Electric Vehicle Driving Force Controller Feed-Forward Compensation
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Solution Overview
Problem
Existing driving force controllers for electric vehicles face challenges in accurately reducing overshooting of actual driving force with respect to the target driving force while suppressing torsional vibrations, due to complex computations and difficulties in estimating disturbance torque.
Innovation Solution
A driving force controller that includes a feed-forward compensator with specific transfer functions and an inverse system for dynamic correction, which sets a target driving force and computes a motor torque command value to minimize deviation between target and actual rotational speeds, thereby reducing torsional vibrations and overshooting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a correction value is calculated based on deviation between target vehicle speed and actual vehicle speed to suppress torsional vibration, then torsional vibration is suppressed, but the actual driving force deviates from the required driving force due to disturbance torque
Solution Approach 1:
The feed-forward compensator calculates a preliminary correction value based on the target driving force and disturbance torque estimation, before the actual driving force is applied. This preliminary correction anticipates the effect of disturbance torque and compensates for it in advance, preventing both torsional vibration and driving force deviation.
Solution Approach 2:
The system uses feedback from the deviation between target vehicle speed and actual vehicle speed, combined with feed-forward compensation based on disturbance torque estimation. The correction value is dynamically adjusted based on this feedback while incorporating predictive compensation, achieving both vibration suppression and accurate driving force control.
2Measurement precision
If an input torque estimator is used to estimate disturbance torque and subtract it from motor request torque, then disturbance torque effect is compensated, but the computation becomes complicated and accurate parameter obtention becomes difficult
Solution Approach 1:
The system changes the approach from using a complex inverse system with difficult-to-obtain parameters to using a simplified disturbance torque estimation method. The estimation is based on readily available parameters such as running resistance torque and braking torque, which can be calculated from vehicle speed, acceleration, and brake pressure without requiring complex system identification.
Solution Approach 2:
Instead of using a complex, difficult-to-tune input torque estimator that requires accurate plant parameters, the system uses a simpler, more robust disturbance torque estimation approach that relies on basic vehicle dynamics parameters. This simpler estimator is easier to implement and maintain, even if it needs to be recalculated based on changing driving conditions.
3Stability of the object's composition
If the deviation between target vehicle speed and actual vehicle speed is used for correction, then torsional vibration is suppressed, but the actual driving force overshoots the target driving force because the deviation does not completely become zero
Solution Approach 1:
The feed-forward compensator applies a preliminary correction based on disturbance torque estimation before the feedback correction is applied. This preliminary action anticipates the disturbance effect and compensates for it in advance, preventing the need for large feedback corrections that would cause overshooting. The total correction value is the sum of this preliminary feed-forward correction and the smaller feedback correction.
Data Source
AI summary
A driving force controller for an electric vehicle includes a feed-forward compensator for computing a second target driving force so as to suppress overshooting of an actual driving force that is actually outputted, with respect to a first target driving force requested by a driver, the feed-forward compensator includes a first transfer function expressing a characteristic that the actual driving force becomes a predetermined response with respect to the first target driving force; and an inverse of a second transfer function approximately expressing a transmission characteristic between a input target driving force and the actual driving force in a control system except the feed-forward compensator.