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Long Lifespan Industrial Use 3 Phase PMSM Motor Without Gearbox
What Is The Permanent Magnet Synchronous Motor?
The Permanent Magnet Synchronous Motor (PMSM) is a type of electric motor that operates using permanent magnets embedded in its rotor. It is also sometimes referred to as a brushless AC motor or a synchronous permanent magnet motor.
In a PMSM, the stator (the stationary part of the motor) contains a series of coils that are energized in a sequence to create a rotating magnetic field. The rotor (the rotating part of the motor) contains a series of permanent magnets that are arranged to produce a magnetic field that interacts with the magnetic field produced by the stator.
As the two magnetic fields interact, the rotor rotates, producing mechanical energy that can be used to power machinery or other devices. Because the permanent magnets in the rotor provide a strong, constant magnetic field, PMSMs are highly efficient and require less energy to operate than other types of electric motors.
PMSMs are used in a wide variety of applications, including electric vehicles, industrial machinery, and household appliances. They are known for their high efficiency, low maintenance requirements, and precise control, which makes them a popular choice for many different types of systems.
The defining feature of PMACMs – the permanent magnets within their rotor – are acted upon by the rotating magnetic field (RMF) of the stator windings, and are repelled into rotational motion. This is a deviation from other rotors, where the magnetic force must be induced or generated in the rotor housing, requiring more current. This means that PMACMs are generally more efficient than induction motors, as the rotor’s magnetic field is permanent and does not need a source of power to be used for its generation. This also means that they require a variable frequency drive (VFD, or PM drive) to operate, which is a control system that smooths out the torque produced by these motors. By switching the current on and off to the stator windings at certain stages of rotor rotation, the PM drive simultaneously controls torque and current and uses this data to calculate rotor position, and therefore the speed of the shaft output. They are synchronous machines, as their rotational speed matches the speed of the RMF. These machines are relatively new and are still being optimized, so the specific operation of any one PMACM is, for now, essentially unique to each design.
PM motor structures
PM motor structures can be separated into two categories: interior and surface. Each category has its subset of categories. A surface PM motor can have its magnets on or inset into the surface of the rotor, to increase the robustness of the design. An interior permanent magnet motor positioning and design can vary widely. The IPM motor’s magnets can be inset as a large block or staggered as they come closer to the core. Another method is to have them embedded in a spoke pattern.
Differences Between The Permanent Magnet Motor And Asynchronous Motor
01. Rotor Structure
Asynchronous motor: The rotor consists of an iron core and a winding, mainly squirrel-cage and wire-wound rotors. A squirrel-cage rotor is cast with aluminum bars. The magnetic field of the aluminum bar cutting the stator drives the rotor.
PMSM Motor: The permanent magnets are embedded in the rotor magnetic poles, and are driven to rotate by the rotating magnetic field generated in the stator according to the principle of magnetic poles of the same phase attracting different repulsions.
02. Efficiency
Asynchronous motors: Need to absorb current from the grid excitation, resulting in a certain amount of energy loss, motor reactive current, and low power factor.
PMSM Motor: The magnetic field is provided by permanent magnets, the rotor does not need exciting current, and the motor efficiency is improved.
03. Volume And Weight
The use of high-performance permanent magnet materials makes the air gap magnetic field of permanent magnet synchronous motors larger than that of asynchronous motors. The size and weight are reduced compared to asynchronous motors. It will be one or two frame sizes lower than asynchronous motors.
04. Motor Starting Current
Asynchronous motor: It is directly started by power frequency electricity, and the starting current is large, which can reach 5 to 7 times the rated current, which has a great impact on the power grid in an instant. The large starting current causes the leakage resistance voltage drop of the stator winding to increase, and the starting torque is small so heavy-duty starting cannot be achieved. Even if the inverter is used, it can only start within the rated output current range.
PMSM Motor: It is driven by a dedicated controller, which lacks the rated output requirements of the reducer. The actual starting current is small, the current is gradually increased according to the load, and the starting torque is large.
05. Power Factor
Asynchronous motors have a low power factor, they must absorb a large amount of reactive current from the power grid, the large starting current of asynchronous motors will cause a short-term impact on the power grid, and long-term use will cause certain damage to the power grid equipment and transformers. It is necessary to add power compensation units and perform reactive power compensation to ensure the quality of the power grid and increase the cost of equipment use.
There is no induced current in the rotor of the permanent magnet synchronous motor, and the power factor of the motor is high, which improves the quality factor of the power grid and eliminates the need to install a compensator.
06. Maintenance
Asynchronous motor + reducer structure will generate vibration, heat, high failure rate, large lubricant consumption, and high manual maintenance cost; it will cause certain downtime losses.
The three-phase Permanent magnet synchronous motor drives the equipment directly. Because the reducer is eliminated, the motor output speed is low, mechanical noise is low, mechanical vibration is small, and the failure rate is low. The entire drive system is almost maintenance-free.
Application of rare earth permanent magnet motor:
Due to the superiority of rare earth permanent magnet motors, their applications are becoming more and more extensive. The main application areas are as follows:
Focus on the high efficiency and energy saving of rare earth permanent magnet motors. The main application objects are large power consumers, such as rare earth permanent magnet synchronous motors for textile and chemical fiber industries, rare earth permanent magnet synchronous motors for various mining and transportation machinery used in oil fields and coal mines, and rare earth permanent magnet synchronous motors for driving various pumps and fans.
SPM versus IPM
A PM motor can be separated into two main categories: surface permanent magnet motors (SPM) and interior permanent magnet motors (IPM). Neither motor design type contains rotor bars. Both types generate magnetic flux by the permanent magnets affixed to or inside of the rotor.
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.
IPM (Interior Permanent Magnet) Motor Features
High torque and high efficiency
High torque and high output are achieved by using reluctance torque
in addition to magnetic torque.
Energy-saving operation
It consumes up to 30% less power compared to conventional SPM
motors.
High-speed rotation
It can respond to high-speed motor rotation by controlling the two
types of torque using vector control.
Safety
Since the permanent magnet is embedded, mechanical safety is
improved as, unlike in an SPM, the magnet will not detach due to
centrifugal force.
Why you should choose an IPM motor instead of an SPM?
1. High torque is achieved by using reluctance torque in addition to magnetic torque.
2. IPM motors consume up to 30% less power compared to conventional electric motors.
3. Mechanical safety is improved as, unlike in an SPM, the magnet will not detach due to centrifugal force.
4. It can respond to high-speed motor rotation by controlling the two types of torque using vector control.
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.
