Virtual Control and Protection System in Real Time Software in the Loop

MTDC systems overlaid on existing AC system infrastructure, enable interconnection of multiple HVDC links, improving flexibility and reliability across regions by decoupling the AC and DC grids. However, recent real world events have shown that high penetrations of PE in the existing infrastructure can lead to undesired interactions and potential blackouts [1]. As a consequence, the need to study PE interactions is key to ensuring a robust and reliable power system.

To study interaction between PE devices, converters need to be modeled, including their control system, and integrated in the same simulation environment. Traditionally, HVDC system interaction with other PE devices has been successfully done using Non-Real Time SoftwareIn-the-Loop (NRT-SIL) and Real Time Hardware-In-the-Loop (RT-HIL) setups using ElectroMagnetic Transient (EMT) simulations. However, if certain software models are unavailable or lack sufficient accuracy, the delivered real hardware setup is the only reliable option. In such cases, a real time environment becomes the sole viable simulation platform for conducting interaction studies and integrating various PE devices and their controls.

The integration of multiple PE devices in a real time environment can require considerable investment to allocate hardware, connect, operate and perform the required studies. A RT-HIL setup requires the power system model of the PE devices to be represented in a Real Time

Simulator (RTS), and the signals required to operate the device to be sent and received from the real physical control and protection (C&P) hardware, all of which must be physically located in the same lab. As a result, the cost, time and space required to host the simulation setup can be significant. For this reason, alternatives to setups with multiple real C&P systems have been made available to support the energy transition and the challenges of power systems with high penetration of PE devices, including MTDC systems.

This paper discusses more affordable, low footprint real time setups that enable fast, integrable and compact real time technology for the integration of multiple PE units in the same real time simulation environment. Two options discussed are:

(i) Real Time Software-In-the-Loop (RT-SIL)

(ii) Real Time Hardware-In-the-Loop (RT-HIL) without input/output boards (I/O-free HIL)

The paper also addresses different variants of RT-HIL setups to highlight the differences of reduced HIL setups that are possible depending on the needed purpose. In the paper, the reader can find a description of the different technologies, what is included in each of them and a comparison between these real time setups. Some results from dynamic simulations and events both in the small- and large-signal range are provided to give an insight into the expected performance for these setups. To address the topic of PE device interaction, impedance scans are provided to give an insight into the frequency spectrum using RT-SIL and an I/O-free HIL setup. Finally, a discussion on the applicability of these technologies in real HVDC projects is provided.