Auxiliary Winding Current Sensing for Electromagnetic Components
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Solution Overview
Problem
Conventional current sensing techniques for electromagnetic components, such as shunt resistors, DCR circuits, Hall effect sensors, and current transformers, face issues like power loss, accuracy errors, temperature dependence, and high frequency limitations, making them unsuitable for accurate current estimation in various electrical devices.
Innovation Solution
A current sense circuit utilizing an auxiliary winding that compensates for the inductance of the main winding, allowing for precise current estimation through measuring the voltage between the main and auxiliary windings without significant current flow through the auxiliary winding, thereby avoiding power loss and temperature-dependent inaccuracies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a shunt resistor is used to measure current, then the current measurement is simple and straightforward, but power is wasted due to I2R losses and the effective resistance of the component increases
Solution Approach 1:
The patent introduces an auxiliary winding as an intermediary element that magnetically couples to the main winding. This auxiliary winding senses the current through magnetic coupling rather than direct electrical connection, eliminating the need for a shunt resistor and its associated I2R power losses while maintaining measurement capability
Solution Approach 2:
The patent replaces the electrical measurement system (shunt resistor with voltage measurement) with a magnetic field-based system. The auxiliary winding detects current through electromagnetic induction, substituting direct electrical measurement with indirect magnetic field sensing to avoid power dissipation
2Loss of energy
If a shunt resistor with very low resistance is used to minimize power loss, then power waste is reduced, but the measured voltage becomes noisy and temperature dependence increases leading to inaccurate results
Solution Approach 1:
The auxiliary winding acts as a magnetic intermediary that transfers current information from the main winding without direct electrical contact. This magnetic coupling provides a stable, low-noise signal that is immune to the temperature drift and noise issues that plague low-value shunt resistors
Solution Approach 2:
The patent extracts the current sensing function from the main current path by using a separate auxiliary winding. This separation removes the measurement device from the high-current path, eliminating the trade-off between low resistance (for power efficiency) and low noise/high accuracy
3Loss of energy
If a DCR sense circuit is used to avoid power loss, then power efficiency is improved, but accuracy issues arise due to capacitor tolerance, temperature dependencies, and frequency dependence
Solution Approach 1:
The auxiliary winding serves as a magnetic intermediary that provides a direct proportional relationship between main winding current and auxiliary winding voltage. This eliminates the need for frequency-dependent capacitive matching circuits and their associated tolerance and temperature drift issues
Solution Approach 2:
The patent changes the sensing parameter from voltage division through frequency-dependent capacitors (DCR method) to direct magnetic coupling through the auxiliary winding. This parameter change eliminates frequency dependence and capacitor tolerance issues while maintaining power efficiency
4Measurement precision
If a current transformer is used to measure current, then voltage measurement is amplified and current through the sensing circuit is reduced, but the device size increases and cost increases and AC insertion loss occurs
Solution Approach 1:
The auxiliary winding is integrated into the same magnetic core structure as the main winding, making the current sensing function universal to the transformer design itself. This eliminates the need for separate current transformer devices, reducing overall device size, complexity, and cost while maintaining measurement capability
Solution Approach 2:
The patent merges the current sensing function with the existing transformer structure by adding an auxiliary winding to the same core. This integration combines power transformation and current sensing into a single device, eliminating the need for separate current transformer components and reducing overall system complexity
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 solution provides accurate and temperature-stable current estimation with minimal extra circuitry, reducing noise and power loss, and is applicable in various electromagnetic components like transformers and motor windings.
Implementation Method 1
The auxiliary winding is configured to compensate for the inductance of the main winding
Data Source
AI summary
Many electronic devices, such as voltage converters, motors, etc., include electromagnetic components through which the current flow must be estimated. Such electromagnetic components include transformer windings, motor windings, and other types of inductors. In order to estimate the current through such components with reasonable accuracy and without unnecessary power loss, the inherent resistance of the electromagnetic component is used in conjunction with an auxiliary winding through which effectively no current flows. A first terminal of the auxiliary winding directly connects to a first terminal of the electromagnetic component and runs in parallel to the component. The voltage across a second terminal of the auxiliary winding and a second terminal of the electromagnetic component is measured and closely approximates the voltage across the equivalent series resistance (ESR) of the electromagnetic component. This measured voltage is used to estimate the current through the component.