Offset-Free Direct Power Control of DFIG Under Continuous-Time Model Predictive Control

This paper presents a robust continuous-time model predictive direct power control for doubly fed induction generator (DFIG). The proposed approach uses Taylor series expansion to predict the stator current in the synchronous reference frame over a finite time horizon. The predicted stator current is directly used to compute the required rotor voltage in order to minimize the difference between the actual stator currents and their references over the predictive time. However, as the proposed strategy is sensitive to parameter variations and external disturbances, a disturbance observer is embedded into the control loop to remove the steady-state error of the stator current. It turns out that the steady-state and the transient performances can be identified by simple design parameters. In this paper, the reference of the stator current is directly calculated from the desired stator active and reactive powers without encompassing the parameters of the machine itself. Hence, no extra power control loop is required in the control structure to ensure smooth operation of the DFIG. The feasibility of the proposed strategy is verified by the experimental results of the grid-connected DFIG and satisfactory performances are obtained

Offset-free feedback linearisation control of a three-phase grid-connected photovoltaic system

In this study, a state feedback control law is combined with a disturbance observer to enhance disturbance rejection capability of a grid-connected photovoltaic (PV) inverter. The control law is based on input-output feedback linearisation technique, while the existing disturbance observer is simplified and adopted for the system under investigation. The resulting control law has a proportional-integral (PI)/almost PI-derivative-like structure, which is convenient for real-time implementation. The objective of the proposed approach is to improve the DC-bus voltage regulation, while at the same time control the power exchange between the PV system and the grid. The stability of the closed-loop system under the composite controller is guaranteed by simple design parameters. Both simulation and experimental results show that the proposed method has significant abilities to initiate fast current control and accurate adjustment of the DC-bus voltage under model uncertainty and external disturbance

The negative effects of the residues of ivermectin in cattle dung using a sustained-release bolus on Aphodius constans (Duft.) (Coleoptera: Aphodiidae)

This paper reports the findings of two trials into the effects of the treatment of cattle with ivermectin slow-release (SR) bolus on the larval development of the dung beetle Aphodius constans Duft. Rectal faecal samples were collected prior to treatment and every 3 and 2 weeks in a first and second trial, respectively, and up to 156 days post-administration of the SR bolus. Faecal ivermectin concentration reached a peak at 63 days post-treatment (1427 ng$\cdot$g$^{-1}$) and ivermectin was detected up to 147 days post-treatment in the first trial (7.2 ng$\cdot$g$^{-1}$). First stage larvae of A. constans were reared with control or contaminated dung and adult beetles were counted after emergence. In the first trial, the comparison of pairwise samples showed that ivermectin prevented the development of larval A. constans until day 105, while at day 135 the rate of emergence was still significantly lower than the corresponding series of control ($p < 0.05$). In the second trial, the difference between control and treated series remained significant until 143 days post-treatment, with no emergence until 128 days post-administration of SR bolus to cattle. These results show the negative effect of ivermectin on the development of larval A. constans, even at a low concentration (38.4 ng$\cdot$g$^{-1}$). The administration of ivermectin sustained-release bolus to cattle was highly effective in killing dung beetle larvae for approximately 143 days after treatment. The results were similar when dung was obtained from a single animal kept alone, or from a blending of faecal pats obtained from a group of animals kept in field conditions during the whole trial period.Effets négatifs des résidus d'ivermectine délivrés par un bolus à diffusion lente sur la survie du coprophage Aphodius constans (Duft.) (Coleoptera: Aphodiidae). À la suite du traitement de bovins par un bolus à diffusion lente d'ivermectine (12 mg$\cdot$j$^{-1}$), deux expérimentations indépendantes ont été conduites pour en étudier les conséquences sur le développement larvaire du coléoptère coprophage Aphodius constans Duft. Des échantillons de bouse ont été prélevés avant le traitement puis régulièrement, respectivement chaque 3 et 2 semaines pour la première et la seconde expérimentation, ceci jusqu'à 156 jours après l'administration du bolus aux animaux. Les bouses utilisées ont été congelées puis stockées plusieurs mois avant leur utilisation. La concentration fécale d'ivermectine atteint un pic 63 jours après le traitement (1427 ng$\cdot$g$^{-1}$) et l'ivermectine était encore détectable dans la bouse après 147 jours (7.2 ng$\cdot$g$^{-1}$). Des larves d'A. constans ont été nourries avec de la bouse (plusieurs séries, correspondant chacune à une date après traitement) et les imagos obtenus à l'issue du développement larvaire ont été décomptés à l'émergence. Dans la première expérience (animal isolé), la mortalité des larves a été totale jusqu'à 105 jours après le traitement, tandis que 135 jours après l'administration du bolus la bouse contenait encore suffisamment d'ivermectine pour que le taux d'émergence soit significativement inférieur à celui du témoin ($p < 0.05$). Dans la seconde expérience (bouses homogénéisées provenant de plusieurs animaux traités), les différences entre séries bolus et séries témoins restaient significatives jusqu'à 143 jours après le traitement, avec une émergence nulle jusqu'à 128 jours après le traitement. Ces résultats démontrent l'effet négatif de l'ivermectine sur le développement larvaire d'Aphodius constans, même à faible concentration (38.4 ng$\cdot$g$^{-1}$). On peut considérer que l'administration d'un bolus à diffusion lente d'ivermectine a un effet négatif sur les larves de coprophages jusqu'à 143 jours après le traitement. Ces résultats sont similaires si la bouse provient d'animaux isolés ou en mélange