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Analysis on common problems of inverter in daily use

Oct 06, 2020

At present, the AC speed regulation system that people call mainly refers to the frequency conversion speed regulation system of the AC motor by the electronic power converter. The frequency conversion speed regulation system is superior to the DC drive and is used as the preferred transmission scheme in many occasions. Modern frequency conversion speed regulation basically uses 16-bit or 32-bit single-chip microcomputer as the control core, so as to realize full digital control and speed regulation. The performance is basically similar to that of DC speed regulation, but when the inverter is used, its maintenance is more complicated than that of DC. Once a fault occurs, it is difficult for ordinary electricians in the enterprise to deal with it. Here, we will analyze the common faults of the inverter and analyze the causes and reasons of the fault. Approach.


   One, parameter setting fault


  Whether the commonly used frequency converter can meet the requirements of the drive system during use, the parameter setting of the frequency converter is very important. If the parameter setting is incorrect, the frequency converter will not work normally.


  1, parameter setting


  Commonly used inverters, generally when leaving the factory, the manufacturer has a default value for each parameter, and these parameters are called factory values. In the case of these parameter values, the user can operate normally with the panel operation, but the panel operation does not meet the requirements of most transmission systems. Therefore, before using the inverter correctly, the user should perform the following aspects of the inverter parameters:


   (1) Confirm the motor parameters. The inverter sets the power, current, voltage, speed, and maximum frequency of the motor in the parameters. These parameters can be obtained directly from the motor nameplate.

   (2) The control method adopted by the inverter, namely speed control, torque control, PID control or other methods. After adopting the control method, it is generally necessary to perform static or dynamic identification according to the control accuracy.

   (3) Set the startup mode of the inverter. Generally, the inverter is set to start from the panel when it leaves the factory. The user can select the startup mode according to the actual situation, using the panel, external terminals, communication methods, etc.

(4) For the selection of the given signal, the frequency setting of the general inverter can also be given in multiple ways, such as panel setting, external setting, external voltage or current setting, communication mode setting, and of course the frequency setting of the inverter Setting can also be the sum of one or several of these methods. After setting the above parameters correctly, the inverter can basically work normally. If you want to obtain a better control effect, you can only modify the relevant parameters according to the actual situation.


  2, the handling of parameter setting faults


   Once a parameter setting fault occurs, the inverter cannot operate normally. Generally, the parameters can be modified according to the manual. If the above does not work, it is best to restore all the parameters to the factory values, and then reset them according to the above steps. The parameter restoration methods are different for each company's inverter.


   2. Overvoltage fault


   The overvoltage of the inverter is concentrated on the tributary voltage of the DC bus. Under normal circumstances, the inverter's DC power is the average value after three-phase full-wave rectification. If calculated with 380V line voltage, the average DC voltage Ud=1.35U line=513V. When an overvoltage occurs, the energy storage capacitor of the DC bus will be charged. When the voltage reaches about 760V, the inverter overvoltage protection will act. Therefore, the inverter has a normal working voltage range. When the voltage exceeds this range, it is likely to damage the inverter. There are two types of common overvoltages.


  1. The input AC power supply is overvoltage. This situation means that the input voltage exceeds the normal range. It usually occurs during holidays when the load is light, the voltage increases or decreases and the line fails. At this time, it is best to disconnect the power supply, check and deal with it.


  2, power generation type overvoltage


  The probability of this situation is high, mainly because the synchronous speed of the motor is higher than the actual speed, which makes the motor in the state of generating electricity, and the inverter is not equipped with a braking unit. There are two cases that can cause this fault.


(1) When the inverter drives a large inertia load, the deceleration time is set to be relatively small. During the deceleration process, the output speed of the inverter is relatively fast, and the load decelerates slowly by its own resistance, so that the load drives the motor speed. The speed corresponding to the frequency output by the inverter is higher. The motor is in the state of generating electricity and the inverter has no energy feedback unit. Therefore, the voltage of the inverter's branch DC circuit rises, exceeds the protection value, and malfunctions, which often occurs in paper machines. In the dry part, to deal with this kind of fault, you can add a regenerative braking unit, or modify the inverter parameters to set the inverter deceleration time longer. The function of adding regenerative braking unit includes energy consumption type, parallel DC bus absorption type, and energy feedback type. The energy consumption type connects a braking resistor in parallel in the inverter DC circuit, and controls the on-off of the power tube by detecting the DC bus voltage. The parallel DC bus absorption type is used in a multi-motor drive system. This system often has one or several motors often working in the power generation state to generate regenerative energy. This energy is absorbed by the motor in the electric state through the parallel bus. The grid-side converter of the energy feedback type frequency converter is reversible. When there is regenerative energy, the inverter can feed the regenerative energy back to the grid.


   (2) This fault may also occur when multiple electric motors actuate the same load, mainly due to lack of load distribution. Taking two motors to drive a load as an example, when the actual speed of one motor is greater than the synchronous speed of the other motor, the motor with the higher speed is equivalent to the prime mover, and the motor with the lower speed is in the power generation state, causing failure. The paper machine often occurs in the press section and the wire section, and load distribution control is required during processing. The characteristics of the frequency converter in the branch of the paper machine transmission speed chain can be adjusted softer.


   Three, overcurrent fault


   Overcurrent faults can be divided into acceleration, deceleration, and constant speed overcurrent. It may be caused by too short acceleration/deceleration time of the inverter, sudden load change, uneven load distribution, output short circuit, etc. At this time, it is generally possible to extend the acceleration and deceleration time, reduce the sudden change of the load, add energy-consuming braking components, carry out load distribution design, and check the line. If the inverter is disconnected from the load or the overcurrent fault occurs, it means that the inverter circuit is looped and the inverter needs to be replaced. 

Four, overload fault

   Overload faults include variable frequency overload and electrical machine overload. It may be caused by too short acceleration time, excessive DC braking, too low grid voltage, and heavy load. Generally, it is possible to extend the acceleration time, extend the braking time, and check the grid voltage. The load is too heavy. The selected motor and inverter cannot drive the load. It may also be caused by poor mechanical lubrication. For the former, high-power motors and inverters must be replaced; for the latter, the production machinery must be overhauled.


   Five, other failures


  1, undervoltage

   indicates that there is a problem with the power input part of the inverter, which can be operated only after inspection.

  2, the temperature is too high

   If the motor has a temperature detection device, check the heat dissipation of the motor; if the temperature of the inverter is too high, check the ventilation of the inverter.

  3, other circumstances

   such as hardware failure, communication failure, etc., you can contact the supplier, of course, welcome to contact us