Two-Stage AC-DC Converter With Dynamic Voltage Ratio Control
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Solution Overview
Problem
Existing three-phase AC-to-DC converters for applications like electric vehicle charging and MRI systems face challenges in efficiently managing voltage ratios, leading to stress on converter components and increased costs when the required output voltage is low, due to the need for over-dimensioning of components.
Innovation Solution
An electrical converter system with two converter stages and a current injection circuit, utilizing pulse width modulation to adjust voltage and current, allowing for reduced DC bus voltage during low voltage requirements, and maintaining sinusoidal current and unity power factor, by operating in different modes based on voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a series-connected galvanically isolated DC/DC converter stage is used to generate the final output voltage, then the converter can operate with decoupled control of both stages, but when the required output voltage is low the isolated DC/DC converter stage must fully absorb a high voltage ratio which places stress on converter components and requires over-dimensioning
Solution Approach 1:
The patent implements a dynamic operating mode selection mechanism that switches between two converter configurations based on real-time voltage conditions. When output voltage requirement is low, the system activates a parallel connection mode where the isolated DC/DC converter operates with reduced voltage ratio, avoiding component stress. When output voltage requirement is high, the system switches to series-connected mode. This dynamic adaptation eliminates the need for over-dimensioning components while maintaining decoupled control capability.
Solution Approach 2:
The patent changes the operational parameters of the isolated DC/DC converter by switching between series-connected and parallel-connected configurations. This parameter change allows the converter to adapt its voltage ratio according to the battery state of charge, operating with high voltage ratio only when necessary and with low voltage ratio when the battery is depleted, thereby extending component service life without sacrificing operational flexibility.
2Power
If the isolated DC/DC converter stage fully absorbs high voltage ratio when battery is depleted, then the converter can maintain required output voltage, but this requires over-dimensioning of converter components increasing cost
Solution Approach 1:
The system dynamically switches between series-connected mode (for high output voltage requirement) and parallel-connected mode (for low output voltage requirement). This eliminates the need to design components for maximum voltage ratio operation, as the converter only operates at high voltage ratio when absolutely necessary. Components can be sized for typical operating conditions, reducing cost while maintaining full power capability when needed.
Solution Approach 2:
The converter alternates between different operational modes based on periodic assessment of battery voltage requirements. The control system continuously monitors battery state and switches between series and parallel configurations, allowing components to operate at reduced stress levels during extended periods while maintaining capability for high power output when required.
3Device complexity
If the converter operates in a single mode with fixed voltage ratio, then the control is simplified, but the converter cannot efficiently adapt to varying output voltage requirements throughout battery charging
Solution Approach 1:
The patent implements dynamic mode switching between series-connected and parallel-connected configurations based on real-time battery voltage requirements. The control system monitors battery state and automatically transitions between modes, providing efficient adaptation to varying voltage requirements. This dynamic approach maintains relatively simple control logic while achieving high versatility in voltage ratio adaptation throughout the battery charging cycle.
Solution Approach 2:
The converter is designed with multi-functionality, capable of operating in both series-connected mode (for high voltage output) and parallel-connected mode (for low voltage output). This universal design allows a single converter system to handle the full range of battery charging requirements without requiring multiple specialized converters, achieving adaptability while keeping control mechanisms manageable.
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 system reduces stress on converter components, allows for efficient operation at low voltage requirements, and maintains high power factor and low distortion, thereby extending component lifespan and reducing costs.
Implementation Method 1
The second converter stage comprises at least one first active switch and is operable to convert between a second signal, e.g. a (switched) voltage or a current, at the third and fourth intermediate nodes and the DC signal at the first and second DC terminals
Data Source
Figure 1
Figure 2A~2C
Figure 2D~2E
AI summary
Electrical converter (100) for converting an AC signal having three phase voltages to a DC signal, comprises three phase terminals (A, B, C), a first DC terminal (P) and a second DC terminal (N), a first converter stage (11) configured for converting between the AC signal at the at least three phase terminals and a first signal at a first intermediate node (x) and a second intermediate node (y), a second converter stage (12) operable to convert between a second signal at third and fourth intermediate nodes (r, s) and the DC signal at the first and second DC terminals (P, N), wherein the second converter stage comprises at least one first active switch (Sxm, Smy). A link connects the first intermediate node (x) to the third intermediate node (r) and the second intermediate node (y) to the fourth intermediate node (s). A current injection circuit comprises second active switches. A controller (40) is implemented with a first mode of operation in which the at least one first active switch (Sxm, Smy) and the second active switches are operated through pulse width modulation. The controller (40) is implemented with a second mode of operation in which the third and fourth intermediate nodes (r, s) are continuously connected to the first and second DC terminals (P, N) respectively such that the second converter stage (12) is inoperative and the second active switches are operated through pulse width modulation.