(1) Since the rotor is made of a permanent magnet, the magnetic flux density is high, excitation current is not required, and excitation loss is eliminated. Compared with the asynchronous motor, the excitation current of the stator side winding and the copper and iron loss of the rotor side are reduced, and the reactive current is greatly reduced. Since the stator and rotor magnetic potentials are synchronized, the rotor core has no fundamental wave iron loss, so the efficiency ( The relationship between active energy and power factor (reactive reactive energy) is higher than that of an asynchronous motor. The permanent magnet synchronous motor is generally designed to have higher power factor and efficiency even in light load operation. Figure 1 is a comparison curve between the efficiency and power factor of a permanent magnet synchronous motor and the same specification asynchronous motor. From the load change of the motor, the rare earth permanent magnet synchronous motor can operate under high power factor and high efficiency within the range of 25% to 120% of rated power, while the general three-phase asynchronous motor can only be 60%~100%. The rated power maintains a higher performance rating.
(2) The fixed relationship between the speed and the frequency of the permanent magnet synchronous motor is strictly constant, which is different from the large slip rate when the asynchronous motor load is running. The permanent magnet synchronous motor has hard mechanical characteristics and is caused by load changes. The motor torque disturbance has a strong bearing capacity. The permanent magnet synchronous motor rotor core can be made into hollow structure to reduce the rotor inertia, and the permanent magnet synchronous motor has much faster start-up and braking time than the asynchronous motor. The high torque/inertia ratio makes the permanent magnet synchronous motor more suitable than the asynchronous motor. Run under fast-responding conditions.
(3) The size of the permanent magnet synchronous motor is greatly reduced compared with the asynchronous motor, and the weight is also greatly reduced. The permanent magnet synchronous motor with the same heat dissipation condition and insulating material has a power density greater than 2 times that of the three-phase asynchronous motor. In large cities with large soils, the impact of equipment footprint on costs is gradually being perceived by users.
(4) The rotor structure is greatly simplified, which is easy to maintain and improves the stability of operation. AC permanent magnet servo motor, the magnetic steel and iron core on the rotor are usually bonded with high temperature glue. The curing time of the glue is generally long, which increases the production cycle and cost, and the magnetic steel changes in temperature during the operation of the motor. Under the repeated action of impact force, there is a risk of deformation or even falling off. In order to solve this technical problem, the CM500 series heavy-duty permanent magnet synchronous motor developed by the company changed the magnetic tile adhesive process into a mechanical fastening method by stainless steel sleeve, as shown in Figure 2, completely eliminating the magnetic steel. The risk of loosening. This innovative application technology has been applied for a patent and is a major advancement in motor rotor technology.
Because of the high power factor, the three-phase asynchronous motor must make the air gap between the stator and rotor very small, and the uniformity of the air gap is also critical to the safe operation and vibration noise of the motor. The requirements for the geometrical tolerances of the components and the concentricity of the assembly are relatively strict, and the freedom of selection for the bearing clearance is also relatively small. The asynchronous motors of the larger bases usually use the oil-lubricated bearings, which must be in the specified work. When the lubricant is filled in time, the oil cavity leaks or the filling is not timely, the bearing failure will be accelerated. In the maintenance of the three-phase asynchronous motor, the maintenance of the bearing accounts for a large proportion. In addition, due to the existence of induced current in the rotor of the three-phase asynchronous motor, the problem of electrical corrosion of the bearing has also been concerned by many researchers in recent years. The permanent magnet synchronous motor does not have such problems. Due to the large air gap of the permanent magnet synchronous motor, the related problems caused by the small air gap of the above asynchronous motor are not obvious on the synchronous motor. At the same time, the bearing of the permanent magnet synchronous motor adopts the grease-lubricated bearing with dust cover. The factory has been sealed with the right amount of high-quality grease, which is maintenance-free for life.
