  Autonomous droop control PV inverters have improved voltage regulation
compared to the inverters without grid support functions, but more flexible
control techniques will be required as the number of solar photovoltaic (PV)
installations increases. This paper studies three inverter future deployment
scenarios with droop control inverters, non-exporting inverters, and
coordinated inverter control (CIC). The network operation and the interaction
between various inverter control methods are studied by simulating inverter
operation on two low-voltage networks. Considering 30% PV penetration as the
base case, we demonstrate that coordinated inverters can mitigate overvoltages
and voltage fluctuations caused by the tripping of passive inverters in 85% of
PV location cases when at least as many coordinated as passive inverters are
deployed on the 114-node test feeder. However, this rate reduced to 37% with
the IEEE 906-node network demonstrating that the deployment of coordinated
inverter control may not be able to reverse passive inverter-related voltage
disturbances when the build-up of passive inverters has reached a certain
threshold.
  The aggregated PV output from coordinated inverters can be also used to
provide grid support services. When the low-voltage networks operate close to
the upper voltage limits, the change in the power output from coordinated
inverters following a regulation request may be partially offset by passive
inverters. Considering an equal number of passive and coordinated inverters,
this paper shows that for each unit of the down-regulation request delivered by
coordinated inverters, passive inverter output may increase by up to 0.2 units
and decrease by up to 0.45 units during coordinated inverter up-regulation.
