Real-time implementation of digital relay models using MATLAB/SIMULINK and RTDS

Software models for protective relays offer an economic and feasible alternative to studying the performance of protective relays. Relay models have been long used in a variety of tasks, such as designing new relaying algorithms, optimizing relay settings and training personnel [1]. In order to be practical, software relay models must reproduce the actual operation of the physical relays. This has been somewhat difficult for electromechanical relays, due to lack of design data. In the case of digital relays, which are the prevailing practice in today’s power systems, this has become simpler. Most of the digital relays are accompanied by technical manuals that describe adequately their algorithms and design characteristics. Based on this information, fairly ‘‘accurate’’ digital relay models can be developed, by using a high level language such as FORTRAN, C, C++[2], or commercial software packages like MATLAB, SIMULINK [3]. In most of the existing applications, digital relay models are used in conjunction with electromagnetic transient programs (EMTP) for off-line open or closed-loop simulation studies [4,5]. Although these applications are useful for relay performance evaluation, it would be desirable to have a real-time implementation of digital relay models. A real-time implementation would enhance the realism of the models and would provide access to hardware and software issues currently not available in off-line simulation studies. Real-time applications make necessary the use of specific devices, like microprocessors and DSPs. These devices require reprogramming of the digital relay model with special machine code, which is a difficult and time consuming task. Also, in order to be practical, the real-time platform needs to be cost effective and easy to set up. In this paper, a low-cost platform is proposed based on MATLAB/SIMULINK, which is used not only as a simulation tool for developing digital relay models, but principally for their real-time execution. By using a general purpose data acquisition board (DAB), the developed digital relay model can act as a physical relay and be integrated with a real-time digital simulator (RTDS) forming thus a hardware-in-the-loop simulation environment [6].