Line-Start Permanent Magnet Synchronous Motors - LSPMSM
Induction (asynchronous) motors are distinguished by robust construction and line-start capability
(i.e. ability to start from zero rotor speed when fed from a constant amplitude and constant frequency voltage source).
On the other hand, the disadvantages of small rated power induction motors, such as the relatively small efficiency and
power factor, prevent the marketing of induction motors on markets with strict regulations regarding electromotor energy efficiency.
Contrarily, permanent magnet synchronous motors are distinguished by high values of torque per unit current
and high efficiency, especially when compared to small rated power induction motors. The main disadvantage of permanent
magnet synchronous motors is their inability to line-start from zero speed under load. Synchronous motors are therefore
equipped with different position sensors and fed from current controlled voltage converters.
The union of advantages of both types of motors, the squirrel-cage induction motor and the permanent magnet
synchronous motor presents the line-start permanent magnet synchronous motor (also called the hybrid permanent magnet
synchronous motor with a squirrel-cage). The squirrel-cage enables line-starting capability and damping of dynamic
oscillations. This type of motor is capable of line-starting under load; it exhibits higher efficiency and power factor values
when compared to an induction motor with equal dimensions and rated data; also the position sensor is no longer needed. The
higher efficiency of the line-start permanent magnet synchronous motor also means that the motor is operating at lower temperature
at equal load, providing opportunities for increasing the rated power.
The motor manufacturers can penetrate markets with strict regulations regarding electromotor efficiency, by supplying high-efficient
line-start permanent magnet synchronous motors instead of less-efficient induction motors, which are not intended for
heavy starting, e.g. ventilator drives.
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