Feed-forward Steering Controller - Two-wheelers

Feedforward controller for two wheelers consisting of two cascaded controllers. The Feedforward control to provide demand lean to follow the path and the Feedback controller to follow the demand lean through steering output.

This controller is used in case of simulating two-wheelers to follow a user provided demand path profile.

The controller employs a cascaded Feedforward and feedback algorithm to follow the specified path using steering angle as the control variable. For more details on the algorithm, please look at the Path following control for two-wheelers section.

The controller block for this controller can be specified as:

[FF_STEER_CONTROLLER]                                                                      
TAG = 'FEEDFORWARD'                                                             
LOOK_AHEAD_TIME = 0.1                                            
PATH = 'PREDEFINED'                                                   
BLOCK = 'PATH'                                                     
LEAN_CONTROL = 'PID_CONTROLLER'                                                   
LAT_KP = 0.03                                            
LAT_KI = 0                                            
LAT_KD = 0                                            
[PID_CONTROLLER]                                                                  
TAG = 'PID'                                                          
TYPE = 'FOLLOW_LEAN'                                                            
KP = 60                                                              
KI = 80                                                              
KD = 20  
[PATH]                                                                                     
TYPE = 'CONSTANT_RADIUS'                                                         
RADIUS = 40000                                                                    
INITIAL_STRAIGHT = 20000                                                            
TURN = 'LEFT'

In the above example, the path following Feedforward controller is specified using the ‘FEEDFORWARD’ tag and providing the required parameters. The demand path is specified in ‘PATH’ which is a constant radius path of radius 40 m with initial straight section of 20 m. The demand path can be specified in other ways as mentioned in the Demand Path for Steering Controllers section.

[FF_STEER_CONTROLLER]
`TAG`	Attr - string	REQUIRED <FEEDFORWARD >
`LOOK_AHEAD_TIME`	Attr - string	REQUIRED Specifies look ahead time for the controller used to predict the curvature of the path ahead.
`LEAN_CONTROL`	Attr - string	REQUIRED Block name for the LEAN_CONTROL block where the parameters for the lean follower controller are defined.
`LAT_KP`	Attr - real	OPTIONAL Proportional constant for the PID controller used to eliminate predicted lateral error after look ahead time. If absent, the default value of 0.03 is assumed.
`LAT_KI`	Attr - real	OPTIONAL Integral constant for the PID controller used to eliminate predicted lateral error after look ahead time. If absent, the default value of 0 is assumed.
`LAT_KD`	Attr - real	OPTIONAL Derivative constant for the PID controller used to eliminate predicted lateral error after look ahead time. If absent, the default value of 0 is assumed.

Note:

The behavior of the controller following a demand lean depends on the values for KP, KI, and KD.
If the behavior is not acceptable for a vehicle, the constants need to be tuned.