A Study of the Degradation of Electronic Speed Controllers for Brushless DC Motors

Brushless DC motors are frequently used in electric aircraft and other direct drive applications. As these motors are notactually direct current machines but synchronous alternating current machines; they are electronically commutated by a power inverter. The power inverter for brushless DC motors typically used in small scale UAVs is a semiconductor base delectronic commutator that is external to the motor and is referred to as an electronic speed control (ESC). This paper examines the performance changes of a UAV electric propulsion system resulting from ESC degradation. ESC performance is evaluated in simulation and on a new developed test bed featuring propulsion components from a reference UAV. An increase in the rise fall times of the switched voltages is expected to cause timing issues at high motor speeds. This study paves the way for further development of diagnostic and prognostic methods for inverter circuits which are part of the overall electric UAV system

Fault Tolerant Control of a X8-VB Quadcopter

In this dissertation new modeling and fault tolerant control methodologies of a quadcopter with X8 configuration are proposed; studies done to actuators faults and possible reconfigurations are also presented. The main research effort has been done to design and implement the kinematic and dynamic model of a quadcopter with X8 configuration in Simulink®. Moreover, simulation and control of the quadcopter in a virtual reality world using Simulink3D® and real world experimental results from a quadcopter assembled for this purpose. The main contributions are the modeling of a X8 architecture and a fault tolerant control approach. In order to show the performance of the controllers in closed-loop, simulation results with the model of a X8 quadcopter and real world experiments are presented. The simulations and experiments revealed good performance of the control systems due to the aircraft model quality. The conclusion of the theoretical studies done in the field of actuators’ fault tolerance were validated with simulation and real experiments

Fault Tolerant Power Electronics Systems

Research work reported in this Ph.D. thesis is in the area of power electronics systems, specifically in the sector of electrical drives. A trustworthy operation of power electronics systems in critical applications like electric vehicles, aircrafts, satellites, and so on, has pushed engineers to develop fault-tolerant solutions. Indeed, in such applications it is necessary for the system to continue its operation, possibly with downgraded performance, even under faulty case. Present thesis reports the studied solutions to make fault-tolerant a class of electric drives under faulty conditions. It has initiated by addressing the need and importance of the usage of power electronic systems in the field of transportation sector, in particular in the automobile and aerospace industry. Permanent magnet (PM) brushless (BL) drives have become very popular thanks to their higher torque-per-ampere capabilities. Among the two different types of PM BL drives, namely those with sinusoidal back-emf (BLAC) and those with trapezoidal back-emf (BLDC), the latter ones are preferred for light-duty propulsion such as minicars and scooters, and in aeronautics as control-surface actuators. However, some concern have emerged on the use of electrical drives in such applications with regard to the fault tolerance and the power capability per volume unit. A way to effectively cope with these concerns is the adoption of multiphase drives. In this sense, a five-phase drive is a promising solution as it is the most simple multiphase structure of practical interest. The thesis starts with the study of the phase current and torque behavior in three-phase PM BLDC drive in healthy conditions. To validate the mathematical findings, a study case is used, represented by an electrical drive with in-wheel motor utilized for the propulsion of a city car. Afterwards, various types of faults in voltage source inverter (VSI) of a three-phase PM BLC drive are considered, such as one leg open, one switch open and one switch shorted. Remedial control strategies for the faults of the VSI are envisaged, that enable the three-phase PM BLDC drive to continue to operate even if in a degraded way. The resulting performance is calculated in terms of developed torque and torque ripple. The mathematical findings are substantiated with graphs obtained by simulation. A five-phase PM BLDC drive is successively considered. First, its operation and its torque capabilities are investigated in healthy conditions under ideal square-wave current supply. The torque capabilities are compared to the three-phase counterpart; torque comparison is carried out by keeping motor size constant and by considering two hypotheses: equal phase back-emf and equal phase rms current. Then, the torque available from a five-phase drive is determined under various supply modes, characterized by the conduction of a reduced number of phases; the torque available is determined by imposing an rms phase current equal to the nominal one. Moreover, the current behavior during the phase commutations for the five-phase PM BLDC drives is analyzed as they exhibit some differences with respect to the three-phase counterpart. The outcomes of the current analysis are used to derive the effective torque developed by the drive and the torque ripple exhibited as a function of the motor speed. The base speed of the drive is also determined. Also for the torque results, the differences from the well-known characteristics of the three-phase PM BLDC drives are pointed out. Lastly, an algebraic approach is developed to describe the operation of a five-phase PM BLDC drive in healthy conditions. The approach has led to the formulation of a model of the phase current supply of the motor in healthy conditions. Further, the model has been suitably adjusted to derive the mode (scheduling and magnitude) of current supplying the survival phases in the case of one or more motor open phase faults. The cases of one /two/three open phase faults have been examined and, in the case of two and three faulty phases, the cases of adjacent and non-adjacent faulty phases. For each case, the current magnitude has been found by imposing that the rms value of the current in the most solicited phase is equal to the nominal value, and the torque that the drive is able to develop as well as the maximum value of the torque ripple have been calculated. The obtained results indicate that the reduction in the motor torque as well as the extent of the torque ripple is depending, besides on the number of the faulty phases, on the relative location of the faults. The thesis work also address the evolution of electrical power generation and conversion methodologies in more electric aircraft, fault-tolerant solutions under faulty Hall sensors, and the concepts of dependability and safety aspects. The thesis work has been carried out at the Laboratory of “Electric systems for automation and automotive” headed by Prof. Giuseppe Buja. The laboratory belongs to the Department of Industrial Engineering, University of Padova, Italy

Design and On-Orbit Experience of Reaction Wheels for Small Satellites

The history of reaction wheel development at the Technische Universität Berlin (TUB) begins early in the 90s. Since then many of these reaction wheels performed on-orbit without a single failure as a part of six micro- and nanosatellite missions. The last one is the S band Network for co-operating Satellites (S-Net). S-Net is a cluster of four nanosats successfully launched in February 2018. Since then a number of communication experiments using intersatellite links have been performed by the S-Net satellites. This paper is focusing on the design and on the on orbit performance of the reaction wheels for S-Net nanosatellites. The design is based on COTS and differs considerably from the state-of-the-art one. The wheel is pressurized, allowing higher rotation speeds due to a better thermal performance as well as the use of commercial motors without any changes in ball bearings and their lubrication. Due to a better ball bearing friction the performance and, consequently, the failure tolerance have increased significantly. The wheels can run at higher speeds continuously allowing their use within momentum bias platforms. A novel suspension system helped to optimize the misalignment of the rotational axis compared to a simple spiral spring based suspension used for TUB wheels earlier. A further outstanding feature is the implementation of some additional control loops alongside with the standard current, speed and torque control. The use of built-in internal angular velocity sensors makes satellite velocity and satellite angle control modes possible. For some operational scenarios, especially for such with high agility requirements, it can be advantageous because these control loops can be closed with a higher frequency as if would be possible with a centralized external attitude controller. The system is characterized by a low steady-state power consumption of 220 mW at the zero motor speed and under 1.5 W at the maximum speed, has the dimensions of 65 x 65 x 55 mm3 and a weight of less than 320 g. Two wheel modifications for different satellite classes with slightly different rotor geometry exist. The angular momentum can be as high as 45 mNms. The modular design allows a scale-up without significant changes in mechanics and electronics. Finally, future work based on the described design is discussed

CONTROL STRATEGY OF MULTIROTOR PLATFORM UNDER NOMINAL AND FAULT CONDITIONS USING A DUAL-LOOP CONTROL SCHEME USED FOR EARTH-BASED SPACECRAFT CONTROL TESTING

Over the last decade, autonomous Unmanned Aerial Vehicles (UAVs) have seen increased usage in industrial, defense, research, and academic applications. Specific attention is given to multirotor platforms due to their high maneuverability, utility, and accessibility. As such, multirotors are often utilized in a variety of operating conditions such as populated areas, hazardous environments, inclement weather, etc. In this study, the effectiveness of multirotor platforms, specifically quadrotors, to behave as Earth-based satellite test platforms is discussed. Additionally, due to concerns over system operations under such circumstances, it becomes critical that multirotors are capable of operation despite experiencing undesired conditions and collisions which make the platform susceptible to on-board hardware faults. Without countermeasures to account for such faults, specifically actuator faults, a multirotors will experience catastrophic failure. In this thesis, a control strategy for a quadrotor under nominal and fault conditions is proposed. The process of defining the quadrotor dynamic model is discussed in detail. A dual-loop SMC/PID control scheme is proposed to control the attitude and position states of the nominal system. Actuator faults on-board the quadrotor are interpreted as motor performance losses, specifically loss in rotor speeds. To control a faulty system, an additive control scheme is implemented in conjunction with the nominal scheme. The quadrotor platform is developed via analysis of the various subcomponents. In addition, various physical parameters of the quadrotor are determined experimentally. Simulated and experimental testing showed promising results, and provide encouragement for further refinement in the future

Fault diagnosis and prognosis of a brushless dc motor using a model-based approach

This paper proposes a model-based fault diagnosis and prognosis approach applied to brushless DC motors (BLDC). The objective is an early detection of mechanical and electrical faults in BLDC motors operating under a variety of operating conditions. The proposed model-based method is based on the evaluation of a set of residuals that are computed taking into account analytical redundancy relations. Fault diagnosis consist of two steps: First, checking if at least one of the residuals is inconsistent with the normal operation of the system. And, second, evaluating the set of the residuals that are inconsistent to determine which fault is present in the system. Fault prognosis consists of the same two steps but instead of considering current inconsistencies evaluates drift deviations from nominal operation to predict futures residual inconsistencies and therefore predict future fault detections and diagnosis. A description of various kinds of mechanical and electrical faults that can occur in a BLDC motor is presented. The performance of the proposed method is illustrated through simulation experiments.Postprint (published version

Parameter Identification And Fault Detection For Reliable Control Of Permanent Magnet Motors

The objective of this dissertation is to develop new fault detection, identification, estimation and control algorithms that will be used to detect winding stator fault, identify the motor parameters and optimally control machine during faulty condition. Quality or proposed algorithms for Fault detection, parameter identification and control under faulty condition will validated through analytical study (Cramer-Rao bound) and simulation. Simulation will be performed for three most applied control schemes: Proportional-Integral-Derivative (PID), Direct Torque Control (DTC) and Field Oriented Control (FOC) for Permanent Magnet Machines. New detection schemes forfault detection, isolation and machine parameter identification are presented and analyzed. Different control schemes as PID, DTC, FOC for Control of PM machines have different control loops and therefore it is probable that fault detection and isolation will have different sensitivity. It is very probable that one of these control schemes (PID, DTC or FOC) are more convenient for fault detection and isolation which this dissertation will analyze through computer simulation and, if laboratory condition exist, also running a physical models

Fault Signature Identification for BLDC motor Drive System -A Statistical Signal Fusion Approach

A hybrid approach based on multirate signal processing and sensory data fusion is proposed for the condition monitoring and identification of fault signal signatures used in the Flight ECS (Engine Control System) unit. Though motor current signature analysis (MCSA) is widely used for fault detection now-a-days, the proposed hybrid method qualifies as one of the most powerful online/offline techniques for diagnosing the process faults. Existing approaches have some drawbacks that can degrade the performance and accuracy of a process-diagnosis system. In particular, it is very difficult to detect random stochastic noise due to the nonlinear behavior of valve controller. Using only Short Time Fourier Transform (STFT), frequency leakage and the small amplitude of the current components related to the fault can be observed, but the fault due to the controller behavior cannot be observed. Therefore, a framework of advanced multirate signal and data-processing aided with sensor fusion algorithms is proposed in this article and satisfactory results are obtained. For implementing the system, a DSP-based BLDC motor controller with three-phase inverter module (TMS 320F2812) is used and the performance of the proposed method is validated on real time data.Comment: 7 Pages, 7 figure

Low-cost, high-resolution, fault-robust position and speed estimation for PMSM drives operating in safety-critical systems

In this paper it is shown how to obtain a low-cost, high-resolution and fault-robust position sensing system for permanent magnet synchronous motor drives operating in safety-critical systems, by combining high-frequency signal injection with binary Hall-effect sensors. It is shown that the position error signal obtained via high-frequency signal injection can be merged easily into the quantization-harmonic-decoupling vector tracking observer used to process the Hall-effect sensor signals. The resulting algorithm provides accurate, high-resolution estimates of speed and position throughout the entire speed range; compared to state-of-the-art drives using Hall-effect sensors alone, the low speed performance is greatly improved in healthy conditions and also following position sensor faults. It is envisaged that such a sensing system can be successfully used in applications requiring IEC 61508 SIL 3 or ISO 26262 ASIL D compliance, due to its extremely high mean time to failure and to the very fast recovery of the drive following Hall-effect sensor faults at low speeds. Extensive simulation and experimental results are provided on a 3.7 kW permanent magnet drive