# Energy Management of a Multi-Source Power System
## 4 Demonstration Example and Results
### Experimental Work--On a Multi-Energy Source Ground Robot  
The following experiment was conducted on a ground robot shown in Figure 7. The ground robot contains three sources: batteries, super capacitor, and fuel cell. The robot was run in remote-control mode while conducting the tests. The robot was controlled by the remote controller to move around a lab bench in a rectangular path. The demand profile for all tests is shown in Figure 8.  
For experimental work, a multi-energy source ground robot was preferred over a drone because of several factors: i.e., (i) limitations related to drone flight height and seeking clearances for flight paths at certain heights, (ii) even if an accurate flight power demand profile was obtained by flying a drone in good weather conditions, the actual flight power demand profile obtained when trying to verify results-cannot be guaranteed because the weather may change and sudden wind gusts may introduce power demand, not accounted for when solving for the dynamic programming solution, and (iii) it is also possible that the wind disturbances introduce differences in the demand profiles when performing an experiment with the heuristic approach, and entirely different power demand profile disturbances occur because of wind gusts when testing the dynamic approach. So, to make a comparison between the proposed approaches, which is free from random power surges due to weather effects, a ground robot with multiple energy sources was favored. Also, it is worth noting that when considering a drone, the demand profile can be easily calculated from first principles, as seen in Equation (15). But when considering a ground robot we have to actually run the robot around a path and acquire a demand curve. This is the procedure followed to get the curve in Figure 8, and therefore it is different from the curve in Figure 1. Please note that the developed approaches are not profile-specific, and can compute a switching sequence for a given demand profile. Figure 8: Demand profile for experimental work. Figure 7: Ground Robot and power sources. The demand profile was uploaded to both the dynamic and heuristic algorithm to obtain a switching sequence. The ground robot has a controller which supplies a given amount of current to the motors if it is given a reference current. The two motors on the robot chassis (one for controlling left side wheel speeds, and one for controlling right side wheel speeds) rotate clockwise or anticlockwise depending on the current received. Based on the direction of the rotation of the motors and the speed of rotation, the robot can be made to move in straight lines, curves, or in circles. This is extremely common in robotics literature and hence the details of the driving process (called differential drive) are not included here. However, there is not necessarily a controller that controls where the current comes from. The switching sequences generated by the dynamic and heuristic approaches tell this same lower level controller what sources to use to supply the required current; to satisfy the demand and still reduce the average power consumption across the sources. The switching sequences were then uploaded to the main controller of the ground robot, an Arduino microcontroller that controls the switches attached to the sources. After the switching sequence was uploaded, the ground robot performed a lap along the rectangular path. The power consumption across all sources after the ground robot completed a lap with the uploaded switching sequences was then compared with the standard mode of operation. For a ground robot, the standard mode of operation assumes no scheduling; however the needed power is first supplied by the battery until it's completely depleted then moving to the other available sources. Figures 9-11 display the system voltages, current, and state-of-charge, respectively, for the standard mode, the dynamic approach, and the heuristic approach. The standard mode of operation did not involve the super capacitor in meeting the demand of the ground robot.