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Maintenance-Free Safe And Durable High Power Permanent Magnet Motor
What Is The Permanent Magnet Synchronous Motor?
A PM motor is an ac motor that uses magnets embedded into or attached to the surface of the motor’s rotor. The magnets are used to generate a constant motor flux instead of requiring the stator field to generate one by linking to the rotor, as is the case with an induction motor. A fourth motor known as a line-start PM (LSPM) motor incorporates characteristics of both motors. An LSPM motor incorporates a PM motor’s magnets within the rotor and a squirrel cage motor’s rotor bars to maximize torque and efficiency.
Back emf is short for back electromotive force but is also known as the counter-electromotive force. The back electromotive force is the voltage that occurs in electric motors when there is a relative motion between the stator windings and the rotor’s magnetic field. The geometric properties of the rotor will determine the shape of the back-emf waveform. These waveforms can be sinusoidal, trapezoidal, triangular, or something in between.
Both induction and PM machines generate back-emf waveforms. In an induction machine, the back-emf waveform will decay as the residual rotor field slowly decays because of the lack of a stator field. However, with a PM machine, the rotor generates its own magnetic field. Therefore, a voltage can be induced in the stator windings whenever the rotor is in motion. Back-emf voltage will rise linearly with speed and is a crucial factor in determining maximum operating speed.
SPM motors have magnets affixed to the exterior of the rotor surface. Because of this mechanical mounting, their mechanical strength is weaker than that of IPM motors. The weakened mechanical strength limits the motor’s maximum safe mechanical speed. In addition, these motors exhibit very limited magnetic saliency (Ld ≈ Lq). Inductance values measured at the rotor terminals are consistent regardless of the rotor position. Because of the near unity saliency ratio, SPM motor designs rely significantly, if not completely, on the magnetic torque component to produce torque.
IPM motors have a permanent magnet embedded into the rotor itself. Unlike their SPM counterparts, the location of the permanent magnets makes IPM motors very mechanically sound, and suitable for operating at very high speeds. These motors also are defined by their relatively high magnetic saliency ratio (Lq > Ld). Due to their magnetic saliency, an IPM motor has the ability to generate torque by taking advantage of both the magnetic and reluctance torque components of the motor.
Small And Lightweight
In special electromagnetic and structural design, the volume-to-weight ratio is reduced by 20%, the length of the whole machine is reduced by 10%, and the full rate of stator slots is increased to 90%.
Highly Integrated
The motor and the inverter are highly integrated, avoiding the external circuit connection between the motor and the inverter, and improving the reliability of the system products.
Energy Efficient
High-performance rare-earth permanent magnet material, special stator slot, and rotor structure make this motor efficient up to IE4 standard.
Custom Design
Customized design and manufacture, dedicated to special machines, reduce redundant functions and design margins and minimize costs.
Low Vibration And Noise
The motor is directly driven, the equipment noise and vibration are small, and the impact on the construction work environment is reduced.
Maintenance Free
No high-speed gear parts, no need to change gear lubricant regularly, and truly maintenance-free equipment.
PM motor inductance variation with load
Only so much flux can be linked to a piece of iron to generate torque. Eventually, the iron will saturate and no longer allow flux to link. The result is a reduction in the inductance of the path taken by a flux field. In a PM machine, the d-axis and q-axis inductance values will reduce with increases in the load current.
The d and q-axis inductances of an SPM motor are nearly identical. Because the magnet is outside of the rotor, the inductance of the q-axis will drop at the same rate as the d-axis inductance. However, the inductance of an IPM motor will reduce differently. Again, the d-axis inductance is naturally lower because the magnet is in the flux path and does not generate an inductive property. Therefore, there is less iron to saturate in the d-axis, which results in a significantly lower reduction in flux with respect to the q-axis.
Analysis on the Application of Modern Permanent Magnet Motor Technology
1. Application of permanent magnet electromechanical technology to the home appliance market
The application of permanent magnet motor technology to the home appliance market is manifested in VCDDVD and computers. At present, it has gradually formed the development of industrialization, and has gradually expanded to multi-phase variable speed drives. For example, people use Inverter air conditioners use modern permanent magnet motor technology to improve the operating efficiency of the air conditioner, gradually reduce the volume of the air conditioner motor, and minimize the noise caused by the air conditioner.
2. Application of permanent magnet electromechanical technology in the elevator market
The permanent magnet motor variable speed system has been used in the elevator market for almost 10 years. For example, by using a low-speed rare earth permanent magnet motor as the elevator traction machine, the use of rare earth permanent magnet motor can save elevator use 20 % of electric energy. Modern permanent magnet motors are usually used in the field of variable-speed drive systems with large load changes and high speed adjustment requirements.
3. Application of permanent magnet electromechanical technology in industrial and mining enterprises
With the development of permanent magnet motors, large torque permanent magnet motors have been well developed, especially the successful launch of permanent magnet variable frequency motors on the market has given heavy industrial and mining enterprises new choices. Since the output torque of the permanent magnet motor is large enough, the use of the mechanical transmission is reduced and the speed is controllable. It can run at low speeds. Therefore, the application of the fluid coupling is eliminated, which saves the cost of purchasing related equipment and the maintenance of the above two equipment, which reduces the safety risk, so the permanent magnet variable frequency motor is very popular in many industrial and mining enterprises. Because of its variable frequency speed regulation function, it provides a strong guarantee for users to improve production efficiency and save electric energy. Therefore, modern permanent magnet variable frequency motors are a necessary choice for industrial and mining enterprises to upgrade their equipment in the future.
Flux weakening/intensifying of PM motors
Flux in a permanent magnet motor is generated by the magnets. The flux field follows a certain path, which can be boosted or opposed. Boosting or intensifying the flux field will allow the motor to temporarily increase torque production. Opposing the flux field will negate the existing magnet field of the motor. The reduced magnet field will limit torque production, but reduce the back-emf voltage. The reduced back-emf voltage frees up the voltage to push the motor to operate at higher output speeds. Both types of operation require additional motor current. The direction of the motor current across the d-axis, provided by the motor controller, determines the desired effect.
