Resilient Control of Power Inverter Network (RCPIN)

The voltage regulation problem for inverter-interfaced power distribution networks has been 
investigated using different approaches in the current literature. Most commonly, it has been 
studied using the distributed droop control technique, which yields voltage stability through 
appropriate reactive power compensation. However, in the literature, these methods seek 
asymptotic voltage stability, which may be insufficient to characterize the reliability of the grid 
under intermittent fault/ attack scenarios.  
For this reason, in this work, we provide a framework of resilient control design in an attempt 
to quantify the desired response of safety-critical systems such as the power distribution grid. 
According to the proposed framework, we deem the power network resilient if i) it satisfies 
the given voltage stability objective under nominal conditions (when the disturbance/ attack 
signal is within the considered bounds) and ii) given an intermittent violation, the system is 
able to recover and re-establish the voltage regulation constraints in finite-time. We define 
these traits to be the durability and recoverability properties, respectively, of the proposed 
resilience framework. Furthermore, to enforce the proposed resilient framework on the in
verter-interfaced power distribution network, finite-time robust control barrier function (FR
CBF)-based design conditions are provided for the control of the consumer inverters.  
The main objective of the current study is to test the efficacy of the proposed resilient control
ler on a dedicated testbed for power inverter networks using hardware-in-the-loop (HIL) ex
periments. Towards that end, in this work, we simulated the power inverter network in real 
time using the OPAL-RT platform. Then, based on the sampled measurements from the grid 
that was being run in the real-time OPAL-RT simulator, the proposed resilient control scheme 
was employed to compute the corresponding control inputs for the consumer inverters, which 
was then fed back to the OPAL-RT simulation yielding the desired reactive power compensa
tion from the consumer inverters. Furthermore, to showcase the effectiveness of our pro
posed approach, the voltage regulation problem was considered under the sign-flipping step 
power injection attack that yielded the maximum deviation of the nodal voltage trajectories. 
The resulting voltage trajectories were then studied to verify if the proposed controller yielded 
resilient characteristics for the grid, given the voltage regulation objective.  
The following conclusions were reached: 
1. Under the proposed resilient control action, the power grid was deemed durable as 
the voltage trajectories remained within the stipulated range when the power injection 
attack remained within the considered bounds.  
2. At the activating (and the sign-flipping) instance of the attack signal, when the consid
ered bounds on the attack vector were violated, the voltage trajectories were per
turbed. However, once nominal conditions returned and the resilient controller was re
instated, the voltage trajectories were observed to recover in finite-time, thereby 
demonstrating the recoverability trait from the resilience framework.  
The following aspects of the study remain unresolved: 
1. The results stated above were obtained for a distribution grid with 5 nodes. The 
scalability of the proposed control design scheme needs to be further investigated to 
see if our approach remains viable for larger networks. 
2. The performance of the proposed controller need to be further evaluated against oth
er attack/ fault scenarios that are commonly encountered.