Solid-State Transformer DC Bus Conversion for Isolated EV 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 of DC EV charging stations from the AC grid while providing different output voltages to meet various EV charging specifications is challenging due to 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 AC-to-DC conversion units coupled in series and bi-directional DC units in parallel to achieve voltage equalization and power balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional AC grid connection is used for DC EV charging stations, then power supply is simple, but electrical isolation from AC grid cannot be achieved
Solution Approach 1:
The patent introduces a solid state transformer as an intermediary device between the AC grid and DC EV charging stations. This transformer includes an AC-to-DC conversion unit and multiple bi-directional DC conversion units that provide galvanic isolation through transformer coupling, enabling electrical isolation while maintaining power transfer capability. The intermediary device resolves the contradiction by providing isolation without requiring direct AC-DC connection.
Solution Approach 2:
The power supply system is segmented into multiple independent conversion units (AC-to-DC conversion unit, first DC conversion unit, second DC conversion unit) that can operate independently. Each unit provides isolation functionality, and they can be configured in series or parallel to achieve different voltage levels and isolation requirements, making the overall system more flexible and manageable.
2Adaptability or versatility
If fixed voltage output is used, then circuit design is simple, but cannot meet various EV charging specifications
Solution Approach 1:
The patent employs bi-directional DC conversion units with dynamic voltage adjustment capability. These units can operate in different modes (boost, buck, or pass-through) to provide variable DC voltage outputs that adapt to different EV charging specifications. The dynamic control of switching devices enables real-time voltage adjustment without changing the physical circuit structure.
Solution Approach 2:
The bi-directional DC conversion units are designed with multi-functionality, capable of performing voltage step-up, voltage step-down, and voltage isolation functions. This universal design allows a single circuit topology to meet various EV charging voltage requirements (e.g., 400V, 800V, or other specifications) without requiring separate dedicated circuits for each voltage level.
3Adaptability or versatility
If multiple voltage outputs are provided, then EV charging specifications are met, but power balance becomes difficult to achieve
Solution Approach 1:
The patent incorporates feedback control mechanisms in the bi-directional DC conversion units to monitor and adjust power flow dynamically. The control system detects voltage and current conditions across different DC buses and adjusts the duty cycles of switching devices to maintain power balance. This feedback control enables automatic equalization of power distribution even when multiple voltage outputs are provided simultaneously.
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 in a solid state transformer structure, enhancing the flexibility and efficiency of power supply systems for EV charging stations.
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
Implementation Method 2
The bi-directional DC conversion units receive the bus voltage of the first DC bus and convert the bus voltage into at least one DC voltage whose number is same as the bus number, or the bi-directional DC conversion units receive at least one external DC voltage whose number is same as the bus number and convert the at least one external DC voltage into the bus voltage of the first DC bus
Data Source
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.