Custom Three Phase Permanent Magnet Synchronous Motor Variable Speed

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.

Structure of the IPM (interior permanent magnet) motor

A conventional SPM (surface permanent magnet) motor has a structure in which a permanent magnet is attached to the rotor surface. It only uses magnetic torque from a magnet. On the other hand, the IPM motor uses reluctance through magnetic resistance in addition to magnetic torque by embedding a permanent magnet in the rotor itself.

SPM vs IPM Motor Rotor Structure

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.

Vector Control Features

While a conventional system (120-degree conduction system) has the current impressed in the motor as a square wave, a vector control impresses voltage which turns into a sine wave towards the rotor's position (angle of the magnet), so it becomes possible to control the motor current.

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 repulsion.

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.

The development trend of rare earth permanent magnet motors

Rare earth permanent magnet motors are developing towards high power (high speed, high torque), high functionality and miniaturization, and are constantly expanding new motor varieties and application fields, and the application prospects are very optimistic. In order to meet the needs, the design and manufacturing process of rare earth permanent magnet motors still need to be continuously innovated, the electromagnetic structure will be more complex, the calculation structure will be more accurate, and the manufacturing process will be more advanced and applicable.

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.

Why are permanent magnet motors more efficient?

The Permanent magnet synchronous motor is mainly composed of the stator, rotor, and housing components. Like ordinary AC motors, the stator core is a laminated structure to reduce iron loss due to eddy current and hysteresis effects during motor operation; the windings are also usually three-phase symmetrical structures, but the parameter selection is quite different.

The rotor part has various forms, including permanent magnet rotors with starting squirrel cages, and built-in or surface-mounted pure permanent magnet rotors. The rotor core can be made into a solid structure or laminated. The rotor is equipped with permanent magnet material, which is commonly called magnet steel.

Under the normal operation of the permanent magnet motor, the rotor, and the stator magnetic field are in a synchronous state, there is no induced current in the rotor part, no rotor copper loss, hysteresis, and eddy current loss, and there is no need to consider the problem of rotor loss and heat generation.

Generally, the permanent magnet motor is powered by a special frequency converter and naturally has a soft start function.

In addition, the permanent magnet motor is a synchronous motor, which has the characteristics of adjusting the power factor of the synchronous motor through the strength of the excitation, so the power factor can be designed to a specified value.

From the perspective of starting, due to the fact that the permanent magnet motor is started by the variable frequency power supply or the supporting frequency converter, the starting process of the permanent magnet motor is easy to realize; similar to the starting of the variable frequency motor, it avoids the starting defects of the ordinary cage-type asynchronous motor.

In short, the efficiency and power factor of permanent magnet motors can reach very high, and the structure is very simple.

ENNENG is devoted to the research and development of various special high & low voltage Low-speed High-torque permanent magnet motors, constant-speed permanent magnet motors, and special direct-drive permanent magnet motors.

ENNENG permanent magnet motors are widely used in China's famous companies in different fields including gold mines, coal mines, tire factories, oil well, and water treatment plants have benefited customers for energy saving as well as for environmental protection.

We would like to jointly work with users all over the world to focus on energy-saving solutions to benefit our society and people.