Hybrid Closed Loop Speed Control Using Estimated Rotor Position

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing systems for controlling the speed of electric machines with low resolution speed wheels struggle to accurately determine the rotor position and produce sufficient torque, especially at zero or low speeds, due to limitations in sensor accuracy and resolution, leading to potential machine performance issues or failure.

Innovation Solution

A hybrid closed loop control method that generates a torque command based on the desired speed and measured speed, using an estimated rotor position derived from the desired speed to control phase current to the stator, allowing for reliable operation even with low resolution speed wheels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a low resolution speed wheel is used, then device complexity is reduced, but measurement precision of rotor position deteriorates

Engineering Contradiction:

Improvespeed wheel complexityVSAvoidrotor position precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary estimation mechanism that uses electrical machine model parameters and measured electrical quantities as mediators to infer rotor position information that would otherwise require high-resolution mechanical sensors. This intermediary approach bridges the gap between low-resolution mechanical sensing and high-precision control requirements.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces reliance on high-resolution mechanical speed wheels with an electrical-based estimation system that uses measurements of electrical quantities (currents, voltages, frequencies) and machine parameters to determine rotor position. This substitution eliminates the need for high-resolution mechanical components while achieving equivalent or superior measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If initial rotor position calculation is performed at zero or close to zero speeds, then ease of operation is improved, but measurement precision deteriorates due to sensor limitations

Engineering Contradiction:

Improvestarting operation easeVSAvoidinitial rotor position precision

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent performs preliminary action by calculating the initial rotor position estimate using electrical machine models and measured electrical quantities before the machine reaches operating speed. This preliminary estimation is done during the starting phase when the machine is stationary or moving very slowly, allowing the control system to be initialized with accurate position information before dynamic operation begins.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces sensor-based mechanical position detection with an electrical-based estimation method that uses measured electrical quantities and machine parameters to determine initial rotor position. This substitution eliminates the limitations of mechanical sensors at zero or low speeds while enabling easy machine startup and direction reversal operations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If sensor feedback is relied upon for tracking absolute rotor position, then reliability of position tracking is improved, but measurement precision deteriorates at zero or low speeds

Engineering Contradiction:

Improveposition tracking reliabilityVSAvoidposition measurement precision at low speeds

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent uses feedback by continuously measuring electrical quantities (currents, voltages, frequencies) during machine operation and using these measurements to update and refine the rotor position estimate. This feedback mechanism maintains reliable position tracking throughout the entire operating range, including zero and low speeds, by continuously adapting the position estimate based on actual electrical machine behavior.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces mechanical sensor feedback systems with an electrical-based estimation and feedback mechanism. Instead of relying on mechanical encoders or resolvers that fail at low speeds, the system uses electrical measurements and machine models to continuously estimate rotor position, providing reliable feedback for control throughout the complete speed range including startup and direction reversal.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS8901869B2Hybrid closed loop speed control using open look position for electrical machines controls

Publication Date: 2014.12.02 CATERPILLAR INC

AI summary

A method of controlling speed of an electric machine having a rotor and a stator is provided. The method may comprise the steps of monitoring a desired speed and a measured speed of the rotor, generating a torque command based on the desired speed and the measured speed, and controlling phase current to the stator based on a hybrid closed loop analysis of the torque command, the measured speed and an estimated position of the rotor. The estimated rotor position may be derived at least partially from the desired speed.