1. Pole change logarithmic speed regulation method
This speed regulation method is to change the number of stator poles of the cage motor by changing the connection method of the stator winding, so as to reach the intention of speed regulation; The wiring is simple, the control is convenient, and the price is low; It can be used in conjunction with pressure and speed regulation and electromagnetic slip clutch to obtain efficient and stable speed regulation characteristics. The method is applicable to metal cutting machine tools, lifting equipment, fans, water pumps, etc.
The primary equipment of the frequency conversion speed regulation system is the frequency converter that supplies the frequency conversion power supply, and the frequency converter can be divided into two categories: communication-DC-communication frequency converter and communication-communication frequency converter. Its characteristics: high power, no additional loss in the process of speed regulation; Suitable for cage asynchronous motor; The speed scale is wide, the characteristics are hard, and the precision is high; The process is complex, the cost is high, and the protection is difficult. This method is suitable for occasions with high precision and good speed regulation performance. Frequency conversion speed regulation is divided into speed regulation below the fundamental frequency and speed regulation above the fundamental frequency, the speed regulation below the fundamental frequency belongs to the constant torque speed regulation method, and the speed regulation above the fundamental frequency belongs to the constant power speed regulation method.
2. Stator pressure and speed regulation method
When the stator voltage of the motor is changed, a set of different mechanical characteristic curves can be obtained, and thus different speeds can be obtained. Because the torque of the motor is proportional to the square of the voltage, the maximum torque drops greatly, and the speed regulation scale is small, so it is difficult to apply it to general cage motors. In order to expand the scale of speed regulation, it is advisable to choose a cage motor with large rotor resistance for voltage and speed regulation, such as using a torque motor for voltage and speed regulation, or connecting a frequency resistor in series on the wound motor.
The primary equipment for voltage and speed regulation is a power supply that can supply voltage change, and the commonly used voltage conditioning methods include series full reactors, autotransformers and thyristors. Characteristics of voltage and speed regulation: the circuit of voltage and speed regulation is simple, and it is easy to complete automatic control; In the process of voltage conditioning, the differential power in the rotor resistor is dissipated by heating, and the power is low. Voltage speed regulation is generally applicable to production machinery below 100kW.
3. Cascade speed regulation method
Cascade speed regulation is to increase the adjustable additional electric potential in series in the rotor circuit of the wound motor to change the slip rate of the motor and achieve the intention of speed regulation. Most of the slip power is absorbed by the additional potential in series, which is then converted back to the grid or by the device where the additional potential is generated. According to the absorption and utilization 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 the primary choice. Its characteristics are: the slip loss in the process of speed regulation can be efficiently fed back to the power grid or production machinery; When the speed regulating equipment fails, it can be switched to full speed operation to avoid shutdown; The power factor of thyristor cascade speed regulation is low, and the harmonic influence is large. This method is applicable to fans, pumps, rolling mills, mine hoists, etc.
4. Hydraulic coupling speed regulation method
A fluid coupling is a hydraulic transmission equipment, which is generally composed of a pump wheel and a water turbine. They are collectively referred to as work wheels and are placed in a sealed housing. When the pump wheel is driven to rotate by the prime mover, the liquid inside the pump wheel is driven by the vanes to rotate. When centrifugal force enters the steam turbine along the outer ring of the pump wheel, the turbine blades are pushed in the same direction to drive the production machinery. The power transfer ability of the fluid coupling is common to the relative amount of liquid in the shell. In the process of operation, changing the filling rate can change the turbine speed of the coupling to complete the stepless speed regulation. Its characteristics are: the power habit is wide in scale, which can meet the needs of different power from tens of thousands of kilowatts to thousands of kilowatts; The utility model discloses a simple structure, reliable operation, convenient use protection, and low cost; Small size, large capacity; Easy to control and adjust, easy to complete automatic control. This method is applicable to the speed regulation of fans and pumps.
5. Winding motor rotor string resistance speed regulation method
The rotor of the wound rotor asynchronous motor is connected with additional resistance in series to improve the slip rate of the motor and make the motor run at low speed. The greater the series resistance, the lower the motor speed. This method is simple and easy, but the slip power is dissipated on the resistor by generating heat. It is a step-by-step speed regulation, and the mechanical characteristics are soft.
6. Electromagnetic speed regulation motor speed regulation method
The electromagnetic speed control motor is composed of three parts: cage motor, electromagnetic slip clutch and DC excitation power supply. The DC excitation power supply is small, and it is generally composed of a single-phase half-wave or full-wave thyristor rectifier, and the conduction angle of the thyristor can be changed to change the size of the excitation current. The electromagnetic slip clutch is composed of three parts: the magnetic pole, the armature and the excitation winding. When the armature and poles are stopped, if the excitation windings pass through direct current, several pairs of poles alternating between N and S polarities will be formed along the circumferential surface of the air gap, and the magnetic flux will pass through the armature.
When the armature rotates with the driving motor, because of the relative motion between the armature and the magnetic pole, the armature current occurs, and the eddy current interacts with the magnetic flux to produce torque, driving the rotor with the magnetic pole to rotate in the same direction, but its speed is lower than the armature speed N1, when the DC excitation current of the differential clutch is changed, the clutch output torque and speed can be changed. The speed regulation characteristics of electromagnetic speed regulating motor are: simple equipment structure and control circuit, reliable operation and convenient protection; Stable and stepless speed regulation; The speed loss is large and the power is low. This method is suitable for small and medium-power production machinery that requires smooth sliding and short low-speed operation time.
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