Inverters are power supply devices that control the frequency (Hz) of three-phase induction motors to vary speed continuously. Speed can be controlled by changing frequency because the speed of rotation of induction motors is determined by the number of poles and the frequency. For example, a four-pole induction motor will rotate at a constant speed of 1500 min-1 at a power frequency of 50 Hz or 1800
min-1 at 60 Hz. Here, the speed of the motor can be freely varied, regardless of power
frequency, by installing an inverter between the power supply and the motor.
These new cylindrical linear motor systems were designed to enable driving with the simplest possible system. They can detect position using flux generated by the shaft, so they operate without external position sensors and generate thrust soon after startup without the need for external magnetic pole detectors, since built-in position sensors detect pole positions directly. The drivers also have built-in positioning functions that enable relatively complex positioning operations.