Introduction to the industry how to extend the life of the four-way inverter
How to extend Quadruple Inverter is a matter of great concern to the people in the industry. Now the application environment, electromagnetic interference and anti-interference, power grid quality of Sifang inverter The other aspects have been analyzed, and the problems that should be paid attention to when using the inverter and the corresponding improvement suggestions are put forward. It is believed that this will have a significant effect on improving the service life of the inverter.
1.Impact of electromagnetic interference on the inverter
In modern industrial control systems, more microcomputer or PLC control technology In the process of system design or transformation, we must pay attention to the interference of the inverter to the microcomputer control board. The inverter is subject to external interference. 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 leads to abnormal operation of the control system, so it is necessary to take Describe the necessary measures.
1) Good grounding. The grounding wire of the strong electric control system such as motor must be grounded reliably through the grounding busbar, and the shielding ground of the microcomputer control board should be grounded separately. For some severe interference situations, it is recommended to connect the sensor and I/0 interface shielding layer to the control ground of the control board.
2) Adding EMI filter, common mode inductor, high frequency magnetic ring, etc. to the input power of the microcomputer control board can effectively suppress the conducted interference. In addition, in the case of severe radiation interference, such as the presence of GSM or PHS base stations, a metal mesh shield can be added to the microcomputer control board for shielding.
3) Adding an EMI filter to the input end of the inverter can effectively suppress the conducted interference of the inverter to the power grid. Adding input AC and DC reactors can improve the power factor. Reduce harmonic pollution, and the overall effect is good. When the distance between some motors and the inverter exceeds 100m, it is necessary to add an AC output reactor on 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. It is worth noting that when the AC output reactor 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 prone to occur. Of course, one or several methods are generally adopted in practical applications. 4) Electrically shield and isolate analog sensor sense inputs and analog control signals. 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 1 m and is installed 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. A standard DC/DC module can be used, or a method of optically isolating the v/f conversion and then using the frequency setting input.
2. The impact of the working environment
In the practical application of the frequency converter, most of the domestic customers except for a few dedicated computer rooms, in order to reduce Cost, the inverter is directly installed on the industrial site. The work site generally has problems of large dust, high temperature and high humidity, as well as metal dust and corrosive gases in the aluminum industry. Therefore, it is necessary to make corresponding countermeasures according to the situation on the spot.
1) The frequency converter should be installed inside the control cabinet.
2) The inverter should be installed in the middle of the control cabinet as much as possible; the inverter should be installed vertically, and the upper and lower sides should be installed to avoid large components that may block the exhaust and air. 3) The distance between the upper and lower edges of the inverter from the top, bottom, or partition of the control cabinet, or large components that must be installed, should be greater than 300mm.
4) If the special user needs to remove the keyboard during use, the keyboard hole of the inverter panel must be tightly sealed with tape or replaced with a dummy panel to prevent dust from entering the frequency conversion. Inside the device.
5) When using a frequency converter in a dusty place, especially in a place with multi-metal dust and floc, the overall requirements of the control cabinet are sealed, and the air inlet and outlet are specially designed. Ventilation; the top of the control cabinet should have a protective net and a protective top cover air outlet; the bottom of the control cabinet should have a bottom plate and air inlet, inlet holes, and a dust net.
6) Most of the printed circuit boards and metal structural parts inside the inverter manufacturers have not been specially treated for moisture and mildew. If the inverter is in a harsh working environment for a long time, the metal structure Pieces are prone to rust. When the conductive copper strip is operated under high temperature, it will be more rusted. Corrosion will be caused to the small copper conductor on the microcomputer control board and the drive power board. Therefore, for applications where it is used in wet and corrosive gases, basic requirements must be placed on the internal design of the frequency converter used. For example, printed circuit boards must be treated with three anti-paints. For structural parts, nickel-chromium plating must be used. Process. In addition, other active, effective and reasonable measures against moisture and corrosion are needed.
3. The impact of grid quality on the frequency converter
In the case of impact loads such as electric welders, electric arc furnaces, rolling mills, etc., the voltage is often Flicker occurs; in a workshop, when there are multiple inverters and other capacitive rectification loads in operation, the harmonics generated by them have serious pollution to the quality of the power grid, and they also have considerable damage to the equipment itself. Continuous normal operation, but the damage to the equipment input circuit. The following measures can be taken.
1) In the impact load such as electric welder, electric arc furnace, rolling mill, etc., it is recommended that the user increase the reactive static compensation device to improve the power factor and quality of the power grid.
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 frequent starting and braking, and the electric motor is in the occasion of electric operation and power generation operation.
3) A passive LC filter is installed on the input side of the inverter to reduce input harmonics, improve power factor, and have high reliability and good effect.
4) The input PFC device is installed on the input side of the inverter, which has good effect but high cost.