With electric power systems becoming more compact and increasingly powerful,
the relevance of thermal stress especially during overload operation is
expected to increase ceaselessly. Whenever critical temperatures cannot be
measured economically on a sensor base, a thermal model lends itself to
estimate those unknown quantities. Thermal models for electric power systems
are usually required to be both, real-time capable and of high estimation
accuracy. Moreover, ease of implementation and time to production play an
increasingly important role. In this work, the thermal neural network (TNN) is
introduced, which unifies both, consolidated knowledge in the form of
heat-transfer-based lumped-parameter models, and data-driven nonlinear function
approximation with supervised machine learning. A quasi-linear
parameter-varying system is identified solely from empirical data, where
relationships between scheduling variables and system matrices are inferred
statistically and automatically. At the same time, a TNN has physically
interpretable states through its state-space representation, is end-to-end
trainable -- similar to deep learning models -- with automatic differentiation,
and requires no material, geometry, nor expert knowledge for its design.
Experiments on an electric motor data set show that a TNN achieves higher
temperature estimation accuracies than previous white-/grey- or black-box
models with a mean squared error of 3.18K2 and a worst-case error of
5.84K at 64 model parameters.Comment: Preprint; Fix typos, streamline math. notation; 10 page