实时多媒体流控中的内模控制器设计

宽带网的普及使VOD(videoondemand)的应用越来越广泛,但传输延迟的抖动影响了播放质量,传统的Smith预估控制难以消除这一缺点。考虑到网络传输过程中的各种延迟,缓冲区长度与速率模型可归结为积分时变时滞过程,本文在速率反馈控制理论框架的基础上,采用内模反馈控制技术,有效地克服了由于传输延迟和抖动对控制性能带来的不利影响,使缓冲区长度运行在一定的范围之内,以此来提高播放质量。     

The cost and performance tradeoffs of buffered memories

An analysis of the performance enhancement achieved and the incremental costs accrued in buffering (using a cache memory) memory systems is made. Buffering is found to be cost-effective even for minicomputer memories. The study indicates that the flagged registered swap algorithm is superior to three other common algorithms used. It is shown that when jobs are switched, a substantial number of memory requests are required before the buffer fills and gives a high hit ratio. It is also shown that individuaIly buffered main-memory modules can be interleaved to achieve very high system performance.     

基于模糊免疫自适应PID的汽车烘房温度控制系统

烘房温度控制是汽车涂装系统的重要环节,对汽车生产的质量、成品率等有重要影响。针对烘房温度控制系统的难点和性能要求,提出了利用模糊免疫自适应PID控制器调节烘房温度。该控制方法兼具模糊控制、免疫控制和传统PID的优点,通过实时调整PID控制器的参数来保持系统的稳定性。仿真结果表明基于自适应模糊免疫PID控制器在响应速度、抗干扰能力上都优于模糊PID控制器和传统PID控制器。该控制方法为汽车烘房温度控制提供了一种新的控制策略。     

Hard disk drive control by model based dual-rate controller. Computation saving by interlacing

This paper addresses the application of multirate control techniques to hard disk drives (HDD) single stage actuation. It applies a model-based dual-rate controller with computation saving at its implementation stage. The main goal is twofold: to study a new dual-rate control scheme in this kind of environment that, as it is known, provides the achievement of more storage space and to reach a saving in computation resources when using this specific dual-rate control. The dual-rate control is planed by considering an N times slower measurement -NT- but a faster frequency for control updating -T- being N a positive integer. The work introduces a new discrete lifting modelling step that allows to compute an exact frequency response that helps the controller implementation with computation saving by interlacing. A system output response improvement is obtained by using this methodology. A comparison with an usual single rate control including its implementation by interlacing is done based on a HDD laboratory set-up.     

Development of a novel dynamic friction model and precise tracking control using adaptive back-stepping sliding mode controller

The LuGre model which has been widely used to describe the friction phenomenon for mechanical systems consists of stiffness and viscous terms. The stiffness term of the LuGre model shows the friction torque to act linearly for the internal state of friction dynamics. Thus it cannot represent the hysteresis phenomenon of friction in the pre-sliding phase. Especially the hysteresis has the non-local memory characteristics. In this paper, the non-local memory hysteresis phenomenon is analyzed through experiments and the improved friction model using the Preisach model is proposed. In order to implement the Preisach model, the neural network algorithm is used to increase the efficiency of the Preisach algorithm. Based on the improved friction model, the adaptive back-stepping sliding mode controller (SMC) is designed to improve tracking performance in the sliding and pre-sliding phases. To evaluate the performance of the proposed friction control system, experiments are executed for a ball-screw servo system and the satisfactory results are shown.     

Torque and velocity ripple elimination of AC permanent magnet motor control systems using the internal model principle

This paper addresses the problem of torque and velocity ripple elimination in AC permanent magnet (PM) motor control systems. The torque ripples caused by DC offsets that are present in the current sensors of the motor driver and the digital-to-analog converters of the motion controller are studied and formulated mathematically. These torque ripples eventually generate velocity ripples at the speed output and degrade the system performance. In this paper the torque ripples are modeled as a sinusoidal function with a frequency depending on the motor speed. The internal model principle (IMP) is then used to design a controller to eliminate the torque and velocity ripples without estimating the amplitude and the phase values of the sinusoidal disturbance. A gain scheduled (GS) robust two degree of freedom (2DOF) speed regulator based on the IMP and the pole-zero placement is developed to eliminate the torque and velocity ripples and achieve a desirable tracking response. Simulation and experimental results reveal that the proposed GS robust 2DOF speed regulator can effectively eliminate the torque ripples generated by DC current offsets, and produce a velocity ripple-free output response.     

Discrete-time control using the quadratic performance index, implicit model following and the specific optimal policy

The term weighting the cross products of the state and control vectors in the quadratic performance index has been shown to arise in the implicit model-following technique and the specific optimal policy for the continuous control case. The discrete-time control problem is presented here.     

Access control of data in integrated voice/data CDMA systems:benefits and tradeoffs

In previous work, access control for data has been proposed as a method to ensure adequate quality of service (QoS) in an integrated voice/data CDMA system. The motivation behind access control is to schedule data packet transmissions in slots when voice activity is low and to curtail data transmissions when the voice load is heavy. In this work, the class of probabilistic access control schemes, wherein data transmissions are controlled by dynamically changing the permission probability, are considered. The trigger for changing the permission probability is a measure of the current uplink load. Perfect power control is assumed first, and the trigger for access control is the power control feasibility condition, Schemes based on prediction are analyzed. While prediction schemes are complex to implement, they do provide an upper bound for performance of access control schemes. A simple and practical access control scheme, proposed earlier in the literature, is then extended. It controls the permission probability for data based on uplink load and a 1-bit broadcast feedback to all of the mobiles. The performance of this scheme depends on the choice of three parameters. It is demonstrated that, through a combined choice of these parameters, access control can be tuned to perform as desired and to yield significant capacity gains over not using access control. Results are then extended to the case of imperfect power control, where the outage criterion is based on limiting the total received power at the base station. In this case, too, the simple control scheme is shown to work well     

Decoupling internal model control for the robust engagement of clutches

Research on the robustness of clutch engagement control is attracting considerable interest because of its wide applications in advanced powertrains. Internal model control (IMC) is advantageous because it can handle model errors and external disturbances with light computational loads. However, during clutch engagement, two control inputs (engine output torque and clutch transmitted torque) and two system outputs (driving speed and the driven part of the clutch) are coupled; moreover, the two reference inputs are considerably different. A method for directly decoupling and stabilizing multi-input multi-output systems controlled by a two-degree-of-freedom (2DOF) IMC is proposed based on the construction of V-canonical matrices. The proposed method allows simple expressions for the control algorithm to be obtained without computing an inverse matrix that is used conventionally. Two filters, considering both the reference inputs and system characteristics, are independently designed considering the decoupling operation. The simulation results show that the proposed decoupling 2DOF IMC gains a considerably less tracking error and better robustness to model error and disturbance compared to classical 2DOF IMC and model predictive control. The performance is validated via dynamometer experiments.     

Electrical performance and reliability improvement by using compositionally varying bi-Layer structure of PVD HfSi/sub x/O/sub y/ dielectric

The effect of a bi-layer structure by varying the Hf composition in Hf-silicate dielectric in improving the electrical performance and reliability of high-/spl kappa/ gate stack n-MOSFETs has been investigated. Introducing Hf-silicate with 19.5% of Hf composition at the bottom layer and 28.5% of Hf on the top of it reduces the leakage current dramatically, while it minimally sacrifices increase in equivalent oxide thickness. Moreover, the structure reduces defect generation rate under gate injection and improves breakdown voltage in comparison to the control samples. Increase in Si-O bonds at the bottom interface, decrease in Coulomb scattering, and increase in dielectric constant in the top layer have been attributed to the overall performance increase of the gate stack.     

Robust speed control of DC servomotors using modern twodegrees-of-freedom controller design

The authors propose a robust speed control system for DC servomotors based on the parametrization of two-degree-of-freedom controllers. The servosystems can dramatically improve the characteristics of the closed loop systems, i.e. the disturbance torque suppression performance and the robustness to system parameter variations, without changing the command input response. The excellent control performances obtained during laboratory experiments by using a microprocessor-based controller are shown     

Automatic flux-weakening control of permanent magnet synchronousmotors using a reduced-order controller

This study presents a novel means of designing a simple and effective position and velocity controller for permanent magnet synchronous motors (PMSM). In contrast to the conventional two-loop control methods with full-state feedback, the proposed controller does not need current information of the motor for feedback purposes. However, under normal operation the steady-state d-axis current can still be controlled to zero to minimize power dissipation. In addition, implementing a simple overmodulation strategy allows the controller to automatically generate a flux-weakening control to expand the range of operating speed when voltage saturation occurs. In addition to not depending on system parameters used by the controller, the automatically generated demagnetizing current is also optimal in the sense of minimum power dissipation that differs from the maximum output torque design or the constant power design of the general flux-weakening control methods. Simulation and experimental results show that the controller can achieve an effective speed and position control with near-minimum power dissipation, even when voltage saturation occurs     

A study of SiC Power BJT performance and robustness

This paper proposes an investigation of 1200 V rated transistors with the twofold purpose of assessing their performance and robustness under representative operational conditions and of extracting guidelines for the design of reliable multi-chip power electronics modules based on SiC technology. It includes a thorough analysis of the devices steady-state and switching characteristics, as well as the investigation of short-circuit events. Taking into account operational conditions of real applications, this study considers the dependence on ambient temperature, bias conditions and driver circuit parameters.     

Performance comparison of fused soft control/hard observer type controller with hard control/hard observer type controller for switched reluctance motors

Both soft computing (SC) and hard computing (HC) techniques are often successful for solving real-world control problems. In cases where problems could be solved by either or both methodologies, an important research problem is to find what are the advantages for fusing SC methods together with HC methods, rather than using the HC method alone. Hence, in this paper, a performance comparison is detailed for a fused soft control/hard observer type controller (where a classical or HC type observer is fused with an adaptive fuzzy or SC type controller) and a hard control/hard observer type controller (where both the observer and feedback linearization controller are classical HC types). The domain in which this comparison is made is for the sensorless speed control of switched reluctance motors (SRMs). This is because this type of motor has highly nonlinear characteristics, and the HC type controller can often be detrimentally affected by modeling inaccuracies, as well as noise. Simulation and experimental results are illustrated to show the performance comparison of the soft control/hard observer type controller and the hard control/hard observer type controller under a wide range of identical operation conditions including transient speed and torque, SRM model parameter variations, and measurement noise. It can be seen from the results that the soft control/hard observer type exhibits a better performance than the hard control/hard observer type controller.     

A method for improving the robustness of PID control

In this paper, an effective method is proposed for robust proportional-integral-derivative (PID) control that is easily implementable on commonly used equipment such as programmable logic controller (PLC) and programmable automation controller (PAC). The method is based on a two-loop model following control (MFC) system containing a nominal model of the controlled plant and two PID controllers. Basic features exhibited by the MFC structure are presented, and a technique to tune both component controllers is given. The proposed structures have been implemented in a programmable logic controller and tested on control plants with perturbed parameters. Also, the proposed control system has been checked for its performance in cases when the operation of PID controllers is based on fuzzy logic. Tuning rules for the fuzzy controllers in the presented MFC system have been proposed. Results of tests lend support to the view that the proposed control structures may find wide application to robust control of plants with time-varying parameters.     

Testing the robustness of two-boundary control policies insemiconductor manufacturing

A simulation model based on a real wafer fabrication is used to investigate the robustness of the two-boundary (TB) production control strategy to the existing uniform loading policy used in a semiconductor fab. Our findings confirm that the TB policy is the most robust of all when random interference, such as machine breakdowns and demand variations, exist. It is also observed that the performance of the wafer fabrication facility under investigation can be improved significantly in terms of reducing cycle time, decreasing work-in-progress (WIP), and cutting down inventory cost     

内模解耦控制在中央空调系统的应用

基于工业空调 PID 控制系统的温湿度控制具有耦合性、非线性和时变性,难以建立精确的数学模型的缺陷。采用将解耦理论与多变量内模控制方法相结合的控制方案,利用对象传递函数模型行列式的静态增益及次对角元素与同行相应主对角元素之商的不合理部分的逆来设计控制器,以弥补常规PID 控制在温湿度控制系统的不足。通过MATLAB进行仿真,实验结果表明：该方案既解决了温湿度耦合问题又提高了控制的精度和稳定性,增强了系统的鲁棒性和适应性,具有较好的动、静态性能。     

Sensorless speed control of nonsalient permanent-magnet synchronous motor using rotor-position-tracking PI controller

This paper presents a new velocity estimation strategy of a nonsalient permanent-magnet synchronous motor (PMSM) drive without a high-frequency signal injection or special pulsewidth-modulation (PWM) pattern. This approach is based on the d-axis current regulator output voltage of the drive system that has the information of rotor position error. Rotor velocity can be estimated through a rotor-position-tracking proportional-integral (PI) controller that controls the position error to zero. For zero and low-speed operation, the PI controller gains of rotor position tracking controller have a variable structure according to the estimated rotor velocity. In order to boost the bandwidth of the PI controller around zero speed, a loop recovery technique is applied to the control system. The proposed method only requires the flux linkage of the permanent magnet and is insensitive to parameter estimation error and variation. The designers can easily determine the possible operating range with a desired bandwidth and perform vector control even at low speeds. The experimental results show the satisfactory operation of the proposed sensorless algorithm under rated load conditions.     

Statistical studies of the robustness of the LHC main dipolemechanical structure

This paper describes two methods used to study the effect of the tolerances of the components on the structure of the LHC main dipole. The first method, called semi-statistical, is useful for the determination of the acceptable variance of the dimensions of magnet components. The second one, fully statistical, allows the study of the combined effect of many parameters. The use of these two methods allowed to evaluate with good confidence the robustness of two different dipole cross-section designs, featuring austenitic and aluminium alloy collars, respectively