Abstract
This paper proposes a model-based two-degree-of-freedom (2DOF) speed control for a medium voltage (MV) variable speed drive (VSD) connected to a centrifugal compressor (CC) train. Torsional mode excitations in the drive shaft due to converter switching behaviour are considered. An effective description of the harmonics transfer is proposed. The tuning strategy aims to optimize the tracking behaviour of the step and ramp command, taking care of critical speed excitations. The stability of the closed-loop dynamics against time delay and drive parameter variations are studied by means of Nyquist diagrams and time-domain simulations. A descriptive method for the process damping behaviour is proposed. The control strategy is evaluated through simulations as well as an experimental setup, based on a hardware in the loop (HIL) in a master–slave configuration.
Highlights
This paper proposes a model-based two-degree-of-freedom (2DOF) speed control for a medium voltage (MV) variable speed drive (VSD) connected to a centrifugal compressor (CC) train
In the oil and gas industry, voltage source drives (VSDs) are key elements from liquefied natural gas trains to subsea scenarios [1], because they adjust their speed according to the centrifugal compressor (CC) train requirements, maximizing overall efficiency and making them suitable as prime movers [2,3]
This paper presents a case study of an 8 MW industrial application, which consists of a VSD directly connected to a CC train through a coupling shaft
Summary
In the oil and gas industry, voltage source drives (VSDs) are key elements from liquefied natural gas trains to subsea scenarios [1], because they adjust their speed according to the centrifugal compressor (CC) train requirements, maximizing overall efficiency and making them suitable as prime movers [2,3]. Looking to the industrial feasibility of a digital signal processor (DSP), this paper proposes a 2DOF controller, based on classical PI cascade control architecture, with the aim to obtain good reference tracking and load torque rejection for each DOF. We aim to achieve a MV-VSD that follows a CC speed-profile in the presence of TNFs excitation. The selection of this control architecture is due to the necessity of implementing this control on existing industrial controllers without changing the implemented control strategy. Model-based pole placement rules are used to design the feedback controller, and aimed to reject the load torque changes. The case-study analysed in the paper considers a mixed-speed profile and a quadratic load torque, both coming from a high-level CC pressure map.
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