Sensorless control for galvanically isolated PMSM submersible pumps

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Recently, there has been significant interest in the ability to recover oil with reduced energy requirements. One option to improve the efficiency of conventional oil recovery is the use of permanent magnet synchronous motors (PMSM) in downhole pumps. Above ground, control algorithms for PMSM typically require the use of encoders or observer-based sensorless control algorithms. PMSM sensorless control typically requires one of high frequency signal injection, harmonic identification or back-emf detection methods. In submersible downhole applications, the drive motor can be a significant distance from the variable speed drive on the surface; the output of the drive must be filtered and pass through an isolation step-up transformer before connecting to the motor cable. Unfortunately, existing PMSM control methods do not work in this case.