Vehicle Propulsion System with Bi-directional Boost Converter
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Solution Overview
Problem
Existing vehicle drive systems, particularly battery-powered electric and hybrid vehicles, experience reduced performance and fuel efficiency at low speeds due to ineffective energy management during urban driving conditions.
Innovation Solution
A vehicle propulsion system incorporating an AC traction drive, a bi-directional boost converter, and a uni-directional current device to decouple the voltage output from a second energy storage system, comprising a high-specific energy battery and ultracapacitors, allowing efficient energy distribution and utilization based on motor speed and torque requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional single energy storage system is used, then the system structure is simple, but the performance and fuel efficiency are reduced at low speeds
Solution Approach 1:
The energy storage system is segmented into two distinct subsystems: a high-voltage energy storage system (HVESS) connected to the DC link and a low-voltage energy storage system (LVESS) decoupled from the DC link. This segmentation allows each subsystem to operate independently at its optimal voltage level, improving overall vehicle performance while maintaining manageable system complexity through modular architecture.
Solution Approach 2:
A bi-directional DC-DC converter is introduced as an intermediary device between the LVESS and the DC link. This converter enables controlled power transfer between the low-voltage and high-voltage systems, allowing the LVESS to contribute to vehicle propulsion and auxiliary loads without directly connecting to the DC link, thus resolving the contradiction between performance improvement and system complexity.
2Use of energy by moving object
If the voltage output from the second energy storage system is decoupled from the DC link using a bi-directional boost converter, then energy distribution efficiency is improved, but device complexity increases
Solution Approach 1:
The bi-directional DC-DC converter is designed to perform multiple functions: it can transfer power from the LVESS to the DC link during vehicle propulsion, charge the LVESS from the DC link during regenerative braking, and provide isolated voltage matching for auxiliary loads. This multi-functionality improves energy distribution efficiency while justifying the added complexity through versatile operational capabilities.
Solution Approach 2:
The converter system enables dynamic parameter changes by adjusting the voltage conversion ratio according to operating conditions. During low-speed urban driving, the converter optimizes power transfer by modifying its duty cycle and control parameters, thereby improving energy distribution efficiency while adapting to varying vehicle demands without requiring hardware changes.
3Weight of moving object
If a high-specific-energy battery is used in the low-voltage system, then weight is reduced, but the voltage rating is lower than the DC link requiring additional conversion equipment
Solution Approach 1:
The system transitions from a single-voltage-dimensional architecture to a two-voltage-dimensional architecture by introducing the LVESS at a lower voltage level. This dimensional change allows the use of lightweight high-specific-energy batteries in the low-voltage system while the bi-directional converter handles the voltage level transition, thereby reducing overall system weight while managing the complexity of voltage conversion through a dedicated interface.
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 enhances performance and efficiency by optimizing energy storage and distribution, minimizing weight and cost, and extending the vehicle's range, especially during low-speed operations and limp-home modes.
Implementation Method 1
a bi-directional boost converter
Implementation Method 2
a uni-directional current device that is poled to conduct current from the low voltage side of the boost converter to the high voltage side of the boost converter
Implementation Method 3
a first ultracapacitor that is coupled on said boost converter high voltage side and wherein said second energy storage system comprises a second ultracapacitor and a high-specific energy battery
Implementation Method 4
a second ultracapacitor and a high-specific energy battery that are each coupled on said boost converter low voltage side
Data Source
Figure 1~3
Figure 2
Figure 4
AI summary
A vehicle propulsion includes an alternating current (AC) traction drive, a first energy storage system electrically coupled to the traction drive through a direct current (DC) link, a second energy storage system electrically coupled to the traction drive such that the voltage output from the second energy storage system is decoupled from the DC link using a bi-directional boost converter, and a uni-directional current device that is poled to conduct current from the low voltage side of the boost converter to the high voltage side of the boost converter.