APIS logic

This documentation on github explains the logic of how APIS works https://github.com/hyphae/apis-main/blob/master/doc/en/apis-main_specification_en.md#2-overview

Below is a summary of the main concepts:

• Nodes: APIS communication takes place between batteries on the DC/DC microgrid, which are connected to the grid via a bidirectional DC/DC converter.  These are called nodes.  One node could have multiple households, appliances or generating assets (e.g. solar panels) connected to it, but it must have one battery and one DC/DC converter.   

• Connections between nodes: The nodes are connected via a communication line (such as Ethernet) as well as through electricity wires on the grid.  

• Decision making: The decisions being made by each node relate to whether the node will charge or discharge into the grid.  Each node makes decisions, in communication with other nodes, to enter into “energy sharing deals”, but without centralised control in deal-making.  The APIS-main software is running autonomously on each node. 

• Clusters: the microgrid can be divided into one or more clusters. There must be one gateway node if more than one cluster, which acts as a node in both clusters.

• Energy sharing: Energy sharing deals are in pairs - one node has agreed to discharge energy to (or send energy to) one other node.  Each energy sharing deal is started in sequence, but multiple energy sharing deals can be operating at the same time, for example node A can be sending energy to node B, node A can also be sending energy to node E, and node D can be sending energy to node C.  One node can be in multiple deals to send energy at the same time, but one node cannot be in multiple deals to receive energy at the same time. If there is more than one cluster, the gateway node cannot be discharging into both clusters at the same time or charging from both clusters at the same time.

• CV mode: At any one time, during energy sharing, only one node can be in Constant Voltage (CV) mode. This node is acting as the voltage reference for the grid.  The node in CV mode is either charging (receiving energy) or idle, but it is never discharging (sending energy). The other nodes are in Constant Current (CC) mode and can be discharging or charging or idle depending on where their voltage is relative to the reference voltage.

• Grid master: At any one time, one of the nodes is acting as “Grid Master”. There is a process for determining which node is the grid master at any one time - either the node which is in CV mode, a fixed or hard coded node, or the first node which claims it.  Therefore the grid master node may be the CV node or may be a CC node depending on which rule is adopted.