WHY IS THE DEMAND RISING FOR PERMANENT MAGNET AC PMAC MOTORS?

“How do we use energy?” while continuing to ask questions such as “Is this energy being used wisely?” As we seek answers to the question, we see increasing government regulation focusing on reducing the burden on existing infrastructure, lower fossil fuel emissions, and advances in materials and electronics. All these factors lead to increased demand for Permanent Magnet AC PMAC motors.

PMAC Motors Vs. What is the Difference Between AC Induction Motors?

When comparing PMAC motors to AC induction motors, there is a big difference in the rotor itself. In a squirrel-cage induction motor, current is induced from the field (stator) through the air gap to the rotor and is transmitted via rods of aluminum (or other material) often cast in the slots of the rotor laminations. In a PMAC motor, on the other hand, the rotor itself contains permanent magnet material that is either surface-mounted in the rotor lamination stack or embedded within the rotor laminations. In both topologies, the electrical power is supplied through the stator windings.

The most obvious performance difference is that a PMAC motor rotates at the same speed as the magnetic field produced by its stator windings, so it is a synchronous machine. If the field "spins" at 1800 rpm, the rotor spins at the same speed. An induction motor, on the other hand, is considered an asynchronous machine. The rotation speed is slightly slower than the "speed" of the magnetic field. An asynchronous motor is said to have slip. This slip is, for example, the difference between the physical speed of the motor at 1750 rpm and the magnetic speed of its stator at 1800 rpm. Because the rotor is constantly trying to "capture" the magnetic field, it cannot generate torque without this speed difference. The synchronization of PMAC motors results in improved efficiency, better dynamic performance and more precise speed control.

Other performance differences include higher efficiency and power factor in a PMAC motor. Since there are no conductors (rotor rods) in a permanent magnet rotor, there is no loss of I2R, so all other things being equal, a PMAC motor is inherently more efficient.

PMAC motors provide higher flux density than a comparable induction motor. This means that more power (torque) can be produced in a given physical size or equal torque in a smaller package. Frame size reduction is very common in PMAC motors.

While there is ongoing research into a "line-start PM" motor, all true PMAC motors available on the market require a variable frequency drive to operate. This design has performance characteristics to consider.

Comparison of PMAC and Induction Motors:

Benefits of PMAC Motors:

Due to lower operating temperatures, reduced vibration and noise, and improved reliability, PMAC motors provide benefits such as energy savings, lower operating temperature, reduced vibration, reduced noise, improved reliability and application flexibility.

Energy-saving

PMAC motors are inherently more efficient due to elimination of rotor conductor losses, lower resistance winding and a flatter efficiency curve. PMAC motors are known to save even more energy at low speed.

Efficiency ratings save electrical energy from day one. This means 10-30% less loss than a conventional engine and provides a fast return on investment. Since electricity is estimated to constitute about 95-97% of the total life cycle cost of electric motors; this energy savings significantly reduces the total investment.

Reliability and Longevity

Due to their lower operating temperatures, PMAC motors require less maintenance and offer longer bearing and insulation life. The engine's rugged construction is suitable for virtually any application and ensures years of trouble-free operation in harsh environments.

Application Flexibility

In most cases, replacing existing induction motors with PMAC motors does not require any mechanical changes to the equipment. Almost any application suitable for the use of asynchronous motors can use PMAC motors by replacing existing motors.

TRANSFER CARTS & AGV'S