In the operation of the inverter, there are still some unsatisfactory, which leads to the shortening of its service life and the increase of the maintenance cost。
Today from the inverter application environment, power grid quality, electromagnetic interference and other aspects of the analysis, we should pay attention to some problems and suggestions for improvement, I believe that these will help you.
In the practical application of frequency converter, most people directly install the frequency converter in the industrial field in order to reduce the cost. Generally, there are problems of dust, high temperature and high humidity in the working site. In some industries, there are metal dust, corrosive gas and so on. Corresponding countermeasures must be made according to the site conditions.
1. The frequency converter shall be installed inside the control cabinet.
2。 It is better to install the frequency converter in the middle of the control cabinet; the frequency converter should be installed vertically, and the installation of large components that may block the exhaust and air intake should be avoided。
3. The minimum distance between the upper and lower edges of frequency converter and the top or bottom of control cabinet, or partition board, or large components that must be installed shall be greater than 300 mm.
4。 If a special user needs to remove the keyboard in use, the keyboard hole of the inverter panel must be sealed with tape or replaced by a false panel to prevent dust from entering into the inverter。
5. Most of the printed circuit boards and metal structures in the inverter are not treated with moisture and mildew. If they are in a bad working environment for a long time, the metal structures are easy to rust. Under the condition of high temperature operation, the conductive copper bar will be more seriously corroded. For the small copper wire on the microcomputer control board and drive power supply board, corrosion will cause damage. Therefore, it is necessary to have basic requirements for the internal design of the frequency converter when it is used in wet and corrosive gas.
6. When the frequency converter is used in the place with much dust, especially in the place with multi metal dust and floccule, the control cabinet shall be sealed as a whole, and the air inlet and outlet shall be specially designed for ventilation; the top of the control cabinet shall be provided with protective net and protective cover, and the air outlet shall be provided with bottom plate, air inlet and wire hole at the bottom of control cabinet, and dust-proof net shall be installed.
In modern industrial control system, microcomputer or PLC control technology is often used. In the process of system design or transformation, attention must be paid to the interference of inverter on microcomputer control board. Due to the fact that the microcomputer control boards designed by some frequency converters do not meet the EMC international standards, the conduction and radiation interference will be generated after using the frequency converter, which often leads to the abnormal operation of the control system. The following methods can be used for your reference.
1. Adding 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 can improve the power factor, reduce harmonic pollution and achieve good comprehensive effect. In some cases where the distance between the motor and the frequency converter exceeds 100m, bpqjs.com It is necessary to add AC output reactor at the inverter side to solve the leakage current protection caused by the distribution parameters of the output conductor to the ground and reduce the external radiation interference.
One method is to wire through the steel pipe or shield the cable, and connect the steel pipe shell or cable shielding layer with the earth reliably。 If the AC output reactor is not added, the distribution capacitance of the output to the ground will be increased by using steel pipe or shielded cable, which is prone to over-current。
2. The analog sensor detection input and analog control signal are electrically shielded and isolated. In the design process of the control system composed of frequency converter, it is recommended not to use analog control as far as possible, especially when the control distance is greater than 1 m and installed across the control cabinet. Because the frequency converter generally has multi-stage speed setting, switching frequency input and output, can meet the requirements. If it is necessary to use analog control, it is recommended to use shielded cable and realize remote point grounding at sensor side or inverter side. If the interference is still serious, DC / DC isolation measures should be implemented. Standard DC / DC module can be used, or the method of optical isolation for V / F conversion and frequency setting input can be adopted.
3. Adding EMI filter, common mode inductor and high frequency magnetic ring to input power supply of microcomputer control board can effectively suppress conducted interference. In addition, in the case of serious radiation interference, such as GSM or PHS base station, the metal mesh shield can be added to the microcomputer control board for shielding treatment.
4. Good grounding. The grounding wire of strong current control system such as motor must be reliably grounded through grounding busbar, and the shielding ground of microcomputer control board shall be separately grounded. For some cases with serious interference, it is recommended to connect the sensor and I / O interface shield with the control ground of the control board.
Power grid quality
In the impact load such as electric welding machine, electric arc furnace, rolling mill and other occasions, the voltage often flickers; in a workshop, there are several frequency converters and other capacitive rectifier loads working, the harmonic generated by them has a very serious pollution to the quality of the power grid, also has a considerable damage to the equipment itself, light can not be able to run normally, heavy will cause damage to the input circuit of the equipment. The following solutions can be taken.
1. In the case of impact load such as electric welding machine, electric arc furnace and rolling mill, it is suggested that users should add reactive static compensation device to improve power factor and quality of power grid.
2. In the workshop with concentrated frequency converters, centralized rectification and DC common bus power supply mode are recommended. It is suggested that users adopt 12 pulse rectification mode. The advantages are small harmonic, energy saving, especially suitable for frequent starting, braking, motor in both electric operation and power generation operation.
3。 A passive LC filter is installed at the input side of the inverter to reduce the input harmonics and improve the power factor。 It has high reliability and good effect。
4。 It is the best to install active PFC device at the input side of frequency converter, but the cost is high。
Starting from the problems in the practical application system of frequency converter, from the interference of external factors, use environment, power grid quality and other aspects, this paper puts forward the influence of adverse factors on the frequency converter in practical application, and then sums up some solutions and improvement suggestions on this problem, which can play a good role in prolonging the service life of frequency converter The application in international engineering has certain reference value。
Of course, one or more of these methods are generally adopted。