Twisted Segmented Inverter Conductors for Accurate Phase Current Sensing
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Solution Overview
Problem
Power inverters in electric vehicles face challenges due to non-uniform current conduction in copper busbars at higher frequencies, leading to increased resistance and complexity in sensing phase currents using magnetic field-based methods.
Innovation Solution
Replace copper busbars with twisted and segmented wire conductors, which reduce current density variations and magnetic field fluctuations, enabling accurate phase current sensing at both low and high frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper busbars are used for current conduction, then current can be conducted at lower frequencies, but current density becomes non-uniform and resistance increases at higher frequencies due to skin and proximity effects
Solution Approach 1:
The patent divides the solid copper busbar into multiple stranded wire conductors. Each strand is further divided into multiple filaments twisted together. This segmentation allows current to distribute more uniformly across all conductive paths, reducing the skin effect and proximity effect that cause non-uniform current density in solid busbars at high frequencies, thereby reducing resistance losses.
Solution Approach 2:
The patent uses twisted wire configurations where individual filaments are twisted around each other in helical patterns. This curved, twisted geometry increases the surface area and distributes the current path more evenly throughout the conductor cross-section, mitigating the skin effect and reducing high-frequency resistance compared to straight solid busbars.
2Measurement precision
If copper busbars are used, then current conduction is achieved, but phase current sensing using magnetic field based methods becomes complex due to varying current density distribution with frequency
Solution Approach 1:
The segmented wire structure creates multiple discrete current paths that can be individually sensed. Magnetic field sensors can be positioned to detect the magnetic field generated by each strand or group of strands, and the individual strand currents can be summed to obtain the total phase current. This approach simplifies the sensing model compared to attempting to measure the complex, frequency-varying current density distribution in a solid busbar.
Solution Approach 2:
The twisted wire structure acts as an intermediary that transforms the current conduction pattern into a form more suitable for magnetic field sensing. The regular geometric pattern of twisted strands creates predictable magnetic field distributions that are easier to model and measure, serving as an intermediate structure between the power switching circuitry and the magnetic sensors.
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 use of twisted and segmented wire conductors simplifies and enhances the accuracy of phase current measurement by minimizing Faraday induction effects, allowing for precise current determination across varying frequencies.
Implementation Method 1
At higher frequencies, current density increasingly accumulates in corners of the busbar due to Faraday induction effects (skin and proximity effects)
Implementation Method 2
At higher frequencies, current density increasingly accumulates in corners of the busbar due to Faraday induction effects (skin and proximity effects)
Implementation Method 3
Sensors are arranged in fixed locations adjacent to the copper busbars to sense magnetic fields produced by phase currents flowing through the copper busbars
Data Source
AI summary
A power inverter includes first and second inputs and a plurality of power switches in communication with the first and second inputs. First, second and third outputs communicate with the plurality of power switches. First, second and third conductors are configured to connect the first, second and third outputs to an electric machine. Each of the first, second and third conductors comprise a plurality of twisted and segmented wires.