Battery

Battery#

There are two battery models currently implemented in Hercules: SimpleBattery and LIB. Both interact with Hercules through a simple wrapper class: Battery.

Parameters#

Battery parameters are defined in the hercules input yaml file used to initialize emulator.

  • py_sim_type: "SimpleBattery" or "LIB"

  • energy_capacity: [kWh]

  • charge_rate: [kW]

  • max_SOC: between 0 and 1

  • min_SOC: between 0 and 1

  • initial_conditions

    • SOC: between min_SOC and max_SOC

Once initialized, the battery is only interacted with using the step method.

Inputs#

Inputs are passed to step() as a dict named inputs, which must have the following fields:

{py_sims:{inputs:{battery_signal: ____,
                 available_power: ____
                 }}}

Outputs#

Outputs are returned as a dict containing the following values

  • power The charging/discharging power of the battery

  • reject The amount of charging/discharging requested of the battery that it could not fulfill. Can be positive or negative.

  • soc The battery state of charge

SimpleBattery#

SimpleBattery is defined by \(E_t = \sum_{k=0}^t P_k \Delta t\), where \(E_t\) is the energy stored and \(P_t\) is the charging/discharging power at time \(t\). Both \(E\) and \(P\) are constrained by upper and lower limits.

\(\underline{E} \leq E \leq \overline{E}\)

\(\underline{P} \leq P \leq \overline{P}\)

LIB#

LIB models a lithium ion battery based on the lithium ion cell model presented in [1.]. The main difference between LIB and SimpleBattery is that LIB includes diffusion transients and losses both of which are modeled as an equivalent circuit model following the approach in [1.].

References#

  1. M.-K. Tran et al., “A comprehensive equivalent circuit model for lithium-ion batteries, incorporating the effects of state of health, state of charge, and temperature on model parameters,” Journal of Energy Storage, vol. 43, p. 103252, Nov. 2021, doi: 10.1016/j.est.2021.103252.