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Currently, a significant number of products continue to operate using AC induction motors. Nevertheless, a shift is occurring as engineers and equipment operators increasingly opt for permanent magnet (PM) motors across various applications, mainly due to their compact size and enhanced efficiency. Applications such as fans, blowers, and pumps are particularly well-matched with the capabilities of permanent magnet drive systems.
A Permanent Magnet Synchronous Motor (PMSM) is an AC synchronous motor that utilizes permanent magnets for magnetic field excitation. These motors are highly efficient, brushless, fast, and safe, with exceptional dynamic performance. Given these advantages, permanent magnet synchronous motors find broad applications across various fields.
A permanent magnet synchronous motor (PMSM) is a type of synchronous motor that uses permanent magnets as inductors. In industrial applications, permanent magnet synchronous motor is an important product.
There are different kinds of synchronous motors for you to choose from on Enneng’s website.A comprehensive list of synchronous motor services for all your needs is available on the Enneng website. Enneng can provide you with a wide range of permanent magnet synchronous motors in various classes suitable for different application conditions.
What is a permanent magnet synchronous motor
A Permanent Magnet Synchronous Motor (PMSM) is a type of brushless motor that is highly regarded for its reliability and efficiency. It has a permanent magnet rotor, which offers several benefits such as high torque, compact size, and no need for rotor current. Instead of using windings, the rotor utilizes permanent magnets to create a rotating magnetic field. This design makes the motor simple and cost-effective, as it eliminates the need for a DC power supply. PMSMs operate as AC synchronous motors, with the magnetic field excitation provided by permanent magnets, resulting in a sinusoidal reverse EMF waveform. This allows the PMSM to generate torque even at zero speed. However, to operate efficiently, these motors require a digitally controlled inverter.
Construction
Like all rotating motors, permanent magnet synchronous motors are comprised of a rotor and a stator. The overall structure of a permanent magnet synchronous motor closely resembles that of a standard synchronous motor, with the primary distinction lying in the design of the rotor. In this motor type, the rotor lacks magnetic field windings and instead features mounted permanent magnets.
These permanent magnets serve to generate magnetic poles within the motor. Typically, the permanent magnets utilized in such motors are made from materials such as samarium cobalt and neodymium iron boron due to their high permeability. Among these options, neodymium iron boron is the most commonly used permanent magnet owing to its cost-effectiveness and widespread availability.
Permanent magnet synchronous motors operate on a similar principle to synchronous motors. Its principle of operation is based on the interaction between the rotating magnetic field of the stator and the constant magnetic field of the rotor. It relies on the rotating magnetic field to generate an electric potential at synchronous speeds.
Upon energizing the stator windings with a three-phase electrical supply, a rotating magnetic field emerges within the air gaps. This field induces torque as the rotor poles lock in synchrony with the rotating magnetic field at a constant speed, resulting in continuous rotation of the rotor. Given that these motors do not possess the capability to start on their own, the provision of a variable frequency power supply is essential to initiate operation.
Features
-Non-sparking, safer in explosive environments
-Clean, fast and efficient
-More compact, efficient and lighter than ACIM
-Designed for high performance servo applications
-Operates with or without position encoder
-Low noise and EMI
-Smooth low and high speed performance
-Combined with Field Oriented Control (FOC) for optimal torque production
Types
1.Classification of PMSM motors based on rotor design:
The rotor consists of permanent magnets. The permanent magnets are made of high coercivity materials. Based on rotor design, synchronous motors can be classified as:
Motors with magnetic pole rotor;
Motors without magnetic pole rotor.
They can also be classified as:
Internal permanent magnet synchronous motors
In this construction, permanent magnets are embedded in the rotor as shown in the figure below. It is suitable and robust for high speed applications. The reluctance torque is due to the prominence of the motor.
Surface permanent magnet synchronous motor
In this configuration, the magnets are mounted on the surface of the rotor. It is suitable for high speed applications but is not robust. The air gap is uniform as the permeability of the permanent magnets and the air gap are the same. No reluctance torque and high dynamic performance makes it suitable for high-speed equipment such as robots and tool drives.
Classification of PMSM motors based on stator design
The stator consists of an outer frame and a core with windings. The most common designs are two-phase and three-phase windings.
Depending on the stator design, permanent magnet synchronous motors can be:
Distributed winding;
Centralised windings.
Permanent magnet synchronous motor control
Since permanent magnet synchronous motors must be driven with sinusoidal waves, the complexity of control increases. Permanent magnet synchronous motors require a control system such as a variable frequency drive or a servo drive.
The control system encompasses a wide array of control techniques, and the choice of the most suitable control method largely depends on the specific requirements of the motorized drive. For simpler tasks, trapezoidal control with Hall sensors is commonly employed, while for optimizing the performance of a motorized drive, field-oriented control is often preferred.
In most cases, PMSMs necessitate a variable frequency drive for initiation. However, certain PMSMs are equipped with squirrel-cage starters in the rotor, known as line starters or self-starters. These configurations are frequently utilized as a highly efficient alternative to induction motors due to the absence of slip. However, it is crucial to ensure that synchronous speeds are attained and that the system can withstand torque ripple during the start-up process.
Do synchronous motors have permanent magnets?
In a permanent magnet synchronous motor (PMSM), permanent magnets placed in a steel rotor provide a continuous magnetic field. The rotating magnetic field is generated by windings in the stator coupled to the AC supply (same as in an asynchronous motor).
Advantages of Permanent Magnet Synchronous Motors
The advantages of permanent magnet synchronous motors include:
-Dynamic performance at high and low speeds
-High power density
-Low rotor inertia for easy control
-No torque ripple during motor commutation
-High and smooth torque
-High efficiency at high speeds
-Resistant to wear and tear
-Available in small sizes in different packages
-Easy maintenance and installation
-Maintains full torque even at low speeds
-High reliability
-Efficient heat dissipation
-Low noise level
Applications
-Applications for permanent magnet synchronous motors include:
-AC compressors
-Automotive electric power steering
-Machine tools
-Large power systems to improve leading and lagging power factor
In recent years, permanent magnet synchronous motors (PMSMs) have been increasingly used in high-performance drives with the development of solid-state electronics, processors and intelligent computing technologies. The advantages of PMSMs are simple structure, small size, high efficiency and high power factor.
