Control of permanent magnet synchronous machines for subsea applications

Medium voltage permanent magnet synchronous motor (PMSM) driven subsea pumps have the potential to improve system efficiency and reliability to lower the operating costs, and reduce the subsea pump module (PM) weight and size. These subsea pumps can be deployed in the well, in a dummy well or on the mudline in a skidded configuration. The higher speeds achieved by such motors, compared to the same size induction machine, allow a wider pump operation envelope, even in high gas volume fractions (GVF) scenarios. Applying rotor oriented sensorless vector control (SVC) requires considering the influence of output filters, long power cables and, in some cases, the presence of one or two transformers between the motor and the drive. These additional components create difficulties to estimate the initial position of the rotor at starting. In addition, SVC is very sensitive to parameter variations. This paper presents simulations and experimental results of a robust sensorless control strategy for PMSM, called voltage vector control (V
²
C), for high-power subsea pumps. A low voltage prototype insulated-gate bipolar transistor (IGBT) inverter is used in a neutral point clamped (NPC) topology for feeding a 5.8-KW PMSM. These preliminary investigations were performed using a reduced scale prototype with the aim being to expand the control concept to the medium voltage system.