## 4 Validation of the Real-Time Optimization Based Strategy
### Experimental Validation  
Simulation tests have been achieved to assess the strategy performances in driving conditions. This section is devoted to the assessment of the EMS in real-time conditions.  
The EMS was implemented in a real system to validate its real-time capabilities. Experimental tests were carried out on the same standard WLTC class 2 driving cycle with the low speed phase. Based on the traction characteristics of the Tazzari Zero, a reduced-scale power hardware-in-the-loop (HIL) simulation is proposed on an experimental platform [46]. It is composed of a 1.2 kW Ballard FC, a bank of Maxwell SC, a DC electric source to emulate the battery, three smoothing inductors, three DC-DC converters, and a controlled current source to emulate the traction subsystem (Figure 13). The controlled current source is chosen as a load drive with a ratio current reduction of 17 compared to the full-scale studied vehicle. Voltages and currents are measured with classical LEM transducers. No additional numerical filters have been added.  
The experimental tests were done to assess the EMS under three real-time constraints: implementation, safety and performance.  
The _\(\lambda\)-control_ EMS was implemented using a dSPACE 1005 prototyping board (Paderborn, Germany). A 3 GHz dual core processor/3.25 Go RAM memory computer was used. The sampling period was set to 1 ms, and a PWM of 10 kHz was used for the DC-DC converters. The EMS was fully implementable in real time and did not result in any computation issues because the proposed _\(\lambda\)-control_ was developed with elementary operations.  
The safety of the system was totally ensured for the experimental tests. In this system, the safety was linked to the maximal limits of the SC voltage and the battery SoC. The EMS enabled us to keep the SC voltage between the desired limits (Figure 14c). The _\(\lambda\)-control_ complied then with the safety requirements. Three SC modules were used in the experimentation; there was hence a ratio of 15 between the simulation tests and the HiL testing. Nevertheless, all experimental tests were achieved with a reduced scale of 1/17 th in power. In order to tackle this issue, the minimal SoC of the supercapacitors has to be increased. This corresponds to a SoC of 0.7. Nevertheless, in order to avoid any failure, the maximal voltage has been set to 44 V (0.98 pu), which implies a minimal SoC of 0.68 in Figure 14c.  
The EMS performances are confirmed by the experimental tests. As shown by Figure 14a, most of the FC current peaks are avoided. The FC current is then smooth, which is a key point to improve the FC lifetime. Furthermore, as expected, the SC allows the battery state of stress to be reduced (Figure 14b). Some current peaks are then avoided for the battery, which will have a direct impact on its lifetime. Hence, the battery SoC varies in a small range (Figure 14d). It may be noted that, in comparison with simulation results, the charge sustaining (zero energy balance) for both battery and SC are not respected. The Lagrange multipliers have actually been designed to be charge-sustaining, which means that the initial and the final SoC should be equal. This is true for the simulation results.  
Figure 13: Experimental test rig.  
Nevertheless, the parameter discrepancies in real time do not allow us to have exactly an energy balance at the end of the driving cycle.