The energy feedback device supplier reminds you that the frequency converter still has some unsatisfactory performance during operation, resulting in a shortened service life and increased maintenance costs for its components.
Analyzing the application environment, power grid quality, electromagnetic interference, and other aspects of frequency converters, some issues that should be noted and improvement suggestions are believed to be helpful to everyone.
working environment
In practical applications of frequency converters, most people install them directly on industrial sites in order to reduce costs. There are generally problems with high dust, high temperature, and high humidity in the workplace. In some industry applications, there are also issues with metal dust, corrosive gases, and so on. Corresponding measures must be taken based on the on-site situation.
1) The frequency converter should be installed inside the control cabinet.
2) It is best to install the frequency converter in the middle of the control cabinet; The frequency converter should be installed vertically, and large components that may block exhaust and intake should be avoided from being installed directly above and below.
3) The minimum distance between the upper and lower edges of the frequency converter and the top, bottom, partition, or necessary large components of the control cabinet should be greater than 300mm.
4) If special users need to remove the keyboard during use, the keyboard hole on the inverter panel must be strictly sealed with tape or replaced with a fake panel to prevent a large amount of dust from entering the interior of the inverter.
5) Most printed circuit boards and metal structural components inside frequency converters have not undergone special treatment to prevent moisture, mold and mildew. If they are exposed to harsh working environments for a long time, metal structural components are prone to rusting. Under high temperature operation, conductive copper bars will undergo more severe corrosion, which will cause damage to the small copper wires on the microcomputer control board and drive power board. Therefore, for applications in humid and corrosive gas containing environments, there must be basic requirements for the internal design of the frequency converter used.
6) When using a frequency converter in dusty areas, especially in areas with multi metal dust and flocculent substances, it is generally required that the control cabinet be sealed as a whole and specially designed with air inlet and outlet for ventilation; The top of the control cabinet should have a protective net and a protective cover air outlet; The bottom of the control cabinet should have a base plate, air inlet, and wire inlet holes, and be equipped with a dust-proof net.
electromagnetic interference
In modern industrial control systems, microcomputer or PLC control technology is often used. In the process of system design or modification, attention must be paid to the interference of frequency converters on the microcomputer control board. Due to the fact that some microcomputer control boards designed for frequency converters do not comply with EMC international standards, there may be conducted and radiated interference after using the frequency converter, which often leads to abnormal operation of the control system. The following methods are provided for your reference.
1) Installing an EMI filter on the input end of the frequency converter can effectively suppress the conducted interference of the frequency converter on the power grid. Installing input AC and DC reactors can improve power factor, reduce harmonic pollution, and achieve good comprehensive effects. In some cases where the distance between the motor and the frequency converter exceeds 100m, bpqjs.com needs to add an AC output reactor on the frequency converter side to solve the leakage current protection caused by the distribution parameters of the output wire to ground and reduce external radiation interference.
One method is to thread steel pipes or shield cables, and reliably connect the steel pipe shell or cable shielding layer to the ground. Without adding an AC output reactor, using steel pipe threading or shielded cables will increase the distributed capacitance of the output to ground, which is prone to overcurrent.
2) Electrical shielding and isolation of analog sensor detection inputs and analog control signals. In the design process of the control system composed of frequency converters, it is recommended not to use analog control as much as possible, especially when the control distance is greater than 1m and installed across control cabinets. Because frequency converters generally have multiple speed settings and switch frequency input and output, they can meet the requirements. If analog control is necessary, it is recommended to use shielded cables and achieve a remote grounding point on the sensor or frequency converter side. If the interference is still severe, DC/DC isolation measures need to be implemented. Standard DC/DC modules can be used, or v/f conversion can be optically isolated and frequency input can be used.
3) Installing EMI filters, common mode inductors, high-frequency magnetic rings, etc. on the input power supply of the microcomputer control board can effectively suppress conducted interference. In addition, in situations where radiation interference is severe, such as when there are GSM or pager base stations around, a metal mesh shielding cover can be added to the microcomputer control board for shielding treatment.
4) Good grounding. The grounding wire of strong current control systems such as motors must be reliably grounded through a grounding busbar, and the shielding ground of the microcomputer control board should be grounded separately. For certain situations with severe interference, it is recommended to connect the sensor and I/O interface shielding layer to the control ground of the control board.
Power grid quality
Voltage flicker often occurs in impact loads such as welding machines, electric arc furnaces, steel mills, etc; In a workshop, when multiple variable frequency converters and other capacitive rectifier loads are in operation, the harmonics generated by them cause serious pollution to the quality of the power grid and have a considerable destructive effect on the equipment itself, ranging from being unable to operate continuously and normally to causing damage to the input circuit of the equipment. The following methods can be adopted to solve the problem.
1) It is recommended that users add reactive power static compensation devices to improve the power factor and quality of the power grid when dealing with impact loads such as welding machines, electric arc furnaces, and steel mills.
2) In workshops where frequency converters are concentrated, it is recommended to use centralized rectification and DC common bus power supply. It is recommended that users adopt the 12 pulse rectification mode. The advantages are low harmonics and energy saving, especially suitable for frequent starting and braking, where the electric motor operates in both electric and power generation scenarios.
3) Installing a passive LC filter on the input side of the frequency converter reduces input harmonics, improves power factor, has high reliability, and achieves good results.
4) Installing an active PFC device on the input side of the frequency converter yields the best results, but the cost is relatively high.
Starting from the problems that arise in the practical application system of frequency converters, this article proposes targeted solutions and improvement suggestions for the impact of adverse factors on frequency converters in practical applications, such as external interference, usage environment, and power grid quality. These solutions can effectively extend the service life of frequency converters and have certain reference value in practical engineering applications.
Of course, one or several methods are generally adopted.