變頻器原理的基本知識

三相380V電網電壓從變頻器的L1， L2， L3輸入端輸入后，首先要經過變頻器的整流橋整流，后經過電容的濾波，輸出一大約530V左右的直流電壓(這也就是我們常用來判斷變頻器整流部分好壞的最常測試點)。

 

當然整流橋最初是要經過斷電測試的)然后經過逆變電路，通過控制逆變電路的通斷來輸出我們想要的合適頻率的電壓(變頻器能變頻最主要的就是控制逆變電路的關斷來控制輸出頻率)，變頻器故障有無數種，好在現在變頻器都趨于智能化，一般的故障它自己都能檢測，并在控制面版上顯示出其代碼，用戶只需查一下用戶手冊就能初步判斷其故障原因。

 

但有時，變頻器在運行中或啟動時或加負載時，突然指示燈不亮，風扇不轉，無輸出。這時我們初學者就不知該怎辦了。其實很簡單的，我們只要把變頻器的電源斷了。斷電測試一下它的整流部分與逆變部分，大多情況下就能知其故障所在了。

 

這里有一點千萬要注意：

 

斷電后不能馬上測量，因變頻器里有大電容存有幾百伏的高壓，一定要等上十幾分鐘再測!

 

? 變頻器上電前整流橋及逆變電路的測試

 

具體測量方法如下：

 

找到變頻器直流輸出端的”+”與”-”，將萬用表調到測量二極管檔，黑表筆接”+”表筆分別接變頻器的輸入端L1， L2， L3端，整流橋的上半橋若是完好，萬用表應顯示0.3…的壓降，若損壞則萬用表顯示”1”過量程。

 

相反將紅表筆接”-”黑表筆分別接L1， L2， L3端應得到上述相同結果，若出現”1”則證明整流橋損壞。然后測試其逆變電路，方法如下：將萬用表調到電阻×10檔將黑表筆接”+”紅表筆接變頻器的輸出端U， V， W應有幾十歐的阻值，反向應該無窮大。反之將紅表筆接到”-”重復上述過程，應得到同樣結果。

 

這樣經過測量在判斷變頻器的整流部分與逆變部分完好時，上電測量其直流輸出端看是否有大約530V高壓，注意有時萬用表顯示幾十伏大家以為整流電路工作了，其實它并沒工作，它正常工作會輸出530V左右的高壓，幾十伏的電壓是變頻器內部感應出來的。若沒530V左右高壓這時往往是電源版有問題。

 

有的變頻器就是由于電源版的一小貼片電阻被燒毀，導致電源板不工作，以致使變頻器無顯示無輸出，風扇不轉，指示燈不亮?！∵@樣就可以初步判斷出變頻器是哪部分出現了故障，然后拆機維修時就可以重點測試懷疑故障部分。

二、技術基礎

 

1、Electronic Line Shafting---ELS，許多工業生產線都由多臺機器組成，各軸之間具有運動關系。過去是使用機械機構連接各軸，如果使用電子方式連接各軸，各州各有其驅動馬達，則稱為”Electronic Line Shafting”(ELS)。

 

2、 Auto Tuning(自動調校)，常見于磁束向量型變頻器的一種技術，能自動監測(找出)馬達的參數，如轉差頻率/場電流/轉矩電流/定子阻抗/轉子阻抗/定子感抗/轉子感抗等.有了這些參數后才能作[專據估算]及[轉差(滑差)補償].也因為此技術，在無編碼器的運轉下仍能獲得良好的運轉精度.

 

3、無編碼器運轉，在速度控制上，與舊式variable frenquency變頻器的開回路比較，磁束向量型變頻器內部由速度觀測計算功能達成閉回路.馬達側不用裝編碼器也能達到良好的速度精度.無編碼器運轉有如下好處:

 

1)，配線精省;

 

2)，不必擔心RF雜訊對編碼器低電壓信號的影響;

 

3)，在多震動的場合不用擔心編碼器的高故障率。

 

4、變頻器的矢量控制，在AC馬達中，轉子由定子繞組感應電流產生磁場.定子電流含兩部分一部分影響磁場，另一部分影響馬達輸出轉矩.要使用AC馬達在需要速度與轉矩控制的場合，必須能夠把影響轉矩的電流分離控制，而磁束矢量控制就能夠分離這兩部分進行獨立控制.(具有大小及方向的物理量稱為矢量)。

 

5、Field WeakeningField Weakening線路可用以減弱馬達的場電流，改變與磁場的平衡關系，使馬達高于基本轉速運轉。

 

6、定轉矩應用，所需轉矩大小不因速度而變的場合，常用到[定轉矩應用].如傳送帶等負載.[定轉矩應用]通常需要較大的起動轉矩.[定轉矩應用]在低速運轉時易有馬達發熱問題，解決的方法:

 

(1)加大馬達功率;

 

(2)使用裝有定速冷卻的變頻器專用馬達(即馬達的冷卻方式為強制風冷)。

 

7、變轉矩應用多見于離心式負載，如泵/風機/風扇等，其使用變頻器的目的一般為節能

 

比如當風扇以50%轉速運轉時，其所需轉矩小于全速運轉所需?？勺冝D矩變頻器能夠僅給與馬達所需轉矩，達到節能效果。次應用中短暫的巔峰負載通常無需給與馬達額外的能量。故變轉矩變頻器的過載能力可以適用于大部分用途。

 

定轉矩變頻器的過載(電流)能力須為額定值150%/1minute，而可變轉矩變頻器所需過載(電流)能力僅需額定值120%/1minute。因為離心式機械用途中很少會超出額定電流。另外，變轉矩用途所需起動轉矩也較定轉矩用途小.。

 

8.變頻器專用馬達,所謂[Inverter-duty Motor]

 

主要特征如下:

 

1)分離式它力通風(它力風冷);

 

2)10Hz-60Hz為定轉矩輸出

 

3)高起動轉矩

 

4)低噪音

 

5)馬達裝有編碼器.*但并非所有稱之為變頻器專用馬達的馬達都具有上列特征。

 

9.關于調速

 

1)調速：根據工況需要調整設備運行速度，以達到節能降耗、減少磨損、按需生產等目的。

 

2)直流調速(DC Controler/motor)：由直流控制器調節直流電機以達到調整速度的目的。

 

3)交流變頻調速(AC inverter/motor)：由變頻器輸出頻率變化的三相交流電流從而控制交流電機的轉速。

 

4)矢量變頻調速(AC vector inverter)：通過復雜的計算變換，使交流變頻器按照直流電機的控制方式去控制交流電機，從而達到精確速度控制、轉矩控制、提高輸出扭矩等特性。

 

5)伺服控制系統(Servo control system)：在運動系統中引入速度反饋或位置反饋元件，通過負反饋作用達到極其精密的速度控制、定位控制及高動態響應。

 

10.幾個常見工業元件

 

1)測速發電機(Tacho-generator)：一種轉速測量元件，有交流、直流之分。

 

2)旋轉變壓器(Resolver)：一種經濟、準確地轉速和角位移測量元件。

 

3)光電編碼器(Encoder)：一種精密的角位移、轉速測量元件，適合在位置控制系統中作為反饋元件。

 

4)PLC：工業用計算、控制裝置，實現邏輯、時序、計算等控制功能，一般作為整個自動化控制系統的上位主機。

 

5)HMI(Human-Machine Interface)：人機界面。

 

6)現場總線(Field-Bus System)：應用于工業控制現場的串行通訊總線系統，大幅度降低接線成本，提高控制的抗干擾能力。

 

7)分布式控制(Distributed control)：區別于傳統的集中式控制，強調各個節點設備的智能化，一般由現場總線系統將各子設備連接起來。極大地提高系統應用的靈活性、可靠性，降低上位機的運算負擔。

 

11.關于電機的術語

 

1)防護等級(Protection Code)：(IP**)考察一個設備防止異物進入和防水的能力，使IEC標準之一。其兩個數字分別代表防異物和防水的能力，數值越高表明可以防止更細小的物體進入以及經受更強烈的水流沖擊。一般為IP54(防塵，防潑灑水滴)以上防護等級的設備可以直接應用于露天。

 

2)絕緣等級(Insulation Grade)：考察一個電氣設備(一般針對電機)在保證良好絕緣特性的前提下所能承受的極限溫升能力，是IEC標準之一。一般有B級(85度)、F級(105度)、H級(125度)。

Of course, the rectifier bridge will go through the power-off test at first) and then go through the inverter circuit to control the on-off of the inverter circuit to output the voltage of the appropriate frequency we want (the main thing that the inverter can convert frequency is to control the off of the inverter circuit to control the output frequency). There are numerous kinds of inverter faults, but now the inverter tends to be intelligent, and general faults can be detected by itself Test, and display its code on the control panel, the user only needs to check the user manual to preliminarily determine the cause of its failure.

But sometimes, when the frequency converter is running or starting or loading, suddenly the indicator light is not on, the fan does not turn, and there is no output. At this time, we beginners don't know what to do. In fact, it's very simple. We just need to turn off the power supply of the inverter. Power off test its rectifier part and inverter part. In most cases, you can know the fault.

Here's one thing to note:

After power failure, it can't be measured immediately, because there is a large capacitance in the frequency converter with hundreds of volts of high voltage, it must wait for more than ten minutes to measure!

? test of rectifier bridge and inverter circuit before power on of frequency converter

The specific measurement method is as follows:

Find "+" and "-" of the DC output terminal of the converter, adjust the multimeter to the measurement diode, connect the black probe with "+" probe to the input terminals L1, L2 and L3 of the converter respectively, if the upper half of the rectifier bridge is intact, the multimeter shall display 0.3 If it is damaged, the multimeter will display "1" over range.

On the contrary, connect the red lead and the black lead to L1, L2 and L3 respectively. The same result above shall be obtained. If "1" appears, it indicates that the rectifier bridge is damaged. Then test the inverter circuit, the method is as follows: adjust the multimeter to the resistance × 10, connect the black probe with "+" red probe to the output terminal u, V, w of the converter, which should have a resistance value of tens of ohms, and the reverse should be infinite. On the contrary, if you repeat the above process, you should get the same result.

In this way, when judging whether the rectifier part and inverter part of the converter are in good condition through measurement, power on and measure the DC output terminal to see if there is about 530v high voltage. Note that sometimes the multimeter shows dozens of volts. We think the rectifier circuit is working, but it is not working. It will output about 530v high voltage when it is working normally, and dozens of volts are induced from the inside of the converter. If there is no high voltage around 530v, it is often a problem with the power version.

Some frequency converters are due to the burning of a small chip resistance of the power version, which causes the power board to not work, so that the frequency converter has no display and output, the fan does not turn, and the indicator light does not light up. In this way, we can initially determine which part of the frequency converter has a fault, and then we can focus on testing the suspected part of the fault when disassembling the machine for maintenance.

2、 Technical basis

1. Electronic line shafting --- els, many industrial production lines are composed of multiple machines, and each axis has motion relationship. In the past, mechanical mechanisms were used to connect the shafts. If the shafts were connected electronically, each state had its own driving motor, it was called "electronic line shifting" (ELS).

2. Auto tuning is a technology commonly used in magnetic beam vector converter. It can automatically monitor (find) motor parameters, such as slip frequency / field current / torque current / stator impedance / rotor impedance / stator reactance / rotor reactance, etc. only with these parameters can we make [Special estimation] and [slip (slip) compensation]. Because of this technology, it can still be obtained without encoder Good running accuracy

3. In the speed control, compared with the open-loop of the old variable frequency converter, the closed-loop is achieved by the speed observation and calculation function in the magnetic beam vector converter. The motor side can achieve good speed accuracy without encoder. The operation without encoder has the following advantages:

1) , fine wiring;

2) , do not worry about the influence of RF noise on the low voltage signal of the encoder;

 

3) In the case of multi vibration, there is no need to worry about the high failure rate of the encoder.

 

 

 

4. In vector control of frequency converter, in AC motor, the rotor generates magnetic field by induced current of stator winding. Stator current includes two parts: one part influences magnetic field, the other part influences motor output torque. In order to use AC motor in the situation of speed and torque control, it is necessary to be able to separate the current that affects torque, and the magnetic beam vector control can separate the two parts independently Control. (the physical quantities with size and direction are called vectors).

 

 

 

5. The field peaking field peaking circuit can be used to weaken the field current of the motor, change the balance relationship with the magnetic field, and make the motor run at a speed higher than the basic speed.

 

 

 

6. Constant torque application, where the required torque does not change due to speed, is often used to [constant torque application]. For example, load such as conveyor belt. [constant torque application] usually requires a large starting torque. [constant torque application] is easy to have motor heating problem when running at low speed. Solution:

 

 

 

(1) Increase motor power;

 

 

 

(2) Use the inverter special motor equipped with constant speed cooling (that is, the cooling mode of the motor is forced air cooling).

 

 

 

7. Variable torque applications are commonly found in centrifugal loads, such as pumps / fans / fans, etc., whose purpose is generally to save energy

 

 

 

For example, when the fan is running at 50% speed, the required torque is less than that required for full speed operation. The variable torque converter can only give the required torque to the motor, achieving energy saving effect. Secondary application