Abstract
The transition towards low-emission offshore oil and gas platforms (OOGPs) is accelerating with the increasing penetration of converter-interfaced devices such as offshore wind turbines and battery energy storage systems (BESS). Offshore platforms present unique challenges in power quality due to their isolated operation, which leads to weak grid conditions, further compounded by the integration of intermittent offshore wind. This thesis investigates the role of power electronic converter-interfaced devices, in enhancing power quality and delivering grid support services including voltage regulation, reactive power support and harmonic mitigation, all within the constraints and standards applied to offshore environments.
Conducted within the framework of the Smart Platform project, this work supports the broader goal of reducing greenhouse gas emissions and improving energy efficiency through coordinated integration of renewable energy and energy storage systems.
First, the thesis addresses voltage disturbances and possible voltage instability on OOGP during direct-on-line heavy induction motor starting and transformer energization. This is achieved using a BESS configured to also provide reactive power support along with active power services via its power conversion system, collectively referred to as a BESS-STATCOM. Cooperative control strategies are first developed between the BESS-STATCOM and offshore wind turbines to provide support during voltage sag events and reduce wind power curtailment, followed by a method to maximize the BESSSTATCOM’s reactive power capability.
Second, the problem of harmonic distortion from non-linear loads is tackled through two retrofit solutions: a multi-functional active front-end converter and an optimally sized shunt active power filter (SAPF). A design methodology considering load-side impedance is proposed to minimize SAPF rating while achieving effective harmonic suppression.
Finally, experimental validation is carried out using a Power Hardware-inthe-Loop (PHIL) test bed, where a scaled-down converter (SDC) is interfaced with a real-time simulator via a high-bandwidth power amplifier. The realtime simulator emulates the OOGP electrical power system, while the SDC physically represents the converter-interfaced device executing the proposed control algorithms under test. Through appropriate scaling, the SDC is made to represent the behavior of a full-scale converter (FSC), allowing the realtime model to interact as if it were connected to the actual full-scale device. A key challenge encountered in PHIL testing is the mismatch of passive elements between the SDC and the FSC. To overcome this, two novel scaling methods are proposed. The first method ensures that the SDC accurately replicates the entire active and reactive power capabilities of the FSC. The second method preserves the harmonic signatures up to the switching frequency, despite differences in impedance and switching frequency between the scaled-down and the full-scale converter. These two methods enable accurate emulation of the FSC and its interaction with OOGP’s power system in PHIL tests.
Together, this research demonstrates that enhanced power quality in lowemission OOGPs is achievable through proposed control stategies utilising converter-interfaced devices. The proposed strategies support efficient and reliable operation of low-emission OOGPs and may serve as a reference for future 100% renewable powered, autonomous offshore energy systems.