Sensorless Motor Drive Circuit for Back-EMF Zero-Crossing Accuracy

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Solution Overview

Problem

Conventional sensorless motor drive circuits for three-phase brushless motors face challenges in maintaining rotation accuracy due to variations in drive voltage waveforms, which affect the motor's actual rotation speed compared to the target speed.

Innovation Solution

A motor drive circuit is designed with a PWM signal generation part, detection part, prediction part, stop part, and reset part to predict and manage the zero crossing of counter electromotive voltage, stopping counter operations and resetting count values to improve rotation accuracy, particularly at constant target rotation speeds.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional sensorless motor drive circuits are used to drive three-phase brushless motors, then the motor can be driven without sensors, but the rotation accuracy deteriorates due to variations in drive voltage waveforms

Engineering Contradiction:

Improvesensorless operation capabilityVSAvoidrotation accuracy

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The counter is stopped at a predetermined timing before the zero crossing of the counter electromotive voltage to preliminarily prepare for accurate position detection. This preliminary action ensures that the count value is frozen at the correct position just before the zero crossing occurs, enabling accurate rotation position measurement without sensors

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system detects the zero crossing of the counter electromotive voltage and uses this feedback information to reset the counter. This feedback mechanism ensures that the counter always starts from a known reference point (zero crossing), compensating for any drift or errors and maintaining accurate rotation position detection throughout motor operation

Inventive Principle:

Principle #23Feedback

2Duration of action of stationary object

If the counter operation continues without stopping, then continuous counting is maintained, but the rotation accuracy deteriorates due to waveform variations

Engineering Contradiction:

Improvecontinuous counting operationVSAvoidrotation accuracy

Core Design Contradiction:

Duration of action of stationary objectVSManufacturing precision

Solution Approach 1:

The counter operates periodically by alternating between counting and stopping phases. The counter counts during normal operation and stops at predetermined timings before each zero crossing, creating a periodic pattern that ensures accurate position measurement at each cycle while maintaining overall continuous operation

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The counter is stopped at a predetermined timing before the zero crossing to preliminarily prepare for accurate position detection. This preliminary stopping action ensures that the count value is frozen at the correct position just before the zero crossing occurs, enabling accurate rotation position measurement

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If the counter is stopped at the zero crossing timing, then accurate position detection is achieved, but the counting operation is interrupted

Engineering Contradiction:

Improvezero crossing detection accuracyVSAvoidcounting operation interruption

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The counter is stopped at a predetermined timing before the zero crossing rather than exactly at the zero crossing. This preliminary stopping action allows the system to prepare for accurate detection in advance, ensuring the count value is captured at the correct position while minimizing the interruption duration

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The counter quickly stops at the predetermined timing before zero crossing, performs the necessary detection and reset operations, and then immediately resumes counting. This rapid stop-and-resume operation minimizes the time loss while ensuring accurate position detection at each cycle

Inventive Principle:

Principle #21Skipping (Rushing through)

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 configuration enhances the rotation accuracy of three-phase brushless motors by predicting zero crossing timings and managing counter operations, ensuring consistent drive voltage waveforms and improved motor performance.

Implementation Method 1

a detection part configured to detect a zero crossing of a counter electromotive voltage generated in a coil of a motor

Methodology Applied

Scientific EffectCounter electromotive voltage generation: Electromagnetic Induction

Data Source

PatentUS12015363B2Motor drive circuit, motor system, and electric device

Publication Date: 2024.06.18 ROHM CO LTD

AI summary

A motor drive circuit includes: a PWM signal generation part configured to generate a PWM signal based on a count value of a counter; a detection part configured to detect a zero crossing of a counter electromotive voltage generated in a coil of a motor; a prediction part configured to predict an arrival timing of the zero crossing of the counter electromotive voltage; a stop part configured to stop a counting operation of the counter after a first time point going back from the arrival timing predicted by the prediction part; and a reset part configured to reset the count value at a timing at which the detection part detects the zero crossing of the counter electromotive voltage.