Equivalent Disturbance Research Articles

Seek Control for Head Positioning Mechanism with Contact Slider

This paper discusses the seek control for head positioning mechanism with a contact slider in hard disk drives (HDDs).In General, to increase the control force is the most popular step used to decrease the seek time; it often results however in transient vibration of HDDs that has start and stop motion. For high-speed, high-precision seeking mechanisms, it is necessary to apply control methods which induce no residual vibration at a target track even with a large control force. The proposed positioning control system consists of two-degrees-of-freedom controller. The optimal point-to-point (PTP) control with a frequency-shaped weighting function is employed in feedfoward input design to eliminate vibratory responses due to mechanical vibration modes. To estimate and compensate the friction force of the contact slider generated by the contact of a disk and a slider, a equivalent disturbance estimate observer is designed. The validity of the proposed approach has been verified by long span seek simulation trials in the benchmark problems for HDDs.

Nonholonomic Equivalent Disturbance Based Backward Motion Control of Tractor-Trailer With Virtual Steering

This paper describes a strategy of backward motion control in a tractor-trailer system. The backward motion of a tractor-trailer requires skilled control, because the position and orientation of the trailer can only be controlled by an input to the tractor. When a driver changes orientation while driving backward, the steering angle must be skillfully controlled. This operation is different in the case of a single vehicle moving backward. An uncontrollable situation of a tractor-trailer motion often happens, for example, the jackknife phenomenon. Such a situation is often induced by the nonholonomic constraint of a wheeled system. In this research, virtual steering is introduced to a trailer. This virtual steering controls the orientation of the trailer and suppresses the nonholonomic equivalent disturbance. With this virtual steering, the tractor-trailer is able to track a straight trajectory in backward driving independently of the nonholonomic constraint. Several numerical and experimental results are shown to confirm the validity of the proposed approach.

Robust speed tracking of permanent magnet synchronous motor servo systems by equivalent disturbance attenuation

A new robust controller consisting of a nominal controller and a robust compensator is proposed. The controller is applied to a permanent magnet synchronous motors servo system to eliminate speed-tracking error due to time-varying load torque uncertainty and parameter perturbations. It is proved that the speed-tracking error can be made as small as desired if the initial conditions are zeros. For cases where the initial conditions are non-zero but bounded, after a finite transient period, the same speed-tracking error reduction can be achieved. Simulation results are presented to confirm the efficiency of the proposed method.

On Kalman Active Observers

The paper introduces the Active Observer (AOB) algorithm in the framework of Kalman filters. The AOB reformulates the Kalman filter to accomplish model-reference adaptive control based on: (1) A desired closed loop system. (2) An extra equation to estimate an equivalent disturbance referred to the system input. An active state is introduced to compensate unmodeled terms, providing a feedforward compensation action. (3) Stochastic design of the Kalman matrices. Stability analysis with model errors is discussed. An example of robot force control with an external and unknown nonlinear disturbance is presented (SISO system). Another example of model-matching control for steer-by-wire (SBW) vehicles with underactuated structure is discussed (MIMO system).

Front-end low-frequency switched-mode rectifier and its control for permanent-magnet synchronous-motor drive

The low-frequency switching-mode rectifier (LF-SMR) possesses the advantages of lower switching frequency, higher conversion efficiency and simpler control, and thus it is extensively utilised in domestic appliances. However, most of the existing LF-SMRs still lack robust operating performance owing to their open-loop control configuration. The development of an AC-switch based LF-SMR and its closed-loop control for PMSM drives are presented. First, the analysis, design and implementation of the power circuit are carried out. The power-circuit components are properly designed considering the compromise between some key performance parameters. Voltage-control aspects of the uncertain effects of double-frequency voltage ripple on the stable closed-loop control behaviour are first studied. On this basis, the voltage-feedback controller type is determined, and its parameters are designed according to the estimated plant model, the properly specified tracking-response requirements and the limitations of LF-SMR. Independently, to improve further the voltage-regulation conrol, an equivalent load-power disturbance is observed and used to perform the disturbance-feedforward-cancellation control. After the effectiveness of the designed LF-SMR has been confirmed, it is applied to serve as a front-end convertor for two types of permanent-magnet synchronous motor (PMSM) drives further to test its validity experimentally.

等価入力外乱推定による外乱除去性能の向上

等価入力外乱推定による外乱除去性能の向上

PID controller design for disturbed multivariable systems

A linear-quadratic-regulator-based (LQ-regulator-based) design methodology is proposed to design proportional-integral-derivative (PID) controllers for multivariable systems with load disturbances. Except for a few parameters that are preliminarily selected, most of the PID parameters are systematically tuned using the developed plant state-feedback and controller state-feedforward LQR approach, such that satisfactory performance with guaranteed closed-loop stability is achieved. In order to access the plant state variables and carry out disturbance rejection, an observer-based disturbance rejection technique is proposed, which through an 'equivalent disturbance' concept, retains the observation error to be used for disturbance compensation. This makes disturbance measurement unnecessary and the disturbance rejection tuning independent of the set-point response adjustment. A robust stability analysis is also included for the modelling error. An illustrative example is given for comparison with alternative techniques.

Robust Control System Design for Rotorcraft

A design method is developed for quantitative robust control of uncertain multivariable systems. This method is then applied for the longitudinal flight control of a rotorcraft. A multivariable equivalent external disturbance rejection design method is introduced. When this method is used, the maximum variations of the system tolerance and the maximum variations of the uncertain plant can be transferred to an equivalent disturbance. This equivalent external disturbance rejection design method is employed to achieve the quantitative robust performance for uncertain multivariable systems. The design method is then applied to the robust control design of a rotorcraft flight control system with various flight conditions and shows that it achieves satisfactory robust performance.

PARAMETRIC IDENTIFICATION FOR ROBUST FAULT DETECTION

The work presents some simulation results concerning the application of robust model–based fault diagnosis to an industrial process by using identification and disturbance de–coupling techniques. The first step of the considered approach identifies several equation error models by means of the input–output data acquired from the monitored system. Each model describes the different working conditions of the plant. In particular, the equation error term of the identified models takes into account disturbances (non–measurable inputs), non–linear and time–invariant terms, measurement errors, etc. The next step of this method exploits state–space realization of the input–output equation error models allowing to define several equivalent disturbance distribution matrices related to the error terms. Moreover, in order to achieve good robustness properties for a process normally working at different operating points, a single optimal equivalent disturbance distribution matrix is selected. Finally, eigenstructure assignment method for robust residual generation and disturbance de–coupling can be successfully exploited for the fault diagnosis of the dynamic process. The fault diagnosis procedure is applied to a benchmark simulation of a gas turbine process.

Applied hydrodynamic wave-resistance computation by Fourier transform

An applied Fourier transform computation for the hydrodynamic wave-resistance coefficient is shown, oriented to potential flows with a free surface and infinity depth. The presence of a ship-like body is simulated by its equivalent pressure disturbance imposed on the un-perturbed free surface, where a linearized free surface condition is used. The wave-resistance coefficient is obtained from the wave-height downstream. Two examples with closed solutions are considered: a submerged dipole, as a test-case, and a parabolic pressure distribution of compact support. In the three dimensional case, a dispersion relation is included which is a key resource for an inexpensive computation of the wave pattern far downstream like fifteen ship-lengths.

Quantitative feedback synthesis of sampled-data systems with time-delay by approximate Z-transform

In this paper, the equivalent disturbance rejection (EDR) in QFT design methodology is proposed for dealing with sampled-data systems with time-delay. This EDR is mainly to overcome the non-minimum phase zero generated by the first order Pade' approximation of the time-delay factor. Due to plant parameter uncertainty, the analogue controller is to be designed so that the system response lies within permissible bounds. By approximate Z-transform, the analogue controller can be transformed directly into a digital one and then the analogue plant is transformed into the digital plant, with sampling time as a free parameter. By adjusting the sampling time, the uncertain sampled-data system can be stabilized. In comparison with other approaches, our design framework is much more systematic by using only algebraic manipulations and transparent enough to guide the designer to realize the physical controller for the plant with prescribed bounds on its parameters.

Linear QFT control of a highly nonlinear multi‐machine power system

AbstractA quantitative feedback theory (QFT) method of Horowitz, treating nonlinearities as equivalent disturbances, is applied to the linear control of a multi‐machine power system. This system has a smooth nonlinear dynamics so the original approach was simplified. From the design point of view good results were obtained with simple controllers (automatic voltage regulator, speed governor, power system stabilizer) when the power system was affected by large load variations and short circuits. To reduce significantly the steady state errors which appeared, a novel rotor speed error amplification scheme was employed. This increased the autonomy of the controlled power system to combat big distortions from normal operating conditions. Copyright © 2001 John Wiley & Sons, Ltd.

Optimal design of robust quantitative feedback controllers using random optimization techniques

Quantitative design of robust control systems proposes a transparent and practical controller design methodology for uncertain single-input single-output and multivariable plants. There are several steps involved in the design of such controllers. The main steps involved in the design are template generation, loop shaping and pre-filter design. In the case of multivariable uncertain plants, manipulation of tolerance bounds within the available freedom, for both sequential and non-sequential designs, consideration of template size of next step in sequential design, and the appropriate selection of the nominal transfer function matrices in the equivalent disturbance attenuation design are also crucial steps. In all the quantitative designs, a time-consuming trial-and-error procedure is adapted and a successful compromise between various design requirements is very much dependent on the designer experience and expertise. In this paper, these steps are reformulated in terms of different cost functions, and it is shown that the optimization of these cost functions leads to an optimal design of quantitative controllers, for both single input single output and multivariable plants. This proposes a nonlinear constrained optimization problem that can be easily solved using any of the random optimization techniques. Simulation results are used to show the effectiveness of the proposed method.

Strong tracking filter based adaptive generic model control

Generic Model Control (GMC) is a control algorithm capable of using nonlinear process model directly. Parameters in GMC controllers are easily tuned, and measurable disturbances can be compensated effectively. However, the existence of large modeling errors and unmeasurable disturbances will make the performance of GMC deteriorate. In this paper, based on the theory of Strong Tracking Filter (STF), a new approach to Adaptive Generic Model Control (AGMC) is proposed. Two AGMC schemes are developed. The first is a parameter-estimation-based AGMC. After introducing a new concept of Input Equivalent Disturbance (IED), another AGMC scheme called IED-estimation-based AGMC is further proposed. The unmeasurable disturbance and structural process/model mismatches can be effectively overcome by the second AGMC scheme. The laboratory experimental results on a three-tank-system demonstrate the effectiveness of the proposed AGMC approach.

Alluvial Burial of Gordion, an Iron-Age City in Anatolia

Geomorphic research at Gordion, an Anatolian Iron-Age city, shows alluvial burial and extensive leveling by the Sakarya River starting prior to the 4th century B.C. The aggrading river eventually buried parts of the city under 3–5 m of silt, beginning during occupation. Subsequent river movements eroded away substantial parts of the site, including 2 km of outer wall. Buried and removed parts of the site total three times the area now visible on the river plain. These alterations, not readily apparent from the surface, were not investigated during previous archaeological research.The site provides the most precise evidence to date about the Beyşehir Occupational phase, a widespread episode of sedimentation affecting SW and central Anatolia beginning in the Iron Age, apparently caused by tree-cutting and over-grazing. The likely equivalent disturbance event at Gordion extends this episode into a new region, is associated directly with an archaeological site, and has a later onset and end.Because the modern channel of the Sakarya has recently been dredged to several meters below its floodplain, Gordion provides an unusually clear display of an alluvially buried city, whose occupants made numerous responses to the rapidly changing river.

Frequency domain design method for uncertain systems under some unknown-but-bounded disturbances

A frequency domain design methodology for a linear, single-input–single-output (SISO), uncertain system with control input and states constraints under some unknown-but-bounded disturbances is developed. The maximum variation of the plant uncertainty is transferred to the values of equivalent external disturbance at the plant output with a fixed nominal plant. Similarly, the control input and states constraints, expressed in the time domain with bandwidth limitation and mapped into a set of target transfer functions, will also be treated as the equivalent external disturbances upon being transferred to the output. The maximum variation of the desired output tolerance will be determined as the fixed values at some specified frequencies. Thus, the uncertain system design problem coping with the control input and states constraints under some unknown-but-bounded disturbances will become an equivalent external disturbance rejection problem. The uncertain plant tracking problems and the problem of uncertain systems with control input and states constraints under some unknown-but-bounded disturbance are respectively provided as illustrative examples.

Design of H∞ Attitude Controllers for Spacecraft Using a Magnetically Suspended Momentum Wheel

This paper suggests a method to design a H ∞ attitude controller for a three-axis-stabilised satellite using a magnetic bearing momentum wheel (MBMW) with gimballing capability. According to our method, we can explicitly take into account non-linearity of the actuator and flexibility of appendages in order to design a high performance attitude control system. A double loops control scheme, consisting of the wheel control loop and the satellite control loop, is adopted as a method to solve problems on controllability and observability occurring in the system model. In the design of the wheel control loop, the magnetic bearing non-linearity is modelled by parameter variations and equivalent disturbances, and a structured model uncertainty matrix is used. In the satellite control loop, structural flexibility resulting from appendages attached to the satellite's main body, such as solar paddles, is considered as a model uncertainty factor causing the satellite's inertia tensor to vary in frequency domain, and an unstructured model uncertainty matrix is used. The effectiveness of the designed H ∞ controllers in improving the control performance is confirmed through computer simulations.

Frequency domain design methodology for uncertain cascaded multiple-loop systems with plant modification

Since the internal signal level increases after using a plant modification loop, Horowitz and Wang (1979, 1988) proposed a quantitative synthesis feedback design method using the bandwidth propagation effect to take care of the internal signal level. The bandwidth increase phenomenon makes it hard work to maintain internal signal level reasonably. Moreover, the noise components are most important in the high-frequency range. It is desirable to decrease loop transmission functions as fast as possible in the high-frequency range to achieve minimum sensor noise sources. In the paper, a frequency domain design methodology for uncertain cascaded multiple-loop systems with plant modification is developed. The plant uncertainties are transferred to the values of equivalent external disturbances at the plant output. Thus, the design problem will become an equivalent external disturbance rejection problem. At the same time the bandwidth propagation effect can be eliminated and loop transmission functions decrease as quickly as possible.

等価外乱トルクオブザーバの推定誤差をファジィ推論により同定したDCサーボモータのロバスト位置制御

等価外乱トルクオブザーバの推定誤差をファジィ推論により同定したDCサーボモータのロバスト位置制御

Robust control of discretized continuous systems using the theory of sliding modes

The idea of sliding mode control (SMC) as a robust control technique is utilized to control systems where the dynamics can be described by [xdot](t) = (A + ΔA)x(t) + (B + ΔB)u(t) + d(t) where ΔA, ΔB and d(t) characterize unknown plant parameters and unexpected disturbances, respectively. The analysis is described in the discrete form using the Euler operator. The proposed controller regards the influence of unknown disturbances and parameter uncertainties as an equivalent disturbance and generates a control function (estimate) to cancel their influence by the mechanism of time delay, The states of the uncertain plant are steered from an arbitrary initial state to a stable surface, s = 0, and the plant output is subsequently regulated. One feature of the control is that the sliding conditions are satisfied without the discontinuous control action used in classical SMC. It therefore retains the positive features of SMC without the disadvantage of control chattering. The controller has been studied through simulations and experiment on an NSK direct drive robot arm driven by a DC motor. The results confirm that the control is robust to disturbances and parameter variations.