Manuel Reyes

Enhanced Decoupled Double Synchronous Reference Frame Current Controller for Unbalanced Grid-Voltage Conditions

In the last few years, restrictive grid codes have arisen to ensure the performance and stability of electrical networks, which experience a massive integration of renewable energy sources and distributed generation systems that are normally connected to the grid through electronic power converters. In these codes, the injection of positive- and negative-sequence current components becomes necessary for fulfilling, among others, the low-voltage ride-through requirements during balanced and unbalanced grid faults. However, the performance of classical dq current controllers, applied to power converters, under unbalanced grid-voltage conditions is highly deficient, due to the unavoidable appearance of current oscillations. This paper analyzes the performance of the double synchronous reference frame controller and improves its structure by adding a decoupling network for estimating and compensating the undesirable current oscillations. Experimental results will demonstrate the validity of the proposed decoupled DSRF controller.

Analysis of the Power Balance in the Cells of a Multilevel Cascaded H-Bridge Converter

Multilevel cascaded H-bridge (CHB) converters have been presented as a good solution for high-power applications. In this way, several control and modulation techniques have been proposed for this power converter topology. In this paper, the steady-state power balance in the cells of a single-phase two-cell CHB is studied. The capability to be supplied with active power from the grid or to deliver active power to the grid in each cell is analyzed according to the dc-link voltages and the desired ac output voltage value. The limits of the maximum and minimum input active powers for a stable operation of the CHB are addressed. Simulation results are shown to validate the presented analysis.

Synthesis of dialkyl, diaryl and metallacyclic complexes of Ni and Pd containing pyridine, α-diimines and other nitrogen ligands: Crystal structures of the complexes cis-NiR2py2 (R=benzyl, mesityl)

Abstract The alkylation of NiCl 2 py 4 or PdCl 2 py 2 with organomagnesium or organolithium reagents affords dialkyl complexes cis -MR 2 py 2 (R=Me, CH 2 SiMe 3 , CH 2 Ph, CH 2 CMe 2 Ph, 2,4,6-C 6 H 2 Me 3 ). The methyl and trimethylsilyl derivatives undergo ligand exchange reactions with chelating nitrogen ligands (α-diimines or 2-imidoylpyridines), yielding the corresponding dialkyl derivatives in good to excellent yields. A catalytic amount of PMe 3 induces the transformation of the nickel complex Ni(CH 2 CMe 2 Ph) 2 py 2 into the metallacyclic derivative NiCH 2 CMe 2 -o- C 6 H 4 ( py ) 2 .The latter, and the related palladacycle Pd ( CH 2 CMe 2 -o- C 6 H 4 ) ( cod ) , also undergo facile ligand exchange reactions.

Digital Implementation Issues for a Three-Phase Power Converter Development Using a Repetitive Control Scheme

In this paper the digital implementation of the repetitive control scheme for the three-phase two-level power converter is investigated. The proposed controller has an outer control loop to regulate the output capacitor voltage and an inner control loop for the current tracking process, which is composed of a damping term plus a repetitive control scheme, with the aim to achieve unity power factor and low THD content at the input currents. The repetitive control scheme consists on a negative feedback array of a single delay line plus a feedforward path. The implementation in a digital signal processor of the repetitive term has some issues that are pointed out in this paper. An adaptation rule to the delay parameter of the repetitive controller is proposed in order to improve the system behavior. The experimental results have been carried out in a 30 kVA three- phase power converter prototype to illustrate the good performance of the digital implementation of the controller, including a comparative study of the system behavior under the repetitive controller with the theoretical and the modified delay parameter.

Synthesis and characterisation of rhodium(I) complexes containing the dihydrobis(pyrazolyl)borate ligands [H2B(pz′)2]. The X-ray structures of Bp*Rh(C2H4)2 and BpRh(PPh3)2 (Bp = H2B(pz)2; Bp* = H2B(3,5-Me2-pz)2

Abstract The formation and some substitution chemistry of the bis(ethylene) complexes Bp′Rh(C2H4)2 (Bp′ - Bp*; 1*; Bp′ - Bp, 1) are described. Reaction of 1* with 1 equiv. of N-donor ligands or monodentate phosphines (L) leads to the isolation of compounds of general formula Bp*Rh(C2H4)(L). Addition of an excess of amine produces the eighteen electron complexes Bp*Rh(C2H4)(L)2 whereas in the case of the PR3 ligands the second equivalent of the donor gives the disubstituted sixteen electron compounds Bp*Rh(L)2. The ethylene groups in 1* and 1 can also be replaced by carbon monoxide and tert-butyl isocyanide, affording the complexes Bp′Rh(L)2 (L - CO, CN1Bu). The solid state structures of the compounds Bp*Rh(C2H4)2 (1*) and BpRh(PPh3)2 (9) have been determined by X-ray diffraction studies. Crystals of 1* are monoclinic, space group P21/c, with a = 15.129(3), b = 17.501(3), c = 13.425(8) A, β = 111.02(4)°, V = 3318(2) A3, and Dcalc = 1.06 g cm 3 for Z = 8; R = 4.3 and Rw = 4.4. Crystals of 9 are triclinic, space group P21/c, with a = 10.281(2), b = 11.637(2), c = 17.836(8) A, α = 90.09(2), β = 95.77(2), γ = 108.410(13)°, V = 2013(2) A3, and Dcalc = 1.4 g cm 3 for Z = 2; R = 0.0302 and wR = 0.0787.

Decoupled Double Synchronous Reference Frame current controller for unbalanced grid voltage conditions

Due to the growing changes in the electrical network related to the new distributed generation scheme and the integration of renewable energy sources, new requirements for grid-connected power converters are being defined in the new grid codes. The injection of positive- and negative-sequence current components is becoming necessary for achieving new capabilities like the reactive power injection during a grid fault. This paper deals with a fundamental issue in this topic, i.e., the performance of the current controller. Classical dq controllers, which are extensively used in industrial applications, degrade its performance when both sequences are involved, as unavoidable oscillations in the dq axes appear. In this paper, a new scheme for controlling positive- and negative-sequence currents using dq controllers is proposed, based on an enhanced Double Synchronous Reference Frame (DSRF) controller. In this paper the DSRF controller is improved by adding a decoupling network which counteracts the oscillations caused by the presence of both sequences. Experimental results will demonstrate the validity of the proposed Decoupled DSRF (DDSRF) controller.

A dual-loop PI controller for a DC/DC full-bridge power converter with ZVS modulation

The analysis and design of a zero voltage switching (ZVS) full bridge DC/DC converter control is discussed in this paper. The power converter is used to regulate the output dc voltage. With this objective, the control strategy presented here is designed based in the equations that describe the output current and output voltage dynamics. The proposed controller employs a dual-loop scheme implemented with two proportional-integral blocks. The performance of the controller is verified through several simulations, showing that the voltage at the dc-link is regulated to the desired reference value ensuring a correct operation of the selected topology.

Flexible and cost effective hybrid energy storage system based on batteries and ultracapacitors

Hybrid Energy Storage Systems (HESS) can supply power more flexibility and balancing to the grid, providing a backup to intermittent renewable energy. Locally, it can improve the management of distribution networks, reducing costs and improving efficiency. In this way, it can ease the market introduction of renewables, accelerate the decarbonization of the electricity grid, improve the security and efficiency of electricity transmission and distribution, stabilize market prices for electricity, while also ensuring a higher security of energy supply. This paper will provide an overview of an hybrid energy storage solution which achieve a cost-effective integration of renewable energies, significant decreases in fuel consumptions, grid stabilization and optimized dimensioning of energy storage systems through the integration of ultracapacitors with batteries under a unique bus.

A voltage measurement based control of a SSSC

Flexible AC Transmission Systems (FACTS) offer the possibility of controlling line transmission parameters in order to optimize and enhance the system characteristics. Static Synchronous Series Compensator (SSSC) is a FACTS that can be used to modify the power flow through a transmission line. Classical SSSC control approach is based on injecting voltage in quadrature with the line current, so that only reactive power is exchanged with the transmission line in order to modify the active power flow. In this paper, a new control approach based on the grid voltage instead of the line current is proposed. Both strategies are compared theoretically. PSCAD/EMTDC simulations have been performed to validate this theory. The results demonstrate that the new control strategy exhibits better results under non-sinusoidal conditions.