Microgrid Concepts

A microgrid is a local electrical grid that connects a set of electrical components together. They are often built around a passive power consumer, to supplement the electricity consumed from the public grid with on-site power generation or storage systems.

Microgrids can also function in island-mode, without a grid connection, or without a local power consumer, but they have to have at least one of the two, to be meaningful.

Frequenz SDK Microgrid Model

The SDK aims to provide an abstract model of the microgrid that enables high-level interactions with microgrid components, without having to worry about (or even be aware of) location-specific details such as:

• where the meters are placed,
• how many batteries,
• whether there's a grid connection or a passive consumer,
• what models the inverters are, etc.
• whether components are having downtimes, because metrics and limits get adjusted automatically when components are having downtimes.

Users of the SDK can develop applications around this interface once and deploy anywhere, and the SDK will take care of translating the requests and instructions to correspond to the specific microgrid configurations.

flowchart LR

subgraph Left[Measurements only]
direction LR
  grid["Grid Connection"]
  consumer["Consumer"]
  pv["PV Arrays"]
  chp["CHP"]
end

junction(( ))

subgraph Right[Measurements and control]
direction LR
  bat["Batteries"]
  ev["EV Chargers"]
end

grid --- junction
consumer --- junction
pv --- junction
chp --- junction

junction --- bat
junction --- ev

Grid

This refers to a microgrid's connection to the external Grid. The power flowing through this connection can be streamed through grid_power.

In locations without a grid connection, this method remains accessible, and streams zero values.

Consumer

This is the main power consumer at the site of a microgrid, and often the load the microgrid is built to support. The power drawn by the consumer is available through consumer_power

In locations without a consumer, this method streams zero values.

Producers: PV Arrays, CHP

The total CHP production in a site can be streamed through chp_power. PV Power is available through the PV pool described below. And total producer power is available through microgrid.producer().power.

As is the case with the other methods, if PV Arrays or CHPs are not available in a microgrid, the corresponding methods stream zero values.

PV Arrays

The total PV power production is available through pv_pool's power. The PV pool by default uses all PV inverters available at a location, but PV pool instances can be created for subsets of PV inverters if necessary, by specifying the inverter ids.

The pv_pool also provides available power bounds through the power_status method.

The pv_pool also provides a control method propose_power, which accepts values in the Passive Sign Convention and supports only production.

Batteries

The total Battery power is available through the battery_pool's power. The battery pool by default uses all batteries available at a location, but battery pool instances can be created for subsets of batteries if necessary, by specifying the battery ids.

The battery_pool also provides soc, capacity, temperature and available power bounds through the power_status method.

The battery_pool also provides control methods propose_power (which accepts values in the Passive Sign Convention and supports both charging and discharging), or through propose_charge, or propose_discharge.

EV Chargers

The ev_charger_pool offers a power method that streams the total power measured for all the EV Chargers at a site.

The ev_charger_pool also provides available power bounds through the power_status method.

The ev_charger_pool also provides a control method propose_power, which accepts values in the Passive Sign Convention and supports only charging.

Component pools

The SDK provides a unified interface for interacting with sets of Batteries, EV chargers and PV arrays, through their corresponding Pools.

• Battery pool
• EV charger pool
• PV pool

All of them provide support for streaming aggregated data and for setting the power values of the components.

Streaming component data

All pools have a power property, which is a FormulaEngine that can

• provide a stream of resampled power values, which correspond to the sum of the power measured from all the components in the pool together.

• be composed with other power streams to for composite formulas.

In addition, the battery pool has some additional properties that can be used as streams for metrics specific to batteries: soc, capacity and temperature.

Setting power

All pools provide a propose_power method for setting power for the pool. This would then be distributed to the individual components in the pool, using an algorithm that's suitable for the category of the components. For example, when controlling batteries, power could be distributed based on the SoC of the individual batteries, to keep the batteries in balance.

Resolving conflicting power proposals

When there are multiple actors trying to control the same set of batteries, a target power is calculated based on the priorities of the actors making the requests. Actors need to specify their priorities as parameters when creating the *Pool instances using the constructors mentioned above.

The algorithm used for resolving power conflicts based on actor priority can be found in the documentation for any of the propose_power methods.

Shifting the target power by an Operating Point power

There are cases where the target power needs to be shifted by an operating point. This can be done by designating some actors to be able to set only the operating point power.

When creating a *Pool instance using the above-mentioned constructors, an optional set_operating_point parameter can be passed to specify that this actor is special, and the target power of the regular actors will be shifted by the target power of all actors with set_operating_point together.

In a location with 2 regular actors and 1 set_operating_point actor, here's how things would play out:

1. When only regular actors have made proposals, the power bounds available from the batteries are available to them exactly.

actor priority	in op group?	proposed power/bounds	available bounds
3	No	1000, -4000..2500	-3000..3000
2	No	2500	-3000..2500
1	Yes	None	-3000..3000

Power actually distributed to the batteries: 2500W

1. When the set_operating_point actor has made proposals, the bounds available to the regular actors gets shifted, and the final power that actually gets distributed to the batteries is also shifted.

actor priority	in op group?	proposed power/bounds	available bounds
3	No	1000, -4000..2500	-2000..4000
2	No	2500	-2000..2500
1	Yes	-1000	-3000..3000

Power actually distributed to the batteries: 1500W