Frequency converter switching mode - Solutions - Huaqiang Electronic Network

The power frequency switching mode of the inverter is divided into manual bypass and automatic bypass:

1, manual switching mode

There is less investment in manual switching mode, and there is obvious power-off time when overhauling the inverter. It can ensure personal safety, but it has complicated operation and long switching time. It needs manual operation after boiler shutdown and ignition, and does not meet the boiler requirements for continuous operation. Stability and economic requirements. As shown below:

Figure 1 power frequency manual bypass wiring diagram

The above manual switching mode is composed of three isolating switches QS1, QS2 and QS3, wherein QS2 and QS3 cannot be closed at the same time and are mechanically interlocked. When the inverter is running, QS1 and QS2 are closed, QS3 is disconnected; when the inverter is faulty, the upper switch QF is automatically tripped; QS1 and QS2 are disconnected, QS3 is closed, and the upper switch QF is closed, and the motor enters the power frequency operation.

2, automatic switching method

The advantage of automatic switching bypass is that it can realize the operation of the frequency conversion automatic cutting power frequency operation and the power frequency automatic cutting frequency conversion. This process is continuous and will not cause the boiler to be shut down and fired, thus ensuring the need for continuous production. This is very important. (http:// copyright) Disadvantages are high investment, complicated programming, and poor handling can easily lead to expansion accidents. As shown below:

Figure 2 power frequency automatic bypass wiring diagram

There are several issues to consider when switching systems automatically:

(1) When the frequency conversion is cut, it is necessary to judge whether the inverter is faulty or the motor itself is faulty, so as to avoid causing an expansion accident;

(2) When the frequency conversion power frequency is cut, it is necessary to solve the automatic operation problem of the damper when cutting to the power frequency operation to maintain the constant pressure and air volume of the boiler, and ensure the stable operation of the boiler. At the same time, it is necessary to consider the switching time to avoid the motor. State process

(3) When the power frequency is cut, the inverter needs to have the flying start function, so that the inverter can track the motor speed and achieve smooth switching. At the same time, the switching time also needs to consider the transition process of the motor to avoid the inverter overvoltage fault. The switch failed, causing the boiler to shut down.