Stator Isolation Mounts for Common Mode Current Reduction
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Solution Overview
Problem
Existing power systems with electrical machines connected to power converters suffer from significant electromagnetic emissions and interference due to common mode currents, which are difficult to control effectively with conventional methods, particularly as they can lead to increased current flow during ground faults and safety issues.
Innovation Solution
The power system achieves substantial reduction of common mode currents by electrically isolating the stator from the stator frame using 'sandwich-type' anti-vibration mounts with elastomeric layers and rigid plates, providing both mechanical decoupling and electrical insulation, and incorporating a parallel RC filter to control common mode voltage and currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the stator is completely electrically isolated from the stator frame, then common mode currents are substantially eliminated, but the stator requires robust mechanical mounting to handle dynamic forces
Solution Approach 1:
The electrical connection between stator and stator frame is segmented into multiple discrete mounting locations (at least two) around the stator circumference. Each mounting location provides both mechanical support and electrical isolation, distributing the mechanical loads while maintaining electrical isolation effectiveness.
Solution Approach 2:
Electrical insulators are introduced as intermediary components between the stator and stator frame at the mounting locations. These insulators mechanically couple the stator to the frame while electrically isolating them, eliminating the need for direct electrical contact and thereby eliminating common mode current paths.
2Object-generated harmful factors
If conventional common mode filters are used to reduce electromagnetic emissions, then emissions are reduced, but the filters increase device complexity and cost
Solution Approach 1:
The common mode current generation source is extracted by eliminating the direct electrical connection between the stator and grounded stator frame. By removing the capacitance path through which common mode currents flow, the need for complex common mode filters is eliminated, simplifying the overall system.
Solution Approach 2:
The electrical insulators, initially introduced to provide mechanical mounting, inadvertently provide the benefit of electrical isolation that eliminates common mode currents. This converts a structural component into a dual-function element that simultaneously provides mechanical support and electromagnetic isolation.
3Ease of manufacture
If direct electrical connection between stator and stator frame is maintained, then mechanical mounting is simplified, but stray capacitance causes common mode current circulation
Solution Approach 1:
Electrical insulators are placed between the stator and stator frame at mounting locations to serve as intermediary components. These insulators maintain the mechanical coupling needed for structural support while eliminating the direct electrical contact that creates stray capacitance and common mode current paths.
Solution Approach 2:
The mounting structure uses composite construction combining mechanical fastening elements with electrical insulating materials. This composite approach provides both the mechanical strength needed for mounting and the electrical isolation needed to eliminate common mode currents.
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 significantly reduces electromagnetic emissions and interference, allows for smaller, cheaper components to manage common mode currents, and enhances safety by preventing excessive voltage stress on the stator insulation, while maintaining effective isolation and vibration reduction.
Implementation Method 1
The stator is electrically isolated from the stator frame by a plurality of stator mounts. Each stator mount is a sandwich-type anti-vibration mount with a plurality of elastomeric layers interleaved with rigid plates.
Implementation Method 2
Each stator mount is a sandwich-type anti-vibration mount with a plurality of elastomeric layers interleaved with rigid plates
Implementation Method 3
incorporating a parallel RC filter to control common mode voltage and currents
Implementation Method 4
incorporating a parallel RC filter to control common mode voltage and currents
Data Source
Figure 1
Figure 2~3
Figure 4~7
AI summary
The invention relates to a power system that includes an electrical machine 1, e.g., a motor or generator. The electrical machine has a stator 2 with a stator winding connected to a power converter. The power system includes an assembly 6 to reduce, and optionally eliminate, common mode currents between the electrical machine 1 and the power converter. The assembly includes a stator frame 8 connected to ground potential and an electrical insulator (e.g., a plurality of stator mounts 14) located between the stator frame 8 and the stator 2.