AC-DC-AC Converter for Subsea Pipeline Heating
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Solution Overview
Problem
Conventional direct electrical heating (DEH) systems for subsea pipelines face challenges such as complex fine tuning, high short circuit levels, and the need for a transformer with tapping capabilities, which can be hazardous and limit flexibility in power adjustment.
Innovation Solution
A power electronic circuit with AC-DC-AC converter cells is used to provide an AC current to the pipeline, allowing for symmetrical load management across three phases without a transformer with tapping capabilities, reducing short circuit risks and enabling flexible power control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional transformer with balancing circuit is used to provide single phase AC current for direct electrical heating, then the heating function is achieved, but the circuit requires complex fine tuning during commissioning and has high short circuit levels
Solution Approach 1:
The patent replaces the conventional transformer-based mechanical/electromagnetic system with a power electronic converter system using controllable switches (IGBTs, MOSFETs, or thyristors). This substitution eliminates the need for complex balancing circuits and fine-tuning, while providing precise control over output current and frequency for reliable pipeline heating.
Solution Approach 2:
The invention changes the operating parameters by using pulse-width modulation (PWM) or phase-angle control to regulate the output current magnitude and frequency. This allows dynamic adjustment of heating power without mechanical transformers or complex balancing circuits, reducing both device complexity and short circuit levels while maintaining heating reliability.
2Adaptability or versatility
If a transformer with tapping is used to change heating power, then power adjustment is possible, but the transformer becomes more complex and requires higher short circuit levels
Solution Approach 1:
The patent implements dynamic power adjustment through controllable switches that can be rapidly switched on and off to vary the effective output power. This electronic control mechanism replaces static transformer tapings, enabling continuous power adjustment without mechanical complexity or high short circuit requirements.
Solution Approach 2:
The invention substitutes mechanical transformer tapings with electronic control circuits using controllable switches and modulation techniques. This replacement eliminates the need for physical transformer complexity while maintaining full adaptability for heating power adjustment through electronic parameter control.
3Ease of operation
If a conventional transformer system is used for direct electrical heating, then single phase power supply is provided, but high short circuit levels are seen at the single phase source terminals
Solution Approach 1:
The patent replaces the transformer-based system with a power electronic converter that inherently limits short circuit currents through the controlled switching characteristics of the controllable switches. This substitution maintains single-phase output capability while eliminating the high short circuit levels that pose damage risks to pipelines.
Solution Approach 2:
The invention applies preliminary protective action by using controllable switches that can detect and respond to short circuit conditions, rapidly disconnecting the load before damage occurs. The control circuitry monitors current levels and preemptively takes protective action, preventing the high short circuit levels from causing pipeline damage.
4Device complexity
If grid frequency is used for heating, then simple power supply is required, but heating efficiency is limited and no frequency adjustment is possible
Solution Approach 1:
The patent changes the frequency parameter by using controllable switches to generate output frequencies different from the grid frequency. This frequency adjustment capability optimizes heating efficiency for different pipeline conditions and lengths, while the power electronic converter maintains relative simplicity through standard electronic components and control algorithms.
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 simplifies the transformer design, reduces short circuit levels, and enhances heating efficiency by allowing frequency adjustment of the AC voltage, improving the overall efficiency and safety of the pipeline heating process.
Implementation Method 1
a first AC-DC-AC converter cell (133) having two converter input terminals (111, 113) connected to at least two transformer output terminals (111, 113), the converter cell having a first converter output terminal (135) and a second converter output terminal (137)
Implementation Method 2
providing an AC current (alternating electrical current) to a load (e.g., a pipe, a pipe system, a tube for transporting oil or gas) for direct electrical heating (e.g., of the pipe)
Data Source
AI summary
An arrangement provides an AC current to a load for direct electrical heating. The arrangement includes a AC-DC-AC converter cell. The converter cell has at least two converter input terminals connected to at least two transformer output terminals. The converter cell has a first converter output terminal and a second converter output terminal, wherein the first converter cell output terminal is adapted to be connected to the load.