混沌映射抑制DC-DC变换器EMI水平的实验研究

探讨了混沌频率调制技术在开关变换器中抑制电磁干扰的实际效果。详细地分析了被调制信号的频谱与混沌系统产生的调制信号的不变密度函数之间的关系。设计了一个简单的、具有均匀分布密度的tent映射混沌电路，并以此电路产生的离散时间混沌信号作为频率调制信号，加入到工作在闭环连续导电模式的Buck变换器中，从而在开关变换器中实现了混沌频率调制，使开关频率随混沌信号随机变化。实验结果证明该技术不但具有有效降低开关谐波峰值和对输出电压影响不大的优点，而且实现电路简单，是解决开关变换器电磁兼容性问题的一种新的有效途径和具有应用前景的技术。     

混沌频率调制降低开关电源传导EMI的研究

利用混沌频率调制技术从噪声产生源头上降低了开关电源传导电磁干扰。将蔡氏电路产生的混沌信号加入脉宽调制芯片,实现了混沌频率调制技术,使开关频率随混沌信号随机变化。简单分析了混沌频率调制降低EMI噪声的原理,并试制了一台混沌频率调制反激变换器电源样机。给出了开关管电流信号的频谱以及传导干扰测试的结果。实验结果表明,该技术能有效降低开关谐波峰值,使开关电源易于通过EMI测试,因此极具应用前景。     

基于混沌扩频的双级矩阵变换器调制策略的研究

双级矩阵变换器由于具有优良的输入输出性能而受到广泛关注。在对双级矩阵变换器调制策略分析的基础上,将扩频调制策略引入到输出双级矩阵变换器调制策略中来抑制电磁干扰和噪声。将混沌扩频技术用于双级矩阵变换器中,用混沌信号改变固定开关频率。为了不影响整流级的零电流换流,采用整流侧和逆变侧同步扩频策略,降低了开关频率和倍频处的谐波幅值,从而达到降低电磁干扰和噪声的目的,仿真结果证实了混沌扩频调制策略的可行性。     

混沌调制对开关变换器EMI抑制有效性的实验研究

探讨了混沌频率调制技术诳元关变换器中抑制电磁干扰(EMI)的实际效果.提出将蔡氏电路加入脉宽调制电路,实现混沌频率调制技术,开关频率随混沌信号随机变化.分析了混沌频率调制抑制EMI噪声的原理,并建立了双管正激变换器的实验样机.实验结果证明,该技术不但具有有效降低开关谐波峰值和对输出电压影响不大的优点,而且电路实现简单,是解决开关变换器电磁兼容性问题的一种新的有效途径.     

周期频率调制降低开关电源传导EMI的比较研究

利用频率调制技术从噪声产生源头上降低了开关电源传导电磁干扰.分析了频率调制降低EMI噪声的原理,并试制了一台周期频率调制反激变换器电源样机.比较了不同周期调制信号情况下开关管电流信号的频谱以及传导干扰测试的结果.实验结果表明,两种调制信号均能有效降低开关谐波峰值,但是三角波调制信号的扩频效果优于正弦波调制信号.     

混沌映射抑制Buck变换器电磁干扰水平的原理研究

为了提高Buck变换器的电磁兼容性能,基于混沌现象的宽频谱特性提出了一种新的变换器控制策略。本文首先详细推导了能够产生可控幅度混沌序列的Logistic映射形式,然后以峰值电流型滞环Buck开关变换器为研究对象,对其在混沌随机与常规周期两种工作模式下的时域和频域特性进行了对比分析,得出了混沌随机模式可以改善开关变换器的电磁兼容性的结论,但电感电流纹波却相应地增加了,从而降低了变换器的效率。仿真结果验证了理论分析。     

频率抖动技术抑制DC/DC变换器电磁干扰的仿真

针对传统的恒定开关频率PwM控制方式引起频谱能量集中、谐波幅值较大的缺点,分析了开关频率抖动技术抑制DC/DC变换器电磁干扰（EMI）噪声的基本原理。采用三角波作为调制信号,应用Matlab实现频率抖动技术的闭环数字仿真。仿真结果表明,频率抖动技术可使输入电流低次谐波幅值得到显著下降,有效地抑制了DC/DC变换器EMI噪声。     

概率密度函数对双随机PWM变换器EMI特性影响研究

电力电子系统中,双随机调制技术能够有效地抑制和减小传导电磁干扰(EMI),而不需增加额外耗费。通过对随机调制开关函数中引入不同的随机分布规律,分析了功率变换器输入电流的谱估计,结果表明应用随机调制技术时,不同的随机分布规律对电力电子系统的EMI特性影响不大;变换器在应用双随机PWM技术时,选择简单的均匀分布规律,可以减少控制系统资源的耗费,通过随机程度参数的调节可以方便地使电力电子系统获得更好的电磁兼容性。     

开关频率抖动技术中调制波优化选取的理论分析

本文采用解析式的方法描述开关频率抖动的过程，对三种常用的正弦波、三角波及指数波在调制正弦载波信号时产生的频谱结构进行详细的计算和分析，得出采用三角波调制可以产生最优的频谱峰值幅度衰减。总结产生不同频谱结构的现象和原因，以此预测任意周期性调制波形对PWM载波调制后的频谱结构，有助于在应用开关频率抖动法降低变换器电磁干扰时调制波形的优化选取。     

混沌扩频抑制交错并联Boost PFC的共模传导EMI

随着电力电子器件的高频化,电磁干扰(EMI)问题日益严峻。为了降低开关电源的传导EMI,这里提出一种基于混沌扩频的交错并联Boost功率因数校正(PFC)变换器调制技术。首先,分析变换器传导EMI路径,建立干扰等效电路;通过推导传统脉宽调制(PWM)和混沌PWM扩频模式下驱动电压的功率谱密度函数,揭示混沌扩频技术降低频谱峰值的基本规律。其次,结合数理统计方法,提出使用概率直方图和概率密度函数来选择更具优越性的蔡氏混沌扩频电路,并利用驱动信号频谱加以验证。仿真与实验结果均表明,与传统PWM相比,在蔡氏混沌PWM作用下,对1 MHz频段内的共模噪声有8～18 dBμV的削弱,对1 MHz以后频段的共模噪声有5～15 dBμV的削弱。该方法能够实现从源头上有效地抑制共模传导EMI,抑制效果明显,并且能够实现频谱连续化。     

Quasi‐active power factor correction on flyback‐based dc/dc converter

This paper presents a novel input current shaper based on a quasi‐active power factor correction (PFC) scheme. In this method, high power factor and low harmonic content are achieved by providing an auxiliary PFC circuit with a driving voltage which is derived from a third winding of the transformer of a cascaded dc/dc flyback converter. It eliminates the use of active switch and control circuit for PFC. The auxiliary winding provides a controlled voltage‐boost function for bulk capacitor without inducing a dead angle in the line current. Since the dc/dc converter operates at high switching frequency, the driving voltage is also of high switching frequency, which results in reducing the size of the magnetic components. Operating principles, analysis and experimental results of the proposed method are presented. Copyright © 2011 John Wiley & Sons, Ltd.     

开关电源电磁干扰抑制技术

讨论了一些新的开关电源电磁干扰(EM I)抑制技术,如EMI滤波器设计技术、软开关技术、共模干扰有源滤波技术、功率管优化驱动技术和扩频调制技术。分析了各EMI抑制技术的原理和设计所面临的问题。这些技术还有待进一步完善。     

Bidirectional isolated three-phase dc-dc converter using coupled inductor for dc microgrid applications

The main objective of this project is to study the analysis and design of an isolated three-phase bidirectional dc-dc converter connected to the dc microgrid system. The proposed topology achieves efficient power conversion with a wide input voltage range, continuous input current, and bidirectional operation. In forward mode operation, the topology acts as a three-phase push-pull converter to reach a step-up voltage conversion ratio (90 to 450 V ). In backward mode operation, the converter acts as an interleaved flyback converter to provide a step-down voltage conversion ratio (450 to 90 V ). Over and above that, in both operation senses, the dc voltage gain is presented. The main advantages of this topology are high-switching frequency, the three-phase transformer that provides galvanic isolation between the dc voltage link bus to the battery or ultra-capacitor storage, and input/output filters size reduction. Besides, a fewer number of power switches, the frequency of output voltage, and input current ripple are three times higher than the switching frequency. The three active switches are connected to the same reference, which simplifies the gate drive circuit. Ultimately, the theoretical analysis of the proposed topology is carefully confirmed with the experimental results of the 4 kW converter prototype.     

dc link voltage control of UPQC for better dynamic performance

The dc link voltage of the Unified Power Quality Conditioner (UPQC) can significantly deviate from its reference during a transient event, caused by load connection/disconnection or/and supply side voltage sag/swell, though in the steady state the average dc link voltage is maintained at a certain preset level. During such transients, due to considerable dc link voltage deviation, the magnitude of the series injected voltage cannot be constant and this has an effect on the load voltage magnitude, which fluctuates. An improved sinusoidal pulse width modulation (PWM) voltage controller for the series compensator is proposed which adjusts continuously the amplitude modulation ratio in response to the dc link voltage deviations. Also, an adaptive dc link voltage controller is proposed which limits the dc link voltage deviation during transients and assures a negligible steady-state error. The effectiveness of the proposed control schemes is demonstrated through simulations.     

Current control of brushless dc motor based on a common dc signal for space operated vehicles

The objective of the paper is to build a simple current controlled modulation technique for brushless dc motors. In electric traction and most other applications, a wide range of speed and torque control of the electric motor is required. The dc machine fulfills these requirements, but it requires constant maintenance. In the brushless permanent magnet motors, they do not have brushes and so there will be lesser maintenance. Brushless dc motors are widely used in applications which require wide range of speed and torque control because of its low inertia, fast response, high reliability and less maintenance. This current controlled technique is based on the generation of quasi-square wave currents using only one controller for the three phases. The current control strategy uses a triangular carrier for the power transistors which is simpler and more accurate than any other options. The advantages of this technique are: (a) The stator currents are completely characterized by their maximum amplitude. (b) The three phases are controlled with the same dc component, and then the phase currents are kept at exactly the same magnitude I_max. (c) The dc link current measurement is not required. (d) Phase currents are kept balanced and phase over currents are eliminated.     

Simplified analysis of fixed-frequency parallel resonant dc/dc converters with pulse-width modulation control

Contents The steady-state analysis of constant (fixed) frequency, parallel resonant dc/dc converters operating under pulse-width modulation control is set forth based on the concepts of harmonic balance analysis and describing function. Performance characteristics in the continuous-conduction mode are fully analyzed for the LC, LLC, LCC and LLCC converters.

---

Vereinfachte Untersuchung von dc/dc-Parallelresonanzumrichtern mit fester Frequenz bei Pulsweitenmodulation

Übersicht Es wird das stationäre Verhalten von dc/dc-Parallelresonanzumrichtern mit fester Frequenz bei Pulsweitenmodulation mittels der Konzepte der harmonischen Balance und der Beschrei-bungsfunktion untersucht. Die Verläufe der Betriebsgrößen werden für LC, LLC, LCC und LLCC-Umrichter umfassend analysiert.

     

A new topology for nonisolated multiport zero voltage switching dc‐dc converter

In this paper, a new multiport zero voltage switching dc‐dc converter is proposed. Multiport dc‐dc converters are widely applicable in hybrid energy generating systems to provide substantial power to sensitive loads. The proposed topology can operate in 3 operational modes of boost, buck, and buck‐boost. Moreover, it has zero voltage switching operation for all switches and has the ability to eliminate the input current ripple; also, at low voltage side, the input sources can be extended. In addition, it has the ability of interfacing 3 different voltages only by using 3 switches. In this paper, the proposed topology is analyzed theoretically for all operating modes; besides, the voltage and current equations of all components are calculated. Furthermore, the required soft switching and zero input currents ripple conditions are analyzed. Finally, to demonstrate the accurate performance of the proposed converter, the Power System Computer Aided Design(PSCAD)/Electro Magnetic Transient Design and Control(EMTDC) simulation and experimental results are extracted and presented.     

Reduced‐order method for mathematical modeling of multiphase dc‐dc converter

A multiphase dc‐dc converter is effective for miniaturization and achieving high‐power density in a switching power supply. However, its mathematical modeling becomes complex as the phase number of the circuit increases. This study proposes a new modeling method to derive a reduced‐order method in a simple manner. The frequency characteristics of the reduced‐order model are fit to those of the original mathematical model of the multiphase dc‐dc converter. Therefore, the efficacy of the proposed method is validated.     

Three-phase step-up/step-down isolated dc-dc converter with wide-range duty cycle for low dc renewable energy sources applications

Renewable sources of low voltage are an important resource in power generation systems. Many provide high output current at low voltage, as the photovoltaic modules and fuel cells systems, therefore, become more popular considering the safety requirements. In this paper, a novel current-fed three-phase dc-dc converter with high-frequency isolation transformer is proposed. This one has the main features as high dc voltage gain, reduced switches count, minimize the volume of the output/input filters, the frequency ripple of the input current and output voltage are three times higher than the switching frequency, best losses distribution and reduced stresses in the circuit. Moreover, it operates with wide-range duty cycle, the soft-start can be used, which allows the input current and the output voltage to be started gradually. Operating with a duty cycle of 1/3 and 2/3, the input current ripple is canceled. The proposed converter is studied qualitatively and quantitatively, being presented the operation principle in continuous and discontinuous conduction mode, dc voltage gain in each operation mode, and the voltage and current stresses for the power components sizing. To validate the operation of the proposed converter, the laboratory design example and experimental results are presented to demonstrate the performance and validate the claims of the converter for wide load variation. Experimental results are presented for a 4-kW prototype, operating in R2 region for continuous conduction mode. Additionally, experimental results in R1 and R3 regions are obtained.     

High-frequency link-type dc/ac converter for ups with a new voltage clamper

This paper proposes a new type of high-frequency dc/ac converter developed for flexible, compact and high-efficiency uninterruptible power supply (UPS) systems. The proposed dc/ac converter consists of a high-frequency inverter, a high-frequency transformer and a cycloconverter with a new voltage clamper. This cycloconverter is capable of being operated by both source-commutation and self-commutation (commutation by turning off the switching device). Consequently, by choosing between the two commutating methods, based on consideration and the internal voltage drop caused by commutating reactance, a compact and efficient UPS can be realized. The voltage clamper effectively reduces power loss of the conversion system. Fabrication of a 10-kVA high-frequency link-type dc/ac converter is described and its loss reduction effect is demonstrated.