Regularization and frequency-domain stability of well-posed systems

We study linear control systems with unbounded control and observation operators using certain regularization techniques. This allows us to introduce a modification of the transfer function for the system even if the input and output operators are not admissible in the usual sense. The modified transfer function is utilized to show exponential stability of sufficiently smooth solutions for the internal system under appropriate admissibility conditions on the system operators and appropriately modified stabilizability and detectability assumptions. If the internal system satisfies additional, yet common, regularity properties, then its uniform exponential stability is obtained.     

Optimal heat release shaping in a reactivity controlled compression ignition (RCCI) engine

The present paper addresses the optimal heat release (HR) law in a single cylinder engine operated under reactivity controlled compression ignition (RCCI) combustion mode to minimise the indicated specific fuel consumption (ISFC) subject to different constraints including pressure related limits (maximum cylinder pressure and maximum cylinder pressure gradient). With this aim, a 0-dimensional (0D) engine combustion model has been identified with experimental data. Then, the optimal control problem of minimising the ISFC of the engine at different operating conditions of the engine operating map has been stated and analytically solved. To evaluate the method viability a data-driven model is developed to obtain the control actions (gasoline fraction) leading to the calculated optimal HR, more precisely to the optimal ratio between premixed and diffusive combustion. The experimental results obtained with such controls and the differences with the optimal HR are finally explained and discussed.     

Closed-loop diesel engine combustion phasing control based on crankshaft torque measurements

Methods for closed-loop combustion phasing control in a diesel engine, based on measurements of crankshaft torque, are developed and evaluated. A model-based method for estimation of cylinder individual torque contributions from the crankshaft torque measurements is explained and a novel approach for identification of crankshaft dynamics is proposed. The use of the combustion net torque concept for combustion phasing estimation in the torque domain is also described. Two different control schemes, one for individual cylinder control and one for average cylinder control, are studied. The proposed methods are experimentally evaluated using a light-duty diesel engine equipped with a crankshaft integrated torque sensor. The results indicate that it is possible to estimate and control on a cylinder individual basis using the measurements from the crankshaft torque sensor. Combustion phasing is estimated with bias levels of less than 0.5 crank angle degrees (CAD) and cycle-to-cycle standard deviations of less than 0.7 CAD for all cylinders and the implemented combustion phasing controllers manage to accurately counteract disturbances in both fuel injection timing and EGR fraction.     

A gradient flow approach to on-line robust pole assignment for synthesizing output feedback control systems

Pole assignment is a basic design method for synthesis of feedback control systems. In this paper, a gradient flow approach is presented for robust pole assignment in synthesizing output feedback control systems. The proposed approach is shown to be capable of synthesizing linear output feedback control systems via on-line robust pole assignment. Convergence of the gradient flow can be guaranteed. Moreover, with appropriate design parameters the gradient flow converges exponentially to an optimal solution to the robust pole assignment problem and the closed-loop control system based on the gradient flow is globally exponentially stable. These desired properties make it possible to apply the proposed approach to slowly time-varying linear control systems. Simulation results are shown to demonstrate the effectiveness and advantages of the proposed approach.     

A new fundamental solution for differential Riccati equations arising in control

The matrix differential Riccati equation (DRE) is ubiquitous in control and systems theory. The presence of the quadratic term implies that a simple linear-systems fundamental solution does not exist. Of course it is well-known that the Bernoulli substitution may be applied to obtain a linear system of doubled size. Here, however, tools from max-plus analysis and semiconvex duality are brought to bear on the DRE. We consider the DRE as a finite-dimensional solution to a deterministic linear/quadratic control problem. Taking the semiconvex dual of the associated semigroup, one obtains the solution operator as a max-plus integral operator with quadratic kernel. The kernel is equivalently represented as a matrix. Using the semigroup property of the dual operator, one obtains a matrix operation whereby the kernel matrix propagates as a semigroup. The propagation forward is through some simple matrix operations. This time-indexed family of matrices forms a new fundamental solution for the DRE. Solution for any initial condition is obtained by a few matrix operations on the fundamental solution and the initial condition. In analogy with standard-algebra linear systems, the fundamental solution can be viewed as an exponential form over a certain idempotent semiring. This fundamental solution has a particularly nice control interpretation, and might lead to improved DRE solution speeds.     

汽油机非线性卡尔曼滤波暂态进气量估计及空燃比控制

暂态工况下缸进气量的准确估计是提高发动机空燃比控制精度的有效措施之一,为此本文提出一种基于无迹卡尔曼滤波的暂态缸进气量估计算法,并利用估计的缸进气量设计了一种前馈-反馈空燃比控制器.MATLAB环境下的仿真实验给出了所提出的算法与现有进气量估计算法的比较,同时基于暂态气量估计的空燃比控制仿真实验验证了估计的有效性.论文与现有成果的区别在于:一是暂态进气量估计模型不仅包含了歧管压力动态还考虑了曲轴角速度动态,并采用了基于非线性辨识的均值模型;二是考虑了泵气波动的影响,采用了移动平均值法的数字滤波器对泵气波动进行滤波;三是采用无迹卡尔曼滤波算法对歧管压力和曲轴角速度进行估计.     

模糊PID控制在液压缸力控制中的应用

液压缸具有非线性和不确定等特性,采用传统的PID控制方法不易于取得良好的控制效果.本文设计了一种模糊PID控制器,将其应用于液压缸力的控制,仿真和试验结果表明,该控制方法能够改善系统的动态特性,提高稳态精度.     

基于MRAC的电液伺服作动器同步控制

为实现在阀控非对称电液伺服作动器并联差动工作方式下两台空气舵面的偏转同步,采用了基于Lyapunov稳定意义下的模型跟踪自适应控制（MRAC）技术。通过引入前馈和反馈可调控制器,补偿控制对象结构参数的漂移及等效负载干扰的影响,使两个作动器分别稳定跟踪同一个参考模型,以达到较理想的伺服控制性能,同时使两个伺服通道的并联差动同步误差趋于零。仿真结果表明,该方案位置伺服精度高,同步误差小,具有较强的鲁棒性。     

3D‐printed cylindrical Luneburg lens antenna for millimeter‐wave applications

A 3D‐printed cylindrical Luneburg lens antenna working at 26 GHz is proposed in this article. The antenna consists of a feeding waveguide, a 3D‐printed cylinder, and a pair of printed metal grids which are stuck on the side faces of the cylinder. 3D‐printed structure ensures the convenience for processing and structural integrity of the Luneburg lens. Hole drilling technology is utilized for the design of the cylindrical lens. In the E‐plane, conversion of spherical waves into planar waves is achieved based on the gradient refractive index which is realized by the gradient equivalent relative dielectric constant. The main part of the lens contains a hole drilling region to realize the desired equivalent permittivity from 1.23 to 2, while another gradual‐thickness region realize the permittivity ranges from 1.23 to 1. H‐probe method is utilized for the optimization of the gradual‐thickness region in this article. And for the H‐plane, with the grids, H‐field distribution is optimized compared with the Luneburg lens antenna without the loading grids. Thus, the side lobe level (SLL) in H‐plane could be reduced. Meanwhile, a narrower half power beamwidth (HPBW) in H‐plane will be obtained due to the metal grids. Experiment results illustrate the feasibility and validity of the proposed 3D‐printed cylindrical Luneburg lens antenna.     

液压支护平台的异步自抗扰平衡控制

迈步式超前支护液压支架主要用于煤矿综掘迎头巷道的临时支护,其关键部件之一是支护平台.巷道底板难以保持水平等因素的影响,使得液压支护平台很难平衡,从而影响了巷道支护的快速性与有效性.为了保持液压支护平台的平衡性,本文提出了该平台的异步自抗扰平衡控制方法.首先,借鉴平台传统四缸同步控制方法,提出逐高双向异步控制方法,基于此方法得到每一立柱油缸位移解耦后的期望值;然后,根据立柱油缸位移控制系统特性,设计了自抗扰控制器,保证每一立柱油缸的位移在复杂工况下精确的达到期望值;最后,将所提方法应用于煤矿综掘巷道迈步式超前支护液压支架调平中,建立了基于MATLAB和AMESim的仿真系统.不同场景的仿真结果表明,液压支护平台在负载和倾角突变时,所提方法仍能很好的保持液压支护平台的平衡,且具有比传统PI控制以及GM(1, 1)灰色预测控制具有更优越的动态性能.     

D/BEM implementation of Robinson's viscoplastic model in creep analysis of metals using a complex variable numerical technique

A new boundary element approach for the solution of time-dependent inelastic problems arising in creeping metallic structures subjected to the combined action of high temperature gradient and quasi-static mechanical loading conditions is investigated. The new approach allows the use of complex variable techniques in the boundary element procedure for the evaluation of stress components as derivatives of the displacement integral equations. This methodology makes faster and more accurate the conventional boundary element method. To validate the efficiency of the proposed method in the implementation of Robinson's viscoplastic model, the results obtained using the present methodology are compared with those obtained by using known analytical and finite element solution for the analysis of a thick-walled internally pressurized cylinder and an experimental cylindrical thrust chamber in plane strain under general thermomechanical loading histories.     

电动缸举升伺服机构高精度复合控制策略

针对电动缸举升机构的高精度伺服控制的现实需求,提出结合辨识伺服环路和差分激励信号的一种基于限定记忆区间的循环最小二乘法(CLS)以及基于迭代控制器参数和观测器参数的一种变参数比例积分控制器(VPI)结合基于卡尔曼滤波器的变参数比例多重积分观测器(VPMISAKF)的复合控制策略.实验结果表明:相比于最小二乘法, CLS辨识法辨识拟合的惯量和阻尼均方根误差分别下降93.61%和82.39%;相比于PI控制器, VPI结合VPMISAKF的复合控制策略使得系统的阶跃响应拟合度在空载和带载工况下分别提高至0.994和0.991;相比于VPI控制器,VPI结合VPMISAKF的复合控制策略使得系统的正弦响应误差在空载和带载工况下分别降低88.89%和86.45%. CLS辨识法和VPI结合VPMISAKF的复合控制策略对电动缸举升机构的高精度伺服控制具有一定的参考意义.     

电动汽车增程器燃油效率优化控制

针对如何提高增程器燃油效率,降低整车油耗的问题,提出了一种基于PRP共轭梯度法的增程器燃油效率优化控制方法.首先,以产生给定能量燃油效率最高为优化性能指标,以发动机转矩和发电机转矩为寻优变量,建立了增程器燃油效率优化控制问题的离散系统模型.然后,对算法实现过程中发动机、发电机的最高转速和最大转矩限制的处理方法进行了阐述,给出了基于PRP共轭梯度法的增程器燃油效率优化控制问题的数值实现方法的详细步骤.最后,仿真和实验结果表明本文提出的优化控制方法可以有效提高增程器的燃油效率.     

Intelligent control of static synchronous series compensator via an adaptive self-tuning PID controller for suppression of torsional oscillations

In this paper, an intelligent controller is proposed to control a static synchronous series compensator (SSSC) in order to mitigate subsynchronous resonance (SSR) oscillations in a power system. This intelligent controller is an adaptive self-tuning PID controller. To train the PID controller, the gradient descent method is employed where the learning rate is adapted in every iteration in order to accelerate the speed of convergence. This control scheme also requires a wavelet neural network (WNN) to identify the controlled system dynamic. To update the parameters of WNN, the gradient descent (GD) along with the adaptive learning rates derived by the Lyapunov method is used. The computer simulations are used to show the ability of the proposed controller. In addition, the performance of the proposed controller is compared with another self-tuning PID controller. The results demonstrate that the proposed controller has a successful performance in minimizing the SSR.     

自校正调节器在具有阻力负载的气动位置伺服系统中的应用

以空气为传输介质的气动位置伺服系统,由于自身结构的特殊性,难以实现高精度位置控制.为研究工作过程中气缸所受柔性作用力,并真实反映气动系统的控制过程,利用气缸模拟实际环境中系统的负载外力,采用三阶模型描述系统,并运用自校正调节器完成了对系统控制律的设计;最后通过实验研究了自校正调节器对气动位置伺服系统的动态、静态特性的影响并根据仿真实验结果分析了气动系统跟踪响应迟滞性的根本原因.     

Hybrid Control Scheme of a Hydraulically Actuated Lower Extremity Exoskeleton for Load-Carrying

In this paper, a lower extremity exoskeleton is developed to help human beings walk and carry heavy loads. The exoskeleton is actuated by a pump-based hydraulic actuation system. The hydraulic actuation system has a high speed on/off valve and a unidirectional cylinder with embedded springs on the cylinder rod. The hybrid control scheme, including two modes, i.e., position control and following control, is proposed to drive the exoskeleton system. The position control mode is employed to support the carrying load in the stance phase. The following control mode is used to shut down the DC motor to disable the pump and open the relief valve in the swing phase. In the position control, an online Gaussian process regression algorithm is proposed to estimate the human gait trajectory using the human robot interaction signals. A general position control strategy, i.e., proportion integration differentiation (PID), is utilized to control the exoskeleton to shadow the estimated human gait trajectory. In the following control, the operator can lead the mechanical legs with the help of embedded springs on the cylinder rod. Experiments are performed on the healthy human subject, who walks on the level ground at natural speed. The experimental results demonstrate that the proposed hybrid control strategy is suitable for the pump-based hydraulically actuated lower extremity exoskeleton.     

Integrated direct/indirect adaptive robust motion trajectory tracking control of pneumatic cylinders

This paper studies the precision motion trajectory tracking control of a pneumatic cylinder driven by a proportional-directional control valve. An integrated direct/indirect adaptive robust controller is proposed. The controller employs a physical model based indirect-type parameter estimation to obtain reliable estimates of unknown model parameters, and utilises a robust control method with dynamic compensation type fast adaptation to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbances. Due to the use of projection mapping, the robust control law and the parameter adaption algorithm can be designed separately. Since the system model uncertainties are unmatched, the recursive backstepping technology is adopted to design the robust control law. Extensive comparative experimental results are presented to illustrate the effectiveness of the proposed controller and its performance robustness to parameter variations and sudden disturbances.     

Non-hydrostatic finite volume model for non-linear waves interacting with structures

An efficient non-hydrostatic finite volume model is developed and applied to simulate non-linear waves interacting with structures. The unsteady Navier–Stokes equations are solved in a 3D grid made of polyhedrons, which are built from a 2D horizontal unstructured grid by adding several horizontal layers. A new grid arrangement in the vertical direction is proposed, which renders the resulting model is relatively simple. Moreover, the discretized Poisson equation for pressure is symmetric and positive definite, and thus it can be solved effectively by the preconditioned conjugate gradient method. Several test cases including solitary wave interacting with a submerged structure, solitary wave scattering from a vertical circular cylinder and an array of four circular cylinders are used to demonstrate the capability of the model on simulating non-linear waves interacting with structures. In all cases, the model gives satisfactory results in comparison with analytical solutions, experimental data and other published numerical results.