% Generate transfer functions for loop shaping stability (uncertainty)
% requirements from parameters specified in uav_params.m
%
% Copyright (C) 2024, Naoki Sean Pross, ETH Zürich
% This work is distributed under a permissive license, see LICENSE.txt
%
% Arguments:
%   PARAMS  Struct of design parameters and constants generated by uav_params
%   PLOT    When set to 'true' it plots the inverse magnitude of the
%           performance transfer function
%
% Return value:
%   UNCERT  Struct of uncertainty transfer functions


function [uncert] = uav_performance(params, do_plots)

s = tf('s');

% relative errors
eps_T = params.aerodynamics.ThrustOmegaPropUncertainty;
eps_r = params.mechanical.GyroscopicInertiaZUncertainty;
eps_S = params.aerodynamics.FlapAreaUncertainty;
eps_l = params.aerodynamics.LiftCoefficientUncertainty;
eps_d = params.aerodynamics.DragCoefficientsUncertainties(1);
% eps_0 = params.aerodynamics.DragCoefficients(2);

eps_omega = max(.5 * eps_T, eps_r);
eps_alpha = max(eps_l + eps_S + 2 * eps_omega, eps_S + eps_d + eps_omega);

% band pass parameters for W_malpha
wh = 20; % high freq
wl = .1; % low freq

W_malpha = eps_alpha * (s / wl) / ((s / wh + 1) * (s / wl + 1));
W_momega = eps_omega * 10 / (s + 10);
W_mState = .01 * 10 / (s + 10);

uncert = struct(...
  'FlapAngle', W_malpha * eye(4), ...
  'Thrust', W_momega, ...
  'StateLinApprox', W_mState * eye(12));

if do_plots
  % Bode plots of performance requirements
  figure; hold on;
  bodemag(W_malpha);
  bodemag(W_momega);
  bodemag(W_mState);

  grid on;
  legend('$W_{m,\alpha}$', '$W_{m,\omega}$', '$W_{m,\mathbf{P}}$', ...
    'interpreter', 'latex')
  title('Stability (Uncertainty) Requirement')
end

end
% vim: ts=2 sw=2 et: