Zero Crossing Detection in PMSM Back-EMF Signals

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Solution Overview

Problem

Existing methods for determining zero crossing occurrence in the back EMF signal of permanent magnet synchronous motors (PMSMs) suffer from high noise immunity and delayed phase changes due to sampling noise, which affects accurate rotor position calibration.

Innovation Solution

A method that involves sampling the AC signal to generate data points, counting consecutive data points with the same sign, and determining zero crossing based on a predefined count value, thereby reducing the impact of sampling noise and achieving low delay.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a low pass filter is applied to the back EMF signal to filter sampling noise, then noise immunity is improved, but zero crossing determination delay increases

Engineering Contradiction:

Improvenoise immunityVSAvoidzero crossing determination delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent segments the back EMF signal analysis into multiple discrete sampling points and uses a counter to track consecutive same-sign points. Instead of filtering the entire signal continuously, it divides the detection into discrete segments (individual sampling points) and counts them, achieving noise filtering without the phase lag of traditional low pass filters.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs preliminary sampling and counting of consecutive same-sign data points before making the zero crossing determination. By pre-counting the number of consecutive points with the same sign, the system prepares the determination criteria in advance, allowing for immediate and accurate zero crossing detection without delayed filtering operations.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If sampling is performed to obtain data points for zero crossing detection, then measurement capability is improved, but sampling noise is introduced

Engineering Contradiction:

Improvezero crossing detection accuracyVSAvoidsampling noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful sampling noise into a useful detection mechanism by counting consecutive sampling points with the same sign. The noise that would normally corrupt individual samples becomes a statistical pattern - when multiple consecutive samples show the same sign, it confirms a genuine zero crossing rather than noise. This transforms the problem of sampling noise into a solution that uses repetition to validate measurements.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If rotor position calibration is performed using back EMF signal zero crossing, then position accuracy is improved, but phase change delay occurs

Engineering Contradiction:

Improverotor position calibration accuracyVSAvoidphase change delay

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent replaces traditional analog filtering mechanisms with a digital counting and comparison system. Instead of using hardware low pass filters that introduce phase lag, the invention uses digital sampling, counting of consecutive same-sign points, and threshold comparison to determine zero crossings, achieving both accuracy and timely detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS11482952B1Method for determining zero crossing occurrence in alternating current signal with constant frequency of permanent magnet synchronous motor with high noise immunity and low delay and associated motor device

Publication Date: 2022.10.25 ELITE SEMICONDUCTOR MEMORY TECHNOLOGY INC

AI summary

A method for determining zero crossing occurrence in an alternating current (AC) signal with constant frequency of a permanent magnet synchronous motor (PMSM) includes: sampling the AC signal to obtain a plurality of data points; starting to count a number of consecutive data points that have sampled values with a same sign in a detection range, to generate a count value, wherein the consecutive data points are included in the plurality of data points; determining whether the count value is equal to a zero crossing determination value; and in response to the count value being equal to the zero crossing determination value, determining that a zero crossing occurs at a last data point of the consecutive data points.