Cable Shield Termination for Motor Drive Transient Damping
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Solution Overview
Problem
High frequency voltage transients generated by mismatched impedance in power electronic systems, such as variable frequency drives and soft-starter systems, can cause over-voltages and damage insulation due to unattenuated reflected waves, with existing solutions like large low pass filters being costly and inefficient.
Innovation Solution
A system that dampens high frequency voltage transients by terminating the cable shield to a grounded resistor, with optional additional resistors connected in series between the shield and ground at both the motor and inverter ends, effectively reducing peak voltage at motor terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large low pass filters are used to attenuate high frequency transients, then voltage transient attenuation is improved, but device size, weight, and cost increase
Solution Approach 1:
The patent extracts only the essential damping function from complex filter systems by using simple resistors connected to cable shields, eliminating the need for large low pass filters while maintaining transient attenuation capability
Solution Approach 2:
The patent replaces expensive, large filter components with inexpensive resistors that can be easily installed and replaced, significantly reducing system cost and complexity while achieving the same protective function
2Reliability
If cable shield is properly terminated to ground, then voltage reflection is reduced, but system complexity increases
Solution Approach 1:
The patent applies damping resistance only at specific locations (cable ends) rather than throughout the entire cable system, achieving effective reflection reduction with minimal added complexity
Solution Approach 2:
The patent uses resistors as intermediary components between the cable shield and ground, providing simple impedance matching that reduces voltage reflections without complex termination circuits
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 grounded resistor system significantly reduces peak motor voltage by limiting it to values below 1.2 per unit, effectively damping transient reflections and preventing insulation damage, while being more cost-effective than traditional filters.
Implementation Method 1
terminating a cable shield to a grounded resistor
Implementation Method 2
grounded resistor system significantly reduces peak motor voltage by limiting it to values below 1.2 per unit, effectively damping transient reflections
Data Source
AI summary
The present application is directed to a method and apparatus operable to damp reflected voltage transients in an electric motor drive system. The system includes an inverter, an electrical cable having at least one conducting cable connected to the inverter, and an electric motor connected to the electrical cable. An inner shield is disposed along a length of the at least one conducting cable. A ground line is operable for connecting the inner shield to a ground location through a resistor connected in series therewith.