Sensorless PWM Drive Control Using Motor Current Ripple

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Solution Overview

Problem

Existing Variable Speed Drives (VSDs) for AC motors face challenges in sensorless control, particularly at low speeds, due to acoustic noise and interference issues with Pulse-Width Modulation (PWM) when using signal injection, and require specialized sensors prone to noise sensitivity.

Innovation Solution

A PWM-based VSD that estimates motor state variables using drive current measurements and computes a state variable estimation support signal to improve estimation accuracy without external probing signals, relying on standard current sensors and standard PWM, which enhances control without noise and interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If signal injection is used to improve sensorless control at low speeds, then estimation accuracy is improved, but acoustic noise increases and interference with PWM occurs

Engineering Contradiction:

Improvestate variable estimation accuracyVSAvoidacoustic noise and PWM interference

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful PWM-induced current ripples into a beneficial resource for state variable estimation. Instead of treating PWM artifacts as noise to be eliminated, the method exploits these ripples as a natural probing signal to extract rotor position and speed information, thereby eliminating the need for separate high-frequency injection signals that cause acoustic noise and interference

Inventive Principle:

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

Solution Approach 2:

The PWM inverter serves dual purposes: it both controls the motor and provides the probing signal for sensorless estimation. The PWM switching artifacts that would normally be considered harmful interference are instead utilized as the excitation signal needed for state variable estimation, making the system self-sufficient without requiring additional injection hardware or signals

Inventive Principle:

Principle #25Self-service

2Measurement precision

If external high-frequency probing signals are injected to improve low-speed estimation, then state variable estimation is improved, but device complexity increases

Engineering Contradiction:

Improvelow-speed state variable estimationVSAvoidsignal injection hardware and control complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The PWM inverter is made multi-functional by having it simultaneously perform motor control and state variable estimation excitation. The same PWM switching signals that control motor operation also serve as the probing signal for sensorless estimation, eliminating the need for separate injection hardware and reducing overall system complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent extracts the estimation function from the control system by utilizing the inherent PWM artifacts rather than adding separate injection hardware. The estimation algorithm extracts rotor position and speed information directly from the PWM-induced current ripples, removing the need for external probing signal generation circuits

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If current derivative measurement is used to derive rotor position and speed, then sensorless control is achieved, but measurement precision deteriorates due to noise sensitivity

Engineering Contradiction:

Improvesensorless control capabilityVSAvoidrotor position and speed measurement

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent uses inexpensive standard current sensors instead of specialized derivative-measuring sensors. By exploiting PWM-induced ripples that naturally contain position and speed information, the system avoids the need for complex derivative calculations that amplify noise, achieving sensorless control with standard, noise-resistant measurement devices

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Data Source

PatentEP3799293B1A variable speed drive for the sensorless PWM control of an ac motor by exploiting PWM-induced artefacts

Publication Date: 2023.12.27 SCHNEIDER TOSHIBA INVERTER EUROPE SAS

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AI summary

A variable speed drive (200) for controlling an electric motor (300) based on a control law, comprising an output (210) for delivering a drive voltage (upwm) to the electric motor (300), a drive voltage generating power inverter (220), a drive controller (230), and a current sensor (240) for measuring the drive current taken up by the electric motor (300), the drive controller (230) including a PWM generator (232), a control law module (234), and a state variable estimator (236) for estimating a state variable of the electric motor (300), wherein the control law module (234) computes a target voltage signal (us) based on state variable estimates (z) provided by the estimator (236) and outputs the target voltage signal (us) to the PWM generator (232), wherein the PWM generator (232) approximates the target voltage signal (us) with a PWM control signal (M), controls the inverter (220) using the PWM control signal, computes, based on the deviation between the PWM control signal (M) and the target voltage signal (us), an estimation support signal (si), and outputs the estimation support signal (si) to the estimator (236), and wherein the estimator (236) estimates a state variable (z) of the motor (300) based on the estimation support signal (si) and the drive current (is), and outputs the estimate (z) to the control law module (234).