Real-Time co-Simulation with RTDS and Opal-RT

  Copyright: RWTH Aachen

In the complex scenario of future power systems, simulation in support of design and Hardware in the Loop methods will have a key role. Simulation tools, which can support such a task, have to allow modeling of different physics as well as analysis at different time scales and resolution levels. As for traditional off-line simulation, also for real time simulation co-simulation approaches need to be developed, since the use of a single simulation tool, able to satisfy all kinds of analysis needed, is not feasible.

Among other platforms, the ACS laboratory is equipped with two state-of-the-art digital simulators: RTDS and Opal- RT. To leverage functionalities and capabilities of both si- mulators, to capitalize different expertise and to allow the use of dedicated libraries, RTDS and Opal-RT are interfaced and integrated into one co-simulation platform. Regarding interface possibilities until now we are focusing on two dif- ferent possibilities.

The first approach, technically the simplest solution, is to interface the two simulators by means of analog signals. Disadvantages of this solution are poor flexibility, quantiza- tion limitation and noise. The main benefit of this approach is the small latency. The use of analog signals is the preferable choice if the coupling of two subsystems, simulated in RTDS and Opal-RT, is intrinsically electrical, which means that the exchanged signals are instantaneous values of vol- tages and currents. An example of such an application is the extension of a standard power system simulation in RTDS with a detailed power electronics simulation in Opal-RT.

In the second approach the two simulators are interfaced by means of digital communication. Signals are exchanged via the IEC 61850-9-2 SV (Sampled Values) protocol. Alt- hough extremely flexible, this approach is limited due to large signal latency to applications that do not require high-speed, low-latency signal exchange. This is the case of electro-thermal or electro-mechanical simulated systems. This approach allows easy and fast extension of power sys- tem simulations in RTDS with multi-domain capabilities of the Opal-RT system.

To overcome the limitation in terms of flexibility of the use of analog signals and the limitation in terms of latency of the IEC 61850-9-2 SV, we are developing a custom interface based on FPGAs. We believe this solution allows for flexible, accurate and high-speed data exchange and will be the de- fault option of choice.