A Current Observer to Reduce the Sensor Count in Three-Phase PM Synchronous Machine Drives

Reduced sensor systems are a topic receiving increasing attention as manufacturers seek to reduce costs by removing components from systems. One popular option is to remove phase current sensors and to estimate the missing currents using the ones remaining. This paper proves that it is possible to estimate the three-phase currents of an anisotropic permanent-magnet synchronous machine drive when only one-phase current sensor is present. The necessary conditions for observability and stability have been derived, providing certainty for the design of a permanent-magnet synchronous machine drive controller. The concept has been verified with high-fidelity simulations and experiments that show the one-phase current sensor observer is capable of controlling the drive system in the presence of sensor noise and significant parameter errors. The proposed phase current observer can be used to remove one sensor from a drive system by employing the two sensor observer with the one sensor observer acting as a failsafe.