PWM Injection Scheme for Sensorless AC Motor State Estimation

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Solution Overview

Problem

Existing sensorless variable speed drives (VSDs) for AC motors face challenges in accurately estimating motor status without external sensors, particularly at low velocities, due to noise from PWM commutations and the need for real-time noise rejection, which is not effectively addressed by current prefiltering methods.

Innovation Solution

A PWM-based sensorless VSD that discards corrupted time segments of the drive current signal corresponding to power inverter switch commutations, using a state variable estimation module to improve noise rejection and estimate motor state variables in real time, without external signal injection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If external high-frequency probing signal is injected to improve motor status estimation at low velocity, then measurement precision is improved, but acoustic noise and excitation of unmodeled dynamics increase

Engineering Contradiction:
Improvemotor status estimation accuracyVSAvoidacoustic noise
Core Design Contradiction:
Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful PWM switching noise into a beneficial probing signal. By treating the PWM commutations as the excitation source rather than filtering them out, the system uses the naturally present high-frequency signal to extract motor status information, thereby eliminating acoustic noise while maintaining estimation accuracy.

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

Solution Approach 2:

The system uses its own PWM switching noise as the probing signal for sensorless control. The PWM inverter's inherent commutation artifacts serve dual purposes: driving the motor and providing the excitation needed for status estimation, eliminating the need for separate external signal injection hardware.

Inventive Principle:
Principle #25Self-service

2Measurement precision

If external high-frequency probing signal is injected to improve motor status estimation at low velocity, then measurement precision is improved, but device complexity increases

Engineering Contradiction:
Improvemotor status estimation accuracyVSAvoidsignal injection hardware
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The system uses its own PWM switching noise as the probing signal for sensorless control. The PWM inverter's inherent commutation artifacts serve dual purposes: driving the motor and providing the excitation needed for status estimation, eliminating the need for separate external signal injection hardware.

Inventive Principle:
Principle #25Self-service

Solution Approach 2:

The patent converts the harmful PWM switching noise into a beneficial probing signal. By treating the PWM commutations as the excitation source rather than filtering them out, the system uses the naturally present high-frequency signal to extract motor status information, thereby eliminating acoustic noise while maintaining estimation accuracy.

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

3Measurement precision

If PWM frequency is increased to allow higher probing signal frequency, then measurement precision is improved, but torque ripple increases

Engineering Contradiction:
Improveprobing signal frequencyVSAvoidtorque ripple
Core Design Contradiction:
Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful PWM switching noise into a beneficial probing signal. By treating the PWM commutations as the excitation source rather than filtering them out, the system uses the naturally present high-frequency signal to extract motor status information, thereby eliminating acoustic noise while maintaining estimation accuracy.

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

4Measurement precision

If prefiltering of measured current is done to reject PWM noise, then measurement precision is improved, but real-time processing capability is lost

Engineering Contradiction:
Improvecurrent measurement accuracyVSAvoidreal-time processing speed
Core Design Contradiction:
Measurement precisionVSProductivity

Solution Approach 1:

The system performs preliminary segmentation of the current signal based on predicted PWM commutation times. By pre-identifying which time segments contain switching noise and marking them for exclusion before estimation processing, the system enables real-time noise rejection without requiring computationally intensive post-acquisition filtering.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The system dynamically adjusts the estimation process by selectively excluding corrupted time segments corresponding to PWM commutations. This dynamic approach allows the estimator to adapt to the timing of switching events and maintain accurate real-time motor status estimation despite the presence of periodic noise.

Inventive Principle:
Principle #15Dynamics

Data Source

PatentUS11791759B2Towards an industrially implementable PWM-injection scheme
Publication Date: 2023.10.17 SCHNEIDER TOSHIBA INVERTER EUROPE SAS
  • US11791759B2 patent drawing
  • US11791759B2 patent drawing
  • US11791759B2 patent drawing

AI summary

A variable speed drive includes an output terminal for delivering a drive voltage; a power inverter for generating the drive voltage; a drive controller for controlling the generation of the drive voltage; and a current sensor for providing a drive current intensity signal to the drive controller. The drive controller includes a PWM generator; a control law module; and a state variable estimator estimating a state variable of the controlled AC electric motor.