Quasi-Z-Source Inverters in Renewable Power Systems Modeling

This paper is devoted to in-detail demonstrationand description of the overall functionality and deailed processes in every component of quasi-z-source voltage inverter. Expressions for currents and voltages on all elements of the circuit in standard and "shoot-trough" modes are provided. These ratios demonstrate one of the main technological advantages of the quasi-z-source topology: which is the possibility of the voltage reduction on one of the capacitor that forms the quasi-z-circuitry that led to the overall size and weight reduction of the resulting device and additional reliability increase. Matlab calculations,that are provided in the practical part of the article,fully confirmed the theoretical dependencies. At the same time, obtained practical results of the simulation demonstrated the main advantage of the quasi-impedance topology - the ability to provide a continuous current of the input source without zero pauses. That is additionally confirmed by a graphical representation of transients and the spectrum of the output voltage of the inverter. As the second topic of the article, the problem of the control system operating principle selection was discussed. As it was determined in the process of the previous research and practical modeling of the quasi-z-source inverter, providing a switching of the inverter valves on the frequency that equal to the frequency of the desired output voltage, which for the most of the world’s electrical power systems is equal to 50-60 Hz, is leading to a size and mass increase of the quasi-z-source circuitry, according to its design ratios. Additionally, such component are either not represented in the modern electronic components lineup or providing sufficient energy losses that in some design cases could neglect the voltage boost effect of the quasi-z-source circuitry implementation. To overcome discovered limitations, several PWM control methods were suggested. All of them could be divided into two groups: classic and vector PWM methods. Classic methods are based on combination of the basic PWM modulation techniques that are widely used in conventional full-bridge invertors with the insertion of the “shoot-trough” state activation mode. A model of the control system for the classical approach is offered. It is shown that the method of simple control of the state of "breakdown" is based on the placement of time intervals of the inverter in the state of "breakdown" within the normal period of operation of the bridge inverter. The only difference between the models is the inclusion of an additional constant signal exceeding the amplitude of which the carrier leads to the activation of the “shoot-trough” state.In conclusion the discussion on topic of the classic control methods implementation in up-to-date designs and possibility of its combination with a different modern approaches aimed on a quasi-z-source topology parameters modification are provided.

Enhanced solar radiation pressure model for GPS satellites considering various physical effects

Solar radiation pressure (SRP) is the dominant non-gravitational perturbation for GPS satellites. In the IGS (International GNSS Service), this perturbation is modeled differently by individual analysis centers (ACs). The two most widely used methods are the Empirical CODE orbit Model (ECOM, ECOM2) and the JPL GSPM model. When using ECOM models, a box-wing model or other a priori models, as well as stochastic pulses at noon or midnight, are optionally adopted by some ACs to compensate for the deficiencies of the ECOM or ECOM2 model. However, both box-wing and GSPM parameters were published many years ago. There could be an aging effect going with time. Also, optical properties and GSPM parameters of GPS Block IIF satellites are currently not yet published. In this contribution, we first determine Block-specific optical parameters of GPS satellites using GPS code and phase measurements of 6 years. Various physical effects, such as yaw bias, radiator emission in the satellite body-fixed − X and Y directions and the thermal radiation of solar panels, are considered as additional constant parameters in the optical parameter adjustment. With all the adjusted parameters, we form an enhanced box-wing model adding all the modeled physical effects. In addition, we determine Block-specific GSPM parameters by using the same GPS measurements. The enhanced box-wing model and the GSPM model are then taken as a priori model and are jointly used with ECOM and ECOM2 model, respectively. We find that the enhanced box-wing model performs similarly to the GSPM model outside eclipse seasons. RMSs of all the ECOM and ECOM2 parameters are reduced by 30% compared to results without the a priori model. Orbit misclosures and orbit predictions are improved by combining the enhanced box-wing model with ECOM and ECOM2 models. In particular, the improvement in orbit misclosures for the eclipsing Block IIR and IIF satellites, as well as the non-eclipsing IIA satellites, is about 25%, 10% and 10%, respectively, for the ECOM model. Therefore, the enhanced box-wing model is recommended as an a priori model in GPS satellite orbit determination.

Effect of a Constant Bias on the Nonlinear Dynamics of a Biharmonically Driven Sinusoidal Potential System

The nonlinear dynamics of an underdamped sinusoidal potential system is experimentally and numerically studied. The system shows regular (nonchaotic) periodic motion when driven by a small amplitude ([Formula: see text]) sinusoidal force (frequency [Formula: see text]). However, when the system is driven by a similarly small amplitude biharmonic force (frequencies [Formula: see text] and [Formula: see text] with amplitudes [Formula: see text] and [Formula: see text], respectively) chaotic motion appear as a function of amplitude ([Formula: see text]) of the [Formula: see text]-frequency component for a fixed [Formula: see text]. We investigate the effect of an additional constant force [Formula: see text] on the dynamics of the system in the ([Formula: see text]) space. We find that [Formula: see text] can cause chaotic motion to move to regular motion and regular motion can also become chaotic in certain ([Formula: see text]) domains.

Cosmological inflationary studying around the type IV singularity within f(T) gravity

In this paper, we investigate the effects of Type IV singularity through [Formula: see text] gravity description of inflationary Universe, where [Formula: see text] denotes the torsion scalar. With the Friedmann equations of the theory, we reconstruct a [Formula: see text] model according to a given Hubble rate susceptible to describe the inflationary era near the Type IV singularity. One obtains an interesting well-known [Formula: see text] model but with additional constant parameter [Formula: see text] staying as the Type IV singularity contribution. Moreover, we calculate the Hubble flow parameters in order to determine the dynamical evolution of the cosmological system. The results show that some of the Hubble flow parameters are small near the Type IV singularity and become singular at Type IV singularity, indicating that a dynamical instability of the cosmological system occurs at that point. This means that the dynamical cosmological evolution up to that point ceases to be the final attractor since the system is abruptly interrupted. Furthermore, by considering the [Formula: see text] trace anomaly equation, the previous result on the Type IV singularity is consolidated by the conditional instability coming from the de Sitter inflationary description of the reconstructed [Formula: see text] model. The model leads to instability strongly governed by the Type IV singularity parameter [Formula: see text] is viewed as the graceful exit from inflation. Our theoretical [Formula: see text] description based on slow-roll parameters not only confirms some observational data on spectral index and the scalar-to-tensor ratio from Planck data and BICEP[Formula: see text]/Keck-Array data, but also shows the property of [Formula: see text] gravity in describing the early and late-time evolution of our Universe.

Implementing Cost-effective Co-treatment of Domestic and Food-industrial Wastewater by Novel Methods for Estimating Industrial Load

Detection and characterization of hidden industrial inflows causing high fluctuations of the inlet load, is a challenging issue pushing plant operators for a cost-effective solution at regional wastewater treatment plants (WWTPs). On the other hand, carbon source of food industrial origin may have a good use at WWTPs facing otherwise inlet carbon source deficiency.In a case study of a regional domestic WWTP receiving seasonally organic carbon-rich discharge from a fruit juice factory, a new method combining on-site measurements and mathematical modelling was developed and successfully applied for estimating the quality and quantity of both industrial influent load and incoming domestic wastewater streams properly. The originally un-staged bioreactor system operated at low dissolved oxygen (low DO) concentration was unable to meet effluent nitrogen requirements with an additional constant risk of encouraging filament growth. A novel screening method based on special sampling campaigns for estimating carbon availability and C:N ratios of influent wastewater streams coming separately from the large catchment area, was developed and applied. Staging of the previously low DO basins into a flexible system containing non-aerated selectors proved to be efficient for enhancing both biological nitrogen removal and sculpturing appropriately settling biomass.

Comments on open string with ‘massive’ boundary term

We discuss possible definition of open string path integral in the presence of additional boundary couplings corresponding to the presence of masses at the ends of the string. These couplings are not conformally invariant implying that as in a non-critical string case one is to integrate over the one-dimensional metric or reparametrizations of the boundary. We compute the partition function on the disc in the presence of an additional constant gauge field background and comment on the structure of the corresponding scattering amplitudes.

Improvement of electric spark surfacing method

Electric spark treatment of wear-resistant coatings is one of the resource-saving technologies that improve the durability of parts of mechanisms and machines. The limitations of the use of this technology are low performance, non-continuity of the coating, high roughness, as well as limited thickness of the surfaced layer. (Research purpose) The research purpose is to study the effect of additional introduced DC voltage between the electrode and the product, as well as the effect of different brands of electrodes on the thickness of the spark coating. (Materials and methods) Conducted research on the SZ-8100 micro-welding apparatus, the source of additional input voltage was the SHE-56 laboratory autotransformer, changed the voltage in the range of 0-75 volts; as materials for the electrode used wolfram, nickel, 65G steel, VK20 metal-ceramic alloy. (Results and discussion) It was found during the spark surfacing with additionally introduced constant voltage between the electrode and the workpiece, that with increasing DC current increasing of coating thickness is observed when using the electrode made of 65G steel on modes 1 and 2, wherein the maximum thickness recorded at a current of 13-17 and 23-26 amps. It was also found that electrodes of nickel, wolfram, ВК20 showed no changes in coating thickness with increasing voltage between the electrode and the workpiece, however, at the maximum modes of operation of SZ-8100 microsurfacing apparatus (mode 3) with increasing voltage, the thickness of 65G steel, wolfram and ВК20 decreases compared to the initial state (without additional imposed voltage between the electrode and the workpiece). It was noted that the destruction of the electrode material occurs in these modes. (Conclusions) An effective electrode for increasing the thickness of the surfacing layer by introducing an additional constant voltage between the electrode and the product was an electrode made of 65G steel.

Duality for dyadic triangles

This paper is a direct continuation of the paper “Duality for dyadic intervals” by the same authors, and can be considered as its second part. Dyadic rationals are rationals whose denominator is a power of 2. Dyadic triangles and dyadic polygons are, respectively, defined as the intersections with the dyadic plane of a triangle or polygon in the real plane whose vertices lie in the dyadic plane. The one-dimensional analogues are dyadic intervals. Algebraically, dyadic polygons carry the structure of a commutative, entropic and idempotent groupoid under the binary operation of arithmetic mean. The first paper dealt with the structure of finitely generated subgroupoids of the dyadic line, which were shown to be isomorphic to dyadic intervals. Then a duality between the class of dyadic intervals and the class of certain subgroupoids of the dyadic unit square was described. The present paper extends the results of the first paper, provides some characterizations of dyadic triangles, and describes a duality for the class of dyadic triangles. As in the case of intervals, the duality is given by an infinite dualizing (schizophrenic) object, the dyadic unit interval. The dual spaces are certain subgroupoids of the dyadic unit cube, considered as (commutative, idempotent and entropic) groupoids with additional constant operations.

Duality for dyadic intervals

In an earlier paper, Romanowska, Ślusarski and Smith described a duality between the category of (real) polytopes (finitely generated real convex sets considered as barycentric algebras) and a certain category of intersections of hypercubes, considered as barycentric algebras with additional constant operations. This paper is a first step in finding a duality for dyadic polytopes, analogues of real convex polytopes, but defined over the ring [Formula: see text] of dyadic rational numbers instead of the ring of reals. A dyadic [Formula: see text]-dimensional polytope is the intersection with the dyadic space [Formula: see text] of an [Formula: see text]-dimensional real polytope whose vertices lie in the dyadic space. The one-dimensional analogues are dyadic intervals. Algebraically, dyadic polytopes carry the structure of a commutative, entropic and idempotent groupoid under the operation of arithmetic mean. Such dyadic polytopes do not preserve all properties of real polytopes. In particular, there are infinitely many (pairwise non-isomorphic) dyadic intervals. We first show that finitely generated subgroupoids of the groupoid [Formula: see text] are all isomorphic to dyadic intervals. Then, we describe a duality for the class of dyadic intervals. The duality is given by an infinite dualizing (schizophrenic) object, the dyadic unit interval. The dual spaces are certain subgroupoids of the square of the dyadic unit interval with additional constant operations. A second paper deals with a duality for dyadic triangles.

Temporal characteristics of exercise-induced diaphragmatic fatigue

There is evidence suggesting diaphragmatic fatigue (DF) occurs relatively early during high-intensity exercise; however, studies investigating the temporal characteristics of exercise-induced DF are limited by incongruent methodology. Eight healthy adult males (25 ± 5 yr) performed a maximal incremental exercise test on a cycle ergometer on day 1. A constant-load time-to-exhaustion (TTE) exercise test was conducted on day 2 at 60% delta between the calculated gas exchange threshold and peak work rate. Two additional constant-load exercise tests were performed at the same intensity on days 3 and 4 in a random order to either 50 or 75% TTE. DF was assessed on days 2, 3, and 4 by measuring transdiaphragmatic twitch pressure (Pdi,tw) in response to cervical magnetic stimulation. DF was present after 75 and 100% TTE (≥20% decrease in Pdi,tw). The magnitude of fatigue was 15.5 ± 5.7%, 23.6 ± 6.4%, and 35.0 ± 12.1% at 50, 75, and 100% TTE, respectively. Significant differences were found between 100 to 75 and 50% TTE (both P < 0.01), and 75 to 50% TTE ( P < 0.01). There was a significant relationship between the magnitude of fatigue and cumulative diaphragm force output ( r = 0.785; P < 0.001). Ventilation, the mechanical work of breathing (WOB), and pressure-time products were not different between trials ( P > 0.05). Our data indicate that exercise-induced DF presents a relatively late onset and is proportional to the cumulative WOB; thus the ability of the diaphragm to generate pressure progressively declines throughout exercise. NEW & NOTEWORTHY The notion that diaphragmatic fatigue (DF) occurs relatively early during exercise is equivocal. Our results indicate that DF occurs during high-intensity endurance exercise in healthy men and its magnitude is strongly related to the amount of pressure and work generated by respiratory muscles. Thus we conclude that the work of breathing is the major determinant of exercise-induced DF.