Bi-directional Current Sensor Using Transformer Extraction
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Solution Overview
Problem
Bi-directional voltage converters face challenges such as significant power loss due to shunts, difficulty in accurately measuring small current signals amidst high frequency noise, and susceptibility to high frequency emissions, which existing current sense amplifiers struggle to address effectively.
Innovation Solution
A method for bi-directional current sensing using force commutated synchronous rectifiers and transformers to measure currents, restore signals, and add correction currents, allowing for accurate reproduction of inductor currents with low power dissipation and minimal special bias voltages, utilizing standard op amps with low gain and high bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt is used in series with the input path to measure current, then current measurement is achieved, but significant power loss occurs
Solution Approach 1:
The patent extracts the current measurement function from the main power path by using a separate sense amplifier circuit that measures voltage across the shunt without requiring the shunt to be in series with the input path. This allows current measurement while eliminating the power loss associated with series shunt placement.
Solution Approach 2:
The patent introduces an intermediary sense amplifier circuit that measures current indirectly by detecting voltage across the shunt. This intermediary measurement approach allows accurate current sensing without forcing the shunt to carry full load current in series, thereby reducing power loss.
2Measurement precision
If the current through the shunt is small during battery charging, then the voltage across the shunt becomes very small (10mV), but this makes accurate measurement difficult due to high frequency noise
Solution Approach 1:
The patent changes the measurement parameters by using a sense amplifier with optimized gain and bandwidth settings that are specifically tuned to amplify small differential voltages (like 10mV) while filtering out high-frequency noise. The amplifier parameters are adjusted to maximize signal-to-noise ratio for small current measurements.
Solution Approach 2:
The patent implements feedback mechanisms in the sense amplifier circuit that actively compensate for noise interference. The feedback loop continuously monitors and corrects measurement errors caused by high-frequency noise, maintaining accurate current measurement even when the shunt voltage is very small.
3Measurement precision
If a wide bandwidth amplifier with very high gain is used to achieve extreme accuracy, then measurement precision is improved, but the amplifier becomes susceptible to high frequency radiated and conducted emissions
Solution Approach 1:
The patent optimizes the amplifier parameters by selecting a bandwidth that is sufficient for the application but limited enough to reject high-frequency emissions. The gain is set to provide adequate signal amplification while the bandwidth is constrained to filter out high-frequency radiated and conducted emissions, achieving a balance between accuracy and emissions immunity.
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
This approach enables accurate bi-directional current sensing with low power dissipation and high frequency immunity, eliminating the need for special bias voltages and achieving efficient power processing in both charge and discharge modes.
Implementation Method 1
A first current is measured through a first force commutated synchronous rectifier via a first transformer to provide a first signal. A second current is measured through a second force commutated synchronous rectifier via a second transformer to provide a second signal.
Data Source
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AI summary
A method and apparatus for bi-directional current sensing for a synchronous rectifier bi-directional converter system is disclosed. A first current is measured through a first synchronous rectifier via a first transformer to provide a first signal. A second current is measured through a second force synchronous rectifier via a second transformer to provide a second signal. The first signal and the second signal are DC restored to provide a first DC restored signal and a second DC restored signal respectively. A first correction current is added to the first DC restored signal to produce a first corrected signal, and a second correction current is added to the second DC restored signal to produce a second corrected signal. The first corrected signal and the second corrected signal are added to produce a combined signal.