Robust Digital Control Research Articles

Robust Attitude Control of a Communication Satellite with Large-scale Flexible Antennas

AbstractNew approach for modelling a physical hysteresis damping the flexible spacecraft structure oscillations, is developed. New results on communication satellite attitude guidance and digital robust control with precise pointing the large-scale flexible antennas, are presented.

Current control of a PWM power amplifier by an approximate 2-degree-of-freedom digital controller

There is a need for robust current control of a pulse width modulation (PWM) power amplifier whose transient response characteristics do not deteriorate with extensive load changes and/or direct-current power supply voltage changes. In this article, we propose a digital robust controller with bumpless mode switching to control the current of a PWM power amplifier to satisfy the demands and extend the range of an inductive load width. It is necessary to measure the value of the load in order to implement this bumpless mode switching automatically depending on the load range. Therefore, a method of estimating the inductive load is shown. The bumpless mode switching is automatically performed by estimating an inductive value without specifying the value of the inductive load beforehand. That is, the value of the inductive load is estimated during the DDC execution, and the control mode is automatically switched bumplessly according to this estimated value. A digital controller equipped with inductance estimation and bumpless mode switching is realized by a DSP. Some experiments show that the digital controller with the proposed bumpless mode switching can satisfy larger specifications.

Robust digital control of fuzzy systems with parametric uncertainties: LMI-based digital redesign approach

This paper presents a new intelligent digital redesign (IDR) method for uncertain nonlinear systems which are represented by a Takagi–Sugeno (T–S) fuzzy model. The term IDR involves converting an analog controller into an equivalent digital one in the sense of state-matching. The IDR problem can be reduced to finding the digital fuzzy gains minimizing the norm distance between the closed-loop states of the analog and digital control systems. The uncertainties in the plant dynamics are considered in the IDR condition that plays an important role in the performance improvement. Also, the robust stability is well guaranteed in the proposed IDR procedure. Its constructive conditions are expressed as linear matrix inequalities (LMIs). Two numerical examples, the chaotic Lorenz system and the Qi system, are demonstrated to visualize the feasibility of the proposed methodology.

Automatic Multi-Operation Bumpless Mode Switching Type Digital Controller for PWM Power Amplifier Using Load Estimation

Robust PWM power ampli¯ers whose transient response characteristics do not deteriorate against an extensive load change and/or direct-current power supply voltage change are needed. A digital robust controller with bumpless mode switching for PWM power amplifiers which can satisfy such demands has been proposed. In this paper a multi-stage switchingtype digital controller is proposed for spreading capacitance load range more and improving transient characteristics for inductance load. In the previous proposed controller, the con¯guration of the controller is the same to all loads. At inductance load, there is a possibility that the transient characteristics may become bad and the speci¯cation may not be satisfied. Therefore, a load current is estimated at inductance load, and the controller which also uses load current for feedback is con¯gured. A inductance is estimated and a controller is switched to this controller bumplessly. In order to extend the range of capacitance load, a controller is increased from two stage to three stage, and these are switched to each other bumplessly. A DSP is implemented to this digital controller. It is demonstrated from experiments that the multi-stage switching type digital controller is realizable and the given speci¯cations are atisfied.

Digital Robust Control for DC-DC Converter with Second-Order Differential Characteristics

Robust DC-DC converter which can covers extensive load changes and also input voltage changes with one controller is needed. The demand to suppressing output voltage changes becomes still severer. We proposed an approximate 2DOF digital controller which realizes the startup response and dynamic load response independently. The controller makes the control bandwidth wider, and at the same time makes a variation of the output voltage small at sudden changes of loads and input voltages. In this paper, a new approximate 2DOF digital control system with additional zeros is proposed. Using additinal zeros second-order differential transfer characteristics between equivalent disturbances and an output voltage are realized. Therefore the new controller makes variations of the output voltage smalerl at sudden changes of loads and input voltages. This controller is actually implemented on a DSP and is connected to a DC-DC converter. Experimental studies demonstrate that this type of digital controller can satisfy given severe specifications.

스마트 스페이스 구축을 위한 강인 지능형 디지털 제어기 개발

본 논문에서는 강인 디지털 제어기를 통한 스마트 스페이스의 안정도에 대해 논의하고자 한다. 제안된 제어기 설계 방법은 지능형 디지털 재 설계 기법을 적용하는 것이다. 좀 더 구체적으로, 불확실성 및 비선형성이 포함된 아날로그 시스템을 Takagi-Sugeno 퍼지 모델을 사용하여 나타낸다. 그리고 전역적 지능형 디지털 재 설계를 위하여 해당 문제를 볼록 최적화 관점으로 변환 한 후, 에러가 가질 수 있는 놈의 영역을 최소화하여 상태 정합을 이루고자 하였다. 전역적 접근을 통해 정리된 식은 선형 행렬 부등식으로 나타나게 된다. 마지막으로, 설계된 제어기를 HVAC (Heating, ventilating, and air conditioning) 시스템에 적용함으로써 효율성을 입증하고자 한다. In this paper, we concern the stability of smart space by using the robust digital controller. The proposed methodologies are based on the intelligent digital redesign (IDR). More precisely, we represent the nonlinear and uncertain analog system as the Takaki-Sugeno (T-S) fuzzy model. Then the IDR problem can be reduced to find the digital gains minimizing the norm distance between the closed-loop states of the analog and digital control. Its constructive conditions are expressed as the linear matrix inequalities (LMIs). At last, a numerical example, HVAC system, is demonstrated to visualize the feasibility of the proposed methodology.

Robust Control for Output Voltage Across Load of DC-DC Converter Matching with Remote Sensing

If the lines which connect the output terminal of DC-DC converter and the load are long, the voltage actually across load will be changed largely to produce the voltage drops by the impedances of the lines. Then, the terminal which senses the voltage across load is prepared apart from the output terminal of DC-DC converter, and it leads to the load, and the voltage across load is adjusted so that it is not changed largely. This method is called remote sensing. When the lines becomes long, the usual method of adjusting the voltage across load cannot suppress enough the change of it. In this paper, the robust digital controller for suppressing the change of the voltage across load is proposed. Experimental studies using DSP demonstrate that this type of digital controller is effective to suppress it.

A Practical Loop Shaping Design Procedure with Classical Control Criteria and Its Application to Hard Disk Drives

This paper is concerned with integration of classical control criteria into the H∞ robust control design with the use of the HInfin; Loop Shaping Design Procedure (LSDP) by McFarlane and Glover. Classical control criteria such as gain crossover frequency and phase margin still play important roles to designing and evaluating feedback control systems in practical applications including Hard Disk Drives (HDDs) where empirical knowledge has great importance. The systematic use of the robust control design has been tried in industry. However, it has yet to be fully adopted simply because of the familiarity with the classical control criteria. In this paper, we will propose a way to design digital robust control systems with the use of the LSDP in which we can specify the classical control criteria. Application to HDDs will be demonstrated with a set of simulations to validate the proposed method.

Digital robust control of a variable speed pitch regulated wind turbine for above rated wind speeds

This paper presents the design of a robust R – S – T controller of a variable speed pitch regulated wind turbine (VSPRWT) for above rated wind speeds (ARWS). An introduction of the subject and a state of the art review for controllers in ARWS are carried out. Afterwards, the studied VSPRWT and its validated model are presented. Then, the operating zone and control scheme are described. This system is non-linear and its linearising allows for the analysis of its behaviour, thereby obtaining the discrete-time control model as well as defining the controller's concrete objectives. The digital controller, which is designed following the pole assignment with sensitivity function shaping method, provides satisfactory simulation trial results.

완화된 안정도 조건을 갖는 강인한 디지털 퍼지 제어기 설계: 전역적 디지털 재설계 접근법

This paper presents the development of digital robust fuzzy controller for uncertain nonlinear systems. The proposed approach is based on the intelligent digital redesign(IDR) method with considering the relaxed stability condition of fuzzy control system. The term IDR in the concerned system is to convert an existing analog robust control into an equivalent digital counterpart in the sense of the state-matching. We shows that the IDR problem can be reduced to find the digital fuzzy gains minimizing the norm distance between the closed-loop states of the analog and digital robust control systems. Its constructive conditions are expressed as the linear matrix inequalities(LMIs) and thereby easily tractable by the convex optimization techniques. Based on the nonquadratic Lyapunov function, the robust stabilization conditions are given for the sampled-data fuzzy system, and hence less conservative. A numerical example, chaotic Lorentz system, is demonstrated to visualize the feasibility of the proposed methodology.

QFT control based on zero phase error compensation for flight simulator

Abstract To improve the robustness of high-precision servo systems, quantitative feedback theory (QFT) which aims to achieve a desired robust design over a specified region of plant uncertainty is proposed. The robust design problem can be solved using QFT but it fails to guarantee a high precision tracking. This problem is solved by a robust digital QFT control scheme based on zero phase error (ZPE) feed forward compensation. This scheme consists of two parts: a QFT controller in the closed-loop system and a ZPE feed-forward compensator. Digital QFT controller is designed to overcome the uncertainties in the system. Digital ZPE feed forward controller is used to improve the tracking precision. Simulation and real-time examples for flight simulator servo system indicate that this control scheme can guarantee both high robust performance and high position tracking precision.

ROBUST GYROMOMENT SPACECRAFT ATTITUDE CONTROL WITH PRECISE POINTING A FLEXIBLE ANTENNA

New approach for modeling a physical hysteresis damping the flexible spacecraft structure oscillations, is developed. New results on spacecraft attitude guidance and digital robust control with precise pointing the large-scale flexible antennas, are presented.

Nonlinear robust digital controller based on fuzzy model for homing missiles

This paper utilizes Takagi and Sugeno’s fuzzy model to approximate the nonlinear homing missile–target dynamics. On the basis of Takagi and Sugeno’s fuzzy model we construct a robust digital controller to handle the missile for intercepting the unpredictable maneuvering target. The derived stability conditions are also proposed to support the stability of the digital closed-loop systems. An example is given to demonstrate the efficiency of the proposed missile digital controller.

Robust digital controllers for uncertain chaotic systems: A digital redesign approach

In this paper, a new and systematic method for designing robust digital controllers for uncertain nonlinear systems with structured uncertainties is presented. In the proposed method, a controller is designed in terms of the optimal linear model representation of the nominal system around each operating point of the trajectory, while the uncertainties are decomposed such that the uncertain nonlinear system can be rewritten as a set of local linear models with disturbed inputs. Applying conventional robust control techniques, continuous-time robust controllers are first designed to eliminate the effects of the uncertainties on the underlying system. Then, a robust digital controller is obtained as the result of a digital redesign of the designed continuous-time robust controller using the state-matching technique. The effectiveness of the proposed controller design method is illustrated through some numerical examples on complex nonlinear systems––chaotic systems.

Robust digital control of a wind turbine for rated-speed and variable-power operation regime

The design of a double-loop robust digital control algorithm for a wind turbine (WT) containing a doubly-fed induction machine is presented. The operating zone considered is that obtained when the rotational speed is limited to its rated value and the generated electricity has not reached its corresponding rated value. It is not particularly easy to find descriptions of controllers for this working zone in the existing literature. The rotational sampling effect may produce drive-train torque oscillations when a WT operates at constant speed. Consequently, its control system, which consists of two levels of control loops, has to be able to address these oscillations and be able to minimise flicker emission and dynamical loads in the drive train. These specifications, along with the robustness of the synthesised controller, lead to a reduced cost for the generated electricity and to a higher power quality, compared to those obtained using more classical WT control strategies that do not account for the peculiarities of the considered operation zone. The inner control loops govern the machine electromagnetic torque. The outer control-loop is synthesised using the discrete pole-placement with sensitivity function shaping method, to keep the rotational speed at its rated value and to reduce electromagnetic torque oscillations. The designed and synthesised control algorithms are tested on a simulation model validated using field data. Simulation results show that the proposed regulator reduces both flicker emission and dynamical drive-train loads, when compared to a classical PI regulator tuned to show an identical cut-off frequency and integral action.

615 非共振型超音波モータを用いた精密ステージの高速モーション制御

This paper proposes a robust digital controller for a high precision stage using a synchronous piezoelectric device driver to attain both high speed and high accuracy. The proposed controller consists of three elements: a friction compensator, a robust feedback controller, and a continuous path tracking system. The friction compensator based on the well-known static model compensates for the nonlinear characteristic of friction. Stability of the high precision stage is provided by the robust feedback controller based on the doubly coprime factorization and the disturbance observer. The tracking performance is further increased by the continuous path tracking system. The effectiveness of the proposed controller is evaluated through experimental results of SPIDER (synchronous piezoelectric device driver) system with an additional load of 20kg.

Structural-parametric synthesis of the digital robust flight control system

The paper is devoted to the synthesis of the digital controller for a system with stochastic disturbances and incomplete measurements of the state vector. Then parametric robust optimization of obtained system is conducted to achieve stabilization and acceptable performance for nominal and parametrically disturbed plants using the same controller. Research is performed at the example of the small Unmanned Aerial Vehicle flight control system.

Robust Digital Control for Multi-Machine Power Systems with Data Transmission Delays

In this paper for a multi-machine power system equipped with Unified Power Flow Controller a robust digital control is designed. Data transmission delays are considered during the design. The main source of uncertainty considered is one line outage of double circuit transmission line. Numerical simulations show that the proposed control can stabilize the system under sever fault conditions.

Design of a robust PWM power amplifier using approximate two‐degree‐of‐freedom digital integral‐type control only with voltage feedback

AbstractThere is a need for robust PWM power amplifiers whose transient response characteristics do not deteriorate in the presence of extensive load variation and/or direct‐current power‐supply voltage variation. In this paper, a methodology is proposed for designing a digital robust controller using only voltage feedback for PWM power amplifiers which can satisfy such demands. The controlled object (PWM power amplifier) is represented by a discrete‐time system with consideration of input dead‐time and the conversion of current feedback to voltage feedback. First, a model matching system using only voltage (output) feedback is created for this controlled object. Next, it is shown that an approximate two‐degree‐of‐freedom digital robust control system can be created by connecting the robust compensator obtained by approximating this model matching system. Furthermore, it is shown that a digital integral‐type controller using only voltage feedback is obtained by equivalent transformation. Methods for determining the parameters of the LC filter and the controller, and a sampling time which satisfies design specifications are shown. Finally, it is verified by simulation and experiment that all the given specifications are satisfied by the proposed digital controller and that the design method with consideration of input dead‐time is useful. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(6): 1–12, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10110

Pole placement with sensitivity function shaping using 2nd order digital notch filters

This technical note deals with the design of robust digital controllers using pole placement with sensitivity shaping by means of the use of digital notch (band-stop) filters. The use of this type of filters drastically simplifies the effective shaping of the sensitivity functions and the resulting procedure competes with the procedure based on the use of Q-parameterization combined with convex optimization (Automatica 35 (1999) 1111). The feasibility of the technique is illustrated by its application to the control of a very flexible arm.