基于Markov链的变频调速系统随机PWM控制技术

将Markov链引入到传统随机脉宽调制(PWM)技术中,提出了一种基于Markov链的变频调速系统随机PWM技术。能够使随机周期值更均匀地分布在期望周期的周围,从而使输出电流频谱分布更加均匀、减小电机的电磁噪声和机械振动,而且与传统随机PWM相比,输出电流的纹波有明显的减小,提高了系统的控制性能。仿真和实验结果验证了算法的有效性。     

概率密度函数对RPWM逆变器的影响

PWM逆变器工作于人耳可听频率范围时会产生环境污染--声学噪声.随机PWM技术是降低声学噪声的经济、有效方法.随机开关频率PWM技术是噪声抑制效果最好的一种随机PWM方法,而有限个开关频率点的PWM技术是易于实现的,并且可用于闭环控制.基于此,首先讨论了如何对有限个频率点进行优化设计;其次,对有限个频率点的不同概率密度函数(Probability Desity Function,简称PDF)对逆变器输出电压和噪声的影响进行了对比分析.     

三相逆变器随机空间矢量脉宽调制选择性电压谐波消除方法

传统随机脉宽调制(RPWM)策略不能选择性消除或降低系统特定次频率谐波。该文提出一种三相电压型逆变器随机SVPWM(RSVPWM)选择性电压谐波消除方法,利用脉宽调制(PWM)脉冲傅里叶级数中的前后项相互抵消,消除特定次频率谐波,并给出两种选择性电压谐波消除思路。在此基础上,利用占空比、随机整数k、开关频率范围和待消除频率,计算开关周期值,推导开关周期、随机整数k以及其对应频率上下限的通用公式。该方法在实现传统RPWM功能的同时,还能选择性降低特定频率及其整数倍频率的噪声功率,仿真和实验结果证明了该方法的有效性。     

混沌PWM逆变器输出电压功率谱密度分析

逆变器采用混沌PWM(pulse width modulation)调制能够有效抑制开关频率及其倍频附近的高次谐波幅值,从而大大减少逆变器驱动电机的电磁干扰。该文对混沌PWM逆变器输出电压的功率谱密度进行了分析,经过合理简化得到了混沌信号概率密度函数与逆变器输出电压功率谱密度之间的关系。根据功率谱密度的表达式,对比分析了概率分布不同的两种混沌序列(Logistic和Chua’s)对逆变器输出电压功率谱密度的影响。实验结果表明,采用混沌PWM调制可以有效抑制逆变器输出电压的高次谐波幅值,并且概率分布不同的2种混沌信号对PWM逆变器输出频谱的影响差别不大。     

级联型逆变器相移PWM的相移量与输出谐波关系分析

阐述了相移PWM技术在级联型逆变器中的应用，并对相移PWM中各单体逆变器的相移与级联型逆变器输出频谱之间的关系进行了分析：当相移量为T1／m时，输出谐波频率为原有的m倍。仿真和实验结果证实了分析的正确性。     

基于混沌PWM的SRM谐波频谱展开研究

开关磁阻电动机(SRM)固有的开关特性使得SRM在运行时会产生大量的电压谐波,而电压谐波会导致SRM的机械振动和噪声问题,阻碍了SRM进一步的应用。为了减小电压谐波的影响,将混沌PWM技术应用于SRM电压谐波频谱的展开。电压谐波频谱的展开可以将谐波分布在较宽的频率范围之内,从而可以降低局部谐波的幅值。通过MATLAB/Simulink仿真和谐波展开因子(HSF),总谐波失真(THD)的计算,验证了混沌PWM能够提高SRM的谐波频谱展开能力,它对于降低SRM的噪声和振动是非常有利的。     

多电平逆变器多载波PWM调制策略的研究

介绍了多电平逆变器的思想,对多电平逆变器不同的拓扑结构进行了比较,研究和分析了用于多电平逆变器不同的多载波PWM调制策略.通过对未滤波的逆变器输出电压的谐波分析,对不同调制方法在线性调制区的谐波特性进行了比较.同时,也提出了一种混合的调制策略.分析了不同调制策略在不同的电平数下所具有的特性.讨论了逆变器电平数的增加对于输出电压频谱的影响,也研究了过调制对于输出电压频谱的影响.     

一种SVPWM逆变器输出电压谐波的分析方法

波形控制技术是逆变器领域的研究热点,需要研究有效的方法来分析相关PWM逆变器的输出电压谐波及其频谱.采用一种基于二维傅里叶级数的数学解析法,对两电平SVPWM逆变器的相电压谐波幅值、线电压频谱的通式进行数值分析,并通过仿真与实验进行验证.     

PWM驱动系统中的共模电压及抑制

针对PWM逆变器在工作时产生的共模电压可能损坏电机轴承,产生电磁干扰等降低系统可靠性的问题,对共模电压的特性及其负面影响进行了理论分析和实验验证,并得出共模电压的抑制方法.提出一种由一个单相逆变器和一个五绕组变压器组成的逆变器输出有源滤波器结构来消除共模电压.该滤波器可以构建一个与PWM逆变器输出的共模电压大小相等、相位相反的共模电压,通过五绕组变压器叠加到电机端,从而消除电机端的共模电压.由统一的控制单元同时输出PWM逆变器和单相逆变器的控制信号,给出滤波器的相关控制策略及设计方法.实验验证了所提出的滤波器消除共模电压及其负面效应的有效性.     

新能源逆变系统中VSG控制时随机激励的谐波抑制研究

虚拟同步发电机通过模拟同步发电机的外特性，为系统提供惯量及阻尼支撑，使逆变系统能安全稳定运行。由于新能源逆变系统中非线性负荷的存在，系统的输出谐波受到污染，影响输出的电能质量。为优化系统输出，本文结合VSG控制算法,在有噪声的系统PWM调制波中引入一个随机激励，再和载波比较而生成驱动信号。通过电压功率谱密度对其谐波分布情况进行分析。仿真结果显示，采用随机激励的方法对VSG逆变器的输出电压波形有一定程度的改善，与引入随机激励前相比，输出的A、B、C三相电压的总谐波因素（THD）分别降低了11.32%、11.60%和11.42%，表明了本方法的合理性及有效性并适用于工程应用中。     

Determination of mechanical resonances in induction motors byrandom modulation and acoustic measurement

Acoustic noise emission from PWM-VSI inverter driven induction motors is a well-known problem. The generated noise depends mainly on two factors: the harmonic content of the supply voltage waveform; and the mechanical resonance frequencies of the induction motor. It is necessary to know the mechanical resonances to optimize the switching scheme of the inverter to reduce the noise emission. Measuring the resonance frequencies is normally a laborious process. This paper introduces a new method for estimating the mechanical resonances from acoustic noise measurements. Employing random modulation of the output voltage of the inverter, the voltage spectrum can be spread over a wide frequency range. Using the spectrum analysis of the measured acoustic noise, the resonances can easily be estimated as the dominant frequencies of the acoustic noise spectrum. The method was tested on a 2.2 kW induction motor at no load and full load. Some of the mechanical resonances of the motor at no load were calculated by the Holzer method. The calculations showed good agreement with the sound measurements. The influence of the fan cowl was investigated and it is concluded that this is an important factor in the acoustic noise emission. Finally, it was observed that new mechanical resonances appeared when the induction motor was loaded by a pump drive system, and they were estimated by the measurement technique     

单相逆变器随机PWM选择性消谐滞环随机扩频方法

在随机脉冲宽度调制(RPWM)中,要求逆变器的瞬时开关频率分布在较宽的频率范围内,以获得较好的随机性.然而,当开关频率持续偏高时,逆变器的开关损耗将会增加;当开关频率持续较低时,会引起输出电流纹波的增加.现有的RPWM选择性谐波消除方法在随机扩频的过程中不能有效地控制逆变器的开关频率.该文提出一种单相逆变器RPWM选择性消谐滞环随机扩频方法.根据RPWM策略中有效随机数k与开关频率的关系,合理选择随机数k,既可以保证逆变器瞬时开关频率在较宽的范围内随机分布,又可以将平均开关频率控制在预先设定的频率范围内.在RPWM选择性消谐过程中,当开关频率较低而引起电流纹波增加时,该方法可以通过提高平均开关频率来减小纹波.     

基于dSPACE的永磁同步电机低振动噪声控制策略

为降低变频器供电引起的永磁同步电机(PMSM)电磁振动噪声,首先理论分析了变频器引入的PMSM振动噪声源,然后利用MATLAB/Simulink建立仿真模型,通过d SPACE进行编译并控制一台PMSM,比较了随机开关频率调制技术和死区补偿技术降低振动噪声的优缺点,提出一种混合随机开关频率-死区补偿技术。试验结果表明,此方法综合随机开关频率调制技术和死区补偿技术的优点,能降低逆变器引入电流谐波引起的中低频振动噪声和逆变器开关频率与电流谐波相互作用引起的高频振动噪声。     

电能变换领域中随机脉宽调制技术研究概况及展望

相较于传统的脉宽调制技术,随机脉宽调制具备有效的谐波频谱分散能力,从而实现机电负载噪声的削弱。随机脉宽调制技术包括起步的随机开关调制、后续的随机脉冲位置与随机开关频率等3个基本方法。随着电力电子技术的整体发展,随机脉宽调制已从传统的载波调制逐渐拓展到空间矢量调制之中,应用范围日趋广泛,谐波频谱分散与功率谱峰值抑制的效果不断提升。同时,新的优化方案不断被提出,对谐波频谱及功率谱的分散效果亦在不断提高。梳理了随机脉宽调制的研究历程,总结了数种典型的随机脉宽调制的基本原理,并对未来随机脉宽调制的研究方向作出展望,为随机脉宽调制技术的深入研究提供参考。     

变频器输出滤波器的模糊优化设计

该文基于模糊集理论研究了变频器输出滤波器的模糊优化设计问题。文中根据基波压降、电容支路电流和谐波总畸变的工程约束范围建立了滤波器电感值及电容值的模糊限制集，提出了以满意度为综合指标的模糊优化目标函数，它是费用因素、谐波总畸变、电容谐波电流和电感基波压降的加权之和，给出了目标函数的求解方法。仿真与实例设计表明，采用模糊优化设计结果，不仅能够满足各种性能指标要求，更重要的是传动系统的安全裕度得以提高。     

Electro-mechanical analysis of the audible noise of an inverter-fedsquirrel-cage induction motor

The audible noise emitted by a three-phase squirrel cage induction motor fed by a frequency inverter is determined by the electromagnetic and mechanical behavior of the components of the drive. A computerized analysis method is described that uses theoretical and experimental data for predicting the audible noise spectrum components. Starting from the inverter voltage and the motor data, the electromagnetic forces are predicted and analyzed. The mechanical natural frequencies are considered, either in a theoretical (finite element calculation) or in an experimental (modal analysis) methodology, to predict the vibrational behavior of the machine. The scheme contains the following steps: analysis of the frequency spectrum of the inverter used; synthesis of the magnetic force spectrum accounting for the motor data: calculation or measurement of the resonant data of the stator assembly; and comparison of the force spectrum and the resonant data. These various steps are discussed     

基于多电平随机脉宽调制技术的共模电压和谐波抑制方法

在PWM电机驱动系统中,多电平逆变技术可以降低系统中的共模电压和谐波含量,但是由于开关频率是固定的,在开关频率处的谐波仍很大。随机开关频率空间矢量调制技术可以通过对零矢量的控制,实现对共模电压的抑制,并且开关频率的随机化,使得开关频率处的幅值较大的谐波分散为一定带宽的幅值较小的谐波,降低了谐波的幅值。给出了混合型七电平逆变器的拓扑结构及控制方法,将高压单元的低频输出和低压单元的高频输出进行叠加,实现七电平的电压输出。分析了不同的开关状态对共模电压的影响,提出了用于共模电压抑制的矢量选择方法和用于降低谐波的开关频率随机化方法,仿真和实验结果显示,多电平逆变技术和随机脉宽调制技术的结合使用,大大降低了系统的共模电压和开关频率处的谐波分量。     

Optimal power control strategies for neutral point clamped (NPC)inverter topology

A programmed pulsewidth modulation (PWM) technique for selectively eliminating several lower-order harmonics at the output of a neutral point clamped (NPC) inverter topology is investigated. The switching function approach is utilized to derive relevant analytical expressions for input/output variables. A thorough evaluation of the NPC inverter topology based on the switching function approach is described. Optimal power control strategies for an NPC inverter employing programmed PWM patterns are proposed. For a constant-frequency variable-voltage NPC inverter power supply, the proposed strategy is to maintain a minimum specified total harmonic distortion employing a low-output impedance filter. In the case of an NPC inverter powering an AC motor drive, the proposed strategy is to maintain a minimum specified harmonic current factor. The proposed power control strategies are achieved without substantial increase in inverter switching frequency and are therefore suitable for high-power applications employing gate-turn-off-thyristor (GTO) type devices     

Comparative investigation of PWM techniques for a new drive for electric vehicles

Results of a comparative investigation of deterministic and random pulsewidth modulation (PWM) techniques to be employed in a new ac drive for electric vehicles are presented. The study, employing the advanced simulation package SABER from Avant! Corporation, was focused on the reduction of electromagnetic interference (EMI) when a deterministic PWM strategy is replaced with an RPWM method. To assess the impact of the PWM technique on the drive performance, the drive efficiency, torque ripple, and dynamic response of the current control system were also investigated. Two RPWM techniques characterized by random variations of switching frequency of the inverter were considered: one with the sampling frequency of the modulator varying in step with the switching frequency, and one with a fixed sampling frequency equal to the average switching frequency. The study has demonstrated good EMI-mitigating potentials of RPWM techniques, whose use results in EMI reduction by 10 dB and more, while the drive performance is barely affected.     

Comparison of PWM and PFM induction drives regarding audible noise and vibration for household applications

This paper is aimed at comparing the performance of pulse frequency modulation (PFM) and pulsewidth modulation (PWM) techniques regarding audible noise generated from inverter-driven induction motors. For the purpose of illustrating the performance of the two modulation techniques, a drive developed for washing machine applications is considered. First, the measured and simulated harmonic content of this inverter is compared with the measured harmonic spectrum of a three-phase input-output commercial variable-frequency inverter. It is found that despite the 8-bit processor inexpensive implementation, the total harmonic distortion (THD) of PFM is comparable to the THD of PWM in more sophisticated applications. It is discovered that the harmonic spectrum of PFM exhibits harmonics of smaller magnitude distributed over 0.9f/sub o/--2.1f/sub o/ (base switching frequency) range, as opposed to a smaller number of dominant harmonics of PWM. Next, the prototype drive is programmed to generate both sine-PWM and PFM waveforms. The motor is driven at several frequencies and the audible noise and vibration level of the motor is measured. It is observed that the type of current harmonic content of PFM leads to reduced noise and vibration.