Underdetermined direction of arrival estimation with nonuniform linear motion sampling based on a small unmanned aerial vehicle platform

Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suffers from significant performance degradation owing to the limited number of physical elements.To improve the underdetermined DOA estimation performance of a ULA radar mounted on a small UAV platform,we propose a nonuniform linear motion sampling underdetermined DOA estimation method.Using the motion of the UAV platform,the echo signal is sampled at different positions.Then,according to the concept of difference co-array,a virtual ULA with multiple array elements and a large aperture is synthesized to increase the degrees of freedom(DOFs).Through position analysis of the original and motion arrays,we propose a nonuniform linear motion sampling method based on ULA for determining the optimal DOFs.Under the condition of no increase in the aperture of the physical array,the proposed method obtains a high DOF with fewer sampling runs and greatly improves the underdetermined DOA estimation performance of ULA.The results of numerical simulations conducted herein verify the superior performance of the proposed method.

Circular Formation Flight Control for Unmanned Aerial Vehicles With Directed Network and External Disturbance

This paper proposes a new distributed formation flight protocol for unmanned aerial vehicles(UAVs)to perform coordinated circular tracking around a set of circles on a target sphere.Different from the previous results limited in bidirectional networks and disturbance-free motions,this paper handles the circular formation flight control problem with both directed network and spatiotemporal disturbance with the knowledge of its upper bound.Distinguishing from the design of a common Lyapunov fiunction for bidirectional cases,we separately design the control for the circular tracking subsystem and the formation keeping subsystem with the circular tracking error as input.Then the whole control system is regarded as a cascade connection of these two subsystems,which is proved to be stable by input-tostate stability(ISS)theory.For the purpose of encountering the external disturbance,the backstepping technology is introduced to design the control inputs of each UAV pointing to North and Down along the special sphere(say,the circular tracking control algorithm)with the help of the switching function.Meanwhile,the distributed linear consensus protocol integrated with anther switching anti-interference item is developed to construct the control input of each UAV pointing to east along the special sphere(say,the formation keeping control law)for formation keeping.The validity of the proposed control law is proved both in the rigorous theory and through numerical simulations.

Direct Yaw Moment Control for Distributed Drive Electric Vehicle Handling Performance Improvement

For a distributed drive electric vehicle（DDEV） driven by four in-wheel motors, advanced vehicle dynamic control methods can be realized easily because motors can be controlled independently, quickly and precisely. And direct yaw-moment control（DYC） has been widely studied and applied to vehicle stability control. Good vehicle handling performance： quick yaw rate transient response, small overshoot, high steady yaw rate gain, etc, is required by drivers under normal conditions, which is less concerned, however. Based on the hierarchical control methodology, a novel control system using direct yaw moment control for improving handling performance of a distributed drive electric vehicle especially under normal driving conditions has been proposed. The upper-loop control system consists of two parts： a state feedback controller, which aims to realize the ideal transient response of yaw rate, with a vehicle sideslip angle observer; and a steering wheel angle feedforward controller designed to achieve a desired yaw rate steady gain. Under the restriction of the effect of poles and zeros in the closed-loop transfer function on the system response and the capacity of in-wheel motors, the integrated time and absolute error（ITAE） function is utilized as the cost function in the optimal control to calculate the ideal eigen frequency and damper coefficient of the system and obtain optimal feedback matrix and feedforward matrix. Simulations and experiments with a DDEV under multiple maneuvers are carried out and show the effectiveness of the proposed method： yaw rate rising time is reduced, steady yaw rate gain is increased, vehicle steering characteristic is close to neutral steer and drivers burdens are also reduced. The control system improves vehicle handling performance under normal conditions in both transient and steady response. State feedback control instead of model following control is introduced in the control system so that the sense of control intervention to drivers is relieved.

Direct adaptive control for lane keeping in intelligent vehicle systems

In this paper, with parametric uncertainties such as the mass of vehicle, the inertia of vehicle about vertical axis, and the tire cornering stiffness, we deal with the vehicle lateral control problem in intelligent vehicle systems. Based on the dynamical model of vehicle, by applying Lyapunov function method, the control problem for lane keeping in the presence of parametric uncertainty is studied, the direct adaptive algorithm to compensate for parametric variations is proposed and the terminal sliding mode variable structure control laws are designed with look-ahead references systems. The stability of the system is investigated from the zero dynamics analysis. Simulation results show that convergence rates of the lateral displacement error, yaw angle error and slid angle are fast.

Research on Direct Yaw Moment Control Strategy of Distributed-Drive Electric Vehicle Based on Joint Observer

Combined with the characteristics of the distributed-drive electric vehicle and direct yaw moment control,a double-layer structure direct yaw moment controller is designed.The upper additional yaw moment controller is constructed based on model predictive control.Aiming at minimizing the utilization rate of tire adhesion and constrained by the working characteristics of motor system and brake system,a quadratic programming active set was designed to optimize the distribution of additional yaw moments.The road surface adhesion coefficient has a great impact on the reliability of direct yaw moment control,for which joint observer of vehicle state parameters and road surface parameters is designed by using unscented Kalman filter algorithm,which correlates vehicle state observer and road surface parameter observer to form closed-loop feedback correction.The results show that compared to the“feedforward+feedback”control,the vehicle’s error of yaw rate and sideslip angle by the model predictive control is smaller,which can improve the vehicle stability effectively.In addition,according to the results of the docking road simulation test,the joint observer of vehicle state and road surface parameters can improve the adaptability of the vehicle stability controller to the road conditions with variable adhesion coefficients.

Multiple Unmanned Underwater Vehicles Consensus Control with Unmeasurable Velocity Information and Environmental Disturbances Under Switching Directed Topologies

A consensus algorithm proposed in the paper is applied to tackle remarkable problems of unmeasurable velocities,the environmental disturbances, and the limited communication environment for the multiple unmanned underwater vehicles(multi-UUVs). Firstly, for a complex nonlinear and coupled model of the unmanned underwater vehicle(UUV), a technique of feedback linearization is developed to transform the nonlinear UUV model into a secondorder integral UUV model. Secondly, to address the problem of the unavailable velocity information and environmental disturbances for the multi-UUVs system, we design a distributed extended state observer(DESO) to estimate the unmeasurable velocities and environmental disturbances using the relative position information. Finally,we propose a protocol based on the estimation information from the DESO and demonstrate that the multi-UUVs system with the switching directed topologies under the protocol can reach consensus asymptotically. The theoretical result proposed in the literature is verified by one numerical example.

Design and Development of the DTC Induction Motor Drive for Electric Vehicle

The design and development of the traction controller for electric vehicle is introduced, which is based on the induction motor. This drive is developed by using a digital signal processor at low cost and carried out with the module design concept of both software and hardware. Nevertheless, a scheme of the sensorless direct torque control is based on the developed hardware, of which the feasibility is tested by a trial program. Additionally, both the interface function of the drive hardware and the feasibility of its software are proved to be good by the trail programs. A test motor can run about 18?r/min by a variable frequency program with the space vector pulse width modulation technology, of which the torque is visible pulsatile. In this presentation, based on the theoretical approach, the sensorless torque control is to be studied and applied to electric vehicles, of which the quick, smooth and stable torque response is emphasized because it quite benefits improving the drive performance of electric vehicles.

Trajectory Tracking of Autonomous Vehicle with the Fusion of DYC and Longitudinal–Lateral Control

The current research of autonomous vehicle motion control mainly focuses on trajectory tracking and velocity tracking. However, numerous studies deal with trajectory tracking and velocity tracking separately, and the yaw stability is seldom considered during trajectory tracking. In this research, a combination of the longitudinal–lateral control method with the yaw stability in the trajectory tracking for autonomous vehicles is studied. Based on the vehicle dynamics, considering the longitudinal and lateral motion of the vehicle, the velocity tracking and trajectory tracking problems can be attributed to the longitudinal and lateral control. A sliding mode variable structure control method is used in the longitudinal control. The total driving force is obtained from the velocity error in order to carry out velocity tracking. A linear time-varying model predictive control method is used in the lateral control to predict the required front wheel angle for trajectory tracking. Furthermore, a combined control framework is established to control the longitudinal and lateral motions and improve the reliability of the longitudinal and lateral direction control. On this basis, the driving force of a tire is allocated reasonably by using the direct yaw moment control, which ensures good yaw stability of the vehicle when tracking the trajectory. Simulation results indicate that the proposed control strategy is good in tracking the reference velocity and trajectory and improves the performance of the stability of the vehicle.

Distributed tracking control of unmanned aerial vehicles under wind disturbance and model uncertainty

A distributed robust method is developed for cooperative tracking control of unmanned aerial vehicles under unknown wind disturbance and model uncertainty. The communication network among vehicles is a directed graph with switching topology. Each vehicle can only share its states with its neighbors. Dynamics of the vehicles are nonlinear and affected by the wind disturbance and model uncertainty. Feedback linearization is adopted to transform the dynamics of vehicles into linear systems. To account for the wind disturbance and model uncertainty, a robust controller is designed for each vehicle such that all vehicles ultimately synchronize to the virtual leader in the three-dimensional path. It is theoretically shown that the position states of the vehicles will converge to that of the virtual leader if the communication network has a directed spanning tree rooted at the virtual leader. Furthermore, the robust controller is extended to address the formation control problem. Simulation examples are also given to illustrate the effectiveness of the proposed method. © 2016 Beijing Institute of Aerospace Information.

A Novel Pre-control Method of Vehicle Dynamics Stability Based on Critical Stable Velocity during Transient Steering Maneuvering

The current research of direct yaw moment control（DYC） system focus on the design of target yaw moment and the distribution of wheel brake force. The differential braking intervention can effectively improve the lateral stability of the vehicle, however, the effect of DYC can be improved a step further by applying the control of vehicle longitudinal velocity. In this paper, the relationship between the vehicle longitudinal velocity and lateral stability is studied, and the simulation results show that a decrease of 5 km/h of longitudinal velocity at a particular situation can bring 100° increasing of stable steering upper limit. A critical stable velocity considering the effect of steering and yaw rate measurement is defined to evaluate the risk of losing steer-ability or stability. A novel velocity pre-control method is proposed by using a hierarchical pre-control logic and is integrated with the traditional DYC system. The control algorithm is verified through a hardware in-the-loop simulation system. Double lane change（DLC） test results on both high friction coefficient（μ） and low μ roads show that by using the pre-control method, the steering effort in DLC test can be reduced by 38% and 51% and the peak value of brake pressure control can be reduced by 20% and 12% respectively on high μ and low μ roads, the lateral stability is also improved. This research proposes a novel DYC system with lighter control effort and better control effect.

Multi-objective reentry trajectory optimization method via GVD for hypersonic vehicles

In the constrained reentry trajectory design of hypersonic vehicles, multiple objectives with priorities bring about more difficulties to find the optimal solution. Therefore, a multi-objective reentry trajectory optimization (MORTO) approach via generalized varying domain (GVD) is proposed. Using the direct collocation approach, the trajectory optimization problem involving multiple objectives is discretized into a nonlinear multi-objective programming with priorities. In terms of fuzzy sets, the objectives are fuzzified into three types of fuzzy goals, and their constant tolerances are substituted by the varying domains. According to the principle that the objective with higher priority has higher satisfactory degree, the priority requirement is modeled as the order constraints of the varying domains. The corresponding two-side, single-side, and hybrid-side varying domain models are formulated for three fuzzy relations respectively. By regulating the parameter, the optimal reentry trajectory satisfying priorities can be achieved. Moreover, the performance about the parameter is analyzed, and the algorithm to find its specific value for maximum priority difference is proposed. The simulations demonstrate the effectiveness of the proposed method for hypersonic vehicles, and the comparisons with the traditional methods and sensitivity analysis are presented.

Nonlinear direct data-driven control for UAV formation flight system

This paper proposes the nonlinear direct data-driven control from theoretical analysis and practical engineering,i.e.,unmanned aerial vehicle(UAV)formation flight system.Firstly,from the theoretical point of view,consider one nonlinear closedloop system with a nonlinear plant and nonlinear feed-forward controller simultaneously.To avoid the complex identification process for that nonlinear plant,a nonlinear direct data-driven control strategy is proposed to design that nonlinear feed-forward controller only through the input-output measured data sequence directly,whose detailed explicit forms are model inverse method and approximated analysis method.Secondly,from the practical point of view,after reviewing the UAV formation flight system,nonlinear direct data-driven control is applied in designing the formation controller,so that the followers can track the leader’s desired trajectory during one small time instant only through solving one data fitting problem.Since most natural phenomena have nonlinear properties,the direct method must be the better one.Corresponding system identification and control algorithms are required to be proposed for those nonlinear systems,and the direct nonlinear controller design is the purpose of this paper.

基于连续可微采样的无人机多向视点规划

无人机在各种工业基础设施的自主巡检中,需要为大型复杂待巡检对象设计大量的数据采集航点,以获取高质量的全覆盖影像数据。逐点飞行作业能耗高采集效率低,限制了无人机大规模的工业应用。为了优化飞行作业模式,有效提升巡检效率,针对已知待巡检复杂设备结构提出一种全新的多向视点规划算法——连续可微采样的无人机多向视点规划算法(MD-VPP)。该方法在满足全面覆盖巡视目标以及数据采集质量要求的前提下,大幅减少航点数量。首先,将云台俯仰角、偏航角和相机成像面积作为约束条件,构建视点采集连续可微的视图质量目标函数,优化求解候选视点集;然后利用贪心算法求解全覆盖待巡检对象的航点位姿。通过实验对比分析了针对不同巡检对象的航点数量和航点数减少率,相比领域内其他优秀方法,所提方法在确保全覆盖的前提下航点数量至少降低77%,极大地提升了无人机单次作业的数据采集效率。

新能源汽车电机节能直接横摆力矩控制研究

为了降低电动汽车在行驶过程中的电机能量消耗,采用直接横摆力矩控制方法,并对车辆的车轮力矩和电机功率变化进行仿真验证。建立了车辆模型简图,根据牛顿第二定律推导出车辆转向运动方程式。针对传统两轮等力矩控制方法进行改进,提出了一种主动直接横摆力矩控制方法,推导出车辆连续行驶和转弯过程中的力矩分配律。利用转弯过程中车辆车轮的力矩变化来调节电机的功率变化,从而降低车辆电机的能量消耗。采用MATLAB软件对车辆横摆角速度、车轮力矩和电机能量消耗进行仿真,与两轮等力矩控制方法进行对比。结果显示:采用两轮等力矩控制方法,车辆横摆角速度跟踪误差较大,车轮力矩变化幅度较小,自适应调节能力较差,导致电机能量消耗较多;采用直接横摆力矩控制方法,车辆横摆角速度跟踪误差较小,车轮力矩变化幅度较大,自适应调节能力较好,使电机能量消耗较少。采用直接横摆力矩控制方法,能够自适应调整车轮力矩的变化,从而达到降低电机能量消耗目的。

新能源汽车的驱动电机系统研究和设计

通过改变新能源汽车的能源消耗方式,能提高节能减排工作效果,促进新能源开发利用工作顺利进行,保证社会经济实现可持续发展。科学技术的发展决定着新能源汽车的研发进程,驱动电机系统作为新能源汽车的关键点,涉及新能源汽车研发的核心技术,相关人员要注重新能源汽车的驱动电机系统研究和设计,提高设计的合理性。

路堤-桥梁过渡段车辆气动力风洞试验研究

为了探究路堤-桥梁过渡段处车辆的气动力,建立1:50的大比例尺路堤-桥梁过渡段和车辆试验模型,在桥梁和路堤段分别布置两种风屏障,并在车辆模型表面布置多个测压点,以研究不同防风措施下处于不同风向角的路桥过渡段车辆气动力。试验结果表明:与无防风措施相比,布置桥梁风屏障后最不利风向角会从-15°变为0°,此风向下过渡段处车辆的三分力最大;再进一步布置路堤风屏障后最不利风向角不变,但大幅度减小了0°风向角下车辆的侧力系数和力矩系数;布置路堤风屏障能有效减小车辆所受三分力;不同风向角下改变陆地风屏障参数产生的影响不同,针对路堤-桥梁过渡段布置防风措施时,应充分考虑其来流方向,以达到最优效果。

基于UN R167法规的商用车直接视野3D虚拟测试方法研究

针对UN R167法规,构建商用车驾驶员直接视野的数字化模型。利用Blender仿真平台开发虚拟测试方法,求得商用车驾驶员直接视野体积。结果表明,所开发的虚拟测试方法的数据与实际尺寸测量法数据高度一致,而且能够提高测量效率,降低测量成本。

高速公路同向双向路拱路面小客车换道舒适性和安全性分析

为了分析同向双路拱路面小客车换道行驶舒适性与安全性,使用Carsim仿真软件建立了小客车换道轨迹模型、车辆动力学模型、同向双路拱和单向坡道路模型,以平曲线极限半径值作为换道轨迹半径值,开展多工况跨路拱换道行驶试验,并通过实车驾驶实验对仿真模型进行了准确性验证。结合横向加速度、横摆角速度、峰值附着系数和横向荷载转移率等四项指标变化情况和判断标准对同向双路拱路面小客车换道行驶状态进行了分析。研究结果表明:道路类型对车辆换道行驶稳定性影响较大,综合评价指标与回正增益系数的变化情况,在同向双路拱路面条件下,SUV(suburban utility vehicle)和微型面包车(minivan)换道行驶稳定性均能满足安全行驶要求;换道行驶稳定性由高到低对应的路面类型为:单向坡路面>抛物线型路拱路面>折线型路拱路面;折线型路拱路面条件下,SUV换道行驶稳定性优于Minivan。超速行驶对小客车换道行驶稳定性有显著影响,超速程度越高,稳定越差,即当基础车速为100 km/h和120 km/h时,超速10%和20%时,车辆换道行驶过程中均不存在侧滑风险,但车辆稳定性均处于较差状态。

美国定向能机动近程防空计划进展分析

美国定向能机动近程防空(directed energy maneuver-short range air defense,DE M-SHORAD)计划通过击伤、摧毁或压制旋转翼无人机、固定翼无人机以及火箭弹、火炮炮弹、迫击炮弹(rockets,artillery and mortar,RAM)等威胁目标,为机动部队提供伴随防空,对抗新兴威胁,属于美国陆军防空反导现代化的优先项目之一。首先介绍了DE M-SHORAD研制计划;其次详细分析了系统结构,并由系统参数评估了系统的作战性能;最后梳理了系统的研制进展。通过综合分析可知,DE M-SHORAD系统采用最佳组件,通过快速原型方法实现激光武器系统在装甲车上的集成;为降低技术风险,该计划在发展方式上分为两个阶段,首先集成、测试2 kW~5 kW机动实验型高能激光器(mobile experimental high-energy laser,MEHEL),然后再研制50 kW级的多任务高能激光器(multi-mission high-energy laser,MMHEL)。经计算可得:MEHEL和MMHEL对无人机的最大射程分别约为0.77 km、4.8 km。

考虑通行方向利用率的交叉口感应式控制

为缓解城市出行延误中交叉口延误占比较大的问题,提高交叉口的通行效率,以标准的四相位交叉口为研究对象,提出了基于交叉口实时路况信息的感应式通行方向利用率信号控制方法。根据车辆空间占用率、交叉口通行效率、车头间距阈值于Python中建立了交叉口相位决策优化模型。以长沙市某交通需求变化大的交叉口为例,通过Vissim 8.0建模,将感应式控制方法与传统的基于车流量的Webster控制方法在多种交通需求下进行仿真对比。结果表明:交叉口平均车辆延误在平峰、PHF15、拥堵交通需求下降低了3.21%、13.1%、4.17%;交叉口的车均延误降低率随着交通需求的增大呈先增后降的趋势。研究成果证实了感应式控制能适应较为广泛的交通环境,能有效降低交叉口车辆延误。