Inverter-Linked DC/DC Converter Switching for Bus Imbalance Control
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Solution Overview
Problem
Existing uninterruptible power supplies (UPSs) face challenges in managing voltage imbalances between positive and negative DC buses, which can lead to transformer saturation in DC/DC converters, affecting performance.
Innovation Solution
A power system design that includes an inverter coupled to both positive and negative DC buses, with a DC/DC converter connected between the inverter output and one of the DC buses. The inverter is controlled to isolate the DC/DC converter from one bus during positive cycles and from the other bus during negative cycles, thereby reducing the risk of transformer saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the DC/DC converter is continuously coupled to both positive and negative DC buses, then power conversion functionality is maintained, but transformer saturation occurs due to voltage imbalances
Solution Approach 1:
The inverter control circuit implements periodic switching of the DC/DC converter connection between positive and negative DC buses based on the polarity of the output AC waveform. During positive half-cycles, the converter connects to the positive bus; during negative half-cycles, it connects to the negative bus. This periodic connection strategy prevents continuous exposure to voltage imbalances that would cause transformer saturation, while maintaining power conversion functionality throughout the AC cycle.
Solution Approach 2:
The patent segments the coupling between the DC/DC converter and DC buses into discrete time intervals corresponding to AC waveform half-cycles. Instead of continuous coupling to both buses, the system divides the operation into separate positive-cycle and negative-cycle modes, with the converter selectively coupling to one bus at a time. This segmentation isolates the converter from simultaneous exposure to both positive and negative bus voltages, preventing saturation conditions.
2Reliability
If the inverter isolates the DC/DC converter from one DC bus during each half-cycle, then transformer saturation is reduced, but control complexity increases
Solution Approach 1:
The inverter control circuit uses feedback from the output AC waveform polarity detection to automatically adjust the DC/DC converter connection state. The control system monitors the instantaneous polarity of the inverter output and accordingly switches the DC/DC converter between positive and negative bus connections. This closed-loop feedback mechanism automates the isolation process, reducing manual intervention while maintaining operational stability and preventing transformer saturation.
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 effectively reduces the risk of transformer saturation by alternately coupling the DC/DC converter to positive and negative DC buses, ensuring stable operation even with voltage imbalances, and enhancing the overall performance of the UPS.
Implementation Method 1
an inverter coupled to the positive DC bus and the negative DC bus, the inverter including an inverter output coupled to the power-system output
Implementation Method 2
a DC/DC converter coupled between the inverter output and at least one of the positive DC bus or the negative DC bus
Data Source
AI summary
Examples of the disclosure include a power system comprising a power-system output configured to be coupled to, and provide an output AC waveform to, one or more loads, a positive DC bus, a negative DC bus, an inverter coupled to the positive DC bus and the negative DC bus, the inverter including an inverter output coupled to the power-system output, and a DC/DC converter coupled between the inverter output and at least one of the positive DC bus or the negative DC bus.