The gap metric: Robustness of stabilization of feedback systems

In this paper we introduce the gap metric to study the robustness of the stability of feedback systems which may employ not necessarily stable open-loop systems. We elaborate on the computational aspects of the gap metric and provide upper bounds to the gap in cases where the exact formulas do not apply, By admissible uncertainties we mean those which preserve closed-loop stability and a specified small tolerance on the I/O behavior of a feedback system. We show that admissible uncertainties are precisely those which are constrained in the gap. Finally, we conclude that any metric which preserves a continuous relationship between open-loop systems and the corresponding stable feedback interconnections must have the topology of the gap metric.     

Dual‐rate sampled‐data stabilization for active suspension system of electric vehicle

In this paper, we consider the dual‐rate sampled‐data state‐feedback control problem for an active suspension system of an electric vehicle. In the active suspension system, there exist 2 accelerometers to measure the heave acceleration of the sprung mass and the vertical acceleration of the unsprung mass, respectively. When the 2 accelerations are measured by sampled data under different sampling periods, the difficulty arising from the dual‐rate sampled data makes the active suspension stabilization problem challenging but interesting. In this paper, a linear hybrid stabilizer is proposed, which is implemented using dual‐rate sampled‐data state feedback. In order to deal with the more difficult stabilization problem under different triggering time instants, a coordinate transformation is proposed. A useful technical theorem is proposed in the stability analysis to show that the proposed hybrid controller can guarantee the states of the active suspension system being asymptotically stabilized or at least bounded to arbitrarily small domains. The experiment result is similar to the simulation result and indicates that the proposed active suspension controlling system is effective.     

Gain-scheduled, model-based anti-windup for LPV systems

The aim of this paper is to show that a recently proposed technique for anti-windup control of exponentially unstable plants can be easily extended to solve the corresponding robust anti-windup problem for linear parameter varying systems, for which the time varying parameters are measured online. The proposed technique is minimally conservative with respect to the size of the resulting operating region (which coincides, up to an arbitrarily small quantity, with the largest set on which asymptotic stability can be guaranteed for the considered plant with the given saturation level and uncertainty characteristics), and is not limited to plants having only small uncertainties or being open-loop stable.     

机组在线监测平板电容式气隙传感器的研制

研究制作了一种测量水轮发电机定、转子间空气间隙的平板电容式气隙传感器探头,介绍了传感器的测量原理、探头的组成结构及各部分的作用。搭建了模拟实际工作环境的实验平台并进行了性能试验。结果表明：探头的各技术指标均已达到设计要求,且具有测量精度高,响应速度快,工作稳定、可靠,安装方便等特点,特别适用于我国各型发电机组的在线气隙测量。     

Electromagnetic levitation micromotor with stator embedded (ELMSE): levitation and lateral stability characteristics analysis

The adhesion, friction, wear in micro system or MEMS is more significant than those in macro system. The levitation or suspension technique is one of the effective techniques to eliminate the adhesion, friction, wear caused by the surfaces contact. The electromagnetic levitation micromotor with stators embedded (ELMSE) is a kind electromagnetic eddy current levitation system, which has special structure including the double sided stator and the hollow annular rotor. Different from the electromagnetic eddy current levitation system with single sided stator, ELMSE has good stability in the vertical and lateral directions. Using the finite element method, the levitation characteristics and lateral stability characteristics are analyzed. The influence of structural parameters and electric parameters on the vertical stiffness and the lateral stiffness has been analyzed and optimized in the paper. The analysis result of the paper provides theoretical reference for the optimal design of ELMSE.     

电动执行机构传递函数的研究

介绍了一种获得电动执行机构传递函数的新方法。该方法从分析电动执行机构的各个组成部分出发,最终推导出以供电电压为输入、反馈电压为输出的开环传递函数,并通过求解微分方程,提出了一种简单、快速确定执行机构传递函数参数的新方法,来求解该传递函数的参数。物理实验和Matlab仿真都表明,这种方法简单、便捷。     

Voltage-induction type electrostatic film motor driven by two- to four-phase ac voltage and electrostatic induction

This paper describes a voltage-induction type electrostatic film motor that operates by feeding electric power to the slider by electrostatic induction. In the electrostatic motor, applying voltages to both of its stator and slider contributes to its fine positioning resolution and better controllability. However, in some cases such as relatively small motors, the electric wires connected to the slider could cause mechanical disturbances to the motor motion. In the new electrostatic motor, electric wires are connected only to the stator, thus the slider motion is not disturbed. The power to the slider is transferred by electrostatic induction between induction electrodes fabricated in both of the stator and the slider. The proposed motor has a two- to four-phase driving-electrode configuration, which consists of a two-phase driving electrode in the slider and a four-phase driving electrode in the stator. The paper first analyzes the thrust force characteristics of the driving-electrode configuration, and then analyzes the characteristics of voltage-induction configuration, both based on capacitance-network analysis. Experimental results showed good agreements with the analyses, confirming the feasibility of the voltage-induction type electrostatic motor.     

感应电机二阶滑模次优算法定子磁链观测器设计

提出了基于二阶滑模次优算法的感应电机定子磁链观测方法,设计了定子磁链观测器,并应用到感应电机直接转矩控制中.本文设计的磁链观测器,通过准确的跟踪电流及其变化率,从而实现对转子磁链的准确估算,然后利用转子磁链与定子磁链的关系,估算出定子磁链.由于本文设计的定子磁链观测器是一个多输入多输出(MIMO)系统,稳定性分析非常复杂,为此将磁链估算误差的微分看作扰动处理,从而将MIMO的观测器模型分解成两个独立的单输入单输出(SISO)系统,简化了稳定性分析.将该观测器用于感应电机直接转矩控制中,达到了很好的控制效果.仿真和实验验证了该方法的有效性.     

Exponential stabilization of a class of unstable bilinear systems

Considers the control design of bilinear systems with multiplicative control inputs. Previous control designs for such systems normally assume that the open-loop bilinear system is (neutrally) stable. In this paper, a nonlinear control design is proposed for open-loop unstable bilinear systems. The new control stabilizes the bilinear system globally and exponentially if a sufficient stability condition, which can be checked by off-line computer simulations in advance of the control, is satisfied     

混合动力汽车系统中的永磁同步电机控制研究

基于混合动力汽车应用中的电机控制,本文分析了电机运行的最大转矩/电流MTPA、弱磁控制和最大输出功率等阶段的数学模型,提出了基于新型内嵌式永磁同步电机IPM的一种最优化定子电流控制算法,调节不同阶段给定定子电流的交直轴分量,充分利用变流器所能提供的电压和电流容量,以维持系统运行所需要的转矩输出,使得每个时刻电机都能充分利用变流器资源并输出最大功率,可靠性和动态性能都很理想,实现了能量最优化,仿真实验和实际平台实验验证了该方法的可行性和优越性。     

Assessment of stability robustness for adaptive controllers

The problem of improving the stability characteristics of discrete-time SISO reduced order adaptive controllers is addressed in this note. A method is proposed to adjust the observer poles of an indirect adaptive scheme in order to ensure stability of the closed-loop system in spite of possible unstructured uncertainties (e.g., process-model order mismatch). Assuming that the identified model transfer function module converges within a previously defined uncertainty range, the frequency response-like compensation method is shown to lead to a stable design, provided that the reduced order estimated model is stable and stably invertible and the system is open-loop stable.     

Robust controller design by linear programming with application to a double-axis positioning system

A linear programming approach is proposed to tune fixed-order linearly parameterized controllers for stable LTI plants. The method is based on the shaping of the open-loop transfer function in the Nyquist diagram. A lower bound on the crossover frequency and a new linear stability margin which guarantees lower bounds for the classical robustness margins are defined. Two optimization problems are proposed and solved by linear programming. In the first one the robustness margin is maximized for a given lower bound on the crossover frequency, whereas in the second one the closed-loop performance in terms of the load disturbance rejection is optimized with constraints on the new stability margin. The method can directly consider multi-model as well as frequency-domain uncertainties. An application to a high-precision double-axis positioning system illustrates the effectiveness of the proposed approach.     

On control relevant criteria in H∞ identification

This paper proposes a technique for using control relevant criteria in H_∞ identification. The work reported here has its background in a desire to understand the closed-loop versus open-loop issue in control relevant identification. The proposed technique has some features in common with the iterative closed-loop Schrama scheme, but is constructed so as to be able to obtain control relevant reduced complexity models also directly from open-loop data (for stable systems). It is demonstrated that the proposed technique solves, with the initial open-loop data only, the examples treated earlier in the literature using the iterative closed-loop Schrama scheme     

一种确定PID参数稳定域的图解法

针对带滞后因子的一阶惯性环节的PID控制器,给出确定其参数稳定域的一种图解方法．基于参数空间的图解稳定性准则,在已知比例增益范围的前提下,针对稳定和不稳定开环对象,直接在积分-微分参数空间绘制和确定稳定区域,避免了复杂的数学计算．该图解稳定性准则给出闭环稳定的一个充分必要条件,所得结果没有任何保守性．此方法也可用来求解系统的相对稳定度问题和应用于其他任意给定被控对象．     

高温超导EMS悬浮系统研究

高温超导EMS悬浮系统,其悬浮能耗小,并可实现大气隙悬浮。本文介绍了该悬浮系统的数学模型,分析了它的一些性质,采用定气隙控制指标,设计了能使系统稳定的控制器,并对所设计的控制器进行了仿真。仿真结果表明,该悬浮系统可以通过控制实现大气隙、低能耗的稳定悬浮。     

A high-power MEMS electric induction motor

An electric induction micromotor with a 4-mm-diameter rotor was designed and built for high-power operation. Operated at partial actuating voltage, the motor has demonstrated an air gap power in excess of 20 mW and torque of 3.5 /spl mu/Nm at speeds in excess of 55 000 rpm. Operation at higher power and speed was limited by bearing stability at higher rotational speeds. The device builds on an earlier micromotor demonstrated by Frechette et al. The high power of the present motor is enabled by its low-loss, high-voltage electric stator, which also offers improved efficiency. The development of this electromechanical device is an important enabling step not only for watt-scale micromotors, but also for the development of microelectric generators. This paper presents the motor's design, the fabrication process that was created to meet its stringent design requirements, and its performance to date.     

On the enhanced passivity of pneumatically actuated impedance-type haptic interfaces

The stable simulation of high-stiffness surfaces remains a challenge in impedance-type haptic simulations of mechanical environments. In this paper, the authors propose an approach to achieving a stable, high-stiffness surface in a haptic interface by leveraging the open-loop properties of pneumatic actuators. By using the open-loop component of the actuator stiffness as a primary component of stiffness simulation in a haptic interface, the system requires a comparatively small component of simulated stiffness from the closed-loop control of the actuator. A passivity analysis is presented describing how the presence of an open-loop stiffness enhances the range of passivity of haptically simulated high-stiffness surfaces. Experimental results both with and without a human operator are presented that demonstrate the effectiveness of the approach and its enhanced passivity relative to motor-actuated devices.     

主被动一体悬架构型的多目标粒子群最优控制

为了解决轮毂电机电动汽车中轮毂电机导致的振动负效应问题,提出了将动态减振与主动悬架结合的悬架新构型方案.针对新构型中结构及控制参数复杂的特点,建立了能够表征平顺性、操稳性以及悬架作动效率的11自由度整车动力学模型.设计基于新构型的多目标粒子群线性二次最优(MOPSO–LQR)控制器.对模型进行仿真分析,仿真结果表明,新构型方案能够实现车辆平顺性、操稳性以及悬架效率的全局最优,对比传统轮毂电机悬架构型方案,在解决轮毂电机振动负效应问题上有良好的效果.     

Pointwise gap metrics on transfer matrices

A family of metrics, pointwise gap metrics, in the space of real rational matrices of fixed size is developed and used to study open-loop and closed-loop stability robustness of linear time-invariant finite-dimensional continuous-time systems. It is shown that pointwise gap metrics have the desired qualitative properties for the study of stability robustness. Necessary and sufficient conditions on the robustness are obtained in terms of the radii of the pointwise gap metric balls centered at the nominal plant and/or the nominal controller. Comparison with the gap metric and the graph metric is made. All of these metrics induce the same topology. Many of the quantitative properties of pointwise gap metrics are the same as those of the gap metric, although they differ in value. Pointwise gap metrics, in the scalar case, have a very simple expression which is potentially useful for accessing the relationship between the uncertainty of physical parameters and uncertainty measured by pointwise gap metrics     

Passivity-based control for variable speed constant frequency operation of a DFIG wind turbine

A standard passivity based control for a double fed induction generator of a wind turbine is presented. The control problem is posed as a variable speed constant frequency operation with the aim to maximise the generated electric power. The controller is designed in such a way that the dual control objective, unity power factor in the stator side and speed tracking in the mechanical port, are satisfied guaranteeing internal stability. The proposed scheme is the first attempt to approach the speed tracking operation from the energy dissipation (passivity) perspective. Simulation results show good performance of the control scheme for wind speeds in different operating regimes.