Adaptive Polynomial Harmonic Distortion Compensation in Current and Voltage Transformers Through Iteratively Updated QR Factorization

Measuring current and voltage harmonics has paramount importance for improving the power quality of distribution grids. However, the achieved accuracy strongly depends on the adopted instrument transformer (IT). This article proposes an adaptive technique that enables an effective compensation of both the filtering behavior and the harmonic distortion (HD) introduced by current and voltage transformers (VTs), namely the strongest nonlinear effect at low-order harmonics. The approach is based on a flexible, linear in the parameters polynomial modeling of HD in the frequency domain. Model complexity can be different from one harmonic to the other, and it is selected through an automatic iterative process to suit the nonlinear behavior at each specific harmonic order, while avoiding overfitting. In particular, the number of parameters is increased by progressively updating the QR factorization of the regressor matrix trough Householder reflections until a convergence condition is reached. Experimental tests performed on an inductive VT and current transformer (CT) highlight the effectiveness of the approach

Frequency-domain nonlinear modeling approaches for power systems components - A comparison

Harmonic simulations play a key role in studying and predicting the impact of nonlinear devices on the power quality level of distribution grids. A frequency-domain approach allows higher computational efficiency, which has key importance as long as complex networks have to be studied. However, this requires proper frequency-domain behavioral models able to represent the nonlinear voltage-current relationship characterizing these devices. The Frequency Transfer Matrix (FTM) method is one of the most widespread frequency domain modeling approaches for power system applications. However, others suitable techniques have been developed in the last years, in particular the X-parameters approach, which comes from radiofrequency and microwave applications, and the simplified Volterra models under quasi-sinusoidal conditions, that have been specifically tailored for power system devices. In this paper FTM, X-parameters and simplified Volterra approaches are compared in representing the nonlinear voltage-current relationship of a bridge rectifier feeding an ohmic-capacitive dc load. Results show that the X-parameters model reaches good accuracy, which is slightly better than that achieved by the FTM and simplified Volterra models, but with a considerably larger set of coefficients. Simplified Volterra models under quasi-sinusoidal conditions allows an effective trade-off between accuracy and complexity

A Low-Cost Approach to the Skin Effect Compensation in Cylindrical Shunts

In this paper the development of a new design solution for high-current shunt resistors is presented, which allows achieving very good accuracy while requiring a simple and low-cost manufacturing process. It is based on a solid cylinder having the voltage measurement circuit which runs through two holes drilled in the cylinder itself. Starting from the well-known expression of the current density in a cylindrical conductor, the frequency response of the shunt is obtained in closed form as a function of the geometric parameters. In turn, the positions of the voltage measurement terminals are chosen by optimizing the frequency response function over a specified range. A shunt prototype has been manufactured and its measurement performance has been evaluated. The experimental results confirm the validity of the approach and highlight the significant improvement with respect to the single-hole cylindrical shunt which has been recently proposed by the authors. The obtained measurement accuracy is noticeable when compared with the ease of manufacturing

Theory and Experimental Validation of Two Techniques for Compensating VT Nonlinearities

Inductive instrument transformers (ITs) are still the most used voltage and current sensors in power systems. Among the numerous applications that require their use, one of the most important is surely represented by harmonics measurement. In this case, the recent literature shows that, since they suffer from both a filtering behavior due to their dynamics and from nonlinear effects produced by their iron core, they can introduce errors up to some percent. This article wants to deeply investigate, in the very same experimental conditions, about the performance of two digital signal processing techniques, recently introduced for the improvement of harmonics measurements performed through ITs, namely, SINusoidal characterization for DIstortion COMPensation (SINDICOMP) and compensation of harmonic distortion through polynomial modeling in the frequency domain (PHD). These methods have been applied to two different voltage transformers, having different specifications, by using two measurement setups based on different architectures. The impact of the voltage generator employed during the identification on the achieved accuracy is theoretically and experimentally evaluated. Modified versions of SINDICOMP and PHD compensation, which are more robust against nonidealities of the measurement setup, are presented. The performances of the techniques are evaluated by adopting voltage waveforms similar to those that can be encountered during the normal operation in a real distribution grid

Hybrid injectable platforms for the in situ delivery of therapeutic ions from mesoporous glasses

Copper-containing bioactive glasses (Cu-MBGs) are attracting increasing interest as multifunctional agents for hard and soft tissue healing due to the ability of released copper ions to stimulate osteogenesis as well as angiogenesis and to impart anti-bacterial properties. The conjugation of these nanomaterials with a vehicle phase based on thermosensitive hydrogels represents an effective strategy to design non-invasive injectable devices for the in situ delivery of therapeutic ions from MBGs. In this contribution, Cu-containing MBGs were prepared by an aerosol-assisted spray-drying method (MBG_Cu 2%_SD) in the form of microspheres (surface area of ca 220m2 g−1) and through a sol-gel synthesis (MBG_Cu 2% _SG) in the form of spheroidal nanoparticles (surface area above 700m2 g−1). Both Cu-containing samples were able to release copper ions, although with different rates and percentage release. MBG_Cu 2%_SG released the total incorporated amount of Cu ions with a faster kinetics compared to MBG_Cu 2%_SD, that released approximately the 60% of copper. Cu-MBGs were incorporated with a final concentration of 20 mg/mL into a thermosensitive sol-gel system consisting of a novel amphiphilic poly(ether urethane) based on a commercialy available Poloxamer 407 (P407), with improved gelation ability, mechanical strength and stability in aqueous solution with respect to native P407. Cu-MBG-loaded hydrogels were characterised in terms of sol-to-gel transition temperature and time, injectability and stability in aqueous environment at 37 °C. The hybrid formulations showed fast gelation in physiological conditions (1 mL underwent complete sol-to-gel transition within 3–5 min at 37 °C) and injectability in a wide range of temperatures (5–37 °C) through different needles (inner diameter in the range 0.6–1.6 mm)

Hybrid injectable sol-gel systems based on thermo-sensitive polyurethane hydrogels carrying pH-sensitive mesoporous silica nanoparticles for the controlled and triggered release of therapeutic agents.

Injectable therapeutical formulations locally releasing their cargo with tunable kinetics in response to external biochemical/physical cues are gaining interest in the scientific community, with the aim to overcome the cons of traditional administration routes. In this work, we proposed an alternative solution to this challenging goal by combining thermosensitive hydrogels based on custom-made amphiphilic poly(ether urethane)s (PEUs) and mesoporous silica nanoparticles coated with a self-immolative polymer sensitive to acid pH (MSN-CS-SIP). By exploiting PEU chemical versatility, Boc-protected amino groups were introduced as PEU building block (PEU-Boc), which were then subjected to a deprotection reaction to expose pendant primary amines along the polymer backbone (PEU-NH2, 3E18 NH2/gPEU-NH2) with the aim to accelerate system response to external acid pH environment. Then, thermo-sensitive hydrogels were designed (15% w/v) showing fast gelation in physiological conditions (approximately 5 min), while no significant changes in gelation temperature and kinetics were induced by the Boc-deprotection. Conversely, free amines in PEU-NH2 effectively enhanced and accelerated acid pH transfer (pH 5) through hydrogel thickness (PEU-Boc and PEUNH2 gels covered approximately 42 and 52% of the pH delta between their initial pH and the pH of the surrounding buffer within 30 min incubation, respectively). MSN-CS-SIP carrying a fluorescent cargo as model drug (MSN-CS-SIP-Ru) were then encapsulated within the hydrogels with no significant effects on their thermo-sensitivity. Injectability and in situ gelation at 37�C were demonstrated ex vivo through sub-cutaneous injection. Hybrid Hydrogels for pH-Triggered Release in rodents. Moreover, MSN-CS-SIP-Ru-loaded gels turned out to be detectable through the skin by IVIS imaging. Cargo acid pH-triggered delivery from PEU-Boc and PEUNH2 gels was finally demonstrated through drug release tests in neutral and acid pH environments (in acid pH environment approximately 2-fold higher cargo release). Additionally, acid-triggered payload release from PEU-NH2 gels was significantly higher compared to PEU-Boc systems at 3 and 4 days incubation. The herein designed hybrid injectable formulations could thus represent a significant step forward in the development of multi-stimuli sensitive drug carriers. Indeed, being able to adapt their behavior in response to biochemical cues from the surrounding physio-pathological environment, these formulations can effectively trigger the release of their payload according to therapeutic needs

Hybrid Injectable Sol-Gel Systems Based on Thermo-Sensitive Polyurethane Hydrogels Carrying pH-Sensitive Mesoporous Silica Nanoparticles for the Controlled and Triggered Release of Therapeutic Agents

Injectable therapeutic formulations locally releasing their cargo with tunable kinetics in response to external biochemical/physical cues are gaining interest in the scientific community, with the aim to overcome the cons of traditional administration routes. In this work, we proposed an alternative solution to this challenging goal by combining thermo-sensitive hydrogels based on custom-made amphiphilic poly(ether urethane)s (PEUs) and mesoporous silica nanoparticles coated with a self-immolative polymer sensitive to acid pH (MSN-CS-SIP). By exploiting PEU chemical versatility, Boc-protected amino groups were introduced as PEU building block (PEU-Boc), which were then subjected to a deprotection reaction to expose pendant primary amines along the polymer backbone (PEU-NH2, 3E18 -NH2/gPEU–NH2) with the aim to accelerate system response to external acid pH environment. Then, thermo-sensitive hydrogels were designed (15% w/v) showing fast gelation in physiological conditions (approximately 5 min), while no significant changes in gelation temperature and kinetics were induced by the Boc-deprotection. Conversely, free amines in PEU-NH2 effectively enhanced and accelerated acid pH transfer (pH 5) through hydrogel thickness (PEU-Boc and PEU-NH2 gels covered approximately 42 and 52% of the pH delta between their initial pH and the pH of the surrounding buffer within 30 min incubation, respectively). MSN-CS-SIP carrying a fluorescent cargo as model drug (MSN-CS-SIP-Ru) were then encapsulated within the hydrogels with no significant effects on their thermo-sensitivity. Injectability and in situ gelation at 37°C were demonstrated ex vivo through sub-cutaneous injection in rodents. Moreover, MSN-CS-SIP-Ru-loaded gels turned out to be detectable through the skin by IVIS imaging. Cargo acid pH-triggered delivery from PEU-Boc and PEU-NH2 gels was finally demonstrated through drug release tests in neutral and acid pH environments (in acid pH environment approximately 2-fold higher cargo release). Additionally, acid-triggered payload release from PEU-NH2 gels was significantly higher compared to PEU-Boc systems at 3 and 4 days incubation. The herein designed hybrid injectable formulations could thus represent a significant step forward in the development of multi-stimuli sensitive drug carriers. Indeed, being able to adapt their behavior in response to biochemical cues from the surrounding physio-pathological environment, these formulations can effectively trigger the release of their payload according to therapeutic needs

A simple method for compensating harmonic distortion in current transformers: Experimental validation

Conventional current transformers (CTs) suffer from nonlinearities due to their ferromag-netic cores. On one hand, it is well-known that severe core saturation may occur because of large overcurrents or unidirectional transient components: this may substantially impact the operation of relays. On the other hand, weaker nonlinear effects are also present during regular working conditions. In particular, the spectral content of typical current waveforms is characterized by a strong fundamental term responsible for harmonic distortion affecting the frequency components at the secondary side. In turn, this has a significant impact on the accuracy that can be reached as long as current harmonics must be monitored. The target of this work is implementing a simple signal processing technique that allows compensating for this effect. The method, characterized by extremely low computational complexity, is first introduced and validated using numerical simula-tions. After this, it was tested experimentally to improve the harmonic measurement capability of inductive CTs. The achieved results highlight a noticeable reduction of errors at low-order harmonics over a wide range of primary current amplitudes. It is worth noting that the black-box approach makes the technique suitable also for compensating nonlinearities introduced by current transducers based on different operating principles. Thanks to this peculiarity and to the low computational complexity, the proposed method is suitable to be employed in power quality analyzers and merging units. In this way, high-accuracy monitoring of current harmonics in power systems can be achieved, opening the way to advanced power quality management and to the location of disturbing users

Model-based maximum power point tracking for photovoltaic panels: Parameters identification and training database collection

Module-level distributed maximum power point tracking (MPPT) represents an attractive solution for photovoltaic systems installed in dense urban areas, where panels are often subject to different solar irradiance levels. Model-based MPPT algorithms are particularly suitable for the purpose: they enable good steady-state accuracy and fast dynamics thanks to an underlying parametric model of the panel. The target of the present study is deeply investigating the estimation of the model parameters, and the collection of the training database, since they heavily affect overall performance. In this work, parameter values result by maximising energy production considering the training database; under some simplifications, it leads to a weighted least squares problem that can be easily solved. One of the main advantages is the robustness in the presence of some identification data that have been collected under partially shadowed conditions. Moreover, the possibility to gather the training database by running a perturb and observe MPPT is investigated and tested for the first time. Energy production is allowed also during this stage, thus opening the way to a periodic update of the parameters to follow degradation and time drift of the module. Experimental results show that performance is virtually the same as that obtained by computing parameters from a large set of volt-ampere characteristics

Frequency-domain modeling of nonlinear power system devices: The quasi-sinusoidal volterra approach

Studying the impact of nonlinear devices on harmonic pollution represents a very important task, especially in modern distribution grids. In this case, harmonics are produced by the large amount of power electronic devices, which is going to further increase because of the growing penetration of diffuse generation and the expected diffusion of plug-in electrical vehicles. Suitable nonlinear frequency-domain models are required for the purpose, and the frequency transfer matrixes approach is typically employed. A possible alternative approach comes out from a suitable simplification of the Volterra series. The derived models are defined by a reduced set of coefficients and they allow reaching good accuracy for a wide range of input values. The performance of this approach is evaluated through numerical simulations by predicting the input current of a bridge rectifier operating in continuous conduction mode