The power supply of the PLC control system of the tube bending machine is one of the main ways for the interference signal to enter the PLC, which is mainly generated by the impedance coupling of the power supply line. The power grid interference into the PLC control system is mainly coupled through the power supply of the PLC system, the power supply of the transmitter, and the power supply of the instrument with direct electrical connection with the PLC system.
Nowadays, the power supply of the PLC system generally uses a power supply with better isolation performance, and the power supply for the transmitter and the instrument power supply with direct electrical connection with the PLC system have not received enough attention. Although certain isolation measures have been taken, they are generally not enough. The main use of the isolation transformers has large distribution parameters, poor interference suppression capability, and common mode interference and differential mode interference through power supply coupling. In addition, the AC magnetic field of cattle produced by various high-power electrical equipment is also the main source of interference, especially the changes inside the power grid, the surge generated by the operation of the gate, the start and stop of large-scale power equipment, and the harmonic caused by the AC-DC transmission. Waves, the impact of the short-circuit transient process of the power grid, etc. will cause serious ten disturbances to the power supply of the PLC connected to the same power grid. In severe cases, the PLC may even crash during operation.
Therefore, for the power supply of the transmitter and the common signal meter, the distributor with small distributed capacitance and suppressed bandwidth (such as multiple isolation, shielding and leakage inductance technology) should be selected to reduce the interference to the PLC control system. In addition, in order to ensure that the power supply of the PLC control system is not interrupted, the online uninterruptible power supply (UPS) can be used to improve the safety and reliability of the power supply. UPS has strong interference isolation performance and is an ideal power supply for PLC control systems. In order to suppress the grid voltage fluctuation and power frequency interference caused by the startup of large-capacity equipment, an isolation transformer and an AC voltage regulator are generally used, and filtering is performed, and all the shielding layers are well grounded. The power grid often contains high harmonic components. When the grid load is large, the grid voltage fluctuations are relatively large. In order to effectively weaken and eliminate the interference signal from the power grid, a high-performance isolated power supply should be selected to suppress the power grid interference.