Three-Phase Solid-State Transformer Using Isolated DC-DC Converters
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Solution Overview
Problem
Solid-state transformers (SSTs) require multiple power electronic conversion stages, which increase component count, cost, and reduce reliability due to the need for rectification, DC-DC conversion, and inversion.
Innovation Solution
An AC-AC solid-state transformer design utilizing three-phase DC-DC converters with high frequency transformer-based galvanic isolation, where each phase has unipolar input and output voltages, and modules are connected in series or parallel for enhanced voltage or current handling, and employing resonant or soft-switching circuits for efficient switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple power electronic conversion stages (rectification, DC-DC conversion, inversion) are used in SST, then voltage conversion and isolation are achieved, but component count increases and reliability decreases
Solution Approach 1:
The patent combines the rectification and DC-DC conversion functions into a single integrated stage using three-phase bridge rectifiers followed by DC-DC converters with high-frequency transformers. This merging eliminates the need for separate rectification and DC-DC stages, reducing component count while maintaining voltage conversion and isolation capabilities.
Solution Approach 2:
The DC-DC converters with high-frequency transformers perform multiple functions simultaneously: voltage step-up/step-down, galvanic isolation, and impedance matching. This multi-functionality eliminates the need for dedicated separate stages for each function, reducing overall system complexity and component count.
2Power
If multiple power electronic conversion stages are used in SST, then voltage conversion and isolation are achieved, but cost increases due to more components
Solution Approach 1:
The patent merges rectification and DC-DC conversion into integrated stages, reducing the total number of power electronic components required. This consolidation directly lowers material costs, assembly costs, and manufacturing complexity while preserving full voltage conversion capability through the high-frequency transformer-based DC-DC converters.
Solution Approach 2:
The patent employs high-frequency switching in the DC-DC converters, operating at frequencies significantly higher than the input AC frequency. This parameter change enables the use of smaller, more cost-effective magnetic components and reduces the size of filtering elements, thereby lowering overall manufacturing cost while maintaining effective voltage conversion.
3Reliability
If high frequency transformer-based galvanic isolation is used in DC-DC converters, then isolation and voltage conversion are achieved, but device complexity increases
Solution Approach 1:
The patent divides the power conversion system into modular DC-DC converter units, each containing its own high-frequency transformer for galvanic isolation. This segmentation allows each module to be independently designed, tested, and assembled, reducing overall system complexity while ensuring reliable isolation between input and output circuits.
Solution Approach 2:
The patent employs dynamic high-frequency switching in the DC-DC converters, where switching devices operate at variable high frequencies to achieve precise voltage conversion and maintain galvanic isolation. This dynamic operation enables adaptive control of the transformation ratio and improves regulation while keeping the physical structure relatively simple.
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 design reduces the number of components, lowers costs, and improves reliability by minimizing power electronic stages while maintaining high power density through efficient high frequency transformer isolation and switching techniques.
Implementation Method 1
Each of the DC-DC converters has high frequency transformer-based galvanic isolation between its input DC side and its output DC side
Implementation Method 2
employing resonant or soft-switching circuits for efficient switching
Data Source
AI summary
A three-phase AC solid-state transformer is provided which comprises three DC-DC converters. Each of the DC-DC converters has an internal transformer for galvanic isolation between its input and output sides. Each of the DC-DC converters has unipolar voltage across its input terminals and unipolar voltage across its output terminals. In one embodiment, the positive input terminals of the three DC-DC converters serve respectively as the three AC input terminals of the solid-state transformer and their positive output terminals provide the three phase AC output of the solid-state transformer. The negative input terminals of the three DC-DC converters are connected together to form a first common node, while the negative output terminals are connected together to form a second common node. The first common node has a voltage offset from the neutral of the input AC phases; and the second common node has a voltage offset from the neutral of the output AC phases.