Electric Motor Drive Speed Control via Current-Based Estimation

Solution Overview

Problem

Conventional methods for controlling the rotational speeds of electric motors in twin drive systems without speed sensors are ineffective in maintaining balanced torques and rotational speeds, especially under adverse conditions like high temperatures or vibratory conditions, leading to uneven rotational speeds and mechanical stress.

Innovation Solution

The system calculates speed variation estimating values based on motor currents and command values, using compensatory calculating sections to adjust the voltages applied to the motors, ensuring equivalent rotational speeds without the need for speed sensors, thereby reducing gear clattering and mechanical stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If speed sensors are installed to control rotational speeds, then rotational speed control precision is improved, but device complexity and installation difficulty increase

Engineering Contradiction:

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts the speed sensing function from physical speed sensors and implements it through calculation sections that compute speed variation estimating values based on motor current and voltage information. This eliminates the need for physical speed sensors while maintaining speed control capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/electrical speed sensor system with a computational system using calculation sections. The speed variation is estimated through mathematical calculations based on motor current, voltage command values, and frequency information, substituting physical measurement with computational estimation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Force

If torque control is performed to balance torques between motors, then torque balance is improved, but rotational speed uniformity deteriorates under unbalanced load torques

Engineering Contradiction:

Core Design Contradiction:

ForceVSSpeed

Solution Approach 1:

Instead of controlling torque to achieve speed balance, the patent inverts the approach by directly calculating and controlling speed variation. The calculation sections compute speed variation estimating values, and the control system adjusts motor operations based on these speed variations, achieving speed uniformity without being constrained by torque balance requirements.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent implements feedback control by calculating speed variation estimating values from motor current and voltage information, then using these calculated values to adjust motor operations. This closed-loop feedback on speed variation enables the system to maintain rotational speed uniformity even when load torques are unbalanced.

Inventive Principle:

Principle #23Feedback

3Device complexity

If conventional speed control methods without speed sensors are used, then device complexity is reduced, but rotational speed uniformity deteriorates under unbalanced loads

Engineering Contradiction:

Core Design Contradiction:

Device complexityVSSpeed

Solution Approach 1:

The patent replaces physical speed sensors with computational calculation sections that estimate speed variation based on motor current and voltage information. This substitution maintains system simplicity while enabling accurate speed control through mathematical estimation rather than physical measurement.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent implements feedback control using calculated speed variation estimating values. The control system continuously monitors motor current and voltage, calculates speed variations, and adjusts motor operations accordingly, achieving rotational speed uniformity without physical speed sensors through computational feedback mechanisms.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8115442B2Electric motor drive system and electric motor control method

Publication Date: 2012.02.14

AI summary

An electric motor drive system having current detecting sections for detecting the currents flowing into electric motors, speed variation calculating sections for calculating the speed variation estimating values for the electric motors in accordance with the motor currents detected by the current detecting sections and the current command values for the motors corresponding to the detected currents and a speed uniformizing voltage compensating section for delivering the values that serve to compensate the amplitudes of the voltages applied to the electric motors in such a manner that the speed variation estimating values calculated by the speed variation calculating sections become equal to a predetermined value.