多电平逆变器分析与仿真

目前,多电平逆变器常采用电力电子开关器件串联的逆变器,或者功率单元串联叠加的级联式逆变器.两者不仅直流供电电源不同,电路的结构形式也不同.新型级联多电平逆变器不仅结构简单,而且在输出电平数相同时,所需开关管较少,具有良好的工业应用前景.通过分析典型逆变器结构,阐述其结构特点与联系,并通过软件仿真,比较冬自的抗缺点,为高电压大容量多电平逆变器的选择提供有益的参考.     

Overdistention operation of cascaded multilevel inverters

In the past decade, the multilevel power converter has transitioned from an experimental concept to a standard product of many medium-voltage drive manufacturers. By utilizing small voltage steps, the multilevel topology offers higher power quality, higher voltage capability, lower switching losses, and improved electromagnetic compatibility over standard topologies. Recently, several researchers have focused on the cascaded multilevel inverter whereby two multilevel inverters are series connected to a motor load by splitting the neutral connection. The resulting performance is exceptional in terms of power quality since the overall number of voltage levels is effectively the product of the two cascaded inverters. This paper demonstrates that it is possible to extend this performance to an even higher number of voltage levels referred to as overdistended operation. This further improves the power quality that is significant in applications that have stringent total harmonic distorsion requirements, such as naval ship propulsion. A new control is introduced for overdistention operation and is validated with computer simulation and laboratory measurements.     

Circuit aspects of multilevel self-commutated inverters

A comparative analysis of the circuits of cell- and bridge-type, high-voltage, multilevel inverters is given.     

Reduced common-mode modulation strategies for cascaded multilevel inverters

This paper presents modulation strategies for cascaded multilevel inverters that substantially eliminate common-mode voltage on the output phases. The paper begins by developing generic multilevel inverter reference waveforms that use only "allowed" space vectors to achieve reduced common-mode voltage. A graphical technique is then proposed that allows various carrier disposition modulation strategies for a diode-clamped inverter to be converted to equivalent modulation of a cascaded inverter for any fundamental reference waveform. This graphical technique is confirmed for both alternative phase opposition disposition and phase disposition equivalent modulation of a cascaded inverter, and is then used to create reduced common-mode modulation strategies for cascaded inverters from their equivalent counterparts for diode-clamped inverters under both continuous and discontinuous switching conditions. The strategies have been confirmed by both simulation and experimental results obtained using a cascaded five-level inverter.     

多电平逆变器通用电容电压平衡优化算法

针对二极管箝位型多电平逆变器电容电压难以控制的问题,分析了一种简单的多电平逆变器等效模型,用于预测结点电压偏差,提出了一种多电平逆变器电容电压平衡优化SVPWM(space vector pulse width modulation)算法。该算法通过预测不同开关状态下直流侧结点电压偏差,建立目标函数并对其寻优,在每个开关周期选取最优的开关组合达到结点电压平衡。理论分析和试验结果表明,该算法适用于任意电平逆变器电容电压平衡的控制,解决了三电平逆变器电容电压平衡的问题,但在三电平以上的逆变器受调制度限制。针对三电平以上高调制度下电容电压失衡的原因进行了分析,并给出了解决方法。仿真和实验验证了算法的正确性。     

Particle swarm optimization for harmonic elimination in multilevel inverters

In this paper, harmonic elimination problem in multilevel inverters with any number of levels is redrafted as an optimization task. A new method based on particle swarm optimization is proposed to identify the best switching angles with the dual objectives of harmonic suppression and output voltage regulation. The advantages of fundamental frequency harmonic elimination and swarm intelligence are combined to improve the quality of output voltage of multilevel inverters. The validity of the proposed method is proved through various simulation results.     

大容量链式STATCOM的三角载波移相-开关频率最优PWM法控制策略的研究

提出了适用于大容量链式静止无功发生器(STATCOM)的一种新的脉冲控制策略,即三角载波移相-开关频率最优PWM法(PS-SFO-PWM)。这种新的PWM方法兼具三角载波移相PWM法(PSPWM)法和开关频率优化PWM法(SFOPWM)的优点,在不提高开关频率的情况下,实现等效高频载波的效果,并提高了直流电压的利用率。研究了链式多电平逆变器的PS-SFO-PWM技术,给出了PS-SFO-PWM控制方法的基本算法,并以2个H桥串联的5电平链式多电平变换器为例,通过Matlab仿真,验证了方法的正确性。     

A power line conditioner using cascade multilevel inverters fordistribution systems

In this paper, a power line conditioner using a cascade multilevel inverter is presented for voltage regulation, reactive power (VAr) compensation, and harmonic filtering. The cascade M-level inverter consists of (M-1)/2 H bridges, in which each bridge has its own separate DC source. This new inverter can: (1) generate almost sinusoidal waveform voltage with only one time switching per line cycle; (2) eliminate transformers of multipulse inverters used in the conventional static VAr compensators; and (3) make possible direct connection to the 13.8 kV power distribution system in parallel and series without any transformer. In other words, the power line conditioner is much more efficient and more suitable to VAr compensation and harmonic filtering of distribution systems than traditional multipulse and pulsewidth modulation inverters. It has been shown that the new inverter is especially suited for VAr compensation. This paper focuses on feasibility and control schemes of the cascade inverter for voltage regulation and harmonic filtering in distribution systems. Analytical, simulated, and experimental results show the superiority of the new power line conditioner     

Dynamic performance and control of a static VAr generator usingcascade multilevel inverters

A cascade multilevel inverter is proposed for static VAr compensation/generation applications. The new cascade M-level inverter consists of (M-1)/2 single-phase full bridges in which each bridge has its own separate DC source. This inverter can generate almost sinusoidal waveform voltage with only one time switching per cycle. It can eliminate the need for transformers in multipulse inverters. A prototype static VAr generator (SVG) system using 11-level cascade inverter (21-level line-to-line voltage waveform) has been built. The output voltage waveform is equivalent to that of a 60-pulse inverter. This paper focuses on dynamic performance of the cascade-inverter-based SVG system. Control schemes are proposed to achieve a fast response which is impossible for a conventional static VAr compensator (SVC). Analytical, simulated, and experimental results show the superiority of the proposed SVG system     

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     

Opportunities for harmonic cancellation with carrier-based PWM fora two-level and multilevel cascaded inverters

Pulsewidth modulation (PWM) strategies have been the subject of many years of research effort, and the merits of the various alternatives investigated have been argued extensively. In general, it is now accepted that natural or asymmetrical regular sampled PWM with a third harmonic injected or a space-vector centered reference waveform gives the best harmonic performance, with discontinuous modulation having some advantages for higher modulation ratios. This paper uses a general analytical solution for carrier-based PWM to mathematically identify the harmonic cancellation that occurs in various PWM implementations and converter topologies. This solution provides a formal justification for the superiority of natural and asymmetrical regular sampling techniques in eliminating half of their sideband harmonics simply by virtue of their phase leg switching. Then, the use of fundamental reference phase shifting between phase legs to create single- and three-phase 1-1 output voltages is reviewed, and the harmonic cancellation that occurs is identified. One significant result from this analysis is the realization that an odd/triplen carrier/fundamental ratio has no intrinsic harmonic benefit, contrary to the generally accepted wisdom. Finally, opportunities for harmonic elimination in multilevel cascaded inverter systems by carrier phase shifting are investigated, and the optimum phase shift is identified     

A method of construction of multilevel inverters on the basis of capacitor up-converters with a varied structure

A nontraditional method for teh construction of multilevel inverters on the basis of switched-capacitor converters with varied structures working on the principle of hte parallel charge of capacitors from a direct-current source with subsequent consecutive discharge to a load is considered. Results of the analysis of electric processes, power parameters, and the quality of an output voltage and the conductive pulse noise on its input are presented.     

Some experiments on semiconductor laser characteristics

The use of an off-axis holograpic optical element (HOE) as a powerful spectrograph to observe the buildup of laser oscillation as excitation is increased through the threshold value is described. The spectrum in the focal plane may be sensed by a charge-coupled device with output displayed on an oscilloscope screen. The lessons that can be learned from this experiment are discussed     

Fundamental characteristics of semiconductor ring laser gyroscopes

Semiconductor ring lasers have many capabilities of realizing new functional devices. In this paper, we propose a novel optical inertial rotation sensor using a semiconductor ring laser. If a semiconductor ring laser operates as an optical inertial rotation sensor, a very small and simple optical gyroscope can be realized. To our knowledge this is the first demonstration of a semiconductor ring laser gyroscope (S‐RLG). Experimental results are as follows. (1) The Sagnac frequency shift can be detected as a beat note by the terminal voltage change of the semiconductor ring laser without branching the circulating optical power. Therefore, the S‐RLG system can be constructed very simply as compared with already proposed optical gyroscopes. (2) The detected beat frequency between two counterpropagating lasers in the S‐RLG is directly proportional to the applied rotation rate. (3) Furthermore, we present data demonstrating the injection locking phenomenon around low rotation rate. These results verify that the proposed S‐RLG operates as an optical inertial rotation sensor based on the Sagnac effect. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 73–78, 2000     

New class of welding inverters

Results of theoretical and experimental investigations of a new type of a welding inverter, namely, an ac inverter welding apparatus with a frequency of 25?C50 kHz, are given. A schematic circuit of the inverter power part is described, and recommendations of enhancing the safety of operation modes are given.     

Plasmonic semiconductor nanogroove array enhanced broad spectral band millimetre and terahertz wave detection

High-performance uncooled millimetre and terahertz wave detectors are required as a building block for a wide range of applications. The state-of-the-art techno...