Subsea DC Power Distribution Using Thyristor Converters
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Solution Overview
Problem
Conventional subsea power transmission and distribution systems face challenges with reactive current generation in long offshore distances, leading to reduced active power transfer capability, and require large and costly AC filters and transformers, which are impractical for deep-water applications.
Innovation Solution
A power transmission and distribution system utilizing a primary DC transmission cable with DC/DC converter modules in subsea power distribution units (SPDUs) to connect onshore AC power to subsea electrical loads, eliminating the need for line-frequency transformers and AC filters, and allowing for modular, compact, and efficient power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If AC transmission cables are used for long offshore distances, then power can be transmitted to subsea loads, but reactive current generation significantly reduces active power transfer capability
Solution Approach 1:
The patent changes the fundamental parameter of power transmission from AC to DC. By converting AC power to DC power for subsea transmission, the system eliminates reactive current generation entirely, as DC cables do not exhibit capacitance effects that cause reactive power flow. This parameter change enables long-distance power transmission without the active power loss that plagues AC systems over 100 km offshore distances.
2Ease of operation
If VSC converters with PWM strategy are used in HVDC systems, then decoupled active and reactive power controls are achieved, but high switching losses limit the switching frequency
Solution Approach 1:
The patent extracts and eliminates the PWM switching stage from the power conversion system. By using phase-controlled rectifiers with thyristors instead of PWM-based VSC converters, the system removes the high-frequency switching components that generate excessive losses. This extraction of the PWM stage while retaining power control capability through thyristor phase control significantly reduces switching losses for high power applications.
3Power
If physically large AC filters and line-frequency transformers are used in HVDC systems, then power conversion is achieved, but the converter station size becomes impractically large for deep-water applications
Solution Approach 1:
The patent changes the operating frequency parameter from line-frequency (50/60 Hz) to higher frequencies enabled by thyristor technology. By using phase-controlled rectification at thyristor switching speeds rather than line-frequency transformation, the system eliminates the need for bulky line-frequency transformers and AC filters. This parameter change in operating frequency enables compact converter station design suitable for deep-water subsea applications where space is constrained.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances power transmission efficiency by reducing reactive current issues and physical size constraints, enabling reliable and economic power delivery to deep-water subsea electrical loads without the need for large AC equipment.
Implementation Method 1
a primary subsea power distribution unit (SPDU) having a DC/DC converter module connected between the primary DC transmission cable and a primary DC distribution network
Data Source
AI summary
A power transmission and distribution system suitable for subsea electrical loads includes a primary dc transmission cable connected to an onshore AC/DC converter module that connects the onshore end of the cable to an ac supply network. The subsea end of the cable is connected to a primary subsea power distribution unit and includes a DC/DC converter module having a modular topology with a series of interconnected DC/DC converter units. The DC/DC converter module is connected between the cable and a primary dc distribution network. Secondary dc transmission cables and associated circuit breakers connect the primary subsea power distribution unit to secondary subsea power distribution units that are located near the subsea loads. Each secondary subsea power distribution unit includes a DC/DC converter module having a modular topology with a series of interconnected DC/DC converter units. Respective secondary dc distribution networks supply power to one or more subsea loads.