Electric Motor Control Phase Shift for Common Mode Filter Saturation
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Solution Overview
Problem
Existing control installations with multiple converters connected to a common DC supply bus face challenges in minimizing common mode voltage generation, leading to over-dimensioning of filters and potential magnetic core saturation, which is not effectively addressed by previous solutions.
Innovation Solution
A control method that determines an optimum phase-shift angle between the chopping frequencies of different converters to minimize the magnetic flux received by the common mode filter, using a data table to store notional optimum phase-shift angles for various ratios of chopping frequencies, and adjusts for asymmetrical architectures to prevent filter saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the chopping frequency of converters is increased to improve control precision, then the common mode voltage generation is exacerbated, but this leads to magnetic core saturation in the common mode filter
Solution Approach 1:
The patent applies periodic action by introducing a phase shift between the chopping frequencies of different converters. Each converter operates at a chopped frequency, but with different phase angles (e.g., 0°, 120°, 240° for three converters), creating a periodic cancellation effect that reduces the total common mode voltage while maintaining high switching frequencies for precise control
Solution Approach 2:
The patent changes the phase angle parameter of the chopping frequencies as a control variable. By adjusting the phase shift between converters (e.g., setting specific phase relationships), the system optimizes the cancellation of common mode voltages, thereby reducing the magnetic flux in the filter inductance and preventing core saturation
2Reliability
If the common mode filter is over-dimensioned to prevent magnetic core saturation, then the filter can handle worst-case scenarios, but this increases the filter size, cost, and space requirements
Solution Approach 1:
The patent converts the harmful common mode voltages into a beneficial cancellation effect. By coordinating the switching phases of multiple converters, the harmful high-frequency common mode voltages are transformed into a pattern where their peaks and valleys cancel each other out, reducing the net common mode voltage to levels that allow smaller, more economical filters
Solution Approach 2:
The patent applies preliminary action by pre-coordinating the phase relationships between converters before the common mode voltages can accumulate to dangerous levels. The control system proactively manages the switching phases to ensure cancellation occurs, preventing the need for oversized filters designed for worst-case scenarios
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 approach optimizes the maximum flux received by the common mode filter, preventing magnetic core saturation and allowing for the appropriate sizing of filters, reducing costs and space requirements while maintaining electromagnetic interference compliance.
Implementation Method 1
the maximum flux received by the inductance of the common mode filter
Implementation Method 2
ensure that its common mode inductance is never saturated
Data Source
AI summary
A control method which is deployed in a control installation of an electric motor, the control installation including a first converter controlled for the application of the first voltage pulse edges to an electric motor of a first pulse width modulation, obtained by comparing a first carrier signal, applied at a first chopping frequency, with a first modulating signal, a second converter controlled of a second pulse width modulation, obtained by comparing a second carrier signal, applied at a second chopping frequency, with a second modulating signal. The control method involves the determination of a notional optimum phase-shift angle on the basis of the first chopping frequency and the second chopping frequency.