Model predictive temperature control and ageing estimation for an insulated cool box

The transport of perishable goods in insulated cool boxes (ICB) is affected by strong disturbances and requires an effective temperature control scheme. Model predictive control (MPC) can provide such a performing control scheme, however, the strong disturbance of irradiation by the sun can be rarely measured. Furthermore, the ageing of the ICB's insulation is a parameter of vital interest for logistic and economic planning although it cannot be directly measured. In this work a MPC and a custom disturbance observer is presented, which provide an estimate of the current irradiation and the ageing state, respectively. This is obtained by first estimating the excess heat loss of the ICB, and then splitting up this heat loss into an irradiation part and a part due to ageing of the ICB's insulation. The ageing model is assumed to be parametric, and a nonlinear estimation scheme is employed for parameter tuning. A suitable MPC formulation guarantees offset-free tracking of the desired temperature. The performance of the overall concept is demonstrated in a simulation for the nominal case, for increasing measurement noise, and for an abrupt change in the ageing parameters. Additionally, a non-parametric estimate for the confidence interval of the end-of-life prediction of the ICB is given.