Fault-Tolerant Control of a Dual-Stator PMSM for the Full-Electric Propulsion of a Lightweight Fixed-Wing UAV

Abstract

The reliability enhancement of electrical machines is one of the key enabling factors for spreading the full-electric propulsion to next-generation long-endurance UAVs. This paper deals with the fault-tolerant control design of a Full-Electric Propulsion System (FEPS) for a lightweight fixed-wing UAV, in which a dual-stator Permanent Magnet Synchronous Machine (PMSM) drives a twin-blade fixed-pitch propeller. The FEPS is designed to operate with both stators delivering power (active/active status) during climb, to maximize performances, while only one stator is used (active/stand-by status) in cruise and landing, to enhance reliability. To assess the fault-tolerant capabilities of the system, as well as to evaluate the impacts of its failure transients on the UAV performances, a detailed model of the FEPS (including three-phase electrical systems, digital regulators, drivetrain compliance and propeller loads) is integrated with the model of the UAV longitudinal dynamics, and the system response is characterized by injecting a phase-to-ground fault in the motor during different flight manoeuvres. The results show that, even after a stator failure, the fault-tolerant control permits the UAV to hold altitude and speed during cruise, to keep on climbing (even with reduced performances), and to safely manage the flight termination (requiring to stop and align the propeller blades with the UAV wing), by avoiding potentially dangerous torque ripples and structural vibrations.

Condition Monitoring of the Torque Imbalance in a Dual-Stator Permanent Magnet Synchronous Motor for the Propulsion of a Lightweight Fixed-Wing UAV

“…In a previous work by the authors [5], the diagnosis of electrical and electronic faults of the TERSA FEPS, the design of fault-tolerant control strategies, and the simulation of The project, led by Sky Eye Systems (Italy) in partnership with the University of Pisa and other Italian industries, was successfully completed in December 2022.…”

“…Electric propulsion would reduce (or eliminate for FEPSs) the CO 2 emissions, abate the noise levels, diminish the thermal signature, and enhance the thrust efficiency and performance of fixed wing UAVs [1][2][3], even if reliability is now an open issue (essentially due to the application novelty) and achievable endurance is much lower than that of UAVs equipped with internal combustion engines (consider that the energy storage of Li-Ion batteries typically reaches about 0.3 MJ/kg, approximately 100 times lower than gasoline data [1]). Within this context, the project TERSA (Tecnologie Elettriche e Radar per Sistemi aeromobili a pilotaggio remoto Autonomi [4,5]) has been funded by the Italian Government together with the Tuscany Regional Government for developing a lightweight full-electric long-endurance UAV (Figure 1 [6]) with the following main characteristics [6]: The project, led by Sky Eye Systems (Italy) in partnership with the University of Pisa and other Italian industries, was successfully completed in December 2022.…”

Diagnosis of Power Switch Faults in Three-Phase Permanent Magnet Synchronous Motors via Current-Signature Technique

“…The failure rate of three-phase Permanent Magnet Synchronous Motors (PMSMs) with conventional three-leg converters is typically around 200 per million flight hours [4,5], which is far from the required levels for airworthiness certification [6]. Specifically, a relevant amount (from 50% to 70%) of PMSMs fault modes originate from motor phases (open-phase [5], inter-turn [7], phase-to-phase [8] and phase-to-ground [9]) and power converters. Among the latter ones, faults of the supply voltage stabilizing capacitor and faults of the power switches are predominant [10,11].…”

“…A common approach to enhancing reliability involves the implementation of hardware redundancies (e.g., redundant motors or drives), but this solution is often unfeasible in UAV applications, due to stringent weight and envelope requirements. As a consequence, the application of hardware redundancy is typically limited to motor phases (using multiple stator modules or multiple phases [9,15]) and/or to converter legs (using unconventional converters [16]).…”

Multirotor Motor Failure Detection with Piezo Sensor

“…In the mentioned statement, the UAV is a critical component, and its ability to confidently and safely perform airspace missions is necessary. One of the most important issues that has been developed and studied intensively is fault tolerant control systems (FTCS) dedicated to different types of unmanned aircraft [ 8 , 9 , 10 , 11 ], which must be accurately mathematically modeled before implementation [ 12 , 13 ]. FTCM can be divided into active and passive kinds.…”