DC-DC Converter Transient Current Management for EV Accessories
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Solution Overview
Problem
Hybrid electric vehicles face challenges in managing transient current demands without resorting to costly and complex solutions like load shedding or larger power supplies, as existing systems are often sized for steady-state conditions and struggle to accommodate short-duration events like EPAS or ABS operations.
Innovation Solution
A method and system that control the duty cycle of a DC-DC converter to limit output current based on temperature thresholds, providing a current boost during transient events while managing thermal conditions, including setting the output current to a first level when temperature is below a threshold, reducing it further when between thresholds, and providing zero output current when temperatures exceed a certain level, thereby accommodating EPAS and ABS operations without shedding loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the DC-DC converter is sized for maximum continuous steady-state current, then it can reliably power accessory loads under normal conditions, but it cannot accommodate transient current demands during events like EPAS or ABS operations
Solution Approach 1:
The patent applies dynamics by implementing a dynamic duty cycle control strategy that adjusts the DC-DC converter's operating parameters in real-time based on thermal conditions. The controller monitors converter temperature and dynamically modifies the duty cycle to allow transient current boosts when cool and limits current when hot, enabling the system to adapt to varying transient demands without requiring a larger continuously-rated converter.
Solution Approach 2:
The patent changes the operating parameters of the DC-DC converter by adjusting the duty cycle based on temperature thresholds. When the converter temperature is below a first threshold, a higher duty cycle permits transient current exceeds the steady-state maximum. When temperature exceeds the threshold, the duty cycle is reduced to limit current, thereby changing the operational characteristics to balance reliability with transient adaptability.
2Power
If load shedding is used to accommodate transient loading, then the power supply can handle transient demands, but accessory loads are temporarily disconnected causing functional limitations
Solution Approach 1:
The patent applies preliminary action by pre-charging an output capacitor during periods when the converter can deliver higher current (when temperature is low), so that energy is stored in advance. During transient events when current demand exceeds steady-state limits, this pre-stored energy in the capacitor provides the necessary current boost without requiring load shedding, thus maintaining continuous operation of accessory loads.
3Adaptability or versatility
If a larger power supply or ultra-capacitor is used to accommodate transient current demands, then transient loading is handled, but cost, weight, complexity, and packaging space increase
Solution Approach 1:
The patent applies self-service by enabling the existing DC-DC converter to serve its own transient current needs through intelligent control of its duty cycle and utilization of its output capacitor. The converter monitors its own thermal state and autonomously adjusts its operation to provide transient current boosts when possible, eliminating the need for external ultra-capacitors or larger power supply components, thereby reducing system complexity and packaging requirements.
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 approach enables effective transient current management in hybrid electric vehicles without load shedding, ensuring sufficient current for short-duration events like EPAS or ABS operations while managing thermal conditions, thus enhancing vehicle performance and reducing costs.
Implementation Method 1
controlling a duty cycle of the DC-DC converter to limit output current to a first level below the maximum current for a first period of time when temperature of the DC-DC converter is below a first threshold
Implementation Method 2
when temperature of the DC-DC converter is below a first threshold... when the temperature of the DC-DC converter is between the first threshold and a second threshold... when the temperature of the DC-DC converter exceeds the second threshold
Data Source
AI summary
An electric or hybrid electric vehicle includes a battery coupled to a traction motor and a DC-DC power converter for managing transient current demands of vehicle accessories such as an electrical power assisted steering (EPAS) motor or antilock braking system (ABS) with a controller coupled to the power converter that generates a first duty cycle signal to supply current at a first level for a first time period to accommodate transient current for an EPAS, ABS, or other short duration event, and a second duty cycle signal that limits the current to a second level lower than the first level for a second time period upon expiry of the first time period to manage temperature of the converter. The controller may also generate a duty cycle signal based on measured or estimated transistor temperature of the DC-DC converter to lower the current limit when transistor temperature exceeds a threshold.