Motor Controller Blind Estimation for EPS Current Detection

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Solution Overview

Problem

In motor controllers for electric power steering systems, the detection of phase current values is limited by the detection time, leading to a reduced voltage utilization factor and inaccurate current detection due to the blind estimation method, which causes noise and power loss, especially when the on time of switching devices becomes shorter than the detection time.

Innovation Solution

A motor controller that estimates the phase current value of an undetectable phase based on the detected values of other phases, maintains the switching state of the undetectable phase, and compensates for power loss by adjusting DUTY command values, ensuring accurate current detection and improved voltage utilization without imposing upper limits on DUTY command values.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the on time of switching devices is increased to improve voltage utilization, then the detection time becomes insufficient leading to inaccurate current detection

Engineering Contradiction:

Improvevoltage utilization factorVSAvoidcurrent detection accuracy

Core Design Contradiction:

PowerVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by pre-calculating and storing the relationship between DUTY command values and phase current values in a lookup table before operation. During runtime, when a phase current becomes undetectable (on time < detection time), the controller immediately queries the pre-prepared table to obtain the corresponding current value, avoiding real-time calculation delays and ensuring continuous accurate current information for control purposes.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses copying by creating a virtual representation of phase current values through the lookup table. When direct detection is impossible due to insufficient on time, the controller copies the pre-stored current value from the table that corresponds to the current DUTY command value, effectively replicating the current information that would otherwise be undetectable, thus maintaining accurate current data for all phases.

Inventive Principle:

Principle #26Copying

2Measurement precision

If the detection time is increased to improve current detection accuracy, then the voltage utilization factor is reduced due to longer dead time

Engineering Contradiction:

Improvecurrent detection accuracyVSAvoidvoltage utilization factor

Core Design Contradiction:

Measurement precisionVSPower

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Inventive Principle:

Principle #26Copying

3Power

If the blind estimation method is used to estimate undetectable phase current values, then the voltage utilization factor improves, but noise and power loss increase

Engineering Contradiction:

Improvevoltage utilization factorVSAvoidnoise and power loss

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent applies this principle by using a simple lookup table approach instead of complex real-time estimation algorithms. The lookup table stores pre-calculated current values that can be quickly retrieved without expensive computation or additional sensing hardware. This disposable-like approach (simple, replaceable table) provides accurate current information without the noise and power consumption of active estimation methods.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Speed

If the on time of switching devices becomes shorter than the detection time, then the detection of phase current values becomes impossible, but maintaining smooth motor rotation requires continuous current feedback

Engineering Contradiction:

Improvemotor rotation smoothnessVSAvoidphase current detection

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent applies self-service by having the system generate its own current information through the lookup table without requiring external assistance or complex additional sensors. The lookup table, populated from system parameters and characteristics, enables the controller to self-determine phase current values even when direct detection fails, ensuring continuous feedback for smooth motor rotation control.

Inventive Principle:

Principle #25Self-service

Data Source

PatentEP2273668B1Motor controller and electric power steering system

Publication Date: 2019.01.16 JTEKT CORP

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AI summary

A motor controller and an electric power steering system including the motor controller are provided. The motor controller has a microcomputer. When the on time of one of the lower potential-side FETs corresponding to the respective phases in a drive circuit becomes shorter than the detection time for detecting the phase current value, the microcomputer estimates the phase current value of the electric current undetectable phase based on the phase current values of the two phases other than the electric current undetectable phase corresponding to the relevant FET (blind estimation). When electric current detection is performed in the blind estimation, motor control signals are output, by which the switching state of the switching arm of the electric current undetectable phase is maintained and the power loss caused by the switching operation of the FETs in the two phases other than the electric current undetectable phase is compensated for.