A device that converts a constant voltage and frequency alternating current into a voltage or variable frequency alternating current is referred to as a "frequency converter." In order to produce a variable voltage and frequency, the device first converts the alternating current of the power supply to direct current (DC). The device that converts direct current (DC) to alternating current (AC) is scientifically termed "inverter" (inverter). Since the main device that generates the changed voltage or frequency in the inverter device is called “inverterâ€, the product itself is named “inverter. The inverter used for motor control can change the voltage and change the frequency.
The number of poles of the motor is determined by the structure and working principle of the motor. It is generally not suitable to adjust the motor speed by changing this value. The frequency can be adjusted in front of the motor and then supplied to the motor so that the rotation speed of the motor can be freely controlled. Therefore, the inverter with the purpose of controlling the frequency is the preferred device for the motor speed control device.
At present, AC power supply used in our country, whether for home or factory, the voltage and frequency are 400V/50Hz or 200V/60Hz (50Hz) and so on.
Changing the frequency and voltage is the best motor control method. If you only change the frequency without changing the voltage, the frequency drop will make the motor over-voltage (over-excitation), resulting in the motor may be burned out. Therefore, the inverter must change the voltage while changing the voltage. When the output frequency is above the rated frequency, the voltage cannot continue to increase. The highest value is equal to the rated voltage of the motor.
For example: In order to reduce the rotation speed of the motor by half, the output frequency of the inverter is changed from 50Hz to 25Hz. At this time, the output voltage of the inverter needs to be changed from 400V to about 200V. The correct choice of motor and frequency converter is normal for the control system. Running is critical. When selecting the inverter, you must fully understand the load characteristics driven by the inverter. In practice, people often divide production machinery into three types: constant-torque loads, constant-power loads, and fans and pump loads. Users can choose different types of inverters according to their actual process requirements and application occasions. When selecting the inverter, pay attention to the following points: When selecting the inverter, use the actual motor current value as the basis for the inverter selection. The rated power of the motor can only be used as a reference.
In addition, it should be fully considered that the output of the inverter is rich in higher harmonics, which will deteriorate the power factor and efficiency of the motor. Therefore, comparing the use of frequency converters to power the motor and the power frequency grid, the motor current will increase by 10% and the temperature rise will increase by about 20%. Therefore, when selecting the motor and the frequency converter, this situation should be taken into account, leaving a margin to prevent excessive temperature rise and affect the service life of the motor.
When the inverter is running a long cable, measures should be taken to suppress the influence of long cable-to-ground coupling capacitance and prevent the inverter from outputting enough power. Therefore, the inverter should amplify one or two gears or install an output reactor at the output of the inverter.
For some special applications, such as high ambient temperature, high switching frequency, high altitude, etc., this will cause derating of the inverter, and the inverter needs to amplify one gear selection. When the inverter is used to control a high-speed motor, high-frequency harmonics are generated due to the small reactance of the high-speed motor. These higher harmonics increase the output current of the inverter. Therefore, when selecting the inverter for high-speed motor, it should be slightly larger than the inverter of the ordinary motor. When using a frequency converter to drive a geared motor, the range of use is limited by the lubrication of the rotating part of the gear. When lubrication oil is lubricated, there is no limit in the low speed range; in the high speed range above the rated speed, there is a risk that the lubricant will run out. Therefore, do not exceed the maximum speed tolerance.
Inverter drives wound rotor asynchronous motors, mostly using existing motors. Winding Motors Compared to ordinary squirrel cage motors, the winding resistance of the winding motor is small. Therefore, the overcurrent trip due to the ripple current is prone to occur. Therefore, a converter slightly larger than the normal capacity should be selected. The general winding motor is mostly used in the occasion where the flywheel moment GD2 is large, and more attention should be paid when setting the acceleration/deceleration time.
When the inverter drives the synchronous motor, the output capacity will be reduced by 10% to 20% compared with the commercial frequency power supply. The continuous output current of the inverter is greater than the product of the synchronous motor rated current and the synchronous pull-in current.
For compressors, vibration machines with large torque fluctuations, and hydraulic pumps with peak loads, if the inverter is selected according to the rated current or power value of the motor, the overcurrent protection operation may occur due to the peak current. . Therefore, it is necessary to understand the frequency operation and select the inverter with a rated output current greater than its maximum current. When selecting a frequency converter, it is important to note whether its degree of protection matches the situation at the site. Otherwise, the dust and moisture on the site will affect the long-term operation of the inverter. For more information on the use of frequency converters, please consult with the home of the OTC Transamerica inverter and participate in the learning and use of the inverter.
The number of poles of the motor is determined by the structure and working principle of the motor. It is generally not suitable to adjust the motor speed by changing this value. The frequency can be adjusted in front of the motor and then supplied to the motor so that the rotation speed of the motor can be freely controlled. Therefore, the inverter with the purpose of controlling the frequency is the preferred device for the motor speed control device.
At present, AC power supply used in our country, whether for home or factory, the voltage and frequency are 400V/50Hz or 200V/60Hz (50Hz) and so on.
Changing the frequency and voltage is the best motor control method. If you only change the frequency without changing the voltage, the frequency drop will make the motor over-voltage (over-excitation), resulting in the motor may be burned out. Therefore, the inverter must change the voltage while changing the voltage. When the output frequency is above the rated frequency, the voltage cannot continue to increase. The highest value is equal to the rated voltage of the motor.
For example: In order to reduce the rotation speed of the motor by half, the output frequency of the inverter is changed from 50Hz to 25Hz. At this time, the output voltage of the inverter needs to be changed from 400V to about 200V. The correct choice of motor and frequency converter is normal for the control system. Running is critical. When selecting the inverter, you must fully understand the load characteristics driven by the inverter. In practice, people often divide production machinery into three types: constant-torque loads, constant-power loads, and fans and pump loads. Users can choose different types of inverters according to their actual process requirements and application occasions. When selecting the inverter, pay attention to the following points: When selecting the inverter, use the actual motor current value as the basis for the inverter selection. The rated power of the motor can only be used as a reference.
In addition, it should be fully considered that the output of the inverter is rich in higher harmonics, which will deteriorate the power factor and efficiency of the motor. Therefore, comparing the use of frequency converters to power the motor and the power frequency grid, the motor current will increase by 10% and the temperature rise will increase by about 20%. Therefore, when selecting the motor and the frequency converter, this situation should be taken into account, leaving a margin to prevent excessive temperature rise and affect the service life of the motor.
When the inverter is running a long cable, measures should be taken to suppress the influence of long cable-to-ground coupling capacitance and prevent the inverter from outputting enough power. Therefore, the inverter should amplify one or two gears or install an output reactor at the output of the inverter.
For some special applications, such as high ambient temperature, high switching frequency, high altitude, etc., this will cause derating of the inverter, and the inverter needs to amplify one gear selection. When the inverter is used to control a high-speed motor, high-frequency harmonics are generated due to the small reactance of the high-speed motor. These higher harmonics increase the output current of the inverter. Therefore, when selecting the inverter for high-speed motor, it should be slightly larger than the inverter of the ordinary motor. When using a frequency converter to drive a geared motor, the range of use is limited by the lubrication of the rotating part of the gear. When lubrication oil is lubricated, there is no limit in the low speed range; in the high speed range above the rated speed, there is a risk that the lubricant will run out. Therefore, do not exceed the maximum speed tolerance.
Inverter drives wound rotor asynchronous motors, mostly using existing motors. Winding Motors Compared to ordinary squirrel cage motors, the winding resistance of the winding motor is small. Therefore, the overcurrent trip due to the ripple current is prone to occur. Therefore, a converter slightly larger than the normal capacity should be selected. The general winding motor is mostly used in the occasion where the flywheel moment GD2 is large, and more attention should be paid when setting the acceleration/deceleration time.
When the inverter drives the synchronous motor, the output capacity will be reduced by 10% to 20% compared with the commercial frequency power supply. The continuous output current of the inverter is greater than the product of the synchronous motor rated current and the synchronous pull-in current.
For compressors, vibration machines with large torque fluctuations, and hydraulic pumps with peak loads, if the inverter is selected according to the rated current or power value of the motor, the overcurrent protection operation may occur due to the peak current. . Therefore, it is necessary to understand the frequency operation and select the inverter with a rated output current greater than its maximum current. When selecting a frequency converter, it is important to note whether its degree of protection matches the situation at the site. Otherwise, the dust and moisture on the site will affect the long-term operation of the inverter. For more information on the use of frequency converters, please consult with the home of the OTC Transamerica inverter and participate in the learning and use of the inverter.
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