With rapid social development and increasing number of high-rise buildings, elevators have become an indispensable tool for people to travel every day. However, elevators consume a large amount of electricity and are one of the devices for high-rise building's maximum energy consumption. According to the elevator association’s estimation, each of China’s average The elevator consumes about 40KWh per day. With the development and application of rare earth permanent magnet synchronous motors, and the realization of electromechanical integration with variable frequency control, permanent magnet synchronous motors have been widely used in elevators.
Permanent-magnet synchronous motors, accurately speaking, should be called permanent-magnet motors that operate synchronously and asynchronously. This kind of motor can use the same size to replace the original Y, Y2, Y3 and other motors. Reduces the hassle of the replacement process. Compared with ordinary motors, permanent magnet motors have their own characteristics.
1, constant speed, synchronous speed. The rotation speed is slightly higher than that of an ordinary motor. For example, the rotation speed of an ordinary motor is 1400n/min, and the rotation speed of a permanent magnet synchronous motor is 1500n/min, and the rotation is less.
2, high power factor. In the normal operation of the permanent magnet motor, the rotor speed and the stator magnetic field speed are consistent, and the rotor pole adopts the permanent magnet steel, there is no current, and the induction current on the stator is reduced, so the power factor is high. It can be designed to work at lagging power factor, unit power factor and leading power factor. Generally, the lagging power factor can reach or exceed 0.95, and a large number of permanent magnet motors can be used to eliminate the need for such devices as reactive power compensators.
3, high efficiency, especially high operating efficiency. When the permanent magnet motor is in normal operation, since the rotor pole uses a permanent magnet - NdFeB magnetic steel, the magnetic field of the permanent magnet can ensure the normal operation of the motor, so the rotor will have no winding loss. Rotor iron consumption is also not, so the efficiency is much higher than the ordinary motor. At present, the general design of permanent magnet synchronous motor can easily reach the level 2 energy efficiency specified in GB/T18613-2012 edition, and even reach the level 1 index; while the ordinary motor, the design achieves the corresponding performance is more troublesome, this performance in the low-power motor Especially obvious.
4. The permanent magnet synchronous motor has a wider economic operating range. The economical operating range of general motors is generally 60~100% of the rated load. When the load is less than 60%, the motor efficiency and power factor curve will drop rapidly, and the operating efficiency and power factor will be very low. The economical operating range of permanent magnet synchronous motor is much wider than that of ordinary motors. It not only has high efficiency under rated load, but also has high efficiency in the range of 25 to 120% of rated load. The efficiency curve is relatively smooth, with little change. . The motor efficiency is basically not less than 80% of the rated efficiency. However, the efficiency of an ordinary motor is rapidly reduced around 35% of the rated load and can be as low as 30 to 40%. When the permanent magnet motor is loaded at 25%, the power factor can also reach 0.9 or more, and the lighter load power factor is higher; while the ordinary motor rapidly drops from about 0.85 at the rated load to less than 0.5.
5, small size, light weight. Since permanent magnet permanent magnet materials are applied to the permanent magnet motor rotor, the loss is low, the efficiency and the power factor are high, and the same power is achieved. On the basis of ensuring the efficiency and power factor, the volume can be made smaller than the ordinary motor and the weight can be light. This has the advantage that ordinary motors can't match in some occasions that require small machine seats and high power.
6. High locked-rotor torque. Ordinary motor locked-rotor torque is generally 1.6 to 2.3 times the rated torque, and permanent magnet motor stall torque is generally up to 2.4 times, and some specifications can even reach 3.5 times. In some cases, permanent magnet motors are called "high-efficiency, high-starting-magnet permanent-magnet synchronous motors." In the case of high starting torque requirements of some equipment, many use high-slip motors, but the efficiency is very low; in addition, it is to increase capacity. To increase the starting torque, but the actual operation, the load rate is very low, efficiency and power factor are very low, resulting in a waste of facilities and energy. The use of permanent magnet motors to achieve the same torque, you can properly reduce the motor capacity, permanent magnet motor power factor and efficiency are high, the energy-saving effect is very obvious.
7, can achieve low speed and high efficiency. The motor with more than 10 poles of ordinary motors is not technically unattainable, but the lower the speed is, the lower the efficiency is, and the more important the frame number is, the power is very small, which was previously considered to be inaccessible. Permanent magnet motors can make poles very high. Asynchronous starting permanent magnet motors have 24 poles or even 32 poles. The rotational speed is very low, and direct drive can be used for some devices, eliminating the need for speed reduction facilities. From the perspective of energy conservation, this can increase efficiency. In addition, since permanent magnet motors have small rotor losses, although the number of poles is high, the efficiency can also be made very high and the energy saving prospects are very good.
8, permanent magnet motor costs high, complex processing technology. Due to the use of a high performance rare earth permanent magnet material, NdFeB, the manufacturing cost is high. The permanent magnets are placed inside the rotor and the design and installation process is complicated, which also increases the manufacturing cost.
9, permanent magnet motor start has its own characteristics. Generally, the permanent magnet motor can not adopt the step-down starting mode, because the ordinary permanent magnet motor (380V, 50HZ), when the voltage is reduced to 330V, the starting is difficult, and the rotor shakes badly. Low-power permanent magnet motors generally use a direct start method. High-power permanent magnet motors can be started directly under the condition that the transformer capacity is large enough and the mechanical impact of equipment is not strict. Otherwise, it is recommended to use inverter-driven soft start method
10. The drive of the three-phase AC permanent magnet synchronous motor can adopt the “stator winding and star” method to provide the braking electromagnetic torque generated by the motor itself when the brake is in the non-driven state, so as to suppress the unexpected state. The “quick roll car” as shown in Figure 4 below, but the role played by this connection mode cannot be confused with the elevator's upward overspeed protection device and the elevator's accidental movement protection device.