  In this paper, we demonstrate the fragility of decentralized load-side
frequency algorithms proposed in [1] against stochastic parametric uncertainty
in power network model. The stochastic parametric uncertainty is motivated
through the presence of renewable energy resources in power system model. We
show that relatively small variance value of the parametric uncertainty
affecting the system bus voltages cause the decentralized load-side frequency
regulation algorithm to become stochastically unstable. The critical variance
value of the stochastic bus voltages above which the decentralized control
algorithm become mean square unstable is computed using an analytical framework
developed in [2], [3]. Furthermore, the critical variance value is shown to
decrease with the increase in the cost of the controllable loads and with the
increase in penetration of renewable energy resources. Finally, simulation
results on IEEE 68 bus system are presented to verify the main findings of the
paper.
