Active Common Mode Current Reduction for Electric Machine Drives
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Solution Overview
Problem
Existing electric machine drive systems face challenges in reducing common mode current applied to ground, particularly when using unshielded cables, as existing solutions like shielded cables and common mode inductors are not feasible due to size constraints or application limitations.
Innovation Solution
An active common mode current reducing device is introduced, which includes a current sensing device and a controlled current source to divert common mode current back to the inverter instead of allowing it to flow to ground, using a return conductor positioned in parallel with the output conductors between the inverter and the electric machine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If shielded cables are used to couple the inverter and the electric motor, then the EMI current including common mode current is reduced, but the device complexity and cost increase
Solution Approach 1:
A common mode inductor is introduced as an intermediary component in the cable assembly. The inductor is positioned within the cable conduit and provides common mode current suppression without requiring the entire cable to be shielded, thus reducing EMI current while maintaining simpler cable structure
Solution Approach 2:
Instead of shielding the entire cable length, the solution applies local quality by placing a common mode inductor at a specific location within the cable assembly. This targeted approach provides EMI suppression where needed while keeping the overall cable structure simpler and more flexible
2Object-affected harmful factors
If common mode inductors are used to reduce common mode current, then the common mode current is reduced, but the size constraints are violated
Solution Approach 1:
The common mode inductor is segmented into multiple smaller inductors that are distributed along the cable length. Each segment provides a portion of the required common mode impedance, and together they achieve the desired current reduction while keeping each individual component compact and suitable for cable integration
3Device complexity
If unshielded cables are used to couple the inverter and the electric motor, then the device complexity is reduced, but the EMI current increases
Solution Approach 1:
A common mode inductor is introduced as an intermediary component within the unshielded cable assembly. This inductor provides the necessary common mode current suppression without requiring the cable to be shielded, thus maintaining simple unshielded cable structure while reducing EMI current
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 solution effectively reduces common mode current injected to ground, minimizing electromagnetic interference and eliminating the need for bulky shielding or inductors, making it suitable for applications where shielded cables are undesirable, such as in the aviation industry.
Implementation Method 1
a controlled current source coupled between the inverter and the load and configured to receive a current level signal from the current sensing device
Data Source
AI summary
An electric machine drive system is described. The system includes an inverter, an electric machine coupled to the inverter by at least one output conductor and including a ground connection, and an active common mode current reducing device coupled between the ground connection of the electric machine and the inverter.