A Modular Subsea Direct-Current Electrical-Power System

IEEE Electrification Magazine, 2019

2000

Power systems for undersea observatories are required to deliver high power with good reliability. For the proposed NEPTUNE observatory, the authors have developed a power scheme that combines ideas from terrestrial power systems and switching power supplies with experience from undersea cable systems. The system is based on a parallel network. This design can be applied to other undersea schemes,

The energy industry is an essential driver for the world economy and global development.

2016 Petroleum and Chemical Industry Conference Europe (PCIC Europe), 2016

Energizing large transformers often cannot be done direct-on-line due to the negative effects of the inrush current. The typical schemes used in the past are energization via a high impedance, or via a tertiary winding connected to an auxiliary AC power source. These schemes require additional equipment resulting in increased foot print and complexity. For offshore and subsea installations, the increase in foot print often greatly exceeds the cost of the additional equipment. This paper presents an alternative solution allowing direct-on-line energization of large transformers, both topsides and subsea. Different solutions for subsea auxiliary AC power supplies not requiring high-voltage circuit-breakers are presented. For offshore and subsea power systems, the circuitbreakers supplying power to the transformers are standard 3.3 kV to 36 kV class devices having a 3-pole operating mechanism. The solution presented allows circuitbreakers to be switched such that the closing of the poles occurs at the point on the voltage waveform where the resulting inrush current is the least. For subsea power distribution systems, the auxiliary power required for the subsea control equipment is provided by a high-voltage DC auxiliary power link from the shore station and the control and communication link is via optical fiber. The solutions presented use standard proven technology and can be integrated within the subsea modules required for supplying power to the loads. This keeps the number of penetrators and subsea connector systems to a minimum. The importance of redundancy and maintenance in obtaining and keeping the required system availability are discussed.

2009

1.0. Introduction 2.0. AC-Link TM technology 3.0. Comparison-AC-Link TM & conventional power conversion technologies 4.0. Functional description of AC-Link TM technology 5.0. AC-Link TM benefits and advantages 10 6. 0. Architecture of AC-Link TM AC-DC conversion 7. 0. Motivation for DC power 8.0. Short-circuit and, overcurrent and overvoltage protection of downstream DC power system and subsystems using AC-Link TM technology 9.0. AC-Link TM converter modularity for medium to high power DC systems 16 10.0 AC-Link TM high frequency transformer-a critical component 11.0. Marine and Offshore EMC Issues 11.1. AC-Link TM technology and EMC 23 12.0. Examples of AC-Link TM applications in marine and offshore sectors 24 12.1. Marine vessels 12.2. Drilling rigs and offshore installations 28 12.3. Offshore oil production platforms 30 12.4. FPSO (floating, production, storage and offloading) vessels 32 13. AC-Link TM derived DC power for marine and offshore VFDs 33 13.1. Examples of AC Link TM applications in the marine and offshore sectors 35 13.1.1. Cutter dredger 35 13.

IEEE Journal of Oceanic Engineering, 2002

Power systems for undersea observatories combine ideas from terrestrial power systems and switching power supplies with experience from undersea cable systems. Basic system tradeoffs for various design decisions are explored in this paper. First, design questions including whether the power delivery should be alternating or direct current and a parallel or series network are examined. This introduces the question of maximum power delivery capability, which is explored in depth. A separate issue, the negative incremental resistance presented to the delivery system by the use of constant-voltage converters, is examined, and the resulting dynamics explored by simulation.

Electronics

Environmental goals set by world leaders to normalize climate changes are quite difficult to achieve without renewable power generation and suitable transmission technologies like low-frequency AC transmission (LFAC). The LFAC is nowadays becoming a popular choice for long-distance power transmission due to its high efficiency and low losses. This research work investigates the feasibility of employing the LFAC system for subsea transmission and distribution of 58 MW power. In this paper, the simulation model of the LFAC-based subsea transmission and distribution system is presented. This model is composed of several parts such as hexverter as a frequency converter, where a novel control strategy to optimize its zero-sequence circulating current is employed. Detailed mathematical modeling based on active, reactive power constraints and DQ transformation is performed to achieve the control strategy for zero-sequence current optimization. An offshore wind farm is proposed to be integr...

Journal of Power Sources, 2008

This paper presents both time-domain and frequency-domain simulated results of a novel marine hybrid renewable-energy power generation/energy storage system (PG/ESS) feeding isolated loads through an high-voltage direct current (HVDC) link. The studied marine PG subsystems comprise both offshore wind turbines and Wells turbines to respectively capture wind energy and wave energy from marine wind and ocean wave. In addition to wind-turbine generators (WTGs) and wave-energy turbine generators (WETGs) employed in the studied system, diesel-engine generators (DEGs) and an aqua electrolyzer (AE) absorbing a part of generated energy from WTGs and WETGs to generate available hydrogen for fuel cells (FCs) are also included in the PG subsystems. The ES subsystems consist of a flywheel energy storage system (FESS) and a compressed air energy storage (CAES) system to balance the required energy in the hybrid PG/ESS. It can be concluded from the simulation results that the proposed hybrid marine PG/ESS feeding isolated loads can stably operate to achieve system power-frequency balance condition.

IEEE Transactions on Industry Applications, 1996

A subsea adjustable-speed motor fed via a long cable in range of several tens of kilometers between the converter and the motor are analyzed by simulations. Due to resonance, one critical frequency range occurs where significant generation of harmonics from the inverter should be avoided. A voltage source inverter is more feasible than a current source inverter since it is easier to modify the output waveform in order to avoid resonance problems. The resistive voltage drop in the long cable reduces the air-gap torque of the motor particular at low frequencies. This causes a problem for the start-up of the motor due to stiction torque. A start-up strategy is envisaged which is a compromise between voltage boost, inverter current, and transformer core dimensions. In normal operation mode the inverter voltage is proportional to the frequency. An open speed loop is used which keeps the system stable for potential load variations. The results from a 1-MW full-scale system test are summaried.