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OEM ODM Service Heavy Duty Direct Drive Permanent Magnet Motor
What Is The Permanent Magnet Synchronous Motor?
The Permanent Magnet Synchronous Motor (PMSM) is an AC synchronous motor whose field excitation is provided by permanent magnets and has a sinusoidal back EMF waveform. The PMSM is a cross between an induction motor and brushless DC motor. Like a brushless DC motor, it has a permanent magnet rotor and windings on the stator. However, the stator structure with windings constructed to produce a sinusoidal flux density in the air gap of the machine resembles that of an induction motor. Its power density is higher than induction motors with the same ratings since there is no stator power dedicated to magnetic field production.
With permanent magnets the PMSM can generate torque at zero speed,
it requires a digitally controlled inverter for operations. PMSMs
are typically used for high-performance and high-efficiency motor
drives. High-performance motor control is characterized by smooth
rotation over the entire speed range of the motor, full torque
control at zero speed, and fast acceleration and deceleration.
To achieve such control, vector control techniques are used for
PMSM. The vector control techniques are usually also referred to as
field-oriented control (FOC). The basic idea of the vector control
algorithm is to decompose a stator current into a magnetic
field-generating part and a torque-generating part. Both components
can be controlled separately after decomposition.
Working of Permanent Magnet Synchronous Motor
The working of the permanent magnet synchronous motor is very simple, fast, and effective when compared to conventional motors. The working of PMSM depends on the rotating magnetic field of the stator and the constant magnetic field of the rotor. The permanent magnets are used as the rotor to create constant magnetic flux and operate and lock at synchronous speed. These types of motors are similar to brushless DC motors.
The phasor groups are formed by joining the windings of the stator with one another. These phasor groups are joined together to form different connections like a star, Delta, and double and single phases. To reduce harmonic voltages, the windings should be wound shortly with each other.
When the 3-phase AC supply is given to the stator, it creates a rotating magnetic field and the constant magnetic field is induced due to the permanent magnet of the rotor. This rotor operates in synchronism with the synchronous speed. The whole working of the PMSM depends on the air gap between the stator and rotor with no load.
If the air gap is large, then the windage losses of the motor will be reduced. The field poles created by the permanent magnet are salient. The permanent magnet synchronous motors are not self-starting motors. So, it is necessary to control the variable frequency of the stator electronically.
Analysis of the principle of the technical advantages of permanent
magnet motor
The principle of a permanent magnet synchronous motor is as
follows: In the motor's stator winding into the three-phase
current, after the pass-in current, it will form a rotating
magnetic field for the motor's stator winding. Because the rotor is
installed with the permanent magnet, the permanent magnet's
magnetic pole is fixed, according to the principle of magnetic
poles of the same phase attracting different repulsion, the
rotating magnetic field generated in the stator will drive the
rotor to rotate, The rotation speed of the rotor is equal to the
speed of the rotating pole produced in the stator.
Back-emf waveform:
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.
Permanent magnet AC (PMAC) motors have a wide range of applications
including:
Industrial Machinery: PMAC motors are used in a variety of
industrial machinery applications, such as pumps, compressors,
fans, and machine tools. They offer high efficiency, high power
density, and precise control, making them ideal for these
applications.
Robotics: PMAC motors are used in robotics and automation
applications, where they offer high torque density, precise
control, and high efficiency. They are often used in robotic arms,
grippers, and other motion control systems.
HVAC Systems: PMAC motors are used in heating, ventilation, and air
conditioning (HVAC) systems, where they offer high efficiency,
precise control, and low noise levels. They are often used in fans
and pumps in these systems.
Renewable Energy Systems: PMAC motors are used in renewable energy
systems, such as wind turbines and solar trackers, where they offer
high efficiency, high power density, and precise control. They are
often used in the generators and tracking systems in these systems.
Medical Equipment: PMAC motors are used in medical equipment, such
as MRI machines, where they offer high torque density, precise
control, and low noise levels. They are often used in the motors
that drive the moving parts in these machines.
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.
Advantages
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.
Self-sensing versus closed-loop operation
Recent advances in drive technology allow standard ac drives to “self-detect” and track the motor magnet position. A closed-loop system typically uses the z-pulse channel to optimize performance. Through certain routines, the drive knows the exact position of the motor magnet by tracking the A/B channels and correcting for errors with the z-channel. Knowing the exact position of the magnet allows for optimum torque production resulting in optimum efficiency.
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.
What applications use PMSM motors?
Permanent magnet synchronous motors have the advantages of simple
structure, small size, high efficiency, and high power factor. It
has been widely used in the metallurgical industry (ironmaking
plant and sintering plant, etc.), ceramic industry (ball mill),
rubber industry (internal mixer), petroleum industry (pumping
unit), textile industry (double twist machine, spinning frame) and
other industries in the medium and low voltage motor.
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.
