TransactionalNetworkOverview
VOLTTRON serves as an integrating platform for the components of the Transactional Network project. It provides an environment for agent execution and serves as a single point of contact for interfacing with devices (RTU HVACs, power meters, etc.), external resources, and platform services such as data archival and retrieval. The VOLTTRON platform provides a collection of utility and helper classes which simplifies agent development. In the Transactional Network project, VOLTTRON connects devices (RTU HVACs, power meters, etc.) to applications implemented in the platform and in the cloud, a data historian, and signals from the power grid. It also provides helper classes to ease development and deployment of agents into the environment.
The components of the Transactional Network are illustrated in the figure above. The Device Interface communicates to the HVAC Controller using Modbus. It periodically scrapes data off the controller and both pushes to the sMAP historian and publishes it to the Message Bus on a topic for each device. The Device Interface also responds to lock and control commands published on the requests topic. Agents must first request and receive a lock on a device for a certain time period. During this time, they have exclusive control of the device and may issues commands. The sMAP agent in the figure represents the Archiver Agent which allows agents to request data from sMAP over the Message Bus. The Archiver Agent isolates agents from the details of the Historian and would allow the platform to use a different or multiple historian solutions (sMAP, a database, and a some other site).
Agents deployed on VOLTTRON can perform one or more roles which can be broadly classified into the following groups:
- Platform Agents: Agents which are part of the platform and provide a service to other agents. Examples are agents which interface with devices to publish readings and handle control signals from other agents.
- Cloud Agents: These agents represent a remote application which needs access to the messages and data on the platform. This agent would subscribe to topics of interest to the remote application and would also allow it publish data to the platform.
- Control Agents: These agents control the devices of interest and interact with other resources to achieve some goal.
Platform Services:
- Message Bus: All agents and services publish and subscribe to topics on the message bus. This provides a single interface that abstracts the details of devices and agents from each other. Components in the platform basically produce and consume events.
- Weather Information: This agent periodically retrieves data from the Weather Underground site. It then reformats it and publishes it out to the platform on a weather topic.
- Modbus-based device interface: The Modbus driver publishes device data onto the message bus. It also handles the locking of devices to prevent multiple conflicting directives.
- Application Scheduling: This service allows the scheduling of agents’ access to devices in order to prevent conflicts.
- Logging service: Agents can publish arbitrary strings to a logging topic and this service will push them to the sMAP historian for later analysis.