Low Noise High Efficiency 3 Phase Motor PMSM 500kw Maintenance Free For Plastic Extruder

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 repulsions.

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.

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

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.

SPM versus IPM

A PM motor can be separated into two main categories: surface permanent magnet motors (SPM) and interior permanent magnet motors (IPM). Neither motor design type contains rotor bars. Both types generate magnetic flux by the permanent magnets affixed to or inside of the rotor.

SPM motors have magnets affixed to the exterior of the rotor surface. Because of this mechanical mounting, their mechanical strength is weaker than that of IPM motors. The weakened mechanical strength limits the motor’s maximum safe mechanical speed. In addition, these motors exhibit very limited magnetic saliency (Ld ≈ Lq). Inductance values measured at the rotor terminals are consistent regardless of the rotor position. Because of the near unity saliency ratio, SPM motor designs rely significantly, if not completely, on the magnetic torque component to produce torque.

IPM motors have a permanent magnet embedded into the rotor itself. Unlike their SPM counterparts, the location of the permanent magnets makes IPM motors very mechanically sound, and suitable for operating at very high speeds. These motors also are defined by their relatively high magnetic saliency ratio (Lq > Ld). Due to their magnetic saliency, an IPM motor has the ability to generate torque by taking advantage of both the magnetic and reluctance torque components of the motor.

Advantages Of Rare-earth Permanent Magnet Motors

High efficiency: The efficiency curve of the asynchronous motor generally falls faster under 60% of the rated load, and the efficiency is very low at light load. The efficiency curve of the rare earth permanent magnet motor is high and flat, and it is in the high-efficiency area at 20%~120% of the rated load.

High power factor: The measured value of the power factor of the rare earth permanent magnet synchronous motor is close to the limit value of 1.0. The power factor curve is as high and flat as the efficiency curve. The power factor is high. Low-voltage reactive power compensation is not required and the power distribution system capacity is fully utilized.

Stator current is small: The rotor has no excitation current, the reactive power is reduced, and the stator current is significantly reduced. Compared with the asynchronous motor of the same capacity, the stator current value can be reduced by 30% to 50%. At the same time, because the stator current is greatly reduced, the motor temperature rise is reduced, and the bearing grease and bearing life are extended.

High out-of-step torque and pull-in torque: Rare earth permanent magnet synchronous motors have higher out-of-step torque and pull-in torque, which makes the motor have higher load capacity and can be smoothly pulled into synchronization.

Disadvantages Of Rare-earth Permanent Magnet Motors

High cost: Compared with the asynchronous motor of the same specification, the air gap between the stator and the rotor is smaller, and the processing accuracy of each component is high; the rotor structure is more complicated and the price of rare earth magnetic steel material is high; therefore, the motor manufacturing cost is high, which is common for asynchronous motors About 2 times.

Large impact at full power start: When starting at full pressure, the synchronous speed can be drawn in a very short time. The mechanical shock is large. The starting current is more than 10 times the rated current. The impact on the power supply system is large, requiring a large capacity of the power supply system.

Rare-earth magnet steel is easy to demagnetize: When the permanent magnet material is subjected to vibration, high temperature,  and overload current, its magnetic permeability may decrease, or the demagnetization phenomenon occurs, which reduces the performance of the permanent magnet motor.

What factors need to be considered when choosing a permanent magnet motor?

① Consider Your Application Requirements

The first step in choosing a neodymium magnet motor is to consider your application requirements. What power output do you need? What speed and torque requirements does your application have? Answering these questions will help you narrow down your options and choose a motor that will work for your specific application.

② Cost

Of course, the cost is always a factor when making any purchase—and that includes choosing a motor. Permanent magnet motors can range in price from a few hundred dollars to several thousand. Make sure to compare prices from different suppliers before making your decision. But also keep in mind that sometimes, you get what you pay for. So don't choose the cheapest option without doing your research first.

③ Size/Weight

The size and weight of the motor will be determined by your power requirements and the application in which it will be used. If space is at a premium, then you'll need to factor that into your decision-making process.

④ Maintenance

Neodymium magnet motors are generally very low maintenance, but it's still important to consider how easy or difficult it will be to perform routine maintenance tasks like oil changes and brake repairs.

⑤ Efficiency Requirements

Efficiency is another important consideration when choosing a PM motor. Motors with higher efficiency ratings will use less energy, which can save you money in the long run. When comparing efficiency ratings, be sure to compare apples to apples by looking at motors that are the same size and have similar power outputs.

⑥ Durability

Permanent magnet motors are designed for long-term use, but some models are more durable than others. If your application is particularly demanding, then you'll need to make sure that you choose a motor that can stand up to the rigors of your specific application.

⑦ Mounting Options

How will the motor be mounted? Some motors come with multiple mounting options while others are limited to just one or two possibilities. You'll need to make sure that the motor you choose can be mounted in the way that's required for your application.

⑧ Pick the Right Supplier

Finally, make sure you pick the right supplier. Working with a reputable supplier who has experience in designing and manufacturing PM motors will help ensure that you get a quality product that meets your specific needs.