Multilevel Bidirectional AC/DC Converter With Flying Capacitor Balancing
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Solution Overview
Problem
Existing three-phase AC/DC converters require multiple stages for buck-boost operations, leading to inefficiencies and high component counts, and lack effective methods for regulating flying capacitor voltages during varying power flow directions.
Innovation Solution
A three-phase bidirectional multilevel flying capacitor converter with independently operable modules, utilizing active switching devices and a control unit to regulate flying capacitor voltages, allowing simultaneous buck-boost operations with reduced passive components and enhanced efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If cascaded arrangement of rectifier and DC/DC converter is used to enable buck-boost capability, then DC and AC voltage ranges can be handled, but the complete output power has to be high-frequency converted twice leading to efficiency losses and increased complexity
Solution Approach 1:
The patent merges the rectifier and DC/DC converter functions into a single integrated AC/DC converter stage. The multilevel bridge-leg topology with flying capacitors enables the converter to simultaneously perform rectification and voltage regulation, eliminating the need for separate cascaded stages while maintaining buck-boost capability across wide voltage ranges.
Solution Approach 2:
The converter stage is designed with multi-functionality to handle both rectification and voltage regulation in a single operation. The flying capacitor-based multilevel bridge-leg structure enables the same circuit to operate in buck mode, boost mode, or bidirectional power flow, replacing multiple specialized stages with one universal converter.
2Adaptability or versatility
If cascaded arrangement of rectifier and DC/DC converter is used, then buck-boost capability is achieved, but the number of passive components and system complexity increases
Solution Approach 1:
The patent merges the rectifier and DC/DC converter functions into a single integrated AC/DC converter stage. The multilevel bridge-leg topology with flying capacitors enables the converter to simultaneously perform rectification and voltage regulation, eliminating the need for separate cascaded stages while maintaining buck-boost capability across wide voltage ranges.
Solution Approach 2:
The converter stage is designed with multi-functionality to handle both rectification and voltage regulation in a single operation. The flying capacitor-based multilevel bridge-leg structure enables the same circuit to operate in buck mode, boost mode, or bidirectional power flow, replacing multiple specialized stages with one universal converter.
3Stability of the object's composition
If flying capacitor bridge-leg is permanently operated with passive balancing strategies, then FC voltage balancing is maintained, but active control is insufficient during varying power flow directions
Solution Approach 1:
The patent transitions from static passive balancing to dynamic active control of flying capacitor voltages. The control unit continuously adjusts switching signals based on real-time detection of power flow direction and capacitor voltage levels, enabling the system to adaptively maintain voltage balance during bidirectional power flow, regenerative braking, and varying load conditions.
Solution Approach 2:
The control unit implements feedback control by continuously monitoring the voltage levels across flying capacitors and adjusting the switching signals accordingly. When voltage imbalance is detected, the control unit modifies the PWM duty cycles to charge or discharge specific capacitors, ensuring voltage balance is maintained under all operating conditions including bidirectional power flow.
Data Source
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AI summary
An electrical converter according to the present disclosure comprises at least three AC terminals, a first and a second DC terminal, a control unit, and at least three converter modules coupled to a respective one of the at least three AC terminals. Each of the at least three converter modules comprises a first converter stage comprising a first switch node, a second converter stage comprising a second switch node, a first inductor, and a first capacitor. The first and second switch nodes are connected to opposite terminals of the first inductor. The respective one of the at least three AC terminals and the second DC terminal are connected to opposite terminals of the first capacitor. The second DC terminal forms a star-point of the first capacitors of the at least three converter modules. The first converter stage and the second converter stage each comprise a flying capacitor circuit comprising at least one flying capacitor operably coupled to the respective first and second switch nodes. A flying capacitor voltage (ufA) of the first converter stage is clamped to a first voltage (uan) across the first capacitor when the first voltage (uan) drops below the flying capacitor voltage (ufA).