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变频(pin)器对电(dian)网的影响

一、变频(pin)器运(yun)行对电网的影响

变(bian)(bian)频器(qi)(qi)是(shi)(shi)(shi)高(gao)新技术产(chan)品,其主要组(zu)成(cheng)是(shi)(shi)(shi)电(dian)力电(dian)子器(qi)(qi)件和(he)微(wei)电(dian)子器(qi)(qi)件。电(dian)网三(san)相交流电(dian)接(jie)入变(bian)(bian)频器(qi)(qi)的(de)(de)(de)输(shu)(shu)入端,变(bian)(bian)频器(qi)(qi)的(de)(de)(de)输(shu)(shu)入侧是(shi)(shi)(shi)整流电(dian)路,输(shu)(shu)出侧是(shi)(shi)(shi)逆(ni)变(bian)(bian)电(dian)路,因此,其输(shu)(shu)入、输(shu)(shu)出侧的(de)(de)(de)电(dian)压(ya)、电(dian)流含有丰富(fu)的(de)(de)(de)谐波,会(hui)引(yin)起(qi)电(dian)网波形的(de)(de)(de)畸变(bian)(bian);同时电(dian)网电(dian)压(ya)是(shi)(shi)(shi)否(fou)对称、平衡,变(bian)(bian)压(ya)器(qi)(qi)容量的(de)(de)(de)大小及配电(dian)母线上是(shi)(shi)(shi)否(fou)接(jie)有非线性(xing)设备等,也(ye)会(hui)影响变(bian)(bian)频器(qi)(qi)的(de)(de)(de)正常工作。现(xian)在的(de)(de)(de)变(bian)(bian)频器(qi)(qi)内部都有计算(suan)机芯(xin)片(pian)或DSP芯(xin)片,用以实现(xian)变(bian)频器的功能(neng)控(kong)制(zhi)和主(zhu)电路逆变(bian)的驱动(dong)控(kong)制(zhi),由于计算机芯(xin)片的电压(ya)电流(liu)小,工作速(su)度高,故极易受到外界的一些(xie)电气干扰。因此,要实现(xian)电网和变(bian)频器都(dou)能(neng)安(an)全可靠运行,必须对两者之间(jian)的相互干扰采取抑制(zhi)措施。

变频(pin)器(qi)的(de)(de)整流电路和逆变电路都是由非(fei)线(xian)性(xing)器(qi)件组(zu)成(cheng),其电路结构会(hui)导致电网的(de)(de)电压(ya)电流波形(xing)发(fa)生畸(ji)变,三(san)相(xiang)交流电压(ya)URUSUT通(tong)过三(san)相桥式整(zheng)(zheng)流电(dian)(dian)路(lu)将交流电(dian)(dian)变换为直流电(dian)(dian),经(jing)电(dian)(dian)解电(dian)(dian)容(rong)滤波(bo)(bo),使直流电(dian)(dian)压(ya)(ya)基本恒定。整(zheng)(zheng)流电(dian)(dian)路(lu)所(suo)用的(de)(de)二极管为非(fei)线性器件,整(zheng)(zheng)流后输出的(de)(de)电(dian)(dian)压(ya)(ya)向滤波(bo)(bo)电(dian)(dian)容(rong)充电(dian)(dian),其充电(dian)(dian)电(dian)(dian)流的(de)(de)波(bo)(bo)形(xing)取决于整(zheng)(zheng)流电(dian)(dian)压(ya)(ya)和电(dian)(dian)容(rong)电(dian)(dian)压(ya)(ya)之(zhi)差。图1所示为变频(pin)器输(shu)入(ru)电压u、电流i实测波(bo)形。可以(yi)看出在各(ge)相线的输入(ru)电(dian)压(ya)为正弦波(bo)的情(qing)况下,各(ge)相线的输入(ru)电(dian)流并不(bu)是正弦波(bo)。

1 变频器输入电压、电流实测波形

当变频(pin)器处于不(bu)同(tong)(tong)频(pin)率、不(bu)同(tong)(tong)电流的工作状态时,输入电流波形也有(you)所不(bu)同(tong)(tong),图2所示为(wei)55kW变频器驱动笼型异步电动机(ji)负载在(zai)10Hz20Hz50Hz时输入(ru)电(dian)流(liu)(liu)的波形(xing)。可见(jian)随着电(dian)动机的频率和电(dian)流(liu)(liu)的增加,输入(ru)电(dian)流(liu)(liu)由断续(xu)变为连续(xu),电(dian)流(liu)(liu)的波形(xing)畸变也越来越小。对这(zhei)些(xie)波形(xing)用(yong)数学上的傅里叶级数分解,将会得到许多谐波电(dian)流(liu)(liu)分量。这(zhei)些(xie)谐波电(dian)流(liu)(liu)分量因变流(liu)(liu)电(dian)路的种类及(ji)其运转状(zhuang)态、系统、条件的不(bu)同(tong)(tong)而(er)有所不(bu)同(tong)(tong),表3记载了变频(pin)器在不同输(shu)出频(pin)率下(xia)各次谐波(bo)电(dian)流实测数据。

2 变频(pin)器输入电流(liu)波形(xing)

3变频器在(zai)不同输出频率下(xia)各次(ci)谐波电流实测数据

实(shi)验还证明(ming),变(bian)频器运行时,由于整流(liu)侧二(er)极管的换相作(zuo)用(yong),会造(zao)成电源电压波形出现一些缺口(kou)和凸口(kou),如图4所示。

4 变频器输入(ru)电(dian)压波形

综(zong)上所述(shu),变(bian)(bian)频器运行(xing)时,会引起电(dian)网电(dian)压、电(dian)流波形发生畸变(bian)(bian),综(zong)合(he)判断这种畸变(bian)(bian)对系统(tong)的影响(xiang),可(ke)用(yong)下式计算综(zong)合(he)电(dian)压畸变(bian)(bian)率D

式中,U1为(wei)基波(bo)相电压(V),U2U3为二(er)次、三次谐(xie)波相电压(V)。

二、电(dian)网质量对(dui)变频(pin)器寿命的影响

在车间,变(bian)(bian)频器会(hui)用(yong)在不同(tong)的负载上面(mian),不同(tong)的负载对变(bian)(bian)频器本身的影(ying)响(xiang)也不尽(jin)相同(tong)。

在冲(chong)击负(fu)载如电焊(han)机(ji)、电弧炉、轧(ya)钢机(ji)等场合(he),电压经常出现闪变。这时(shi)候变频器产(chan)生的(de)(de)谐(xie)波对(dui)于电网质量有(you)很严重(zhong)的(de)(de)污(wu)染,对(dui)设(she)备本身(shen)也有(you)相当的(de)(de)破(po)坏作用,轻(qing)则不(bu)能(neng)够连(lian)续正常运行(xing),重(zhong)则造成设(she)备输(shu)入回(hui)路的(de)(de)损坏,这样的(de)(de)话会(hui)对(dui)产(chan)品的(de)(de)寿命造成很严重(zhong)的(de)(de)影(ying)响。

(1)在冲(chong)击负载如电(dian)焊机、电(dian)弧(hu)炉、轧钢机等场合建议用户(hu)增加无功静补装置,提高(gao)电(dian)网功率因数和质量(liang)。

(2)在变(bian)频器比较集中(zhong)的车(che)间,建议采用(yong)(yong)集中(zhong)整(zheng)流,直流共母线(xian)供电(dian)方式。建议用(yong)(yong)户(hu)采用(yong)(yong)12脉冲整(zheng)流模式。优(you)点是谐波小、节能(neng),特别(bie)适用于频(pin)繁起动(dong)、制动(dong),电动(dong)机处(chu)于既(ji)电动(dong)运行与发电运行的场合。

(3)变(bian)频器输入侧加装无(wu)源LC滤波(bo)器,减小输入谐(xie)波(bo),提高功率因数,可靠性高,效果(guo)好。

(4)变(bian)频器输入侧加装有源PFC装(zhuang)置(zhi),效果最好,但(dan)成(cheng)本较高。

通过这(zhei)些方式的(de)话(hua)可以帮助变频器充分(fen)的(de)延长(zhang)使用寿命。


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