DZ242電火花線切割機(jī)電氣控制系統(tǒng)的設(shè)計(jì)
DZ242電火花線切割機(jī)電氣控制系統(tǒng)的設(shè)計(jì),dz242,電火花,切割機(jī),電氣,控制系統(tǒng),設(shè)計(jì)
電 火 花 線 切 割 機(jī) 電氣系統(tǒng)設(shè)計(jì),姓 名：劉洪義
專 業(yè)：自動化
指導(dǎo)教師：白文峰,1.本文研究的目的和意義,從老式的電火花線切割機(jī)到此時(shí)的數(shù)控電火花線切割機(jī)，不論從走絲方式還是控制方式上都得到了很大的改進(jìn)，最重要的就是數(shù)字程序控制取代了過去的模仿形控制和光電跟蹤控制。
當(dāng)電火花線切割機(jī)生產(chǎn)工藝要求的提高，原有的線切割機(jī)電氣系統(tǒng)將不能滿足生產(chǎn)工藝的要求。而設(shè)計(jì)的電氣控制系統(tǒng)的好壞將直接影響到整臺切割機(jī)的生產(chǎn)工藝系數(shù)。,電火花線切割機(jī)工作原理,電火花線切割加工的工作過程主要包括以下三個(gè)部分
1.電極絲與工件之間的脈沖放電。
2.電極絲沿其軸向（垂直或z方向）做走絲運(yùn)動。
3.工件對于電極絲在X.Y平面內(nèi)做數(shù)控運(yùn)動。,2.電火花線切割機(jī)電氣系統(tǒng)的設(shè)計(jì),1.根據(jù)電火花線切割的工作原理，采用微型計(jì)算機(jī)來控制步進(jìn)電機(jī)，使電極絲按照事先所編訂好的程序圖形做運(yùn)動。系統(tǒng)具有自動顯示功能，由鍵盤控制系統(tǒng)啟、停及選擇需要程序圖形等功能。
2.主要幾項(xiàng)技術(shù)指標(biāo):
（1）加工軌跡：任意平面曲線及直線
（2）加工精度：輪廓線--±0.01毫米
圓弧隨圓度--±0.02毫米,3. 系統(tǒng)結(jié)構(gòu)框圖,4.控制單元的設(shè)計(jì),5.系統(tǒng)主電路的設(shè)計(jì),系統(tǒng)的主電路主要是由芯片 CH250 和步進(jìn)電機(jī)組成，步進(jìn)電機(jī)在驅(qū)動脈沖的作用下，實(shí)現(xiàn)其功能，CH250輸出雙三拍，單六拍等脈沖信號，供不同性能步進(jìn)電機(jī)驅(qū)動需要，適當(dāng)施加有關(guān)引出端的電平，可控制步進(jìn)電機(jī)正轉(zhuǎn)和反轉(zhuǎn)。當(dāng)CPU給定CH250以驅(qū)動信號，CH250將信號分配給電機(jī)驅(qū)動電路,6.位置檢測反饋裝置 （1）光柵傳感器的選擇,QH-200型光柵尺實(shí)物圖,光柵傳感器輸出兩路相位相差為90的方波信號A和B,（2）.四倍頻電路,采用10MB晶振產(chǎn)生全局時(shí)鐘CLK，假設(shè)信號A超前于B時(shí)代表指示光柵朝某一方向移動，A滯后于B時(shí)表示光柵的反方向移動。A，B信號分別經(jīng)第一級D觸發(fā)器后變?yōu)锳＇，B＇信號，再經(jīng)過第二級D觸發(fā)器后變?yōu)锳″，B″信號。D觸發(fā)器對信號進(jìn)行整形，消除了輸入信號中的尖脈沖影響，在后續(xù)倍頻電路中不再使用原始信號A，B，因而提高了系統(tǒng)的抗干擾性能。在四倍頻辨向電路中，采用組合時(shí)序邏輯器件對A＇A″，B＇B″信號進(jìn)行邏輯組合得到兩路輸出脈沖：當(dāng)A超前于B時(shí)，ADD為加計(jì)數(shù)脈沖，MIMUS保持高電平；反之，當(dāng)A滯后于B時(shí)，ADD保持高電平,MINUS為減計(jì)數(shù)脈沖．,7.外圍電路的設(shè)計(jì),（1）矩陣式鍵盤和6LED顯示電路,8279是一種管理鍵盤和LED顯示器的專用可編程控制芯片。它能對8位共陰極LED顯示器或64個(gè)LED發(fā)光管進(jìn)行管理和驅(qū)動，同時(shí)能對多達(dá)8又8的鍵盤矩陣的按鍵情況進(jìn)行監(jiān)視，具有自動消除鍵抖動并識別按鍵代碼的功能，從而可以提高CPU工作的效率。因此，在微型控制器、智能儀表、控制面板和家用電器等領(lǐng)域中日益獲得廣泛的應(yīng)用。,(2)顯示電路硬件圖,8.軟件設(shè)計(jì),,,,閉環(huán)調(diào)節(jié)子程序程序：,第一象限直線差補(bǔ)運(yùn)算程序流程圖：,,全文總結(jié),經(jīng)過三個(gè)月的畢業(yè)設(shè)計(jì)，使我對電火花線切割機(jī)的電氣部分有了初步的認(rèn)識，對本專業(yè)又有了更進(jìn)一步的了解。
由于本人能力有限，本文所介紹的電火花電氣系統(tǒng)還不夠完善，還有很多不足之處，希望大家能多提寶貴意見，來慢慢完善這個(gè)系統(tǒng)。,謝謝各位老師四年來對我們的教育和培養(yǎng)！,祝各位老師在以后的工作中
一帆風(fēng)順，萬事如意！,摘 要隨著數(shù)控線切割機(jī)床應(yīng)用的不斷擴(kuò)大，機(jī)床本身也得到了不斷的發(fā)展。十多年前， “負(fù)旦型”數(shù)控線切割機(jī)床首先應(yīng)用于實(shí)際生產(chǎn)，最早控制臺是由晶體管分離元件組裝而成，逐漸采用集成電路，現(xiàn)在正向采用微型計(jì)算機(jī)控制的方向發(fā)展，因此本論文設(shè)計(jì)的“電火花線切割機(jī)的電氣控制系統(tǒng)”是以 89C55 單片機(jī)作為控制核心，步進(jìn)電機(jī)作為驅(qū)動電機(jī)，光柵作為位移檢測元件而構(gòu)成的一個(gè)閉環(huán)控制系統(tǒng)。電火花線切割機(jī)的核心技術(shù)就是控制位移量的精度。本文采用了 QH-200 型光柵尺傳感器來檢測位移量，通過 ATMEL 公司的 89C55 作為控制元件，輸出的兩路方波，送入單片機(jī)，通過 CH250 來驅(qū)動電機(jī)，控制電機(jī)移動，完成想要的工件圖形。本文設(shè)計(jì)的電火花電氣系統(tǒng)，控制精度及檢測精度都能達(dá)到±0.01 毫米。系統(tǒng)具有加工狀態(tài)自動顯示功能，由鍵盤控制系統(tǒng)啟、停以及對位移量進(jìn)行設(shè)定。關(guān)鍵詞：電火花 線切割 單片機(jī) 步進(jìn)電機(jī)AbstractAlong with the numerical control line cutting engine bed application unceasing expansion, engine bed itself also arrived the unceasing development. More than ten years ago, “the negative day” the numerical control line cutting engine bed first applies and the actual production, starts the control bench is uses the transistor separative element assembly to become, after but uses the integrated circuit, now to is using the direction which the microcomputer controls to develop, Therefore this definition design “the electrical fire colored thread cutter automatic control” is by 8031 shrapnel machine took the control core, step-by-steps the electrical machinery achievement to actuate the electrical machinery, the diffraction grating a closed-loop control system which constitutes as the position examination part.WEDM the core technology is to control the accuracy of displacement. In this paper, the QH-200-foot grating sensors to detect displacement through ATMEL's 89C55 as a control device, the output of two-way square, into the microcontroller, through CH250 to drive motor, control motor movement, would like to complete To the workpiece graphics. In this paper, the design of the EDM electrical system, control accuracy and precision of detection to achieve ± 0.01MM. State system has automatically display processing functions from the keyboard control system Kai, stopped and the displacement of a set.KeyWord：electrical sparkle linear cutting microcomputer Stepper motorIn the frequency changer movement process existsquestion and countermeasureThis paper analyzed the problem of harmonic wave, matching of load and calorification for inverters in running, and made the relatively the measure. Keywords: inverter harmonic wave loading calorification1 foreword has entered the Chinese market since the 80's general frequency changers, obtained the extremely widespread application in the short several year time.At present, the general frequency changer by its merits and so on intellectualization, digitization, network more and more receives people's favor.Along with the general frequency changer application scope expansion, the question which exposes more and more are also many, mainly has following several aspects:① Overtone question ② Frequency changer matching of load question ③ Gave off heat above the question these questions already to cause the related control section and the factory and mine attention and has formulated the related technical standard.If the overtone question, our country and in 1993 passed “the electrical power system overtone management temporary provisions” in 1984 and the GB/T-14549-93 standard, with limits the power supply system and the current collector overtone pollution. In view of the above question, this article carried on has analyzed and proposed the solution and the countermeasure.2 overtone questions and the countermeasure general frequency changer main circuit form is composed generally by three parts: Rectification part, contravariant part and filter part.The rectification part for the three-phase bridge type uncontrolled rectifier, the invertor part is the IGBT three-phase bridge type invertor, also the output is the PWM profile.Regarding the bipolarity modulation frequency changer.because the general frequency changer rectification part uses the diode uncontrolled bridge type leveling circuit, the middle filter part uses the big electric capacity to take the filter, therefore the rectifier input current in fact is the capacitor charging current, assumes a higher more and precipitous pulse wave, its harmonic component is big.For the harmonic cancellation, may use following countermeasure: ① Increase frequency changer electric power supply internal resistance In the usual situation, the power equipment internal resistance may play the cushion frequency changer cocurrent filter electric capacity reactive power role.This kind of internal resistance is the transformer short-circuit impedance.When power source capacity relative frequency changer capacity hour, then internal resistance value relative bigger, the harmonic content is smaller; When the power source capacity relative frequency changer capacity is bigger, then internal resistance value relative bigger, the harmonic content is bigger. Regarding Mitsubishi FR-F540 series frequency changer, when internal resistance is 4%, may play the very good harmonic suppression role .Therefore time choice frequency changer electric power supply transformer, best choice short-circuit impedance big transformer.(2) Installs the reactor to install the reactor in fact from exterior increase frequency changer electric power supply internal resistance. Installs the direct current reactor in the frequency changer exchange side installment exchange reactor or in the frequency changer direct current side, or also installs, suppression harmonic current. The table as soon as listed the Mitsubishi FR-A540 frequency changer to install the reactor and not to install the reactor the content comparative table.(3) The transformer heterogeneity movement general frequency changer rectification part is six pulse waves rectifiers, therefore produces the overtone is bigger. If applies the transformer the heterogeneity movement, causes mutually to miss 30° like Y- △, △ - △ the combination two transformers constitution is equal to 12 pulse waves effects may reduce the harmonic current 28%, played the very good harmonic suppression role.(4) Adjusts the frequency changer the carrier compared to from (1), (2), (3) the formula may see, so long as the carrier enough is bigger than, comparatively 低次 the overtone may effectively suppress, specially the reference wave peak-to-peak value and the carrier peak-to-peak value are smaller than 1 o'clock, 13 below odd number overtone no longer appears.(5) Special-purpose filter this special-purpose filter uses in to examine the frequency changer harmonic current the peak-to-peak value and the phase, and produces to be same also the phase just right opposite electric current with the harmonic current peak-to-peak value, passes through in the frequency changer, thus may extremely effectively absorb the harmonic current.3 matchings of load question and its the countermeasure produce machinerythe type to be many, performance and technological requirement respectively different, its torque characteristics is complex, roughly divides into three kind of types: The permanent torque loading, the air blower pump a kind of load and the permanent power load. In view of the different load type, should choose the different type the frequency changer.(1) The permanent torque loading permanent torque loading is refers to the load moment to have nothing to do with with the rotational speed, under any rotational speed, the torque maintains constantly. The permanent torque loading divides into the friction class load and the potential energy type load. About friction class load starting moment general request nominal torque 150%, about brake torque general request nominal torque 100%, therefore the frequency changer should choose these to have the constant torque characteristics, and starts and the brake torque all quite big, the overload time is long and the overload capacity big frequency changer. If Mitsubishi frequency changer FR-A540 series. The potential energy type load generally requests the big starting moment and the energy back coupling function, can fast realize is reversing, the frequency changer should choose has four quadrants running ability the frequency changer. If Mitsubishi frequency changer FR-A241 series. (2) air blower pumps the kind of load air blower to pump a kind of load is present industry field application most equipment, although pumps the gentle breeze machine characteristic many and varied, but mainly by the centrifugal pump and the centrifugal air blower application primarily, the general frequency changer are most in this kind of load application. The air blower pumps a kind of load is one square torque loading, its rotational speed n and current capacity Q.May see from the previous type, the air blower load system rotation inertia computation is wants extremely again. When frequency changer concrete design, presses down the type computed result, carries on the suitable revision, starts when the frequency changer in the situation which does not have the class to trip decelerates with the frequency changer when does not occur 過電壓 trips, choice shortest time.Pumps a kind of load in the actual movement process, is easy to have the buzz, the build the pressure and the water hangs the effect, therefore time frequency changer shaping, must choose is suitable for to pump a kind of load the frequency changer also the frequency changer when the function hypothesis must aim at the above question to carry on alone establishes:Buzz: Surveys easily to have the buzz frequency spot, jumps the frequency through the hypothesis and the width, avoids the phylogeny resonance effect.Build the pressure: Pumps a kind of load when the low speed movement, causes the current capacity as a result of the system build the pressure is zero, thus creates pumps burn outs. When frequency changer function hypothesis, through defines the frequency changer the most low frequency, but had defined pumps the current capacity the critical point place system lowest rotational speed, this has avoided this kind of phenomenon occurrence.The water hangs the effect: Pumps a kind of load when the sudden power failure, as a result of pumps in the pipeline the liquid gravity to flow backwards. If the check valve is lax or does not have the check valve, will cause the electrical machinery reverse, will cause the frequency changer because of the electrical machinery electricity generation to break down to report to the police burn outs. When frequency changer system design, should cause the frequency changer to stop according to the deceleration curve, separates the main circuit electricity again after electrical machinery dead stop, or the hypothesis "the power failure decelerates stops" the function, has like this avoided this phenomenon occurrence.(3) The permanent power loadpermanent power load is refers to the torque roughly with to transfer the intensive inverse ratio the load, like coiler, opening a book machine and so on. Actuates the permanent power load when using the frequency changer, should be, the usual consideration which speaking of the certain speed change scope below some rotational speed selects the permanent torque velocity modulation method, but when is higher than this rotational speed only then selects the permanent power velocity modulation method. We usually are called this rotational speed spot the base frequency, this point correspondence voltage for frequency changer output rated voltage.Theoretically speaking, must want to realize in the true significancepermanent power control, Frequency changer output frequency f and output voltage U must follow the U2/f=const coordination control, but this is does not permit in the actual frequency changer movement process, because above the base frequency, the frequency changer output voltage cannot increase along with its output frequency, only can maintain the rated voltage,therefore only can be in one kind of approximate significance permanent power control.4 gives off heat the question and its the countermeasureFrequency changer giving off heat is produces by the internal loss. In the frequency changer in each part of losses mainly by the main circuit primarily, approximately composes 98%, the control circuit accounts for 2%. In order to guarantee the frequency changer normal reliable movement, must carry on the radiation to the frequency changer, usually uses following method:(1) Uses the ventilator radiation: The frequency changer internal installation ventilator may carry off the frequency changer box body interior radiation, if the ventilator cannot the normal work, be supposed to stop the frequency changer movement immediately.(2) Reduces installs the ambient temperature: Because the frequencychanger is the electronic installation, content electron Yuan, electrolysis electric capacity and so on, therefore the temperature quite is big to its life influence. The general frequency changer environment operating temperature generally requests -10 ℃ ~-50 ℃, if can take the measure to reduce the frequency changer operating temperature as far as possible, then the frequency changer service life lengthens, the performance quite is also stable.We adopt two methods: One method is the construction independent frequency changer low pressure, the interior installs the air conditioning, the maintenance low pressure the temperature in +15 ℃ ~+20 ℃ between. Another method is the frequency changer installment space needs to satisfy the frequency changer instruction for use the request.Above talks about the frequency changer gives off heat is refers to the frequency changer in the fixed scope the normal operation loss. When the frequency changer has the unusual movement (for example class, crosses pressure, the loss which overload and so on) produces must avoid this kind of phenomenon through the normal shaping the occurrence.Pumps a kind of load regarding the air blower, when we choose Mitsubishi frequency changer FR-F540, its overload can be 1.20%/6 million second, its overload cycle is 300 seconds, in other words, when the frequency changer is opposite to its rated load 120% overload, it the duration is 60 seconds, and does not allow within 300 seconds to appear the second overload. When the frequency changer appears the overload, the power unit because it has flowed the excess current elevates temperature, causes the frequency changer heat,by now had to cause its temperature decrease to cause the frequency changer the hot protection movement as soon as possible to eliminate, this undercooling was the frequency changer overload cycle. The different frequency changer, its overload multiple, the overload time and the overload cycle are not same, and its overload multiple bigger,the overload time is shorter,Electrical machinery actuates which regarding the frequency changer, may divide into two kinds according to its working condition: Long lasting work system and repetition short-term operation system. The long lasting work system electrical machinery may according to its name brand stipulation data long-term movement. In view of this kind of load, the frequency changer may carry on the shaping according to the electrical machinery data plate data, like continuous running oil pump, if its electrical machinery power is time 22kW, may choose the FR-F540-22k frequency changer then. The repetition short-term operation system electrical machinery, its characteristic is the duplication and the short time, namely the electrical machinery operating time and the idle time time carry on in turn, moreover quite is all short, sum of the two, according to the country stipulated does not have to surpass for 60 seconds. The repetition short-term operation system electrical machinery permits its overload also has certainly certainly Temperature elevation.This time, if chooses the frequency changer according to the electrical machinery data plate data, inevitably will create the frequency changer the damage. In view of this kind of load, the frequency changer in the reference electrical machinery data plate data situation must according to the electrical machinery load diagram and the frequency changer overload multiple, the overload time, the overload cycle comes the shaping. If duplicates the short-time movement the elevator, its electrical machinery power is 18.5kW, may choose the FR-A540-22k frequency changer.5 conclusions this article through has the problem to the general frequency changer movement process in the analysis, proposed solves these questions actual countermeasures, along with the new technology and the new theory unceasingly on the frequency changer application, these questions which the frequency changer exists hopefully and compensates through the frequency changer itselffunction solves. Unceasingly enhance along with the industry scene and the social environment to the frequency changer request, meets the actual needs the falsehood "the green" the frequency changer also to be able soon to appear on the market.6 references (1) Han Anrong General frequency changer and its application Beijing: Mechanical industry publishing house, 2,000 (2)Mitsubishi frequency conversion velometer FR-A500 user's manual (3)Mitsubishi frequency conversion velometer FR-F500 user's manual 在頻率變運(yùn)行過程中存在的疑問和對策本文針對變頻器運(yùn)行過程中存在的諧波問題、負(fù)載匹配問題和發(fā)熱問題，進(jìn)行了分析，并提出了相對應(yīng)的解決方案自從 80 年代以來頻率變進(jìn)入中國市場, 在那短好幾年時(shí)間獲得廣泛的應(yīng)用。目前，通用變頻器以其智能化、數(shù)字化、網(wǎng)絡(luò)化等優(yōu)點(diǎn)得到越來越受到人們好評。隨著通用變頻器應(yīng)用范圍的擴(kuò)大，暴露出來的問題也越來越多，主要有以下幾方面:①偕波問題②頻率變負(fù)荷相配問題③發(fā)熱問題以上問題已經(jīng)引起那相關(guān)的控制區(qū)段和工廠礦的注意而且制定那相關(guān)的技術(shù)上的標(biāo)準(zhǔn)。如偕波問題, 我們的國家和以 1993 年 " 電力系統(tǒng)偕波問題管理暫時(shí)的規(guī)定 " 在 1984 年GB/T-14549-93標(biāo)準(zhǔn), 與極限力量補(bǔ)給系統(tǒng)和現(xiàn)在的搜集家泛音污染。 對于以上的問題, 本文章進(jìn)行了分析和提出解決和對策。2 諧波問題和對策通用變頻器的主電路形式一般由三部分組成:整流部分、逆變部分和濾波部分。整流部分為三相橋式不可控整流器，逆變器部分為IGBT三相橋式逆變器，且輸出為PWM波形。通用變頻器的輸出電壓中確實(shí)含有除基波以外的其他諧波。較低次諧波通常對電機(jī)負(fù)載影響較大，引起轉(zhuǎn)矩脈動，而較高的諧波又使變頻器輸出電纜的漏電流增加，使電機(jī)出力不足，故變頻器輸出的高低次諧波都必須抑制。因?yàn)橐话愕耐ㄓ米冾l器的整流部分采用二極管不可控橋式整流電路, 中間濾波部分采用大電容作為濾波器，所以整流器的輸入電流實(shí)際上是電容器的充電電流，呈較為陡峻的脈沖波，其諧波分量較大。為了消除諧波，可采用以下對策: ① 增加變頻器電源內(nèi)在的阻抗在平常的情形中, 電源設(shè)備內(nèi)在的抵抗可能起到緩沖變頻器直流濾波電容的無功功率的角色。這種內(nèi)阻抗是變壓器發(fā)生短路阻抗的。當(dāng)電源容量相對變頻器容量越小時(shí)，則內(nèi)阻抗值相對越大，諧波含量越小；電源容量相對變頻器容量越大時(shí)，則內(nèi)阻抗值相對越大，諧波含量越大。對于三菱FR-F540系列變頻器，當(dāng)電源內(nèi)阻為4%時(shí)，可以起到很好的諧波抑制作用。所以選擇變頻器供電電源變壓器時(shí)，最好選擇短路阻抗大的變壓器。 ② 安裝電抗器 安裝電抗器實(shí)際上從外部增加變頻器供電電源的內(nèi)阻抗。在變頻器的交流側(cè)安裝交流電抗器或在變頻器的直流側(cè)安裝直流電抗器，或同時(shí)安裝，抑制諧波電流。表一列出了三菱FR-A540變頻器安裝電抗器和不安裝電抗器的含量對照表。③ 變壓器多相運(yùn)行 通用變頻器的整流部分是六脈波整流器，所以產(chǎn)生的諧波較大。如果應(yīng)用變壓器的多相運(yùn)行，使相位角互差 30°如 Y-△、△-△組合的兩個(gè)變壓器構(gòu)成相當(dāng)于12脈波的效果則可減小低次諧波電流 28%，起到了很好的諧波抑制作用。 ④ 調(diào)節(jié)變頻器的載波比 只要載波比足夠大，較低次諧波就可以被有效地抑制，特別是參考波幅值與載波幅值小于1時(shí)，13次以下的奇數(shù)諧波不再出現(xiàn)。 ⑤ 專用濾波器 該專用濾波器用于檢測變頻器諧波電流的幅值和相位，并產(chǎn)生一個(gè)與諧波電流幅值相同且相位正好相反的電流，通到變頻器中，從而可以非常有效地吸收諧波電流。 3 負(fù)載匹配問題及其對策 生產(chǎn)機(jī)械的種類繁多，性能和工藝要求各異，其轉(zhuǎn)矩特性是復(fù)雜的，大體分為三種類型:恒轉(zhuǎn)矩負(fù)載、風(fēng)機(jī)泵類負(fù)載和恒功率負(fù)載。針對不同的負(fù)載類型，應(yīng)選擇不同類型的變頻器。 ① 恒轉(zhuǎn)矩負(fù)載 恒轉(zhuǎn)矩負(fù)載是指負(fù)載轉(zhuǎn)矩與轉(zhuǎn)速無關(guān)，任何轉(zhuǎn)速下，轉(zhuǎn)矩均保持恒定。恒轉(zhuǎn)矩負(fù)載又分為摩擦類負(fù)載和位能式負(fù)載。 摩擦類負(fù)載的起動轉(zhuǎn)矩一般要求額定轉(zhuǎn)矩的 150%左右，制動轉(zhuǎn)矩一般要求額定轉(zhuǎn)矩的 100%左右，所以變頻器應(yīng)選擇那些具有恒定轉(zhuǎn)矩特性,并且起動和制動轉(zhuǎn)矩都比較大，過載時(shí)間長和過載能力大的變頻器。如三菱變頻器 FR-A540系列。 位能式負(fù)載一般要求大的起動轉(zhuǎn)矩和能量回饋功能，能夠快速實(shí)現(xiàn)正反轉(zhuǎn)，變頻器應(yīng)選擇具有四象限運(yùn)行能力的變頻器。如三菱變頻器 FR-A241系列。 ② 風(fēng)機(jī)泵類負(fù)載 風(fēng)機(jī)泵類負(fù)載是目前工業(yè)現(xiàn)場應(yīng)用最多的設(shè)備，雖然泵和風(fēng)機(jī)的特性多種多樣，但是主要以離心泵和離心風(fēng)機(jī)應(yīng)用為主，通用變頻器在這類負(fù)載上的應(yīng)用最多。這類負(fù)載對變頻器的性能要求不高，只要求經(jīng)濟(jì)性和可靠性，所以選擇具有U/f=const控制模式的變頻器即可。如三菱變頻器 FR-F540（L）系列。風(fēng)機(jī)負(fù)載的系統(tǒng)轉(zhuǎn)動慣量計(jì)算是非常重要的。變頻器具體設(shè)計(jì)時(shí)，按上式計(jì)算結(jié)果，進(jìn)行適當(dāng)修正，在變頻器起動時(shí)不發(fā)生過流跳閘和變頻器減速時(shí)不發(fā)生過電壓跳閘的情況下，選擇最短時(shí)間。 泵類負(fù)載在實(shí)際運(yùn)行過程中，容易發(fā)生喘振、憋壓和水垂效應(yīng)，所以變頻器選型時(shí)，要選擇適于泵類負(fù)載的變頻器且變頻器在功能設(shè)定時(shí)要針對上述問題進(jìn)行單獨(dú)設(shè)定: 喘振:測量易發(fā)生喘振的頻率點(diǎn)，通過設(shè)定跳躍頻率點(diǎn)和寬度，避免系統(tǒng)發(fā)生共振現(xiàn)象。 憋壓:泵類負(fù)載在低速運(yùn)行時(shí)，由于系統(tǒng)憋壓而導(dǎo)致流量為零，從而造成泵燒壞。在變頻器功能設(shè)定時(shí)，通過限定變頻器的最低頻率，而限定了泵流量的臨界點(diǎn)處的系統(tǒng)最低轉(zhuǎn)速，這就避免了此類現(xiàn)象的發(fā)生。 水垂效應(yīng):泵類負(fù)載在突然斷電時(shí)，由于泵管道中的液體重力而倒流。若逆止閥不嚴(yán)或沒有逆止閥，將導(dǎo)致電機(jī)反轉(zhuǎn)，因電機(jī)發(fā)電而使變頻器發(fā)生故障報(bào)警燒壞。在變頻器系統(tǒng)設(shè)計(jì)時(shí)，應(yīng)使變頻器按減速曲線停止，在電機(jī)完全停止后再斷開主電路電，或者設(shè)定“斷電減速停止”功能，這樣就避免了該現(xiàn)象的發(fā)生。 ③ 恒功率負(fù)載 恒功率負(fù)載是指轉(zhuǎn)矩大體與轉(zhuǎn)速成反比的負(fù)載，如卷取機(jī)、開卷機(jī)等。利用變 頻器驅(qū)動恒功率負(fù)載時(shí)，應(yīng)該是就一定的速度變化范圍而言的，通?？紤]在某個(gè)轉(zhuǎn)速點(diǎn)以下采用恒轉(zhuǎn)矩調(diào)速方式，而在高于該轉(zhuǎn)速點(diǎn)時(shí)才采用恒功率調(diào)速方式。我們通常將該轉(zhuǎn)速點(diǎn)稱為基頻，該點(diǎn)對應(yīng)的電壓為變頻器輸出額定電壓。從理論上講，要想實(shí)現(xiàn)真正意義上的恒功率控制，變頻器的輸出頻率 f和輸出電壓 U必須遵循U2/f=const協(xié)調(diào)控制，但這在實(shí)際變頻器運(yùn)行過程中是不允許的，因?yàn)樵诨l以上，變頻器的輸出電壓不能隨著其輸出頻率增加，只能保持額定電壓，所以只能是一種近似意義上的恒功率控制。 4 發(fā)熱問題及其對策 變頻器的發(fā)熱是由內(nèi)部的損耗產(chǎn)生的。在變頻器中各部分損耗中主要以主電路為主，約占 98%，控制電路占 2%。為了保證變頻器正?？煽窟\(yùn)行，必須對變頻器進(jìn)行散熱，通常采用以下方法: ① 采用風(fēng)扇散熱:變頻器的內(nèi)裝風(fēng)扇可將變頻器的箱體內(nèi)部散熱帶走，若風(fēng)扇不能正常工作，應(yīng)立即停止變頻器運(yùn)行。 ② 降低安裝環(huán)境溫度:由于變頻器是電子裝置，內(nèi)含電子元、電解電容等，所以溫度對其壽命影響比較大。通用變頻器的環(huán)境運(yùn)行溫度一般要求-10℃~-50℃，如果能夠采取措施盡可能降低變頻器運(yùn)行溫度，那么變頻器的使用壽命就延長，性能也比較穩(wěn)定。 我們采取兩種方法:一種方法是建造單獨(dú)的變頻器低壓間，內(nèi)部安裝空調(diào)，保持低壓間溫度在+15℃~+20℃之間。另一種方法是變頻器的安裝空間要滿足變頻器使用說明書的要求。 以上所談到的變頻器發(fā)熱是指變頻器在額定范圍之內(nèi)正常運(yùn)行的損耗。當(dāng)變頻器發(fā)生非正常運(yùn)行（如過流，過壓，過載等）產(chǎn)生的損耗必須通過正常的選型來避免此類現(xiàn)象的發(fā)生。 對于風(fēng)機(jī)泵類負(fù)載，當(dāng)我們選擇三菱變頻器 FR-F540時(shí)，其過載能為 120%/60秒，其過載周期為 300秒，也就是說，當(dāng)變頻器相對于其額定負(fù)載的 120%過載時(shí)，其持續(xù)時(shí)間為 60秒，并且在 300秒之內(nèi)不允許出現(xiàn)第二次過載。當(dāng)變頻器出現(xiàn)過載時(shí)，功率單元因其流過的過載電流而升溫，導(dǎo)致變頻器過熱，這時(shí)必須盡快使其降溫以使變頻器的過熱保護(hù)動作消除，這個(gè)冷卻過程就是變頻器的過載周期。不同的變頻器，其過載倍數(shù)、過載時(shí)間和過載周期均不相同，并且其過載倍數(shù)越大，過載時(shí)間越短。對于變頻器所驅(qū)動的電機(jī)，按其工作情況可分為兩類:長期工作制和重復(fù)短時(shí)工作制。長期工作制的電機(jī)可以按其名牌規(guī)定的數(shù)據(jù)長期運(yùn)行。針對該類負(fù)載，變頻器可根據(jù)電機(jī)銘牌數(shù)據(jù)進(jìn)行選型，如連續(xù)運(yùn)行的油泵，若其電機(jī)功率為22kW時(shí)，可選擇FR-F540-22k變頻器即可。重復(fù)短時(shí)工作制電機(jī)，其特點(diǎn)是重復(fù)性和短時(shí)性，即電機(jī)的工作時(shí)間和停歇時(shí)間交替進(jìn)行，而且都比較短，二者之和，按國家規(guī)定不得超過60秒。重復(fù)短時(shí)工作制電機(jī)允許其過載且有一定的溫升。此時(shí)，若根據(jù)電機(jī)銘牌數(shù)據(jù)來選擇變頻器，勢必造成變頻器的損壞。針對該類負(fù)載，變頻器在參考電機(jī)銘牌數(shù)據(jù)的情況下要根據(jù)電機(jī)負(fù)載圖和變頻器的過載倍數(shù)、過載時(shí)間、過載周期來選型。如重復(fù)短時(shí)運(yùn)行的升降機(jī)，其電機(jī)功率為18.5kW，可選擇FR-A540-22k變頻器 結(jié)論本文通過對通用變頻器運(yùn)行過程中存在問題的分析，提出了解決這些問題的實(shí)際對策，隨著新技術(shù)和新理論不斷在變頻器上的應(yīng)用，變頻器存在的這些問題有望通過變頻器本身的功能和補(bǔ)償來解決。隨著工業(yè)現(xiàn)場和社會環(huán)境對變頻器的要求不斷提高，滿足實(shí)際需要的真正“綠色”變頻器也會不久面世。 6 參考文獻(xiàn) (1) 韓安榮.通用變頻器及其應(yīng)用.北京:機(jī)械工業(yè)出版社，2000 (2) 三菱變頻調(diào)速器FR-A500使用手冊. (3) 三菱變頻調(diào)速器FR-F500使用手冊.
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