Bidirectional Converter Variable-Frequency Soft Switching
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Solution Overview
Problem
Conventional on-board charging/discharging systems for electric vehicles have limited soft switching range and efficiency due to fixed-frequency control methods, which restricts the bidirectional converter's ability to achieve soft switching across various output gains and can lead to hard switching when output gain is not close to 1, resulting in suboptimal efficiency and increased cost.
Innovation Solution
The proposed on-board charging/discharging system employs a bidirectional converter with a first and second bridge circuit, a resonant circuit, and a transformer, allowing for soft switching across output gains greater than, less than, or equal to 1 by controlling the on/off states of switches based on zero-crossing points and phase-shift times, and operates in multiple modes to optimize energy transfer and voltage regulation, thereby enhancing efficiency and reducing volume and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed-frequency control method is used in bidirectional converter, then control simplicity is maintained, but soft switching range is limited and efficiency deteriorates
Solution Approach 1:
The patent implements variable-frequency control for the bidirectional converter, dynamically adjusting the switching frequency based on operating conditions to maintain soft switching across different output gain ranges. This dynamic adjustment enables the system to achieve soft switching whether output gain is greater than, less than, or equal to 1, thereby resolving the contradiction between control simplicity and efficiency by automating the frequency adaptation process.
2Adaptability or versatility
If bidirectional charger and dc-dc converter are superimposed separately, then functional requirements are met, but volume and cost increase
Solution Approach 1:
The patent merges the bidirectional charger and dc-dc converter into a single integrated three-port circuit topology. This integration shares magnetic components and switching devices between the two functions, enabling the system to perform both bidirectional charging and dc-dc conversion without requiring separate physical components, thereby reducing volume and cost while maintaining all necessary functional capabilities.
Solution Approach 2:
The integrated three-port circuit topology is designed to perform multiple functions: bidirectional power flow control, high-voltage battery charging, high-voltage battery discharging, and low-voltage battery charging. This multi-functional design allows a single system to replace what would traditionally require separate components, achieving volume and cost optimization while meeting all functional requirements.
3Loss of energy
If full-bridge topology is used with low-voltage output, then soft switching range is expanded, but application range is limited to low-power outputs
Solution Approach 1:
The patent employs parameter changes by implementing variable-frequency control that adapts the switching frequency based on the output gain conditions. This allows the system to achieve soft switching across different power levels and output conditions, extending the application range beyond low-power outputs to include high-power applications while maintaining the benefits of soft switching.
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 widens the soft switching range, improving efficiency and reducing costs by enabling soft switching across all output gains, and ensures the bus capacitor voltage remains within reasonable limits, optimizing the system's performance and integration.
Implementation Method 1
a transformer (T), including a primary winding (Np) and a secondary winding (Ns)
Implementation Method 2
a resonant circuit (21), including a resonant inductor (Lr) and a resonant capacitor (Cr)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An on-board charging/discharging system (1) includes a bidirectional converter (2) and a low-voltage converter (3). When the high-voltage battery (8) is charged or discharged by the bidirectional converter (2), the bidirectional converter (2) is operated in a variable-frequency mode and the low-voltage converter (3) is also operated in the variable-frequency mode. The on/off states of different switches are controlled according to the output gain of the bidirectional converter (2), and thus the on-board charging/discharging system (1) has optimized volume and reduced cost. Moreover, the soft switching is achieved when the output gain is lower than 1, greater than 1 or equal to 1. Consequently, the efficiency of the on-board charging/discharging system (1) is enhanced. Moreover, while the low-voltage converter (3) is operated in a fixed-frequency mode, the first bridge of the bidirectional converter (2) is correspondingly controlled. Consequently, the voltage of the bus capacitor (Cbus) is within a reasonable range.