Battery Impedance Calibration Using Frequency-Domain Error Correction
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Solution Overview
Problem
Existing battery electrochemical impedance spectroscopy (EIS) systems face issues with phase shifts and signal distortion due to low-pass filters and inductance in measurement circuits, leading to inaccurate impedance measurements.
Innovation Solution
A calibration method using a high-precision resistor with known frequency response to correct for circuit errors by generating a correction function, which is applied to measured impedances to obtain accurate battery impedance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If low-pass filters are used in measurement circuits to reduce noise, then noise reduction is improved, but phase shifts and amplitude errors are introduced causing measurement precision to deteriorate
Solution Approach 1:
A calibration device with known impedance is introduced as an intermediary between the measurement circuit and the device under test. The calibration device allows the system to measure and characterize the frequency-dependent errors introduced by low-pass filters and circuit inductance, enabling correction of these errors in subsequent measurements.
Solution Approach 2:
The system performs calibration by sweeping the excitation frequency across the full measurement range and measuring the calibration device's response at each frequency. This generates a frequency-dependent correction function that accounts for how the circuit's phase shift and amplitude error parameters change with frequency, allowing accurate compensation.
2Measurement precision
If factory calibration is performed by sweeping frequency with constant amplitude AC signal, then measurement precision is improved, but device complexity and calibration cost increase
Solution Approach 1:
The calibration process is designed to be self-contained, using only the existing measurement circuitry and a simple calibration device. The system automatically performs frequency sweeping, measures the calibration device response, computes correction functions, and stores them for use in measurements, eliminating the need for external calibration equipment or complex manual procedures.
Solution Approach 2:
Instead of requiring complex physical calibration equipment, the system creates a digital copy or model of the circuit's frequency-dependent behavior through measurement and computation. The correction function stored in memory represents a mathematical model of the circuit's errors, which can be applied to correct measurements without physically modifying the circuit.
3Ease of operation
If wires and board traces are used to connect batteries, then ease of operation is improved, but inductance is introduced causing signal distortion
Solution Approach 1:
The calibration device serves as an intermediary that allows the system to measure and characterize the electrical characteristics of the connection wires and board traces. By measuring the calibration device through the same physical connections used for battery measurements, the system captures the inductive effects of these connections and includes them in the correction function.
Data Source
AI summary
An apparatus comprises a calibration device; a device under test (DUT) connected in series with the calibration device; an electrical interface coupled to the calibration device; a voltage measurement circuit coupled to the electrical interface; a current measurement circuit coupled to the electrical interface; an impedance computation circuit configured to: generate a first impedance of the calibration device in the frequency domain based on first outputs of the voltage measurement circuit and of the current measurement circuit and generate a second impedance of the DUT in the frequency domain based on second outputs of the voltage measurement circuit and of the current measurement circuit; a correction circuit configured to generate parameters representing a correction function based on the first impedance and a reference frequency response of the calibration device and provide a third impedance of the DUT based on combining the parameters with the second impedance.