Advanced Pulsewidth Modulated Inverter Techniques

Since its introduction in the mid 1960's the pulsewidth modulated (PWM) inverter has offered a number of significant advantages over other inverter types for low and medium frequency applications. The generation of an acceptable waveform at higher frequency, however, was limited by the characteristics of available power thyristors and modulator design. With the advent of the fast turn-off thyristor and advances in PWM modulator techniques, the PWM inverter now offers application advantages to 200 Hz. PWM design considerations are analyzed, with a discussion of second-generation PWM operation provided.     

Several Modulation Techniques for a Pulsewidth Modulated Inverter

Pulsewidth modulation of a six-step inverter can be accomplished in different ways. Comparisons between different modulation techniques are based primarily on harmonic content in the output waveform and circuit constraints imposed by semiconductor characteristics. Adaptive ratio is a modulation scheme which combines the beneficial features of several available techniques and makes the necessary compromises to optimize the operating characteristics of a modulated six-step inverter.     

Pulsewidth Modulated Inverter Motor Drives with Improved Modulation

The performance of inverter drives, which use the pulsewidth modulated (PWM) technique to control motor applied voltage and frequency, are critically influenced by the choice of the modulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.     

Spectral Errors in the Application of Pulsewidth Modulated Waveforms

Possible spectral errors resulting from the application of theoretically optimized pulsewidth modulated (PWM) waveforms to physical power converters are considered. These errors, produced by commutation rise and fall times, timing errors, and amplitude ripple, are synthesized and analyzed in terms of switching, ramp, and ripple functions. Probabilistic and heuristic results show the relative sensitivity of the error producing terms independent of the PWM technique.     

A Sinusoidal Pulsewidth Modulated Three-Phase AC to DC Converter-Fed DC Motor Drive

The external performances such as power factor, displacement factor, harmonic factor, and ripple factor of a three-phase ac to dc converter-fed separately excited dc motor drive employing sinusoidal pulsewidth modulation (SPWM) control technique are obtained for different speeds and modulation indexes. Since separately excited dc motors with armature voltage control provide constant torque operation, the external performance is also determined for the drive motor operating at different values of constant load torque. Motoring and regenerating operations of the dc drive machine are considered. The three-phase PWM converter-motor drive system is analyzed, taking commutation effects into account in motoring and regenerating operations. The analysis has revealed 27 common modes in one repetitive period of the output voltage. The sequence of modes for all pulses in one period of the output voltage is established. Experimental oscillograms of typical waveforms from a laboratory-sized dc motor are illustrated to verify the basic principles of operation. Although the converter circuit requires some additional components in comparison with the commonly used phase-controlled converter, the improved performance characteristics make it attractive for industrial applications involving large power ratings.     

A Symmetry Correcting Pulsewidth Modulator for Power Conditioning Applications

A wide variety of power converters is of the transformer-coupled push-pull type and uses pulsewidth modulation for output regulation. In designing and operating such converters, serious complications usually arise as a result of unsymmetrical switching of the two power transistors. Caused by small parameter dissymmetries of these transistors, asymmetrical switching normally drives the transformer into saturation. Resulting excessive saturation currents reduce efficiency and put a severe strain on the power transistors, which can eventually cause circuit failure. This paper presents a new pulsewidth modulator circuit which can be advantageously utilized in the design of such converters, and which can effectively cope with the aforementioned symmetry problem. Symmetry correction is accomplished by monitoring the two primary currents and by providing proper feedback of the integrated difference between these two currents.     

18合1主电路模块化空间矢量调制矩阵变换器

提出矩阵变换器(MC)4步换流中一种通用的解码器算法,并给出具体实现过程,可适用于别的开关表和开关换流策略,具有参考价值。分析该MC的空间矢量调制策略和开关表的优化,讨论了硬件电路的设计,提出了基于数字信号处理器(DSP)28335和复杂可编程逻辑器件(CPLD)的联合控制方案,首次解密了4步换流中9个双向开关状态定量求解的步骤,推导出其表达式。搭建了基于AST965驱动的18合1双向开关模块的三相-三相交-交MC样机,实验研究较好地验证了系统设计和控制策略的正确性、可行性和可靠性,为该MC的实际应用和早日产品化提供了有效的设计方法和实验基础。     

分布式太阳能最大功率跟踪系统与PFM／PWM混合调制电源电路特征与应用

文章介绍了分布式太阳能最大功率跟踪系统（DMPPT）的特征及在太阳能路灯系统中的应用,介绍了新型高效率升压/降压DC-DC转换器及带内部开关的高效降压型（DC/DC）转换器、对PFM/PWM混合调制电路技术特征与应用进行了详细分析。     

Characterization of Programmed-Waveform Pulsewidth Modulation

Programmed-waveform pulsewidth modulated (PWM) waveforms, applicable to ac-dc/dc-ac converters, are synthesized and analyzed in terms of several structural parameters. By invoking sensitivity studies and heuristics, optimal PWM structures are identified and contrasted. The results show total harmonic performance as a function of switching levels, waveform types, commutations per cycle, and filter bandpass.     

一种功率MOSFET半桥驱动电路设计

设计了一种用于MUPS装置的功率MOSFET半桥驱动电路,该电路基于TC4420芯片配合SG3525芯片作为驱动和控制模块,提高了逆变器驱动电路正常运行的稳定性。揭示了该MOSFET驱动电路的机理,设计计算了控制和驱动芯片外围电路及主要参数。并通过软件Saber搭建了该模块的仿真模型,仿真结果证明了该驱动电路的可行性。     

A Pulsewidth Controlled AC-to-DC Converter to Improve Power Factor and Waveform of AC Line Current

As a method for improving power factor and waveform of ac line current drawn by an ac-to-dc converter a new pulsewidth controlled converter is proposed, its commutation mechanism is described, and experimental results are given which show a good power factor, a good waveform of the line current, and a wide adjustable range of dc output voltage.     

一种三相应急电源电路的探讨

提出了一种三相应急电源（Emergency Power Supply,EPS）的电路拓扑。它采用双向DC／DC电路作为蓄电池充放电电路,双向PWM变流器作为整流、逆变电路,采用数字信号处理器（Digital Signal Processor,DSP）进行全数字控制。对电路进行了原理分析、仿真和实验。仿真和实验表明了这种电路拓扑的可行性。     

一种改进型单级功率因数校正电路的设计

分析了改进型单级功率因数校正（PFC）电路的电压应力、电流应力,并采用Psim仿真软件对电路进行仿真,给出了样机试验数据表及仿真曲线图。结果表明,断续导电模式下的PFC与DC／DC的单级PFC电路比较适用于小功率AC／DC变换器,且可以得到很好的性能,具有良好的经济效益。     

一起电缆线路事故的分析及对策

分析了一起电缆事故发生的原因,提出了相应的预防对策。     

A Field Modulated Frequency Down Conversion Power System

A new concept in power generation has been theoretically developed and experimentally tested at Oklahoma State University. The generator design incorporates new techniques in field modulation and solid-state alternator output processing. The resulting generator is smaller and lighter than comparable commercial models presently available, and it will operate such that frequency output is independent of the shaft speed of a prime mover.     

Tm-Doped Fiber Lasers: Fundamentals and Power Scaling

We describe fundamental measurements of the properties of thulium (Tm)-doped silica and power scaling studies of fiber lasers based on the material. Data on the high-lying Tm:silica energy levels, the first taken to our knowledge, indicate that pumping at 790 nm is unlikely to lead to fiber darkening via multiphoton excitation. Measurement of the cross-relaxation dynamics produces an estimate that, at the doping levels used, as much as 80% of the decay of the Tm level pumped is due to cross relaxation. Using a fiber having a 25- $mu$m-diameter, 0.08 numerical aperture (NA) core, we observed fiber laser efficiencies as high as 64.5% and output powers of 300 W (around 2040 nm) for 500 W of launched pump power, with a nearly diffraction-limited beam. At these efficiencies, the cross-relaxation process was producing 1.8 laser photons per pump photon. We generated 885 W from a multimode laser using a 35-$mu$ m, 0.2-NA core fiber and set a new record for Tm-doped fiber laser continuous-wave power.      

Power Flow Control of a Power Conversion Circuit for Contactless Power Transformer Systems with Coil Misalignment

The coupling coefficient between the coils of a noncontact power supply system is reduced by coil misalignment. This reduces the output voltage and the active power in the coils. To cope with these problems, an instantaneous current control method is applied to a single‐phase contactless power transformer system in order to apply the equivalent impedance of the PWM rectifier at the load side of the transformer. We propose a control method to supply power constantly to the load even when there is a misalignment in the receiving coils. The limit of the transferred power associated with the proposed control method is investigated. The proposed system, including the control method, is verified by experimental tests over a power range of several tens of watts.     

一种高性能功率因数校正电路研究

给出了一种新型高性能的功率因数校正电路。通常的功率因数校正电路由二极管桥式整流电路和升压式变换器组成。其缺陷是电路工作时,一直有3个半导体器件存在导通压降。在所研究的电路中,当升压变换器功率管导通时,有3个半导体器件存在导通压降;而当升压变换器功率管关断时,只有两个半导体器件存在导通压降。因此,电路工作效率提高到97%。分析了这种电路的工作原理,并给出了仿真和实验结果,证明了理论分析的正确性。     

非正弦及不对称电路中功率现象的探讨

从物理和数学的角度 ,对单相电路、三相电路瞬时有功功率和瞬时无功功率的概念进行了剖析。本文提出 ,瞬时有功功率和瞬时无功功率并不是绝对的 ,瞬时有功功率应该是对应于某一目的的理想功率流动 ,即使对于同一电路 ,瞬时有功和瞬时无功的结果也应随着分析者的目的的不同而不同。本文同时提出 ,三相三线电路的无功流动不仅存在于各相之间 ,而且也可能存在于电源与负载之间。最后 ,本文通过两个具体实例证实了前面的论点