Nonlinear control of a pressurised water supply driven by a permanent magnet synchronous motor

In this paper, a flatness-based multivariable control of a permanent magnet synchronous motor (PMSM) as the main drive of a pressurised water supply system is presented. The fluidic subsystem consists of a pump and a storage volume connected to the high pressure side. The pump has to provide the supply volume flow into the storage volume, whereas the drain volume flow is considered as a disturbance. Based on a nonlinear mathematical model of the PMSM in a rotor-fixed coordinate system and the attached fluidic system, a nonlinear tracking control strategy is proposed. Here, the differential flatness of the model with the d-current of the rotor and the storage pressure as flat outputs can be exploited to derive a combined feedforward and feedback control strategy. The coupling torque between the PMSM and the pump follows from an analysis of the fluidic circuit. The disturbance torque acting on the pump is determined by a nonlinear reduced-order observer and can be used in a compensation strategy to improve the tracking behaviour of the electric drive. Simulations point out the effectiveness and the excellent tracking properties of the proposed control structure.