Numerical stability of multi-rate system using Lyapunov´s theorem: Applied to real-time simulation

This paper proposes a method to analyse stability of multi-rate system. Multi-rate systems are used to simulate different part of the circuit with different sampling rate. This allows to reduce computational burden of stiff system; by choosing the most appropriate time-step according to the time constant of the phenomena studied. Traditionally, stability of discrete system is done by studying the eigenvalues of the system which can only uses a single sampling time and therefore cannot be applied to multi-rate systems. Many examples, where simulation is done with multiple rate, can be found in literature with no proof of stability other than simulation results. In this paper, multi-rate system are first represented as non-linear system using a single time-step and their stability is then demonstrated using Lyapunov´s theorem. The proposed method is supported by a numerical example.