Model Predictive Anti-Surge Control of Centrifugal Compressors with Variable-Speed Drives

In this article torque assisted anti-surge control (TASC), a compressor anti-surge control system based on model predictive control (MPC) is presented. TASC is implemented on an embedded system for the control of compressor stations with electrical variable-speed drives (VSD) which are used in applications such as natural gas transportation via pipelines. The manipulated variables of the proposed advanced controller are the electric motor torque and the position of a recycle valve, whereas the measured quantities are the same as those of a typical compressor control application including the pressure ratio and the gas flow. The TASC scheme uses the linear approximation of a nonlinear dynamic model to predict the behavior of the compression system. The information contained in the compressor map is incorporated into the nonlinear model as a 3rd order polynomial approximation. The surge line is taken into account as a constraint in the MPC formulation. Control action is calculated by solving an optimization problem in real-time at the control unit level with cycle times as low as 20 ms. The potential benefits of the proposed control strategy are evaluated in a simulation scenario corresponding to a potential deep surge event typically used in anti-surge control validation exercises. The simulations are carried out in a hardware-in-the-loop setting. In the evaluation, the performance of TASC is compared to a conventional anti-surge control approach. Due to the predictive capability and the manipulation of the motor torque, TASC is observed to achieve a safer and more efficient operation of the compressor station.