Synchronous Motor Harmonic Current Control for Torque Ripple

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Solution Overview

Problem

Conventional synchronous electric motors in electric and hybrid-electric vehicles suffer from torque ripples, particularly at low-speed conditions, causing vibrations and inefficiencies, and existing harmonic current injection techniques do not consider motor efficiency or direct current link voltage limitations.

Innovation Solution

A torque ripple reduction system for synchronous electric motors that optimizes harmonic current injection based on a constrained objective function, using lookup tables to determine direct and quadrature currents and voltages, ensuring efficiency and adherence to DC link voltage limits, with a control system to manage the harmonic currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional harmonic current injection techniques are used to reduce torque ripples, then torque ripple reduction is achieved, but motor efficiency is not optimized and DC link voltage limitations are not considered

Engineering Contradiction:

Improvetorque rippleVSAvoidmotor efficiency

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The patent changes the parameters of harmonic current injection by optimizing the amplitude and phase of injected harmonics based on a constrained objective function that simultaneously considers torque ripple reduction and motor efficiency. The control system dynamically adjusts current parameters (id, iq, and harmonic components) to achieve optimal performance across different operating conditions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements a dynamic control approach where the harmonic current injection parameters are continuously adjusted based on real-time operating conditions (speed, torque demand). The lookup tables store pre-optimized parameters that are dynamically selected and applied by the control system to adapt to changing motor operating points.

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If harmonic current injection is applied to reduce torque ripples, then torque ripple reduction is achieved, but DC link voltage limitations may be exceeded

Engineering Contradiction:

Improvetorque rippleVSAvoidDC link voltage constraint compliance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent applies preliminary anti-action by pre-calculating and storing in lookup tables the optimal harmonic current parameters that satisfy both torque ripple reduction and DC link voltage constraints. The constrained objective function proactively prevents voltage constraint violations by limiting the magnitude of injected harmonics before they can cause problems, rather than reacting after violations occur.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The control system uses feedback from the motor's operating state (speed, torque) to select appropriate parameters from the lookup tables. The system continuously monitors operating conditions and adjusts the harmonic injection parameters accordingly, ensuring that DC link voltage constraints are maintained while achieving torque ripple reduction.

Inventive Principle:

Principle #23Feedback

3Object-affected harmful factors

If mechanical redesign is performed to reduce torque ripples, then torque ripple reduction is achieved, but system cost increases

Engineering Contradiction:

Improvetorque rippleVSAvoidsystem cost

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent replaces mechanical redesign solutions with an electrical control solution. Instead of modifying the motor's physical structure (which would increase cost and complexity), the system uses intelligent control algorithms with harmonic current injection to achieve torque ripple reduction. This substitution of mechanical approach with electrical/control approach reduces system cost while maintaining effectiveness.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS20250309797A1Efficient torque ripple reduction for synchronous electric motors in electric and hybrid-electric vehicles

Publication Date: 2025.10.02 FCA US LLC

AI summary

A torque ripple reduction method for a synchronous electric motor of a vehicle includes obtaining, by a control system, look-up tables (LUTs) that each include harmonic currents that satisfy a constrained objective function for phase current magnitude for the synchronous electric motor, based on a requested motor torque, determining, by the control system and using the LUTs, a plurality of currents including fundamental direct and quadrature currents and 6th order and 12th order harmonic quadrature currents, determining, by the control system, direct and quadrature voltages for the synchronous electric motor based on the plurality of currents including injection of the 6th and 12th order harmonic quadrature currents, and controlling, by the control system, the synchronous electric motor based on the determined direct and quadrature voltages to at least one of reduce torque ripples and increase efficiency of the synchronous electric motor.