Dual-String Power Converter for Low DC Link Voltage Operation
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Solution Overview
Problem
Existing power converters fail to operate effectively when the DC link voltage is lower than the instantaneous AC max phase voltage, as seen in applications requiring variable DC link voltage below the AC max phase voltage, such as when the AC max phase voltage is 11.27 kV and the DC link voltage is 6 kV.
Innovation Solution
A power converter design incorporating a first string with switching units and unidirectional current switches, coupled across a first and second bus, and a second string with unidirectional current switches, connected via connecting nodes to a third and fourth bus, with a controller to manage switching units, allowing for efficient operation across varying voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the DC link voltage is made variable and lower than the instantaneous AC max phase voltage, then the power converter can operate in new application scenarios, but the existing power converter design does not work under these conditions
Solution Approach 1:
The power converter is divided into two independent strings: a first string with controllable switches for active power conversion, and a second string with unidirectional switches for passive power flow. This segmentation allows each string to be optimized for specific operating conditions, enabling reliable operation across a wider voltage range including cases where DC link voltage is lower than AC max phase voltage.
Solution Approach 2:
The dual-string configuration provides multi-functionality: the first string handles bidirectional power flow control while the second string provides a passive conduction path. This universal design enables the converter to operate reliably in both traditional modes (DC voltage higher than AC voltage) and new modes (DC voltage lower than AC voltage), expanding adaptability without sacrificing reliability.
2Adaptability or versatility
If a dual-string configuration with unidirectional current switches is used, then the power converter can operate when DC link voltage is lower than AC max phase voltage, but the component count increases
Solution Approach 1:
The patent extracts the power conduction function from the controllable switches and places it in dedicated unidirectional current switches in the second string. This separation allows the first string to focus on active control with fewer components, while the second string provides passive power flow capability, reducing overall device complexity despite the dual-string configuration.
Solution Approach 2:
The two strings are merged into a single integrated converter structure sharing common DC link and control architecture. This merging allows the system to achieve expanded voltage operation range while avoiding the complexity of completely separate converter systems, as the strings work cooperatively within a unified framework.
3Productivity
If the first string includes multiple switching units and unidirectional current switches, then the power converter achieves efficient operation across varying voltage conditions, but the control complexity increases
Solution Approach 1:
The second string with unidirectional current switches provides a passive power conduction path that operates automatically based on voltage conditions without requiring active control. This self-service mechanism reduces control complexity by handling power flow automatically, while the first string focuses control efforts on active power conversion, maintaining high efficiency without proportionally increasing control burden.
Data Source
AI summary
Provided is a power converter that includes at least one leg having a first string that includes a plurality of switching units, a plurality of unidirectional current switches, a first connecting node, and a second connecting node, such that the first string is operatively coupled across a first and a second bus, and a second string operatively coupled to the first string via the first connecting node and the second connecting node such that the second string includes a plurality of unidirectional current switches and a fourth connecting node operatively coupled to a fourth bus. The power converter also includes a controller configured to control switching of the plurality of switching units.