Cascade Bridge DC-AC Converter Single DC Source Design
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Solution Overview
Problem
Conventional cascade bridge-type DC-AC power converters face inefficiencies due to high switching power loss and complex circuitry, requiring multiple DC sources and additional circuits, which increase manufacturing costs and electromagnetic interference.
Innovation Solution
A cascade bridge-type DC-AC power conversion method that connects a low-frequency and a high-frequency bridge-type power converter in series, with the low-frequency converter synchronized to the AC voltage frequency and the high-frequency converter using PWM, reducing switching power loss and simplifying the driving circuit, while requiring only a single DC source circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cascade bridge-type DC-AC power converters use multiple DC sources and additional circuits, then the converter can operate, but the circuit complexity increases and manufacturing cost increases
Solution Approach 1:
The patent combines multiple DC sources into a single DC source by using a common DC bus that supplies power to both the high-frequency bridge-type power converter and the low-frequency bridge-type power converter. This merging eliminates the need for separate DC sources and additional circuits, thereby reducing circuit complexity while maintaining converter operation.
Solution Approach 2:
The single DC source circuit is designed to serve multiple functions: it provides DC power to the high-frequency converter, provides DC power to the low-frequency converter, and establishes a common reference potential for both converters. This multi-functionality eliminates the need for dedicated DC sources for each converter stage.
2Productivity
If high-frequency PWM is used to control power electronic switches, then the converter can generate AC output, but switching power loss increases
Solution Approach 1:
The patent segments the power conversion function into two distinct converter stages with different switching frequencies: a high-frequency bridge-type power converter that handles high-frequency switching, and a low-frequency bridge-type power converter that operates at line frequency. This segmentation allows each stage to be optimized for its specific frequency range, reducing overall switching losses while maintaining AC output generation capability.
Solution Approach 2:
The patent employs dynamic frequency selection where the low-frequency bridge-type power converter operates synchronously with the AC voltage frequency (line frequency), while the high-frequency converter operates at a higher switching frequency. This dynamic operation allows the system to minimize switching losses by matching the low-frequency converter's switching to the natural grid frequency, reducing unnecessary high-frequency switching losses.
3Loss of energy
If conventional multi-level DC-AC converter is used, then switching voltage is reduced, but filter capacity and electromagnetic interference increase
Solution Approach 1:
The patent uses dynamic switching frequency control where the low-frequency converter operates synchronously with the AC voltage frequency, and the high-frequency converter operates at a higher frequency. This dynamic frequency management reduces switching losses while the natural frequency separation between the two converters helps filter electromagnetic interference, reducing the burden on output filters.
Solution Approach 2:
The low-frequency bridge-type power converter operates at periodic intervals synchronized with the AC voltage frequency, creating a natural filtering effect that reduces high-frequency harmonics. This periodic operation at line frequency inherently reduces electromagnetic interference and decreases the required filter capacity compared to continuous high-frequency switching.
Data Source
AI summary
A cascade bridge-type DC-AC power converter device includes a low-frequency bridge-type power converter including an AC terminal and a DC bus and a high-frequency bridge-type power converter including an AC terminal. A power conversion method includes: serially connecting the AC terminal of the high-frequency bridge-type power converter and the AC terminal of the low-frequency bridge-type power converter; operating frequency of the low-frequency bridge-type power converter synchronized with frequency of an AC source; and operating the high-frequency bridge-type power converter with high-frequency PWM to generate a multilevel AC voltage. A DC power source connects to the DC bus of the low-frequency bridge-type power converter. No additional power supply circuit will be required for power supply to a DC bus of the high-frequency bridge-type power converter. Accordingly, the power circuit is simplified, and the manufacturing cost is reduced.