Electric Machine Torque Control for Drivetrain Vibration Reduction
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Solution Overview
Problem
Electric machines in vehicle drive trains experience significant oscillations during dynamic load changes, leading to discomfort and mechanical stress due to vibrations, which existing control methods fail to adequately address.
Innovation Solution
A method and system that utilize a torque pre-control approach, modeling the drive train as a two-mass oscillator to determine a pilot control transfer function, allowing for the superposition of a pre-control torque to reduce or eliminate vibrations, and optionally using an observer to estimate and compensate for oscillations based on measured speed signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional drivetrain or electric axle is used during dynamic load changes, then the electric motor can deliver torque, but significant vibrations and speed fluctuations occur causing discomfort and mechanical stress
Solution Approach 1:
The feedforward control unit calculates a pilot torque in advance based on the specified target torque and the determined transfer function, before the actual torque application occurs. This preliminary calculation allows the control system to anticipate and compensate for vibrations before they manifest, rather than reacting after they occur.
Solution Approach 2:
The system uses an observer to estimate the vibration component from measured speed signals and feeds this information back to calculate a compensation torque. This closed-loop feedback mechanism continuously monitors the actual system behavior and adjusts the control torque to counteract detected vibrations.
2Object-affected harmful factors
If feedforward control with physical modeling is implemented, then drivetrain vibrations are reduced, but the device complexity increases due to model definition and transfer function determination
Solution Approach 1:
The system determines a transfer function that characterizes the drivetrain's vibration behavior through parameter identification. By changing the control approach to use this transfer function, the system can predict and compensate for vibrations without requiring complex real-time simulations or multiple sensors.
Solution Approach 2:
The feedforward control unit acts as an intermediary between the target torque specification and the actual motor control. It processes the target torque through the determined transfer function to generate a pilot torque that inherently compensates for vibrations, simplifying the overall control architecture compared to direct complex vibration control.
3Stability of the object's composition
If an observer-based compensation system is added to estimate and compensate vibrations, then speed oscillations are further reduced, but the quantity of components and computational requirements increase
Solution Approach 1:
The observer uses the existing speed signals from the motor control system to estimate the vibration component. Rather than requiring separate sensors or external measurement systems, the control system serves itself by extracting vibration information from its own operational data, minimizing additional hardware requirements.
Solution Approach 2:
The same control unit that manages motor torque control also performs vibration estimation and compensation calculations. By making the control unit multi-functional, the system avoids adding separate dedicated vibration control hardware, reducing overall system complexity while achieving enhanced vibration compensation.
Data Source
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Figure 3~4
AI summary
A pilot unit (10) having transfer function associated with oscillation component of model of drive train (1) is determined based on predetermined target torque of electric machine. The rotational speed of electric machine is determined from a torque at which the electric machine is operated. A control unit for electric machine determines a corrected target torque for electric machine, such that pre-torque and preset target torque are superimposed, and controls the electric machine in response to corrected target torque. An independent claim is included for system for controlling electric machine of power train used in motor vehicle.