Multi-Converter DC/DC System for Balanced EV Low Voltage Bus
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Solution Overview
Problem
Existing electric vehicle power systems face challenges in efficiently converting high voltage from a battery pack to a lower voltage for low voltage components while maintaining balanced electrical load and avoiding undesirable power drain or high costs due to the use of single DC/DC converters or unbalanced power distribution among battery cells.
Innovation Solution
A system comprising a plurality of DC/DC converters with inputs coupled to respective battery units and outputs in parallel to a low-voltage bus, controlled by a first controller to regulate bus voltage and a second controller distributing current based on battery states of charge, ensuring uniform state of charge and stable output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single DC/DC converter is used to convert high voltage to low voltage, then the voltage conversion is achieved, but the cost increases due to high voltage components required in the converter
Solution Approach 1:
The battery pack is divided into multiple series-connected battery units, with each unit connected to a separate DC/DC converter. This segmentation allows each converter to operate at lower voltage levels, avoiding the need for expensive high voltage components while achieving the required voltage conversion through parallel connection of converter outputs.
2Stability of the object's composition
If a bank of DC/DC converters is used with each converter connected to a different battery unit, then the electrical load is balanced among battery cells, but the common output voltage may not remain constant at the desired value due to independent power variation from each converter
Solution Approach 1:
A control system continuously monitors the actual bus voltage and compares it to a target voltage. Based on this feedback, the controller adjusts the current allocation to individual DC/DC converters, ensuring that the common output voltage remains stable at the desired value while maintaining balanced electrical load distribution.
3Stability of the object's composition
If independently varying the power from each DC/DC converter is used to decrease the rate of divergence of battery state from reference state, then the states of charge for battery units are more uniform, but the common output voltage may not remain constant
Solution Approach 1:
The control system uses feedback from actual bus voltage measurements to dynamically adjust current allocation to each converter. This allows the system to maintain uniform state of charge across battery units while compensating for power variations to keep the common output voltage constant at the desired value.
Solution Approach 2:
The system dynamically adjusts the operating point of each DC/DC converter based on real-time conditions. By continuously varying the power contribution from each converter according to battery state of charge and bus voltage requirements, the system achieves both state of charge uniformity and voltage constancy.
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 stabilizes the low-voltage bus voltage, balances electrical load among battery cells, and maintains uniform state of charge, improving overall battery pack performance and reducing voltage fluctuations.
Implementation Method 1
A plurality of DC/DC converters each has an input coupled to a respective battery unit, and the DC/DC converters have respective outputs coupled in parallel to a low-voltage bus
Data Source
AI summary
An electrified vehicle high voltage battery pack has series-connected battery units or cells combining to provide the high voltage. To power a low voltage bus (e.g., for low voltage accessories or charging a low voltage battery) in a balanced manner, a plurality of DC/DC converters each has an input coupled to a respective battery unit and the converters have respective outputs coupled in parallel to the low voltage bus. A first loop controller receives an actual bus voltage. The first controller generates a target current in response to the bus voltage adapted to regulate the actual bus voltage to a target voltage less than the high voltage. A second controller distributes the target current into a plurality of allocated current commands for respective converters according to respective states of charge of the battery units connected to the converters.