Modular Multilevel Converter DC-DC Assembly for HVDC Interconnection
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Solution Overview
Problem
Current methods for connecting high voltage DC power transmission networks require large, heavy, and costly high power transformers, which are unsuitable for many installation locations and not commercially available on a large scale, especially when operating at higher frequencies.
Innovation Solution
A DC to DC converter assembly using modular multilevel converters with switchable modules to vary voltage and current ratios, eliminating the need for a high power transformer by synthesizing alternating voltages and controlling power balance between networks, and incorporating series inductance for reactive power management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high power transformer is used to connect DC power transmission networks, then power transmission between networks is enabled, but the system becomes large, heavy, and costly
Solution Approach 1:
The invention divides the power conversion function into multiple modular multilevel converter units, each handling a portion of the power transmission task. This segmentation eliminates the need for a single large transformer while distributing the power conversion function across multiple smaller, manageable modules that can operate in parallel
Solution Approach 2:
The invention replaces the mechanical transformer system with an electronic power conversion system using modular multilevel converters. These converters use semiconductor switches and control electronics to transform power between different voltage levels, substituting the electromagnetic transformation mechanism of transformers with an electronically controlled conversion process
2Power
If conventional voltage converters operating at 50 or 60Hz are used, then power transmission is achieved, but the transformer and passive energy storage elements become very large and heavy
Solution Approach 1:
The invention changes the operating frequency parameter from conventional 50 or 60Hz to much higher frequencies, enabling the use of smaller passive energy storage elements and reducing the volume of transformer components while maintaining power transmission capability
Solution Approach 2:
The invention employs dynamically controllable modular converter units that can adjust their operation in real-time, allowing flexible power transmission at variable frequencies and enabling optimized performance that adapts to different operating conditions
3Speed
If high power high frequency transformers are used, then power transmission at higher frequencies is enabled, but the components become costly and are not commercially available on a large scale
Solution Approach 1:
The invention segments the high frequency power transmission function into multiple standardised modular converter units, each handling a fraction of the total power. This allows the use of commercially available high frequency converter modules rather than requiring custom-built high power high frequency transformers
Solution Approach 2:
The invention creates a universal modular converter design that can be replicated and scaled to meet different power transmission requirements. The same standardised module design can be used across multiple installations, improving commercial availability and reducing costs through economies of scale
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
The solution allows for efficient and flexible connection of high voltage DC networks without the need for high power transformers, resulting in a smaller, lighter, and less expensive system that can handle varying voltage levels and prevent fault propagation between networks.
Implementation Method 1
each converter including a first converter limb extending between the first and second terminals and having first and second limb portions separated by a third terminal of the converter, each limb portion including a least one module switchable to selectively provide a voltage source and thereby vary the ratio of magnitude of a DC voltage across the first and second terminals of a respective converter and a magnitude of an AC voltage synthesised at the third terminal of the corresponding converter
Implementation Method 2
The first link includes a series inductance
Data Source
Figure 1~2
Figure 3~4(d)
Figure 5~6
AI summary
A DC to DC converter assembly, for connecting first and second high voltage DC power transmission networks, comprising first and second modular multilevel converters, each converter including a first converter limb having first and second limb portions, each limb portion including a least one module switchable to selectively provide a voltage source and thereby vary the magnitude ratio of a DC voltage (V1, V2 ) across the first and second terminals of a respective converter and an AC voltage (VAC) at the third terminal, the DC to DC converter assembly further including a first link electrically connecting the third terminal of one converter, with the third terminal of the other converter, and at least one converter further including a controller configured to switch the first and second limb portions in the first converter limb of the said converter into simultaneous conduction to divert a portion (IDiV1) of current flowing within the said converter away from the first link.