Hardware-in-the-Loop (HIL) experiment is a powerful technique used to integrate real-time simulation with physical hardware. This approach allows the virtual models of a system to interact with actual physical devices in real-time, creating a realistic and dynamic testing environment. By using this method, engineers can simulate complex systems and test their performance under various conditions without needing a full-scale physical setup. This approach reduces the risk of damage and increases the flexibility of the testing process. HIL has been successfully applied to many engineering disciplines, including aerospace and power systems.

There are three main categories of HIL experiments that can be used in power systems engineering. Internal HIL focuses on testing the software models built in a simulator, which ensures that the simulation models (or algorithms) are functioning correctly. Controller HIL (CHIL) connects real-world controllers to a plant model, allowing engineers to evaluate how well these controllers will perform when integrated with the rest of the system. Power HIL (PHIL) goes one step further, involving real power hardware, such as converters or inverters, to assess how the system responds to actual power flows and dynamics. This is crucial for understanding real-time performance in energy systems.