Control of Permanent Magnet Synchronous Machines for Subsea Applications

Permanent magnet synchronous motor (PMSM)-driven subsea pumps have the potential to lower the operating costs of subsea pumping modules by improving efficiency, enhancing reliability, and by reducing weight and size. The higher operating speed of PMSM compared with an induction motor of similar size allows for a wider operating envelope for the pump, including operation in high gas volume fractions scenarios. In applying rotor-oriented sensorless vector control to the adjustable speed drive (ASD), the influence of output filters, long motor cables, and transformer between the ASD and the motor needs to be considered. These additional components in the motor circuit make it difficult to estimate correct rotor position during starting. In addition, sensorless vector control is very sensitive to parameter variations. This paper presents simulations and experimental results of a robust sensorless vector control strategy, called voltage vector control for a PMSM driving a high-power subsea pump. The test inverter was a low-voltage insulated-gate bipolar transistor inverter with neutral point clamped topology. This inverter was used driving a PMSM for testing of the control strategy, with an aim of expanding this concept to medium-voltage ASDs.