Commissioning of Off-Shore Gas Compressor with 9-Axes Magnetic Bearing System: Controller Design

This paper presents the system model, model validation, controller design and test measurements for an industrial 9-axes oil-free integrated motor-compressor (tandem HOFIM(TM)) manufactured by MAN Diesel & Turbo (MAN) to be installed off-shore on an oil rig. The magnetic bearing controller of such machines must be designed with high robustness due to large expected uncertainties in the control plant. In addition, the magnetic bearings must have a high force slew rate, and thus a high dynamic controller, since compressor surge that causes high alternating process forces cannot always be avoided in field operation. These two requirements are conflicting and it is a difficult task to find a good compromise. This paper presents an application of robust controller design and a solution to this problem: the LQG/LTR method, well described in literature, is applied for the design of the position controller. Using the proposed method, the compressor was successfully commissioned at the MAN test facility and all specifications were met.