The power supply of China tube bending machine PLC control system 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 of the PLC control system is mainly through the power supply of the PLC system, the power supply of the transmitter, and the power supply of the instrument that has a direct electrical connection to the PLC system. At present, the power supply of the PLC system is generally based on a power source with good insulation performance, and the power source of the transmitter and the power source of the instrument that has direct electrical contact with the PLC system have not received enough attention. Although certain isolation measures are taken, they are generally not sufficient. The main reason is that the isolation transformer used has large distributed parameters and poor anti-interference capabilities. Common mode interference and differential interference are sequentially coupled through the power supply. In addition, the alternating current magnetic field produced by various high-power electrical equipment is also the main source of interference, especially the internal changes of the power grid, the sudden rise caused by the shutdown process, the start and stop of large power equipment, and the harmonics caused by the AC and current transmission devices continuous. The waves and short-circuit operation effects of the electric power grid, etc., will cause serious disturbances in the power supply of the PLC connected to the power grid itself, and even cause the PLC to malfunction during operation.
Therefore, power distributors with small distributed capacitance and suppression bandwidth (such as the use of isolation, shielding and multiple leakage inductance techniques) should be selected to power the transmitters and common signal counters to reduce interference in the PLC control system. In addition, in order to ensure that the power supply to the PLC control system is uninterrupted, an online uninterruptible power supply (UPS) can be used to supply power to improve the safety and reliability of the power supply. UPS has strong interference isolation performance and is an ideal power source for PLC control systems. In order to suppress network voltage fluctuations and power frequency interference caused by large-capacity equipment starting, isolating transformers and AC voltage stabilizers are generally used, filtered, and all shielding layers must be well grounded. The power grid often has high harmonic components, and when the grid load is heavy, the grid voltage fluctuates relatively large. In order to effectively weaken and eliminate the interference signals from the power grid, high-performance isolated power sources should be selected to suppress the grid interference.