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aged by a future system where vehicles autonomously
navigate as needed regarding the battery’s state of
charge. (Ruzmetov et al., 2013) proposes a platform
where an electric vehicle is automatically assigned to
a charging station based on parameters like the power
level of the battery, distance to travel, and status of
the road traffic. Moreover, the driver is guided to this
charging station with a mobile application.
Open Charge Point Protocol (OCPP) 1.5 (OCPP
Steering Group, 2012) is a standard open protocol
for communication between charging stations and
a central system that manages them. It defines
message types for authorization of customers, start-
ing/stopping charging of electric vehicles, configura-
tion and reservation of charging stations. However,
it lacks a mechanism for the management of parking
spaces assigned to the charging station. On the other
hand, (U.S. DOT, 2011) and (Litman, 2013) summa-
rize current solutions in parking management but do
not consider parking lots with charging stations.
3 APPROACH
This section describes our approach on an abstract
level. The charging station is equipped with an occu-
pancy sensor for each single parking space and each
parking space is assigned to a socket of the charg-
ing station. Charging stations are connected to a cen-
tral system. We modeled the contexts of a charg-
ing station as a set of states – free, occupied, au-
thorized, charging, warning, violated – depending on
three sources:
1. Sensor Information: Occupancy sensors can de-
tect whether a parking space is free (no vehicle
parking) or occupied (vehicle parking). Subse-
quently, the central system can be informed about
the change.
2. Customer Interaction with the Charging Sta-
tion: After a parking space is occupied, the cus-
tomer must be authorized (allowed to charge) and
start charging his/her electric vehicle (for exam-
ple by plugging in the cable).
We also added the state warning which implies
that the vehicle has to leave the parking space:
I. The charging station changes from occupied
to the warning state, if the authorization
fails.
II. The charging station changes from charging
to the warning state, if the charging process
is stopped (for example by unplugging the
cable).
3. Timeouts: In order to prevent misuses or abuses
of the parking space we introduced time con-
straints for three states, occupied, authorized and
warning. While a vehicle is parking, the customer
must take actions within a fixed period of time so
that the parking space is not blocked for a long
time and the charging station can offer its service
to others.
I. In the occupied state, the customer must
authorize himself/herself within a fixed pe-
riod of time, otherwise the charging station
changes to the warning state.
II. In the authorized state, the customer must
start charging within a fixed period of time,
otherwise the charging station changes to the
warning state.
III. In the warning state, the vehicle has to leave
the parking space within a fixed period of
time, otherwise the charging station changes
to the violated state. Changing to the vio-
lated state is the only transition where a net-
work communication is essential since cen-
tral system must be informed about the sit-
uation and additional steps should be taken
(such as reporting to law enforcement offi-
cials).
Timeouts are handled by each charging station in-
ternally, so the task will not be burden on the cen-
tral system.
Figure 1 illustrates the functionality of the charging
station with the states. It is important to note that state
changes are managed by the charging station. This
enables to continue using the functionality if the net-
work connection fails and the charging station is not
connected to the central system. Beside the obvious
hardware-enhancement of including occupancy sen-
sors, the solution proposes changes on the software
of both the charging station and the central system.
First, the charging station must be able to process in-
formation gathered by sensors and change states ac-
cordingly. Second, the charging station’s internal pro-
cesses must trigger state changes when authorization
succeeds or fails, and when charging process starts
and stops. Third, the functionality suggests a commu-
nication between the charging station and the central
system.
Authorization. We made no distinction between
different authorization mechanisms since the chosen
mechanism does not affect the way state changes
function. They all serve the purpose of allowing the
customer to charge or not, hence trigger a transition
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