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Tips and Tricks for E- and Hybrid-Simulation in KULI 9.0

KULI 9 contains two new electric components: The battery cell and the electric motor / generator. These components can be used to simulate the thermal load electric systems put on cooling systems. Battery cells furthermore allow the simulation of the state of charge for transient driving cycles so that the overall efficiency of an electric vehicle can be evaluated.

Tip 1: Quick Modeling of Modules and Battery Packs (Easy)
Although the KULI battery cell model is mainly intended for simulating the behavior of one individual battery cell, it can also be used to simulate battery modules (i.e. several cells grouped together) or even complete battery packages. To do so (for a battery module):

  • Enter the geometric size, so that it represents the complete module
  • Enter the total module mass and the effective surface for heat transfer
  • For simple geometries (e.g. several cylindrical cells grouped to a “stick”) plate theory can be used for convective heat approximation, for more complex layouts we recommend using measurements and direct input into 2d-curves.
  • Enter electric properties for the complete module. Be aware that depending on whether the individual cells are connected in parallel or in serial, either the total capacity or the external voltage will be a multiple of the individual cell values.

Modeling modules and battery packages this way allows quick and easy “black box” assessments, but does not allow the evaluation of individual cell temperatures. If this is required, model each cell individually. KULI 9.1 will contain dedicated “Battery Module” and “Battery Pack” components, which will further facilitate this process.

 

Tip 2: Using KULI to Compare Different Hybrid Strategies (Advanced)

One general strong point of KULI is to quickly compare different variants of cooling systems. Such variants can implement different cooling concepts, but also e.g. different driving strategies. Using the simple driving simulation template provided as a standard KULI example, a model like the homepage example “HybridTruckExample_Variant1.scs” can be set up. In its base variant whether the e-motor is boosting or not is controlled based on the current power requirement.

Alternatively (see the example “HybridTruckExample_Variant2.scs”) the boost strategy can also be based on the current acceleration.

Comparison of these two strategies yields completely different SOC (state of charge) characteristics for the same driving cycle.

 

In this simple example the used simple hybrid strategies are of course not realistic. Complex driving strategies can be included in KULI using e.g. the MATLAB / Simulink Interface.

 

Tip 3: Modeling Capacitive Effects in a Battery Cell (Expert)

The standard battery cell model included in KULI 9.0 implements the relatively simple equivalent circuit diagram of an ideal voltage source (no-load voltage) in serial with an internal resistance (depending on SOC and temperature). In order to get a more realistic battery model it is also possible to consider additional capacitive effects modeled by a capacitor in parallel to the ohmic inner resistance. This yields a differential equation the solution of which can be modeled in the KULI signal path.

 

The result of this is then mapped as an “effective inner resistance” to the inner resistance actuator of a battery cell. Using such a model in a standard driving cycle will show e.g. the following results.

 

For close to steady state load cases such a more complex model is not necessary, for highly transient driving cycles the influence can be important.