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, such as those encountered during typical urban driving conditions.
Innovation Solution
The implementation of a vehicle propulsion system that includes a high specific-energy battery, an ultracapacitor, and a bi-directional boost converter, along with a uni-directional current device and an Energy Management System (EMS) to decouple the voltage output from the DC link, allowing efficient power distribution and management between the battery and ultracapacitor, optimizing energy use during various driving modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional battery system is used directly connected to the DC link, then the system structure is simple, but the vehicle performance and fuel efficiency are reduced at low speeds
Solution Approach 1:
The battery system is segmented into multiple battery cells that can be independently controlled and managed. Each battery cell is connected to the DC link through separate switching devices, allowing independent control of power flow from each cell. This segmentation enables optimized power distribution at low speeds while maintaining overall system performance.
Solution Approach 2:
A DC-DC converter is introduced as an intermediary device between the battery system and the DC link. This converter acts as a mediator that can efficiently manage power transfer, particularly improving low-speed performance by optimizing the voltage and current characteristics between the battery and the motor drive system.
2Use of energy by moving object
If the battery voltage rating is lower than the DC link voltage, then a high specific-energy battery can be used, but a boost converter is required which increases system complexity
Solution Approach 1:
The boost converter functionality is merged with the battery management system by integrating the voltage boosting capability directly into the battery connection architecture. Multiple battery cells are connected in series through switching devices, allowing the system to achieve the required voltage level while maintaining the benefit of using lower-voltage, high-specific-energy battery cells.
Solution Approach 2:
The system dynamically configures the battery cell connections by using switching devices to connect or disconnect individual battery cells based on the required voltage level and power demand. This dynamic reconfiguration allows the system to adapt between different operating modes, using the boost converter only when necessary while maintaining simpler direct connections during normal operation.
3Power
If multiple battery cells are connected in series to increase voltage, then the system voltage matches the DC link, but the system weight increases
Solution Approach 1:
Instead of changing the physical configuration to use more battery cells in series, the system changes the electrical parameters by using the DC-DC converter to transform the voltage from the lower-voltage battery configuration to the required higher DC link voltage. This parameter transformation allows the system to maintain lower battery voltage (and thus lower weight) while achieving the necessary operating voltage.
4Power
If a diode is used to allow current flow from ultracapacitor to battery, then power transmission is enabled, but the system cannot recover regenerative braking energy
Solution Approach 1:
Instead of using a diode that allows current flow in only one direction (from ultracapacitor to battery), the system uses bidirectional switching devices that can conduct current in both directions. This inversion of the unidirectional constraint enables the system to capture and store regenerative braking energy by allowing current to flow from the DC link back to the battery during regenerative braking events.
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 configuration enhances the vehicle's efficiency and range, especially at low speeds, by effectively utilizing the ultracapacitor and battery energy storage, minimizing weight and cost, and ensuring efficient pre-charging of the ultracapacitor, thereby improving overall system performance and reducing the weight of the vehicle.
Implementation Method 1
a bi-directional boost converter, allowing efficient power distribution and management between the battery and ultracapacitor
Implementation Method 2
an ultracapacitor, and a bi-directional boost converter
Implementation Method 3
a uni-directional current device that is poled to conduct current from low voltage side of the boost converter to the high voltage side of the boost converter
Data Source
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AI summary
A vehicle propulsion (100) includes an alternating current (AC) traction drive (147), a first energy storage system electrically coupled to the traction drive through a direct current (DC) link (114), 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 (120), and an energy management system configured to control said first and second energy storage systems when the vehicle is operating in at least one of a pre-charge mode and a normal operation mode with the traction drive system (147) enabled.