Electric Vehicle Propulsion Control Device Speed Estimation

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Solution Overview

Problem

In electric vehicle speed-sensorless control, stable initial speed estimation is challenging due to changes in induction motor efficiency and simplified current f search methods, which are susceptible to errors and instability, especially with varying overhead wire voltages and circuit constants.

Innovation Solution

An electric vehicle propulsion control device with a power converter and a controller that calculates d-axis and q-axis voltage commands, incorporating interference terms to estimate the free-run speed of the induction machine, using both primary and secondary magnetic fluxes for improved stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If simplified current f search method is used for initial speed estimation, then device complexity is reduced, but measurement precision and stability of speed estimation deteriorate

Engineering Contradiction:

Improvecontrol algorithm complexityVSAvoidinitial speed estimation accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent transforms the simplified current-based f search into a voltage-based f search by changing the fundamental parameter used for speed estimation. This parameter change allows accurate speed estimation without requiring complex algorithms or additional sensors, as voltage measurements are more reliable and easier to obtain accurately in the free-run state.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes the electrical current measurement approach with a voltage measurement approach. By using voltage instead of current as the basis for speed estimation, the system achieves higher measurement precision while maintaining simplicity, as voltage measurements are less susceptible to errors from dead time and resistance variations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If conventional f search is used, then device simplicity is maintained, but reliability of speed estimation deteriorates under varying overhead wire voltages and circuit constants

Engineering Contradiction:

Improvecontrol system structureVSAvoidspeed estimation stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent changes the measurement parameter from current to voltage, which fundamentally improves reliability under varying operating conditions. Voltage measurements remain stable and accurate regardless of overhead wire voltage variations or circuit constant changes, whereas current measurements are highly sensitive to these variations.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces voltage as an intermediary parameter that mediates between the power converter output and the speed estimation process. By using voltage as the intermediate measurement, the system achieves reliable speed estimation without being directly affected by variations in circuit constants or overhead wire voltage, as voltage provides a stable reference point.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If current-based f search is used, then initial speed estimation can be performed, but measurement precision deteriorates due to susceptibility to dead time and resistance errors

Engineering Contradiction:

Improveinitial speed estimation capabilityVSAvoidspeed estimation accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent substitutes current measurement with voltage measurement for speed estimation purposes. This substitution eliminates the problems associated with current measurements, such as susceptibility to dead time effects and resistance errors, while maintaining the ability to perform initial speed estimation in the free-run state.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses voltage as an intermediary that provides accurate speed estimation information without being affected by the errors inherent in current measurement. The voltage signal serves as a clean, reliable intermediary that translates power converter output directly into accurate speed information without the noise and errors present in current-based methods.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11264927B2Electric vehicle propulsion control device

Publication Date: 2022.03.01 MITSUBISHI ELECTRIC CORP

AI summary

An electric vehicle propulsion control device includes a power converter that applies an alternating-current voltage to an induction machine and a controller that controls the power converter based on an external operation command. The controller includes a first calculation unit. The first calculation unit calculates, from current information (id and iq) detected at the induction machine and current command values (id*1 and iq*1) that are based on the operation command, a d-axis voltage command (Vd*1) and a q-axis voltage command (Vq*1) for the power converter, and a primary magnetic flux φds and a secondary magnetic flux φdr of the induction machine. The first calculation unit also adds to or subtracts from a term including the q-axis voltage command (Vq*1) an interference term stemming from the d-axis voltage command (Vd*1) in calculating a first speed ω1 that is a free-run speed of the induction machine.