7 Position Measurement

It is important to know the accurate rotor position for the FOC to work properly. An incremental optical encoder provides two pulse trains which are in quadrature with each other as shown in the following figures. Some encoders have an index pulse which helps in finding the precise rotor position spatially. If the pulse train A leads the pulse train B, the motor would be rotating in one direction, and if the pulse train B leads the pulse train A, the motor would be rotating in the opposite direction. The larger the number of encoder pulses, higher is the precision of position measurement.

Figure 7-1. Encoder Phase Signals and Index Pulse for certain Direction of Rotation

Figure 7-2. Encoder Phase Signals and Index Pulse for Opposite Direction of Rotation

Microchip Technology’s 32-bit MCUs provide position decoders to obtain the exact position and speed from speed sensors, such as incremental encoders, hall sensors, resolvers etc.