# Research on Composite Control Strategy of Quasi-Z-Source DC-DC Converter for Fuel Cell Vehicles
## 4 Simulation and Experimental Results
### Experimental Results  
A 400 W experiment prototype was built as shown in Figure 14. The parameters of the prototype are shown in Tables 1 and 2. The TMS320F28335 is adopted as controller and the MOSFET (IXTK102N30P)  
Figure 11: The output voltage of a fuel cell under the WLTP. Figure 12: The output voltage of a converter under the WLTP. Figure 13: The duty cycle variation curve. is adopted as power switch. The experiment platform is shown in Figure 15. The input voltage and output voltage are measured by the voltage hall sensors. During the input voltage disturbance experiment, the output voltage reference value is set at 400 V and the input voltage jumps between 60 V and 50 V. The output voltage waveform is shown in Figure 16.  
In Figure 16a, the maximum output voltage excursion is around 8% without feedforward compensation. With feedforward compensation, the maximum output voltage excursion is less than 2%, as in Figure 16c. The output voltages in Figure 16b,d are measured by using the oscilloscope AC coupling mode. From Figure 16, it can be verified that the feedforward compensation improves the system's ability to resist input voltage disturbance. During the 50% load step disturbance experiment, the input voltage is fixed at 40 V and the output voltage reference value is set at 400 V. The load resistance is step changed between 400 \(\Omega\) and 200 \(\Omega\) by using the electronic load. The input current and output voltage waveforms of the converter are shown in Figure 17. The input current of the converter can quickly follow the output load variation, providing demand power for the load. The maximum output voltage excursion is less than 5% and the adjustment time is less than 30 ms. The output voltage fluctuation in Figure 17b is measured by using the oscilloscope AC coupling mode. The maximum excursion of the output voltage is slightly higher than that in the simulation; this is caused by the parasitic parameters of the circuits and components. The system shows good dynamic performance during load disturbance. Figure 14: The experiment prototype. Figure 15: The experiment platform. The converter is tested under the WLTP. In Figure 15, a programmable power supply is adopted to simulate the variation rule of fuel cell output voltage under the WLTP according to the simulation results in Figure 11. According to Equation (30), the demand power of fuel cell vehicles under the WLTP is programmed in the electronic load. From Figure 8, the total time of the WLTP driving cycle is 1750 s. The first 1000 s is the low speed and medium speed driving cycles. Compared with the high speed and extra-high speed driving cycles in the last 750 s, the power demand in the low speed and medium speed driving cycles is smaller. Therefore, the low speed and medium speed driving cycles of the WLTP are simulated in the electronic load and the total test time is scaled down to 200 s as shown in Figure 11:0  
According to the fluctuation rule of fuel cell output voltage under the WLTP driving cycles in Figure 11, the fuel cell output voltage waveform is obtained by using a programmable power supply, as shown in Figure 11:1 The overall decreasing trend of fuel cell output voltage is simulated in the last 80 s in Figure 11:2  
Figure 11:3 The output voltage waveform during input voltage disturbance. (**a**) Without feedforward compensation (DC coupling measurement); (**b**) without feedforward compensation (AC coupling measurement); (**c**) with feedforward compensation (DC coupling measurement); (**d**) with feedforward compensation (AC coupling measurement). Figure 11:4 The output voltage and input current waveforms of converter during 50% load disturbance experiment. (**a**) The converter output voltage (oscilloscope DC coupling mode) and input current; (**b**) the converter output voltage (oscilloscope AC coupling mode). The load current waveform is shown in Figure 20 and changes with the load demand power. The output current waveform of the fuel cell is shown in Figure 21 and can follow the load current variation.