Fractional Systems’ Identification Based on Implicit Modulating Functions

This paper presents a new method for parameter identification based on the modulating function method for commensurable fractional-order models. The novelty of the method lies in the automatic determination of a specific modulating function by controlling a model-based auxiliary system, instead of applying and parameterizing a generic modulating function. The input signal of the model-based auxiliary system used to determine the modulating function is designed such that a separate identification of each individual parameter of the fractional-order model is enabled. This eliminates the shortcomings of the common modulating function method in which a modulating function must be adapted to the investigated system heuristically

On MPC-based Strategies for Optimal Voltage References in DC Microgrids

Modern power systems are characterized by low inertia and fast voltage dynamics due to the increase of sources connecting via power electronics and the removal of large traditional thermal generators. Power electronics are commonly equipped with fast controllers that are able to reach a desired voltage setpoint within seconds. In this paper, we propose and compare two approaches using Model Predictive Control (MPC) to compute optimal voltage references for the power electronic devices in order to minimize the losses in a DC microgrid: i) a traditional setpoint-tracking MPC which receives a previously computed optimal setpoint; ii) an economic MPC which does not require a priori computed setpoints. We show that the economic MPC outperforms the setpoint-tracking MPC in simulations with the CIGRE benchmark system when multiple load disturbances occur. Some insights and discussions related to the stability of the closed-loop system using its dissipativity properties are highlighted for both approaches

Passivity-Based Plug-and-Play Voltage and Frequency Control in Islanded Inverter-Based AC Microgrids

In this paper, we propose a decentralized scalable, plug-and-play control of voltage-source inverters (VSIs) in islanded, inverter-based AC microgrids at primary level. Particularly in islanded mode without inertia from conventional generators in the main grid, voltage and frequency stabilization must be performed exclusively by these VSIs. In contrast to existing approaches, we propose a systematic procedure that does not require the proposition of a Lyapunov function as well as avoids computationally expensive and possibly infeasible numerical optimization. It follows passivity techniques, namely interconnection and damping assignment passivity-based control (IDA-PBC) on the basis of port-Hamiltonian systems (PHSs) theory. By employing the Hamiltonian naturally obtained from the PHS approach as Lyapunov function and analyzing load dynamics, we prove microgrid-wide asymptotic voltage and frequency stability. A simulation validating our theoretical results concludes our work

'n Evaluering van hengelsensusstatistieke van vis in geselekteerde hengelwaters in Transvaal

M.Sc. (Zoology)The present investigation was conducted over a period of five years, from 1981 to 1986. The study comprised creel surveys on four selected angling waters in the Transvaal. Information obtained included the fish species caught, the numbers and mass contributed by each species towards the total catches, and the number of anglers who visited the angling waters during each month of the period of survey. This investigation was complemented by fish population studies in 1984 on each of the waterbodies concerned. The information obtained in this way was compared with results on fish populations estimates obtained during earlier studies, when use was made of mark recapture investigations of the angling fish species of these waters. In view of the dramatic changes that took ~lace in the population structures of some of these fish species over a period of 10 to 20 years, supported by recent fish catch statistics on anglers obtained during the creel survey, certain recommendations are made aimed at the improvement of the management of these and other popular angling waters in the Transvaal

Fractional Systems’ Identification Based on Implicit Modulating Functions

This paper presents a new method for parameter identification based on the modulating function method for commensurable fractional-order models. The novelty of the method lies in the automatic determination of a specific modulating function by controlling a model-based auxiliary system, instead of applying and parameterizing a generic modulating function. The input signal of the model-based auxiliary system used to determine the modulating function is designed such that a separate identification of each individual parameter of the fractional-order model is enabled. This eliminates the shortcomings of the common modulating function method in which a modulating function must be adapted to the investigated system heuristically