A permanent magnet synchronous motor (PMSM) is a hybrid of an induction motor and a brushless DC motor, and it has a better power density than an induction motor. It features a permanent magnet rotor and windings on the stator, just like a brushless DC motor. However, the stator construction with windings designed to create a sinusoidal flux density in the machine's air gap is similar to that of an induction motor. Due to their advantages, permanent synchronous motors are a very popular solution in electrical drives. PMSM exhibits best performance because of its characteristics such as high power density, high efficiency, lower mass and lower moment of inertia. 

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In this construction, the magnet is mounted on the surface of the rotor. It is suited for high-speed applications, as it is not robust. It provides a uniform air gap because the permeability of the permanent magnet and the air gap is the same. No reluctance torque, high dynamic performance, and suitable for high-speed devices like robotics and tool drives. 

• 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 that operates and locks at synchronous speed.  
• 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, 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. 

Permanent Magnetic Synchronous Motors

What Are Permanent Magnet Synchronous Motors?

The permanent magnet synchronous motors (PMSM) are similar to the traditional AC synchronous motors, but the field, in this case, is excited by permanent magnets that create sinusoidal back EMF. They are similar to typical rotating electric motors that consist of a rotor and a stator. However, permanent magnet synchronous motors use just a rotor, which creates the magnetic field.

Construction

Permanent magnet synchronous motors are very efficient, brushless, secure, very fast, and offer high dynamic performance. Due to their advantages, permanent synchronous motors have many applications in various industries. Many manufacturers now produce permanent magnet synchronous motors with varying specifications for different applications. Note that AC synchronous motors are the most widely-used steady-state 3-phase AC motors in electrical systems, where they help to convert electrical energy into mechanical energy. The motors operate at a synchronous speed that is constant and synchronous with the supply frequency of AC cycles. Since AC synchronous motors have a speed of the motor that is equal to the rotating magnetic field, they are mostly used in power systems to improve the power factor of the system.

Rare Earth Permanent Magnet Motors

How Permanent Magnetic Synchronous Motors Work

The operation principle of permanent magnet synchronous motors is based on the interaction of the rotating magnetic field of the stator and the constant magnetic field of the rotor. Permanent magnet synchronous motors (PMSM) are known to be pretty efficient, brushless, very fast, safe, and provide high dynamic performance when compared to conventional motors. They are equally very reliable. In this case, instead of using winding for the rotor, the permanent magnets are mounted to generate a rotating magnetic field. These types of motors are very simple and less costly. With a stator (having 3 windings installed on it) and a rotor with a permanent magnet mounted (for creating a rotating field), the 3-phase AC supply is provided to the stator so it can start working. Note that the PMSM is AC synchronous motors whose field excitation is provided by permanent magnets with a sinusoidal back EMF waveform. With the help of the permanent magnets, the PMSM can generate torque at zero speed.

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Types of PMSM

PMSM types depend on how the magnets are attached to the rotor, as well as the design of the rotor. Permanent magnet synchronous motor can be classified into two types:

• Surface permanent magnet synchronous motor (SPMSM)
• Interior permanent magnet synchronous motor (IPMSM).
• SPMSM mounts all magnet pieces on the surface
• IPMSM places magnets inside the rotor

Additionally, depending on the design of the stator, a PMSMs can also be classified as:

• With distributed winding
• With concentrated winding

Properties of Permanent Magnetic Synchronous Motors

• PMSM do not emit sparks and are safer in explosive environments.
• They are clean, very fast, and efficient.
• They are more compact and lighter than an ACIM.
• PMSM typically runs with/without position encoders.
• Smooth low- and high-speed performance. Work well for high-performance applications.
• Produces low audible noise and EMI.
• They generate high torque if coupled with Field-Oriented Control (FOC).

Core Advantages

Here are some of the core advantages of a permanent magnet synchronous motor:

• High power density
• Much less noise
• Dynamic performance in both high and low-speed operation
• High-efficiency at high speeds
• Efficient dissipation of heat
• Low rotor inertia makes it easy to control
• No torque ripple when the motor is commutated
• High and smooth torque and dynamic performance
• Resistant to wear and tear
• Available in small sizes at different packages
• Easy maintenance and installation than an induction motor
• Capable of maintaining full torque at low speeds
• High reliability

Further Reading: Advantages and Applications of Permanent Magnet Synchronous Motor

Disadvantages

The main disadvantages of permanent magnet synchronous motors are:

• High initial costs and very expensive compared to induction motors.
• Can be difficult to start up since they are not self-starting motors.

Applications of Permanent Magnetic Synchronous Motors

Permanent magnet synchronous motors have applications in the following areas:

• AC compressors
• Refrigerators
• Direct-drive washing machines
• Automotive electrical power steering
• Machine tools
• Air conditioners
• Control of traction
• Data storage units
• Servo drives
• Electric vehicle drivetrain
• Large power systems where improved leading and lagging power factors are required
• Robotics
• Aerospace

Conclusion

PMSM is a 3-phase AC synchronous motor that runs at synchronous speed with the applied AC source. It produces smooth torque and low noise. It is mainly used for high-speed applications like robotics. The principle of operation of permanent magnet synchronous motors is based on the interaction of the rotating magnetic field of the stator and the constant magnetic field of the rotor. Thank you for reading our article and we hope it can help you to have a better understanding of permanent magnet synchronous motors.

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