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There are still some unsatisfactory aspects during the operation of frequency converters, which lead to a shortened service life and correspondingly increase the maintenance of its components, thus increasing the maintenance cost.

Today, an analysis will be made from the aspects of the application environment, power - grid quality, electromagnetic interference, etc. of frequency converters, and some problems that should be noted and improvement suggestions will be put forward. It is believed that these will be helpful to everyone.

Working Environment

In the actual application of frequency converters, most people install the frequency converters directly on the industrial site to reduce costs. The work site generally has problems such as a lot of dust, high temperature, and high humidity. In some industrial applications, there are also problems such as metal dust and corrosive gases. In fact, customers have to take corresponding countermeasures according to the on - site situation.

1.The frequency converter should be installed inside the control cabinet.

2.The frequency converter is preferably installed in the middle of the control cabinet; the frequency converter should be installed vertically, and Avoid installing large components that may block exhaust and intake air above and below.

3.The minimum distance between the upper and lower edges of the frequency converter and the top and bottom of the control cabinet should be greater than 300 mm, as well as the partition or the large components that must be installed.

(4) If special users need to remove the keyboard during use, the keyboard hole on the frequency converter panel must be strictly sealed with adhesive tape or replaced with a fake panel to prevent a large amount of dust from entering the inside of the frequency converter.

(5) The printed circuit boards and metal structural parts inside most frequency converters have not undergone special treatment for moisture-proof and mildew - proof. If they are in a harsh working environment for a long time, the metal structural parts are prone to rust. The conductive copper bars will accelerate the rusting process under high - temperature operation, and the small copper wires on the micro - computer control board and the drive power supply board would cause damage due to rusting. Therefore, for applications that are in wet and contain corrosive gasesplace, there must be basic requirements for the internal design of the frequency converter used.

(6) When using a frequency converter in a dusty place, especially a place with a lot of metal dust and flocculent matter, the general requirement is that the control cabinet should be sealed as a whole, and the air inlet and outlet should be specially designed for ventilation; thereshould be a protective net and a protective top cover air outlet on the top of the control cabinet; there should be a bottom plate, an air inlet, a wire inlet hole at the bottom of the control cabinet, and a dust-proof net should be installed.

Electromagnetic Interference

In modern industrial control systems, micro-computers or PLC (Programmable Logic Controller) control technologies are often used. During system design or renovation, attention must be paid to the problem of interference of the frequency converter on the micro-computer control board. Because the micro - computer control boards designed for some frequency converters do not conform to the international EMC (Electromagnetic Compatibility) standards, conductive and radiated interference will occur after using the frequency converter, which often leads to the control system abnomal. The following methods can be used for your reference.

1.Installing an EMI filter at the input end of the frequency converter can effectively suppress the conducted interference of the frequency converter to the power grid. Installing input AC and DC reactors can improve the power factor and reduce harmonic pollution, with a good comprehensive effect. In some cases where the distance between the motor and the frequency converter exceeds 100m, it is necessary to add an AC output reactor on the side of the frequency converter, to solve the leakage current protection problem caused by the distributed parameters of the output wire to the ground and reduce the radiation interference to the outside.

One method is threading steel pipe or shielded cables and connect the shell of the steel pipe or the shielding layer of the cable reliably to the ground. Without adding an AC output reactor, using threading steel pipe or shielded cables will increase the distributed capacitance to the ground of the output ,which is prone to overcurrent.

2) Electrically shield and isolate the detection analog sensors inputs and analog control signals. During the design process of the control system of frequency converters, it is recommended to avoid using analog control as much as possible, especially when the control distance is greater than 1m and the installation is across control cabinets. Because frequency converters generally have multi-stage speed settings and switching frequency input and output, which can meet the requirements. If analog control must be used, it is recommended to definitely use shielded cables and implement one-point grounding at the far end on the sensor side or the frequency converter side. If the interference is still severe, DC/DC isolation measures need to be implemented. Standard DC/DC modules can be adopted, Or adopt the method of optically isolating the V/F conversion and then using the frequency setting input.

(3)Installing an EMI filter, a common-mode inductor, a high-frequency magnetic ring, 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 PHS base stations nearby, a metal mesh shielding cover can be added to the microcomputer control board for shielding treatment.

(4)Good grounding. The grounding wire of the strong current control system such as motors must be reliably grounded through the grounding busbar. The shielding ground of the microcomputer control board should be grounded separately. For some situations with severe interference,it is recommended to connect the sensors and the shielding layers of I/O interfaces to the control ground of the control board.

Power Grid Quality

In situations with impact loads such as electric welding machines, electric arc furnaces, and rolling mills, voltage flicker often occurs. In a workshop, when there are multiple capacitive rectifier loads of frequency converters in operation, the harmonics they generate will cause serious pollution to the power grid quality, and also have a considerable damaging effect on the equipment itself. At best, the equipment may not be able to operate continuously and normally, and at worst, the input circuit of the equipment may be damaged. The following methods can be adopted to solve the problem.

1) In situations where there are impact loads such as electric welding machines, electric arc furnaces and rolling mills, it is recommended that users install static var compensation devices to improve the power factor and quality of the power grid.

2) In workshops where frequency converters are relatively concentrated, it is recommended to adopt the centralized rectification and DC common bus power supply mode. It is recommended that users adopt the 12-pulse rectification mode. Its advantages are that it generates fewer harmonics and saves energy, and The advantages are small harmonics and energy saving, especially suitable for frequent starting and braking, and the motor is in both electric operation and power generation operation.

3) Install a passive LC filter on the input side of the frequency converter to reduce input harmonics, improve the power factor, It hasthe high reliability and good effect.

4) Install an active Power Factor Correction (PFC) device on the input side of the frequency converter. It has the best effect, but the cost is relatively high.

Starting from the problems that occured in the actual application system of the frequency converter, and from aspects such as interference from external factors, the use environment, and the quality of the power grid, and Point out the influence of bad factors on frequency converter in practical , Then summarize some solutions and suggestions for improvement, which can have a good effect on prolonging the service life of the frequency converter and has a certain reference value in practical engineering applications.

Definitely, you can adopt one or more of these methodsif necessary.