Reference Electrode Voltage Sensing With Impedance Compensation
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Solution Overview
Problem
Polarization of the reference electrode in battery electric systems leads to reduced measurement accuracy of battery voltages, affecting estimation of state of charge and other battery management processes.
Innovation Solution
A compensation circuit with switches and an isolation capacitor is used to minimize the voltage drop across the reference electrode by controlling the switching sequence of the switches, matching the reference voltage at a previous time step, and minimizing parasitic bias currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a reference electrode is used to measure battery voltage, then measurement stability is improved, but measurement precision deteriorates due to electrode polarization
Solution Approach 1:
The measurement system is segmented into two distinct modes: a first mode for stable voltage measurement using the reference electrode, and a second mode for compensating polarization effects by measuring voltage without the reference electrode. This segmentation allows each mode to optimize for its specific function, resolving the contradiction between stability and precision.
Solution Approach 2:
The system changes the measurement parameter by switching between two different measurement configurations: one with the reference electrode connected (prioritizing stability) and one without (prioritizing precision). By dynamically changing which parameter configuration is active, the system resolves the contradiction between the two competing requirements.
2Stability of the object's composition
If the reference electrode is continuously connected for voltage measurement, then measurement stability is maintained, but polarization effects increase reducing measurement accuracy
Solution Approach 1:
The reference electrode connection is applied periodically rather than continuously. The system alternates between connecting the reference electrode (for stable measurements) and disconnecting it (to prevent polarization accumulation). This periodic action maintains measurement stability while preventing the buildup of polarization effects that would compromise accuracy.
Solution Approach 2:
The system performs preliminary measurements without the reference electrode to detect and compensate for polarization effects before they significantly degrade measurement accuracy. By proactively measuring and compensating for polarization, the system maintains both stability and accuracy over time.
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
Improves measurement accuracy by reducing the impact of electrode polarization, enabling precise estimation of battery state and optimizing battery management processes.
Implementation Method 1
The compensation circuit includes a voltage source, an isolation capacitor connected in parallel with the sense circuit
Implementation Method 2
The battery controller is configured to control operation of the compensation circuit to minimize a voltage drop across the reference electrode due to the parasitic bias current
Data Source
AI summary
A battery electric system, e.g., of a vehicle, includes a battery cell, reference electrode, voltage sensing circuit, compensation circuit, and battery controller. The sensing circuit measures a cell voltage of the battery cell as a measured battery voltage, and outputs a digital voltage signal indicative of the battery voltage. The compensation circuit includes a capacitor and first and second switches. In accordance with a method, the first switch closes to connect the voltage source to the capacitor for charging thereof, with the capacitor connected in parallel with the sensing circuit. The second switch closes out-of-phase with the first switch to connect the compensation circuit to the sensing circuit. The controller outputs switching control signals to control respective duty cycles of the switches when measuring the cell voltage, and thereafter uses the digital voltage signal to perform a battery management action.