This paper presents the development of a hardware-in-the-loop testbed for a three-bus power grid interfaced with a simulated networked control system (NCS) for studying cyber security threats and their possible impacts on the power grid. The three-bus grid consists of two generator buses, configured as slack bus (constant voltage and angle) and PV bus (constant power and constant voltage), and a load bus (PQ bus). The synchronous generators are driven by dynamometers serving as prime movers, and the field circuits controlled by insulated gate bipolar junction transistor (IGBT) DC/DC choppers. The load bus operates switchable resistors, capacitors, and inductors that are connected to the generator buses through transmission lines. The simulated NCS is implemented on an Opal real-time (Opal-RT) platform, which is a PC/FPGA based real-time simulator that can integrate hardware with software simulations, commonly referred to as hardware-in-the-loop (HIL). In general, HIL setups have the advantage that physical elements under test interact in real time with a simulated model of a large scale system and provide a better insight of performance of both the physical system and the controller. In this HIL experiment, the data acquisition unit (DAQ), and the controller are both implemented on the Opal-RT platform. The controller determines the duty cycle of the pulse width modulated (PWM) signals applied to the gate of the IGBT which controls the voltage applied the generator field circuits, thus producing desired terminal voltages of the generators. Experimental results are presented that show the effects of cyber-attacks on a generator control system. A baseline for the behavior of the three-bus system is first established by operating the generator under various load conditions for which the controller maintains the desired terminal voltage. Then, a series of denial-of-service (DoS) attacks in the feedback loop were launched. With no attack prevention mechanism in place, the developed experimental platform provides a facility to observe and evaluate the impacts of various cyber-attacks on a real physical microgrid. The developed HIL platform allows students to experiment with various cyberattack scenarios, defense strategies, and control algorithms due to the reconfigurable nature of the HIL system.
