The three-phase induction motor speed control method
Three-phase asynchronous motor speed formula: N = 60f / p (1-s) Can be seen from the above formula, change the power supply frequency f, motor pole number p and the slip s may be too much to change the speed of purpose. From the speed of the essence of view, is simply a different way to change speed synchronous AC motor does not change the sync transfer speed or two.
Widespread use in production machines without changing the synchronous speed of motor speed control method Wound Rotor Series Resistance Speed, chopper speed control, cascade control, and application of electromagnetic slip clutch, fluid couplings, clutches and other film speed. Change the synchronous speed of change on the number of stator pole multi-speed motor to change the stator voltage and frequency to frequency conversion with no change to the motor speed and so on.
Energy from the speed point of view when, with high speed method and inefficient methods of two kinds of speed: high speed when the slip refers to the same, so no slip losses, such as multi-speed motors, Slip frequency control and loss can speed recovery methods (such as cascade control, etc.). A deteriorating loss of speed control methods are inefficient speed, such as series resistance of the rotor speed method, the energy loss in the rotor circuit on; Electromagnetic Clutch The speed method, the energy loss in the clutch coils; fluid coupling speed, energy loss in the fluid coupling of the oil. General deterioration in loss increased with the expansion speed range, if not speed range, the energy loss is minimal.
1, variable speed control method of pole pairs
This speed is then used to change the stator winding way to change the red cage motor stator pole pairs to achieve speed control purposes, the following featuresWith hard mechanical properties, good stability;
No slip loss, high efficiency; Wiring simple, easy to control, low price; A level speed, differential large, can not get smooth speed control;
With pressure and speed adjustment, with the use of electromagnetic slip clutch, smooth and efficient access to high speed characteristics.
This method is suitable for the production does not require variable speed
machinery, such as metal cutting machine Bed , Lift , Lifting equipment, Fans Water Pump And so on. 2,
Frequency Control Method Frequency control is to change the motor stator Power
supply Frequency, thus changing the speed of its synchronous speed method. Frequency control system main equipment is to provide variable frequency power supply Inverter , Inverter can be divided into AC - DC - AC inverter and AC - AC converter two categories, most of the current domestic use of AC - DC - AC inverter. Its characteristicsHigh
efficiency, speed the process without additional loss;
Wide range of applications, can be used for cage induction motor;
Speed range, features a hard, high accuracy;
Technical complexity, high cost, difficult maintenance and overhaul.
This method is suitable for the high accuracy, good speed performance occasions. 3,
cascade control method Cascade control is wound into the rotor circuit in the series
of additional potential can be adjusted to change the motor's slip, to achieve speed control purposes. Most of the deterioration in power to be in series with the added potential absorbed, re-use generate additional devices to absorb the deterioration in power to return power to use or conversion of energy. Slip-power absorption under way, cascade control can be divided into Motor Cascade control, mechanical and thyristor cascade control cascade control, and multi-use cascade control thyristor, characterized byCan speed the process of deterioration in loss of feedback to the network or production
machinery, more efficient;
Installed capacity and speed range in direct proportion to investment, applicable
speed range 70% -90% rated speed of production machinery;
peed device failure can switch to full speed, to avoid the cut-off; Thyristor cascade speed low power factor, harmonics greater impact.
This method is suitable for fans, pumps and rolling mills, mine hoist, extrusion machines. 4,
wound rotor motor speed control method of Series Resistance
Wound Rotor Motor additional resistance in series, so that the motor slip up, motor running at low speed. The greater the resistance in series, the motor speed is lower. This method is simple, easy to control, but deteriorate the power consumption in the form of heat in the resistor. Is a class speed, soft mechanical properties. 5,
the stator pressure and speed adjustment method
Stator voltage when changing the motor, you can get a different set of mechanical properties of curves, which were different speeds. Since the motor torque and voltage proportional to the square, the largest decline in a lot of torque, speed range of its small cage motors in general and difficult to apply. In order to expand the speed range, pressure and speed adjustment should be larger rotor resistance value cage motors, such as dedicated voltage regulator with speed torque motor, or series wound motor frequency sensitive resistors. In order to expand the range of stable operation, when the speed of 2:1 or more occasions in the feedback control should be adopted to achieve the purpose of automatic adjustment of speed.
Pressure and speed adjustment is a key device to provide power supply voltage,
the current way of a tandem common saturation voltage regulator Reactor , Auto
Transformer And several other Thyristor Surge. Thyristor Surge is the best way. Adjusting Speed featuresPressure and speed adjustment circuit is simple, easy to realize automatic control;
Poor power surge process to heat transfer in the rotor resistance in the form of
consumption, low efficiency.
Pressure and speed adjustment generally applies to 100KW below production
machinery. 6.
electromagnetic speed regulating motor speed control method of electromagnetic speed regulating electric motor squirrel cage motor, electric slip clutch and DC
excitation power supply (Controller) consists of three parts. DC excitation power small, usually consisting of single phase half-wave or full wave rectifiers thyristors composition, change thyristor conduction angle, you can change the magnetizing current size.
Electromagnetic slip clutch armature, poles and excitation windings composed of
three parts. Armature and the latter has no mechanical contact, are free to rotate. Armature motor coaxial connection active part, driven by motors; docking with the load axis magnetic pole coupling from the moving parts. When the armature poles are at rest, such as excitation windings for DC, along the circumferential surface will form a number of air gap on the n, s, of alternating polarity poles, the magnetic flux through the armature. Dang electric armature with drag motor rotating Shi, due to electric armature and pole between relative movement, and makes electric armature induction produced Eddy, this Eddy and magnetic pass mutual role produced go moments, led has pole of rotor by same direction rotating, but its speed constant below electric armature of speed N1, this is a go difference adjustable speed way, changes go difference clutch device of DC Lai magnetic current, will can change clutch device of output go moments and speed. Characteristics of electromagnetic speed regulating motor speed:
appliances, structure and control circuit is simple, reliable operation, easy maintenance;
speed and smooth, stepless speed regulation
the power network harmonic effects; lost speed, low efficiency.
This method applies to medium and small power, requires low speed when the smooth, short run production machinery. 7.
the hydraulic coupler speed regulating hydraulic Coupler is a device for hydraulic
drive, is made up of the pump and turbine, they collectively work wheels, placed in a sealed case. Shell filled with a certain amount of working fluid, when pump is impulse driven by rotation, in which liquid propelled by blades which rotate, and under the action of centrifugal force along the outer wheels when entering the turbine pump, to thrust to the
turbine blades on the same turn, make it drive production machinery running. Power transfer capacity of the hydraulic coupler and shell filled with fluid volume sizes are consistent. In the course of work, changing the filling rate can change the coupler of turbine speed, stepless speed regulation, characterized by:
power scope, can meet the needs of from a couple of different power 10-kilowatt to shuqianqian;
simple structure, reliable performance, easy to operation and maintenance, and low cost;
small size, capacity;
easy to adjust, easy to fulfill automatic control.
This method applies to the speed of the fan and water pump.
三相异步电动机的几种调速方式
三相异步电动机转速公式为：
n=60f/p(1-s)
从上式可见，改变供电频率种。
在生产机械中广泛使用不改变同步转速的调速方法有绕线式电动机的转子串电阻调速、斩波调速、串级调速以及应用电磁转差离合器、液力偶合器、转速的有改变定子极对数的多速电动机，调速等。
从调速时的能耗观点来看，有高效调速方法与低效调速方法两种：高效调速指时转差率不变，因此无转差损耗，如多速电动机、变频调速以及能将转差损耗回收的调速方法（如串级调速等）。有转差损耗的调速方法属低效调速，子回路中；电磁离合器的调速方法，在液力偶合器的油中。损耗是很小的。
一、变极对数调速方法
这种调速方法是用改变定子绕组的接红方式来改变笼型电动机定子极对数达到调速目的，特点如下：
1、具有较硬的机械特性，稳定性良好；2、无转差损耗，效率高；3、接线简单、控制方便、价格低；
4、有级调速，级差较大，不能获得平滑调速；
5、可以与调压调速、电磁转差离合器配合使用，获得较高效率的平滑调速特性。本方法适用于不需要无级调速的生产机械，水泵等。
二、变频调速方法
变频调速是改变电动机定子电源的频率，从而改变其同步转速的调速方法。变频调速系统主要设备是提供变频电源的变频器，
变频器可分成交流－直流－交流变频器和交流－交流
变频器两大类，目前国内大都使用交－直－交变频器。其特点：
1、效率高，调速过程中没有附加损耗2、应用范围广，可用于笼型异步电动机
如金属切削机床、升降机、起重设备、风机、如转子串电阻调速方法，
能量就损耗在转
能量损耗
能量损耗在离合器线圈中；液力偶合器调速，
油膜离合器等调速。
改变同步
改变定子电压、频率的变频调速有能无换向电动机
f、电动机的极对数
p及转差率s均可太到改变转速的目的。
从调速的本质来看，不同的调速方式无非是改变交流电动机的同步转速或不改变同步转两
一般来说转差损耗随调速范围扩大而增加，如果调速范围不大，能量
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