Seven methods for three-phase asynchronous motor drive

The seven kinds of three-phase asynchronous motor control method and characteristics:Introduces seven kinds of three-phase asynchronous motor speed control mode and its characteristic, pointed out its

applicable occasions and situations. For three-phase asynchronous motor speed formula: n = 60 f/p (1

- s) from the type, change the power supply frequency f, slip ratio of the motor very logarithmic p

and s can be too much to change speed.A,classification:1,from the www.facebook.com/dongfeng.motor perspective of the nature of speed regulation,different way of speed adjustment is nothing but change synchronous ac motor synchronous speed or not turn two. Don't change the synchronous speed control methods are: 1) the wound rotor motor rotor series resistance speed dc chopper, 2), 3) cascade speed regulation and application of the electromagnetic slip clutch, 4) hydraulic coupling, such as 5) oil-film clutch speed regulation. Don't change the synchronous speed of speed regulation method is widely used in the production of machinery.2, the change of the synchronous speed logarithmic multi- speed motor, stator can change of the stator voltage, frequency, frequency control of motor speed has no commutator motor speed regulation and so on.

3, from the energy point of view, when there are 1) high speed control method and (2) low speed regulation method two: an induction refers to the effective speed control is constant, so there is no slip loss, such as multi-speed motor, frequency control of motor speed and slip loss can be recovered speed control methods (such as cascade speed regulation, etc.). Have slip loss speed regulation method belongs to the low speed, such as rotor series resistance speed control method, the energy loss in the rotor circuit; Electromagnetic clutch speed regulation method of energy loss in the clutch coil; Hydraulic coupler speed regulation and energy loss in the oil of hydraulic coupling. In general slip loss increases with expanding range of speed regulation, if the speed range is not big, energy loss is small.A, logarithmic pole change speed regulation method: this method of speed control is in change of the stator winding red way to change the speed cage motor stator polar logarithmic to achieve. This method is suitable for don't

need a stepless speed regulation of production machinery, such as metal cutting machine tools,

elevators, lifting equipment, fan, water pump, etc.Characteristics are as follows: 1, with a hard

mechanical properties, good stability; 2, no rotor cutting machine slip loss, high efficiency; 3, simple

wiring and convenient control, low price; 4, have used differential is bigger, cannot obtain smooth

speed regulation; 5, can be used with regulating speed control, electromagnetic slip clutch, smooth

speed characteristics of high efficiency. Second, the method of frequency control of motor speed:

frequency control of motor speed is to change the frequency of the motor stator power, to change its

synchronous speed control method. 

Variable frequency speed regulation system is the main equipment to provide frequency conversion power of inverter, the inverter can be divided into ac - dc - ac frequency converter and ac - ac frequency converter two kinds big, cross - straight - to pay inverter are mostly used in China at present. This method is suitable for the requirement of high precision, better speed control performance. Its features: 1, high efficiency, speed the process of no additional loss; 2, wide application range, can be used in the cage type asynchronous motor; 3, large range of speed regulation, and the characteristics of hard, high precision; 4, complex technology, high cost, maintenance difficulties. Three, cascade speed regulation method: cascade speed regulation refers to the wound rotor motor rotor loop series adjustable the additional

potential to change the slip of the motor, to achieve the purpose of speed control. Most of the slip

power is absorbed by series of additional potential to recycle produce additional device, the

absorption of returning the slip power grid or conversion of energy use. According to the slip power

utilization way, cascade speed regulation can be divided into motor cascade speed regulation,

mechanical cascade speed regulation and thyristor cascade speed regulation form, adopts thyristor

cascade speed regulation. This method is suitable for the ac synchronous motor fan, water pump and the rolling mill, mine hoist, the extrusion machine use. 

Its characteristic is: 1, but will slip loss in the process of speed feedback to the grid or production machinery, high efficiency; 2, unit capacity is proportional to the speed range, saving investment, apply to speed range in production machinery from 70% to 90% of the rated speed; 3, speed regulating device failure can switch to run at full speed, avoid production; 4, thyristor cascade speed regulation low power factor, harmonic impact is bigger. Four, wound rotor motor rotor series resistance speed control methods: wound rotor asynchronous motor rotor string into the additional resistance, make the slip of the motor, motor under low speed running. The series resistance, the greater the lower the speed of the motor. This method is simple, easy to control, but the slip power consumption in the form of heat on the

resistance. Step speed, mechanical properties of soft. Five, the stator voltage regulating speed

control methods: changes of motor stator voltage, be able to get a different set of mechanical

characteristic curve, in order to gain different speed. Due to the torque of the motor and the

voltage is proportional to square, thus maximum torque decreased a lot, the smaller range of speed

regulation, and makes difficult to apply general squirrel-cage motor. In order to enlarge the speed

range, regulating speed rotor resistance value should be adopted for the big cage motor, such as

torque motor, USES for regulating speed or frequency on the wound rotor motor series resistor. 

In order to expand the stable operation range, speed above 2:1 Settings when feedback control should be

adopted to achieve automatic adjustment speed. Regulating speed control is a main device can provide

voltage change of power supply, the current commonly used ways with saturable reactor in series

voltage regulator, autotransformer and thyristor voltage regulation. Thyristor voltage regulation

mode is the best. Regulating speed generally applicable to the production machinery under 100 kw.

The characteristics of the pressure regulating speed: 1, the pressure regulating speed control

circuit is simple, easy to realize automatic control; 2, in the form of heat transfer differential

pressure regulating process power consumption in the rotor resistance and low efficiency. Six,

electromagnetic speed regulating motor speed adjustment method: by cage motor electromagnetic speed

control motor, electromagnetic slip clutch and dc excitation source (controller) of three parts. Dc

excitation power is small, usually by a single-phase half-wave or full wave thyristor rectifier,

change the thyristor conduction Angle, can change the size of the field current. Electromagnetic slip

clutch armature, poles and excitation windings of three parts. The armature and the latter is no

mechanical contact, can free rotation. Armature and motor rotor coaxial connecting said active part,

by the motor drive; Pole docking with the shaft coupling and load according to secondary part. When

the armature and pole are static, such as passing a dc excitation winding, the surface will form

several along the air gap circle on N, S alternating polarity magnetic pole, the magnetic flux

through the armature. 

When the armature motor rotates with drag, because of the relative movement between the armature and pole, thus make the armature induced eddy current, the eddy current and magnetic flux interact to produce torque, driving a pole rotor according to the same direction, but its speed constant is lower than the speed of the armature N1, this is a way of slip speed, change of slip clutch dc excitation current, you can change the clutch output torque and rotational speed. This method is suitable for medium and small power, the requirement is smooth, short-time running at low speed production machinery. Electromagnetic speed regulating motor speed control features: 1, device structure and the control circuit is simple, reliable operation and convenient maintenance; 2, speed smooth, stepless speed regulation; 3, no harmonic of power grids affected; 4, the speed loss and low efficiency. Seven, and hydraulic coupler speed regulation method: hydraulic coupler is a kind of hydraulic transmission device, generally consists of pump wheel and turbine, working, they referred in the seal housing. Into a certain amount of working fluid in the shell, when the impeller rotates, under the prime in the liquid by the rotating blades to promote, in under the action of centrifugal force along the outer ring into the turbine and pump wheel is on the same shift to the turbine blades to thrust, the mechanical operation of the production. Hydraulic coupler shell power transfer capacity and the relative to the size of the amount of liquid is the same. In the process of work, the change rate of liquid can change coupler turbine speed, achieve stepless speed regulation. This method is suitable for the fan and water pump speed. Its characteristic is: 1, the power to adapt to the scope is big, can meet different power from tens of kilowatts to thousands of kilowatts of needs; 2, simple structure, reliable operation, convenient use and maintenance, and low cost. 3, small size, can let big; 4, convenient control, easy to realize automatic control.