VI. THE BANDWIDTH AND LATENCY BARRIER IN THE
ADVANCED METER INFRASTRUCTURE
An AMI uses a power line based communications architecture that allows the easy broadcast of messages from a central controller to many connected devices (meters) but only slow communications back from the connected devices to the central controller. There is no possibility of peer-to-peer communication. The connected meters are a low cost device and this places limitations on the communications transceiver
at the meter.
An inspection of the Victorian AMI functionality specification, [18], reveals a system that offers a step change in capability relative to the pre-existing meter infrastructure that will allow the consumer to play a much more active role in optimizing their energy usage. This functionality is finite and the AMI is designed to deliver specific outcomes. Some more advanced smart grid concepts will lay beyond the capabilities of an AMI with a reasonable level of sophistication. Key restrictions are the asymmetric bandwidth of the communications channel and latency. Load control is one of the faster AMI commands. The Victorian functional specification, [18], requires 99% of meters respond in one minute to group commands but for individual meter commands only 90% need respond in 30 minutes. Only 2% of meters may be switched individually within a 24 hour period.
As an example of the latency and bandwidth barrier, many SmartGrid functionalities related to electric vehicles could not be realized through an AMI. Electric vehicles are technically capable of adjusting their charging currents on a second by second basis and can regenerate real and reactive power to support the grid. Plug-in hybrids and electric vehicles will carry battery packs of up to 53 kWhr, [20], and will typically
re-use their drive inverters to provide a bi-directional charger capability. An intermediate rating for a charging circuit, SAE 1772 Level 2, is a 230Vrms 48Arms 11kVA interface. A highly responsive load control on an electric vehicle fleet could be used to balance large scale intermittent renewable energy inputs. A penetration of few percent of Vehicle to Grid capable (V2G) electric vehicles into the Australian vehicle fleet, 13 million vehicles, would provide thousands of MVA of installed inverter capacity, enough to provide the entire network spinning reserve, [22]. Such critical functions could only be realized through a robust, responsive and secure communications infrastructure.
On a more modest level even a feeder scale micro-grid with distributed generation, storage and load control would be unable to operate within the limitations of an AMI. Any communications to individual devices are potentially subject to very long delays.
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