Emerson frequency converter common three major interference
Emerson inverter manufacturers today tell you about the three major disturbances of the inverter, I hope to be able to Helpful
1, the inverter is controlled by the microcomputer
interference in the control panel of the frequency converter system, the use of the computer or PLC control, system design or transformation process, must pay attention to interference inverter microcomputer control panel. Because the user's own design of the microcomputer control board is generally poor in process level and does not comply with EMC international standards, the conduction and radiation interference generated after the inverter is used often causes the control system to work abnormally, so it is necessary to take necessary measures. 1 good grounding. The grounding wire of the high-power control system such as the motor must be reliably grounded through the grounding busbar, and the shielding ground of the microcomputer control board should be grounded as much as possible. For some severe interference situations, it is recommended to connect the sensor and I/O interface shield to the control ground of the control board.
2 Add power to the microcomputer control board to install EMI filter, common mode inductor, high frequency magnetic ring, etc., and the cost is low. It can effectively suppress conducted interference. In addition, in the case of severe radiation interference, such as the presence of GSM or PHS stations, a metal mesh shield can be added to the microcomputer control board for shielding.
3 Adding an EMI filter to the inverter input can effectively suppress the conducted interference of the inverter to the power grid. Adding input AC and DC reactors L1 and L2 can improve the power factor and reduce the harmonics. Wave pollution, the comprehensive effect is good. In the case where the distance between some motors and the inverter exceeds 100m, it is necessary to add an AC output reactor L3 to the inverter side to solve the leakage current protection caused by the distribution parameters of the output wires to the ground and reduce the external radiation interference. An effective method is to use a steel pipe to thread or shield the cable and reliably connect the steel casing or cable shield to the ground. Please note that when the AC output reactor L3 is not added, if the steel pipe is threaded or shielded, the distributed capacitance of the output to the ground is increased, and overcurrent is likely to occur. Of course, in practice, only one or several methods are generally adopted. 4 electrically shields and isolates the analog sensor sense input and the analog control signal. In the design process of the control system composed of the inverter, it is recommended not to use the analog control as much as possible, especially if the control distance is greater than 1M and the installation is across the control cabinet. Because the inverter generally has multi-speed setting and switching frequency input and output, it can meet the requirements. If it is necessary to use analog control, it is recommended to use a shielded cable and ground the remote point on the sensor side or the inverter side. If the interference is still severe, DC/DC isolation measures are required. Standard DC/DC modules can be used, or V/F conversion, optical isolation and frequency setting input can be used.
2. Anti-interference problem of the inverter itself. When there is a high-frequency impact load near the power supply system of the inverter, such as electric welding machine, electroplating power supply, electrolysis power supply or slip ring In the case of power supply, the inverter itself is susceptible to protection due to interference. Users are advised to take the following measures:
1 Add inductors and capacitors on the input side of the inverter to form an LC filter network. 2 The power line of the inverter is directly powered from the transformer side. 3 A separate transformer may be employed where conditions permit. 4 When using external switch control terminal control, shielded cable is recommended when the connection line is long. When the control circuit and the main circuit power supply are buried in the trench, except for the control cable, the shielded cable must be used. The main circuit must be shielded by the steel pipe to reduce mutual interference and prevent the inverter from malfunctioning. 5 When using external analog control terminal control, if the connection line is within 1M, use shielded cable to connect, and implement one point of grounding on the inverter side; if the line is long and the site interference is serious, it is recommended that The DC/DC isolation module is installed on the inverter side or V/F conversion is adopted, and the frequency command given mode is used for control. 6 When using external communication control terminal control, it is recommended to use shielded twisted pair and ground the shield on the inverter side (PE). If the interference is very serious, it is recommended to connect the shield to the control power ground (GND). . For the RS232 communication mode, pay attention to the control line as far as possible not to exceed 15m. If you want to lengthen, you must reduce the communication baud rate. When the distance is about 100m, the baud rate of normal communication is less than 600bps. For RS485 communication, terminal matching resistors and the like must also be considered. For high-speed control systems using fieldbus, the communication cable must be a dedicated cable and multi-point grounding to improve reliability.
3. Grid quality problems. In high-frequency impact loads such as electric welders, electroplating power supplies, electrolysis power supplies, etc., the voltage often flickers; in a workshop, there are When hundreds of inverters are used in the capacitive rectification load, the harmonics of the power grid are very large, and there is a serious pollution to the quality of the power grid. It also has a considerable damage to the equipment itself, but it cannot be continuously operated normally, but it is caused by Damage to the equipment input circuit. The following measures can be taken: (1) In high-frequency impact loads such as electric welding machines, electroplating power supplies, electrolysis power supplies, etc., it is recommended that users increase the reactive static compensation device and improve the power grid. Power factor and quality.
(2) In the workshop where the inverter is concentrated, it is recommended to use centralized rectification and DC common bus power supply. Users are advised to use a 12-pulse rectification mode. The utility model has the advantages of small harmonics and energy saving, and is particularly suitable for occasions where frequent braking, electric operation and power generation operation are simultaneously performed. (3) A passive LC filter is installed on the input side of the inverter to reduce input harmonics, improve power factor, lower cost, high reliability and good effect.
(4) The input PFC device is installed on the input side of the inverter, the effect is good, but the cost is higher.