How does the inverter change the rotation speed of the motor? First of all, you have to understand the principle of motor speed regulation. There are many methods for motor speed regulation, such as adjusting voltage, changing frequency, changing poles, and electromagnetic speed regulation. The inverter changing the rotation speed of the motor is only one of them, and the inverter realizes speed regulation by changing the frequency of the power supply. The inverter can change the synchronous speed by changing the frequency of the power supply in the stator coil of the three-phase asynchronous induction motor (the single-phase inverter can also drive the motor started by the single-phase capacitor).
We know that the usual power supply is AC with a frequency of 50Hz, but the frequency cannot be directly converted, it must go through the process of AC→DC→AC. First, the three-phase 50Hz power supply is converted into a DC power supply through a rectifier, and then an inverter is used to convert the DC voltage into an AC power supply (the frequency is changed according to the need). This is the principle of frequency conversion by the inverter.
As for the principle of inverter frequency control, it is generally realized by the traditional V/F method. According to the formula n=60*F/p, the speed can be realized by changing the power frequency of the input motor. However, when the frequency converter changes the power supply frequency, the voltage also needs to be changed, that is to say, the power supply voltage V and the frequency F are in a proportional relationship to keep the magnetic flux constant, which is also the principle of the V/F control method.
This starts with the motor speed calculation formula.
The formula for calculating the speed of a three-phase motor is expressed as: n=60f/p
Among them, n represents the speed of the motor (r/min); 60 represents per minute (seconds); f represents the power frequency (Hz); p represents the number of pole pairs of the motor’s magnetic field. The country stipulates that the standard power frequency is 50Hz. According to the fixed frequency, if it is substituted into the calculation formula, the number of pole pairs of the motor is inversely proportional to the speed, that is, the more the number of pole pairs, the lower the speed of the motor.
When the number of pole pairs p=1, the synchronous speed of the rotating magnetic field of the motor is n=3000; when p=2, the synchronous speed of the rotating magnetic field is n=1500; p=3, n=1000; p=4, n= 750;p=5,n=600;
It needs to be known here that since the electromagnetic induction of the rotor of the three-phase asynchronous AC motor is induced by the synchronous rotational speed of the stator, it has a slip, so the rotational speed of the motor rotor is always lower than the rotational magnetic field rotational speed of the stator coil winding, which is why The reason why it is called a three-phase asynchronous induction motor.
With the continuous improvement of electronic technology, electronic engineers have designed and produced frequency converters with the help of the above speed calculation formula. Inverters are classified according to the modulation technology VWF, which can be divided into PMA and PWM. PAM is completed by separating VW and VF, which is commonly called “pulse amplitude modulation mode”, or PAM mode for short. The PWM is completed by concentrating VW and VF on the inverter, commonly known as “pulse width modulation method”, or PWM method for short. Most of the inverters currently used are AC → DC → AC.
The characteristics of this frequency converter:
1. High efficiency, no additional loss during speed regulation;
2. It has a wide range of applications and can be adapted to squirrel-cage induction motors;
3. Wide range of speed regulation, good mechanical characteristics and high control precision.
The disadvantage is that the technology is complex, the cost of electronic components is high, the technical requirements for maintenance personnel are high, and the maintenance price is high.
How does the inverter change the rotation speed of the motor? First of all, you have to understand the principle of motor speed regulation. There are many methods for motor speed regulation, such as adjusting voltage, changing frequency, changing poles, and electromagnetic speed regulation. The inverter changing the rotation speed of the motor is only one of them, and the inverter realizes speed regulation by changing the frequency of the power supply. The inverter can change the synchronous speed by changing the frequency of the power supply in the stator coil of the three-phase asynchronous induction motor (the single-phase inverter can also drive the motor started by the single-phase capacitor).
We know that the usual power supply is AC with a frequency of 50Hz, but the frequency cannot be directly converted, it must go through the process of AC→DC→AC. First, the three-phase 50Hz power supply is converted into a DC power supply through a rectifier, and then an inverter is used to convert the DC voltage into an AC power supply (the frequency is changed according to the need). This is the principle of frequency conversion by the inverter.
As for the principle of inverter frequency control, it is generally realized by the traditional V/F method. According to the formula n=60*F/p, the speed can be realized by changing the power frequency of the input motor. However, when the frequency converter changes the power supply frequency, the voltage also needs to be changed, that is to say, the power supply voltage V and the frequency F are in a proportional relationship to keep the magnetic flux constant, which is also the principle of the V/F control method.
This starts with the motor speed calculation formula.
The formula for calculating the speed of a three-phase motor is expressed as: n=60f/p
Among them, n represents the speed of the motor (r/min); 60 represents per minute (seconds); f represents the power frequency (Hz); p represents the number of pole pairs of the motor’s magnetic field. The country stipulates that the standard power frequency is 50Hz. According to the fixed frequency, if it is substituted into the calculation formula, the number of pole pairs of the motor is inversely proportional to the speed, that is, the more the number of pole pairs, the lower the speed of the motor.
When the number of pole pairs p=1, the synchronous speed of the rotating magnetic field of the motor is n=3000; when p=2, the synchronous speed of the rotating magnetic field is n=1500; p=3, n=1000; p=4, n= 750;p=5,n=600;
It needs to be known here that since the electromagnetic induction of the rotor of the three-phase asynchronous AC motor is induced by the synchronous rotational speed of the stator, it has a slip, so the rotational speed of the motor rotor is always lower than the rotational magnetic field rotational speed of the stator coil winding, which is why The reason why it is called a three-phase asynchronous induction motor.
With the continuous improvement of electronic technology, electronic engineers have designed and produced frequency converters with the help of the above speed calculation formula. Inverters are classified according to the modulation technology VWF, which can be divided into PMA and PWM. PAM is completed by separating VW and VF, which is commonly called “pulse amplitude modulation mode”, or PAM mode for short. The PWM is completed by concentrating VW and VF on the inverter, commonly known as “pulse width modulation method”, or PWM method for short. Most of the inverters currently used are AC → DC → AC.
The characteristics of this frequency converter:
1. High efficiency, no additional loss during speed regulation;
2. It has a wide range of applications and can be adapted to squirrel-cage induction motors;
3. Wide range of speed regulation, good mechanical characteristics and high control precision.
The disadvantage is that the technology is complex, the cost of electronic components is high, the technical requirements for maintenance personnel are high, and the maintenance price is high.
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