Filter Circuit With Compensation Resistance For Battery Voltage Detection
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Solution Overview
Problem
Existing filter circuits in electric and hybrid vehicles fail to adequately remove noise in the intended frequency domain due to fluctuations in capacitance caused by high DC bias voltages, leading to inaccurate voltage measurements and potential capacitor size increases.
Innovation Solution
A filter circuit is designed with a resistor connected between battery pack circuit output terminals and voltage detection circuit input terminals, and a capacitor connected to ground, with a compensation resistance value determined to maintain a predetermined cutoff frequency despite capacitance fluctuations, using ceramic capacitors to ensure adequate noise reduction and withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a capacitor is connected between the terminal of each battery cell and the ground to improve noise removal capability, then the capability of removing noise is improved, but the voltage applied between the terminals of the capacitor becomes high, requiring increased withstand voltage of each capacitor
Solution Approach 1:
The filter circuit is divided into multiple independent filter units, each handling a specific battery cell. Each filter unit consists of a resistor and capacitor connected in series between the battery cell terminal and ground, with the voltage detection circuit connected to the resistor-battery cell interface. This segmentation allows each capacitor to handle only the voltage of its associated battery cell rather than the total pack voltage.
Solution Approach 2:
A resistor is introduced as an intermediary component between the battery cell terminal and the capacitor. This resistor limits the voltage applied across the capacitor to a manageable level while still allowing the filter unit to remove noise from the battery cell voltage signal. The intermediary resistor protects the capacitor from high voltage stress.
2Weight of stationary object
If a ceramic capacitor with high withstand voltage and small size is employed, then the filter size and cost are reduced, but the capacitance fluctuates depending on the applied DC bias voltage, causing cutoff frequency variation and inadequate noise removal
Solution Approach 1:
The resistance value of the resistor in each filter unit is specifically selected based on the expected DC bias voltage range and the capacitance characteristics of the ceramic capacitor. By adjusting the resistance parameter, the cutoff frequency is maintained within the desired range despite capacitance fluctuations caused by DC bias voltage. The resistor value is calculated to compensate for the capacitor's voltage-dependent capacitance changes.
3Object-affected harmful factors
If the cutoff frequency of the filter is set too low to remove noise adequately, then noise removal is improved, but the effect of the filter appears in fast fluctuations in voltage of the battery cell itself, deteriorating voltage monitoring capability
Solution Approach 1:
Each filter unit is designed with locally optimized parameters (resistor and capacitor values) tailored to the specific noise characteristics and voltage monitoring requirements of its associated battery cell. The filter parameters are selected to achieve the optimal balance between noise removal and signal preservation for each individual cell, rather than using a uniform low cutoff frequency for all cells.
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 filter circuit effectively reduces noise in the intended frequency domain, maintaining accurate voltage detection and ensuring necessary withstand voltage, even with varying DC bias voltages, while keeping the filter size and cost minimal.
Implementation Method 1
a capacitor (Cf) connected between the any one of the input terminals (Ti01 to Ti10) of the voltage detection circuit (30) and a ground terminal
Implementation Method 2
the capability of removing the noise that arises between the terminal of each battery cell and the ground is low
Implementation Method 3
a resistor (Rf) connected between any one of the output terminals (T01 to T10) of the battery pack circuit (10) and any one of a plurality of input terminals (Ti01 to Ti10) of the voltage detection circuit (30)
Data Source
AI summary
By configuring low-pass filters each with a resistor and a capacitor, noise is removed. Based on a reference value of DC voltage that appears at output terminals of a battery pack circuit, a lowering portion of capacitance that arises in the respective capacitors is estimated in advance, and a compensation value is included in the resistance value of the respective resistors such that the cutoff frequencies of the low-pass filters are within an intended range. Even when a high voltage is handled, the variance in cutoff frequencies can be prevented from arising and the noise in an unnecessary frequency domain can be adequately reduced.