Solid-State Transformer DC Bus Topology for Isolated Multi-Voltage Charging

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Solution Overview

Problem

Designing a power apparatus and three-phase power system for solid state transformers that can maintain electrical isolation from the AC grid while providing different output voltages to meet various EV charging specifications is challenging, particularly in terms of circuit design and cost considerations.

Innovation Solution

The power apparatus includes an AC-to-DC conversion unit, a first DC bus, and bi-directional DC conversion units that can convert bus voltage into multiple DC voltages or external DC voltages, allowing for flexible voltage adjustment and isolation, with the bi-directional DC conversion units configured in series and parallel to achieve voltage equalization and power balance in a three-phase power system.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If electrical isolation from AC grid is implemented in DC charging station, 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 conversion unit is designed to perform multiple functions: electrical isolation from AC grid, voltage conversion to different DC levels, and bidirectional power flow capability. This multi-functional design eliminates the need for separate isolation transformers and multiple conversion stages, reducing overall system complexity while maintaining reliability

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The DC/DC conversion unit acts as an intermediary component between the AC grid and DC charging outlets. It provides galvanic isolation through high-frequency transformer while enabling controlled power transfer, thus achieving electrical isolation without requiring direct physical separation or complex protection circuits

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If multiple output voltages are provided for different EV charging specifications, then adaptability is improved, but device complexity increases

Engineering Contradiction:

Improvevoltage output optionsVSAvoidpower conversion system

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The DC/DC conversion unit employs dynamic voltage regulation capability, allowing it to adjust output voltage levels in real-time based on charging requirements. The controller dynamically modifies switching duty cycles and conversion ratios to provide different DC voltage outputs (e.g., 400V, 800V) from a single input, eliminating the need for multiple fixed-output converters

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes operational parameters (switching frequency, duty cycle, conversion ratio) of the DC/DC conversion unit to achieve different output voltages. By varying these parameters, the same hardware configuration can adapt to different EV charging specifications without requiring physical reconfiguration or additional components

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If bi-directional DC conversion units are used for voltage conversion, then flexibility is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvevoltage conversion flexibilityVSAvoidconversion structure

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The power conversion system is segmented into modular units: AC/DC conversion module, DC/DC conversion units, and control module. Each DC/DC conversion unit is an independent module with standardized interfaces, allowing for simplified manufacturing, testing, and assembly. The modular design enables parallel production and reduces overall manufacturing complexity

Inventive Principle:

Principle #1Segmentation

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 enables the power apparatus to provide different voltages, meet isolation requirements, and achieve voltage equalization and power balance, enhancing the flexibility and efficiency of power supply and demand management in EV charging stations and other applications.

Implementation Method 1

An AC-to-DC conversion unit 11, a first DC bus 12

Methodology Applied

Scientific EffectAC-to-DC conversion:

Implementation Method 2

bi-directional DC conversion units 13 that can convert bus voltage into multiple DC voltages or external DC voltages

Methodology Applied

Scientific EffectDC-to-DC conversion:

Data Source

PatentUS11811327B2Power apparatus applied in solid state transformer structure and three-phase power system having the same

Publication Date: 2023.11.07 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.