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Abstract Power quality is a crucial determinant for integrating wind energy into the electrical grid. This integration necessitates compliance with certain standards and levels. This study presents cascadedfuzzy power control (CFPC) for a variable-speed multi-rotor wind turbine (MRWT) system. Fuzzy logic is a type of smart control system already recognized for its robustness, making it highly suited and reliable for generating electrical energy from the wind. Therefore, the CFPC technique is proposed in this work to control the doubly-fed induction generator (DFIG)-based MRWT system. This proposed strategy is applied to the rotor side converter of a DFIG to improve the current/power quality. The proposed control has the advantage of being model-independent, as it relies on empirical knowledge rather than the specific characteristics of the DFIG or turbine. Moreover, the proposed control system is characterized by its simplicity, high performance, robustness, and ease of application. The implementation of CFPC management for 1.5 MW DFIG-MRWT was carried out in MATLAB environment considering a variable wind speed. The obtained results were compared with the direct power control (DPC) technique based on proportional-integral (PI) controllers (DPC-PI), highlighting that the CFPC technique reduced total harmonic distortion by high ratios in the three tests performed (25%, 30.18%, and 47.22%). The proposed CFPC technique reduced the response time of reactive power in all tests by ratios estimated at 83.76%, 65.02%, and 91.42% compared to the DPC-PI strategy. Also, the active power ripples were reduced by satisfactory proportions (37.50%, 32.20%, and 38.46%) compared to the DPC-PI strategy. The steady-state error value of reactive power in the tests was low when using the CFPC technique by 86.60%, 57.33%, and 72.26%, which indicates the effectiveness and efficiency of the proposed CFPC technique in improving the characteristics of the system. Thus this control can be relied upon in the future.

This paper addresses the problem of high communication frequency in the multi-rotor unmanned aerial vehicles swarm system. A novel sliding mode control method based on event-triggering is proposed, using a dual-loop structure control model based on sliding mode control of multi-rotor UAVs swarm. The model consists of a position subsystem and an attitude subsystem, where the position subsystem serves as the outer loop control object, and the attitude subsystem serves as the inner loop auxiliary control object. In the position subsystem, a sliding mode controller with event triggers is used to achieve position control of the multi-rotor UAVs swarm by introducing sliding mode surfaces and sliding mode variables. The stability of the system under this control strategy is proved by the Lyapunov stability theorem, and the absence of the Zero phenomenon is also proved. Simulation results demonstrate that the proposed control scheme reduces the reliance on high-frequency sampling of multi-rotor UAVs communication. This research provides a useful reference for the application of multi-rotor UAVs swarms in collaborative path following.

The demand for payload transportation has shown exceptional growth owing to its inherent convenience and ability to reduce manpower requirements. To address the limitations of previous studies that primarily employed a single multi-rotor to deploy payloads within a limited reach, we designed a cable-suspended aerial payload deployment system with a large workspace that allowed payload deployment at a distance from the multi-rotor platforms. Our system comprised two multi-rotors, a payload deployment device (PDD, hereafter) with ducted fans, servomotors and a microcomputer. The ducted fans were used not only for swing suppression during payload transportation, but also to ensure that the PDD maintained a certain angle to the vertical plane where the dual multi-rotors were located during the deployment phase. Compared to existing research results, our design has a larger working distance in the vertical and horizontal directions. The controller designed for the PDD was adaptive and robust to variation of the payload mass and distance between the dual multi-rotors. We verified the effectiveness of our design and algorithms through several experiments.

This research paper investigates the applicability and scalability of the Rotor Control Equivalent Turbulence Input models for multi-rotor vehicles. Initially, a Rotor Control Equivalent Turbulence Input model is developed for an isolated rotor using rotor RPM as the input and the rotor hub-load coefficient as the output. Subsequently, the model is applied to multi-rotor vehicle example to show that the effect of turbulence on vehicle response can be replicated using the Rotor Control Equivalent Turbulence Input models. This study further incorporates rotor collective deflections, which could be used in multi-rotor vehicles, to develop a collective input model. Additionally, the effect of altering rotor parameters on the Rotor Control Equivalent Turbulence Input model is studied and presented. The results demonstrate that the Rotor Control Equivalent Turbulence Input model effectively captures the turbulence-induced behaviors in multi-rotor vehicles, offering a generalizable and scalable framework for use to replicate the effect of turbulence in multi-rotor vehicles.

Abstract The paper proposes a nonlinear controller called dual super-twisting sliding mode command (DSTSMC) for controlling and regulating the rotor side converter (RSC) of multi-rotor wind power systems that use doubly-fed induction generators. It was proposed that this controller be developed as an alternative to the direct power control (DPC), which makes use of a pulse width modulation (PWM) strategy to regulate the RSC's functioning. Overcoming the power/current quality issue with the proposed technique (DPC-DSTSMC-PWM) is characterized by great robustness and excellent performance. The designed strategy was contrasted with the standard method of control and other methods already in use. So, the unique proposed control strategy’s robustness, performance, efficiency, and efficacy in enhancing system characteristics were tested and validated in Matlab/Simulink. In both tests, the proposed method resulted in significant improvements, reducing active power ripples by 83.33%, 57.14%, and 48.57% in the proposed tests. When compared with the traditional regulation method, the reduction rates of reactive power ripples are 64.06%, 52.47%, and 68.7% in the tests. However, in contrast to the conventional method, the proposed tests showed a decrease of between 72.46%, 50%, and 76.22% in the value of total harmonic distortion (THD) of the provided currents. These ratios show how effective the proposed plan is in ameliorating and enhancing aspects of the energy system.

Experimental work using Hardware-in-the-loop simulation is performed in this article for a power system based on multi-rotor wind energy for power generation. Power is generated using a doubly-fed induction generator (DFIG), where the suggested approach to regulate the energy is different from the direct power command (DPC) in terms of idea and structure, even though the same equations are used to estimate the powers. Two parallel super-twisting controls are used to control the power, and modified space vector modulation (MSVM) is used to operate the rotor side converter. The designed command is unrelated to the system’s mathematical model and uses only a few gains, which makes it an effective and distinctive effectiveness compared to the DPC based on the super-twisting controller (DPC-STC). Also, simplicity, robustness, and ease of application are the most notable characteristics of the suggested command. Moreover, an uncontrolled grid-side converter was used to demonstrate the efficacy and competence of the suggested command in ameliorating the features of the designed power system. The suggested command was first verified in MATLAB, and the results were confirmed using experimental work, where Hardware-in-the-loop using the dSPACE 1104 was used for this purpose. In this work, the results obtained with the DPC-STC technique were compared in terms of undulations and oscillation minimization ratio, total harmonic distortion (THD) of stream, and steady-state error (SSE) value. The designed command minimized the THD of current with an efficiency of 45.94%, 46.95%, and 45.93% in the first test, second test, and third test, respectively. Also, the active power undulations were minimized compared to the DPC-STC by58.33%, 45.60%, and 44.88% in the first test, second test, and third test, respectively. The SSE of reactive power was also reduced by 68%, 71.32%, and 70.80% in the first test, second test, and third test, respectively. These ratios indicate the effectiveness, ability, and efficiency of the suggested command to ameliorate the efficiency of the power system.

This new paper describes an experimental investigation of a proportional-integral (PI) controller that uses feedback control to regulate an energy system that uses multi-rotor wind energy systems. Pulse width modulation (PWM) is used by the proposed controller to control the power of the doubly-fed induction generator controlled by direct power control (DPC), which is intended to regulate and control the inverter. The proposed strategy differs from the traditional DPC strategy. The proposed control was studied in the case of variable wind speed, where the MATLAB and Dspace 1104 environment was used to implement this proposed feedback PI (FPI) controller, with a comparison with the proposed control technique and some existing works. The suggested FPI controller outperforms the traditional controller and certain other controllers in terms of lowering energy ripples, overshoot, steady-state error (SSE), response time, and the total harmonic distortion (THD) of supplied system currents, as demonstrated by experimental and simulation results. The THD value of current was reduced by 64.86% and 69.44% in the two proposed tests compared to the traditional DPC technique. Also, the value of ripples and overshoot of active power was reduced compared to the DPC method by 95.42% and 90.86%, respectively, in the case of step wind speeds. Moreover, ripples and SSE of reactive powers compared to the DPC technique were reduced by 37.51% and 84.13%, respectively. These high ratios indicate the high performance of the proposed DPC-FPI technique in enhancing the features of the system in contrast to the conventional DPC technique.

Multi-rotor drones have expanded their range of applications, one of which being search and rescue (SAR) missions using infrared thermal imaging. This paper addresses thermal target tracking with track segment association (TSA) for SAR missions. Three types of associations including TSA are developed with an interacting multiple model (IMM) approach. During multiple-target tracking, tracks are initialized, maintained, and terminated. There are three different associations in track maintenance: measurement–track association, track–track association for tracks that exist at the same time (track association and fusion), and track–track association for tracks that exist at separate times (TSA). Measurement–track association selects the statistically nearest measurement and updates the track with the measurement through the IMM filter. Track association and fusion fuses redundant tracks for the same target that are spatially separated. TSA connects tracks that have become broken and separated over time. This process is accomplished through the selection of candidate track pairs, backward IMM filtering, association testing, and an assignment rule. In the experiments, a drone was equipped with an infrared thermal imaging camera, and two thermal videos were captured of three people in a non-visible environment. These three hikers were located close together and occluded by each other or other obstacles in the mountains. The drone was allowed to move arbitrarily. The tracking results were evaluated by the average total track life, average mean track life, and average track purity. The track segment association improved the average mean track life of each video by 99.8% and 250%, respectively.

Industrial inspection is a well-known application area for unmanned aerial vehicles (UAVs), but are modern market-available drones fully suitable for inspections of larger-scale industrial facilities? This review summarizes the pros and cons of aerial large-scale facility inspection, distinguishing it from other inspection scenarios implemented with drones. Moreover, based on paper analysis and additionally performed experimental studies, it reveals specific issues related to modern commercial drone software and demonstrates that market-available UAVs (including DJI and Autel Robotics) more or less suffer from the same problems. The discovered issues include a Global Navigation Satellite System (GNSS) Real Time Kinematic (RTK) shift, an identification of multiple images captured from the same point, limitations of custom mission generation with external tools and mission length, an incorrect flight time prediction, an unpredictable time of reaching a waypoint with a small radius, deviation from the pre-planned route line between two waypoints, a high pitch angle during acceleration/deceleration, an automatic landing cancellation in a strong wind, and flight monitoring issues related to ground station software. Finally, on the basis of the paper review, we propose solutions to these issues, which helped us overcome them during the first autonomous inspection of a 2400 megawatts thermal power plant.

【Objective】The effects of operation parameters of multi-rotor plant protection unmanned aerial vehicle (UAV) at different growth stages of maize on deposition quality and the control efficacy of Spodoptera frugiperda were compared to select the optimal operation parameters, with an aim to provide scientific basis for precise pesticide application of S. frugiperda.【Method】DJI T20 six-rotor plant protection UAV was used as the research object, the operation parameters including flight altitude, flight speed and nozzle type were tested for optimization of deposition distribution at the trumpet stage and heading stage of maize, and the population decline rate and control effect of S. frugiperda 7 d after the application of pesticides were investigated.【Result】At trumpet stage of maize, when a SX110015VS nozzle operated at a flight speed of 4 m/s and at a flight altitude of 2.5 m above the maize canopy, the maximum normalized average droplet deposition was 0.45 μL/cm2. When a SX110015VS nozzle operated at a flight speed of 4 m/s and a flight altitude of 1.5 m, both average droplet coverage and average droplet density were the highest, which were 44.92 drops/cm2 and 9.31%, respectively. At heading stage of maize, the normalized average droplet deposition, average droplet coverage and average droplet density were the highest when a SX110015VS nozzle operated at a flight speed of 4 m/s and a flight altitude of 2.5 m, which were 0.50 μL/cm2, 82.92 drops/cm2 and 7.67%, respectively.【Conclusion】The actual occurrence level of pests should be taken into consideration in the selection of operation parameters at trumpet stage and heading stage of maize. The highest droplet deposition was achieved when the UAV flew at a speed of 4 m/s, an altitude of 2.5 m and a nozzle type of SX110015VS, the corrected control efficiency was more than 85% after 7 days of application.

Multi-rotor drones, a kind of unmanned equipment which is widely used in the military, commercial consumption and other fields, have been developed very rapidly in recent years. However, their short flight time has hindered the expansion of their application range. This can be addressed by utilizing hydrogen fuel cells, which exhibit high energy density, strong adaptability to ambient temperature, and no pollution emissions, as the power source. Accordingly, the application of hydrogen fuel cells as the power source in multi-rotor drones is a promising technology that has attracted significant research attention. This paper summarizes the development process of hydrogen fuel cell multi-rotor drones and analyzes the key obstacles that need to be addressed for the further development of hydrogen fuel cell multi-rotor drones, including structural light weight, hydrogen storage methods, energy management strategies, thermal management, etc. Additionally, prospects for the future development of hydrogen fuel cell multi-rotor drones are presented.

In recent years, with the miniaturization of high-precision position and orientation systems (POS), precise motion errors during SAR data collection can be calculated based on high-precision POS. However, compensating for these errors remains a significant challenge for multi-rotor UAV-borne SAR systems. Compared with large aircrafts, multi-rotor UAVs are lighter, slower, have more complex flight trajectories, and have larger squint angles, which result in significant differences in motion errors between building targets and ground targets. If the motion compensation is based on ground elevation, the motion error of the ground target will be fully compensated, but the building target will still have a large residual error; as a result, although the ground targets can be well-focused, the building targets may be severely defocused. Therefore, it is necessary to further compensate for the residual motion error of building targets based on the actual elevation on the SAR image. However, uncompensated errors will affect the time–frequency relationship; furthermore, the ω-k algorithm will further change these errors, resulting in errors in SAR images becoming even more complex and difficult to compensate for. To solve this problem, this paper proposes a novel improved precise topography and aperture-dependent (PTA) method that can precisely compensate for motion errors in the UAV-borne SAR system. After motion compensation and imaging processing based on ground elevation, a secondary focus is applied to defocused buildings. The improved PTA fully considers the coupling of the residual error with the time–frequency relationship and ω-k algorithm, and the precise errors in the two-dimensional frequency domain are determined through numerical calculations without any approximations. Simulation and actual data processing verify the effectiveness of the method, and the experimental results show that the proposed method in this paper is better than the traditional method.

Multi-rotor aircraft have the advantages of a simple structure, low cost, and flexible operation in the unmanned aerial vehicle (UAV) family, and have developed rapidly in recent years. Radar surveillance and classification of the growing number of multi-rotor aircraft has become a challenging problem due to their low-slow-small (LSS) characteristics. Estimation of the blade number is an important step in distinguishing LSS targets. However, most of the current research on micro-motion parameters estimation has focused on the analysis of rotational frequency, length, and the initial phase of blades with a prior of blade number, affecting its ability to identify LSS targets. In this article, a micro-motion parameters estimation method for multi-rotor targets without a prior is proposed. On the basis of estimating the flashing frequency of the blades, a validation function is constructed through spectral analysis to judge the number of blades, and then the rotational frequency is estimated. The blade length is calculated by estimating the maximum Doppler shift. Moreover, the variational mode decomposition (VMD)-based atomic scaling orthogonal matching pursuit (AS-OMP) method is jointly applied to estimate the blade length when suffering from the low PRF and insufficient SNR conditions. Extensive experiments on the simulated and measured data demonstrate that the proposed method outperforms robust micro-motion parameter estimation capability in low PRF and insufficient SNR conditions compared to the traditional time-frequency analysis methods.

Regarding the airfoil optimization design of multi-rotor unmanned aerial vehicles, this paper proposes an integral airfoil design method based on upper airfoil contour optimization. Firstly, by designing concave descent input curves with 0-1 distribution, the upper arc of different optimized airfoils is obtained using the Tangent circles method. Secondly, an integral airfoil generation method is developed after establishing the middle arc. As the upper and lower arcs of different shapes are randomly combined, various airfoil profiles are obtained by random assortment. Finally, the effectiveness and accuracy of the designed airfoil are validated through Python programming. The airfoil is generated by the XFOIL program, and the optimal airfoil is output with a lift-todrag ratio as the target. Meanwhile, an accurate Fluent analysis model is established, and a comparison verification is conducted on the data with the attack angle falling within [-8.02, 12.04] and lift-to-drag ratio falling within [- 50, 100]. After Fluent modeling of the designed airfoil, the Euclidean distance between the calculated angle-lift-drag ratio data curve and the data curve tested by the wind tunnel is 0.0331, while the Euclidean distance between the simulated data in the literature and the wind tunnel data is 0.0408. It indicates that our precise model achieves 18.9% higher accuracy than the literature model. Testing and verification results indicate that our designed airfoil based on upper arc optimization and its corresponding airfoil library can meet the design requirements for the aerodynamic performance of airfoils in practical applications. It provides a valuable reference for the development of airfoil design, optimization, and generation methods. [ABSTRACT FROM AUTHOR]

This article presents a trajectory‐tracking controller for multi‐rotor unmanned aerial vehicles (UAVs) in scenarios where only the desired position and heading are known without the higher‐order derivatives. The proposed solution modifies the state‐of‐the‐art geometric controller, effectively addressing challenges related to the non‐existence of the desired attitude and ensuring positive total thrust input for all time. We tackle the additional challenge of the non‐availability of the higher derivatives of the trajectory by introducing novel nonlinear filter structures. We formalize theoretically the effect of these filter structures on the system error dynamics. Subsequently, through a rigorous theoretical analysis, we demonstrate that the proposed controller leads to uniformly ultimately bounded system error dynamics. To demonstrate the controller's effectiveness and potential to enhance multi‐rotor performance and reliability in practical applications, we present a simulation study considering two examples with time‐varying trajectories. [ABSTRACT FROM AUTHOR]

In recent years, with the miniaturization of high-precision position and orientation systems (POS), precise motion errors during SAR data collection can be calculated based on high-precision POS. However, compensating for these errors remains a significant challenge for multi-rotor UAV-borne SAR systems. Compared with large aircrafts, multi-rotor UAVs are lighter, slower, have more complex flight trajectories, and have larger squint angles, which result in significant differences in motion errors between building targets and ground targets. If the motion compensation is based on ground elevation, the motion error of the ground target will be fully compensated, but the building target will still have a large residual error; as a result, although the ground targets can be well-focused, the building targets may be severely defocused. Therefore, it is necessary to further compensate for the residual motion error of building targets based on the actual elevation on the SAR image. However, uncompensated errors will affect the time–frequency relationship; furthermore, the ω-k algorithm will further change these errors, resulting in errors in SAR images becoming even more complex and difficult to compensate for. To solve this problem, this paper proposes a novel improved precise topography and aperture-dependent (PTA) method that can precisely compensate for motion errors in the UAV-borne SAR system. After motion compensation and imaging processing based on ground elevation, a secondary focus is applied to defocused buildings. The improved PTA fully considers the coupling of the residual error with the time–frequency relationship and ω-k algorithm, and the precise errors in the two-dimensional frequency domain are determined through numerical calculations without any approximations. Simulation and actual data processing verify the effectiveness of the method, and the experimental results show that the proposed method in this paper is better than the traditional method. [ABSTRACT FROM AUTHOR]

ObjectiveTo solve the problem of the autonomous and safe landing of multi-rotor unmanned aerial vehicles (UAVs) in the application of unmanned platforms at sea, this paper studies multi-rotor UAV landing devices and their safety boundary assessment methods.MethodBased on the idea of the "Harpoon-Grid" rapid securing system, a new type of "V-foot–net" landing device is designed for multi-rotor UAVs. Multi-rigid body dynamic models of the UAV and deck are established, and simulations of the landing process are carried out using ADAMS under different rolling amplitudes and period conditions to obtain the attitude change process, landing critical period and attitude stabilization time of the UAV. ResultsThe simulation results show that the proposed "V-foot–net" device has higher docking redundancy under a smaller rolling period and larger rolling amplitude, and achieves attitude stability faster than ordinary landing devices.ConclusionThe results show that this device has superior safety compared to ordinary devices, and its safety boundary obtained through simulation can provide valuable references for improving the reliability of the autonomous landing of UAVs on offshore platforms.

In recent years, many researches have been carried out on piezoelectric multi-rotor structures. This paper describes the analysis, development and experimental process of an ultrasonic multi-cell piezoelectric motor using a multi-rotor structure. In this design, three independent cells have been integrated into a mechatronic system. Analytical model and finite element method are used for modal and dynamic analysis of the proposed motor. The multicell motor prototype has been manufactured and tested in the laboratory. Finally, the results of analytical, simulations and experimental investigation have been compared. The compared results are in satisfactory agreement. The measured parameters were: resonance frequency characteristics, mechanical characteristics of the single actuator and the complete assembled motor. The maximum speed and load of the motor have been determined. The maximum speed of 512 rpm was obtained with a voltage of 86 Vrms and the maximum stall torque was 120 mNm. Finally, the multi-rotor structure was compared with other rotary ultrasonic structures.

This work provides regulation of active and reactive power for asynchronous generator-based multi-rotor wind power (MRWP) systems using a synergetic control based on fractional order control theory. The traditional synergetic control theory achieves an undesirable chattering effect, which can damage the system. For this, it is relevant to combine the traditional synergetic control theory with fractional order control to avoid these drawbacks. Two control schemes are proposed, analyzed, and compared: traditional direct power control (DPC) and DPC based on fractional-order synergetic controllers, the latter needs only the information of the sliding surface. Their characteristics are compared in terms of current quality, active and reactive power reference tracking, robustness against generator parameter variations, and power ripple. Simulation results using Matlab software have demonstrated the characteristics and robustness of the suggested DPC based on fractional-order synergetic controllers compared to the DPC because of its efficacy in improving the quality of power/current.