1. Classification of electric motors

　　( 1 ) Classification by working power source: According to the different working power sources of motors, they can be divided into DC motors and AC motors. AC motors are also divided into single-phase motors and three-phase motors.

　　( 2 ) Classification according to structure and working principle: Motors can be divided into asynchronous motors and synchronous motors according to their structure and working principles. Synchronous motors can also be divided into permanent magnet synchronous motors, reluctance synchronous motors and hysteresis synchronous motors. Asynchronous motors can be divided into induction motors and AC commutator motors. Induction motors are further divided into three-phase asynchronous motors, single-phase asynchronous motors and shaded pole asynchronous motors. AC commutator motors are further divided into single-phase series motors, AC and DC dual-purpose motors and repulsion motors  .

　　( 3 ) Classification according to starting and running modes: Motors can be divided into capacitor starting motors, capacitor running motors, capacitor starting running motors and split-phase motors according to starting and running modes.

　　( 4 ) Classification by use: Motors can be divided into drive motors and control motors according to their use. Driving motors are further divided into motors for power tools, motors for household appliances and motors for other general-purpose small mechanical equipment. Control motors are divided into stepper motors and servo motors.

　　( 5 ) Classification according to the structure of the rotor: Motors can be divided into cage induction motors and wound rotor induction motors according to the structure of the rotor.

　　( 6 ) Classification according to operating speed: Motors can be divided into high-speed motors, low-speed motors, constant-speed motors and speed-regulating motors according to operating speed.

　　2.Motor model and selection

　　( 1 ) Model

　　( 2 ) Selection of motor

　　The choice of motor type is related to safe operation and equipment cost: the motor type is determined according to environmental conditions: open type, protective type, closed type, airtight type or explosion-proof type.

　　Selection of power The size of the load torque is the main basis for selecting the power of the motor. It is safe to choose a large power, but a low power factor will increase investment and operating costs. The rated power PN marked on the motor nameplate refers to the mechanical power output by the motor shaft. In order to improve the natural power factor of the equipment, the motor should be operated at full load as much as possible. The efficiency of the motor is generally above 80% .

　　( 3 ) How to start the motor

　　1 ) Direct starting Direct starting is also called full voltage starting and only uses one control device. Its characteristics are:

　　a. The starting current is large, generally 4 to 7 times the rated current.

　　b. The starting method is simple, but generally only suitable for motors less than 10KW . Specific wiring methods include star connection and delta connection.

　　2 ) Decompression starting When the motor capacity is large, in order to reduce the starting current, decompression starting is often used.

　　a. Star - delta starting method ( Y-Δ ) When the motor must be connected in a delta connection for normal operation, start with a star connection first. Since the stator voltage is reduced by 10 times, the starting current is reduced, and it is changed to delta connection operation immediately after starting.

　　b. Auto-decompression starting control cabinet (box) decompression starting. This starting method can be used regardless of whether the motor is star-connected or delta-connected. It can perform infrequent auto-decompression starting of three-phase cage asynchronous motors to reduce the impact of motor starting current on the power transmission network, and can accelerate the motor speed to the rated speed and artificially stop the motor operation. It has overload, phase failure, short circuit and other protection for the motor.

　　c. Starting method of wound rotor asynchronous motor In order to reduce the starting current, the wound rotor asynchronous motor is started by inserting a resistor in series with the rotor circuit. This not only reduces the starting current, but also increases the starting torque. Before starting, adjust the resistance to the maximum value. After closing the switch, the rotor starts to rotate. As the speed increases, the resistance gradually decreases. After the motor speed stabilizes, short-circuit the starting resistor, that is, cut off all starting resistors.

　　d.  Soft starter

　　Soft starters were introduced on the market in the late 1970s and early 1980s . They are similar to frequency converters and are based on electronics and thyristors . Using a soft starter, the voltage of the motor can be controlled so that it gradually increases during the starting process, naturally limiting the starting current, which means that the motor can start smoothly and the mechanical and electrical stress is reduced to a minimum; this device There is also an accompanying feature that can be used for a " soft " shutdown. Since the starter uses electronic circuitry, it is relatively easy to enhance its basic functions with safety and accident indicators, improve motor protection and simplify fault finding, such as phase loss, overcurrent and over-temperature protection, as well as normal operation, motor full voltage and certain fault indications. All settings like ramp voltage and initial voltage can be easily set on the starter panel.

　　In addition, in addition to fully meeting the basic requirement of smooth starting of the motor, the soft starter also has many advantages, such as high reliability, low maintenance, good motor protection, and simple parameter settings.

　　e. Frequency conversion start

　　The inverter is a device that converts industrial frequency power ( 50Hz or 60Hz ) into AC power of various frequencies to achieve variable speed operation of the motor. The control circuit completes the control of the main circuit, and the rectifier circuit converts the AC power into DC power. The DC intermediate The circuit smoothes and filters the output of the rectifier circuit, and the inverter circuit inverts the DC power into AC power. For inverters that require a lot of calculations, such as vector control inverters, sometimes a CPU for torque calculation and some corresponding circuits are needed. Variable frequency speed regulation achieves the purpose of speed regulation by changing the frequency of power supply to the motor stator winding. The low-voltage universal variable frequency output voltage is 380 ~ 650V , the output power is 0.75 ~ 400kW , and the operating frequency is 0 ~ 400Hz.