Flying Capacitor Inverter Charging for Low-Voltage DC Stations
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Solution Overview
Problem
Existing vehicles with high-voltage traction batteries face challenges in efficiently charging from DC charging stations with lower charging voltages without requiring significant additional components or incurring high losses.
Innovation Solution
Employing a flying capacitor inverter, particularly a three-phase, three-level inverter, to convert DC charging voltages lower than the nominal battery voltage into the required level using the motor inductance and inverter capacitors to form a resonant circuit, minimizing semiconductor losses and utilizing existing components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional charging system is used to charge a high-voltage traction battery from a lower voltage DC charging station, then additional voltage boosting components are required, but this increases device complexity and component quantity
Solution Approach 1:
The inverter is designed to perform multiple functions: it can convert DC voltage from charging stations to charge the traction battery, and it can also convert DC battery voltage to AC to drive the three-phase motor. By making the inverter universal, the patent eliminates the need for separate voltage boosting components when charging from lower voltage stations, thus reducing device complexity while maintaining charging compatibility
Solution Approach 2:
The patent merges the voltage conversion function for charging with the existing inverter component used for motor drive. Instead of adding separate boosting converters or transformers, the inverter handles both voltage conversion tasks, effectively combining multiple functions into a single component and reducing overall system complexity
2Adaptability or versatility
If voltage boosting components are added to enable charging from lower voltage stations, then charging compatibility is improved, but energy losses increase
Solution Approach 1:
The inverter uses the motor inductance and its own internal capacitors to form a resonant circuit that enables voltage boosting. Instead of relying on external passive components that would introduce additional losses, the system uses its own active components (inverter switches, motor inductance) to achieve the voltage conversion, thereby minimizing energy losses while maintaining charging compatibility
3Adaptability or versatility
If additional components are added to enable charging from lower voltage stations, then charging capability is improved, but electromagnetic interference increases
Solution Approach 1:
The inverter acts as an intermediary between the charging station and the traction battery, using controlled switching of semiconductor elements to transfer energy. This active switching mechanism allows for controlled energy transfer with reduced harmonic distortion compared to passive component-based solutions, thereby minimizing electromagnetic interference while enabling charging from lower voltage stations
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
Enables efficient charging of high-voltage batteries from lower voltage DC charging stations with minimal additional components and reduced harmonic interference, optimizing power transmission and electromagnetic compatibility.
Implementation Method 1
using the motor inductance and inverter capacitors to form a resonant circuit
Data Source
AI summary
A vehicle includes a traction battery, a drive unit having a three-phase motor and an inverter electrically coupled to the three-phase motor, the inverter being electrically coupled to the traction battery, and a charging connection for electrically coupling to a vehicle-external DC charging station. The inverter is a flying capacitor inverter.