Abstract
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 integrated with the LFAC subsea system to fulfill the compatibility requirements of the system. The control system of both the grid side and the machine-side inverter of the wind farm is designed to eliminate the real-time disturbances such as wind speed fluctuations and harmonics due to heavy inductive load operating at 16 Hz. To drive the subsea pump, a vector control-based variable-speed drive is employed for the heavy induction motor. A 5 MW, 16 Hz RL load is also added in the model to analyze the effect of general-purpose load. Each component of this system is carefully designed to make it as close to real-time as possible. The whole system is designed for 16 Hz and is compared with the standard 50 Hz system to validate this design.
Highlights
There is an increasing demand for deep-water oil and gas production due to the depletion of existing oil and gas reserves
The system consists of several parts, including a hexverter, harmonics from the high inductive load at the low-frequency AC transmission (LFAC) and the resonance effect in long subsea cables, the which contains a novel control strategy for optimizing its zero-sequence circulating current, subsea obtained results were so close to reality that the desired voltage and power were successfully delivered power transmission and distribution through subsea cables, a 20 MW offshore wind farm integrated to the load
The simulation model of the LFAC-based subsea transmission and distribution system was successfully implemented in this work
Summary
There is an increasing demand for deep-water oil and gas production due to the depletion of existing oil and gas reserves. A 20 MW wind farm is integrated into the system to make the power rating of the system compatible with the same frequency, i.e., 16 Hz. Details of hexverter control, VSD control and transmission line parameters along with motor specifications are discussed . A lot of work has been done on offshore wind farm integration with LFAC and FFT systems interim of inverter control, converter control for the resonance contingency of long transmission lines and harmonics problem in inverters [17,18,19,20]. For driving the pump and compressors, high-power subsea motors are employed These motors are driven by the variable speed drive using the vector control method, and an RL load for the general-purpose undersea applications (e.g., lighting, heating and maintenance, etc.) is used.
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