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Showing papers on "Describing function published in 1987"


Journal ArticleDOI
TL;DR: In this paper, the authors describe experiments in which digital processing of experimental records is used to determine viscous and Coulomb friction terms associated with a prototype electro-rheological (ER) damper.

309 citations


Proceedings ArticleDOI
21 Jun 1987
TL;DR: In this paper, three single phase current fed converters operating in pwm mode, are combined as an active power filter of 15 kVA, which behaves as an accurate, fast active filter for distortion in power networks.
Abstract: Three single phase current fed converters operating in pwm mode, are combined as an active power filter of 15 kVA. The undesired limit cycle shown by the system is eliminated by feedback loop compensation. Analog, computer and analytical models which predict remarkably similar system responses are used to investigate the technique. The analytical model involves describing function methods. The losses in the converters are modelled, and used as a feedback reference to allow losses in the system to be accurately covered from the supply. The system behaves as an accurate, fast active filter for distortion in power networks. Results illustrating this include a comparison between the system response without control loop compensation and that with control loop compensation. This is shown for the computer simulation as well as the practical system. Some more results include the response of the system to both a balanced and an unbalanced set of references in the three phases. The last results shown, illustrate the ability of the system to compensate a non-linear load.

22 citations


Journal ArticleDOI
TL;DR: A computer-aided engineering (CAE) environment for input/output characterization of highly nonlinear systems based on obtaining the sinusoidal-input describing function (SIDF) models of the nonlinear plant is presented.

18 citations


DOI
01 Mar 1987
TL;DR: In this paper, a detailed computer model for an HVDC link is developed which allows the calculation of both the DC and the AC harmonics in the steady state and the describing function for subharmonics of the firing frequency of the convertor.
Abstract: The adoption of voltage-controlled oscillator based firing systems has almost completely eliminated the harmonic instabilities experienced in early HVDC systems. However, the basic feature of such systems (equidistant firing) is adversely affected by the feedback action of the current control loop, since the direct current may contain uncharacteristic harmonics which are not filtered out by the controller. Under certain circumstances (such as an imbalance and/or a distortion in the alternating voltage, DC-or AC-side resonances near DC or AC harmonic frequencies, respectively) instabilities may occur which are characterised by oscillations synchronised with the alternating voltage, i.e. harmonic instabilities. Nonlinear control-system theory, namely the describing-function method, was used to show that these oscillations are limit cycles whose conditions of occurrence can be predicted. A detailed computer model for an hvdc link was developed which allows the calculation of both the DC and the AC harmonics in the steady state and the describing function for subharmonics of the firing frequency of the convertor. Limit cycles can be predicted by the Nichols chart technique.

6 citations


Journal ArticleDOI
TL;DR: The describing series proposed by Teodorescu (1970, 1971) allow one to compute the equivalent gain vector n of any symmetric non-linearity (non- linearity vector z) by means of a linear transformation n = Hz, where H is a constant matrix, i.e. independent of the non- Linearity shape.
Abstract: Unlike the customary describing functions, the describing series proposed by Teodorescu (1970, 1971) allow one to compute the equivalent gain vector n of any symmetric non-linearity (non-linearity vector z) by means of a linear transformation n = Hz, where H is a constant matrix, i.e. independent of the non-linearity shape. The inverse transformation z = H -1 n is useful for computing non-linear systems with desired steady-state and/or transient properties. Such transformations with constant matrices H, H -1 can be combined with a recently proposed criterion for the non-existence of limit cycles in interconnected systems (Skar et al. 1981 a, b) to yield a straightforward design technique.

4 citations


Journal ArticleDOI
M. Paluszek1
TL;DR: This note discusses the computation and application of frequency-dependent describing functions to nonlinear digital controllers once the controller has been implemented on a computer.
Abstract: Once a digital control system has been coded and implemented on a computer, simulation must usually be relied on for testing the controller. Proving that a controller is stable requires exhaustive testing. This note discusses the computation and application of frequency-dependent describing functions to nonlinear digital controllers once the controller has been implemented on a computer.

3 citations


Proceedings ArticleDOI
10 Jun 1987
TL;DR: In this article, a numerical method for the limit cycle analysis of multiloop nonlinear control systems with multiple nonlinearities is presented, where the least damped eigenvalue to the imaginary axis is sought by driving the smallest eigen value to the real axis.
Abstract: A numerical method is presented for the limit cycle analysis of multiloop nonlinear control systems with multiple nonlinearities. Describing functions are used to model the first harmonic gains of the nonlinearities. Existence of a limit cycle is sought by driving the least damped eigenvalue to the imaginary axis. The evolution of the limit cycle is studied next as a function of a critical system-parameter. It is shown that by defining a suitable error function it is possible to use both the eigenvalue as well as the eigenvector sensitivities to formulate a generalized Newton Raphson method to solve simultaneously for the updates of state variable amplitudes in a minimum norm sense. A case study involving a fifth order control system with three nonlinearities is included to illustrate the application of the method.

2 citations


Journal ArticleDOI
TL;DR: In this paper, the experimental results of an actual implementation of a robust tracking controller on a robotic manipulator are presented, where the objective is to follow a ramp reference input with zero steady state error in the presence of a disturbance and system parameter variations.

1 citations


Journal ArticleDOI
TL;DR: A new numerical method, based on an iterative technique using describing functions, has been developed for calculating and plotting jump resonance curves for single-input single-output and multi-input multi-output feedback systems.

1 citations


Journal ArticleDOI
TL;DR: In this article, a combined graphical and numerical procedure is employed to develop new computer based methods to improve the prediction of the describing function in a class of single loop nonlinear feedback systems.