• Stationfinder device

Overview#

Although SUMO offers output regarding emissions and energy/fuel usage, by default SUMO vehicles would travel as long as wanted without need to charge. Charging stations for battery electric vehicles have been introduced with the battery device.

The stationfinder device lets equipped vehicles monitor their energy buffer (currently battery only) when traveling and reroute to nearby charging stations in case they won't make it to their destinations otherwise. Optionally, vehicles can break down due to low battery charge.

Decision logic for charging#

This paragraph shall convey the major conditions used in the decision logic of the device. The device has to decide whether and where to reroute the vehicle to charge. The user can configure multiple thresholds to change how different vehicles behave.

• As long as the battery state of charge (SoC) is above needToChargeLevel, no action is taken. This condition is rechecked each time the SoC has lowered by 10%.
• When the SoC reaches needToChargeLevel, possible charging stations are searched and evaluated using the target function. If a valid charging station is found within radius travel time, the vehicle is immediately rerouted to go there. Other programmed stops will be served after charging.
• If no charging station is available, the vehicle continues its original route. It will search again after repeat seconds.
• If the charging station is occupied on arrival, the vehicle will wait waitForCharge seconds before looking for an alternative site.
• The vehicle will charge enough to complete the planned route multiplied by reserveFactor and try to keep the SoC above emptyThreshold.
• Equipped vehicles monitor every second (not necessarily every time step) whether the battery state of charge (SoC) goes beyond emptyThreshold. If it does, the configured rescueAction is executed.

Charging station target function#

When there are more sites to choose from, the device sorts the charging stations according to a target function and chooses the one with the lowest score. The target function works as follows:

score = travel_time + charging_time + waiting_penalty/charging_points

The score consists of the travel time to get to the charging station and back to the original route, the charging time considering the charging speed and a penalty time if the charging station is already occupied.

Break down due to lack of energy#

Vehicles may not always manage to reach a free charging point before they run out of energy. This can be due to a number of reasons:

• low battery capacity (actual or maximum battery capacity)
• high energy consumption
• low number of charging stations nearby
• high occupancy of charging stations

The stationfinder device can be configured using the parameters rescueTime and rescueAction to handle the lack of energy in the following ways:

• rescueAction="none": let vehicles continue on their route although they don't have enough energy
• rescueAction="remove": the vehicle will come to a standstill and then will be removed from the simulation
• rescueTime="TIME" rescueAction="tow": the vehicle will come to a standstill and wait for TIME seconds (waiting time for a tow truck). Then it will be teleported to a free charging point, charge and continue its route. Thus the travel from the break down to the charging station is not included in emissions output.

Configuration#

The following table gives the full list of possible parameters for the stationfinder device. Each of these parameters must be specified as a child element of the form <param key=device.stationfinder.<PARAMETER NAME> value=<PARAMETER VALUE> of the appropriate demand definition element (e.g. <vehicle ... />, <vType ... />, or <flow ... />).