Showing papers by "Matias Diaz published in 2021"

Design of Efficient Off-Grid Solar Photovoltaic Water Pumping System Based on Improved Fractional Open Circuit Voltage MPPT Technique

Abstract: The main application of off-grid solar photovoltaic (SPV) systems is water extraction in rural areas where access to the grid is restricted. In this application, photovoltaic (PV) and pump system regulation are crucial to increase its overall efficiency. In this context, this work presents a simple and efficient off-grid SPV water pumping system (SPVWPS). The designed system is based on a DC-DC boost converter, a three-phase DC-AC inverter, and a three-phase induction motor (IM) coupled to the centrifugal pump. The proposed solution is operated using a control strategy that associates an improved fractional open-circuit voltage (FOCV) method for maximum power point tracking (MPPT) and closed-loop scalar control. This association avoids the use of a speed sensor/encoder and a current sensor for the IM. Finally, the effectiveness of the proposed off-grid SPVWPS and its control system for both steady-state and dynamic conditions of insolation change is verified using a 1KVA rated prototype. The relevance of the drive is also checked in various operating conditions and is found to be adequate for pumping water. Moreover, the proposed method guarantees a fast response, less oscillations around the MPP, a system efficiency of 99%, and a high flow rate due to the extraction of maximum power.

Four Jovian planets around low-luminosity giant stars observed by the EXPRESS and PPPS

Abstract: We report the discovery of planetary companions orbiting four low-luminosity giant stars with M ⋆ between 1.04 and 1.39 M ⊙ . All four host stars have been independently observed by the EXoPlanets aRound Evolved StarS (EXPRESS) program and the Pan-Pacific Planet Search (PPPS). The companion signals were revealed by multi-epoch precision radial velocities obtained in nearly a decade. The planetary companions exhibit orbital periods between ~1.2 and 7.1 yr, minimum masses of m p sin i ~ 1.8–3.7 M J , and eccentricities between 0.08 and 0.42. With these four new systems, we have detected planetary companions to 11 out of the 37 giant stars that are common targets in the EXPRESS and PPPS. After excluding four compact binaries from the common sample, we obtained a fraction of giant planets (m p ≳ 1– 2 M J ) orbiting within 5 AU from their parent star of . This fraction is slightly higher than but consistent at the 1σ level with previous results obtained by different radial velocity surveys. Finally, this value is substantially higher than the fraction predicted by planet formation models of gas giants around stars more massive than the Sun.

A pair of warm giant planets near the 2:1 mean motion resonance around the K-dwarf star TOI-2202

Abstract: TOI-2202 b is a transiting warm Jovian-mass planet with an orbital period of P=11.91 days identified from the Full Frame Images data of five different sectors of the TESS mission. Ten TESS transits of TOI-2202 b combined with three follow-up light curves obtained with the CHAT robotic telescope show strong transit timing variations (TTVs) with an amplitude of about 1.2 hours. Radial velocity follow-up with FEROS, HARPS and PFS confirms the planetary nature of the transiting candidate (a$_{\rm b}$ = 0.096 $\pm$ 0.002 au, m$_{\rm b}$ = 0.98 $\pm$ 0.06 M$_{\rm Jup}$), and dynamical analysis of RVs, transit data, and TTVs points to an outer Saturn-mass companion (a$_{\rm c}$ = 0.155 $\pm$ 0.003 au, m$_{\rm c}$= $0.37 \pm 0.10$ M$_{\rm Jup}$) near the 2:1 mean motion resonance. Our stellar modeling indicates that TOI-2202 is an early K-type star with a mass of 0.82 M$_\odot$, a radius of 0.79 R$_\odot$, and solar-like metallicity. The TOI-2202 system is very interesting because of the two warm Jovian-mass planets near the 2:1 MMR, which is a rare configuration, and their formation and dynamical evolution are still not well understood.

A Decoupled Control Strategy for a Shunt-Series Modular Multilevel Converter in Wind Energy Conversion System Applications

Abstract: In recent years, the rated power of Wind Energy Conversion Systems (WECS) has been growing significantly, to this date, reaching power ratings above 10 MW per wind turbine. Consequently, Modular Multilevel Converters appear as a proper solution to replace conventional power converter in the power conversion stage of multi-megawatts WECS. This paper abords the application of a Shunt-Series Modular Multilevel Converters that interface a single WECS with a medium-voltage AC grid. It is proposed and studied a new control strategy that enables the decoupled operation at both ports of the converter as well as enables to track the maximum power point at the generator side. Simulation results are presented to validate both the proposed topology in WECS application and the control strategy applied.

A LVRT Control Strategy for a Shunt-Series Modular Multilevel Converter in Wind Energy Conversion System Applications

Abstract: Massive wind turbines are currently under development, reaching power ratios above 12 MW and rotors diameters of 220 m. At this power ratio, wind energy conversion system must be equipped with high-power converters featuring redundancy and fault tolerance, high efficiency, controllability and grid voltage fault-ride through capabilities. Consequently, this paper presents the novel application of a Shunt-Series Modular Multilevel Converter based wind energy conversion system, and a decoupled Low Voltage Ride Through control strategy is developed. Simulations results for a 10 MVA are presented to validate the effectiveness of the proposed decoupled control strategy.

Impact of the Electrical Energy-Tariff and Vehicle-to-Grid in the Total Cost of Ownership of Electromobility Projects

Abstract: This paper evaluates the impact of the electric power tariff on the total cost of ownership of electric vehicle purchase projects. Projects are analysed comparing electric vehicles with equivalent internal combustion engines vehicles. The annual equilibrium distance, Chilean energy tariffs, government incentives, and vehicle-to-grid utilities are considered in the analyses. Additionally, the current regulation in Chile is compared with special electrical vehicle energy tariffs applied in other countries is analysed to find possible spots to make electric vehicle projects more convenient.

Modelling and control of a multi-cell converter based on Input-Parallel Output-Parallel bridge-cells with discontinuous interleaved modulation

Abstract: Multi-cell converters increase their current rating by adding more cells in parallel, if also the cells are interleaved the output THDi and input ripple get lower reducing the filter requirements. However interleaving causes circulating currents that need to be mitigated. This work proposes a model and control strategy that decouple the circulating currents from the output current under discontinuous modulation of a multi-cell converter based on Input-Parallel Output-Parallel (IPOP) bridge-cell. The discontinuous modulation eliminates the circulating current between one leg of the bridge cells. The proposed model and control are verified by simulations in Plecs.

A Power Loss Ride Through Control Strategy for Variable Speed Drives based on the Modular Multilevel Matrix Converter

Abstract: Modern variable-speed drives must be able to deal with ride-through faults with dips of 70–90% to ensure the continuity of the process without the energy store station discharge and carry out significant effects to its performance. So, the existent contingencies to such case are tripping-method from grid, robust DC-Link with higher capacitors and additional power electronic hardware. Nevertheless, they comprehend a common drawback for being costly in the industry. Therefore, the Power Loss Ride Through behaviour on variable-speed drives is an important feature which is a worst-case where the system can suffer dips near to 99% on grid. Recently, Modular Multilevel Cascade Converters have been applied in Variable-Speed Drives applications due to their capability to operate at high-power rates and features such as enhanced fault-ride through capability during critical dip voltage (e.g., 99% of amplitude) in grid. Therefore, this paper presents a control strategy based on a transition mechanism between outer control loops on the nested control of a Modular Multilevel Matrix Converter drive with the aim to improve the Power Loss Ride-Through performance through keeping the energy store station uniform and stable. Simulation results obtained using PLECS software are presented to validate the effectiveness of the proposed control strategy.

Design and implementation of dual active bridge converter with single phase shift modulation for electric vehicle charging system

Abstract: This article presents the implementation of a Dual Active Bridge converter with Single Phase Shift modulation, capable of controlling current and voltage at the converter output independently, through the design of simple PI controllers based on the model's transfer functions small phasor signal. It is validated in a 1 kW converter prototype, whose main passive components are designed and the graphs of the current and voltage controls at the output of the converter are obtained as an experimental result.

A Droop Based Control Strategy for Bidirectional Power Regulation in Hybrid ACmC Microgrids

Abstract: Hybrid Alternating Current (AC) and Direct Current (DC) microgrids have been in the spotlight in the last years because they allow connection of AC and DC resources and reduces multiple power conversion in single AC or DC microgrids. The AC and DC stages are connected through interlinking converters, which manage the power transference among both sub-microgrids using droop control strategies for each single AC or DC microgrid. This paper proposes a threestage droop control strategy to regulate the power inside the sub-microgrids at the same time that bidirectional AC-DC power transference is enabled. Simulation results obtained with a hybrid microgrid model composed of five generation units are presented to validate the effectiveness of this proposal..

An Overview of Challenges related to Power-Electronics Based Power Systems

Abstract: The Role of power electronics in the future of power system is becoming critical due to the growth in renewable energy generation and the evolution of technologies such as flexible alternating or direct current transmission systems. Consequently, electrical power systems are facing new challenges related to the reduction of inertia and increment of the requirements in terms of control and flexibility. In this context, this paper aims to facilitate future research in this subject by providing a compact overview of the main challenges of power electronic-based power systems, inertia management, stability and control issues.