Stator Current Modifier for Enhanced Flux Weakening
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Solution Overview
Problem
Existing electric machine designs face challenges in enhancing flux weakening at higher speeds, which limits power characteristics and motor torque linearity due to voltage and current constraints.
Innovation Solution
A controller-based method that modifies stator current by calculating a stator current modifier using characteristic angles and a flux weakening factor, allowing for improved flux weakening beyond conventional voltage constraints, enhancing high-speed current control and motor torque linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional voltage constraints are applied for flux weakening, then voltage control is simple, but flux weakening capability is limited at higher speeds
Solution Approach 1:
The patent changes the control parameters from simple voltage magnitude control to a more sophisticated approach using characteristic angles (θi) and flux weakening factors (ΔIS). The controller calculates modified stator currents using the formulas ΔId=(ΔIS*cosine (θi)) and ΔIq=(ΔIS*sine (θi)), where θi varies based on torque thresholds and machine parameters. This parameter transformation enables enhanced flux weakening capability beyond conventional voltage constraints while maintaining systematic control structure.
2Power
If stator current is increased for high speed operation, then power output is improved, but motor torque linearity deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of the characteristic angle θi based on operating conditions. The angle is selected from three possible values (θ1, θ2, θ3) depending on the torque command magnitude relative to thresholds TL and TH. This dynamic adaptation allows the control strategy to optimize torque linearity across different operating ranges while maintaining high speed power capability. The ratio R=(|T|−TL)/(TH−TL) provides smooth transition between different characteristic angles as operating conditions change.
Data Source
AI summary
An electric machine assembly includes an electric machine having a stator configured to have a stator current and a controller configured to receive a torque command (T). The controller has a processor and tangible, non-transitory memory on which is recorded instructions for executing a method of modifying the stator current for enhanced flux weakening. The controller is programmed to obtain a base stator current [IdLU, IqLU] from a look-up table based at least partially on the torque command (T). The controller is programmed to obtain a characteristic angle (θi, i=1, 2, 3) based at least partially on a value of the torque command (T) and the base stator current [IdLU, IqLU]. A stator current modifier [ΔId, ΔIq] is obtained based at least partially on the characteristic angle (θi, i=1, 2, 3) and a flux weakening factor (ΔIS) such that: ΔId=(ΔIS*cosine (θi)) and ΔIq=(ΔIS*sine (θi)).