现象。为了揭示其本质,建立了系统线性控制模型,推导出系统特征方程,根据Routh-Hurwitz稳定判据得出重要结论:并网逆变器LCL接口直接输出电流无论采用P、PI还是PID控制,系统均不稳定。该问题简单直接的解决方案是在LCL上串联电阻,以增大相角裕度,提高系统稳定性。本文在系统线性模型的基础上,针对电阻三种可能的串联位置,深入分析了电阻大小、调节器参数以及稳定裕度之间的内在联系并得出精确量化的结论,最后探讨了系统非线性因素如开关动作和过调制饱和等对结论有效性的影响。     

四桥臂微网逆变器高性能并网H-∞控制研究

微网三相逆变器输出电压波形受电网畸变电压、负载谐波电流和直流侧电压中点平衡的共同作用,为使直流侧电压中点维持稳定,并使输出电压波形跟踪参考电压,针对一种四桥臂逆变器结构进行建模,采用H-∞控制策略构造高带宽鲁棒控制器对中线桥臂和三相桥臂进行统一控制。仿真和实验表明,在较大中线电流和电网电压畸变情况下,中线桥臂能够控制中点输入和输出电流近似相等,三相桥臂能够使输出电压维持较低的谐波畸变率,提升微网供电质量。