At present, what people call the AC speed control system mainly refers to the frequency conversion speed control system of the AC power motor. Frequency conversion speed control system is superior to DC transmission in many occasions as the preferred transmission scheme. Modern frequency conversion speed control basically adopts 16-bit or 32-bit microcontroller as the control core, so as to achieve full digital control and speed regulation. The performance is similar to that of DC speed control. However, when the inverter is used, the maintenance work is more complicated than that of DC. Once the fault occurs, the general electrician of the company is difficult to deal with. Here, the common faults of the inverter are analyzed and the cause of the fault is analyzed. Approach.
First, the parameter setting type breakdown Commonly used frequency converter in use, whether can meet the transmission system request, the frequency changer parameter hypothesis is very important, if the parameter setting is not correct, will cause the frequency changer not to work normally.
1. Parameter setting Common frequency converters. Generally, the factory has a default value for each parameter. 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 drive systems. Therefore, before the user correctly uses the inverter, it is necessary to perform the following aspects when the inverter parameters:
(1) To confirm the motor parameters, the inverter sets the motor power, current, voltage, rotation speed, and maximum frequency in the parameters. These parameters can be obtained directly from the motor nameplate.
(2) The control method adopted by the inverter, ie speed control, torque control, PID control or other methods. After the control method is adopted, it is generally required to perform static or dynamic identification according to the control accuracy.
(3) Set the start mode of the inverter. Normally, the inverter is set to start from the panel at the factory. The user can select the start mode according to the actual situation, and can use the panel, external terminals, and communication methods.
(4) For the selection of the given signal, the frequency setting of the general frequency converter can also have multiple modes. The panel given, the external setting, the external voltage or current given, the communication method given, of course, for the frequency of the frequency converter It can also be the sum of one or more of these methods. After correctly setting the above parameters, the inverter can basically work normally. If you want to get better control effect, you can only modify the relevant parameters according to the actual situation.
2. 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 instructions. If the above fails, it is best to restore all parameters to their factory values ​​and then reset them according to the above steps. For each company's inverter, the parameter recovery method is not the same.
2. Overvoltage fault The overvoltage of the inverter is concentrated on the DC bus's tributary voltage. Under normal circumstances, the inverter DC is the average value after three-phase full-wave rectification. If calculated by 380V line voltage, the average DC voltage Ud = 1.35U line = 513V. When the over-voltage occurs, the storage capacitor of the DC bus will be charged. When the voltage reaches about 760V, the inverter overvoltage protection action. Therefore, the inverter has a normal operating voltage range. When the voltage exceeds this range, the inverter may be damaged. There are two types of common overvoltages.
1, the input AC power overvoltage This situation refers to the input voltage exceeds the normal range, generally occurs in the holiday load is lighter, the voltage rises or falls and the line fails, it is best to disconnect the power at this time, check, handle.
2. The probability of occurrence of overvoltage in the power generation category is higher. The main reason is that the synchronous speed of the motor is higher than the actual speed, so that the motor is in the power generation state, and the inverter has no brake unit installed. There are two situations that can cause this. A failure.
(1) When the frequency converter drags a large inertial load, the deceleration time is set to a relatively small value. In the deceleration process, the output speed of the frequency converter is faster, and the load decelerates more slowly by its own resistance, so that the load drags the motor's rotation speed. The inverter output frequency is even higher than the corresponding frequency, the motor is in the state of power generation, and the inverter has no energy feedback unit, so the inverter DC DC link voltage rises, exceeds the protection value, failure occurs, and the paper machine often occurs In the dry section, to deal with such faults can increase the regenerative braking unit, or modify the inverter parameters, set the inverter deceleration time longer.
The functions of regenerative braking unit include energy consumption type, parallel DC bus absorption type and energy feedback type. The energy consumption type connects a braking resistor in parallel with the DC link of the frequency converter. By detecting the voltage of the DC bus, it controls the on-off of the power tube. The parallel DC bus absorption type is used in a multi-motor transmission system. This type of system often has one or several motors that are often operated in a power generation state to generate regenerative energy that is absorbed by a motor that is in an electric state through a parallel bus. The energy feedback type converter-side grid-side converter is reversible, and when a regenerative energy is generated, the inverter can feed the regenerated energy back to the grid.
(2) This failure may also occur when multiple electric actuators act on the same load, mainly due to no load distribution. Take two motors to drive one load. For example, when the actual speed of one motor is greater than the synchronous speed of another motor, the motor with a high speed corresponds to the prime mover, and the motor with a low speed is in a power generation state, causing a failure. The paper machine often occurs in the press section and the net section, and the load distribution control must be added during processing. It is possible to adjust the characteristics of the frequency converter in the branch of the drive speed chain of the paper machine.
Third, overcurrent fault overcurrent fault can be divided into acceleration, deceleration, constant overcurrent. This may be due to the fact that the frequency converter's acceleration/deceleration time is too short, the load is suddenly changed, the load distribution is not uniform, and the output is short-circuited. At this time, it is generally possible to extend the acceleration/deceleration time, reduce the sudden change in load, apply dynamic braking elements, design the load distribution, and inspect the line. If you disconnect the load inverter or overcurrent fault, it means that the inverter inverter circuit has been looped and you need to replace the inverter.
IV. Overload Fault Overload fault includes inverter overload and motor overload. It may be caused by too short acceleration time, excessive DC braking, low grid voltage, and heavy loads. Generally, it can increase the acceleration time, extend the braking time, check the grid voltage, and so on. The load is too heavy, the selected motor and frequency converter cannot drag the load, or it may be due to poor mechanical lubrication. For example, the former must replace the high-powered motors and inverters; if the latter, the production machines should be overhauled.
V. Other faults 1. Undervoltage indicates that there is a problem in the power input section of the inverter. Check it before it can operate.
2, the temperature is too high If the motor has a temperature detection device, check the motor cooling; inverter temperature is too high, check the ventilation of the inverter.
First, the parameter setting type breakdown Commonly used frequency converter in use, whether can meet the transmission system request, the frequency changer parameter hypothesis is very important, if the parameter setting is not correct, will cause the frequency changer not to work normally.
1. Parameter setting Common frequency converters. Generally, the factory has a default value for each parameter. 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 drive systems. Therefore, before the user correctly uses the inverter, it is necessary to perform the following aspects when the inverter parameters:
(1) To confirm the motor parameters, the inverter sets the motor power, current, voltage, rotation speed, and maximum frequency in the parameters. These parameters can be obtained directly from the motor nameplate.
(2) The control method adopted by the inverter, ie speed control, torque control, PID control or other methods. After the control method is adopted, it is generally required to perform static or dynamic identification according to the control accuracy.
(3) Set the start mode of the inverter. Normally, the inverter is set to start from the panel at the factory. The user can select the start mode according to the actual situation, and can use the panel, external terminals, and communication methods.
(4) For the selection of the given signal, the frequency setting of the general frequency converter can also have multiple modes. The panel given, the external setting, the external voltage or current given, the communication method given, of course, for the frequency of the frequency converter It can also be the sum of one or more of these methods. After correctly setting the above parameters, the inverter can basically work normally. If you want to get better control effect, you can only modify the relevant parameters according to the actual situation.
2. 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 instructions. If the above fails, it is best to restore all parameters to their factory values ​​and then reset them according to the above steps. For each company's inverter, the parameter recovery method is not the same.
2. Overvoltage fault The overvoltage of the inverter is concentrated on the DC bus's tributary voltage. Under normal circumstances, the inverter DC is the average value after three-phase full-wave rectification. If calculated by 380V line voltage, the average DC voltage Ud = 1.35U line = 513V. When the over-voltage occurs, the storage capacitor of the DC bus will be charged. When the voltage reaches about 760V, the inverter overvoltage protection action. Therefore, the inverter has a normal operating voltage range. When the voltage exceeds this range, the inverter may be damaged. There are two types of common overvoltages.
1, the input AC power overvoltage This situation refers to the input voltage exceeds the normal range, generally occurs in the holiday load is lighter, the voltage rises or falls and the line fails, it is best to disconnect the power at this time, check, handle.
2. The probability of occurrence of overvoltage in the power generation category is higher. The main reason is that the synchronous speed of the motor is higher than the actual speed, so that the motor is in the power generation state, and the inverter has no brake unit installed. There are two situations that can cause this. A failure.
(1) When the frequency converter drags a large inertial load, the deceleration time is set to a relatively small value. In the deceleration process, the output speed of the frequency converter is faster, and the load decelerates more slowly by its own resistance, so that the load drags the motor's rotation speed. The inverter output frequency is even higher than the corresponding frequency, the motor is in the state of power generation, and the inverter has no energy feedback unit, so the inverter DC DC link voltage rises, exceeds the protection value, failure occurs, and the paper machine often occurs In the dry section, to deal with such faults can increase the regenerative braking unit, or modify the inverter parameters, set the inverter deceleration time longer.
The functions of regenerative braking unit include energy consumption type, parallel DC bus absorption type and energy feedback type. The energy consumption type connects a braking resistor in parallel with the DC link of the frequency converter. By detecting the voltage of the DC bus, it controls the on-off of the power tube. The parallel DC bus absorption type is used in a multi-motor transmission system. This type of system often has one or several motors that are often operated in a power generation state to generate regenerative energy that is absorbed by a motor that is in an electric state through a parallel bus. The energy feedback type converter-side grid-side converter is reversible, and when a regenerative energy is generated, the inverter can feed the regenerated energy back to the grid.
(2) This failure may also occur when multiple electric actuators act on the same load, mainly due to no load distribution. Take two motors to drive one load. For example, when the actual speed of one motor is greater than the synchronous speed of another motor, the motor with a high speed corresponds to the prime mover, and the motor with a low speed is in a power generation state, causing a failure. The paper machine often occurs in the press section and the net section, and the load distribution control must be added during processing. It is possible to adjust the characteristics of the frequency converter in the branch of the drive speed chain of the paper machine.
Third, overcurrent fault overcurrent fault can be divided into acceleration, deceleration, constant overcurrent. This may be due to the fact that the frequency converter's acceleration/deceleration time is too short, the load is suddenly changed, the load distribution is not uniform, and the output is short-circuited. At this time, it is generally possible to extend the acceleration/deceleration time, reduce the sudden change in load, apply dynamic braking elements, design the load distribution, and inspect the line. If you disconnect the load inverter or overcurrent fault, it means that the inverter inverter circuit has been looped and you need to replace the inverter.
IV. Overload Fault Overload fault includes inverter overload and motor overload. It may be caused by too short acceleration time, excessive DC braking, low grid voltage, and heavy loads. Generally, it can increase the acceleration time, extend the braking time, check the grid voltage, and so on. The load is too heavy, the selected motor and frequency converter cannot drag the load, or it may be due to poor mechanical lubrication. For example, the former must replace the high-powered motors and inverters; if the latter, the production machines should be overhauled.
V. Other faults 1. Undervoltage indicates that there is a problem in the power input section of the inverter. Check it before it can operate.
2, the temperature is too high If the motor has a temperature detection device, check the motor cooling; inverter temperature is too high, check the ventilation of the inverter.
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