Dynamic Battery Current Limit Calculation for Power Prediction
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Solution Overview
Problem
Manufacturer-defined current limits for battery packs can be overly conservative or aggressive, leading to suboptimal system control decisions due to inaccurate estimation of true battery power capability, which affects motor speed, torque, and charging efficiency in vehicles equipped with electric machines.
Innovation Solution
A controller-executed method that calculates the maximum current and predicts power capability by determining the open-circuit voltage and internal resistance of the battery pack, selecting the lower absolute value between calculated and predetermined current limits, and adapting to the battery's age and state of charge to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If manufacturer-defined current limits are used for battery pack control, then battery safety is ensured, but the true power capability is inaccurately estimated leading to suboptimal system performance
Solution Approach 1:
The patent changes the parameter used for current limit determination from fixed manufacturer-defined values to dynamically calculated values based on real-time battery characteristics (open-circuit voltage and internal resistance). This allows the system to adapt the current limit parameter to the actual battery state, improving both safety and performance simultaneously.
Solution Approach 2:
The patent implements a feedback mechanism where the controller continuously monitors battery open-circuit voltage and internal resistance, calculates the maximum current based on these measurements, and uses this calculated value to control battery charging and discharging. This closed-loop feedback replaces the open-loop manufacturer-defined limits, enabling accurate power capability estimation while ensuring safety.
2Reliability
If predetermined current limits are applied to battery pack, then conservative safety margins are maintained, but motor speed, torque, and acceleration are unnecessarily restricted
Solution Approach 1:
The patent transforms the static, predetermined current limits into dynamic limits that are continuously updated based on real-time battery measurements. The controller calculates maximum current dynamically using current open-circuit voltage and internal resistance values, allowing motor speed to adapt to the battery's true instantaneous power capability rather than being constrained by fixed conservative limits.
Solution Approach 2:
The patent changes the current limit parameter from a fixed manufacturer-specified value to a dynamically calculated value based on measured battery parameters. This parameter transformation enables the system to achieve optimal motor speed, torque, and acceleration by using the actual battery power capability rather than conservative predetermined limits.
3Reliability
If manufacturer-defined voltage limits are used for battery pack control, then battery protection is ensured, but continuous power output is restricted over time
Solution Approach 1:
The patent implements feedback control where the controller continuously monitors battery voltage, current, and temperature, and dynamically adjusts the maximum current limit based on real-time battery state. This feedback mechanism replaces fixed voltage-time limits with adaptive current control, enabling continuous power output to match the battery's actual capability while maintaining protection through real-time monitoring.
Solution Approach 2:
The patent changes the control parameter from fixed voltage-time limits to dynamically calculated current limits based on real-time battery characteristics. This parameter transformation allows the system to optimize continuous power output by using the battery's actual power capability rather than being restricted by conservative predetermined voltage limits over time windows.
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 allows for more accurate prediction of battery power capability, optimizing motor control, acceleration, and charging efficiency, ensuring optimal vehicle performance and reducing the risk of underestimating or overestimating battery capacity.
Implementation Method 1
determining an open-circuit voltage of the battery pack via a controller
Implementation Method 2
calculating an internal resistance of the battery pack using a measured voltage and current
Data Source
AI summary
A method for predicting power capability of a battery pack in a system includes determining an open-circuit voltage of the battery pack via a controller, calculating pack resistance using measured voltage and current during a charge or discharge event, and calculating a maximum current of the pack using the open-circuit voltage and internal resistance. The method includes selecting the lower of an absolute value of each of the calculated maximum discharge current and predetermined current limit, calculating the discharge power capability of the battery pack using the selected lower absolute value, and controlling a state of the system using the calculated power capability. The method also controls the charging current and parameters during a DC fast-charging operation. A system includes the battery pack, electric machine, and controller. The system may be a vehicle having an electric powertrain, with an electric machine powered by the battery pack.