**4. Experimental Results**

On the control pilot, the EVSE generates a 1 kHz square wave at ±12 volts in order to detect whether the EV is correctly plugged, to communicate the maximum power allowed by the cable and for charging begin/end process control initiated by the EV (see Figure 4a) or initiated by EVSE (see Figure 4b).

**Figure 4.** Communication signals between EVSE and EV. Ch 1 – *uCP* and Ch 2 – *iL*<sup>1</sup> (**a**) Control from EV; (**b**) Control from EVSE.

All charging stages can be generated by EVSE through the status of switch S1 (presented in Figure 2) and by EV simulator through the status of switches S2, S3 (presented in Figure 3c). These charging stages are detailed in Table 1.


**Table 1.** EV charging stages.

Because the people safety in stations is very important, an RCD (residual current device) has been mounted. Of course, it must be periodically tested for the proper functionality of protection by the maintenance employer. The RCD protection of the EVSE is very easy to be tested using an EV simulator and the switches S4–S8 (see Figure 3c). The experimental results at different values of residual current are presented in Figure 5 and it is shown how the RCD tripping time is reduced as the residual current increases.

**Figure 5.** Residual current device (RCD) experimental tests; Ch 1 – *uCP,* Ch 2 – *iRCD,* Ch 3 – *iL*1: (**a**) *iRCD* = 30 mA; (**b**) *iRCD* = 35 mA; (**c**) *iRCD* = 60 mA; (**d**) *iRCD* = 150 mA.

The charging stations can be installed in the office or mall parking area, where the customers have the benefit of being able to charge their EVs for free. The solution must offer customers the certainty that their EV will not be disconnected from the charging station by an unauthorized person. Usually, the customers must have an RFID card that will be used to control the beginning and the end of the charging processes. The proposed solution offers the same facility to the customers without any RFID card. To test the solution proposed by the authors for the charging station, a PLC has been used to control the implemented prototype. A friendly HMI connected with PLC has been implemented in order to be easily used by the customers. For example, when a customer plugs his EV in the charging station, he should wait the confirmation on HMI and, after that, he must introduce an identification code and press the START button. In this moment the locking system of the station socket will block the charging cable connector in the station socket, preventing the unauthorized disconnection of the EV from the charging station. This type of application can be simple extended for more than one station, all controlled by the same PLC and HMI. These stations can be in the office or mall parking area. Before starting the charging command, the user must choose in HMI the number of station and a unique identification code. When the user wants to command the end of charging, he must choose the number of station and to input the identification code. After the PLC recognizes the code, the charging process is interrupted and the cable connector is unlocked. So, the features of the PLC software are as follows:


The programmable logic controller (PLC) type S7-1200 and a human-machine interface (HMI) type TP700 Comfort, both from Siemens, have been used but other types of PLC or HMI can be used in order to implement the proposed solution as well. A sequence of program (realized in the dedicated software Totally Integrated Automation Portal—TIA Portal, from Siemens) and the HMI screen are presented in Figure 6a,b: The sequence from the main program, presented in Figure 6a, confirms the communication between PLC and three phase energy meter device.

**Figure 6.** Software application: (**a**) programmable logic controller (PLC) software; (**b**) human-machine interface (HMI) screen.

This research helps the developers of Charging Station as [23–25]:

