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Speed regulation method of three-phase motor
source：织梦技术论坛 time：2024-10-18 09:20nbsp; click：
According to the speed formula of three-phase asynchronous motor: n=60f/p(1-s), we can know from the formula that the purpose of changing the speed can be achieved by changing the power supply frequency f, the number of motor poles p and the slip rate s. From the essence of speed regulation, different speed regulation methods are nothing more than changing the synchronous speed of the AC motor.
In production machinery, the speed regulation methods that do not change the synchronous speed include rotor series resistance speed regulation, chopper speed regulation, cascade speed regulation, and the application of electromagnetic sliding clutch, hydraulic coupling, oil film clutch, etc. The synchronous speed can be changed by changing the number of stator poles of multi-speed motors, changing the stator voltage and frequency of variable frequency speed regulation, and speed regulation with or without commutation motors.
From the perspective of energy consumption during speed regulation, there are two types of high-efficiency speed regulation methods and low-efficiency speed regulation methods: high-efficiency speed regulation means that the slip rate is constant, so there is no slip loss, such as multi-speed motors, variable frequency speed regulation and speed regulation methods that can recover slip loss (such as cascade speed regulation, etc.). ). Speed regulation methods with slip loss are inefficient, such as the rotor series resistance speed regulation method, where energy is lost in the rotor circuit; in the electromagnetic clutch speed regulation method, energy is lost in the clutch coil; when the speed of the hydraulic coupling is adjusted, energy is lost in the oil of the hydraulic coupling. Generally speaking, slip loss increases with the expansion of the speed control range. If the speed control range is not large, the energy loss is small.
1. Variable pole pair speed regulation method
This speed regulation method is to change the number of poles of the cage motor stator by changing the red connection of the stator winding to achieve the purpose of speed regulation. Its characteristics are as follows:
It has hard mechanical characteristics and good stability;
No kilowatt loss, high efficiency;
Simple wiring, convenient control, low price;
There is step speed regulation, and the step difference is large, so smooth speed regulation cannot be obtained;
It can be used in conjunction with voltage regulation and electromagnetic slip clutch to obtain efficient and smooth speed regulation characteristics.
This speed regulation method is suitable for production machinery with stepless speed regulation, such as metal cutting machine tools, elevators, lifting equipment, fans, pumps, etc.
2. Frequency conversion speed regulation method
Frequency conversion speed regulation is a speed regulation method that changes the synchronous speed by changing the frequency of the motor stator power supply. The main equipment of the frequency conversion speed regulation system is the frequency converter that provides the frequency conversion power supply. Frequency converters can be divided into two categories: AC-DC-AC frequency converters and AC-AC frequency converters. At present, AC-DC-AC frequency converters are mostly used in China. Its characteristics:
High efficiency and no additional loss during speed regulation;
Wide application range, can be used for cage-type asynchronous motors;
Wide speed regulation range, hard characteristics, high precision;
Complex process, high cost, difficult maintenance.
This speed regulation method is suitable for occasions requiring high precision and good speed regulation performance.
3. Cascade speed regulation method
Cascade speed regulation refers to adding an adjustable additional potential to the rotor circuit of a wound-rotor motor to change the slip rate of the motor to achieve the purpose of speed regulation. Most of the slip power is absorbed by the series additional potential, and then an additional device is used to return the absorbed slip power to the grid or convert energy for use. According to the absorption and utilization method of slip power, cascade speed regulation can be divided into motor cascade speed regulation, mechanical cascade speed regulation and thyristor cascade speed regulation, and thyristor cascade speed regulation is mostly used. Its characteristics are as follows:
The slip loss during the speed regulation process can be fed back to the power grid or production machinery, which is more efficient;
The capacity of the device is proportional to the speed regulation range, saving investment, and is suitable for production machinery with a speed regulation range of 70%-90%
The rotor of the wound asynchronous motor is connected in series with an additional resistor, which increases the slip rate of the motor and makes the motor run at a low speed. The larger the series resistance, the lower the motor speed. This method is simple in equipment and easy to control, but the slip power is consumed in the form of heating on the resistor. It belongs to step speed regulation and has soft mechanical characteristics.
4. Speed regulation method of winding motor rotor series resistance
When the stator voltage of the motor changes, a set of different mechanical characteristic curves can be obtained, thereby obtaining different speeds. Since the torque of the motor is proportional to the square of the voltage, the maximum torque drops a lot, and its speed regulation range is small, it is difficult to apply general cage motors. In order to expand the speed regulation range, the voltage and speed regulation should use a cage motor with a larger rotor resistance value, such as a torque motor dedicated to voltage and speed regulation, or use a frequency sensitive resistor in series with a wound motor. In order to expand the stable operating range, when the speed is above 2: 1, feedback control should be used to achieve the purpose of automatic speed regulation.
The main device for voltage and speed regulation is a power supply that can provide voltage changes. At present, the commonly used voltage regulation methods include series saturated reactors, autotransformers and thyristor voltage regulation. Thyristor voltage regulation is the best. Voltage and speed regulation characteristics:
The voltage regulation circuit is simple and easy to realize automatic control;
During the voltage regulation process, the differential power is consumed in the form of heat on the rotor resistance, and the efficiency is low.
Voltage and speed regulation is generally suitable for production machinery below 100 kilowatts.
VI. Speed regulation method of electromagnetic speed regulation motor
The electromagnetic speed regulation motor consists of three parts: a cage motor, an electromagnetic slip clutch and a DC excitation power supply (controller). The power of the DC excitation power supply is relatively small, and it is usually composed of a single-phase half-wave or full-wave thyristor rectifier. By changing the conduction angle of the thyristor, the magnitude of the excitation current can be changed.
The electromagnetic slip clutch consists of three parts: the armature, the magnetic pole, and the excitation winding. The armature and the latter have no mechanical connection and can both rotate freely. The armature is coaxially connected to the motor rotor and is called the active part, which is driven by the motor; the magnetic pole is connected to the load shaft with a coupling and is called the driven part. When the armature and the magnetic pole are both stationary, if the excitation winding is passed with direct current, a number of pairs of magnetic poles with alternating N and S poles will be formed along the circumferential surface of the air gap, and their magnetic flux passes through the armature. When the armature rotates with the drag motor, the armature induces eddy currents due to the relative motion between the armature and the magnetic poles. The eddy currents interact with the magnetic flux to generate torque, driving the rotor with magnetic poles to rotate in the same direction, but its speed is always lower than the speed N1 of the armature. This is a slip speed regulation method. By changing the DC excitation current of the slip clutch, the output torque and speed of the clutch can be changed.
Speed regulation characteristics of electromagnetic speed regulation motor:
The device structure and control circuit are simple, the operation is reliable, and the maintenance is convenient;
Smooth speed regulation, stepless speed regulation;
No harmonic effect on the power grid;
Large speed loss and low efficiency.
This speed regulation method is suitable for medium and small power production machinery that requires smooth sliding and short-term low-speed operation.
VII. Hydraulic coupling speed regulation method
Hydraulic coupling is a hydraulic transmission device, generally composed of a pump wheel and a turbine, which are collectively called working wheels and placed in a sealed housing. A certain amount of working fluid is filled in the shell. When the pump wheel rotates under the drive of the prime mover, the fluid in it is driven by the blades to rotate. When it enters the turbine along the outer ring of the pump wheel under the action of centrifugal force, it gives thrust to the turbine blades in the same direction, so that it drives the production machinery to operate. The power transmission capacity of the hydraulic coupling is consistent with the relative amount of fluid in the shell. During the working process, changing the fluid filling rate can change the turbine speed of the coupling, and achieve stepless speed regulation. Its characteristics are:
The power adaptation range is large, which can meet the needs of different powers from tens of kilowatts to thousands of kilowatts;
Simple structure, reliable operation, easy to use and maintain, and low cost;
Small size, large capacity;
Convenient control and adjustment, easy to achieve automatic control.
This speed regulation method is suitable for the speed regulation of fans and water pumps.
Wolong Nanyang Explosion Protection, Flameproof three-phase asynchronous motor, high voltage motors
In production machinery, the speed regulation methods that do not change the synchronous speed include rotor series resistance speed regulation, chopper speed regulation, cascade speed regulation, and the application of electromagnetic sliding clutch, hydraulic coupling, oil film clutch, etc. The synchronous speed can be changed by changing the number of stator poles of multi-speed motors, changing the stator voltage and frequency of variable frequency speed regulation, and speed regulation with or without commutation motors.
1. Variable pole pair speed regulation method
This speed regulation method is to change the number of poles of the cage motor stator by changing the red connection of the stator winding to achieve the purpose of speed regulation. Its characteristics are as follows:
It has hard mechanical characteristics and good stability;
No kilowatt loss, high efficiency;
Simple wiring, convenient control, low price;
There is step speed regulation, and the step difference is large, so smooth speed regulation cannot be obtained;
It can be used in conjunction with voltage regulation and electromagnetic slip clutch to obtain efficient and smooth speed regulation characteristics.
This speed regulation method is suitable for production machinery with stepless speed regulation, such as metal cutting machine tools, elevators, lifting equipment, fans, pumps, etc.
2. Frequency conversion speed regulation method
Frequency conversion speed regulation is a speed regulation method that changes the synchronous speed by changing the frequency of the motor stator power supply. The main equipment of the frequency conversion speed regulation system is the frequency converter that provides the frequency conversion power supply. Frequency converters can be divided into two categories: AC-DC-AC frequency converters and AC-AC frequency converters. At present, AC-DC-AC frequency converters are mostly used in China. Its characteristics:
High efficiency and no additional loss during speed regulation;
Wide application range, can be used for cage-type asynchronous motors;
Wide speed regulation range, hard characteristics, high precision;
Complex process, high cost, difficult maintenance.
This speed regulation method is suitable for occasions requiring high precision and good speed regulation performance.
3. Cascade speed regulation method
Cascade speed regulation refers to adding an adjustable additional potential to the rotor circuit of a wound-rotor motor to change the slip rate of the motor to achieve the purpose of speed regulation. Most of the slip power is absorbed by the series additional potential, and then an additional device is used to return the absorbed slip power to the grid or convert energy for use. According to the absorption and utilization method of slip power, cascade speed regulation can be divided into motor cascade speed regulation, mechanical cascade speed regulation and thyristor cascade speed regulation, and thyristor cascade speed regulation is mostly used. Its characteristics are as follows:
The slip loss during the speed regulation process can be fed back to the power grid or production machinery, which is more efficient;
The capacity of the device is proportional to the speed regulation range, saving investment, and is suitable for production machinery with a speed regulation range of 70%-90%
The rotor of the wound asynchronous motor is connected in series with an additional resistor, which increases the slip rate of the motor and makes the motor run at a low speed. The larger the series resistance, the lower the motor speed. This method is simple in equipment and easy to control, but the slip power is consumed in the form of heating on the resistor. It belongs to step speed regulation and has soft mechanical characteristics.
4. Speed regulation method of winding motor rotor series resistance
When the stator voltage of the motor changes, a set of different mechanical characteristic curves can be obtained, thereby obtaining different speeds. Since the torque of the motor is proportional to the square of the voltage, the maximum torque drops a lot, and its speed regulation range is small, it is difficult to apply general cage motors. In order to expand the speed regulation range, the voltage and speed regulation should use a cage motor with a larger rotor resistance value, such as a torque motor dedicated to voltage and speed regulation, or use a frequency sensitive resistor in series with a wound motor. In order to expand the stable operating range, when the speed is above 2: 1, feedback control should be used to achieve the purpose of automatic speed regulation.
The main device for voltage and speed regulation is a power supply that can provide voltage changes. At present, the commonly used voltage regulation methods include series saturated reactors, autotransformers and thyristor voltage regulation. Thyristor voltage regulation is the best. Voltage and speed regulation characteristics:
The voltage regulation circuit is simple and easy to realize automatic control;
During the voltage regulation process, the differential power is consumed in the form of heat on the rotor resistance, and the efficiency is low.
Voltage and speed regulation is generally suitable for production machinery below 100 kilowatts.
VI. Speed regulation method of electromagnetic speed regulation motor
The electromagnetic speed regulation motor consists of three parts: a cage motor, an electromagnetic slip clutch and a DC excitation power supply (controller). The power of the DC excitation power supply is relatively small, and it is usually composed of a single-phase half-wave or full-wave thyristor rectifier. By changing the conduction angle of the thyristor, the magnitude of the excitation current can be changed.
The electromagnetic slip clutch consists of three parts: the armature, the magnetic pole, and the excitation winding. The armature and the latter have no mechanical connection and can both rotate freely. The armature is coaxially connected to the motor rotor and is called the active part, which is driven by the motor; the magnetic pole is connected to the load shaft with a coupling and is called the driven part. When the armature and the magnetic pole are both stationary, if the excitation winding is passed with direct current, a number of pairs of magnetic poles with alternating N and S poles will be formed along the circumferential surface of the air gap, and their magnetic flux passes through the armature. When the armature rotates with the drag motor, the armature induces eddy currents due to the relative motion between the armature and the magnetic poles. The eddy currents interact with the magnetic flux to generate torque, driving the rotor with magnetic poles to rotate in the same direction, but its speed is always lower than the speed N1 of the armature. This is a slip speed regulation method. By changing the DC excitation current of the slip clutch, the output torque and speed of the clutch can be changed.
Speed regulation characteristics of electromagnetic speed regulation motor:
The device structure and control circuit are simple, the operation is reliable, and the maintenance is convenient;
Smooth speed regulation, stepless speed regulation;
No harmonic effect on the power grid;
Large speed loss and low efficiency.
This speed regulation method is suitable for medium and small power production machinery that requires smooth sliding and short-term low-speed operation.
VII. Hydraulic coupling speed regulation method
Hydraulic coupling is a hydraulic transmission device, generally composed of a pump wheel and a turbine, which are collectively called working wheels and placed in a sealed housing. A certain amount of working fluid is filled in the shell. When the pump wheel rotates under the drive of the prime mover, the fluid in it is driven by the blades to rotate. When it enters the turbine along the outer ring of the pump wheel under the action of centrifugal force, it gives thrust to the turbine blades in the same direction, so that it drives the production machinery to operate. The power transmission capacity of the hydraulic coupling is consistent with the relative amount of fluid in the shell. During the working process, changing the fluid filling rate can change the turbine speed of the coupling, and achieve stepless speed regulation. Its characteristics are:
The power adaptation range is large, which can meet the needs of different powers from tens of kilowatts to thousands of kilowatts;
Simple structure, reliable operation, easy to use and maintain, and low cost;
Small size, large capacity;
Convenient control and adjustment, easy to achieve automatic control.
This speed regulation method is suitable for the speed regulation of fans and water pumps.
Wolong Nanyang Explosion Protection, Flameproof three-phase asynchronous motor, high voltage motors
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