**5. Experimental Validation**

The designed Split-pi converter is shown in Figure 9. It was built as a prototype using the components available in the lab, among them an integrated power module STGIPS10K60A encompassing an IGBT-based three-phase H-bridge. In order to validate the converter and the related control laws experimentally, the storage system connected to port 1 was emulated using a TDK-Lambda GEN60-40 power supply (set to 50 V) and a parallel-connected 10 Ω, 300 W power resistor. The latter component was used to dissipate power during the recharge of the emulated storage system. On the other hand, a Sorensen SLH-500-6-1800 electronic load and a TDK-Lambda GEN600-5.5 power supply were connected to port 2 of the converter. The first device was used as the resistor *Rload* of the load model, whereas the other device was used as either the voltage generator *Ed* or the current generator *I*, depending on the specific test.

**Figure 9.** Picture of the realized Split-pi converter.

The control systems and the PWM modulator were implemented on a dSPACE DS1103 board connected to a desktop computer. Several electrical quantities were measured using LEM sensors, acquired and processed by the dSPACE board: *IL*1, *V*2, *I*2, *IR*. The current of the external generator was computed as *Ig* = *IR* − *I*2.

The prototypal Split-pi converter and the related control schemes were tested experimentally in several conditions covering the baseline and the other five scenarios. The obtained results showed good matching with the simulations presented in Section 4. Thus, they confirmed the good performance attainable in each scenario and, implicitly, the result comparison among the five scenarios. Furthermore, it is worth highlighting that a result comparison based on simulations rather than experiments inevitably gave a more accurate picture of the differences among the scenarios. In fact, the simulations allowed considering a much higher number of transients among operating conditions in each scenario compared to the experimental tests.

The waveforms of the most relevant signals acquired during the experimental tests were exported from dSPACE Control Desk to MATLAB and then plotted to analyze the results. The obtained plots are presented and commented on in the following.

#### *5.1. Experimental Validation in the Baseline Scenario and Scenario #1 (SS-GN)*

The Split-pi converter was used in these two tests to form a stiff microgrid supplying a passive load; no other generator was present in the microgrid. The converter was controlled using only the current and voltage loops in the baseline scenario, whereas the FF action was also included in scenario #1 (SS-GN). The electronic load was operated to reproduce a stepwise variation of load from 1300 Ω to 130 Ω; consequently, the load power instantly increased from 25 W to 250 W and produced a voltage undershoot.

The signals acquired during the tests are shown in Figure 10 and allow comparing the performance obtained with and without the FF action. All the waveforms were coherent with those obtained in the simulations. Thanks to the FF action, the reference for *IL1* (and, in turn, the duty cycle) was instantly increased when the output current varied. Therefore, in scenario #1 (SS-GN), the current waveforms were pretty squared, the voltage undershoot on *V*<sup>2</sup> was reduced from −5.73% to −1.86%, and the dynamics of *V*<sup>2</sup> were faster compared with the baseline scenario. An even higher under/overshoot reduction would be expected for higher stepwise variations of output power.

**Figure 10.** Experimental results in the baseline scenario and scenario #1 (SS−GN): (**a**) input inductor current; (**b**) duty cycle; (**c**) percentage variation of microgrid voltage; (**d**) grid−side current.

#### *5.2. Experimental Validation in Scenario #2 (SD-GN)*

In this test, the Split-pi converter was controlled using the FF action to form a non-stiff microgrid using a droop resistance of 1.33 Ω. The microgrid encompassed a passive load and an external power supply that was operated as a current generator. First, a current limit of 1.3 A and a voltage set point slightly higher than 180 V were set in the power supply; then, the device was turned on and off. The load resistance was 130 Ω, corresponding to a nominal current of about 1.385 A and a nominal power of 250 W.

The most relevant acquired signals are shown in Figure 11 and are coherent with those obtained in the simulations. Before t = 0 s, the load was entirely supplied by the converter. According to the droop resistance value, a 1.83 V voltage drop was exhibited, corresponding to a voltage variation of −1.02%; consequently, the load current was 1.375 A. At t = 0 s, the external current generator was turned on and supplied the load almost entirely, so the output current of the converter automatically dropped to almost zero. As a result, the voltage variation was almost zero, and the load current increased from 1.375 A to 1.382 A, reproducing the intended behavior. Finally, at about t = 1 s, the external current generator was turned off, and the converter took over the current again. In that condition, the load voltage and current again decreased slightly because of the droop control.

**Figure 11.** Experimental results in scenario #2 (SD−GN): (**a**) grid−side currents; (**b**) percentage variation of microgrid voltage.

It is worth noting that the external power supply did not offer a proper current-mode operation; actually, it tried to impose the preset voltage (185 V) and continuously adjusted its output voltage aiming to respect the current limit. This behavior explains the initial peak in the generator's current. Nevertheless, the converter's control system was fast enough to effectively compensate for the connection and disconnection of the external generator. Therefore, the over/undershoot of microgrid voltage was minimal (+1.1% and −0.5%).
