Model-Based Controller for Battery Impedance Compensation
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Solution Overview
Problem
Current battery testers face challenges in accurately and quickly tracing a varying reference current due to the influence of battery impedance, leading to slow control behavior and significant overshooting, which worsens with age and state of charge.
Innovation Solution
Integrating a model of the battery impedance into the control loop using a model-based controller design method, allowing for predictive compensation of the counter-voltage and enabling faster, more robust current control by accounting for physical limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power electronics are designed to have an output impedance as high as possible, then the influence of the unit under test on the current control is reduced, but the achievable control bandwidth is reduced and material costs and space requirement increase
Solution Approach 1:
The invention changes the parameter of output impedance from high (conventional) to low (innovative), and compensates by actively modeling and compensating for load voltage drops through software-based impedance simulation. This allows maintaining control independence while achieving high control bandwidth without requiring large physical inductors.
Solution Approach 2:
The invention replaces the mechanical/electrical solution of using large physical inductors to achieve high output impedance with a software-based model-based controller that simulates impedance effects and compensates for load variations computationally, thereby reducing material costs and space while maintaining or improving control performance.
2Reliability
If feedforward disturbance control is used to compensate for counter voltage, then compensation is achieved, but the assumption that disturbance variable is independent of controlled variable is violated due to finite battery impedance
Solution Approach 1:
The invention implements feedback by continuously measuring the actual current and using it to update the model-based controller's prediction of voltage drops. The controller adjusts its compensation strategy based on the actual state of the battery, creating a closed-loop system that adapts to changing impedance conditions rather than relying on open-loop predictions.
Solution Approach 2:
The invention performs preliminary action by pre-calculating and storing impedance characteristics through identification routines, and by proactively compensating for expected voltage drops before they significantly affect control accuracy. The model-based controller predicts future states and adjusts control signals in advance to maintain precision.
3Device complexity
If a conventional control loop is used without load modeling, then the control structure is simple, but the actual current cannot trace the reference current exactly and without delay
Solution Approach 1:
The invention performs preliminary action by conducting identification routines that characterize the load impedance before normal operation. These pre-acquired impedance models are then used during testing to predict and compensate for voltage drops, enabling accurate current tracing without requiring complex real-time measurements during the actual test cycles.
Solution Approach 2:
The invention introduces an intermediary element - the model-based controller with integrated load model - that acts as a mediator between the power electronics and the battery. This intermediary compensates for the imperfect coupling caused by finite impedance, allowing accurate current control without requiring direct high-precision measurement or modification of the physical battery characteristics.
Data Source
AI summary
A method for testing electrical energy storage systems for driving vehicles provides that the load current of the energy storage system traces by means of a control loop, if possible without delay, a reference current that varies over time according to predetermined test cycles. The control loop is created by means of a model-based controller design method in which a model of the impedance of the energy storage system is integrated in the model of the controlled system.