Modeling, Control System Design and Preliminary Experimental Verification of a Hybrid Power Unit Suitable for Multirotor UAVs

Abstract

A key drawback of multirotor unmanned aerial vehicles (UAVs) with energy sources based solely on electrochemical batteries is related to the available on-board energy. Flight autonomy is typically limited to 15–30 min, with a flight duration upper limit of 90 min currently being achieved by high-performance battery-powered multirotor UAVs. Therefore, propulsion systems that utilize two or more different energy sources (hybrid power systems) may be considered as an alternative in order to increase the flight duration while retaining key performance benefits of battery energy storage use. The research presented in this work considers a multirotor UAV power unit, based on the internal combustion engine (ICE) powering an electricity generator (EG) connected to the common direct current (DC) bus in parallel with the lithium-polymer (LiPo) battery, and the respective modeling and identification of individual power unit subsystem, along with the dedicated control system design. Experimental verification of the proposed hybrid power unit control system has been carried out on the custom-build power unit prototype. The results show that the proposed control system combines the two power sources in a straightforward and effective way, with subsequent analysis showing that a two-fold energy density increase can be achieved with a hybrid energy source, consequently making it possible to achieve higher flight autonomy of the prospective multirotor (hover load around 1000–1400 W) equipped with such a hybrid system.

Hybrid Power Systems in Multi-Rotor UAVs: A Scientific Research and Industrial Production Perspective

“…Table 5 lists the methodology used in each study more specifically by defining the generation sources for the hybrid system and control system strategies. As shown in this table, the PID control method was the most widely used in [27], [42], [44], [45], [50]. In addition, most of the empirical studies depended on using ICE to generate the required power and on batteries as energy storage.…”

“…Other studies have developed the control system in the HPSs to: obtain a constant voltage [41]; store data digitally [51]; control the charging and discharging states of batteries [42]; matching the main engine with the generator [27]. In the same context, Krznar et al [45] indicated that it is possible to carry out experimental validation of the control components in the HPS by designing a laboratory test platform.…”

“…In order to achieve that, Hageman and McLaughlin in their article [48], have pointed out the need to define carefully the mechanical linkage between the engine and the generator. Beyond that, the two studies [35] and [42] have dealt with one of the performance factors related to weight, which is specific energy. Based on the results using a test bench, it was concluded that the HPS (ICE + EG) has a specific energy of 300 Wh/kg, while the battery pack's specific energy is around 140 Wh/kg [42].…”

“…• Field/Objective of the research • Design Methodology • Future Works Several studies [27], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50] have used ICE in the designing of propulsion systems. The main results of these studies indicated the advantages of using HPS in the possibility of doubling the energy density [42]; obtaining high efficiency and longer endurance in tilt-rotor type vertical take-off and landing (VTOL) UAVs [27]; qualitative development of multirotor UAVs [48]; expanding flight endurance with efficient power consumption [41]. In the study by Cabanas et al [39], an ICE (DLE-111-Two Stroke: 8.4 kW, 2.86 kg) was coupled mechanically with Brushless DC (BLDC) motor (ROTOMAX 150 cc:9.8 kW, 2.5 kg) as a generator to produce a 3-phase AC voltage.…”

“…A hybrid system composed of ICE (Zenoah G320RC: 2.4 kW, 2.3 kg), EG (MTO6374-170-HA-C: 3.55 kW, 0.83 kg), with a battery was modeled and implemented in the work by Krznar et al [42]. From their findings of simulation and practical experiments using a test bench, it was concluded that the total weight of the hybrid system is two times smaller compared to the battery-based system.…”