Common problems and solutions of the hottest inver

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Common problems and solutions of frequency converter drive circuit

1 introduction

in recent ten years, with the penetration of power electronics technology, microelectronics technology and modern control theory into the field of AC electric drive, frequency conversion AC speed regulation has gradually replaced the past slip speed regulation, pole changing speed regulation, DC speed regulation and other speed regulation systems. It can almost be said that where there is an AC motor, there is a frequency converter. Its main characteristics are high efficiency driving performance and good control characteristics

the current general-purpose frequency converter generally includes the following parts: rectifier bridge, inverter bridge, intermediate DC circuit, precharge circuit, control circuit, drive circuit, etc. The driving circuit plays an important role in the quality of a frequency converter. Now let's talk about the common problems and solutions of the driving circuit

drive circuit is just a general term. With the continuous development of technology, the drive circuit itself has also experienced from pin element drive circuit to optocoupler drive circuit, then to thick film drive circuit, and relatively new integrated drive circuit. Now the last three drive circuits mentioned above are often encountered in maintenance

2 maintenance methods of several drive circuits

(1) causes and inspection of drive circuit damage

there are various reasons for drive damage. Generally speaking, the problems are no output of u, V and W phases, or the output is unbalanced, or the output is balanced but jitters at low frequency, as well as startup alarm, etc. When the fast fuse behind a large capacitor of a frequency converter is open, or the IGBT inverter module is damaged, the driving circuit can hardly be intact. Do not replace a good fast fuse or IGBT inverter module, which is likely to cause damage to the good device just replaced. At this time, we should focus on checking whether there is a spark mark on the lower drive circuit. Here, we can first unplug the drive pin wiring of the IGBT inverter module, and use the multimeter resistance block to measure whether the resistance values of the six drive circuits are the same (but very few inverter drive circuits do not have the same resistance values: such as Mitsubishi, fujishi and other inverters). If the resistance values of the six drive circuits are basically the same, it cannot fully prove that the drive circuit is intact, Then it is necessary to use an electronic oscilloscope to measure whether the voltage on the six channel drive circuit is the same, and whether the waveform of the six channel drive circuit is natural curl in the toothpaste tube when a start signal is given; If you don't have an electronic oscilloscope in your hand, you can also try to use a digital electronic multimeter to measure the DC voltage of six circuits of the drive circuit. Generally speaking, the DC voltage on each circuit of the drive circuit when it is not started is about 10V, and the DC voltage after starting is about v. if the measurement results are normal, you can basically judge that the drive circuit of the frequency converter is good. Then, connect the BT inverter module to the driving circuit, which has strict requirements for the loading mode, time and accuracy of Ig in the experiment. However, remember that the most safe way is to disconnect the P of the IGBT inverter module from the DC bus and connect a group of series connected bulbs or a resistor with a higher power in the middle, so that when there is a large current in the circuit, To protect the IGBT inverter module from being burnt out by the discharge current of the large capacitor, the following are some examples related to the drive circuit when maintaining the frequency converter:

(2) the frequency converter of Yaskawa 616G5 and 3.7KW

the frequency converter of Yaskawa 616G5 and 3.7KW. The fault phenomenon is that the three-phase output is normal, but the motor jitters at low speed and cannot operate normally. First of all, it is estimated that most of the drive circuits of the frequency converter are damaged. The correct solution should be to open the frequency converter after determining the fault phenomenon, remove the IGBT inverter module from the printed circuit board, use a comfortable and durable touch electronic oscilloscope to observe whether the waveforms of the six drive circuits are consistent when opening, find out the inconsistent drive circuit, and replace the optocoupler on the drive circuit, generally PC923 or pc929, If the frequency converter has been used for more than 3 years, it is recommended to replace all the electrolytic capacitors of the drive circuit, and then observe with an oscilloscope. After the six waveforms are consistent, install the IGBT inverter module for load test to eliminate the jitter

(3) Fuji G9 frequency converter

Fuji G9 frequency converter, the fault is no display when powered on. It is estimated by hand that the switching power supply of the frequency converter may be damaged. Turn on the frequency converter to check the switching power supply circuit. However, the circuit of the switching power supply components is not damaged, and the DC voltage at the positive and negative DC positions is not displayed. At this time, it is estimated that it may be a driving problem. Remove all the capacitors at the beginning of the driving circuit. If some capacitors are found to be leaking, replace them with new electrolytic capacitors, and work normally after being powered on again

(4) delta frequency converter

delta frequency converter, the fault phenomenon is that the output end of the frequency converter is ignited. After disassembly and inspection, it is found that the IGBT inverter module is broken down, and the driving circuit PCB is seriously damaged. The correct solution is to remove the damaged IGBT inverter module first, and try to protect the PCB from secondary damage, Replace the damaged electronic components on the drive circuit one by one and connect the open circuit on the printed circuit board with wires (here, it is necessary to scratch the scorched part to prevent ignition again). When the resistance value of the six drive circuits is the same and the voltage is the same, use the video camera to measure the waveform, but once the frequency converter is turned on, When OCC failure is reported (delta inverter has no IGBT inverter module, which will give an alarm when starting up), connect P1 of the module to the printed board with a light bulb, and connect other modules with wires. When starting up again, the OCC jumps. It is determined that there is still a problem in the drive circuit. Replace the optocouplers one by one. After that, it is found that the optocoupler of the drive circuit has a detection function. One of the optocoupler detection functions is damaged. After replacing the new one, the startup is normal

3 conclusion

today, with the continuous development of frequency converters, the drive circuit technology of frequency converters is also changing with each passing day. What can be involved here is only rare. I hope it can help the vast number of technicians and frequency converter enthusiasts. I hope that the frequency converter practitioners can communicate more, so that everyone can improve their technology

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