Transformer Current Sensor With Pulsed Auxiliary Saturation
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Solution Overview
Problem
Current current measurement technologies face challenges in achieving high-bandwidth, high-accuracy, low-power consumption, low temperature sensitivity, and low cost, while also providing isolation and being able to measure both direct and alternating currents, especially at zero amps and bidirectional currents.
Innovation Solution
A current sensor using a transformer with a magnetic core, a primary winding for measuring current, a secondary winding for sampling, and an auxiliary winding to selectively saturate the core, allowing for pulsed auxiliary current to reduce power consumption and eliminate the need for a constant bias current, enabling high-bandwidth and accurate measurement of currents down to zero amps with reduced power loss and offset voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall-effect current sensor is used, then isolation and good resolution are achieved, but bandwidth is limited to a few hundred kilohertz and cost is high
Solution Approach 1:
The patent replaces the Hall-effect sensor mechanism with a transformer-based electromagnetic induction system. The transformer uses magnetic coupling between primary and secondary windings to transfer current information, eliminating the need for Hall-effect devices and their inherent bandwidth limitations while maintaining isolation and measurement capability.
Solution Approach 2:
The patent changes the operating parameters by using a transformer core that can be selectively saturated through pulsed auxiliary current. This allows the system to operate in different magnetic states (saturated and unsaturated) to achieve both high bandwidth for AC measurements and high precision for DC and low-current measurements, overcoming the fixed parameter limitations of Hall-effect sensors.
2Measurement precision
If a bias winding carrying steady current is added to measure currents near zero, then measurement capability is improved, but power drain increases and bandwidth decreases
Solution Approach 1:
The patent replaces continuous bias current with periodic pulsed auxiliary current applied to the auxiliary winding. The pulsed current selectively saturates the transformer core only during measurement cycles, eliminating continuous power drain while maintaining the ability to measure currents near zero. The pulses are synchronized with the measurement process, providing bias only when needed.
Solution Approach 2:
The patent makes the auxiliary current dynamic by controlling it through switches that enable pulsed operation. The auxiliary winding receives current only during specific time intervals when saturation is required for measurement, rather than maintaining a steady state. This dynamic control allows the system to adapt power consumption to measurement requirements.
3Measurement precision
If ferrite or permalloy core with large cross-sectional area is used, then accuracy is improved, but temperature dependence increases and device size increases
Solution Approach 1:
The patent changes the magnetic operating parameters by using pulsed auxiliary current to selectively saturate the core. This allows the use of smaller core cross-sections that can be rapidly driven into and out of saturation, achieving high accuracy through controlled magnetic states rather than relying on large core size for linear operation. The saturation technique reduces temperature sensitivity by operating in a controlled magnetic regime.
Solution Approach 2:
The patent employs periodic pulsing of the auxiliary winding to repeatedly saturate and reset the magnetic core. This periodic saturation technique allows the use of smaller, less temperature-sensitive core materials while maintaining measurement accuracy through controlled magnetic cycling, rather than requiring large ferrite or permalloy cores that are highly susceptible to temperature changes.
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 high-accuracy and high-bandwidth current measurements with low temperature sensitivity and cost, capable of measuring currents down to zero amps and bidirectional currents, while reducing power consumption and offset voltage, and allowing for direct interface with analog-to-digital converters.
Implementation Method 1
an auxiliary winding used to selectively bring the core into saturation
Implementation Method 2
a transformer comprising a magnetic core, having a primary winding with one or more turns that carries the current to be measured, a secondary winding that is used to sample the primary current
Data Source
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AI summary
A current sensor is provided that employs a primary winding that carries the current to be measured, and a secondary winding that controls the flux inside the magnetic core, provides a sample of the primary current, and also helps to control the flux at small primary currents and to saturate the transformer. An auxiliary winding is optionally used to control the flux in order to simplify control of the sensor. By periodically applying a certain voltage at the secondary winding, the transformer core is forced out of saturation, and a sample of the primary current is taken by a sensing circuit that may include a sample-and-hold circuit and an analog-to-digital converter. A control circuit is employed to control the currents flowing in the secondary winding and optional auxiliary winding and to manage the sensing circuit.