Galvanic Isolation in Current Measurement Using Switching Elements
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Solution Overview
Problem
Current current sensors in power electronic circuits lack high bandwidth, stability, and efficiency, particularly in measuring dynamic currents and are prone to interference, power losses, and physical limitations such as high cooling requirements and size constraints.
Innovation Solution
A method and device for potential-free current measurement using a series connection of switching elements with current transformers, where secondary-side partial currents are summed to form a total current, and magnetic energy is stored during switching interruptions, allowing for low power loss and high-bandwidth measurement from direct current to multi-digit MHz range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If measuring resistors with high current carrying capacity are used, then the measuring range is extended, but the power losses increase significantly requiring elaborate cooling
Solution Approach 1:
The patent divides the current measurement function into multiple parallel paths, each with its own measuring resistor and switching element. By segmenting the measurement system, each resistor operates at lower current levels, reducing individual power losses while maintaining the ability to measure high total currents through parallel combination.
Solution Approach 2:
The patent employs periodic switching of measurement paths using switching elements that alternately connect different measuring resistors to the measurement circuit. This periodic action allows the system to distribute the measurement burden over time, reducing instantaneous power losses in any single resistor while maintaining continuous measurement capability.
2Speed
If high bandwidth measurement is implemented, then dynamic current measurement capability is improved, but the system complexity and cooling requirements increase
Solution Approach 1:
The measurement system is segmented into multiple independent parallel paths, each capable of high-bandwidth measurement. This segmentation allows the system to achieve high overall bandwidth while keeping each individual path relatively simple, reducing the complexity burden on any single component.
Solution Approach 2:
The patent introduces dynamic switching elements that can rapidly connect and disconnect different measurement paths. This dynamic capability enables the system to adapt to different measurement conditions in real-time, achieving high bandwidth performance while managing complexity through intelligent temporal control rather than permanent complex interconnections.
3Reliability
If galvanic isolation is implemented, then measurement safety and stability are improved, but the device complexity and cost increase
Solution Approach 1:
The patent uses switching elements as intermediary components that can be positioned to provide galvanic isolation between the high-current measurement paths and the low-voltage evaluation circuitry. These switching elements act as mediators, enabling safe signal transfer while maintaining isolation, thus improving reliability without requiring complex isolation transformers or optocouplers throughout the entire system.
4Adaptability or versatility
If multiple parallel measurement paths are used, then the measuring range and dynamic capability are improved, but the power losses and device complexity increase
Solution Approach 1:
The patent implements periodic switching control where only one or a few measurement paths are active at any given time, rather than all paths operating simultaneously. This temporal multiplexing approach allows the system to maintain a wide measuring range through multiple parallel paths while reducing total power losses by ensuring that not all paths are conducting at full load simultaneously.
Solution Approach 2:
The system uses dynamic control to allocate measurement paths based on instantaneous current requirements. When high currents are present, the system activates only the necessary paths, reducing redundant power losses. This dynamic resource allocation maintains full measurement capability while optimizing energy efficiency under varying load conditions.
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 a scalable, efficient, and stable current sensor with low power consumption, suitable for direct integration into power electronic circuits, capable of measuring both monopolar and bipolar currents with minimal interference and no voluminous cooling needs, achieving a significant reduction in power loss and size compared to existing solutions.
Implementation Method 1
current transformers (33, 34; 33n, 34n) which are switched on and off via switching elements (39; 39n)
Implementation Method 2
during interruption times of the switching elements, a stored magnetic energy of the current transformers is discharged into voltage-limiting elements
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Method and apparatus for galvanically isolated current measurement of monopolar and bipolar electric currents from direct current up to the MHz range. The current sensors are suitable for applications in highly dynamic measurement, control, and regulation systems. The current transformer(s) (33, 34, 33n, 34n) is cyclically switched off via primary switching elements (39, 39n) and completely demagnetized via voltage-limiting elements (37, 37n). Due to an overlapping operating mode of the primary switching elements (39, 39n), a total primary-side current (22) is continuously supplied. The secondary-side partial currents (25, 26) can be summed via diodes (35, 35n) as a total secondary-side current (29) across a measuring resistor (38). At the measuring terminals (27, 28) a potential-isolated, offset-free voltage signal proportional to the total primary current (22) is available for higher-level systems.