Active Core Current Sensor PWM Saturation Control
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Solution Overview
Problem
Current sensors, such as current transformers and Hall effect sensors, face limitations in accurately measuring high currents, especially direct currents, and are susceptible to foreign magnetic fields, with active core solutions requiring significant power for flux control.
Innovation Solution
A current sensing technique using a closed magnetic path in a high permeability core, where the core is driven to saturation and then altered out of saturation to maintain accuracy, allowing for reliable measurement of both alternating and direct currents, even in the presence of foreign fields, using control circuitry and measurement circuitry to sample the current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current transformers are used to sense high currents, then the core may saturate, but this rendering reliable sensing impossible
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation (PWM) to periodically drive the core into saturation and then reset it. The control circuit switches the primary winding with PWM signals, allowing the core to operate in a controlled saturation cycle that prevents permanent saturation and maintains measurement reliability for high current sensing.
Solution Approach 2:
The patent changes the operating parameters of the core by dynamically adjusting the flux level through PWM control. By varying the duty cycle of the PWM signal, the control circuit can adjust the amount of flux in the core, allowing it to operate in different regions including controlled saturation, thereby maintaining measurement accuracy across a wide current range.
2Measurement precision
If active core solutions are used to control flux, then flux control is achieved, but considerable power is required
Solution Approach 1:
The patent implements self-service by using the energy from the primary current itself to generate the flux in the core, rather than requiring an external power source. The primary winding carries the current to be measured, and this same current creates the magnetic flux, eliminating the need for separate excitation power and significantly reducing overall power consumption.
Solution Approach 2:
The primary winding serves multiple functions: it carries the current to be measured and simultaneously generates the magnetic flux in the core. This multi-functionality eliminates the need for separate excitation windings and power sources, reducing both device complexity and power requirements while maintaining accurate flux control.
3Measurement precision
If Hall effect sensors are used, then current sensing is achieved, but susceptibility to foreign magnetic fields occurs
Solution Approach 1:
The patent converts the potential harmful effect of foreign magnetic fields into a beneficial feature by using the same magnetic core that provides flux control. The high permeability core concentrates and directs the magnetic flux, including any foreign field components, through a defined path that does not interfere with the measurement. The PWM-controlled saturation technique further immune the measurement by operating in a regime where foreign fields have minimal impact.
4Measurement precision
If current transformers are used for high currents, then sensing capability is provided, but core saturation occurs
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation (PWM) to periodically drive the core into saturation and then reset it. The control circuit switches the primary winding with PWM signals, allowing the core to operate in a controlled saturation cycle that prevents permanent saturation and maintains measurement reliability for high current sensing.
Solution Approach 2:
The patent implements feedback by using a secondary winding to sense the core flux and feeding this information back to the control circuit. The control circuit adjusts the PWM duty cycle based on the secondary winding output to maintain the core flux within desired limits, ensuring stable operation even at high current levels where saturation might otherwise occur.
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
Enables accurate measurement of high currents with smaller core structures, capable of handling both AC and DC, and operates effectively in various applications by adapting to different current levels without requiring significant power for saturation control.
Implementation Method 1
allow a primary current through the conductor to create a flux in a closed core of a sensing coil
Implementation Method 2
including flux levels that saturate the core
Implementation Method 3
The flux, proportional to the flowing current, induces a current or a voltage in the sensing coil
Data Source
Figure 1~2
Figure 3A~4
Figure 5~6
AI summary
Methods and system for sensing current include detecting current through a sensing coil resulting from a field produced by current through a primary conductor. The sensing coil has a core that may become saturated by the primary current field. If the core is not saturated, a sensing circuit may detect the current through the sensing coil by changing the state of at least one controlled switch. If the core is saturated, the sensing circuit changes the state of the at least one controlled switch to pull the core out of saturation, at which time a current measurement is made. The technique may be used with AC currents, including changing currents, as well as with DC currents, and currents that may be AC at times and become essentially DC at other times.