Advancement of power conversion technologies for decarbonizing drilling rig operations in oil and gas industries

• Illustrating the evolution of drilling rig energy systems with steam-powered, hybrid and electric rigs. • Analyzing the energy system scenarios: hybrid, diesel-mechanical, diesel-electric, efficiency and sustainability-oriented systems. • Evaluate recent significant innovations, including signal-feedback power management, digital twin technology and high-efficiency energy conversion. • To distinguish different aspects of regenerative energy capture, such as waste heat recovery, regenerative braking and carbon capture and storage (CCS). • Evaluate how the drilling rigs are incorporating renewable energy sources such as solar, wind, hydrogen, geothermal and microgrid systems. • Identify potential themes and areas of future study, including economics, regulatory changes, and highly efficient regenerative energy storage technologies for the green transition. The power systems of drilling rigs have changed considerably since the early days of steam driven machinery. This paper reviews that progression, from mechanical and diesel electric configurations through to modern hybrid and renewable integrated systems, with a focus on the power conversion technologies that enable each stage. Coverage includes the electrical architecture of drilling rig power systems with rectifier and inverter topologies, variable frequency drive control schemes (V/f, field oriented control, direct torque control), and energy management strategies (deterministic, rule based, and optimization based). Digital technologies such as AI driven power load management and digital twin platforms are examined in terms of their effect on fuel consumption and load coordination. Regenerative energy capture through drawworks braking (recovering 50 to 150 kWh per cycle depending on string weight and depth) and waste heat recovery using organic Rankine cycles are also treated in detail. On the decarbonization side, renewable energy integration (solar, wind, hydrogen fuel cells), carbon capture and storage at the rig level, and the policy milestones that have shaped industry adoption are reviewed. Reported performance data from the literatures indicate that VFD integration can improve energy efficiency by 30 to 40%, hybrid systems including diesel and battery energy storage systems can reduce CO₂ emissions by 20 to 25%, and optimization based energy management strategies can deliver fuel savings of 15 to 30%. Though these figures originate from different studies with varying baselines and operating conditions, open challenges include the cost and scalability of battery storage for offshore rigs, the immaturity of DC protection systems for HVDC distribution, and the limited transferability of AI training data across geologically different drilling sites. Future research directions point toward standardized benchmarking protocols for rig energy management, field validation of AI power control under real drilling transients, and techno economic optimization of hydrogen storage for mobile drilling units.