With the operation of low-floor trams, unavoidable nonlinear factors such as backlash and parameter perturbation are present in electromechanical brake (EMB) systems. This results in poor clamping force tracking performance and challenges the operational safety of trams. Thus, an adaptive nonsingular fast terminal sliding-mode control algorithm is proposed to address this thorny problem. Firstly, a differentiable function approximates the backlash nonlinearity. Then, a dynamic mathematical model for an EMB system with backlash nonlinearity and parameter perturbation is established. Based on the backstepping control principle, this paper divides the system into three subsystems, and the nonsingular fast terminal sliding-mode control (NFTSMC) algorithm is adopted to design the controller of each subsystem. Notably, the NFTSMC algorithm can solve the parameters perturbation problem by the large switching gains, which may cause the chattering phenomenon. This paper utilizes the adaptive law to establish an adaptive NFTSMC algorithm to improve this phenomenon. Furthermore, the global asymptotic stability of the system is analyzed using Lyapunov theory. Finally, experimental results clearly validate the effectiveness and superiorities of the proposed control algorithm.

针对低地板有轨电车电子机械制动(EMB)系统压力传感器故障问题,提出一种强耦合条件下的无压力传感器制动力伺服控制策略.基于系统转矩特征曲线,提出一种不依赖于附加机械调节机构及压力检测装置的EMB间隙调整方法.同时,考虑系统制动和缓解过程中存在的"迟滞"特性,在EMB系统刚度特征曲线的基础上,提出一种强耦合条件下的制动力估算策略,与传统方法相比,其可有效地改善制动力的估计精度,能够作为备份制动方案,提高系统的可靠性.在此基础上,设计基于Sigmoid函数的改进型扩张状态观测器(ESO)对系统中的未建模部分与外界扰动进行估计与补偿,并将观测值前馈补偿至积分反步控制器,消除系统的观测误差,提高系统的鲁棒性.通过静态实验平台验证了所提控制策略的有效性.

In this paper, an integral-type half-tangent phase-locked loop (IHTan-PLL) is proposed for the varying-frequency AC grids of more electric aircraft (MEA). First, the performance of the synchronous reference frame phase-locked loop (SRF-PLL) and half-tangent phase-locked loop (HTan-PLL) is discussed from a large-signal viewpoint. When the frequency changes largely, the SRF-PLL has many oscillations and endures a rather long transient process. The HTan-PLL can address the large frequency jumps. However, for the varying-frequency AC grids with harmonic disturbances, the HTan-PLL still has oscillations in estimating the frequency when the frequency jumps largely. To enhance the performance of the SRF-PLL and HTan-PLL, the IHTan-PLL is developed for the varying-frequency AC grids with harmonic disturbances. The IHTan-PLL performs better than the SRF-PLL and HTan-PLL in addressing the large frequency jumps. Specifically, under any large frequency changes, the IHTan-PLL still converges to the equilibrium point (0,0), and no oscillations emerge. In addition, the IHTan-PLL has better steady-state accuracy in estimating the frequency than the SRF-PLL and HTan-PLL. The experimental results also demonstrate the superior performance of the proposed IHTan-PLL.

在建立电动舱门非线性数学模型的基础上,为解决舱门启闭过程中风载、系统结构参数及未知扰动等影响,提出了滑模控制和改进PID控制相结合的复合控制策略,外环采用滑模控制实现系统建模不精确或有干扰时给定舱门启闭角度的跟踪控制,并产生内环电流控制的给定信号.采用抗积分饱和的改进PID控制舱门作动电机的PWM信号实现内环的电流跟踪控制.仿真及实验结果表明,该文所提的控制方法在系统参数变化或有扰动时,可降低系统稳态误差,改善动态性能.

针对并网虚拟同步发电机(VSG)在功率指令和电网频率变化时输出有功功率存在超调和振荡的问题,提出基于有功功率偏差前馈的改进阻尼策略.首先,建立VSG并网小信号模型,分析了传统VSG方案振荡问题,并介绍了有功功率微分阻尼方案;然后,在传统VSG摇摆方程输出处引入有功功率偏差前馈环节,通过前馈增益单独调节系统阻尼,并利用闭环极点分布分析了前馈增益对系统稳定性的影响.在此基础上,给出了前馈增益的设计方法.最后,搭建了仿真和实验平台,对所提阻尼策略进行验证.仿真和实验结果表明,该方案提高了系统阻尼,减小了在功率参考和电网频率变化时VSG输出功率超调,改善了系统动态性能,同时不影响稳态下垂特性.

This paper presents a new type of all-electric braking (AEB) system with electromechanical actuator (EMA) redundancy for unmanned aerial vehicles (UAVs). The proposed system adopts a redundancy design. When a channel is faulty, the channel is removed, and the other channel outputs the total braking force. Firstly, its composition structure and mathematical model with nonlinear characteristics are proposed. Meanwhile, the integral sliding-mode control (SMC) algorithm is used in the pressure-tracking loop to improve the robustness for disturbance. In addition, the enhanced nonlinear extended state observer (NESO) is introduced as the feedforward compensation to weaken the chattering phenomenon further. Finally, the experimental results verified the feasibility of the proposed redundancy design and the superiority of the control strategy.

In rail transportation, electromechanical brake (EMB) technology is seen as the next generation of the braking system. Due to the deplorable working conditions (such as wading, impact vibration, and voltage surge), the clamping force sensor can encounter bridge-cut-off, zero shift, cable transmission faults, and other problems. Hence, the reliability of the clamping force sensor is greatly challenged. For the thorny problem, this paper proposed a novel clamping force sensor fault-tolerant control strategy that can be a backup control loop to enhance the reliability of the system. Firstly, the paper describes the working principle of the EMB system and establishes its nonlinear mathematical model. Combined with the piezoresistive sensor working principle, the cause of clamping force sensor failure is analyzed. Meanwhile, the corresponding relationship between motor output torque and the braking process is explained, and a gap adjustment control strategy without a clamping force sensor is proposed. Then, a clamping force estimation method is presented under strong coupling conditions, considering the different hysteresis characteristics between foreign clamping forces. In addition, the designed enhanced extended state observer (ESO) utilizes the sigmoid function to solve the high-frequency chattering phenomenon of the conventional nonlinearity ESO. With the enhanced ESO, the power fast terminal sliding-mode (PFTSM) control can ensure the dynamic response and improve the anti-interference ability of the system. Finally, compared with a conventional method, a static experimental platform verifies the effectiveness of the proposed control strategy.

In order to solve the problems of complex system design and high maintenance cost in the application of traditional hydraulic brakein small aircraft, based on the background of a certain type of UAV’s leading engineering application of the all-electric braking system, the all-electric braking system and key components model of the UAV were established. Based on the model, the hardware and software design of theall-electric braking system were completed, and the system requirements, architecture and simulation were realized. The ground test shows thatthe design of the all electric braking system is reasonable. Compared with the traditional hydraulic braking system, it has high control accuracy,fast response, advanced technology and easy maintenance. It has high technical superiority and economy in the application of small aircraftbraking system.

Virtual synchronous generator (VSG) control has attracted significant research interest for its ability to provide inertial support for distributed generation (DG)-based microgrids. However, VSG control cannot ensure proportional reactive and harmonic power sharing among DG units when the line impedances are mismatched. To address this problem, an adaptive virtual impedance regulation (AVIR) strategy is proposed in this paper. In this method, a fixed virtual inductance is introduced to generate the reactive power reference, and then it is removed to recover output voltage. After that, the virtual inductance is regulated adaptively according to the error between instantaneous reactive power and its reference. When the AVIR process completes, equivalent impedance mismatches at fundamental and harmonic frequencies are reduced. The reactive and harmonic powers sharing accuracy can be improved with a relatively small virtual inductance, good voltage quality is maintained. The small-signal model of paralleled DG units is built for stability analysis, based on which, the key regulator parameters are selected. Simulation and experimental results are presented to verify the effectiveness of the proposed strategy.(c) 2017 Elsevier Inc. All rights reserved.

Fluorides and their CO $$_{2}$$ mixtures are considered as promising choices of SF $$_{6}$$ -substitute gases due to their low global warming potentials and high dielectric strength. This paper investigates physical and chemical properties and breakdown characteristics of different common fluorides and their mixtures for application in the power system. For dielectric characteristics of fluorides and their mixtures, their power frequency breakdown voltages are determined experimentally, and the results are compared with SF $$_{6}$$ . For physical and chemical characteristics, the saturated vapor pressures, global warming potentials (GWPs), toxicities, prices of fluorides and their mixtures are calculated, and the corresponding characteristic curves are obtained. Based on characteristics mentioned above, a method for obtaining the optimal gas parameters of a specific fluoride mixture is proposed, which can be used as a feasible solution to find an SF $$_{6}$$ alternative gas that meets the application requirements. The results show that CO $$_{2}$$ mixtures with hexafluoropropene (HFP), 1,1,1,2-tetrafluoroethane (HFC-134a) and perfluoroisobutyronitrile (C4-PFN) are three types of good SF $$_{6}$$ -substitute gases. HFP/CO $$_{2}$$ mixtures with HFP component ratios 0.32 to 0.6 are suitable for applications at 0.1 to 0.3 MPa. HFC-134a/CO $$_{2}$$ mixtures (HFC-134a component ratios from 0.16 to 0.2) are suitable for applications at 0.3 to 0.5 MPa. C4-PFN/CO $$_{2}$$ mixtures (C4-PFN component ratios from 0.09 to 0.12) could be used for the applications at 0.1 to 0.5 MPa, regardless of the gas price.

The main idea of iterative learning control (ILC) was exposed when Arimoto's first paper was published. Industrial tasks mainly in repetition are controlled by an iterative teaching controller in both iteration and time-domain which makes ILC unique. ILC is becoming very popular among control engineers because of its very simple and effective control techniques. This paper describes the basic key knowledge about ILC and its types of applications. The core concern of this paper is to elaborate and explore the future scope and key application areas of iterative learning control in engineering as well as other all subjects of interest.

设计了一种适用于城轨列车的电子机械制动系统,推导其数学模型,以常规小区段设定预置PI控制算法为基础,提出了一种双曲正割非线性PI控制算法,以提高系统的鲁棒性与适应性.此外,通过改进型变结构抗积分饱和算法,减小了系统稳态误差.静态试验结果验证了本文控制算法的有效性.最后,由等比例惯性台制动试验验证了电子机械制动系统在轨道交通领域应用的可行性,为电子机械制动系统在轨道交通领域的应用提供了理论基础.

The control of clamping force has a significant influence on the braking performance of low-floor trams.However, the load torque variations, strong nonlinearity and complex structure of electromechanical brake (EMB) systems present challenging the clamping force control issues.In this paper, an EMB system mathematical model is established.Then, an enhanced sliding-mode reaching law (ESMRL) is investigated to address these issues.In addition, novel gap distance elimination and adjustment strategies are proposed to improve the response quality and adjust the gap distance in a simple and low-cost way.Taking advantages of minimal chattering and short reaching times, the proposed ESMRL enhances the dynamic performance and tracking accuracy of the clamping force control.Finally, simulation and experimental results are offered to validate the effectiveness and superiority of the proposed control strategy.

The problem encountered in this paper is to design a robust, feedback-based improved control system for the plant that involves systematic uncertainty. This paper proposes a fault estimation algorithm based on iterative learning control. This algorithm is constructed through an optimization function to prove the robustness and convergence of the algorithm. Through linear matrix inequality (LMI), the observer gain matrix and iterative learning parameter matrix in the algorithm are solved. The two comprehensive parameters in LMI represent the parameter selection in the two specifications to make selected adjustments in learning and control. A numerical example shows the improvement process and the effectiveness of these methods. Through LMI techniques, we have obtained satisfactory results and controller stability and robustness against fault-tolerant control. Lastly, the simulation results show the effectiveness and accuracy of the proposed algorithm.

An iterative learning robust fault-tolerant control algorithm is proposed for a class of uncertain discrete systems with repeated action with nonlinear and actuator faults. First, by defining an actuator fault coefficient matrix, we convert the iterative learning control system into an equivalent unknown nonlinear repetitive process model. Then, based on the mixed Lyapunov function approach, we describe the stability of the nonlinear repetitive mechanism on time and trial indices and have appropriate conditions for the repeated control system’s stability in terms of linear matrix inequality theory. Through LMI techniques, we have obtained satisfactory results and controller stability, and robustness against fault tolerance is also discussed in detail. Finally, the simulation results of the output tracking control of the two exemplary models verify the effectiveness of the proposed algorithm.

The Hall sensor is the most commonly used position sensor of the permanent magnet brushless direct current (PMBLDC) motor. Its failure may lead to a decrease in system reliability. Hence, this article proposes a novel methodology for the Hall sensors fault diagnosis and fault-tolerant control in PMBLDC motor drives. Initially, the Hall sensor faults are analyzed and classified into three fault types. Taking the Hall signal as the system state and the conducted MOSFETs as the system event, the extended finite state machine (EFSM) of the motor in operation is established. Meanwhile, a motor speed observer based on the super twisting algorithm (STA) is designed to obtain the speed signal of the proposed strategy. On this basis, a real-time Hall sensor fault diagnosis strategy is established by combining the EFSM and the STA speed observer. Moreover, this article proposes a Hall signal reconstruction strategy, which can generate compensated Hall signal to realize fault-tolerant control under single or double Hall sensor faults. Finally, theoretical analysis and experimental results validate the superior effectiveness of the proposed real-time fault diagnosis and fault-tolerant control strategy.

Traditional and typical iterative learning control algorithm shows that the convergence rate of error is very low for a class of regular linear systems. A fast iterative learning control algorithm is designed to deal with this problem in this paper. The algorithm is based on the traditional P-type iterative learning control law, which increases the composition of adjacent two overlapping quantities, the tracking error of previous cycle difference signals, and the current error difference. Using convolution to promote Young inequalities proved strictly that, in terms of Lebesgue-p norm, when the number of iterations tends to infinity, the tracking error converges to zero in the system and presents the convergence condition of the algorithm. Compared with the traditional P-type iterative learning control algorithm, the proposed algorithm improves convergence speed and evades the defect using the norm metric’s tracking error. Finally, the validation of the effectiveness of the proposed algorithm is further proved by simulation results.

The monotonic convergence of the PD alpha-type fractional-order iterative learning control algorithm is considered for a class of fractional-order linear systems. First, a theoretical analysis of the monotonic convergence of 1st and 2nd order PD alpha-type control algorithms is carried out in the typical terms of Lebesgue-p (L-p), and the sufficient conditions for their monotonic convergence are comprehended and extended to the case of N-order control algorithms; then the speed of convergence of the two is explained in detail. It is concluded that the conditions for convergence of the control algorithm are determined by the learning gain and the system's properties are together determined. Simulation experiment verifies the accuracy of proposed scheme and the validity of the control algorithm.

An iterative learning control method is better to control the high-order nonlinear strong coupling and external disturbances in the permanent magnet synchronous motor position servo system. This paper proposes a second-order P.D. type iterative learning control strategy, which can effectively achieve the optimal tracking control algorithm. By using the generalization of the Young inequality of convolution, the Lebesgue-p norm is obtained under the adequate condition that the tracking error converges monotonously. Furthermore, the convergence rate of second-order iterative learning control is compared, and it is proved by the mathematical knowledge that second-order iterative learning control is much better than a first-order iterative learning control under satisfactory conditions. Simulation results show that the effectiveness of the proposed algorithm is better than that of the traditional method, and the error of the iterative learning control strategy is smaller but with higher accuracy.

This paper proposes a backstepping fuzzy sliding mode control method for the antiskid braking system (ABS) of unmanned aerial vehicles (UAVs). First, the longitudinal dynamic model of the UAV braking system is established and combined with the model of the electromechanical actuator (EMA), based on reasonable simplification. Subsequently, to overcome the higher-order nonlinearity of the braking system and ensure the lateral stability of the UAV during the braking process, an ABS controller is designed using the barrier Lyapunov function to ensure that the slip ratio can track the reference value without exceeding the preset range. Then, a power fast terminal sliding mode control algorithm is adopted to realize high-performance braking pressure control, which is required in the ABS controller, and a fuzzy corrector is established to improve the dynamic adaptation of the EMA controller in different braking pressure ranges. The experimental results show that the proposed braking pressure control strategy can improve the servo performance of the EMA, and the hardware in loop (HIL) experimental results indicate that the proposed slip ratio control strategy demonstrates a satisfactory performance in terms of stability under various runway conditions.