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
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
On the impact of high-power grid-connected thyristor rectifiers on the efficiency of hydrogen electrolyzers
(IEEE, 2024-08-30) Iribarren Zabalegui, Álvaro; Barrios Rípodas, Ernesto; Rivera, Marco; Wheeler, Patrick; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This paper investigates the impact of power supply and dc current ripple on the efficiency of water electrolyzers and demonstrates that optimally sized thyristor rectifiers meeting grid power quality regulations can effectively supply high-power electrolyzers with minimal impact on electrolyzer efficiency. Firstly, an equivalent electrical model for the electrolyzer is developed, and the efficiency reduction caused by dc current ripple is analyzed. This is validated by means of experimental data from a 5-kW alkaline electrolyzer operated with both thyristor- and IGBT-based rectifiers. Next, the paper explores the operation of high-power electrolyzers supplied by 6- and 12-pulse thyristor rectifiers complying with grid power quality standards. Results show that with optimal sizing of ac-side source voltage and filtering inductances, these solutions exhibit negligible dc current ripple impact on electrolyzer efficiency. These findings, validated through simulation of a 5.5 MW electrolyzer, highlight the viability of thyristor rectifiers in high-power electrolysis applications, and emphasize the importance of an optimal power supply design and sizing for enhancing water electrolyzers' performance.
Open Access
Winding resistance measurement in power inductors - understanding the impact of the winding mutual resistance
(IEEE, 2021) Barrios Rípodas, Ernesto; Elizondo Martínez, David; Ursúa Rubio, Alfredo; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Inductors are cornerstone components in power electronics converters. Since winding loss is the dominant loss mechanism in these components, its accurate measurement is fundamental for the validation of the inductor's operation and design. The techniques for the winding resistance R_{w} measurement in power inductors can be classified into two groups, indirect and direct. Both techniques use coupled inductors to separate winding and core power losses. If coupled inductors with non-zero winding mutual resistances R_{w,m} are used, invalid results are obtained with these techniques. Understanding the meaning of R_{w,m} in coupled inductors is complex. In this paper, the impact of R_{w,m} on the inductor R_{w} measurement techniques is demonstrated and practical guidelines for the design of the zero R_{w,m} coupled inductors are given. Particularly, the location of the auxiliary winding for the direct technique is investigated. In order to compare the R_{w} measurement techniques and to validate the coupled inductor's R_{w,m} impact, two different inductors are built and tested. The results are compared with the values for R_{w} calculated by FEA simulation. It is found that only the direct technique with an auxiliary winding carefully designed and located following the guidelines given in this paper makes the accurate measurement of R_{w} in power inductors possible.
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.
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
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
High frequency power transformers with foil windings: maximum interleaving and optimal design
(IEEE, 2015) Barrios Rípodas, Ernesto; Urtasun Erburu, Andoni; Ursúa Rubio, Alfredo; Marroyo Palomo, Luis; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Foil conductors and primary and secondary interleaving are normally used to minimize winding losses in high frequency transformers used for high-current power applications. However, winding interleaving complicates the transformer assembly, since taps are required to connect the winding sections, and also complicates the transformer design, since it introduces a new tradeoff between minimizing losses and reducing the construction difficulty. This paper presents a novel interleaving technique, named maximum interleaving, that makes it possible to minimize the winding losses as well as the construction difficulty. An analytical design methodology is also proposed in order to obtain free cooled transformers with a high efficiency, low volume and, therefore, a high power density. For the purpose of evaluating the advantages of the proposed maximum interleaving technique, the methodology is applied to design a transformer positioned in the 5 kW 50 kHz intermediate high frequency resonant stage of a commercial PV inverter. The proposed design achieves a transformer power density of 28 W/cm3 with an efficiency of 99.8%. Finally, a prototype of the maximum-interleaved transformer is assembled and validated satisfactorily through experimental tests.
Open Access
On the stability of advanced power electronic converters: the Generalized Bode Criterion
(IEEE, 2019) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Urtasun Erburu, Andoni; Ursúa Rubio, Alfredo; Marroyo Palomo, Luis; Sanchis Gúrpide, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
A key factor in the design of power electronic converters is the development of control systems and, in particular, the determination of their stability. Due to ease of application, the Bode criteria are currently the most commonly used stability criteria, both with regard to its classic version and to the subsequent revisions proposed in the literature. However, as these criteria have a limited range of applicability, on occasions it is necessary to resort to other universally applicable criteria such as the Nyquist criterion. Unlike Bode, the Nyquist criterion can always be applied, although its use considerably complicates the tuning of the controller. This paper proposes a new stability criterion, called Generalized Bode Criterion, which is based on the Nyquist criterion and, therefore, always applicable, but calculated from both the Bode diagram and the 0 Hz phase of the open-loop transfer function, thus making the criterion easy to be applied. This way, the proposed criterion combines the advantages of Nyquist and Bode criteria and provides an interesting and useful tool to help in the controller design process. The validation of the criterion is made on a voltage control loop for a stand-alone PV system through simulation and experimental tests made on a voltage control loop for a stand-alone PV system including a battery, a boost converter, an inverter and an ac load. The tests are also used to show the limitations of the classic Bode criterion and its revisions to correctly determine the stability of complex systems. IEEE