Implementation and Long-step Sensorless Control of Permanent Magnet Synchronous Machines (pmsm) for Subsea Applications

By design, the operation of a large 3MW permanent magnet motor-driven pump system has the potential to improve system efficiency and reliability to lower operator costs. Subsea electrical system design and motor performance must be predictable and validated prior to deployment. Critical elements of this system include successful remote start-up and step up–step down transformers. A number of different strategies for open loop control systems were analyzed. One of these models is presented in this paper. The model has been recently validated by the test data obtained from a 3.2MW-rated subsea motor-driven pump system at the Sulzer Pumps Ltd. facilities in Leeds, United Kingdom. INTRODUCTION One of the main challenges in using an open loop long-step start-up system consists in the incertitude of the initial position of the permanent magnet rotor relative to the stator’s initial excitation. When step up–step down transformers are used, their sizing, as a function of the starting frequency and the initial motor current consumption, is a key factor in the system optimization design. From a subsea multiphase boosting perspective the permanent magnet motor provides the following advantages: • The larger liquid-filled gap between rotor and stator of a PMSM results in significantly lower drag losses and thus allows operation at higher speeds than a liquid-filled asynchronous machine. This enables multiphase boosting at high rates and high pressure rise. • The torque characteristics of the PMSM, controlled with vector control, is optimally suited for multiphase boosting application as it enables generation of high pressure rise over a wide range of gas void fractions (GVF).