Rate-Limited Relay Control for System Parameter Identification

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional motion control systems face challenges in achieving optimal controller tuning due to issues like system noise, uncertainties, and dead time, which affect stability and performance, particularly in systems with rate-limited control signals.

Innovation Solution

The implementation of a system parameter identification method using a combination of rate-limited relay-based control with hysteresis and open-loop sinusoidal signal injection, allowing the system to oscillate and derive accurate parameters without requiring complex describing functions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If controller bandwidth is increased to improve response speed and disturbance rejection, then tracking error decreases and response time improves, but system stability deteriorates due to increased sensitivity to noise and reduced closed-loop robustness

Engineering Contradiction:

Improveresponse speedVSAvoidsystem stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The system performs preliminary identification of plant parameters (gain, time constant, dead time) before final controller tuning. By using relay-based oscillation and sinusoidal injection to accurately measure system characteristics in advance, the controller can be tuned with precise knowledge of plant dynamics, enabling optimal bandwidth selection that balances response speed and stability without requiring excessively high bandwidth that would cause instability

Inventive Principle:

Principle #10Preliminary action

2Ease of operation

If conventional tuning methods are used for systems with dead time, then tuning simplicity is maintained, but system performance deteriorates due to oscillations and degraded stability

Engineering Contradiction:

Improvetuning simplicityVSAvoidsystem stability

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The patent replaces manual trial-and-error tuning with an automated parameter identification system. The system automatically performs relay-based oscillation, measures the oscillation frequency and amplitude, injects sinusoidal signals, and calculates plant parameters (gain, time constant, dead time) using mathematical models. This substitution of automated measurement and calculation for manual tuning eliminates the difficulties of tuning systems with dead time while maintaining ease of operation through automation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If rate-limited relay control is applied to satisfy actuator rate constraints, then physical system constraints are respected, but measurement accuracy deteriorates due to distortion of the control signal

Engineering Contradiction:

Improveconstraint satisfactionVSAvoidparameter estimation accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary computational step: the relay control signal is rate-limited to satisfy actuator constraints, but instead of directly using this distorted signal for measurement, the system measures the actual control signal applied to the plant and uses this measured signal (which respects rate limits) as the reference for sinusoidal injection. The plant parameters are then identified based on the relationship between this rate-limited control signal and the plant output, thereby maintaining both constraint satisfaction and measurement accuracy

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enables accurate estimation of system parameters, such as gain, time constant, and dead time, facilitating robust control and stability while adhering to rate limits, thus improving performance and stability in motion control systems.

Implementation Method 1

rate-limited relay-based control with hysteresis is used to bring the system into oscillation

Methodology Applied

Scientific EffectHysteresis: Hysteresis

Implementation Method 2

control switches from relay-based control to open-loop sinusoidal signal injection control, where the sinusoidal control signal is configured to have a phase that substantially aligns with the phase of the relay-based control output

Methodology Applied

Scientific EffectSinusoidal excitation: Driven Harmonic Oscillation

Implementation Method 3

The plant output signal resulting from the sinusoidal control signal is bandpass filtered to obtain a relatively clean signal

Methodology Applied

Scientific EffectBandpass filtering: Filter (electronic)

Data Source

PatentUS10386808B2System parameter identificatino method based on rate-limited relay with hysteresis and sinusoidal injection

Publication Date: 2019.08.20 DANFOSS POWER ELECTRONICS AS

AI summary

A system parameter identification system uses a combination of relay control and sinusoidal injection to derive accurate estimates of system parameters of a controlled system or process while satisfying the rate-limit associated with some control applications. The system uses rate-limited relay control with hysteresis to place the system in oscillation. The system then switches the control signal from relay-based control to open-loop sinusoidal control using oscillation frequency, amplitude, and phase information obtained during the relay control stage. During the sinusoidal control phase, the plant output passes through a bandpass filter at the oscillation frequency to get a clean sinusoidal signal. The phase difference between the input and output signals and the output/input amplitude ratio are then obtained and used to calculate of the system parameters.