Generalized characteristic ratios assignment for commensurate fractional order systems with one zero

In this paper, a new method for determination of the desired characteristic equation and zero location of commensurate fractional order systems is presented. The concept of the characteristic ratio is extended for zero-including commensurate fractional order systems. The generalized version of characteristic ratios is defined such that the time-scaling property of characteristic ratios is also preserved. The monotonicity of the magnitude frequency response is employed to assign the generalized characteristic ratios for commensurate fractional order transfer functions with one zero. A simple pattern for characteristic ratios is proposed to reach a non-overshooting step response. Then, the proposed pattern is revisited to reach a low overshoot (say for example 2%) step response. Finally, zero-including controllers such as fractional order PI or lag (lead) controllers are designed using generalized characteristic ratios assignment method. Numerical simulations are provided to show the efficiency of the so designed controllers.     

Decentralized PI/PID controllers based on gain and phase margin specifications for TITO processes

In this paper, a decentralized PI/PID controller design method based on gain and phase margin specifications for two-input-two-output (TITO) interactive processes is proposed. The decouplers are designed for systems to minimize the interaction between the loops, and the first order plus dead time (FOPDT) model is achieved for each decoupled subsystem based on the frequency response fitting. An independent PI/PID controller is designed for each reduced order decoupled subsystem to obtain the desired gain and phase margins, and the performance is verified on the original interactive system to show the effectiveness of the proposed design method for the general class of TITO systems. Simulation examples are incorporated to validate the usefulness of the presented algorithm. An experimentation is performed on the Level-Temperature reactor process to show the practical applicability of the proposed method for the interactive system.     

ZERO PHASE ERROR REAL TIME CONTROL FOR FLIGHT SIMULATOR SERVO SYSTEM

Flight simulator is an important device and a typical high performance position servo system used in the hardware-in-the-loop simulation of flight control system. Without using the future desired output, zero phase error controller makes the overall system's frequency response exhibit zero phase shift for all frequencies and a very small gain error at low frequency range can be achieved. A new algorithm to design the feedforward controller is presented, in order to reduce the phase error, the design of proposed feedforward controller uses a modified plant model, which is a closed loop transfer function, through which the system tracking precision performance can be improved greatly. Real-time control results show the effectiveness of the proposed approach in flight simulator servo system.     

基于有限带宽期望模型的超精密机床伺服跟踪控制研究

为实现超精密机床的高速高精度跟踪，提出了一种利用未来信息的有限带宽期望模型。该模型的幅频特性在期望频段内为1，其它频段内为0，在所有频段内相位滞后恒为零。系统设计中，采用了反馈+前馈补偿形式的控制器近似实现该模型。将该控制器应用于实际系统中，得到了跟踪正弦信号时系统的最大稳态跟踪误差不超过±25nm的控制精度。     

Fixed structure compensator design using a constrained hybrid evolutionary optimization approach

This paper presents an efficient technique for designing a fixed order compensator for compensating current mode control architecture of DC−DC converters. The compensator design is formulated as an optimization problem, which seeks to attain a set of frequency domain specifications. The highly nonlinear nature of the optimization problem demands the use of an initial parameterization independent global search technique. In this regard, the optimization problem is solved using a hybrid evolutionary optimization approach, because of its simple structure, faster execution time and greater probability in achieving the global solution. The proposed algorithm involves the combination of a population search based optimization approach i.e. Particle Swarm Optimization (PSO) and local search based method. The op-amp dynamics have been incorporated during the design process. Considering the limitations of fixed structure compensator in achieving loop bandwidth higher than a certain threshold, the proposed approach also determines the op-amp bandwidth, which would be able to achieve the same. The effectiveness of the proposed approach in meeting the desired frequency domain specifications is experimentally tested on a peak current mode control dc−dc buck converter.     

Position/force control with a lead compensator for PMLSM drive system

Currently, many efforts are made to simplify the control algorithms and shorten the sampling period in the applications with permanent magnet linear synchronous motors (PMLSMs). In this paper, a proportional integral derivative (PID) position/force control with a lead compensator is presented. Different from the conventional cascade control method, the position/force control strategy, with a simple control structure, directly realizes the transformation from the position reference to the drive force in the drive system. The lead compensator enlarges the phase angle margin at low frequency and improves the dynamic performance of the system. To verify the effects of the proposed control strategy, the approach is applied in a PMLSM drive system with force disturbance compensation. The results of the simulation and experiment illustrate the correctness and effectiveness of the proposed control method.     

Design of PI controllers for achieving time and frequency domain specifications simultaneously

This paper deals with the design of PI controllers which achieve the desired frequency and time domain specifications simultaneously. A systematic method, which is effective and simple to apply, is proposed. The required values of the frequency domain performance measures namely the gain and phase margins and the time domain performance measures such as settling time and overshoot are defined prior to the design. Then, to meet these desired performance values, a method which presents a graphical relation between the required performance values and the parameters of the PI controller is given. Thus, a set of PI controllers which attain desired performances can be found using the graphical relations. Illustrative examples are given to demonstrate the benefits of the method presented.     

A novel auto-tuning method for fractional order PI/PD controllers

Fractional order PID controllers benefit from an increasing amount of interest from the research community due to their proven advantages. The classical tuning approach for these controllers is based on specifying a certain gain crossover frequency, a phase margin and a robustness to gain variations. To tune the fractional order controllers, the modulus, phase and phase slope of the process at the imposed gain crossover frequency are required. Usually these values are obtained from a mathematical model of the process, e.g. a transfer function. In the absence of such model, an auto-tuning method that is able to estimate these values is a valuable alternative. Auto-tuning methods are among the least discussed design methods for fractional order PID controllers. This paper proposes a novel approach for the auto-tuning of fractional order controllers. The method is based on a simple experiment that is able to determine the modulus, phase and phase slope of the process required in the computation of the controller parameters. The proposed design technique is simple and efficient in ensuring the robustness of the closed loop system. Several simulation examples are presented, including the control of processes exhibiting integer and fractional order dynamics.     

基于Matlab设计频率法的控制系统校正环节

根据用户要求的性能指标进行自动控制系统的串联校正设计有很重要的现实意义。对于给定的线性定常系统,通常通过加入串联超前、滞后或超前滞后综合校正装置,以达到提高系统的精度和稳定性的目的。该文分别给出基于频率特性法串联校正的具体设计方法,应用Matlab对系统进行通用程序设计,并对实例进行仿真。仿真实例结果表明了此设计方法的有效性和实用性。     

基于ASTFA的广义解调方法及应用

结合自适应最稀疏时频分析（ASTFA）和广义解调的优点提出了基于ASTFA的广义解调方法。该方法首先采用ASTFA对原始信号进行分解,得到分量信号及其相位函数;然后,提取该相位函数的二次项及高次项,获得解调相位函数;之后利用解调相位函数对分量信号进行广义解调;最后对广义解调后的信号进行频域分析,提取特征信息。仿真和实验分析结果表明,基于ASTFA的广义解调方法非常适用于处理多分量频率调制信号,能够有效提取滚动轴承在变速工况下的故障特征信息。     

Modified Smith predictor based cascade control of unstable time delay processes

An improved cascade control structure with a modified Smith predictor is proposed for controlling open-loop unstable time delay processes. The proposed structure has three controllers of which one is meant for servo response and the other two are for regulatory responses. An analytical design method is derived for the two disturbance rejection controllers by proposing the desired closed-loop complementary sensitivity functions. These two closed-loop controllers are considered in the form of proportional-integral-derivative (PID) controller cascaded with a second order lead/lag filter. The direct synthesis method is used to design the setpoint tracking controller. By virtue of the enhanced structure, the proposed control scheme decouples the servo response from the regulatory response in case of nominal systems i.e., the setpoint tracking controller and the disturbance rejection controller can be tuned independently. Internal stability of the proposed cascade structure is analyzed. Kharitonov's theorem is used for the robustness analysis. The disturbance rejection capability of the proposed scheme is superior as compared to existing methods. Examples are also included to illustrate the simplicity and usefulness of the proposed method.     

相位补偿器的软件设计与实现

在控制过程中,如果控制系统是一个高阶的系统(高于1阶)．那么系统会由于相位延时造成不稳定.为了解决这一问题．就需要在控制回路中加入相位补偿器来对相位进行补偿。在本文中将介绍一种相位补偿器快速设计的方法．它通过对相位补偿系数的预估．利用MATLAB辅助快速地设计出满足实际控制需要的相位补偿器.     

Determination of all feasible robust PID controllers for open-loop unstable plus time delay processes with gain margin and phase margin specifications

This paper proposes a novel alternative method to graphically compute all feasible gain and phase margin specifications-oriented robust PID controllers for open-loop unstable plus time delay (OLUPTD) processes. This method is applicable to general OLUPTD processes without constraint on system order. To retain robustness for OLUPTD processes subject to positive or negative gain variations, the downward gain margin (GM_down), upward gain margin (GM_up), and phase margin (PM) are considered. A virtual gain-phase margin tester compensator is incorporated to guarantee the concerned system satisfies certain robust safety margins. In addition, the stability equation method and the parameter plane method are exploited to portray the stability boundary and the constant gain margin (GM) boundary as well as the constant PM boundary. The overlapping region of these boundaries is graphically determined and denotes the GM and PM specifications-oriented region (GPMSOR). Alternatively, the GPMSOR characterizes all feasible robust PID controllers which achieve the pre-specified safety margins. In particular, to achieve optimal gain tuning, the controller gains are searched within the GPMSOR to minimize the integral of the absolute error (IAE) or the integral of the squared error (ISE) performance criterion. Thus, an optimal PID controller gain set is successfully found within the GPMSOR and guarantees the OLUPTD processes with a pre-specified GM and PM as well as a minimum IAE or ISE. Consequently, both robustness and performance can be simultaneously assured. Further, the design procedures are summarized as an algorithm to help rapidly locate the GPMSOR and search an optimal PID gain set. Finally, three highly cited examples are provided to illustrate the design process and to demonstrate the effectiveness of the proposed method.     

Practical control of precision positioning mechanism with friction

This paper describes the practical control of precision positioning mechanisms with friction. In a controller design, the microdynamic characteristic of these mechanisms is taken into account. First, the behavior of an experimental mechanism immediately before stopping is examined experimentally and its characteristics, namely, the micro- and macrodynamic ones are modeled. Next, a practical control method is proposed for the mechanism. The controller is designed based on the nominal characteristic trajectory following (NCTF) controller design procedure. It consists of a nominal characteristic trajectory (NCT) and a PI compensator. The NCT is determined using an open-loop time response of the mechanism and is represented on a phase plane. The compensator is used to make the mechanism motion follow the NCT and to stop the motion at the origin of the phase plane. Although the compensator is designed based on the microdynamic characteristic, it is useful in a wide working range. The positioning performance of the system with the proposed controller is examined in comparison with those of the system with conventional PID controllers. These results prove that the system with the proposed controller has a better positioning performance than those with conventional PID controllers and its positioning resolution is higher than 50 nm.     

Delay-dependent anti-windup synthesis for stability of constrained state delay systems using pole-constraints

This paper proposes the design of anti-windup compensator gain for stability of actuator input constrained state delay systems using constrained pole-position of the closed-loop. Based on Delay-Dependent Lyapunov-Krasovskii functionals and local sector conditions, a new LMI characterization is derived that ensures closed-loop asymptotic stability of constrained state delay systems while accounting upper bound fixed state delay and largest lower bound of the system’s pole-position in the formulation of anti-windup gain. Besides, at saturation, the method significantly nullifies the inherent slow dynamics present in the system. It is shown in the comparative numerical examples that the LMI formulation draws stability with improved time-domain performance.     

A frequency response model matching method for PID controller design for processes with dead-time

In this paper, a PID controller design method for the integrating processes based on frequency response matching is presented. Two approaches are proposed for the controller design. In the first approach, a double feedback loop configuration is considered where the inner loop is designed with a stabilizing gain. In the outer loop, the parameters of the PID controller are obtained by frequency response matching between the closed-loop system with the PID controller and a reference model with desired specifications. In the second approach, the design is directly carried out considering a desired load-disturbance rejection model of the system. In both the approaches, two low frequency points are considered for matching the frequency response, which yield linear algebraic equations, solution of which gives the controller parameters. Several examples are taken from the literature to demonstrate the effectiveness and to compare with some well known design methods.     

Symbolic representation for analog realization of a family of fractional order controller structures via continued fraction expansion

This paper uses the Continued Fraction Expansion (CFE) method for analog realization of fractional order differ-integrator and few special classes of fractional order (FO) controllers viz. Fractional Order Proportional-Integral-Derivative (FOPID) controller, FO[PD] controller and FO lead–lag compensator. Contemporary researchers have given several formulations for rational approximation of fractional order elements. However, approximation of the controllers studied in this paper, due to having fractional power of a rational transfer function, is not available in analog domain; although its digital realization already exists. This motivates us for applying CFE based analog realization technique for complicated FO controller structures to get equivalent rational transfer functions in terms of the controller tuning parameters. The symbolic expressions for rationalized transfer function in terms of the controller tuning parameters are especially important as ready references, without the need of running CFE algorithm every time and also helps in the synthesis of analog circuits for such FO controllers.     

Control system design of a linear motor feed drive system using virtual friction

This paper proposes a friction compensator and a design method for control systems to improve the response characteristics of linear motor feed drive systems. The proposed friction compensator cancels the real nonlinear friction of feed drive systems by using the nonlinear friction model proposed in this study and introduces virtual linear friction to facilitate the control system design. The proposed design method enables the determination of servo gains and friction compensator parameters that lead to desirable tracking performance and disturbance rejection without many trial-and-error tuning processes. In addition, the proposed method facilitates the design of the velocity feedforward compensator by using the inverse transfer function of the velocity control loop to correct the position tracking errors for various position commands. The effectiveness of the proposed method with the friction compensator and the velocity feedforward compensator was verified in simulations and experiments using a one-axis feed drive system consisting of a rod-type linear motor and linear roller guides. The results confirmed that the proposed method enables desirable overshoot-free responses and corrects motion trajectory errors due to nonlinear friction characteristics, and the proposed velocity feedforward compensator can correct tracking errors in both constant velocity motion and circular motion.     

Adaptive filter design based on the LMS algorithm for delay elimination in TCR/FC compensators

Thyristor controlled reactor with fixed capacitor (TCR/FC) compensators have the capability of compensating reactive power and improving power quality phenomena. Delay in the response of such compensators degrades their performance. In this paper, a new method based on adaptive filters (AF) is proposed in order to eliminate delay and increase the response of the TCR compensator. The algorithm designed for the adaptive filters is performed based on the least mean square (LMS) algorithm. In this design, instead of fixed capacitors, band-pass LC filters are used. To evaluate the filter, a TCR/FC compensator was used for nonlinear and time varying loads of electric arc furnaces (EAFs). These loads caused occurrence of power quality phenomena in the supplying system, such as voltage fluctuation and flicker, odd and even harmonics and unbalancing in voltage and current. The above design was implemented in a realistic system model of a steel complex. The simulation results show that applying the proposed control in the TCR/FC compensator efficiently eliminated delay in the response and improved the performance of the compensator in the power system.     

Application of polynomial control to design a robust oscillation-damping controller in a multimachine power system

This paper addresses the application of a static Var compensator (SVC) to improve the damping of interarea oscillations. Optimal location and size of SVC are defined using bifurcation and modal analysis to satisfy its primary application. Furthermore, the best-input signal for damping controller is selected using Hankel singular values and right half plane-zeros. The proposed approach is aimed to design a robust PI controller based on interval plants and Kharitonov׳s theorem. The objective here is to determine the stability region to attain robust stability, the desired phase margin, gain margin, and bandwidth. The intersection of the resulting stability regions yields the set of k_p–k_i parameters. In addition, optimal multiobjective design of PI controller using particle swarm optimization (PSO) algorithm is presented. The effectiveness of the suggested controllers in damping of local and interarea oscillation modes of a multimachine power system, over a wide range of loading conditions and system configurations, is confirmed through eigenvalue analysis and nonlinear time domain simulation.