EV Battery DC/DC Converter Balancing Control
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Solution Overview
Problem
Existing electric vehicle power systems face challenges in efficiently balancing the state of charge among battery units, leading to voltage instability and rapid degradation of low-voltage batteries due to unbalanced power draw from DC/DC converters.
Innovation Solution
A control strategy and architecture that uses a central module with an outer loop controller to regulate the low-voltage bus voltage and distribute target currents to local controllers, allowing for bidirectional current flow and weighting factors to balance battery units with extreme states of charge, thereby maintaining stable voltage and extending battery life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If each DC/DC converter independently adjusts power according to battery state to balance charge states, then battery state uniformity is improved, but output voltage stability deteriorates
Solution Approach 1:
The system divides the battery pack into multiple battery units, each with its own DC/DC converter for independent control. This segmentation allows individual adjustment of each battery unit's power output to balance charge states while maintaining overall system voltage stability through coordinated control.
Solution Approach 2:
The control system continuously monitors battery states and output voltage, using feedback signals to adjust converter operations. The controller receives voltage feedback from the common output bus and battery state information, then modulates each converter's duty cycle to simultaneously achieve charge balancing and voltage stabilization.
2Stability of the object's composition
If a bank of DC/DC converters is used to convert high voltage to low voltage and balance electrical load, then battery cell load balancing is improved, but system complexity increases
Solution Approach 1:
Each DC/DC converter in the bank is designed as a universal module capable of operating in multiple modes (buck, boost, or bidirectional) to serve different battery units with varying voltage levels and charge states. This multi-functionality reduces the need for specialized converters for each battery unit, simplifying the overall system architecture.
Solution Approach 2:
The control system dynamically adjusts operating parameters (duty cycle, switching frequency, current limits) of each converter based on real-time battery state measurements. By changing these parameters rather than the physical converter configuration, the system achieves load balancing without requiring complex hardware reconfiguration.
3Loss of energy
If the ratio of converter input voltage to output voltage is close to unity for higher efficiency, then energy conversion efficiency is improved, but voltage conversion capability is reduced
Solution Approach 1:
The DC/DC converters employ dynamic control strategies that continuously adjust the voltage conversion ratio based on the instantaneous operating conditions. When battery voltage is close to the target low voltage, the converter operates in buck mode with high efficiency. When battery voltage diverges significantly, the converter dynamically switches to boost mode or adjusts duty cycle to maintain efficient operation across a wide voltage range.
Solution Approach 2:
The converter design combines multiple switching topologies (buck, boost, and bidirectional circuits) into a single integrated converter module. This composite approach allows the converter to operate efficiently across a wide range of input-to-output voltage ratios by selecting the appropriate topology based on real-time conditions, thereby maintaining both efficiency and adaptability.
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 quickly balances battery units, reduces state of charge divergence, and protects weaker cells, enhancing overall battery pack performance and extending battery life by maintaining stable voltage and balanced power distribution.
Implementation Method 1
a DC/DC converter has been used to down convert the high voltage to an appropriate lower voltage to drive a low voltage power bus
Data Source
AI summary
A high voltage battery pack comprises series-connected battery units, each separately powering a respective DC/DC converter. The converter outputs are coupled in parallel to supply a low-voltage DC bus. A central module has 1) an outer loop controller generating a target current to regulate the bus voltage and 2) an allocator distributing the target current via allocated current commands for respective converters. Local controllers each regulate an output current of a respective converter. The allocator identifies battery units having a predetermined deviation from a reference metric that characterizes the battery pack, allocates reverse currents to respective converters for the identified battery units, and increases the target current commanded for the DC/DC converters not allocated to have a reverse current by the allocated reverse currents. Battery units with extremely low or high states as compared with the other units are quickly balanced, thereby improving overall performance of the battery pack.