Double-Isolated Auxiliary Supply in Medium-Frequency MV DC/DC Transformers
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Solution Overview
Problem
Conventional isolated DC/DC converters for Solid-State Transformers face challenges in meeting insulation requirements between medium-voltage and low-voltage sides, leading to complex and expensive auxiliary power solutions, either by direct supply from the medium-voltage side or large, expensive external converters.
Innovation Solution
A converter design incorporating a magnetic core with medium-voltage and low-voltage windings, along with an auxiliary winding, utilizing galvanic insulation to withstand Basic Insulation Levels, and providing auxiliary power through an auxiliary unit connected to control circuits, which is configured to operate within the insulation barrier, reducing the need for complex and costly solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If auxiliary power is provided directly from the MV-side DC-link, then the insulation requirements are circumvented, but the auxiliary converter becomes complex and expensive
Solution Approach 1:
An auxiliary transformer is introduced as an intermediary component to provide galvanic isolation between the MV and LV sides. This transformer with its insulation barrier enables compliant auxiliary power supply while maintaining system reliability, avoiding the complexity of complex converters
2Reliability
If an external isolated DC/DC converter is employed from the LV-side, then insulation requirements are met, but the converter becomes large and expensive
Solution Approach 1:
The auxiliary power supply function is merged with the existing MFT structure. The auxiliary transformer shares the same core and insulation infrastructure as the main transformer, eliminating the need for separate large external converters and reducing overall system size and cost
3Reliability
If a large external converter is used to provide auxiliary power, then insulation voltage requirements are met, but the power rating is excessively high for the actual low power needs
Solution Approach 1:
The auxiliary transformer is designed with local quality - it provides the full insulation voltage capability of the MFT's insulation barrier while being rated for only the small auxiliary power actually needed (typically watts to low kilowatts), rather than the full MV power level
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 effectively provides necessary insulation while minimizing the complexity and cost of auxiliary power systems, ensuring reliable operation while maintaining insulation integrity and reducing core saturation effects and grid current harmonics.
Implementation Method 1
at least one DC/AC cell configured for generating an AC voltage from a MV DC voltage... at least one AC/DC cell configured for generating a DC voltage from a LV AC voltage... a magnetic core with a LV winding being wound around the magnetic core... a MV winding being wound around the magnetic core
Implementation Method 2
a galvanic insulation to galvanically insulate the LV winding from the MV winding and the auxiliary winding. The galvanic insulation between the LV and the MV winding and the auxiliary winding is configured to withstand the Basic Insulation Level (BIL) of the converter
Data Source
AI summary
A converter for transferring power from a medium-voltage, MV, to a low-voltage, LV, side is provided. The converter includes at least one DC/AC cell with a MV AC terminal configured for generating an AC voltage from a MV DC voltage, and includes at least one AC/DC cell with a LV AC terminal configured for generating a DC voltage from a LV AC voltage. The converter has a magnetic core with a LV winding, and a LV terminal connected to the LV AC terminal, additionally with a magnetic core with a MV winding, and a MV terminal connected to the MV AC terminal. The converter includes an auxiliary unit with an auxiliary winding, and an auxiliary terminal connected to control circuits for operating the MV DC/AC cell. Galvanic insulation between the LV and the MV winding and the auxiliary winding is configured to withstand the Basic Insulation Level of the converter.