Comparison of speed control mode of three-phase asynchronous motor
From the viewpoint of energy consumption adjustment in the point of view, there are efficient and inefficient governing speed regulation method of two methods: highspeed refers to slip the same, so no slip loss, speed control methods such as multispeed motor, variable frequency speed regulation and energy will slip loss recovery(such as cascade speed etc.). A slip speed control method for loss belongs toinefficient control, such as rotor series resistance speed method, energy loss in the rotor circuit; speed control method of the electromagnetic clutch, the energy loss inthe clutch coil; hydraulic coupling, energy loss in the hydraulic coupling in oil. In general the slip loss with speed range to expand, if the speed range is not big, the energy loss is very small.
A, cascade control method
Cascade speed control refers to the additional potential wound into the adjustablestring line type motor rotor circuit to change the motor slip, achieve the purpose of speed. Additional potential absorbed most of the slip power are in series, then use to generate additional devices, absorb the slip power back into the grid or conversion of energy use. According to the slip power absorption use, cascade speed regulationcan be divided into motor cascade speed control, mechanical cascade speed controland thyristor cascade speed form, uses the thyristor cascade speed regulation, its characteristic is:
It can be speed in the process of slip loss feedback to the grid or productionmachinery, high efficiency;
Device capacity and speed range is proportional to, investment, suitable for speed regulating range of production machinery in the rated speed 70%90%;
Speed regulating device fault could be switched to run at full speed, to avoidproduction;
Thyristor cascade speed low power factor, harmonic influence great.
This method is suitable for the fan, water pump and rolling machine, mine hoist, the use of extrusion machine.
Two, a winding type motor rotor series resistance speed control method
Asynchronous motor rotor string into the additional resistance, so that the motor slip is increased, the motor operates in the low speed. On resistance is more big, the speed of the motor is low. This method has the advantages of simple equipment, convenient control, but the slip power to the heating in the form of consumption in the resistor.The genus level speed, the mechanical characteristics of soft.
Three, variable frequency speed regulation method
Frequency conversion speed regulation is to change the motor stator powerfrequency speed control method, so as to change the synchronous speed. The mainequipment of frequency conversion system is frequency inverter power supply,inverter can be divided into AC - DC - AC frequency converter and AC - AC frequency converter in two categories, the current domestic mostly use AC-DC-AC frequency converter. Its characteristics:
High efficiency, no additional loss of speed regulation process;
A wide range of applications, can be used for cage asynchronous motor;
Wide speed range, the properties of hard, high precision;
The technology is complex, high cost, difficult maintenance and inspection.
This method is suitable for the requirement of high precision, good speed regulation performance occasions.
Four, hydraulic coupler method
The hydraulic coupler is a kind of hydraulic transmission device, generally by thepump wheel and turbine wheel, they are referred to as job, put in the sealed shell.The working liquid filled in a certain amount of shells, when the pump wheel in the prime mover rotates under the drive, in which liquid is promoted by the blade and the rotation, under the action of centrifugal force along the impeller outer ring into theturbine, in the same turn to turbine blade to thrust, driving the production machineryoperation. The power of hydraulic coupler shell transfer ability and the relative size of filling liquid quantity is the same. In the work process, changing the rotational speed of the turbine liquid filling rate can change the coupler, achieve stepless speed regulation, its characteristic is:
Power adaptation range, can meet the needs from tens of kilowatts to thousands ofkilowatts of different power;
Has the advantages of simple structure, reliable work, convenient use and repair, and low cost;
Small in size, can accommodate large;
Easy to control, easy to realize automatic control.
This method is suitable for variable speed fan, water pump.
Five, the log speed control method of pole changing
The speed control method is to use the ground red way change the stator winding to change the cage type motor stator pole pairs to reach the purpose of regulating speed, features are as follows:
Mechanical properties of hard, good stability;
No slip loss, high efficiency;
Simple wiring, convenient control, low price;
A stepless speed regulation, large span, can obtain smooth speed regulation;
Can the electromagnetic slip clutch matched with the pressure regulating speed,smooth speed control characteristics, to obtain higher efficiency.
The method is suitable for the production of machinery does not require the stepless speed regulation, such as metal cutting machine tools, elevators, lifting equipment, air blower, water pump etc..
This method is suitable for medium and small power, the requirements of productionmachinery flat sliding, short time low speed running.
Six, stator variable voltage speed regulation method
When the stator voltage to change the motor, can get a different set of mechanical characteristic curve, so as to obtain the different rotating speed. Because the torque of the motor voltage is proportional to the square of the maximum torque, so down a lot, the regulating range is smaller, the squirrel cage motor is difficult to apply general.In order to enlarge the speed range, the pressure regulating speed should be adopted in the rotor resistance value heavy cage type motor, such as torque motorfor pressure regulating and speed control with frequency sensitive resistor in series,or winding type motor. In order to extend the stable operation range, when the speedabove 2:1 occasions should be used to achieve automatic adjustment of the speedfeedback control objective.
The main device of the pressure regulating speed is a can provide the voltage change of power, the common voltage regulation mode with series reactor, self coupling transformer and thyristor voltage regulating several. Voltage for thyristor.The characteristics of the pressure regulating speed:
The pressure regulating speed circuit is simple, easy to realize automatic control;
Pressure regulating process and transfer the power of difference in heating mode is consumed in the rotor resistance, low efficiency.
The production of mechanical pressure regulating speed generally applies to thefollowing 100KW.
Seven, electromagnetic adjustable speed motor speed regulating method
By the cage type motor, electromagnetic speed regulating motor slip clutch and DCexcitation source (controller) is composed of three parts. DC excitation power is small,usually composed of single-phase half wave and full wave thyristor rectifier, changing the thyristor conduction angle, can change the size of the excitation current.
Electromagnetic slip clutch is composed of an armature and pole and the excitationwindings of the three. There is no mechanical contact armature and the latter canrotate freely. The armature and the motor rotor coaxial connection known as activepart, driven by the motor; magnetic pole for coupling and load shaft butt said driven part. When the armature and pole pieces are static, such as the excitation winding inDC, along a circle of air gap surface will form N, S alternating polarity magnetic polesof the magnetic flux through the armature number. When the armature rotates with thedrive motor, due to the relative motion between the armature and pole pieces, thusmake the armature induces vortex, the eddy current and magnetic flux interactiontorque is generated to drive the rotor magnetic poles are rotating in the samedirection, but the speed constant below the armature speed N1, this is a slip speed control mode, the DC excitation the current change slip clutch, clutch can change theoutput torque and rotational speed. Speed control characteristics of electromagnetic adjustable speed motor:
The structure of the device and its control circuit is simple, reliable operation,convenient maintenance;
Speed smooth, stepless speed regulation;
No impact on the power grid harmonic;
Speed loss and low efficiency.
