Current Sensor Shielding Against EMI in Wireless Power Transfer
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Solution Overview
Problem
Current sensors for measuring current in wireless power transfer systems face challenges such as high voltage design complexities, costly components, and electromagnetic interference (EMI) due to switching noise, which complicates accurate current measurement and increases component costs.
Innovation Solution
A current sensor design that includes a sense element coupled to a magnetic field generated by the conductor's current, with a shield comprising ferrite and conductive materials to oppose external magnetic fields and prevent interference, and capacitive shields to avoid electric field coupling, allowing for accurate current measurement without EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage drop measurement across series capacitors is used to measure current, then current measurement can be achieved, but circuit complexity and component cost increase significantly
Solution Approach 1:
The patent replaces the electrical voltage measurement system with a magnetic field-based sensing system. Instead of measuring voltage drop across capacitors using complex buffer and amplifier circuits, the invention uses a magnetic sensor (such as a Hall effect sensor or fluxgate magnetometer) to detect the magnetic field generated by the current-carrying conductor, thereby substituting an electrical measurement approach with a magnetic field detection approach that avoids the complexity of high-voltage circuitry.
Solution Approach 2:
The patent introduces a magnetic field as an intermediary between the current to be measured and the sensing element. The current generates a magnetic field around the conductor, and the magnetic sensor detects this field to infer the current magnitude. This intermediary approach allows non-contact measurement and isolates the sensor from the high-voltage environment, simplifying the overall system design.
2Measurement precision
If voltage measurement is performed directly across high voltage leads, then current information can be obtained, but electromagnetic interference and safety issues arise
Solution Approach 1:
The patent uses the magnetic field surrounding the conductor as an intermediary to transfer information about the current to the sensor without direct electrical contact. This allows the measurement system to remain electrically isolated from the high-voltage circuit, eliminating electromagnetic interference and safety hazards associated with direct voltage measurement across high-voltage leads.
Solution Approach 2:
The invention substitutes direct electrical voltage measurement with non-contact magnetic field sensing. By detecting the magnetic field generated by the current-carrying conductor using a magnetic sensor, the system avoids exposure to high-voltage electromagnetic fields, thereby eliminating EMI and safety issues while maintaining current measurement capability.
3Speed
If fast switching of voltages is implemented for measurement, then current measurement speed improves, but electromagnetic interference due to switching noise increases
Solution Approach 1:
The patent replaces the fast-switching voltage measurement method with continuous magnetic field sensing. The magnetic sensor continuously detects the magnetic field around the conductor, providing real-time current information without the need for fast switching operations. This eliminates switching noise generation while maintaining measurement speed, as the magnetic field detection is inherently continuous and noise-free.
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 enables accurate and cost-effective current measurement in wireless power transfer systems by isolating the sensor from external magnetic and electric fields, reducing EMI, and eliminating the need for costly components, thus improving measurement precision and system efficiency.
Implementation Method 1
a sense element configured to couple to a magnetic field generated by a flow of current in a conductor and to produce a signal that is representative of the flow of current in the conductor
Implementation Method 2
a shield configured to generate a magnetic field that opposes an external magnetic field so that the signal produced by the sense element is substantially free of influence from the external magnetic field
Implementation Method 3
The shield comprises a first material that sandwiches the sense element to define a stack, and a second material that sandwiches the stack
Implementation Method 4
a capacitive shield disposed adjacent the sense element to avoid capacitive coupling of an electric field between the conductor and the sense element
Data Source
Figure 1~3
Figure 4A~4B
Figure 5
AI summary
Disclosed is a current sensor (600) that senses current flow in a conductor (604) by coupling a first magnetic field generated by the conductor to a sense element (602). The current sensor includes a shield (700) including a first material (702a,702b) that sandwiches the sense element to define a stack and a second material (704a,704b) that sandwiches the stack. The shield is configured to generate a second magnetic field, responsive to a third magnetic field external to the current sensor that opposes the third magnetic field. The shield is further configured to prevent production of a magnetic field that opposes the first magnetic field generated by the flow of current in the conductor.