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1、PWM直流电机脉冲宽度调制(Pulse Width Modwtated-简称PWM)调速系统产生于70年代中期.最早用于不可逆、小功率驱动,例如自动跟踪天文望远镜、自动记录仪表等 。近十多年来,由于晶体管器件水平的提高及电路 技术的发展,同时又因出现了宽调速永磁直流电机, 它们之间的结合促使PWM技术的高速发展,并使电气驱动技术推进到一个新的高度. 在国外,PWM最早是在军事工业以及空间技术中应用。它以优越的性能,满足那些高速度、高精度随动跟踪系统的需求。近八、九年来,进一步扩散到民用工业,特别是在机床行业、自动生产线及机器人等领域中广泛应用。 可以这样说,六十年代中期发展起来的晶体管OTL电
2、路、OCL电路,特别是桥型无变压器输出的BTL电路,为PWM系统的发展奠定了电路基础,而各种先进的功率器件(如GTR,IGBT模块等)及宽调速直流电机的出现,更为PWM技术的应用提供了良好的条件。PWM系统的特点1)开关损耗小,变流器效率高。2)系统主回路电源是经过整流及大容量电容器虑波后供电,因而不会因电网电压波形的失真而影响调节质量。3)以1KHZ-8KHZ的高频脉冲电流给电机的电枢供电,由于是感性负载,脉冲电流得以滤平,所以波系数小,电机发热量小,可以减小机械变形,从而能提高工作机械的精度。也正是由于波形系数小,电机利用率高,从相同发热量的角度考虑,PWM系统获得可以比SCR系统高1.3
3、-1.8倍的转矩,因此PWM系统可以选用较小容量的电机.特别是工作在正反转频繁的伺服系统中,其优点尤为突出。4)系统的响应频带很宽,可达到100-200HZ以上。因此起制动非常快,而且超调量小,可以大大提高高冲击率机械的生产效率。5)因系统采样频率高,频带宽,所以抗负载扰动的性能好,动态速度下降小,恢复时间快,因此动态硬度好,加工零件表面光洁度高。6)同样由于采样频率高,避开了电机及传动机械的共振点,所以运动平稳,这也是提高加工光洁度的一个有利因素。7)PWM系统很容易地实现四象限运行。当用于2千瓦以下的电机时,在再生制动的情况下,再生的能量可储存在功率电容器中,2千瓦以上的电机,再采用特殊电
4、子线路,让能量馈送到再生负载电阻上去,以加快制动过程,并防止电子元件因过压而造成损坏。8)PWM系统调速范围宽,最低速度可达到1转/24小时。这特别适用于自动记录系统。例如地震监测站的地磁变化曲线的记录等。而在机床伺服驱动系统中应用时,1转/分钟即够用。PWM系统的最低速度实际取决于速度调节器的零点飘移量、速度给定电压的精度与分辩率、以及测速电机的纹波系数和电动机的波动力矩等。从PWM伺服单元本身看,其潜力是很大的。9)有于PWM本身性能的优越,因此不必象SCR系统那样,为了提高系统性能而费尽心机,添加了许多环节,增加了系统的复杂性。例如各种滤波环节、电抗器之类的惯性环节、电流自适应环节以及函
5、数发生器环节等等。使驱动系统的结构更加简单可靠,调整于维护都十分方便。同时对个种参数不同的直流电机均有很好的适应性。PWMThe direct current machine pulse width modulation (Pulse Width Modwtated- is called PWM) to modulate velocity the system to produce in the 70s intermediate stagesUses in most early irreversiblily, the low power actuation,For example automa
6、tic tracking tracking telescope, self-registering instrument and so on. Nearly more than ten for years,As a result of transistor component level enhancement and electric circuit technology development,At the same time and further because appeared the width velocity modulation permanent magnetism dir
7、ect current machine, Between them the union urges the PWM technology the high speed development,And causes the electrical actuation technology to advance newly to highly In overseas,PWM is most early applies in war industry as well as the spatial technology. It by superior performance,Satisfies thes
8、e high velocity, the high accuracy follow-up tracking system demand. Nearly eight, for nine years,Further proliferates to the consumer industry,Specially in domain and so on in engine bed profession, automatic production line and robot widespread application. May say like this,The 60s intermediate s
9、tages develop transistor OTL electric circuit, OCL electric circuit,Specially the bridge no change depressor outputs BTL electric circuit,Has laid the electric circuit foundation for the PWM system development,But each kind of advanced power component (for example GTR,IGBT module and so on) and widt
10、h velocity modulation direct current machine appearance,More the PWM technology application has provided the good condition.PWM system characteristic1) the switch loses slightly,The converter efficiency is high.2) the systematic host ring current is ponders the wave after the rectification and the l
11、arge capacity capacitor to supply power,Thus cannot but affect the adjustment quality because of the electrical network voltage waveform distortion.3) gives the electrical machinery by the 1KHZ-8KHZ high frequency pulse electric current the armature power supply,Because is the perceptual load,The pu
12、lse electric current can filter evenly,Therefore the wave coefficient is small,The electrical machinery calorific capacity is small,May reduce the machinery distortion,Thus can enhance the work machinery the precision. Also is precisely because the wave form factor is small,The electrical machinery
13、use factor is high,Considered from the same calorific capacity angle,The PWM system obtains may SCR system be higher than 1.3-1.8 time of torque,Therefore the PWM system may select the low-power electrical machinerySpecially works in is reversing in the frequent servosystem,Its merit outstandingly.4
14、) the system response frequency band is very wide,May achieve above 100-200HZ. Therefore gets up applies the brake extremely quickly,Moreover over is small,May enhance the high impact rate machinery greatly the production efficiency.5) because the system sampling frequency is high,Band width,Therefo
15、re the anti- load perturbation performance is good,The dynamic speed drops slightly,Restores the time to be quick,Therefore the dynamic degree of hardness is good,Processing components superficially attractive fineness is high.6) similarly because the sampling frequency is high,Has avoided the elect
16、rical machinery and the gearing resonance point,Therefore the movement is steady,This also is enhances the processing smooth finish a favorable factor.7) the PWM system very easily realizes four quadrants movements. When uses in 2 kilowatt below electrical machinery,In electric regenerative braking situation,The regeneration energy may store up in the power capacitor,2 kilowatt above electrical machinery,Again uses the special
