## 5 Experimental Results  
For the experimental setup, the required load profile must be imported into the source in one direction and into the load in the opposite direction. For this scenario, a four-quadrant power supply was used to sink and source power. In this power supply, the load profile was programmed to reflect the proposed profile shown in Figure 1. Firstly, the constants of the PI regulators were tuned to obtain the proper response of the system. This experiment used a lead-acid 24 V accumulator to substitute the unregulated bus accumulator. The advantage of a lead-acid accumulator is that it can be charged, so the operation where power is delivered from the load to the SC module and the accumulator simultaneously can be tested. The testing plan was divided into several sections:  
1. **Testing of the SC module. ** The procedure involved inspecting the accuracy of the measured signal and subsequently verifying the even distribution of voltages on the individual cells of the SC module. 2. **Testing the DC/DC converter in a supply mode to the load. ** The primary goal was the verification of a full-power operation in boost mode. 3. **Testing of the DC/DC converter in a recovery energy mode. ** The primary goal was the verification of a full-power operation in buck mode. 4. **Testing bidirectional mode with a designed SC module and parallel-connected 24 V accumulator. **  
Figure 12 shows the results of the measurement for scenario 1. The profile is divided into two sections. The first section is when the load is sinking power. It represents the negative value of the load current _I_Load_ (blue waveform). In this section, the accumulator provides a nearly constant output current _I_bat_ of 1 A (green waveform) as set in the control algorithm, and the remaining current _I_DCDC_ is supplied from the SC module and bidirectional DC/DC converter. In section 2, when the load is sourcing power, the accumulator is charged with a value of current 1 A, and the remaining current flows through the DC/DC converter to the SC module (magenta waveform). The load voltage is identical to the unregulated bus voltage, which is 24 V.  
Figure 11: DC/DC converter efficiency in both operational modes. In the other case, when the load is sourcing current/power (blue waveform in Figure 13) is positive, the current is delivered to the SC module to recharge it and to the unregulated bus. In this scenario, the accumulator current was set to 1 A, and as can be seen, the accumulator was charging with a constant current of 1 A. The detailed waveform in Figure 13 shows the regulator response to the load waveform in detail. In the second experiment, Figure 14, the unregulated bus current was set to 0 A in both scenarios, where the load is sinking and sourcing power. This means the whole power to the load is delivered from the SC module, and during the recuperation, the entire power is used to charge the SC module. The results from the measurement can be seen in the following figure:  
The green waveform shows that the accumulator current is nearly zero. The entire power flows from and to the SC module. As mentioned, the internal variables at the distribution board were also monitored. The system sampling frequency is 2 kHz and can simultaneously log four variables. Figure 15 shows the SC module voltage and current in the scenario, where the accumulator current was set to 0 A in both ways. Figure 12: Scenario 1: unregulated bus/accumulator current limited to 1 A.  
Figure 13: Detail waveform during sourcing current/power. As can be seen, the initial SC module voltage was 13 V (blue waveform). The load is sinking current from time 4.5 s to 5 s, and the SC module is discharged. The peak current during this operation is 25 A. After the discharge cycle, the steady-state voltage is 12.3 V, which confirms the results calculated in Equations (6) and (7). In the second cycle, where the load is sourcing power, the SC module is charged.