基于ΣΔ调制的D类放大器系统设计与仿真

针对传统D类放大器脉宽调制技术引起的电磁干扰问题,将一个5阶低通ΣΔ调制器应用于一种带反馈闭环结构的D类放大器中。通过建立ΣΔ调制D类放大器的非理想模型,考察输出信号的功率谱特性。仿真分析表明,该模型能够有效抑制低频段的噪声和谐波失真,在基带内实现较高的信噪比,应用于D类功放,与传统脉宽调制方式相比,有效地改善电磁干扰性能。     

随机频率调制降低开关变换器电磁干扰的研究

利用随机频率调制技术从噪声产生源头上降低了开关变换器的电磁干扰。分析了具有不变概率密度分布的随机频率调制降低开关变换器EMI噪声的原理。将嵌入式系统产生的均匀分布离散随机信号加入脉宽调制芯片,开关频率随机变化,试制了一台随机频率调制开关变换器电源样机。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,使开关变换器易于通过EMI测试,具有应用前景。     

用D类放大器提高音频放大效率

D类采用脉宽调制(PWM)信号取代AB类放大器通常采用的线性信号。PWM信号包括音频信号以及PWM开关频率与谐波。D类音频放大器比AB类放大器效率高得多，因为输出MOSFET可从极高阻抗转变为极低阻抗，从而在作用区操作只有几纳秒。利用上述技术，输出级上损失的功率极低。此     

D类放大器的未来趋势——改善音质与系统性能

传统的D类放大器在通过功率MOSFET进行放大前,需使用一个控制器将模拟或数字音频转换为脉宽调制(PWM)信号,这个控制器一般集成在一个功率后端器件当中。这类放大器拥有高效率的优点,可采用小型(或不使用)散热器,并降低电源输出的功率要求。然而,与A类和B类放大器相比,这类放大器在成本、性能和电磁干扰(EMI)等方面的存在着固有的系统问题。在设计人员的不懈努力下,现代D类解决方案与以往推出的产品相比在性能方面已有了长足的进步,系统更为耐用,音质也更加完美。降低辐射EMI自从D类放大器诞生以来,放大器轨对轨交换所带来的高强度辐…     

D类放大器的未来趋势-改善音质与系统性能

传统的D类放大器在通过功率MOSFET进行放大前,需使用一个控制器将模拟或数字音频转换为脉宽调制(PWM)信号,这个控制器一般集成在一个功率后端器件当中.这类放大器拥有高效率的优点,可采用小型(或不使用)散热器,并降低电源输出的功率要求.然而,与A类和B类放大器相比,这类放大器在成本、性能和电磁干扰(EMI)等方面的存在着固有的系统问题.在设计人员的不懈努力下,现代D类解决方案与以往推出的产品相比在性能方面已有了长足的进步,系统更为耐用,音质也更加完美.     

功放新品种--G类功率放大器

在音频领域里,B类放大器的效率比较高,其他类型的放大器,如A类、AB类效率都低。 后来出现的D类放大器,借助超声脉宽调制技术有可能得到高效率,但若设计不周,效果并不佳。D类放大器的效率在很大程度上取决于电路设计的具体细节和所有器件的特性。其LC输出滤波器只对一个负载阻抗有平整的响应,而且存在有电磁干扰(EMC)的危险。对于有多个声道扬声器的高品质放大器而言,D类放大器难以当此重任。 这付重担留给了G类放大器,在这里,功率是按信号的     

应用于无滤波器D类放大器的改进PWM调制方案

D类放大器的高效特性,使其成为便携式和大功率应用的理想选择。传统的D类放大器需戋一个外部低通滤波器,以从脉宽调制信号（PWM）输出波形中提取音频信号。文章阐述了一种应用于无滤波器D类放大器的改进PWM调制方案,分析了其工作原理、优缺点和引起失真的主要原因。利用这种方法实现的D类功率放大器具有高效率高性能的特点,省掉外部滤波器不仅降低了电路板的空间要求,同时也大幅降低了很多便携式应用的成本。     

混沌频率调制增强开关变换器EMC的研究

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.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Ber noulli映射混沌电路,并加入到工作在双环控制模式的Boost变换器,使开关频率随机变化.实验结果证明了提出的技术能有效降低开关变换器的谐波峰值和应用于开关变换器的可行性.     

功率因数电路的扩频校正和电磁抑制

分析了脉冲宽度调制的频谱特征,利用PWM集成电路和直流母线的脉动纹波电压,实现有源功率因数校正电路中的频率调制;分散干扰噪声频谱,降低噪声信号峰值,抑制电磁干扰;同时减小输入电流谐波失真,提高输入功率因数。调制电路简单实用,在高压钠灯电子镇流器上成功应用。     

一种改进型免滤波D类音频放大器的设计

本文描述了一种基于华虹NEC0.35μmBCD工艺的改进型免滤波D类音频放大器。这种创新的结构基于归一化脉冲宽度调制技术,通过对回路滤波的输出信号进行合理的采样与保持,同时采用迟滞比较和反馈回路控制技术,很好地解决了传统脉宽调制方法中对于互调失真抑制能力较差的问题。     

Selective harmonic control: a general problem formulation and selected solutions

Selective harmonic elimination/control has been a widely researched alternative to traditional pulse-width modulation techniques. Previous and current work has made fundamental assumptions that enforce output waveform quarter-wave symmetry, presumably in order to reduce the complexity of the resulting equations. However, the quarter-wave symmetric assumption is not strictly necessary. It restricts the solution space, which can result in sub-optimal solutions with regards to the uncontrolled harmonic distribution. A more general formulation is proposed, removing the quarter-wave symmetry constraint for two classes of the m-level, n-harmonic harmonic control problem. The special cases of two- and three-level harmonic elimination are presented in detail along with representative solutions for each harmonic control problem. New solutions previously unattainable based on quarter-wave symmetric techniques are identified.     

A digital dual-modulation control for single-phase UPS inverters

A trip-point modulation strategy is proposed for single-phase uninterruptible power supply inverters with an LC filter, which operates simultaneously with pulse-width modulation, named dual-modulation (DM) control. Current estimation and offset current approximation are used conjointly to facilitate the proposed control law. It is shown analytically that the DM control leads to reduced total harmonic distortion (THD) and gains fast transient-state recovery. The simulation and experimental results demonstrate significant amelioration to THD and dynamic state compared to proportional–integral–derivative control under both linear and non-linear loads.     

Virtual stage pulse-width modulation technique for multilevelinverter/converter

The main theme of this paper is to present a new pulse-width modulation (PWM) technique for multilevel inverter/converter control, which provides more degrees of freedom for specifying the cost function than that for step modulation technique, for a given hardware. Therefore, the presented technique eliminates more specified low order harmonics without resorting to the increase of hardware. In comparison with the selective harmonic elimination PWM technique, for the same number of eliminated low order harmonics, the presented technique provides the advantages of both lower total harmonic distortion (THD) and less switching. Simulation and experimental results are presented to confirm the above-mentioned claims     

Flux-based two-degrees-of-freedom algorithm for three-phase electronic converter control

This letter integrates the tracking robustness of two-degrees-of-freedom control and fast dynamic response of flux-based, pulse-width modulation to develop a new current controller for high performance, three-phase electronic converter control. Theoretical analysis shows that the controller can simultaneously achieve good steady-state, transient and harmonic performance, which are challenges not previously met by existing current controllers reported in the literature. Experimental results are presented to verify the performance and practicality of the proposed controller.     

三电平SPWM波的改进算法研究与谐波分析

以提高正弦波脉宽调制（SPWM）供电质量为主要目的,SPWM脉宽调制法通常可分为两电平、三电平和多电平调制法,其中,三电平SPWM波比两电平SPWM波有更好的消除谐波特性。并且基于三电平的SPWM规则采样法是一种为简化SPWM波开关点计算衍生出来的计算方法,一定程度上可以替代比较调制算法。本文提出了一种三电平SPWM波开关点实时计算的方法,并且给出一般性计算公式。通过MATLAB编程,对计算结果进行了谐波分析,同时为了与实际应用相结合,提出了一种包含死区时间的三电平SPWM规则采样算法。在设计开关点算法时,把死区时间计算在内,分析了谐波含量,为工程应用作了铺垫。     

Four-wire dynamic voltage restorer based on a three-dimensional voltage space vector PWM algorithm

A modified voltage space vector pulse-width modulated (PWM) algorithm for a four-wire dynamic voltage restorer (DVR) is described. The switching strategy based on a three-dimensional (3-D) /spl alpha//spl beta/O voltage space is applicable to the control of three-phase four-wire inverter systems such as the split-capacitor PWM inverter and the four-leg PWM inverter. In contrast to the conventional voltage space vector PWM method, it controls positive, negative and zero sequence components of the terminal voltages instantaneously. Three 3-D modulation schemes are analyzed with respect to total harmonic distortion (THD), weighted total harmonic distortion (WTHD), neutral line ripple and switching loss over the whole range of the modulation index when the DVR experiences both balanced and unbalanced sags with phase angle jumps. Experimental results from a 9 kW DVR system using a split-capacitor PWM inverter are presented to validate the simulation results.     

Performance Determination of a Chopper-Controlled Separately Excited DC Motor

Chopper-controlled dc motors have a wide field of application as variable speed drives. The techniques used for chopper control of dc power make use of pulse-width modulation (PWM), pulse-frequency modulation (PFM), and current-limit control. Of these, the pulse-width modulation and current-limit control are more widely used.     

A harmonic injection SPWM method for the high-responsive PMSM control system

In a permanent magnet synchronous motor (PMSM) control system, usually, the phase voltage instruction is limited independently to prevent a three-phase pulse width modulation (PWM) wave from overflowing. This method decreases the efficiency of the bus voltage and causes voltage vector direction errors. To solve these problems, we propose a harmonic injection sinusoidal pulse-width modulation (SPWM). This method uses harmonic injected sinusoidal PWM to improve the utilisation ratio of the bus voltage, and consequently improve system performance. In this paper, we analyse the problem in terms of potential difference. The simulation results show that the proposed method can increase the utilisation ratio of the bus voltage up to 15.4%, and the voltage vector mode obtained with the proposed algorithm is larger than that obtained with the conventional one. The method with harmonic injection consequently improves current response, without affecting voltage vector accuracy. The experiment results validate the proposed method.     

Low switching frequency space vector modulators for high power multimodule converters

Force-commutated multiconverter systems have been proposed and recently implemented for high power applications, particularly high-voltage direct current (HVDC) transmission and flexible ac transmission systems (FACTS) devices, including STAtic var COMpensators (STATCOM). This paper demonstrates that pulse-width modulation (PWM) based on space vector modulation (SVM), and using low switching frequencies (a few hundred Hertz) can be implemented in multimodule power converter systems. The proposed scheme is based on a delayed sampling technique and allows output voltage control and minimization of harmonic components. Pattern generation options are analyzed and system waveforms are presented for different switching frequencies and number of modules. Results are validated by simulation and confirmed by experiments on a 5-kVA prototype unit.     

An AC VRM topology for high frequency AC power distribution systems

In this paper, a series resonant converter with pulse-width modulation (PWM) control is presented as an ac voltage regulator module (VRM) for high frequency ac power distribution systems. The proposed topology has close-to-unity rated power factor, low total harmonic distortion in input current, zero voltage switching under all load conditions, low voltage stress of the active switch and high overall efficiency. Simulation and experimental results are presented to prove the performance of the proposed ac VRM converter.