A Comparative Study of Z-source Inverter and Enhanced Topologies

This paper does some theoretical analysis and simulation studies on the most common topologies of Z-source inverter.As we all know,the traditional Z-source inverter has some problems,such as the voltage of the capacitor which belongs to this topology is higher and there is a startup shock,which caused researchers proposed a variety of improved Z-source topologies to solve these problems.Some of these topologies can increase boost capacity,and some can reduce the capacitor voltage.However,these topologies can improve only part of the problems of the traditional Z-source inverter,which leads to that the users are hard to choose which topologies.Faced with this situation,eleven Z-source topologies are analyzed in terms of boost capacity,inductance start-up current,capacitance stress and economy in this paper.Finally,two kinds of promising topologies were gotten.

A Comparison of Control Methods for Z-Source Inverter

In recent years, Z-source inverters (ZSI) have been proposed as an replacement power conversion concept which it has both voltage buck and boost abilities. In addition, ZSI doesn’t require dead-time to protection short circuit at two switches any of the same phase leg in the inverter bridge and to achieve optimal harmonic of current, voltage. This paper presents two different control methods (CM) for ZSI. The aim of this study to compare between two modulation methods, there are modi?ed space vector pulse width modulation method (MSVM) and the simple boost control (SBC) about the unique harmonic performance features, the total average and peak switching device power of the inverter system. In addition, this paper also analyzes about the ability exceed modulation index in linear region of two CM using MATLAB/Simulink.

The Control Technology Research of the Z-source Three-phase Four-bridge Arm Inverter

Z-source inverter can boost the voltage of the DC-side, allow the two switches of the same bridge arm conducting at the same time and it has some other advantages. The zero-sequence current flows through the fourth leg of the three-phase four-leg inverter so the three-phase four-leg inverter can work with unbalanced load. This paper presents a Z-source three-phase four-leg inverter which combines a Z-source network with three-phase four-leg inverter. The circuit uses simple SPWM modulation technique and the fourth bridge arm uses fully compensated control method. The inverter can maintain a symmetrical output voltage when the proposed scheme under the unbalanced load.

A New Switching Scheme for Z-source Inverter to Minimize Ripples in the Z-source Elements

This paper presents a modification in pulse width modulation （PWM） scheme with unequal shoot-through distribution for the Z-source inverter （ZSI） which can minimize ripples in the current through the Z-source inductors as well as the voltage across the Z-source capacitors. For the same system parameters, the proposed control technique provides better voltage boost across the Z-source capacitor, DC-link, and also the AC output voltage than the traditional PWM. The ripples in the Z-network elements are found to be reduced by 75 % in the proposed modulation scheme with optimum harmonic profile in the AC output. Since the Zqnetwork requirement will be based on the ripple profile of the elements, the Z-network requirements can be greatly reduced. The effectiveness of the proposed modulation scheme has been simulated in Matlab/Simulink software and the results are validated by the experiment in the laboratory.

A Review on Industrial Applications of Z-Source Inverter

Nowadays, Z-source inverters (ZSI) are one of the most emerging topologies in field of power electronics. This paper deals with brief review of Z-source inverter, comprehensive study of its various topologies and significance of ZSI in modern industry. Different PWM techniques are used to obtain wider modulation range and easier real time implementation. This paper provides a systematic reference for future scientists for further development and advancement of ZSI.

Practical Implementation of Embedded Controlled Reduced Switch Z-Source Inverter-Fed Induction Motor Drive

A cost-effective component minimized embedded controlled Z-source inverter for induction motor drive is presented. The proposed topology combines the advantages of a traditional four-switch three-phase inverter with the advantages of the z impedance network (two inductors in series and two X connected capacitors). This new topology, besides the self-boost property, has low switch count and it can operate as a buck-boost inverter. As a result, the new embedded controlled reduced switch Z-source inverter system provides ride through capability during voltage sags, reduces line harmonics, improves power factor, reliability and extends output voltage range. Analysis, simulation and experiment result will be presented to demonstrate these new features.

Ride through Strategy for a Three-Level Dual Z-Source Inverter Using TRIAC

A new ride through strategy is introduced in a three-level dual Z-source inverter, for isolation under semiconductor switching failure condition. Here the output will have no significant decrease in the amplitude and quality. Instead of diodes, the triacs are added to the inverter source ends, as it can perform a bidirectional power transfer also it can operate well in both low and high voltage operating conditions. The faulted part can be isolated by simply altering the firing pulses for turning on/off the triacs using the carrier based SPWM technique and resulting in a boosting output with zero common mode voltage. Consequently, it forms a common floating point or null point with a zero common mode voltage. It is experimentally verified by using MATLAB, and digital oscilloscope.

Control of Z-Source Inverter Connected to a Single-Phase AC Utility System

This paper presents a single-phase Z-source inverter as a power conditioning system for a single phase utility connected system. Z-source inverter is a single-stage topology that has buck-boost feature, which is possible because of additional shoot through state introduced in zero state of the conventional inverter pulse width modulation and provides desired output AC voltage. Small distributed generation （DG） system with alternate energy sources requires power conditioning units with low cost, high efficiency and tolerance to wide range of input voltage variation and has to perform various functions such as dc-ac conversion, system control and achieve power quality norms. To meet some of these requirements a two-loop control strategy for ac side control with grid current feedback with PI control and inner filter capacitor current feedback with proportional control and on dc side PID control for Z-source capacitor voltage regulation are employed, which gives good transient response also suppress load and source disturbances effectively. Theoretical analysis of proposed scheme is established and then simulation results are presented to validate proposed control strategy.

基于EEWT的电力系统超高次谐波检测

随着电力系统逐渐电力电子化,导致大量超高次谐波注入电网,引发了新的电能质量问题。为了解决这一问题,首要任务是对其进行精准的测量。此处提出了一种基于改进经验小波变换(EEWT)的超高次谐波检测方法。根据超高次谐波信号的频域特点,对经验小波变换中原有的频带边界划分方法进行了改进,并通过计算过零率和相关系数对信号中的噪声进行有效滤除。再利用经验小波变换技术,实现各超高次谐波信号的分离,从而对幅值和频率的参数进行检测。通过仿真与实验对实际高频光伏逆变器所产生的超高次谐波进行检测。结果表明了理论分析的准确性以及参数检测结果的精度,从而最终验证了所提方法在实际应用中的可行性以及有效性。

Enhanced adaptive nonlinear extended state observer for pure feedback systems with matched and mismatched disturbances

In this paper, an enhanced adaptive nonlinear extended state observer (EANESO) for single-input single-output pure feedback systems in the presence of external time-varying disturbances is proposed. In this paper, a nonlinear system with matched and mismatched disturbances is considered. The conventional extended state observer (ESO) can only be applied to systems that are in the form of integral chains. Moreover, this method has limitations in the face of mismatched disturbances. In the presence of time-varying disturbances, the traditional ESOs cannot estimate the disturbances accurately. To overcome this limitation, an EANESO is proposed in this paper. The main idea is to design the nonlinear ESO (NESO) to estimate the states of the system and multiple disturbances simultaneously. The observer gains are considered time-varying and adjusted with adaptation laws to improve the estimation accuracy and overcome the peaking phenomenon. Next, the proposed controller is designed based on output feedback to eliminate the effects of multiple disturbances and stabilize the closed-loop system. Subsequently, the stability analysis of the closed-loop system and convergence of the observer error are discussed. Finally, the proposed method is applied to the inverted pendulum system. The simulated results show good performance of the proposed method as compared with a recently published scheme in the related literature.

多功能并网逆变器的预测-等效滑模控制策略

为满足分布式发电系统中新能源消纳和电能质量治理的需求,对多功能并网逆变器(multifunctional grid-tied inverter,MTGTI)兼具电能质量治理功能的关键技术进行研究,针对传统控制方案中补偿电流检测方法精度不高、控制跟踪效果较差的问题,提出一种基于改进型滑模的整体控制方案。首先,将平均值算法引入基于FBD(Fryze-Buchholz-Depenbrock)功率理论的谐波及无功检测方法,提高了补偿电流检测的精度及响应速度,从而提升指令电流的准确度。然后,在滑模控制(sliding mode control,SMC)的基础上结合模型预测控制(mode predictive control,MPC),提出预测-等效滑模控制策略,进一步提高了多功能并网逆变器对复杂指令电流的高精度快速跟踪的控制性能。最后,基于MATLAB/Simulink仿真平台,在并网、负载不平衡、负载突变等不同状态下,验证所提整体控制方案的可行性及有效性。

基于有源阻尼系数优化的逆变器电压前馈控制策略

采用LCL型逆变器的并网系统是新能源并网的主要方式,然而数字控制的延迟和并网电压扰动影响LCL型并网系统的稳定性。为解决上述影响因素,提出了考虑数字延时的并网电压前馈控制策略,降低了并网电流的谐波畸变率和电压带来的影响;分析了有源阻尼系数对谐振尖峰的影响,提出了增强粒子群有源阻尼系数优化方法,提升了并网系统的电能质量和抗扰能力,最后通过仿真验证了所提方法的正确性和有效性。

一种改进线性扩张状态观测器的自抗扰控制宽频带振荡抑制方法研究

针对自抗扰控制策略在并网系统参数变化时能否维持逆变器接入弱电网的稳定性展开了进一步研究。首先,建立了计及频率耦合的自抗扰控制型并网逆变器等效单输入单输出序阻抗模型,并采用Nyquist稳定判据定量分析逆变器输出功率、电网短路比、锁相环以及自抗扰控制器参数变化对并网系统稳定性的影响。其次,针对上述参数变化所导致的弱电网下自抗扰控制型逆变器稳定性降低、宽频带振荡等问题,提出了一种改进线性扩张状态观测器(enhanced linear expansion state observer,e-LESO)的自抗扰控制宽频带振荡抑制方法。通过在传统一阶自抗扰控制器中LESO内部增添比例支路和滤波环节,重塑自抗扰控制型并网逆变器输出阻抗,拓宽其中频段(100 Hz~1 kHz)内呈正阻尼特性的频率范围,从而增强自抗扰型并网逆变器鲁棒性,实现宽频带振荡抑制。最后,通过仿真验证了所提方法的有效性。

非线性负载接入孤网的电压与谐波协同控制

此处首先建立了并联逆变器系统的分层控制模型,提出了增强型虚拟阻抗与谐波补偿器实现了对非线性负载电流和功率的均分且同时抑制了谐波电压,并通过二次控制将微电网电压和频率恢复到额定值。最后通过系统仿真与原理样机实验充分验证了所提控制技术对于并联逆变器系统在非线性负载条件下稳定运行的可行性。

Value of magnetic resonance imaging including dynamic contrast-enhanced magnetic resonance imaging in differentiation between inverted papilloma and malignant tumors in the nasal cavity

Background Distinguishing inverted papilloma （IP） from malignant tumors in the nasal cavity is difficult in a substantial number of cases,thus hindering the administration of appropriate therapeutic strategies.This study aimed to evaluate whether magnetic resonance imaging （MRI）,including dynamic contrast enhanced MRI （DCE-MRI）,could improve differentiation between IP and malignant tumors,and to identify which MRI features were the best in discriminating IP from malignant tumors in the nasal cavity.Methods Non-enhanced,static,and dynamic contrast enhanced MRI was performed in 88 patients with an IP or a malignant tumor in the nasal cavity that had been confirmed by histological results.MRI features of IP and malignant tumors including side,margin,T1 signal intensity,T1 homogeneity,T2 signal intensity,T2 homogeneity,lobulation signs,convoluted cerebriform pattern,extra-sinonasal involvement,pattern of enhancement,Tpeak,Tmax,Clmax,and TIC type were evaluated and correlated with histological findings.Results There were significant differences between IP and malignant tumors in T2 homogeneity,Iobulation signs,convoluted cerebriform pattern,extra-sinonasal involvement,Tpeak,Tmax and TIC types.A convoluted cerebriform pattern had a higher sensitivity and specificity in diagnosis of IP while washout-type TIC had a higher sensitivity and specificity in diagnosis of malignant tumors in the nasal cavity.Non-enhanced combined with static and dynamic enhancement MRI was significantly superior to non-enhanced combined with static enhancement MRI in the differentiation of IP and malignant tumors in the nasal cavity.Multivariate logistic regression analysis identified that the best MRI features were a convoluted cerebriform pattern,extra-sinonasal involvement,and washout-type TIC for both observers （Wang XY and Zhang ZY）.Conclusion Non-enhanced and static combined with dynamic contrast-enhanced MRI improves differentiation of IP and malignant tumors in the nasal cavity.

倒置AAO工艺在地下式市政生活污水处理厂中的应用

贵阳市中心城区某大型污水处理厂设计规模为50000m^(3)/d。采用曝气沉砂池+倒置AAO+二沉池+高效沉淀池/砂滤池的工艺。运行近三年以来,出水水质稳定达到设计标准。其中,实际平均出水COD为7.1 mg/L,NH_(3)-N为0.07 mg/L,TN为6.08 mg/L,TP为0.06 mg/L。该工艺对优先脱氮的污水具有较好的处理能力,为高TN生活污水处理提供了较好的工程实践经验。

增强型Z源逆变器的直流链电压直接控制策略

增强型Z源逆变器与传统Z源逆变器相比不仅具有很强的升压能力,而且很大程度减小Z源网络电容、开关器件电压应力。但Z源逆变器现有控制策略是通过测量电容电压构建闭环间接控制直流链峰值电压,而Z源网络电容电压并不能准确反映直流链电压的动态特性。为了提高增强型Z源逆变器的直流链电压动态响应速度和控制精度,借助于数学建模,提出一种直流链电压直接控制的闭环控制策略,通过直接测量直流链峰值电压来提高系统的控制精度,采用电感内环、直流链峰值电压外环的双闭环控制提高了系统的动态响应速度,有效地抑制非最小相位特性对系统地影响。仿真和实验结果证明控制器对输入和负载扰动具有很好抑制能力。

Z-源/准Z-源逆变器拓扑的演绎机理

为合理选择、设计新型Z-源逆变器(ZSI),需准确理解和把握众多Z-源/准Z-源逆变器拓扑的内在联系。通过分析传统Z-源逆变器的特点、工作原理及拓扑演绎的可行性,结合现有Z-源/准Z-源逆变器拓扑的特征,提出了其拓扑演绎的位置变换原理、替代原理及增强原理,并详细阐释了每一原理的含义及其演化方法。应用替代原理和增强原理,还可演化出多种新型Z-源逆变器拓扑,如带抽头电感的非对称ZSI拓扑和对称增强型ZSI拓扑等,以满足工程应用。研究结果表明:在输入电压为48 V、直通占空比为0.17、调制比为0.8的实验条件下,根据上述原理演绎得到的新拓扑的输出电压为80 V,明显高于传统拓扑的35 V及改进型拓扑的45 V。

通用变频器使用中的几个问题

以英国CT公司通用变频器为例，对变频器的控制方式、制动以及压频比控制作了介绍。文中对富士公司的FRENIC－G9S有关性能也作了说明。

翻转单元对融化过程传热强化作用的数值模拟

为了提高板式相变储能单元的融化传热速率,提出了在相变材料融化过程的适当阶段翻转储能单元以起到传热强化作用的方法,并采用数值法对该方法的传热强化效果进行了分析。研究表明,在融化过程的适当阶段翻转储能单元可提高融化速率30%,其传热强化作用的大小取决于R ay leigh数和Stefan数的大小,且Stefan数越大或R ay leigh数越小,翻转单元的传热强化效果越明显。相比较而言,单元高宽比的改变对传热强化作用的影响相对较小。