外文翻译--变频器使用浅谈.doc

《外文翻译--变频器使用浅谈.doc》由会员分享，可在线阅读，更多相关《外文翻译--变频器使用浅谈.doc（10页珍藏版）》请在三一文库上搜索。

1、河南科技学院机电学院The frequency converter is used and discussed lightlyThe asynchronous motor is such main power equipment of manufacturing enterprise as electricity , chemical industry ,etc. As the high energy consumption equipment, its output power cant be up to the change pro rata of load, majority can o

2、nly turn on through guard or valve degree regulate , but the energy that the motor consumes does not change much, thus cause very great energy to loss . In recent years, one that is with the maturity of the production technology of the frequency converter and range of application of frequency conver

3、ter is extensive day by day, use the frequency converter to carry on technology to transform to the motor power into the energy-conserving , high-efficiency important means of every enterprise.1. Frequency conversion adjusts the speed principle n60 f(1s)/p (1) In the type n-Rotational speed of the a

4、synchronous motor;f-Frequency of the asynchronous motor ;s-The motor is transfered to the difference rate ;p-Logarithm very much of the motor。Can know by type (1 ) rotational speed n in direct proportion to frequency f , only need change frequency f and change the rotational speed of the motor, moti

5、ve power frequency realize that speed regulate.The frequency converter is mainly adopted and handed in- frank- hand over the side when frequency f changes in the range of 0-50Hz, the rotational speed of the motor regulates the range very widely. Frequency conversion transfer speed pass person who ch

6、anges electricity , exchange frequently worker power change through the rectifier into a direct current source first just, then change the direct current source into the frequency , exchange power controllable in voltage in order to supply the motor. The frequency converter one there is generally fr

7、om rectification circuit, in the middle of direct current link, go against not becoming and controlling parting of 4 pieces not to make up. Rectification part three-phase bridge controlled rectifier, is it change some into IGBT three-phase bridge type go against the ng device to go against, and outp

8、ut for PWM wave form, middle direct current for strain wave , direct current energy storage and buffer inactive power link. The wave in harmony is suppressed Outstanding problem that frequency converter use whether in harmony wave interfere, as frequency converter when working, output in harmony wav

9、e electric current of electric current will lead to the fact interfering to the power. Though every frequency converter producer take measures and reach to frequency converter in harmony administration of wave national standard require basically, question needing to pay close attention to most in bu

10、t the wave in harmony remains the selecting type of the frequency converter and uses. Contain other waves in harmony besides base wave in the voltage of output of the frequency converter. Low times of in harmony wave usually exert a great influence on electrical machinery load, cause the torque to p

11、ulse, and higher wave in harmony makes the frequency converter export leaking the electric current to increase of the cable again, make electrical machinery exert oneself insufficient, so level times of in harmony wave that frequency converter output must suppress. Because the rectification part of

12、the frequency converter adopts the controlled bridge type rectification circuit of diode, the middle strain wave part adopt large electric capacity as wave filter , so introduction of rectifier electric current to charge electric current condenser in fact, it is a steeper pulse wave, its wave in har

13、mony is relatively large in weight. In order to dispel the wave in harmony , adopt the following countermeasure mainly: a. Increase frequency converter supply power power impedance generally , interior impedance , power of equipment can is it buffer frequency converter direct current strain function

14、 of inactive power , wave of electric capacity to play. Impedance is short circuit impedance of the voltage transformer in this kind. Look on power capacity relative capacity little frequency converter as, interior impedance value relative and heavy, the less the content of wave in harmony is; The r

15、elative frequency converter of capacity of the power is the larger in capacity, impedance value is relative low , the larger the content of wave in harmony is. Choose frequency converter at supplying power power transformering , had better is it short out impedance heavy voltage transformer to choos

16、e. b. Install reactor install reactor to increase from outside frequency converter supply power interior impedance of power actually. Installs the reactor or installs at the same time on the exchange side of the frequency converter or the direct current side of the frequency converter, can suppress

17、the electric current of wave in harmony . c. The rectification part of the frequency converter is 6 pulse wave rectifiers that the voltage transformer usually operates heterogeneously, so the wave in harmony produced is relatively big. Use heterogeneous operation of voltage transformer, such as make

18、 phase place corner bad Y of 30each other Y、2 voltage transformers made up are formed and equivalent to 12 pulse wave rectifiers, can reduce the electric current of wave in harmony , play a going to the wave in harmony to suppress role.d. Regulate year of the frequency converter Bob Improve Bob in y

19、ear of the frequency converter, can suppress wave in harmony once effectively low . e. Use the wave filter Wave filter can measure frequency converter in harmony wave amplitude and phase place of electric current, produce the electric current contrary to electric current phase place the same in ampl

20、itude of wave in harmony, thus absorb effectively .3. Match of load3.1 Square torque load Air blower, pump load whether industry use equipment most live, frequency converter at most application at the load. It plants square torque load . Generally speaking , have U/f =Const control frequency convert

21、er of mode can meet the demand of load basically, below foundation the main characteristic question that need notice when introducing personning who select of frequency converter. 3.1.1 Have avoided loadingAir blower difficult overload as water pump, guarantee it greater than or mean the capacity of

22、 the motor slightly at the capacity to choose frequency converter; Overload capacity of frequency converter that choose at the same time require to be lower even , up to 120% generally, 1min. But should notice when the function parameter of the frequency converter is chosen and presetted, because th

23、e load one hinders the torque in direct proportion to the square of rotational speed, when the operating frequency is higher than the specified frequency of the motor, to hinder torque can exceed the specified torque load, overfreight motor. So is it control supreme operating frequency can exceed th

24、e specified frequency of the electrical machinery strictly to want.3.1.2 Match that the frequency converter accelerates time and moderates time while opening / stoppingBecause air blower and load of pump rotate inertia to be heavy, it start and when stopping with to accelerate time and moderate time

25、 it matches to be one important problem very frequency converter. Person who select when using , should calculate to accelerate time and moderate according to load parameter time choose short time most frequency converter in frequency converter, in order to take place situation that voltage trip whe

26、n the frequency converter has not flowed to trip while starting and the frequency converter is moderated . But in the production technology sometimes , demand to be very strict to the start-up time of air blower and pump, if above-mentioned time that calculate can at meeting demanding , should redes

27、ign the selecting type to the frequency converter. 3.1.3 Avoid the resonance Because frequency converter through change power frequency of motor is it change electrical machinery rotational speed realize energy-conserving result to come, possible under a certain electrical machinery rotational speed

28、 and load some resonance , axle of department, resonance frequency coincident, cause load axle vibration that department can tolerate , cause equipment stoppage in transit or equipment damage sometimes, so when the function parameter of the frequency converter is chosen and presetted , should follow

29、 the resonance frequency of the axle department of load , through is it jump some frequency and width to establish , prevent system from the resonance phenomenon take place. 3.1.4 Suppress and press it with water hammer effect Pump load easy to is it suppress keep and water hammer effect to happen i

30、n the course of operating actually, so at the time of the selecting type of the frequency converter, should establish alone to this question when the function is established . a. Suppress and press While running at a low speed , because it export the door to make the pressure rise to close in pump l

31、oad, thus cause the vapour of the pump to lose. When the function of the frequency converter is established , through limit minimum frequency of frequency converter is it limit minimum rotational speed of critical point , pump of flow to come, can avoid the emergence of this kind of phenomenon . b.

32、Water hammer effect Pump load flows backwards because of liquid gravity in the pump pipeline while suddenly cutting out. Is it stop valve to be tight against stop valve , leading to the fact electrical machinery overturn , make frequency converter break down or burn out because the electrical machin

33、ery generates electricity to go against. In the systematic design of the frequency converter , should make the frequency converter stop according to the contours of moderating , disconnect the main circuit after the electrical machinery totally stops, or establish the cutting out and moderating stop

34、ping function, can avoid the emergence of this phenomenon . 3.2 Permanent torque load The bringing type conveyer is a typical example of permanent torque load. The basic characteristic of permanent torque load is, in a situation that load is certain, it depends on the friction obstruction and radius

35、 of the cylinder among the belt and cylinder that load hinders the torque . This kind of load torque has nothing to do with the speed of the rotational speed, so in the course of regulating the rotational speed, the hindering the torque of load keeps intact. Permanent torque load, while choosing fre

36、quency conversion to adjust the speed systematically, except according to the routine demand, should choose the frequency converter control method . a. Adjusting the speed range of load. In case of adjusting the speed range not big , choose the frequency converter of comparatively simple and easy V/

37、F control method. When adjusting the speed range very largly , should consider adopting vector control method feedbacked . b. Just load hinders the torque not to change in with certain load cases in permanent torque load, but their transfer to distance yet vary with load when changing to load. When

38、not quite on the torque change range, can choose the frequency converter of comparatively simple and easy V/F control method , to torque change range heavy load , should is it adopt vector control method feedbacked to have to consider. c. If does not have high expectations for mechanical characteris

39、tic , can consider choosing the frequency converter of comparatively simple and easy V/F control method in load, and is requiring higher occasion , must adopt arrow feedbacked. 变频器使用浅谈异步电动机是电力、化工等生产企业最主要的动力设备。作为高能耗设备，其输出功率不能随负荷按比例变化，大部分只能通过挡板或阀门的开度来调节，而电动机消耗的能量变化不大，从而造成很大的能量损耗。近年来，随着变频器生产技术的成熟以及变频器应

40、用范围的日益广泛，使用变频器对电动机电源进行技术改造成为各企业节能、高效率的重要手段。1.变频调速原理n60 f(1s)/p (1)式中n异步电动机的转速； f异步电动机的频率； s电动机转差率； p电动机极对数。由式(1)可知，转速n与频率f成正比，只要改变频率f即可改变电动机转速，动机电源频率实现速度调节的。变频器主要采用交直交方当频率f在050Hz的范围内变化时，电动转速调节范围非常宽。变频调速就是通过改变电式，先把工频交流电源通过整 器转换成直流电源，然后再把直流电源转换成频率、电压均可控制的交流电源供给电动机。变频器的电路一般由整流、中间直流环节、逆变和控制4个部分成。整流部分为三相

41、桥式不可控整流器，逆变部分为IGBT三相桥式逆变器，输出为PWM波形，中间直流环节为滤波、直流储能和缓冲无功功率。2.谐波抑制 变频器使用的突出问题就是谐波干扰，当变频器工作时，输出电流的谐波电流会对电源造成干扰。虽然各变频器厂家对变频器谐波的治理均采取了措施且基本达到国家标准要求，但谐波仍然是变频器选型和使用中最需要关注的问题。 变频器的输出电压中含有除基波以外的其他谐波。较低次谐波通常对电机负载影响较大，引起转矩脉动，而较高的谐波又使变频器输出电缆的漏电流增加，使电机出力不足，故变频器输出的高低次谐波都必须抑制。 由于变频器的整流部分采用二极管不可控桥式整流电路，中间滤波部分采用大电容作为

42、滤波器，所以整流器的输入电流实际上是电容器的充电电流，呈较陡的脉冲波，其谐波分量较大。为了消除谐波，主要采用以下对策：a.增加变频器供电电源内阻抗通常情况下，电源设备的内阻抗可以起到缓冲变频器直流滤波电容的无功功率的作用。这种内阻抗就是变压器的短路阻抗。当电源容量相对变频器容量越小，内阻抗值相对越大，谐波含量越小；电源容量相对变频器容量越大，则内阻抗值相对越小，谐波含量越大。所以选择变频器供电电源变压器时，最好选择短路阻抗大的变压器。 b.安装电抗器安装电抗器实际是从外部增加变频器供电电源的内阻抗。在变频器的交流侧或变频器的直流侧安装电抗器或同时安装，可抑制谐波电流。c.变压器多相运行通常变频

43、器的整流部分是6脉波整流器，所以产生的谐波较大。应用变压器的多相运行，如使相位角互差30的Y、组合的2台变压器构成相当于12脉波整流器，则可减小谐波电流，起到谐波抑制作用。d.调节变频器的载波比提高变频器载波比，可有效抑制低次谐波。e.应用滤波器滤波器可检测变频器谐波电流的幅值和相位，并产生与谐波电流幅值相同、相位相反的电流，从而有效地吸收3. 负载的匹配3.1平方转矩负载 风机类、泵类负载是工业现场应用最多的设备，变频器在这类负载上的应用最多。它是一种平方转矩负载。一般情况下，具有U/fconst控制模式的变频器基本都能满足这类负载的要求，下面根据这类变频器的主要特点介绍选型时需要注意的问题

44、。3.1.1 避免过载 风机和水泵一般不容易过载，选择变频器的容量时保证其稍大于或等于电动的容量即可；同时选择的变频器的过载能力要求也较低，一般达到120，1min即可。但在变频器功能参数选择和预置时应注意，由于负载的阻转矩与转速的平方成正比，当工作频率高于电动机的额定频率时，负载的阻转矩会超过额定转矩，使电动机过载。所以，要严格控制最高工作频率不能超过电机额定频率。3.1.2启/停时变频器加速时间与减速时间的匹配 由于风机和泵的负载转动惯量比较大，其启动和停止时与变频器的加速时间和减速时间匹配是一个非常重要的问题。在变频器选型和应用时，应根据负荷参数计算变频器的加速时间和减速时间来选择最短时

45、间，以便在变频器启动时不发生过流跳闸和变频器减速时不发生过电压跳闸的情况。但有时在生产工艺中，对风机和泵的启动时间要求很严格，如果上述计算的时间不能满足需求时，应该对变频器进行重新设计选型。3.1.3避免共振由于变频器是通过改变电动机的电源频率来改变电机转速实现节能效果的，就有可能在某一电机 转速下与负荷轴系的共振点、共振频率重合，造成负荷轴系不能容忍的振动，有时会造成设备停运或设备损坏，所以在变频器功能参数选择和预置时，应根据负荷轴系的共振频率，通过设定跳跃频率点和宽度，避免系统发生共振现象。3.1.4憋压与水锤效应泵类负载在实际运行过程中，容易发生憋压和水锤效应，所以变频器选型时，在功能设

46、定时要针对这个问题进行单独设定。a.憋压泵类负载在低速运行时，由于关闭出口门使压力升高，从而造成泵汽蚀。在变频器功能设定时，通过限定变频器的最低频率来限定泵流量的临界点最低转速，可避免此类现象的发生。b.水锤效应泵类负载在突然断电时，由于泵管道中的液体重力而倒流。若逆止阀不严或没有逆止阀，将导致电机反转，因电机发电而使变频器发生故障或烧坏。在变频器系统设计时，应使变频器按减速曲线停止，在电机完全停止后再断开主电路，或者设定“断电减速停止”功能，可避免该现象的发生。3.2恒转矩负载带式输送机是恒转矩负载的典型例子。恒转矩负载的基本特点为，在负荷一定的情况下，负载阻转矩取决于皮带与滚筒间的磨擦阻力

47、和滚筒的半径。这类负载转矩和转速的快慢无关，所以在调节转速过程中，负载的阻转矩保持不变。恒转矩负载在选择变频调速系统时，除了按常规要求外，应对变频器的控制方式进行选择。a.负荷的调速范围。在调速范围不大的情况下，选择较为简易的V/F控制方式的变频器。当调速范围很大时，应考虑采用有反馈的矢量控制方式。 b.恒转矩负载只是在负荷一定的情况下负载阻转矩是不变的，但对于负荷变化时其转距仍然随负荷变化。当转矩变动范围不大时，可选择较为简易的V/F控制方式的变频器，但对于转矩变动范围较大的负载，应考虑采用无反馈的矢量控制方式。c.如果负载对机械特性的要求不高，可考虑选择较为简易的V/F控制方式的变频器，而在要求较高的场合，则必须采用有反馈的矢-10 -