Electric Drive Unit Galvanic Isolation for Noise Reduction
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Solution Overview
Problem
Existing electric drive units experience high-frequency electromagnetic noise emission due to the impedance difference between the stator and bearing routes, leading to external noise and potential bearing degradation.
Innovation Solution
The electric drive unit design modifies the bearing route to have a higher impedance than the stator route by increasing the resistance and inductance of the bearing route, or decreasing the capacitance, to redirect high-frequency currents away from external emission paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bearing is provided between the motor and the inverter, then the rotor is retained and supported, but the impedance of the electric current path through the shaft and bearing becomes lower, causing high-frequency current to flow and electromagnetic noise to be emitted
Solution Approach 1:
The inverter is extracted and placed in a separate inverter casing that is galvanically isolated from the motor housing. This separation removes the inverter from the high-frequency current path, preventing the bearing from becoming part of the noise-generating circuit while maintaining its rotor support function.
Solution Approach 2:
A galvanic isolation barrier is introduced as an intermediary between the inverter and motor components. This isolation prevents direct electrical connection, blocking the high-frequency current from flowing through the bearing and shaft, thus eliminating electromagnetic noise while preserving mechanical support.
2Reliability
If the inverter and inverter casing are arranged inside from the bearings, then the inverter is protected, but the bearing route impedance becomes lower than the stator route impedance, causing high-frequency current to flow through the bearing
Solution Approach 1:
The inverter is extracted from the motor housing and placed in a separate inverter casing. This extraction changes the electrical topology so that the bearing is no longer part of the low-impedance return path, preventing high-frequency current from flowing through the bearing even though the inverter remains protected.
Solution Approach 2:
Galvanic isolation acts as an intermediary that breaks the electrical continuity between the inverter casing and motor components. This isolation ensures that the bearing route impedance becomes higher than the stator route impedance, redirecting high-frequency current away from the bearing.
3Ease of operation
If the impedance of the bearing route is lower than the stator route, then current flows more easily through the bearing, but electromagnetic noise is emitted externally and bearing degradation occurs
Solution Approach 1:
Galvanic isolation is introduced as an intermediary that increases the impedance of the bearing route. This isolation barrier prevents high-frequency current from preferentially flowing through the bearing, thereby eliminating electromagnetic noise and preventing bearing degradation while still allowing necessary current flow through the stator.
Solution Approach 2:
The electrical impedance parameters of the bearing route are changed by introducing galvanic isolation. This parameter change increases the bearing route impedance above that of the stator route, fundamentally altering the current distribution to eliminate harmful high-frequency current flow through the bearing.
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
This configuration reduces high-frequency electric current flow through the shaft and bearings, alleviating external electromagnetic noise and extending bearing lifespan.
Implementation Method 1
a stator that receives an AC current from the inverter and forms a magnetic field; a rotor rotated by the magnetic field formed by the stator
Implementation Method 2
modifies the bearing route to have a higher impedance than the stator route by increasing the resistance and inductance of the bearing route
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
An electric drive unit includes an inverter, a stator that receives an AC current from the inverter and forms a magnetic field, a rotor rotated by the magnetic field formed by the stator, a shaft that protrudes into both sides in an axial direction of the rotor and moves in synchronization with the rotor, an inverter casing that stores the inverter in a galvanic isolation state, and a motor housing. The motor housing stores the stator and the rotor in a galvanic isolation state, rotatably supports one end of the shaft using a first bearing, and rotatably supports the other end of the shaft using a second bearing. The inverter and the inverter casing are arranged in an inner side from a pair of bearings including the first and second bearings.