Open Access
Analysis of the active inertia power provided by grid-forming strategies during a RoCoF
(IEEE, 2024-08-30) Urtasun Salinas, Ibai; Urtasun Erburu, Andoni; Bautista Portillo, Guillermo Antonio; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, PJUPNA2024-11695
Power electronic-based generators are becoming increasingly prevalent in the electrical grid, necessitating their support in disturbances previously handled only by synchronous generators. One of the tests proposed by regulations is to evaluate the response of grid-forming inverters to a Rate of Change of Frequency (RoCoF). However, there is no detailed analysis of the effect of control parameters on the active inertia power. This article presents the temporal response equation of an inverter subject to a RoCoF and introduces the concept of equivalent inertia showing that it also depends on the damping factor. Thanks to this analysis and the flexibility of inverters, the parameter design of existing grid-forming strategies is proposed to achieve the desired active inertia power and system damping ratio. Theoretical analysis and control strategies have been validated by simulation.
Open Access
Analysis of a CIS based PV generator versus a multicrystalline generator under outdoor long-term exposure
(IEEE, 2021) Parra Laita, Íñigo de la; Guerra Menjívar, Moisés Roberto; Marcos Álvarez, Javier; García Solano, Miguel; Marroyo Palomo, Luis; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
The worldwide growth of the PV market has been almost exponential during the last years. Together with conventional crystalline (c-Si) PV modules, “new” commercially available PV technologies such as copper indium selenide (CIS) based solar cells have appeared achieving a similar efficiency comparable to c-Si at similar production cost. In addition to the use of cheaper materials, CIS solar cells manufacturers claim some enhancements such as lower temperature coefficient or higher absorption of diffuse light that achieve to reduce the cost of electrical energy. Although several papers deal with this topic, little is known about real comparisons between CIS technology and conventional crystalline at a PV generator level with real test conditions. This paper analyses the in-field performance and degradation of a commercially available CIS solar based PV generator compared to a conventional c-Si one during four years of operation attributing the differences observed to the possible factors that can influence in both technologies.
Open Access
Small wind turbines sensorless MPPT: robustness analysis and lossless approach
(IEEE, 2014) Urtasun Erburu, Andoni; Sanchis Gúrpide, Pablo; Marroyo Palomo, Luis; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The configuration Permanent Magnet Synchronous Generator (PMSG) with diode bridge is frequently used in small Wind Energy Conversion Systems (WESC) thanks to its reliability and low cost. In order to perform a sensorless Maximum Power Point Tracking (MPPT), a suitable method consists of imposing the relationship between the dc current and the dc voltage in optimum operation. However, this strategy requires having knowledge of the system parameters, which are inaccurately known and can vary in real applications. Thus, optimum curve is not precisely obtained, leading to power losses. This paper evaluates to what extent the power is reduced due to parameter errors. It is shown how the power can be drastically decreased due to some parameter variation whereas it is not affected by others such as the resistance, which can then be neglected in order to simplify the model. Simulation results for an actual wind profile validate the theoretical analysis.
Open Access
Control method to coordinate inverters and batteries for power ramp-rate control in large PV plants: minimizing energy losses and battery charging stress
(Elsevier, 2023) González Moreno, Alejandro; Marcos Álvarez, Javier; Parra Laita, Íñigo de la; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work presents a novel control method for multi-megawatt photovoltaic (PV) plants that is able to regulate each plant inverter and the battery system to mitigate PV power fluctuations. The proposed control method makes it possible to implement different PV ramp-rate control strategies based on the use of batteries and the limitation of inverters during positive fluctuations, which have been conceptually proposed in the specialized bibliography, but have omitted how to perform the coordination between PV generators. The dynamic model and the tuning of the control parameters are presented and the method is used to correctly implement different inverter-limitation strategies using 5-second data from a real 45 MWp PV plant. Furthermore, a new control strategy is proposed. This strategy reduces curtailment losses to negligible values and takes into account and addresses the intrinsic asymmetry in the battery charging and discharging capability, an issue that has been overlooked in the specialized bibliography. The results show that the proposed control method can effectively control each of the multiple inverters in order to obtain the desired PV plant operation to regulate the battery charging power, even during highly fluctuating scenarios.
Open Access
Power angle-frequency droop control to enhance transient stability of grid-forming inverters under voltage dips
(IEEE, 2022) Erdocia Zabala, Ioseba; Urtasun Erburu, Andoni; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Due to the replacement of synchronous generators, grid operators are currently demanding to control grid-connected inverters in grid–forming mode to make them participate in the maintenance of the grid. To carry this out, the traditional droop controls based on the active and reactive powers are usually adopted, achieving a satisfactory performance in normal operation. Nevertheless, the power-frequency (P-ω) droop may become transiently unstable under voltage dips. This is because of the modification of the active power response caused by the inverter current limitation together with the voltage reduction. To enhance this, the power angle-frequency (δinv-ω) droop is proposed, consisting in employing an estimation of the inverter power angle as input to obtain the inverter frequency. The proposed method provides the inverter with the same performance as the P-ω droop in normal operation, while enhancing considerably the transient stability margins under current limitation. This is thanks to the higher variation of the inverter power angle with the phase difference between the inverter and the grid. Simulation results show the transient stability problems of the P-ω droop as well as the superior performance of the proposed δinv-ω droop control, which has also been verified by means of HIL results.
Open Access
Control strategy for an integrated photovoltaic-battery system
(IEEE, 2017) Urtasun Erburu, Andoni; Sanchis Gúrpide, Pablo; Marroyo Palomo, Luis; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
In photovoltaic-battery systems, more attention is usually paid to the MPPT control while the battery management is put aside. This paper proposes two control strategies for an integrated PV-battery system, both of them making it possible to perform MPPT or regulate the battery voltage to its maximum value in order to prevent it from overcharging. Simulation results prove the feasibility of both controls.
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
Fuzzy-based energy management of a residential electro-thermal microgrid based on power forecasting
(IEEE, 2018) Arcos Avilés, Diego; Gordillo, Rodolfo; Guinjoan Gispert, Francesc; Sanchis Gúrpide, Pablo; Pascual Miqueleiz, Julio María; Marietta, Martin P.; Marroyo Palomo, Luis; Ibarra, Alexander; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
In this paper, an energy management strategy based on microgrid power forecasting is applied to a residential grid-connected electro-thermal microgrid with the aim of smoothing the power profile exchanged with the grid. The microgrid architecture under study considers electrical and thermal renewable generation, energy storage system (ESS), and loads. The proposed strategy manages the energy stored in the ESS to cover part of the energy required by the thermal generation system for supplying domestic hot water to the residence. The simulation results using real data and the comparison with previous strategy have demonstrated the effectiveness of the proposed strategy.
Open Access
Dynamic analysis of the conductance-frequency droop control during current limitation
(IEEE, 2024-08-30) Urtasun Erburu, Andoni; Erdocia Zabala, Ioseba; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, PJUPNA2024-11695
In inverter-based stand-alone microgrids, the P-f and O-V droop methods are frequently used to keep control of the microgrid voltage. However, in the presence of overloads or short-circuits, in which the inverter must perform a current- limiting strategy, the P-f droop becomes prone to transient instability. In order to remain stable under any possible overload or fault, the conductance-frequency $({G-f})$ droop is a promising alternative, however no analysis about its dynamic response has been carried out so far. This paper proposes a small-signal model of the system during current limitation, proving that the ${G-f}$ droop is also superior to the existing droop methods in terms of rapidity. Simulation results validate the theoretical analysis.
Open Access
Energy management for an electro-thermal renewable based residential microgrid with energy balance forecasting and demand side management
(Elsevier, 2021) Pascual Miqueleiz, Julio María; Arcos Avilés, Diego; Ursúa Rubio, Alfredo; Sanchis Gúrpide, Pablo; Marroyo Palomo, Luis; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This paper proposes an energy management strategy for a residential microgrid comprising photovoltaic (PV) panels, a small wind turbine and solar thermal collectors. The microgrid can control the power exchanged with the grid thanks to a battery and a controllable electric water heater, which provide two degrees of freedom to the control strategy. As input data, the proposed control strategy uses the battery state of charge (SOC), the temperature of the hot water tank, the power of each microgrid element as well as the demand and renewable generation forecasts. By using forecasted data and by controlling the electric water heater, the strategy is able to achieve a better grid power profile while using a smaller battery than previous works, hence reducing the overall cost of the system. The strategy is tested by means of simulation with real data for one year and it is also experimentally validated in the microgrid built at the Renewable Energy Laboratory at the UPNA.