Abstract: AC speed control system, mainly refers to the electronic power converter AC motor frequency control system. Frequency control system with its superior DC drive characteristics, in many cases have been as the preferred transmission program, the modern frequency control basic use of 16-bit or 32-bit microcontroller as the control center, in order to achieve full digital control, speed Performance and DC speed control are basically similar, but the use of inverter , the maintenance work than the DC complex, in the event of failure, the company's general electrical staff is difficult to deal with, here on the inverter common fault analysis of the cause of the fault and Approach.

First, the parameter settings class fault

Commonly used inverter in use, whether to meet the requirements of the drive system, inverter parameter setting is very important, if the parameter is set incorrectly, will lead to the inverter can not work properly.

1, parameter setting

Common inverter, the general factory, manufacturers have a default value for each parameter, these parameters are called plant value. In the case of these parameter values, the user is able to operate normally in panel mode, but the panel operation does not meet the requirements of most driveline systems. Therefore, users in the proper use of the inverter, to the inverter parameters from the following aspects:

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

(2) The inverter adopts the control method, namely speed control, torque control, PID control or other methods. Take the control method, generally based on the control accuracy, the need for static or dynamic identification.

(3) Set the start mode of the inverter. Generally, when the inverter is set from the factory, it can be started from the panel. The user can select the start mode according to the actual situation. You can use the panel, external terminals, and communication methods.

(4) The choice of the given signal, in general, the inverter frequency can also be given a variety of ways, panel given, external given, external voltage or current given, communication given, of course, the frequency of the inverter to It can also be the sum of one or more of these ways. After the above parameters are set correctly, the inverter can basically work normally. For better control effect, the related parameters can only be modified according to the actual conditions.

2, parameter setting fault handling

Once the parameter setting fault occurs, the inverter can not operate normally, generally according to the instructions to modify the parameters. If the above does not work, it is best to be able to restore all the factory default values, and then re-set the above steps, for each company's inverter recovery parameters are not the same.

Second, overvoltage fault

The over-voltage of the inverter is concentrated on the DC voltage of the DC bus. Under normal circumstances, the DC converter for the three-phase full-wave rectified average. If 380V line voltage calculation, the average DC voltage Ud = 1.35U line = 513V. When overvoltage occurs, the storage capacitor of the DC bus will be charged. When the voltage reaches about 760V, the inverter will overvoltage protection. Therefore, the frequency converter, has a normal operating voltage range, when the voltage exceeds this range is likely to damage the inverter, there are two common over-voltage.

1, input AC power over-voltage

This situation refers to the input voltage exceeds the normal range, usually occurs in the holiday light load, the voltage increases or decreases and the line fails, it is best to disconnect the power supply, check, handle.

2, power generation over-voltage

The probability of this situation is higher, mainly the motor synchronous speed is higher than the actual speed, the motor is in power generation, and the inverter is not installed brake unit, there are two situations can cause this failure.

(1) When the drive dragging a large inertia load, the deceleration time set relatively small, the deceleration process, the inverter output speed faster, and the load by its own resistance to slow down more slowly, so that the load drag the motor speed The inverter output frequency is higher than the corresponding speed, the motor is in power generation, and the inverter does not have energy feedback unit, so the inverter DC DC link voltage increases, beyond the protection value, failure, and machine often occur In the dry part, to deal with this kind of failure can increase regenerative braking unit, or modify the inverter parameters, the inverter deceleration time set longer. The function of adding regenerative braking unit includes energy consumption type, parallel DC bus absorption type and energy feedback type. Energy Consumption Inverter DC circuit in parallel with a braking resistor, DC bus voltage through the test to control the power tube off. Parallel DC bus absorption type used in multi-motor drive system, this system often have one or several motors often work in the state of power generation, regenerative energy, the energy through the parallel bus is in electric state motor absorption. Regenerative converter The grid-side converter is reversible. When regenerative energy is generated, the converter inverts the regenerative energy back to the grid.

(2) This fault may also occur when more than one electric actuator is operating on the same load, mainly due to no load sharing. For example, when two motors drag a load, when the actual speed of one motor is greater than the synchronous speed of the other motor, the motor with the higher speed corresponds to the prime mover, and the generator with the lower speed is in a generating state, causing the fault. In the paper machine often occurs in the press department and the Ministry of network, the processing load control should be added. It is possible to adjust the inverter characteristics that are at the branch of the speed chain of the paper machine to be softer.

Third, over-current fault

Overcurrent fault can be divided into acceleration, deceleration, constant speed over current. It may be due to the inverter acceleration and deceleration time is too short, the load changes suddenly, the load distribution is uneven, the output short circuit and other causes. At this time, generally, the acceleration and deceleration time can be prolonged to reduce the sudden change of load, and the energy consumption braking element can be used to carry out the load distribution design and check the line. If you disconnect the load inverter or over-current fault, inverter inverter circuit is ring, you need to replace the inverter.

Fourth, overload fault

Overload faults include inverter overload and motor overload. It may be due to acceleration time is too short, excessive DC braking, power grid voltage is too low, overloaded and other causes. Generally by extending the acceleration time, extended braking time, check the grid voltage. The load is too heavy, the selected motor and inverter can not drag the load, it may be due to

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