Solid-State Transformer Topology for Lower Insulation Stress
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Solution Overview
Problem
Conventional solid-state transformers face challenges in achieving high power density for higher voltage classes due to the coupling of AC/DC stages, which require large creepage and insulation distances, and are susceptible to phase-to-ground potential issues during AC grid faults.
Innovation Solution
A two-stage solid-state transformer design with a first stage operating at a modulation index higher than 1, decoupling the AC/DC stages, and utilizing a DC bus to reduce insulation requirements, along with a modular structure and advanced grounding schemes to manage voltage differences and faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the cascade H-bridge structure is adopted for MVAC to LVDC conversion, then the transformer volume can be reduced, but the insulation requirements increase due to voltage potential difference between primary and secondary sides
Solution Approach 1:
The patent divides the conventional single-stage transformer into two separate stages: an AC/DC conversion stage and an isolated DC/DC conversion stage. This segmentation allows each stage to operate at optimized voltage levels, with the DC bus isolating the high-voltage AC side from the low-voltage DC side, thereby reducing insulation requirements while maintaining compact transformer design.
Solution Approach 2:
The patent introduces a DC bus as an intermediary component between the AC/DC conversion stage and the isolated DC/DC conversion stage. This DC bus acts as a voltage isolator and energy transfer medium, enabling the system to handle high voltage on the AC side while maintaining lower voltage requirements on the DC side, thus reducing insulation distance requirements.
2Adaptability or versatility
If the AC/DC stage and isolated DC/DC stage are coupled together, then the modular structure achieves good scalability, but the creepage distance and insulation distance increase, reducing power density
Solution Approach 1:
The patent segments the power conversion system into independent AC/DC and DC/DC stages connected through a DC bus. This segmentation enables modular scalability while allowing each stage to be optimized independently, reducing the insulation distance requirements that would otherwise limit power density in coupled configurations.
Solution Approach 2:
The patent changes the operating parameters by introducing a DC bus that operates at a specific voltage level, creating a voltage decoupling effect. This parameter change allows the system to maintain high power density by reducing insulation requirements while preserving the modular architecture's scalability benefits.
3Reliability
If the MFT insulation voltage is increased to handle AC grid faults, then the fault ride-through capability is improved, but the space required for insulation increases, further reducing power density
Solution Approach 1:
The patent segments the fault handling capability into two stages: the AC/DC stage handles AC grid faults with proper grounding, while the DC/DC stage operates independently with reduced insulation requirements. This segmentation allows fault ride-through capability to be achieved without increasing MFT insulation voltage, thereby maintaining compact design and high power density.
Solution Approach 2:
The DC bus serves as an intermediary that isolates the DC/DC stage from AC grid faults. By placing the DC/DC stage after the DC bus, the system achieves fault ride-through capability without requiring the MFT to withstand high fault voltages, thus reducing insulation space requirements.
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 design enhances power density and fault tolerance by reducing insulation voltage needs and enabling efficient fault ride-through capabilities, while maintaining high voltage compatibility.
Implementation Method 1
The first stage is configured to receive an AC power and convert the AC power into a first DC power
Implementation Method 2
a first DC bus...electrically connected to the first DC power
Implementation Method 3
The second stage is electrically connected to the first stage through the first DC bus, and is configured to perform isolated step-down DC/DC conversion on the first DC power to generate a second DC power
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A solid-state transformer (100) is provided. The solid-state transformer (100) includes a first stage (1), a first DC bus (3) and a second stage (2). The first stage (1) is configured to receive an AC power and convert the AC power into a first DC power. The first DC bus (3) is electrically connected to the first DC power. The second stage (2) is electrically connected to the first stage (1) through the first DC bus (3), and is configured to perform isolated step-down DC/DC conversion on the first DC power to generate a second DC power. The first stage (1) is configured to operate at a modulation index (M) higher than 1, and the modulation index (M) is defined by a ratio of twice AC voltage provided by the AC power to voltage across the first DC bus (3).