On Numerical Integration Techniques and Time step selection for Real-time Emulation - Case study of Microgrid System Emulation

Abstract

Real-time (RT) emulation has emerged as a popular testing technique of late. In order to achieve RT power level emulation the model of the target system has to be implemented on a processor to generate the reference signals so that these can be tracked in real-time and the target system behaviour can be mimicked. The model of the target consists of a set of differential (or difference) equations describing the behaviour of the target system which could be a source, load or a system consisting of both. To solve the differential equations numerical integration techniques must be employed. The selection of a suitable time step is crucial to ensure a stable simulation. The work explores the choice of numerical integration techniques and a systematic approach to select the choice of time step. In order to meet RT constraints, the study focuses on three explicit methods (the Forward Euler method, Modified Euler (Heun method) and the Adam-Bashforth 2 step method) and outlines the procedure to select the time step through an example of emulation of a two-inverter based microgrid system. The procedure is validated through coding and off-line simulations on Matlab-Simulink.