Solid-State Transformer DC Bus Isolation for Flexible EV Charging

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Solution Overview

Problem

Existing DC EV charging stations face challenges in electrical isolation from AC grids and designing power supply systems with varying output voltages to meet different EV charging specifications, particularly in terms of circuit design and cost considerations.

Innovation Solution

A power apparatus and system for solid state transformers (SST) incorporating an AC-to-DC conversion unit, first DC bus, and bi-directional DC conversion units, which can provide multiple isolated DC power sources and convert voltages to meet diverse requirements, including single-stage and two-stage conversion structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If electrical isolation is implemented between DC side and AC grid, then safety and fault isolation are improved, but circuit design complexity and cost increase

Engineering Contradiction:

Improveelectrical isolationVSAvoidcircuit design

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The DC-DC converter is designed to perform multiple functions simultaneously: electrical isolation between AC grid and DC loads, voltage regulation to different output levels, and fault protection. This multi-functional design achieves electrical isolation without requiring separate dedicated isolation circuits, thereby reducing overall system complexity while maintaining reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If multiple isolated DC power sources are provided, then adaptability to different EV charging specifications is improved, but device complexity increases

Engineering Contradiction:

Improvevoltage output flexibilityVSAvoidpower supply system

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The DC-DC converter employs dynamic voltage regulation capability that allows it to adaptively output different voltage levels based on real-time charging requirements. Instead of requiring multiple fixed-output power sources, the system dynamically adjusts the output voltage to match different EV charging specifications, achieving versatility without proportionally increasing system complexity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the voltage parameter of the DC output according to different charging needs. By implementing adjustable voltage output in the DC-DC converter, the system can provide different voltage levels (e.g., 400V, 800V) to meet various EV charging standards, achieving adaptability through parameter variation rather than through complex multi-source architecture.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If single-stage conversion structure is used, then device complexity is reduced, but conversion efficiency and voltage regulation precision may be insufficient

Engineering Contradiction:

Improveconversion structureVSAvoidvoltage conversion precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The single-stage DC-DC converter incorporates dynamic control mechanisms that enable precise voltage regulation despite the simplified structure. Through advanced control algorithms and real-time parameter adjustment, the system achieves high voltage conversion precision and efficiency comparable to multi-stage converters, while maintaining lower structural complexity.

Inventive Principle:

Principle #15Dynamics

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 enables electrical isolation and provides flexible voltage output to meet various EV charging specifications, achieving voltage equalization and power balance while optimizing power supply and demand.

Implementation Method 1

The AC-to-DC conversion unit has a first side and a second side, wherein the first side of the AC-to-DC conversion unit is coupled to an AC power source. The first DC bus is coupled to the second side of the AC-to-DC conversion unit

Methodology Applied

Scientific EffectAC-to-DC conversion:

Implementation Method 2

Each of the bi-directional DC conversion units has a first side and a second side... wherein the first sides of the bi-directional DC conversion units are coupled to the first DC bus, the second side of the bi-directional DC conversion units are configured to form at least one second DC bus

Methodology Applied

Scientific EffectDC-DC conversion:

Data Source

PatentUS12500521B2Power apparatus applied in solid state transformer structure and three-phase power system having the same

Publication Date: 2025.12.16 DELTA ELECTRONICS INC(CN)

AI summary

A power apparatus applied in a solid state transformer structure includes an AC-to-DC conversion unit, a first DC bus, and a plurality of bi-directional DC conversion units. First sides of the bi-directional DC conversion units are coupled to the first DC bus. Second sides of the bi-directional DC conversion units are configured to form at least one second DC bus, and the number of the at least one second DC bus is a bus number. The bi-directional DC conversion units receive a bus voltage of the first DC bus and convert the bus voltage into at least one DC voltage, or the bi-directional DC conversion units receive at least one external DC voltage and convert the at least one external DC voltage into the bus voltage.