*4.1. Test Description*

The main equipment involved in the tests is shown in Figure 12. A V2G charger has been used as a HUT and it has been connected to the EVE through a CHAdeMO connection. The bottom box of the emulator is the AC/DC converter and the upper box is the DC/DC converter. Both of them are connected to the EBox, which is also connected to the grid analyzer (Circutor CVM-MINI) via RS-485 and to the HMI through TCP/IP. The transformer is also inside an enclosure for safety reasons.

**Figure 12.** General overview of the testbench used for the power tests done with the proposed EVE. On the left, a 50 kW EVE together the EBox gateway; On the right the HUT system built up with a 50 kW V2G charger; and the power transformer in the centre.

V

The simplified sequence of the complete test is shown in Figure 13, where it is explained how the system works, and the main processes with their interactions that are running, which are needed to emulate the behaviour of an EV. First, the user has to start the EVE system through the HMI and wait until the DC/DC system is ready to initiate the charge/discharge operation in order to test the HUT accordingly. Then, the user has to plug-in the cable and begin the operation needed to launch the charging/discharging process of the HUT. The user can change the voltage and/or power manually at any time or load a script with the profile of EV charging/discharging, indicating every 0.5 s the required voltage and power via HMI. The test will be finished whenever: the user stops it via HMI, the EVE battery model determines that it has finished the charging/discharging process, or there is any error during the operation.

#### *4.2. Manual Set-Point Adjustment*

With the aim to test the stability of the emulator, the voltage response at different set-points has been analyzed. Figure 14 shows the manual change of current set-point from 65 to −65 A, with the emulator controlling the same set-point voltage at 300 V. It must be noticed that the slope of the current increment by the charger is 10 A/s, which is within the limits of the CHAdeMO standard [19]. Furthermore, the PI controller implemented in

the emulator has a reduced velocity error during the transition of this current variation in the HUT.

**Figure 13.** Simplified operation sequence diagram of the complete EVE test procedure.

**Figure 14.** Experimental results of the variation of the current set-point from 65 A to −65 A at 300 V set-point. Voltage (**top**) and current (**bottom**) transient evolution is depicted in the figure.

Furthermore, it is possible to verify the behaviour of the system for grid managemen<sup>t</sup> purposes. For example, thanks to this test, it has been verified that this charger could be used to perform frequency grid operation for current set-point changes up to 50 A [26]. Furthermore, the smooth transition between the two set-points, indicates that it is possible to use this EVSE with V2G capability for operations such as peak shaving or managemen<sup>t</sup> of renewable energy surplus.

The variation of the set-point voltage from 300 V to 200 V is shown in Figure 15. These kinds of battery voltage fluctuations are abnormal in EV batteries, but they allow the user to know the stability and response of the charger to be tested. In this case, the emulator keeps the same set-point power, which produces an increment in the demanded current to the V2G charger. Depending on the time response of the chargers, maximum or minimum power peaks can appear during the voltage transition, which will be larger if the voltage transition is more abrupt.

#### *4.3. Load an EV Battery Profile*

In this case, a user defined EV battery charge profile has been defined. It consists of a charging process of 5 min, starting the voltage at 350 V with a demanded power of 12 kW. This demanded power decreases until reaching 6.5 kW and the voltage increases up to 358 V, the moment when the emulator sends a stop command to the charger through CHAdeMO communication. The evolution of the voltage and current measured at the emulator output is shown in Figure 16. At the beginning of the charging process, the CHAdeMO's isolation test procedure is performed by the charger, setting 500 V at the input of the emulator. Once the charger verifies that there is not any isolation problem, it closes the emulator power relay. From this point, the emulator control the output voltage and it sends the demanded power to the EVSE, which is defined in the loaded profile of the emulator. This profile can be modified in order to perform different user tests, changing current, voltage and time of the vehicle charge and executed as many times as needed. This feature allows the repeatability of the test, which makes it possible to compare and analyze the response of different HUTs.

**Figure 15.** Experimental results of the variation of the voltage set-point from 300 V to 200 V at 10 kW set-point. Voltage (**top**) and current (**bottom**) transient evolution is depicted in the figure.

**Figure 16.** Emulation of an EV charging for 5 min. The upper graph is the output voltage of the charger and the lower graph is the charged current.

To test the reactive power compensation, the previous EV battery charging profile has been used, but also adding a profile of reactive power consumption to the charger. A profile with abrupt changes in the reactive consumption has been configured in order to verify the behaviour of the emulator. In this case, the grid analyzer has been placed at the output of the HUT, with an open-loop control implemented in the EBox. Figure 17 shows the results of the test, measured with a power analyzer data logger (Fluke 435-II) at the PCC of the facility. Firstly, the reactive power consumption, without compensating it by the emulator, has been measured by a grid analyzer. Secondly, the same test has been repeated and measured, but this time compensating the reactive power consumption by the emulator. The data from the two measurements have been downloaded and synchronized.

**Figure 17.** Reactive power consumption of the EV charging with (blue) and without (red) reactive power compensation, measured at the facility's PCC.

The steady reactive power consumption of the HUT is completely compensated by the emulator. However, if the HUT has quick step changes in the reactive power consumption in less than the execution time control of the EBox, it cannot be compensated properly. This behaviour can cause problems in the facility's PCC if the electric protection devices are less than the peak current occurred during the transition. To resolve this issue, it is possible to perform a power consumption characterization of the HUT at every charge/discharge current, and configure a charge/discharge profile in the emulator, including the reactive power that has to be generated by the emulator in order to compensate it.
