The preceding post discussed why PMSM motors are so interesting and how they improve and make EVs more cheap. This article delves further into the PMSM's design and operation. It will discuss how intriguing the laws of physics work with various sorts of motor construction. 

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 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. 

 Working Principle :  

The PMSM motor operates on the same principle as the synchronous motor. PMSM motors begin as squirrel-cage induction motors. A rotating magnetic field is created in the air-gap when the three-phase winding of the stator is energised by the three-phase power source. At synchronous speed, the rotor field magnetically locks with the stator poles, producing torque and allowing the rotor to continue rotating.        

Motor Construction and Types 

A permanent magnet synchronous motor, like any rotating electric motor, consists of a rotor and a stator. The stator is the fixed part. The rotor is the rotating part. The permanent magnets are mounted on the rotor and the rotor doesn&#;t have any field winding.  

The permanent magnets are used to create field poles. The permanent magnets used in the motor are made up of samarium-cobalt and medium, iron, and boron because of their higher permeability. The most widely used permanent magnet is neodymium-boron-iron because of its effective cost and ease of availability. 

1. Classification of PMSM Motors based on Rotor Design 

The rotor consists of permanent magnets. Materials with high coercive force are used as permanent magnets. 

According to the rotor design, synchronous motors are divided into: 

• electric motors with salient pole rotor; 
• electric motors with non-salient pole rotor. 

They are also be classified  into: 

• interior permanent magnet synchronous motor 

In this type of construction, the permanent magnet is embedded into the rotor as shown in the figure below. It is suitable for high-speed applications and gets robustness. Reluctance torque is due to the saliency of the motor. 

• surface permanent magnet synchronous motor: 

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. 

2. Classification of PMSM Motors based on Stator Design 

The stator consists of an outer frame and a core with windings. The most common design with two- and three-phase winding. 

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Depending on the stator design, a permanent magnet synchronous motor can be: 

• with distributed winding; 
• with concentrated winding. 

 Working 

• 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. 

Wrapping Up 

With recent advancements in solid state electronics, processors, and intelligent computing, the permanent magnet synchronous motor (PMSM) is gaining traction in the field of high performance drives. The advantages of permanent magnet synchronous motors are their simple structure, compact size, great efficiency, and high power factor. The benefits of PM machines have lately made them very appealing candidates for 'direct drive' applications such as hybrid electric vehicles (HEV) and electric cars (EV). 

It's no surprise that PMSM motors have swiftly risen to prominence in EVs today. They provide everything an electric vehicle needs, from higher power to enhanced safety and efficiency. 

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.

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.

If you want to learn more about magnets, we would like to advise you to visit Stanford Magnets for more information. As a leading magnet supplier across the world, Stanford Magnets has been involved in the R&D, manufacturing, and sales of magnets since the s. It provides customers with high-quality permanent magnets like SmCo magnets, neodymium magnets, AlNiCo magnets, and ferrite magnets (ceramic magnets) at a very competitive price.