Winchcontroller Settings

Introductions

Three .yaml files are needed to configure the winch controller:

1. system.yaml
2. settings.yaml
3. wc_settings.yaml

The first file lists the yaml files that shall be used for the current project. The second file defines the model parameters. The third file defines the parameters of the winch controller. All of these files must be stored in the data directory.

Example for a system.yaml file:

system:
    sim_settings:  "settings.yaml"       # model and simulator settings
    wc_settings:   "wc_settings.yaml"    # winch controller settings

The following sequence of commands will load the model and the winch controller settings for a given project:

using WinchControllers, KiteUtils

set_data_path("data") # set the path where the yaml files are stored
set = load_settings("system.yaml")
wcs = WCSettings()
update(wcs)

Both, set and wcs are simple structs. You can see the content of the struct by typing the name of one of these variables. If you type wcs. <TAB><TAB> you can see all elements of the wcs struct.

The file wc_settings.yaml

wc_settings:
    dt: 0.02         # time step of the winch controller
    test: false      # if true, a simplified formula for the calculation of v_set will be used
    fac: 0.25        # factor for I and P of lower force controller
    max_iter: 100    # max iterations limit for the PID solvers
    iter: 0          # actual max iterations of the PID solvers
    t_startup: 0.25  # startup time for soft start  
    t_blend: 0.1     # blending time of the mixers in seconds
    v_sat_error: 1.0 # limit of reel-out speed error, used by the input sat block of the speed controller
    v_sat: 8.0       # limit of reel-out speed, used by the output sat block of the speed controller
    v_ri_max: 8.0    # maximal reel-in speed [m/s]
    p_speed: 0.125   # P value of the speed controller
    i_speed: 4.0     # I value of the speed controller
    kb_speed: 4.0    # back calculation constant for the anti-windup loop of the speed controller
    kt_speed: 5.0    # tracking constant of the speed controller
    vf_max: 2.75     # reel-out velocity where the set force should reach it's maximum
    pf_low: 0.00014  # P constant of the lower force controller 0.013,  0.00014 also works
    if_low: 0.01125  # I constant of the lower force controller 0.0225, 0.01125 also works
    df_low: 0.0      # D constant of lower force controller 0.000017
    nf_low:  0       # filter constant n of upper force controller
    kbf_low: 8.0     # back calculation constant for the anti-windup loop of the lower force controller
    ktf_low: 8.0     # tracking constant of the lower force controller
    f_low: 350       # lower force limit [N]
    f_reelin: 700    # set force for reel-in phase [N]
    f_high: 3800     # upper force limit [N]
    pf_high: 0.0002304 # P constant of upper force controller
    if_high: 0.012     # I constant of upper force controller
    df_high: 2.04e-5  # D constant of upper force controller
    nf_high: 15.0    # filter constant n of upper force controller
    kbf_high: 1.0    # back calculation constant for the anti-windup loop of the upper force controller
    ktf_high: 10.0   # tracking constant of the upper force controller
    winch_iter: 10   # iterations of the winch model
    max_acc: 8.0     # maximal acceleration of the winch (derivative of the set value of the reel-out speed)
    damage_factor: 0.05 # damage at max acceleration for jerk_factor=0
    jerk_factor: 0.90   # factor for the jerk (derivative of the acceleration), 0..1 
    kv: 0.06         # proportional factor of the square root law, see function calc_vro

    # --- Soft force limiting (REEL_OUT mode), see calc_vro_soft --------------
    force_limit: "hard"    # "hard" (default) or "soft"; see WCSettings.force_limit
    softplus_beta: 1e-3     # "soft" only: corner sharpness of the UPPER limit [1/N]
    softminus_beta: 1e-3    # "soft" only: corner sharpness of the LOWER limit [1/N]
    force_limit_tau: 1.0    # "soft" only: low-pass time constant on the force [s]
    soft_lfc: false     # "soft" only: also replace the LowerForceController with a reel-in line
    v_reel_in: -2.0         # soft_lfc only: reel-in speed at zero force [m/s]
    reel_in_beta: 20.0      # soft_lfc only: sharpness of the smooth line/curve handover [s/m]
    use_awe_trim: 0.0       # "soft" only: default calc_vro_soft blend towards AWETrim's
                             # own curve constants, in [0, 1]; 0.0 leaves the law unchanged

soft_lfc draws a straight line, SHIFTED DOWN by log(2) / reel_in_beta, from the one through (0, v_reel_in) to (f_low, 0) — the whole physically valid range below f_low, since force is never negative — so there is no separate ramp-width setting; the slope is -v_reel_in / f_low, unaffected by the shift or by reel_in_beta.

Above f_low the line hands over to the reel-out tension curve via a smooth minimum (soft_min, sharpness reel_in_beta) rather than a hard min, so the handover has no kink; the tension curve itself is HARD-clamped at f_low here (softminus_beta plays no part — it only smooths the plain, line-less curve used when soft_lfc = false). reel_in_beta is therefore the SOLE tuning knob for the whole handover, and changing it can never un-straighten the line below f_low (only the constant shift moves). Larger is sharper; the curve sits log(2) / reel_in_beta below the hard minimum right at f_low. Just above f_low the (hard-clamped) tension-curve inverse jumps from 0 to kv * sqrt(f_low) almost immediately rather than ramping up gently, so reel_in_beta needs to be sharp relative to that jump for the line to actually govern near f_low instead of a visible hump: reel_in_beta * kv * sqrt(f_low) >= 8 (the shipped defaults above satisfy this comfortably). WinchController validates this, and every other soft_lfc invariant, at construction time.