380V High Power Density Motor

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

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.

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.

Self-sensing versus closed-loop operation

Recent advances in drive technology allow standard ac drives to “self-detect” and track the motor magnet position. A closed-loop system typically uses the z-pulse channel to optimize performance. Through certain routines, the drive knows the exact position of the motor magnet by tracking the A/B channels and correcting for errors with the z-channel. Knowing the exact position of the magnet allows for optimum torque production resulting in optimum efficiency.

Flux weakening/intensifying of PM motors

Flux in a permanent magnet motor is generated by the magnets. The flux field follows a certain path, which can be boosted or opposed. Boosting or intensifying the flux field will allow the motor to temporarily increase torque production. Opposing the flux field will negate the existing magnet field of the motor. The reduced magnet field will limit torque production, but reduce the back-emf voltage. The reduced back-emf voltage frees up the voltage to push the motor to operate at higher output speeds. Both types of operation require additional motor current. The direction of the motor current across the d-axis, provided by the motor controller, determines the desired effect.

The characteristics and advantages of permanent magnet motors:

Motor From the source of excitation can be divided into two categories: permanent magnet motor, and electric excitation motor. A permanent magnet motor is an electric motor that produces an excitation magnetic field from a permanent magnet. The most widely used three-phase asynchronous motors in industry and civil use, such as Y-Series, Y2-Series, YE2-Series, YX3 Series, Series YB, series YB2 series, etc. all belong to electric excitation motors. ENNENG Motor products are ultra-efficient permanent magnet synchronous motors.

Compared with traditional electric excitation motors, permanent magnet motors, especially rare earth permanent magnet motors, have the advantages of simple structure, reliable operation, small size, lightweight, small loss and high efficiency, and flexible and diverse shape and size of the motor. The application is extremely wide, covering almost all areas of aerospace, national defense, industrial and agricultural production, and daily life.

The permanent magnet synchronous motor has the following characteristics:

1. Rated efficiency is 2% to 5% higher than normal asynchronous motors;

2. The efficiency rises rapidly with the increase of the load. When the load changes within the range of 25% to 120%, it maintains high efficiency. The high-efficiency operating range is much higher than that of ordinary asynchronous motors. Light-load, variable-load, and full-load all have significant energy-saving effects;

3. Power factors up to 0.95 and above, no reactive compensation required;

4. The power factor is greatly improved. Compared with asynchronous motors, the running current is reduced by more than 10%. Due to the decrease in operating current and system losses, energy-saving effects of about 1% can be achieved.

5. Low-temperature rise, high power density: 20K lower than three-phase asynchronous motor temperature rise, the design temperature rise is the same and can be made into a smaller volume, saving more effective materials;

6. High starting torque and high overload capacity: according to requirements, it can be designed with high starting torque (3-5 times) and high overload capacity;

7. The variable frequency speed control system is used, which is better in dynamic response and better than that of asynchronous motors.

8. The installation dimensions are the same as the asynchronous motors currently widely used, and the design and selection are very convenient.

9. Due to the increase in power factor, the visual power of the power supply system transformer is greatly reduced, which improves the power supply capacity of the transformer, and can also greatly reduce the cost of the system cable (new project);

10. When the new project is built, all the drive systems use permanent magnet synchronous motors, the project investment is basically the same as the use of asynchronous motors, and the project can continue to obtain energy-saving benefits after the project is put into operation;

In the general industrial sector, the replacement of low-voltage(380/660/1140V) high-efficiency asynchronous motors, the system saves 5% to 30% energy, and the high-voltage(6kV/10kV) high-efficiency asynchronous motors, the system saves 2% to10%.