Driving force controller for electric vehicle
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.
1. A driving force controller for an electric vehicle, which controls a driving force of a motor in a vehicle drive system, the driving force controller configured to:
set a driving force requested by a driver as a first target driving force;
compute a target rotational speed of the motor from an input target driving force by using a vehicle model in which the vehicle drive system is assumed to be a perfect rigid body;
compute, based on the target rotational speed and an actual rotational speed of the motor, a correction amount for reducing deviation between the target rotational speed and the actual rotational speed;
compute a motor torque command value by adding the correction amount to the input target driving force, the driving force controller comprising:
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 the first target driving force, wherein 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 the input target driving force and the actual driving force in a control system including the driving force controller except the feed-forward compensator; and
the second target driving force is inputted as the input target driving force to the control system.
2. The driving force controller for the electric vehicle according to claim 1 , wherein
the second transfer function approximates the control system by a secondary delay element;
a damping ratio of the secondary delay element is set to a predetermined damping ratio corresponding to a response of the actual driving force; and
a characteristic frequency of the secondary delay element is made a predetermined characteristic frequency corresponding to the response of the actual driving force.
3. The driving force controller for the electric vehicle according to claim 2 , wherein
the first transfer function is a secondary delay element, and
a damping ratio of the first transfer function is larger than the damping ratio of the second transfer function.
4. The driving force controller for the electric vehicle according to claim 3 , wherein respective characteristic frequencies of the first transfer function and the second transfer function are the same value.
5. The driving force controller for the electric vehicle according to claim 1 , further configured to:
set the characteristic frequency of the first transfer function to a larger value, as a change speed of an acceleration request value of the driver is smaller.
6. The driving force controller for the electric vehicle according to claim 5 ,
further configured to: differentiate the first target driving force and processes a differential value of the first target driving force as the change speed of the acceleration request value of the driver.