## 3 Results
### Comparing Active and Direct Turbine Control Data  
One of the first noteworthy differences in ATC and DTC operating modes appears in the voltage data acquired. The voltage supplied to the load is solely dictated by the generator shaft RPM in DTC operating mode. In ATC, current flow is provided both by the turbogenerator and the battery assembly in parallel. Because of this parallel battery-turbine arrangement in ATC, the voltage supplied behaves much more like that offered by only a battery. This battery-like behavior results in the voltage dropping when a higher load is demanded. The power provided by the ATC system increased despite the voltage dropping when comparing Figures 13 and 14. This behavior contrasts against DTC, where increasing throttle settings result in a higher voltage due to an increasing shaft RPM. The ATC arrangement also kept the supplied voltage much closer to the desired 12S voltage range. This fact is because the 12S battery configuration strongly drives the overall voltage behavior. Figure 11: ATC transient throttle testing results. Figure 12: Results from the negative throttle step changes during ATC experimentation. Another takeaway that is apparent from Figures 13 and 14 is that the ATC scheme has a faster response time in general when compared to DTC. This faster response time is due to the average flow response time of the battery pack in the system. The battery can respond almost instantaneously relative to the time it takes for the turbine to spool up or down between two different throttle settings. Table 3 displays a comparison of the response times between the ATC and DTC modes. A key challenge for an active controller to overcome is how to handle excess power produced by the turbine. The electrical load can change the power it consumes much more rapidly than the turbine can respond. Because of this difference in response time, a sudden voltage increase will occur if the turbine is spinning at a high throttle when the load is cut. This can be seen in an electric load cutoff test performed, where the load motor was throttled fully to zero percent from full throttle. A path needs to be provided for excess power to flow, increasing the current coming from the generator and lowering the voltage supplied to mitigate the potential voltage spike. It is important to note that the results shown in Figure 15 include a battery integrated into the system for excess power to flow to, while voltages still reached above 60 V. A battery was included for all testing due to the potential that the voltage increases produced would have been high enough to damage the load ESCs and current sensors used in the test. In other tests where the throttle reduction  
Figure 14: A comparison of power supplied by ATC and DTC systems during the 50–100% throttle experimentation. Figure 13: A comparison of voltage supplied by ATC and DTC arrangements was taken from the 50–100% tests. was less severe, the voltage only appeared to rise above 49 V in one test, as seen in Figure 16. However, the mentioned voltage spike stayed within the acceptable limits of the 12S Li-Po battery. The load cutoff test and other throttle transients displayed that the battery could withstand excess power produced by the turbine in a sudden load shutoff up to 30-A. Data from the BMS (Figure 17) show that the battery could successfully switch from discharge (positive) to recharge (negative) during the load shutoff test, successfully switching from providing power to the load to absorbing excess power from the turbine. The battery did not see a high voltage spike because resistors were included on the bench test circuitry to guarantee the battery did not ingest too much electrical current. These resistors, alongside the battery charging, ensured that voltages remained nearly constant during the load cutoff test (Figure 17). In other tests where the throttle reduction was less severe, the voltage only appeared to rise above 49 V in one test. However, the mentioned voltage spike stayed within the acceptable limits of the 12S Li-Po battery.