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Smart V2G algorithm

Source: R/v2g.R
smart_v2g.Rd

Prototype vehicle-to-grid simulation built on top of smart_charging() helpers. The current implementation mirrors the classic workflow (responsiveness filtering, setpoint definition and scheduling placeholder) but it isolates the new optimisation pieces so the existing API remains untouched.

Usage

smart_v2g(
  sessions,
  opt_data,
  opt_objective = "grid",
  window_days,
  window_start_hour,
  responsive = NULL,
  power_th = 0,
  charging_power_min = 0,
  energy_min = 1,
  energy_max = 1,
  discharge_eff = 1,
  include_log = FALSE,
  show_progress = FALSE,
  lambda = 0,
  soc_min = 0.2
)

Arguments

sessions

tibble, sessions data set containig the following variables: "Session", "Timecycle", "Profile", "ConnectionStartDateTime", "ConnectionHours", "Power" and "Energy".

opt_data

tibble, optimization contextual data. The first column must be named datetime (mandatory) containing the date time sequence where the smart charging algorithm is applied, so only sessions starting within the time sequence of column datetime will be optimized. The other columns can be:

  • static: static power demand (in kW) from other sectors like buildings, offices, etc.

  • import_capacity: maximum imported power from the grid (in kW), for example the contracted power with the energy company.

  • export_capacity: maximum exported power from the grid (in kW), for example the contracted power with the energy company.

  • load_capacity: maximum charging power (in kW) allowed for the flexible EV demand at every time slot. By default the algorithm already limits the optimized setpoint to the nominal power of the connected EVs (the physical charging envelope). This variable can be used to tighten that limit further (e.g. a charging point or transformer power limit).

  • production: local power generation (in kW). This is used when opt_objective = "grid".

  • price_imported: price for imported energy (Euro/kWh). This is used when opt_objective = "cost".

  • price_exported: price for exported energy (Euro/kWh). This is used when opt_objective = "cost".

  • price_turn_down: price for turn-down energy use (Euro/kWh). This is used when opt_objective = "cost".

  • price_turn_up: price for turn-up energy use (Euro/kWh). This is used when opt_objective = "cost".

If columns of opt_data are user profiles names, these are used as setpoints and no optimization is performed for the corresponding user profiles.

opt_objective

character, optimization objective being "none", "grid", "cost", "capacity" or a value between 0 (cost) and 1 (grid). See details section for more information about the different objectives.

window_days

integer, number of days to consider as optimization window.

window_start_hour

integer, starting hour of the optimization window.

responsive

Named two-level list with the ratio (between 0 and 1) of sessions responsive to smart charging program. The names of the list must exactly match the Time-cycle and User profiles names. For example: list(Monday = list(Worktime = 1, Shortstay = 0.1))

power_th

numeric, power threshold (between 0 and 1) accepted from setpoint. For example, with power_th = 0.1 and setpoint = 100 for a certain time slot, then sessions' demand can reach a value of 110 without needing to schedule sessions.

charging_power_min

numeric, minimum power in kW (default 0), for charging and for discharging alike: a responsive session charges at charging_power_min or more, discharges at charging_power_min or more (e.g. "discharge only from 4 kW upwards"), or does nothing. When the SoC floor or the energy deadline would only allow a smaller discharge (say -2 kW against a 4 kW minimum), the session does not discharge in that slot. The one exception is a session's last charging slot, where it may charge less than the minimum because it only needs that much to finish (the tail of its charge). A session whose nominal Power is below charging_power_min is not flexible: it is never responsive, charges as uncontrolled, never discharges, and the setpoint carries its load as fixed. Up to version 1.12.0 a value below 1 was a share of the nominal power; it is now always kW.

energy_min

numeric, minimum allowed ratio (between 0 and 1) of required energy. Every session charges at least this share of the energy it requires, net of discharge. The scheduler never discharges or curtails a session below it, and the setpoint optimization may drop energy down to it - and no further - when the grid capacity cannot fit energy_max. When even this minimum does not fit, the grid capacity is relaxed only as far as the minimum-energy profile needs.

energy_max

numeric, maximum allowed ratio (between 0 and 1) of required energy. Every session charges at most this share of the energy it requires, net of discharge (energy discharged, grossed up by discharge_eff, has to be charged back on top), and the setpoint optimization targets this share for the responsive sessions. Must be higher than 0 and at least energy_min.

discharge_eff

numeric, discharge efficiency (0, 1], applied to energy losses when discharging. For example, 0.9 means that for every 1 kWh discharged, 1/0.9 kWh must be recharged.

include_log

logical, whether to output the algorithm messages for every user profile and time-slot

show_progress

logical, whether to output the progress bar in the console

lambda

numeric, penalty on change for the flexible load.

soc_min

numeric, State-of-Charge floor of every V2G session, as a fraction of its battery capacity (default 0.2, 0 <= soc_min < 1). A session never discharges below it. A session that arrives below it (StateOfCharge < soc_min) charges up to the floor first, as fast as it needs to (at nominal power when necessary), and can neither be curtailed nor discharge before it reaches the floor.

Value

list with setpoints, sessions and demand similar to smart_charging(). Scheduling is still charging-only while the V2G-specific session logic is under development.

Details

The sessions tibble can carry a StateOfCharge column, the State-of-Charge of each vehicle at arrival as a fraction (0 <= StateOfCharge < 1); when it is absent every session arrives at 0.5. Each session's Energy takes its battery from StateOfCharge to full, so its battery capacity is Energy / (1 - StateOfCharge) (twice the energy at 0.5). With energy_max below 1 the session charges only that share of its energy and leaves below full, at StateOfCharge + energy_max * (1 - StateOfCharge).

The setpoint plans charge and discharge only while the responsive sessions are connected, within their nominal power in both directions (and load_capacity), and keeps the energy owed to every session by its departure: the cumulative flexible load never drops below the energy_min share of the energy of the sessions that have left, minus what the connected sessions can still discharge down to soc_min.