  Voltage control plays an important role in the operation of electricity
distribution networks, especially when there is a large penetration of
renewable energy resources. In this paper, we focus on voltage control through
reactive power compensation and study how different information structures
affect the control performance. In particular, we first show that using only
voltage measurements to determine reactive power compensation is insufficient
to maintain voltage in the acceptable range. Then we propose two fully
decentralized and robust algorithms by adding additional information, which can
stabilize the voltage in the acceptable range. The one with higher complexity
can further minimize a cost of reactive power compensation in a particular
form. Both of the two algorithms use only local measurements and local
variables and require no communication. In addition, the two algorithms are
robust against heterogeneous update rates and delays.
