Battery String Midpoint Voltage Sensing Against Common-Impedance Errors
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Solution Overview
Problem
Existing battery monitoring systems require direct connections to each battery in a string for accurate midpoint voltage measurements, which is impractical and prone to errors due to common-impedance coupling and complex system integrations.
Innovation Solution
A battery system with a midpoint voltage sensor that measures the voltage at a terminal with an equal number of batteries between system cables at both ends of the string, using a logarithmic ratio amplifier to minimize the effects of common-impedance coupling and provide accurate error signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct connections to each battery are used for monitoring, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the midpoint voltage measurement function from the complex direct-connection monitoring system. By measuring only the midpoint voltage and comparing it to half the total string voltage, the system eliminates the need for direct connections to each individual battery while maintaining measurement accuracy. This extraction of the essential measurement function resolves the contradiction between precision and complexity.
Solution Approach 2:
The patent introduces an intermediary measurement approach using the midpoint voltage as a reference point. Instead of directly monitoring each battery, the system uses the midpoint voltage and total string voltage as intermediaries to infer battery conditions. This intermediary method simplifies the monitoring system while maintaining the ability to detect battery defects.
2Measurement precision
If direct connections to each battery are used for monitoring, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The patent extracts the monitoring function to require only two connection points (string terminals) and one midpoint connection, eliminating the need for complex direct connections to each battery. This extraction dramatically simplifies installation and operation while maintaining measurement precision through the midpoint voltage comparison method.
3Measurement precision
If complex battery monitoring systems are implemented, then measurement precision is improved, but reliability deteriorates due to common-impedance coupling
Solution Approach 1:
The patent uses the midpoint voltage as an intermediary reference that is electrically close to both battery terminals. By comparing the midpoint voltage to half the total string voltage, the system creates a measurement method that is insensitive to common-impedance coupling effects. This intermediary approach maintains measurement reliability while achieving the required precision.
Solution Approach 2:
The patent applies the equipotentiality principle by measuring voltages at points that are electrically close to each other (midpoint and string terminals). This minimizes the potential difference caused by common-impedance coupling, as the measurement points are at nearly the same electrical potential relative to the battery string, thereby improving measurement reliability.
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
The system accurately measures the midpoint voltage of each battery string, minimizing errors from common-impedance coupling and allowing for precise health monitoring of battery strings, thereby extending battery life and preventing failures.
Implementation Method 1
using a logarithmic ratio amplifier to minimize the effects of common-impedance coupling and provide accurate error signals
Data Source
AI summary
A mid-string voltage sensor is disposed in proximity to a storage-battery string and determines an error signal between the expected mid-string voltage and the actual mid-string voltage to aid in detecting faults in one or more of the batteries of the string. Each sensor is connected to or close to the battery string terminals and to a terminal at the midpoint of the group of batteries connected in series. The arrangement suppresses errors due to common-impedance coupling, and the measured voltages are decoupled from the battery system, prior to determining the error. A fractional error voltage is derived using a logarithmic ratio amplifier so that the error signal determination is performed at the sensor, with the resultant error signal suitable for coupling to a battery health monitor.