Subsea Variable Speed Drive with Capacitor-less DC Link
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Solution Overview
Problem
Existing Variable Speed Drives for subsea installations, vessels, and vehicles face constructional challenges due to pressure sensitivity of capacitors, requiring thick housings, complex pressure compensation, and cooling systems, which increase space and material usage.
Innovation Solution
A Variable Speed Drive with a current-controlled capacitor-less DC link and a liquid-tight housing filled with an electrically isolating liquid, which reduces the need for pressure compensation and simplifies the design, allowing the converter to withstand external pressure and efficiently dissipate heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common voltage-controlled AC/AC converters with capacitors are used in subsea applications, then the converter can provide voltage control and power conversion, but the capacitors are sensitive to environment pressure requiring thick walls and complex pressure compensation
Solution Approach 1:
The patent removes the capacitor component from the converter circuit, replacing the traditional voltage-controlled AC/AC converter with a current-controlled AC/AC converter that uses an inductor instead. This extraction of the pressure-sensitive capacitor eliminates the need for complex pressure compensation measures and thick housing walls, directly resolving the technical contradiction between converter reliability and housing construction complexity in subsea applications
Solution Approach 2:
The patent changes the control parameter of the converter from voltage control to current control. This parameter change fundamentally alters the converter's operating characteristics, allowing the use of an inductor-based DC link instead of a capacitor-based DC link, thereby eliminating pressure sensitivity and the associated complex housing requirements
2Reliability
If pressure compensation with internal air pressure is implemented, then capacitors can operate at standard pressure, but the housing requires thick walls and support rods taking much space
Solution Approach 1:
The patent removes the capacitor from the converter circuit, which eliminates the need for pressure compensation systems entirely. Without capacitors, there is no need to maintain internal air pressure at standard levels, allowing the housing to be designed with thinner walls and reduced volume while still protecting the pressure-insensitive inductor-based converter
3Reliability
If the converter is placed in a pressure-resistant housing, then the converter is protected from subsea pressure, but the housing requires complex sealing and penetrators for electrical connections
Solution Approach 1:
The patent removes the capacitor and replaces it with an inductor-based DC link, making the converter inherently insensitive to pressure changes. This allows the housing to be designed with simpler sealing systems and penetrators, as the converter components can withstand external pressure directly without requiring complex pressure equalization or isolation mechanisms
4Strength
If a pressure-resistant housing with thick walls is used, then the converter withstood subsea pressure, but the housing has high heat capacity making heat dissipation difficult
Solution Approach 1:
The patent removes the capacitor and adopts a current-controlled converter design with inductor-based DC link, which generates less waste heat and allows for more efficient thermal management. The simplified converter design enables better integration with cooling systems and reduces the thermal mass issue associated with thick-walled pressure-resistant housings
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 results in a compact, lightweight, and reliable Variable Speed Drive with reduced construction complexity, simpler sealing requirements, and a lower probability of failure, enabling efficient operation in deep-sea environments.
Implementation Method 1
the liquid can serve as a coolant for dissipating waste heat from the converter circuits to the outside of the housing
Implementation Method 2
As liquids are nearly incompressible the liquid serves for supporting the housing on all sides against any external pressure
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a Variable Speed Drive (1) for subsea installations (20), subsea vessels or subsea vehicles, as well as to a corresponding subsea installation (20), subsea vessel or subsea vehicle, comprising an alternating current /alternating current converter (2) having a current - controlled capacitor- less direct current link (7).