Quadrotor helicopter control problem

Quadrotor helicopter control problem
State dimension:	1
Differential states:	6
Continuous control functions:	1
Discrete control functions:	3
Interior point equalities:	6

The mixed-integer optimal control problem of a quadrotor helicopter in two dimensions is taken from [7] and [8]. The evolution of the quadrotor can be defined with respect to a fixed two dimensional reference frame using six dimensions, where the first three dimensions represent the position along a horizontal axis, the position along the vertical axis, and the roll angle of the helicopter, respectively, and the last three dimensions represent the time derivative of the first three dimensions.

Mathematical formulation

The mixed-integer optimal control problem is given by

$\begin{array}{llclr} \displaystyle \min_{x, w, s} & x_2(t_f) + 10s \\[1.5ex] \mbox{s.t.} & \dot{x}_0 & = & x_0 - x_0 x_1 - \; c_0 x_0 \; w, \\ & \dot{x}_1 & = & - x_1 + x_0 x_1 - \; c_1 x_1 \; w, \\ & \dot{x}_2 & = & (x_0 - 1)^2 + (x_1 - 1)^2, \\[1.5ex] & x_0 & \geq & 1.1 - s, \\ & x(0) &=& (0.5, 0.7, 0)^T, \\ & w(t) &\in& \{0, 1\}, \\ & s & \geq & 0. \end{array}$

Here the differential states $(x_0, x_1)$ describe the biomasses of prey and predator, respectively. The third differential state is used here to transform the objective, an integrated deviation, into the Mayer formulation $\min \; x_2(t_f)$. This problem variant penalizes a biomass x(0) that is below 1.1 at the end of the time horizon.

Parameters

These fixed values are used within the model.

$\begin{array}{rcl} [t_0, t_f] &=& [0, 12],\\ (c_{0}, c_{1}) &=& (0.4, 0.2), \end{array}$

Reference Solutions

If the problem is relaxed, i.e., we demand that $w(t)$ is in the continuous interval $[0, 1]$ rather than being binary, the optimal solution can be determined by means of direct optimal control.

The optimal objective value of the relaxed problem with $n_t=12000, \, n_u=200$ is $x_2(t_f) =1.36548113$. The objective value of the solution with binary controls obtained by Combinatorial Integral Approximation (CIA) is $x_2(t_f) =1.38756111$.

• Reference solution plots
• 

  Optimal relaxed controls and states determined by an direct approach with ampl_mintoc (Radau collocation) and $n_t=12000, \, n_u=200$.

• 

  Differential states and binary cotnrol determined by an direct approach (Radau collocation) with ampl_mintoc and $n_t=12000, \, n_u=200$. The relaxed controls were approximated by Combinatorial Integral Approximation.