核电站蒸发器水位的二自由度模型驱动控制

针对核电站蒸发器水位被控对象的非自平衡、非线性等特性,传统PID控制难以获得期望的控制要求,设计了二自由度模型驱动PID(TDF MD PID)串级控制系统,并加入前馈控制,以克服蒸汽流量的影响。该方法通过PD反馈补偿器改善蒸发器水位对象的开环不稳定特性,使其达到稳定,然后进行控制。仿真结果表明,与传统串级PID相比,TDF MD PID结构简单,参数易于整定,具有快速的跟踪能力和很强的鲁棒性,有效地提高了系统的控制性能。     

ADVANCED CONTROL STRATEGIES FOR FLUIDIZED BED DRYERS

Generating the best possible control strategy comprises a necessity for industrial processes, by virtue of product quality, cost reduction and design simplicity. Three different control approaches, namely an Input-Output linearizing, a fuzzy logic and a PID controller, are evaluated for the control of a fluidized bed dryer, a typical non-linear drying process of wide applicability. Based on several closed loop characteristics such as settling times, maximum overshoots and dynamic performance criteria such as IAE, ISE and ITAE, it is shown that the Input-Ouput linearizing and the fuzzy logic controller exhibit a better performance compared to the PID controller tuned optimally with respect to the IAE, for a wide range of disturbances; yet, the relevant advantage of the fuzzy logic over the conventional nonlinear controller issues upon its design simplicity. Typical load rejection and set-point tracking examples are given to illustrate the effectiveness of the proposed approach.     

ADVANCED CONTROL STRATEGIES FOR FLUIDIZED BED DRYERS

ABSTRACT

Generating the best possible control strategy comprises a necessity for industrial processes, by virtue of product quality, cost reduction and design simplicity. Three different control approaches, namely an Input-Output linearizing, a fuzzy logic and a PID controller, are evaluated for the control of a fluidized bed dryer, a typical non-linear drying process of wide applicability. Based on several closed loop characteristics such as settling times, maximum overshoots and dynamic performance criteria such as IAE, ISE and ITAE, it is shown that the Input-Ouput linearizing and the fuzzy logic controller exhibit a better performance compared to the PID controller tuned optimally with respect to the IAE, for a wide range of disturbances; yet, the relevant advantage of the fuzzy logic over the conventional nonlinear controller issues upon its design simplicity. Typical load rejection and set-point tracking examples are given to illustrate the effectiveness of the proposed approach.     

Analysis of a predictor—regulator system

A high-performance control system called “predictor—regulator” is proposed, its governing laws are derived, and it is applied to simulated processes to evaluate its characteristics, and to real processes to demonstrate its feasibility. The proposed system is made up of a two-loop configuration[4]: a fast auxiliary loop consisting of a controller and a simple lag element, and a main loop provided with another controller operating on the process. Both the controllers are conventional PID type commercial controllers. Theoretical study reveals that, by suitable choice of the compensator parameters, the control arrangement could result in remarkably superior performance. While, for the key loads, both steady state and transient errors become practically zero with the aid of only two P-controllers, inclusion of integral action aids in achieving control against secondary (unmeasured) disturbances also. The design and performance of the regulator system are evaluated via simulation. Several practical aspects of the control problem are examined, and criteria for choosing the auxiliary lag, the modes of control, and the controller settings are established. Applicability of the technique to a wide range of processes (e.g. complex higher order and dead time processes) is also discussed. The results obtained confirm that the control approach could match combined feedforward—feedback regulation in its performance, and classical feedback in design simplicity and ease of implementation.     

A novel two-dimensional PID controller design using two-dimensional model predictive iterative learning control optimization for batch processes

It is known that the key indicators of batch processes are controlled by conventional proportional–integral–derivative (PID) strategies from the view of one-dimensional (1D) framework. Under such conditions, the information among batches cannot be used sufficiently; meanwhile, the repetitive disturbances also cannot be handled well. In order to deal with such situations, a novel two-dimensional PID controller optimized by two-dimensional model predictive iterative learning control (2D-PID-MPILC) is proposed. The contributions of this paper can be summarized as follows. First, a novel two-dimensional PID (2D-PID) controller is developed by combining the advantages of a PID-type iterative learning control (PIDILC) strategy and the conventional PID method. This novel 2D-PID controller overcomes the aforementioned disadvantages and extends the conventional PID algorithm from one-dimension to two-dimensions. Second, the tuning guidelines of the presented 2D-PID controller are obtained from the two-dimensional model predictive control iterative control (2D-MPILC) method. Thus, the proposed approach inherits the advantages of both PID control, PIDILC strategy, and 2D-MPILC scheme. The superiority of the proposed method is verified by the case study on the injection modelling process.     

区间二型模糊免疫PID在环己烷无催化氧化温度控制系统中的应用

环己烷无催化氧化过程具有非线性、多变量耦合、大时滞等特点,使用常规比例积分微分(PID)控制方案无法达到理想的控制性能。提出了一种区间二型模糊免疫PID控制器,其本质上是一种基于免疫PID的非线性控制器,利用区间二型模糊逻辑系统来逼近免疫反馈律中的非线性函数,以提升控制器处理和逼近复杂不确定非线性系统的能力。将所提出的控制器应用于环己烷无催化氧化温度控制系统,仿真结果表明该方法是有效的。     

Simplified design of proportional-integral-derivative (PID) controller to give a time domain specification for high order processes

An efficient simplified method is proposed for the time domain design of industrial proportional-integral-derivative (PID) controllers and lead-lag compensators for high order single input single output (SISO) systems. The proposed analytical method requires no trial error steps for a lead-lag compensator design in the time domain by using the root-locus method. A practical PID controller design method was obtained based on the corresponding lead-lag compensator to give a required time-domain specification. Simulation studies were carried out to illustrate the control performance of the controllers by the proposed method. The proposed PID controller and lead-lag compensator directly satisfied time domain control specifications such as damping ratio, maximum overshoot, settling time and steady sate error without trial and error steps. The suggested algorithm can easily be integrated with a toolbox in commercial software such as Matlab.     

COMPENSATOR FOR CONSTANT RELATIVE STABILITY IN PROCESS CONTROL SYSTEMS

Process control systems are designed for a closed-loop peak magnitude of 2 dB, which corresponds to a damping coefficient (ζ) of 0.5 approximately. With this specified constraint, the designer should choose and/or design the loop components to maintain a constant relative stability. However, the manipulative variable in almost all chemical processes will be the flow rate of a process stream. Since the gains and the time constants of the process will be functions of the manipulative variable, a constant relative stability cannot be maintained. Up to now, this problem has been overcome either by selecting proper control valve flow characteristics or by gain scheduling of controller parameters. Nevertheless, if a wrong control valve selection is made then one has to account for huge loss in controllability or eventually it may lead to an unstable control system. To overcome these problems, a compensator device that can bring back the relative stability of the control system was proposed. This compensator is similar to a dynamic nonlinear controller that has both online and offline information on several factors related to the control system. The design and analysis of the proposed compensator is discussed in this article. Finally, the performance of the compensator is validated by applying it to a two-tank blending process. It has been observed that by using a compensator in the process control system, the relative stability could be brought back to a great extent despite the effects of changes in manipulative flow rate.     

区间二型模糊免疫PID在环己烷无催化氧化温度控制系统中的应用

环己烷无催化氧化过程具有非线性、多变量耦合、大时滞等特点,使用常规比例积分微分(PID)控制方案无法达到理想的控制性能。提出了一种区间二型模糊免疫PID控制器,其本质上是一种基于免疫PID的非线性控制器,利用区间二型模糊逻辑系统来逼近免疫反馈律中的非线性函数,以提升控制器处理和逼近复杂不确定非线性系统的能力。将所提出的控制器应用于环己烷无催化氧化温度控制系统,仿真结果表明该方法是有效的。     

模糊自整定PID控制器的设计与仿真

制浆碱回收蒸发工段第一步就是通过蒸汽将黑液进行浓缩,蒸汽的温度控制效果对后续燃烧工段和苛化工段起着举足轻重的作用。主管道蒸汽温度控制通常具有大惯性、大延迟、时变等特性,采用常规的PID控制难以获得满意的控制效果。为此,提出一种模糊自整定PID控制器的串级控制算法,该算法很大程度上提高了主蒸汽温度的控制品质。针对隶属度函数对模糊推理模型的精度影响和控制算法的特点编写了模糊规则,并且根据动态性要求的不同,分两种情况进行比较。仿真表明,模糊自整定PID串级控制算法在整体性能上要优于传统PID串级控制。     

基于模糊控制的螺杆挤出机温度控制系统设计

以螺杆挤出机温控系统的扰动多、非线性、时变以及大滞后的特性,研究得到了智能化的控制算法,对于现场无法充分预料的情况,这种温度控制系统能够发挥重要的作用。使用Zig Bee无线传感技术可实现温度监控的远程操作,提升检测效率和水平。对远程无线温度控制系统的硬件系统进行了设计,对CC2430射频主控芯片的外围电路、温度传感电路以及温度控制电路进行设计。针对螺杆挤出机温度控制系统进行实例分析,研究结果表明:使用常规PID控制器,在阶跃信号和脉冲干扰信号作用下,系统超调量和稳定时间不能够满足螺杆挤出机温度控制的要求。使用模糊PID控制器,相比常规PID控制器的超调量和稳定时间要明显增强。以尼龙6/Ca Cl2复合材料挤出为例,分别使用常规PID控制算法和模糊控制算法进行对比分析,研究温度控制精度对产品成型质量的影响。在模糊控制算法下,三种产品(温度设置分别为240,260,280℃)的缺口冲击强度合格率比较使用常规PID控制算法时提高了6.87%,弯曲应力合格率、断裂伸长率合格率、拉伸强度合格率分别提高了8.67%,9.33%,8.77%。     

带前馈的PID控制回路的控制器性能评估

提出一种评估带前馈的PID控制回路的控制器性能的方法.该方法通过求取在最优前馈和反馈控制器作用下的最小过程输出方差,并将其与实际的输出方差比较,以评估控制器的性能,同时可以得到实现该最小方差的最优PID控制器的参数.仿真结果表明,引入前馈作用可以改善PID控制回路的性能,并且采用本文提出的评估方法可以得到一个合理的评估结果.     

化工过程多回路PID控制系统模式切换参数自整定

化工过程一般为多变量系统,但其主要控制方案为分散多回路PID常规控制。由于多变量系统内部存在不同程度的耦合作用,各控制回路之间存在相互影响,当其他回路进行手动/自动模式切换时,本回路等效被控对象将会发生突变,导致本回路的原有控制参数不能适应等效被控对象的变化,造成控制性能下降,甚至闭环系统不稳定。为避免这种情况的发生,从整个系统的角度研究控制回路模式切换时的稳定性,采用多变量频域Nyquist阵列设计法。基于对角优势下正Nyquist稳定性判据,从Gershgorin圆边界点的角度定量分析各个控制回路在模式切换前后的稳定性变化程度,从而确定各回路控制器增益的调整方向及程度,实现各回路的控制器参数在控制回路模式切换瞬间的自动整定,尽可能抵消控制回路模式切换对整个系统的扰动,保证整个系统的闭环稳定性。以Shell公司重油分馏塔的多回路PID控制系统为例,将3个PID控制回路依次投用时,根据Gershgorin圆边界点进行控制参数的自整定,闭环系统仍能保持一定的控制性能,否则闭环系统将不稳定。     

Performance assessment of cascade controllers for nitrate control in a wastewater treatment process

A cascade control strategy is proposed to the benchmark simulation model 1 (BSM1) to enhance the treatment performance of nitrogen removal in a biological wastewater treatment plant. The proposed control approach consists of two control loops, a primary outer loop and a secondary inner loop. The method has two controllers of which the primary loop has a model predictive control (MPC) controller and the secondary loop has a proportional-integralderivative (PID) controller, which is a cascade MPC-PID controller. The primary MPC controller is to control the nitrate concentration in the effluent, and the secondary PID controller is to control the nitrate concentration in the final anoxic compartment. The proposed method controls the nitrate concentrations in the effluent as well as in the final anoxic reactor simultaneously to strictly satisfy the quality of the effluent as well as to remove the effects of disturbances more quickly by manipulating the external carbon dosage rate. Because the control performance assessment (CPA) technique has the features of determining the capability of the current controller and locating the best achievable performance, the other novelty of this paper is to suggest a relative closed-loop potential index (RCPI) which updates the CPA technology into a closed-loop cascade controller. The proposed method is compared with a cascade PID-PID control strategy and the original PID controller in BSM1 and an improved performance of the suggested cascade MPC-PID controller is obtained by using the CPA approach.     

强制循环蒸发器的非线性解耦控制

强制循环蒸发器是一个多输入多输出的且回路间存在着较强耦合的强非线性的复杂化工过程。针对单纯的采用常规控制方法很难满足实际的工业要求的问题,在深入研究上述过程的动态特性的基础上,根据模型的结构特点,采用全局输入输出反馈线性化的方法实现了其解耦控制,并证明了系统的零动态稳定性。通过仿真表明采用全局输入输出反馈线性化解耦方法能够有效地解决系统的强非线性对系统带来的影响,而且还能消除密度回路与液位回路间的耦合作用,该方法对提高产品质量和提高系统的蒸发效率具有重要意义。     

不稳定时滞过程PID控制器时域直接设计法

直接在时域上设计不稳定时滞过程比例积分微分(PID)控制器.采取双回路三环节的控制结构,满足时域指标-阻尼系数的要求,并对积分增益进行优化.首先设计出满足时城指标要求的理想PID控制器,然后将微分运算等效移动到内部反馈支路,最后合并3个环节得到设定值加权PID控制嚣.仿真表明该方法是有效的,所整定的控制系统具有好的鲁棒...     

Control of pure time delay processes

The general problem of controlling a physical process with predominant time delay is analysed. An effective method of controlling such a process is proposed and successfully applied. The control scheme consists of a two-loop configuration: a fast auxiliary loop consisting of a proportional controller and a simple lag element, and a main (process) loop provided with another proportional controller operating on the process. While the auxiliary loop output acts as common feedback to both the controllers, the process output adjusts the set point of the auxiliary controller. Disturbances entering the process, for which compensation is desired, are transmitted to the auxiliary loop where a corrective action is generated even before an error appears in the controlled variable. Digital simulation study reveals that, by suitable choice of the compensator parameters, this control arrangement results in remarkably superior performance compared to other known methods of dead time control. The technique is applied to a real process having a dead time of 2·7 min to demonstrate its easy implementability and to confirm its superiority over existing control schemes.     

强制循环蒸发系统线性自抗扰解耦控制的鲁棒设计

针对强制循环蒸发系统液位与出料密度两个回路的非线性耦合问题,提出了一种基于粒子群算法的线性定常自抗扰解耦控制设计。首先通过引入虚拟控制量,将对象解耦配置为两个单输入单输出子系统,并对每个回路设计降维线性扩张状态观测器。随后,对观测器动态线性化得到的近似积分器环节进行比例控制。最后,在可能的大工况内通过粒子群算法优化控制增益耦合矩阵和比例增益。该算法使用观测器估计并补偿动态耦合部分,降低了控制器对数学模型的依赖程度;使用粒子群算法优化定常控制增益矩阵,避免了实时测量出料温度,降低了对传感测量的要求,提高了可靠性并降低了实施难度。数学仿真结果表明该算法能有效地消除液位回路和出料密度回路的耦合作用,在大工况内具有很强的鲁棒性。     

基于单片机80C51的加热炉模糊PID控制器设计

对于加热炉温度控制系统,采用传统的接触器控制已不能满足复杂工艺的控制要求。提出基于单片机的模糊PID电热炉控制器,根据炉温情况和工艺的要求,调整控制系统相应PID参数,满足快速动态响应的要求。仿真实验表明基于电热炉模糊PID温度控制超调量小、响应速度快,解决了电热炉系统智能控制问题。     

Monitoring and retuning of low-level PID control loops

In this work, we focus on the problem of monitoring and retuning of low-level proportional-integral-derivative (PID) control loops used to regulate control actuators to the values computed by advanced model-based control systems like model predictive control (MPC). We consider the case where the real-time measurement of the actuation level is unavailable, and thus PID controller monitoring has to be achieved on the basis of process state measurements. A fault detection and isolation (FDI) method involving process models and real-time process measurements is used to monitor the PID control loops and compute appropriate residuals. Once poor tuning is detected and isolated, a PID tuning method based on the estimated transfer function of the control actuator is applied to the isolated, poorly functioning PID controller. An example of a non-linear reactor–separator process operating under MPC with low-level PID controllers regulating the control actuators is used to demonstrate the approach.