In industrial and commercial applications, most pumps and fans are driven by AC induction motors. An “AC induction motor” is an asynchronous motor that relies on electric current to rotate the rotor. The torque is generated by the current in the rotor. The current is generated by the magnetic field of the stator winding through electromagnetic induction. The rotor always rotates at a speed lower than the magnetic field.The "permanent magnet synchronous motor" relies on a magnet to rotate the rotor, and the speed of the rotor is the same as the speed of the internal rotating magnetic field of the permanent magnet synchronous motor.
Permanent magnet motors must use drives: AC induction motors can drive pumps or fans without frequency conversion drives. Frequency conversion drives are usually installed in the pump system or fan system to improve system efficiency.Permanent magnet synchronous motors require a drive to work and cannot operate without a drive.In order to accurately control the speed of the permanent magnet synchronous motor to meet the application requirements of pressure, flow, volume, etc., a frequency converter is required.Some new frequency converters are already equipped with permanent magnet motor control options as a standard function, allowing the operator to control the permanent magnet motor to drive the fan and/or pump, which is more efficient.Compared with AC induction motors, permanent magnet motors can significantly improve efficiency. The full load efficiency of permanent magnet motors is higher than that of AC induction motors. The efficiency range between the two standards of AC induction motors and permanent magnet motors is shown below.
Variable frequency drives will not improve motor efficiency. Variable frequency drives help to improve system efficiency within the operating speed range, because most systems will not always run at the highest speed.Variable frequency drives help improve system efficiency because they have the ability to reduce the speed of the motor, fan, or pump, rather than turning the valve to throttle the pump or closing the damper to prevent air flow.
Advantages and disadvantages of permanent magnet motors: Although AC induction motors are more common in motor drive systems, they are usually larger and less efficient than permanent magnet motor solutions.Although permanent magnet motor solutions tend to have a higher initial cost, they can provide a smaller size for a more compact mechanical package and, more importantly, provide higher efficiency.Permanent magnet motors are often more expensive than AC induction motors and more difficult to start than AC induction motors.However, the advantages of permanent magnet motors include higher efficiency, smaller size (permanent magnet motors can reach one-third of the size of most AC motors, which makes installation and maintenance much easier), and the ability to maintain full torque at low speeds.
The trend is changing: the combination of permanent magnet motors and variable frequency drives is not brand new. Design engineers and equipment owners are beginning to choose more permanent magnet motor solutions for fan and pump application installation because they are smaller and more efficient. Variable frequency drives require a special algorithm to drive permanent magnet motors.Now, there are some new frequency conversion drives on the market, they have a built-in standard feature to control permanent magnet motors without additional costs.As more and more manufacturers of variable frequency drives begin to increase the high-performance control functions of permanent magnet motors, users will tend to install motor systems with higher operating efficiency, smaller packages, and lower costs.
