Rotor-Angle D-Axis Current Ramping for Smooth EV Discharge
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Solution Overview
Problem
Electric vehicles experience unwanted torque and noise during DC bus capacitor discharge after deactivation due to dwell time effects and current control inaccuracies, leading to potential vehicle movement or harshness felt by the driver.
Innovation Solution
A controller generates d-axis current commands with ramp portions that adjust the rate of change in current magnitude based on the electric angle between the rotor and stator, optimizing the discharge of the DC bus capacitor by varying the ramp rate according to specific ranges of electric angles to minimize torque production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the DC bus capacitor is discharged rapidly after vehicle deactivation, then the discharge time is reduced, but unwanted torque and noise increase causing vehicle movement or harshness
Solution Approach 1:
The patent applies dynamics by making the discharge rate variable rather than constant. The controller dynamically adjusts the discharge rate based on real-time rotor position feedback, switching between different discharge rates depending on the rotor's angular position. This dynamic adjustment allows the system to achieve rapid overall discharge while minimizing torque and noise at critical rotor positions where they would otherwise be problematic.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the rotor position and using this information to adjust the discharge rate. The controller receives rotor position signals and uses them to determine the appropriate discharge rate to apply at any given moment. This closed-loop feedback mechanism ensures that the discharge process adapts to the changing rotor position, preventing unwanted torque and noise while maintaining efficient discharge timing.
2Device complexity
If a constant discharge rate is used during DC bus capacitor discharge, then the control system is simple, but torque ripple and noise increase due to dwell time effects
Solution Approach 1:
The patent applies segmentation by dividing the discharge process into multiple segments based on rotor position ranges. Instead of using a single constant discharge rate, the controller segments the discharge into different phases, each with its own optimized discharge rate. This segmentation allows the system to handle different rotor position scenarios differently, reducing torque ripple and noise while keeping each individual control segment relatively simple.
Solution Approach 2:
The patent implements parameter changes by varying the discharge rate parameter based on rotor position. The controller changes the discharge rate parameter dynamically as the rotor moves through different angular positions, optimizing the discharge process for each position range. This parameter adjustment approach reduces torque ripple and noise without requiring a completely complex control system architecture.
3Productivity
If the discharge rate is increased at all rotor positions, then the overall discharge speed increases, but torque and noise increase during sensitive rotor position ranges
Solution Approach 1:
The patent applies local quality by applying different discharge rates to different rotor position ranges rather than using a uniform discharge rate throughout. The controller identifies sensitive rotor position ranges where high discharge rates would cause excessive torque and noise, and applies lower discharge rates specifically to these local regions. Meanwhile, non-sensitive positions can utilize higher discharge rates, maintaining overall discharge productivity while minimizing harmful effects at critical positions.
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 effectively reduces unwanted torque and noise during DC bus capacitor discharge, ensuring safe and smooth vehicle deactivation by proactively managing the ramp rate of the d-axis current command in response to the electric angle, resulting in reduced peak torque and RPM.
Implementation Method 1
The inverter may include a DC bus capacitor and the d-axis current command may result in discharge of the DC bus capacitor to the electric machine
Data Source
AI summary
A controller, responsive to a signal indicating deactivation of a vehicle and disconnection of a traction battery from an inverter, generates a d-axis current command for the inverter having a ramp portion that defines a rate of change in current magnitude that depends on an electric angle between a rotor and stator of an electric machine.