Open Access
Analytical design methodology for Litz-wired high-frequency power transformers
(IEEE, 2015) Barrios Rípodas, Ernesto; Ursúa Rubio, Alfredo; Marroyo Palomo, Luis; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In the last quarter of a century, high-frequency (HF) transformer design has been one of the major concerns to power electronics designers in order to increase converter power densities and efficiencies. Conventional design methodologies are based on iterative processes and rules of thumb founded more on expertise than on theoretical developments. This paper presents an analytical design methodology for litz-wired HF power transformers that provides a deep insight into the transformer design problem making it a powerful tool for converter designers. The most suitable models for the calculation of core and winding losses and the transformer thermal resistance are first selected and then validated with a 5-kW 50-kHz commercial transformer for a photovoltaic application. Based on these models, the design methodology is finally proposed, reducing the design issue to directly solve a five-variable nonlinear optimization problem. The methodology is illustrated with a detailed design in terms of magnetic material, core geometry, and primary and secondary litz-wire sizing. The optimal design achieves a 46.5% power density increase and a higher efficiency of 99.70% when compared with the commercial one.
Open Access
Zero-loss switching in LLC resonant converters under discontinuous conduction mode: analysis and design methodology
(IEEE, 2023) Elizondo Martínez, David; Barrios Rípodas, Ernesto; Larequi, Íñigo; Ursúa Rubio, Alfredo; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Publikoa Unibertsitate
Many thriving applications where isolation is required, such as LED drivers, traction and EV fast charging, implement LLC resonant converters, particularly when voltage regulation is not required or an additional conversion stage is in charge of it. The LLC converter can be operated under discontinuous conduction mode (DCM), due to its advantages such as unregulated and sensorless operation, fixed switching frequency and voltage gain, and zero-current switching (ZCS). However, ZCS results in EMI and switching losses in the primary converter, particularly for≥1200-V devices. Alternatively, zero-loss switching (ZLS) can be accomplished by means of a proper design of the LLC converter, overcoming the drawbacks of ZCS. The focus of this paper is to perform an exhaustive research on the LLC converter under DCM-ZLS: discontinuous conduction mode with lossless switching in the primary and secondary sides. As a result of this analysis, a set of design boundaries are deduced for parameters such as the magnetizing inductance, the leakage inductance, and the gate resistance. A comprehensive, step-by-step design methodology is proposed and applied to a 18-kW, 200-kHz test bench. The designed parameters are implemented in the converter and several experiments are conducted, including a test at rated input voltage and rated power (600 V, 18 kW). The conduction states studied theoretically in the analysis of the LLC converter are identified in the experimental results, and the operation of the test bench under DCM-ZLS is verified.
Open Access
Asymmetrical firing angle modulation for 12-pulse thyristor rectifiers supplying high-power electrolyzers
(IEEE, 2023) Iribarren Zabalegui, Álvaro; Barrios Rípodas, Ernesto; Elizondo Martínez, David; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This paper presents an asymmetrical firing angle modulation strategy for 12-pulse thyristor rectifiers aimed at supplying high-power electrolyzers, which allows to reduce the size of the passive filter and the static compensator (STATCOM) required to comply with grid harmonic regulations and achieve unity power factor. Usually, 12-pulse thyristor rectifiers follow a symmetric modulation strategy in which the same firing angle is applied to both 6-pulse bridges. In this case, large passive ac-side inductances are required to reduce grid current harmonics, which increase the reactive power consumption and thus the required STATCOM size. However, this paper demonstrates that by applying different firing angles to the two 6-pulse bridges it is possible to comply with the harmonic regulation limits using smaller filtering inductances and therefore reducing the STATCOM size. The methodology to find the optimal firing angle values that should be applied in order to minimize the filtering inductance and the STATCOM size for a given electrolyzer is explained. This strategy is validated by simulation, and results show that the required filtering inductance and the apparent power of the STATCOM can be effectively reduced by 62% and 31%, respectively, using this asymmetrical firing angle modulation.
Open Access
Control of a photovoltaic array interfacing current-mode-controlled boost converter based on virtual impedance emulation
(IEEE, 2019) Urtasun Erburu, Andoni; Samanes Pascual, Javier; Barrios Rípodas, Ernesto; Sanchis Gúrpide, Pablo; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Due to the nonlinear characteristics of a photovoltaic (PV) array, its regulation is highly dependent on the operating point. Focusing on a dc-dc boost converter, this paper first shows how the PV voltage and inductor current controls are affected by the PV array. It then proposes to emulate an impedance virtually connected to the PV array, making it possible to greatly improve the control robustness. Thanks to the proposed strategy, the crossover frequency variation for the whole operating range is reduced from 42 times for the traditional control to 3.5 times when emulating parallel resistance or to 1.4 times when emulating series and parallel resistances, all with simple implementation. Experimental results with a commercial PV inverter and a 4-kWp PV array validate the theoretical analysis and demonstrate the superior performance of the proposed control.
Open Access
Medium-voltage cascaded sequential topology for large-scale PV plants
(Institute of Electrical and Electronics Engineers Inc., 2021) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Balda Belzunegui, Julián; Navarrete, Manuel; González Senosiain, Roberto; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Photovoltaic (PV) conversion systems are in continuous development due to their increasingly competitive prices. The traditional configuration of large-scale PV plants is based on high-power central inverters, which have reduced their cost by increasing their power rating. However, this cost reduction is expected to saturate in the near future, mainly due to an increase in the cost of the dc wiring. Cascaded conversion systems have appeared as potential solutions to continue reducing the PV plant cost. They consist of several conversion units whose ac outputs are connected in series. This enables the power-rating reduction of each individual conversion unit, while maintaining the power rating of the conversion structure. Thus, the conversion units are placed closer to the PV panels, reducing the dc wiring cost. In this paper, a novel three-phase topology for medium-voltage cascaded conversion systems is presented. The proposed topology is formed of several conversion units, each one with a reduced number of conversion stages, namely, dc/ac, medium-frequency isolation and ac/ac. Moreover, thanks to its sequential operation and modulation technique, zero-voltage switching and zero-current switching are achieved in all conversion stages. In this way, with respect to the configuration with central inverters, the proposed topology has the advantages of cascaded conversion systems. In comparison to previously investigated cascaded topologies, the proposed topology also presents promising characteristics, representing a potential cost reduction and efficiency increase. An experimental validation of the topology is carried out in a laboratory prototype consisting of three conversion units.
Open Access
Dynamic modeling and simulation of a pressurized alkaline water electrolyzer: a multiphysics approach
(IEEE, 2021) Iribarren Zabalegui, Álvaro; Barrios Rípodas, Ernesto; Ibaiondo, Harkaitz; Sánchez Ruiz, Alain; Arza, Joseba; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this paper a dynamic model for the simulation of pressurized alkaline water electrolyzers is presented. The model has been developed following a multiphysics approach, integrating electrochemical, thermodynamic, heat transfer and gas evolution processes in order to faithfully reproduce the complete dynamical behavior of these systems. The model has been implemented on MATLAB/Simulink and validated through experimental data from a 1 Nm3h-1 commercial alkaline water electrolyzer, and the simulated results have been found to be consistent with the real measured values. This model has a great potential to predict the behavior of alkaline water electrolyzers coupled with renewable energy sources, making it a very useful tool for designing efficient green hydrogen production systems.
Open Access
On the stability criteria for inverter current control loops with LCL output filters and varying grid impedance
(IEEE, 2017) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Ursúa Rubio, Alfredo; Marroyo Palomo, Luis; Sanchis Gúrpide, Pablo; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
The use of LC and LCL filters and grid impedance variations are creating new challenges on the controller design for current control loops of photovoltaic and wind turbine inverters. In the design process, stability criteria such as Bode and revised Bode are commonly used. This paper analyses the limitations of Bode and revised Bode criteria to reliably determine stability and proposes a sufficient and necessary stability criterion, based on the Nyquist criterion, but that makes use of the Bode diagram. The proposed criterion, named generalized Bode criterion, is always reliable and helps the controller design. Relative stability in complex control loops is also studied and a relative stability analysis is proposed. Finally, the generalized Bode criterion and the proposed relative stability analysis are illustrated with a practical example in which a PI is designed in order to guarantee stability and achieve relative stability.
Open Access
Novel three-phase topology for cascaded multilevel medium-voltage conversion systems in large-scale PV plants
(IEEE, 2020) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Balda Belzunegui, Julián; González Senosiain, Roberto; Sanchis Gúrpide, Pablo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Solar photovoltaic renewable energy systems are expanding in the power sector thanks to its increasingly competitive prices. Traditionally, large-scale PV plants have reduced their cost by increasing the power ratings of the inverters and the line-frequency transformers. However, cost-reduction limits of large-scale PV plants are being reached. Cascaded converters have appeared as a solution to continue reducing the cost of large PV plants as they reduce the wiring cost. In this paper, a novel three-phase topology for cascaded conversion structures is proposed. It only has 2 conversion steps, one without switching losses. Hence, it increases the efficiency and reduces the cost of the previously proposed cascaded conversion systems. The topology is patent pending.
Open Access
Control design and stability analysis of power converters: the discrete generalized Bode criterion
(IEEE, 2021) Urtasun Erburu, Andoni; Samanes Pascual, Javier; Barrios Rípodas, Ernesto; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
For the controller design and stability analysis of power electronic converters, the Bode stability criterion and its subsequent revisions are the most practical tools. However, even though the control of the power converter is usually implemented in a microprocessor, none of these methods is infallible when applied to a discrete system. This article therefore proposes a new stability criterion, named the Discrete Generalized Bode Criterion (DGBC). This method is based on the Nyquist criterion but developed from the open-loop Bode diagram, evaluated also at 0 Hz and at the Nyquist frequency. The proposed criterion combines the advantages of the Nyquist and Bode criteria, since it is always applicable and provides an interesting and useful tool for the controller design process. The method is applied to design an active damping control of an inverter with LCL filter, showing how the proposed criterion accurately predicts stability, in contrast to the existing Bode criteria. The theoretical analysis is validated through experimental results performed with a three-phase inverter and an LCL filter.
Open Access
Dynamic modeling of a pressurized alkaline water electrolyzer: a multiphysics approach
(IEEE, 2023) Iribarren Zabalegui, Álvaro; Elizondo Martínez, David; Barrios Rípodas, Ernesto; Ibaiondo, Harkaitz; Sánchez Ruiz, Alain; Arza, Joseba; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
In this paper a dynamic model for the simulation of pressurized alkaline water electrolyzers is presented. The model has been developed following a multiphysics approach, integrating electrochemical, thermodynamic, heat transfer and gas evolution processes in order to faithfully reproduce the complete dynamical behavior of these systems. The model has been implemented on MATLAB/Simulink and validated through experimental data from a 1 Nm3/h commercial alkaline water electrolyzer. Validations have been performed under real scenarios where the electrolyzer is working with power profiles characteristic from renewable sources, wind and photovoltaic. The simulated results have been found to be consistent with the real measured values. This model has a great potential to predict the behavior of alkaline water electrolyzers coupled with renewable energy sources, making it a very useful tool for designing efficient green hydrogen production systems.