Embedded Magnetic Absolute Encoder in SPMSM with Permanent Magnets of Different Magnetic Flux Densities

Surface-mounted permanent magnet synchronous motors (SPMSMs) are used in various fields because of their high efficiency and high power density characteristics. Because they are generally driven by vector control, a type of current control, the position of the rotor must be detected. Rotor position detection is generally achieved by attaching an encoder or resolver to the exterior of a motor. This inevitably increases the volume and weight of the exterior of a motor. Although sensorless methods are available for determining the rotor position, their detection accuracy is low and it is difficult to acquire stable position information over the entire speed range. An embedded magnetic absolute encoder, which detects the rotor position by observing its magnetic flux, can acquire the rotor position without requiring the need for an external position sensor. However, calculating the absolute angle when two or more SPMSM pole pairs exist is difficult. This study proposes an embedded magnetic absolute encoder in an SPMSM that can calculate absolute angles. The proposed SPMSM enables the calculation of absolute angles using permanent magnets with different magnetic flux densities.