Why choose permanent magnet ac motors?

Permanent magnet AC (PMAC) motors offer several advantages over other types of motors, including:

High Efficiency: PMAC motors are highly efficient due to the absence of rotor copper losses and reduced winding losses. They can achieve efficiencies of up to 97%, resulting in significant energy savings.

High Power Density: PMAC motors have a higher power density compared to other motor types, which means they can produce more power per unit of size and weight. This makes them ideal for applications where space is limited.

High Torque Density: PMAC motors have a high torque density, which means they can produce more torque per unit of size and weight. This makes them ideal for applications where high torque is required.

Reduced Maintenance: Since PMAC motors have no brushes, they require less maintenance and have a longer lifespan than other motor types.

Improved Control: PMAC motors have better speed and torque control compared to other motor types, making them ideal for applications where precise control is required.

Environmentally Friendly: PMAC motors are more environmentally friendly than other motor types since they use rare earth metals, which are easier to recycle and produce less waste compared to other motor types.

Overall, the advantages of PMAC motors make them an excellent choice for a wide range of applications, including electric vehicles, industrial machinery, and renewable energy systems.


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.

Working Principle
The permanent magnet synchronous motor working principle is similar to the synchronous motor. It depends on the rotating magnetic field that generates electromotive force at synchronous speed. When the stator winding is energized by giving the 3-phase supply, a rotating magnetic field is created in between the air gaps.

This produces the torque when the rotor field poles hold the rotating magnetic field at synchronous speed and the rotor rotates continuously. As these motors are not self-starting motors, it is necessary to provide a variable frequency power supply.

EMF and Torque Equation
In a synchronous machine, the average EMF induced per phase is called dynamic induces EMF in a synchronous motor, the flux cut by each conductor per revolution is Pϕ Weber
Then the time taken to complete one revolution is 60/N sec

The average EMF induced per conductor can be calculated by using

( PϕN / 60 ) x Zph = ( PϕN / 60 ) x 2Tph

Where Tph = Zph / 2

Therefore, the average EMF per phase is,

= 4 x ϕ x Tph x PN/120 = 4ϕfTph
Where Tph = no. Of turns connected in series per phase

ϕ = flux/pole in Weber

P= no. Of poles

F= frequency in Hz

Zph= no. Of conductors connected in series per phase. = Zph/3

The EMF equation depends on the coils and the conductors on the stator. For this motor, the distribution factor Kd and pitch factor Kp are also considered.

Hence, E = 4 x ϕ x f x Tph xKd x Kp

The torque equation of a permanent magnet synchronous motor is given as,

T = (3 x Eph x Iph x sinβ) / ωm


Surface-mounted PMSM
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.

Buried PMSM or Interior PMSM
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 robust. Reluctance torque is due to the saliency of the 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.

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.

Advantages

The advantages of permanent magnet synchronous motor include,

provides higher efficiency at high speeds

available in small sizes in different packages

maintenance and installation are very easy than with an induction motor

capable of maintaining full torque at low speeds

high efficiency and reliability

gives smooth torque and dynamic performance

Disadvantages

The disadvantages of permanent magnet synchronous motors are:

These types of motors are very expensive when compared to induction motors

Somehow difficult to start up because they are not self-starting motors.

There are many ways to start a permanent magnet synchronous motor, including direct start, self-coupling decompression start, Y-Δ decompression start, soft start, inverter start, etc. So what's the difference between them?

1. When the grid capacity and load allow full voltage direct start, full voltage direct start can be considered. The advantages are convenient operation and control, simple maintenance, and high economy. It is mainly used to start small power motors.

2. The automatic transmission starts using the multi-touch of the automatic transmission to reduce the pressure, which can not only meet the needs of different loads but also the starting torque will be larger. It is a decompression starting method and is often used to start high-capacity motors.

3. Y-Δ starts to run normally. The squirrel cage asynchronous motor is wound and connected to the delta stator. If the stator is wound into a star when starting, and then connected to the delta after starting, the starting current can be reduced and the impact on the power grid can be alleviated. This start-up mode is referred to as a star-delta decompression start, or star-delta start (Y-delta start). It is suitable for no-load or light-load starting. Compared to any other decompression starter, it has the simplest structure and is also less expensive. In addition, the star-delta starting mode has another advantage, that is, the permanent magnet synchronous motor can be operated in star-connected mode when the load is light. At this time, the rated torque and load can be matched, thereby improving the efficiency of the motor and saving power consumption.

4. The soft starter adopts the phase-shift voltage regulation principle of the silicon-controlled rectifier to realize the voltage regulation start of the motor. It is mainly used for starting control of permanent magnet synchronous motor, with good starting effect and high cost.

5. The frequency converter is a motor control device with the highest technical content, the most complete control functions, and the best control effect in the field of modern motor control. It adjusts the speed and torque of the permanent magnet synchronous motor by changing the frequency of the power grid, and it is mainly used in fields that require high requirements for speed regulation and high-speed control.

Decompression start, a common star-delta start, the disadvantage is that the starting torque is small, only suitable for a no-load or light-load start. The advantage is that it is cheap. Soft start, you can set the start time and the initial torque of the starting equipment, realize a soft start and soft stop and can limit the starting current, the price is moderate. Frequency conversion start, start smoothly according to the set time and let the equipment run at the set frequency, the price is high.