Causes of Variable Frequency Drive Overcurrent Problem
一、Forward
In the field of industrial automation, variable frequency drive vfd, as key power control equipment, are widely used in scenarios such as motor speed regulation. Understanding the variable frequency drive working principle is crucial as the problem of overcurrent in the vfd variable frequency drive has been a source of problem for engineers and maintenance personnel. Not only can it cause equipment downtime and affect productivity, but it can also cause damage to the equipment itself. Therefore, it is of great significance to deeply explore the causes of the overcurrent problem of the variable-frequency drive and formulate effective improvement strategies.
二.the cause of overcurrent of the inverter
(1) External load factors
1.Motor Overload
When the load driven by the motor exceeds its rated value, the motor needs more torque to maintain operation, which will increase the current absorbed by the motor from the inverter, which in turn will cause the inverter to overcurrent. For example, in a conveyor belt system, this can be a problem if there is too much material on the belt and the motor is too heavily loaded.
2.Load Mutation
In some application scenarios, the load may change suddenly. For example, in a stamping machine, when the punch starts stamping, the load increases instantaneously. This sudden change in load causes the motor speed and torque requirements to change rapidly, and the inverter does not have time to adjust the output, which causes overcurrent.
3.Mechanical Failure
If the mechanical equipment connected to the motor fails, such as the bearing is stuck, the coupling is damaged, etc., the motor will be blocked, which is equivalent to the infinite load of the motor, and the current rises sharply, causing the overcurrent of the inverter. Taking a fan as an example, if the fan blades are stuck by foreign objects, the motor will be overloaded, causing the inverter to overcurrent.
(2) The parameter setting of the inverter is unreasonable
1.Acceleration time is too short
If the acceleration time of the inverter is set too short, the motor needs to reach the set speed quickly when starting, and a large torque is required at the moment of starting, which will cause the motor to draw too much current from the inverter, resulting in overcurrent. For some motors with large inertial loads, too short acceleration time cannot meet their smooth starting needs.
2.Deceleration time is too short
It also takes the right amount of time for the motor to slow down. If the deceleration time is unreasonably short, regenerative electrical energy will be generated during the motor deceleration process, which will be fed back to the inverter, and if the inverter does not have a suitable braking resistor or braking unit to deal with it, it may lead to overcurrent. In elevator control systems with frequent starts and stops, improper deceleration time settings can cause such problems.
3.Improper torque compensation parameters
The torque compensation parameter is used to improve the torque characteristics of the motor during low-frequency operation. If this parameter is set too high, the current of the motor will be too high when running at low frequencies, which will cause the inverter to overcurrent. For example, in textile machinery that requires low-frequency constant torque operation, unreasonable torque compensation settings can easily lead to overcurrent.
三. the detection method of the overcurrent problem of the inverter
(1) Observe the indicator light and alarm information
Most drives have status indicators and alarm displays. When an overcurrent problem occurs, the overcurrent alarm indicator will light up, and the overcurrent fault code will also be displayed on the operation panel. Based on this information, you can preliminarily determine whether there is an overcurrent problem and the type of overcurrent (such as accelerated overcurrent, running overcurrent, etc.).
(2) Measure with an instrument
1.Current Measurement
Instruments such as clamp ammeters can be used to measure the input and output currents of the frequency converter. During normal operation, the measured current value should be within the rated current range of the inverter and motor. If the measured value exceeds the rated current and persists for a long time, there may be an overcurrent problem.
2.Voltage Measurement
Measure the input voltage of the inverter and the DC bus voltage, etc. If the input voltage is too high or too low, it may affect the normal operation of the inverter and cause overcurrent. At the same time, abnormal DC bus voltage may also be related to overcurrent problems, such as high DC bus voltage may be caused by the inability of regenerated power to be effectively processed, which in turn may cause overcurrent.
四.the improvement measures of the overcurrent problem of the inverter
(1) Measures to address the problem of external loads
1.Optimize load management
For the problem of motor overload, it is necessary to reasonably evaluate the load situation and avoid exceeding the rated load of the motor. In conveyor belt systems, load cells and other equipment can be installed to monitor the weight of the material and adjust it in time when it is close to overload. For equipment with large load mutations, buffer devices can be added, such as elastic couplings in the drive system of the press to reduce the impact of load mutations on the motor and frequency converter.
2.Timely Handling of Mechanical Failures
Establish a regular mechanical equipment inspection system to find and deal with mechanical failures in a timely manner. For example, regularly inspect the wear and tear of bearings, blades and other components of equipment such as fans and pumps. Replace the bearing in time when abnormal sound or signs of wear are found; When the blades are stuck by foreign bodies, they should be cleaned up in time to ensure the smooth rotation of the motor and avoid overload of the motor and overcurrent of the inverter.
(2) Measures to solve the problem of inverter parameter setting
1.Set acceleration and deceleration times reasonably
According to the inertia of the motor and the load, the acceleration and deceleration time of the inverter is reasonably adjusted. For motors with large inertial loads, the acceleration time should be extended appropriately to make the motor start smoothly. When setting the deceleration time, consider the regenerative braking capacity of the motor and the braking configuration of the inverter. For example, for equipment with frequent starts and stops, such as elevators, on-site debugging can be used to gradually increase or decrease the acceleration and deceleration times, and observe the current changes to find the optimal setting value.
2.Optimize Torque Compensation Parameters
Through actual testing and experience accumulation, the torque compensation parameters are reasonably set. In the equipment that requires low-frequency constant torque operation such as textile machinery, when the motor is running at low frequency, the torque compensation parameters are gradually adjusted and the motor current is measured, so that the current does not exceed the rated value while the motor meets the torque requirements.
五.Conclusion
The problem of overcurrent in the inverter is complex, but it can be solved. It needs to be comprehensively analyzed and processed from various aspects such as load and parameter setting. Through reasonable load management, correct parameter setting, and timely equipment maintenance and troubleshooting, the occurrence of overcurrent problems of inverters can be effectively reduced, equipment reliability and operation efficiency can be improved, and industrial production can be guaranteed normally. In practical applications, engineers and maintenance personnel should continue to accumulate experience, and take targeted measures to solve the problem of overcurrent of inverter according to specific equipment and operating environment.
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