Since the introduction of inverter technology in the 80s of the last century, inverters have been widely used in industrial equipment due to their significant energy saving and convenient speed regulation. Since the author first came into contact with the inverter in 08, 16 years have quietly passed. It's really time flies, and time flies.
Recall that the first inverter, is the unit to introduce Japan's Mitsubishi 75kW inverter, at that time, specially invited someone to debug, with a high-power motor as a blower, from the afternoon to the evening, it was rare at that time, the whole team around this inverter. Looking at today, the power of the inverter has reached the MW (megawatt) level, which is no longer what it used to be.
Off topic, today's topic is to talk about inverter maintenance technology, do the math, the inverter that has been repaired should not be less than 1,000 times, imported brands have mainstream AB B, Siemens, Schneider, AB, Lenze, Sanken, Danfoss, etc., domestic brands have mainstream Inovance, Delta, INVT, Blue Ocean Huateng and so on. Looking back, I found that no matter what brand of inverter, its structural principle is similar, nothing more than some inverters have a little more protection, detection, and safety functions, and some inverters omit some redundant configurations.
As mentioned earlier, since the introduction in the 80s of the last century, it is mainly because of energy saving and convenience to regulate the speed of the motor, so no matter what brand and model of inverter, the principle of the main circuit is the same. After rectification, it becomes DC energy storage on the main filter capacitor of the inverter, and then the switching pulse width of the six-channel IGBT is controlled through the main control board of the inverter, so that the output frequency and voltage can be adjusted.
Mastering this diagram can solve 80% of inverter failures:
I remember that in 15 years, the unit was profitable, and the unit required each master to bring an apprentice out, because I was responsible for the maintenance of the unit's equipment, and the leader asked me to take two apprentices to repair the inverter. I remember giving them two tasks is to make great efforts to understand the principle of the main circuit of the inverter, understand the working principle of the inverter, and then expand the driving circuit, current detection circuit, voltage sampling circuit, main control chip, external I/O circuit, steady and steady, regardless of the brand, any inverter can be at your fingertips.
Rectifier & Filtering Circuits
For the inverter with a line voltage of 380V, the maximum DC voltage after rectification is 537V, √2*380V=537V, and there are 6 small peaks in each cycle, which also need to be filtered out.
The input of the inverter is three-phase sinusoidal alternating current, which becomes direct current after passing through a three-phase rectifier bridge composed of six diodes. P+ and N- are the bus voltage terminals often referred to in frequency converters, which are connected to both ends of the large capacitor.
C1, C2 filter capacitors, R1, R2 equalizing resistors, filter capacitors are to make the rectified DC more smooth and uniform, at this time the average bus voltage is 537V.
The voltage after rectification filtering is 537V, there is no display on the power of the common inverter, the first measurement is whether the input voltage is 380V AC, after the AC input is normal, and then use the DC voltage gear to measure whether the bus voltage at both ends of the inverter P+ and N- is there. In many cases, there is no display on the inverter, in addition to the problem of the switching power supply, the current limiting resistance RL in the inverter, if it is open, will also cause the entire inverter to have no display.
Current limiting resistors and bypass relays
After the inverter is rectified out, it is then filtered, because the filter capacitor, before charging, the two-point voltage is almost 0V, if there is no series buffer current limiting resistor, the moment of power-on, the rectifier of more than 500 volts of DC will directly lead to the trip of the pre-circuit breaker or the failure of the rectifier bridge, and a current limiting resistor is connected in series to limit the current.
When the filter capacitor is charged in place, the bus voltage is established, and the relay next to the current limiting resistor will be shorted synchronously to prepare for operation.
Inverter part
The inverter part of the inverter is the core part of the inverter, the common inverter fried module, the main fried is the inverter IGBT, which becomes DC after rectification filtering, and the inverter finally controls the three-phase AC asynchronous motor, so it needs six IGBTs to control the output, and only needs to control the six-way PWM drive IGBT through the main control board to adjust the frequency and voltage of the actual output. Therefore, it is also called pulse-width modulated PWM.
It is not difficult for the inverter to be repaired, but it will not be difficult for the difficult!
With the development and progress of technology, the protection function of the inverter is becoming more and more completely standardized, and common faults such as fried modules are limited to the periphery and will not damage the core components, so the maintenance can basically be familiar.
This diagram is the core of the inverter, and the master who maintains it in the industrial field, mastering this diagram, can handle 80% of the inverter failures. Based on this diagram, you can extend the inverter voltage detection circuit, current sampling circuit, IGBT drive circuit, fan detection circuit, etc., to master the backbone, and the rest of the branches are to serve this diagram.
I'll talk about it here today, and I'll talk about it next time I have a chance~
Article source: original Jicheng training network, author: You Youfeng; Unauthorized reproduction is prohibited, offenders will be prosecuted!
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