Permanent Magnet Motor Current Setpoints for Torque Split Control

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Solution Overview

Problem

Existing methods for determining current setpoints for generating desired motor torque in permanent magnet electric motors are inefficient, particularly in optimizing torque distribution between permanent flux and reluctance torque, leading to suboptimal performance and increased material costs.

Innovation Solution

A method and device that determine current setpoints by calculating a coefficient for the permanent flux torque component based on the operating point, allowing for efficient allocation of torque-forming and magnetic field-weakening currents, using a motor torque equation to derive specific current setpoints for regulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a control system uses d-current as a manipulated variable to optimize intermediate circuit voltage utilization, then voltage utilization is improved, but the complexity of determining current setpoints increases

Engineering Contradiction:

Improveintermediate circuit voltage utilizationVSAvoidcomplexity of determining current setpoints

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent segments the torque determination process into distinct steps: first determining the permanent flux torque component, then the reluctance torque component, and finally calculating the corresponding current setpoints. This segmentation simplifies the overall control complexity by breaking down the complex torque optimization problem into manageable sequential steps, while still achieving optimal intermediate circuit voltage utilization.

Inventive Principle:

Principle #1Segmentation

2Quantity of substance

If reluctance torque is used in addition to synchronous permanent flux torque, then material costs are reduced, but the precision of torque regulation deteriorates

Engineering Contradiction:

Improvemagnetic materialVSAvoidprecision of torque regulation

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent dynamically adjusts the distribution between permanent flux torque and reluctance torque based on operating conditions. By changing the parameter of torque component distribution according to the operating point, the system maintains precise torque regulation while utilizing reluctance torque to reduce magnetic material requirements. The control system optimizes the mix of torque components to achieve both material reduction and regulation precision.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If efficiency-optimal current setpoints are determined for each operating point, then motor performance is improved, but computational effort increases

Engineering Contradiction:

Improvemotor performanceVSAvoidcomputational effort

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent performs preliminary determination of the permanent flux torque coefficient based on the operating point before calculating the final current setpoints. This preliminary action allows the system to pre-calculate key parameters that will be used in subsequent torque and current calculations, thereby reducing the computational effort required during real-time control while still achieving efficiency-optimal current setpoints for each operating condition.

Inventive Principle:

Principle #10Preliminary action

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 efficient and optimal current setpoints to be determined for each operating point, reducing material costs and improving motor performance by optimizing torque distribution and reducing computational effort.

Implementation Method 1

synchronous machines with embedded magnets can use a reluctance torque in addition to a synchronous permanent flux torque

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

Due to a higher magnetic conductance in a transverse axis (q-axis) compared to a longitudinal axis (d-axis) oriented on a permanent magnet, synchronous machines with embedded magnets can use a reluctance torque

Methodology Applied

Scientific EffectMagnetic reluctance: Magnetic Reluctance

Data Source

PatentEP3790185B1Method and device for determining current setpoint for achieving a desired motor torque setpoint on a permanent magnet electric motor

Publication Date: 2023.10.25 VOLKSWAGEN AG

Figure 1~2

AI summary

The invention relates to a method for determining current setpoints (Iqsoll, Idsoll) for generating a desired motor setpoint torque (Mson) in a permanent magnet excited electric motor, wherein a current operating point (3) and the desired motor setpoint torque (Msoll) are obtained by means of a control device (2), a coefficient (Kpm) for a permanent flux torque component is determined depending on the operating point, a permanent flux torque (Mpm) and a reluctance torque (Mreluctanz) are determined from the desired motor setpoint torque (Msoll) using the determined coefficient (Kpm), a torque-generating current setpoint (Iqsoll) is determined starting from the determined permanent flux torque (Mpm), a magnetic field-weakening current setpoint (Idsoll) is determined starting from the determined reluctance torque (Mreluctanz), and the determined current setpoints (Iqsoll, Idsoll) are made available for control. Furthermore, the invention relates to an associated device (1).