Open Access
On the testing, characterization, and evaluation of PV inverters and dynamic MPPT performance under real varying operating conditions
(Wiley, 2007) Sanchis Gúrpide, Pablo; López Taberna, Jesús; Ursúa Rubio, Alfredo; Gubía Villabona, Eugenio; Marroyo Palomo, Luis; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua
The increasing number of photovoltaic inverters that are coming on to the PV marketstresses the need to carry out a dynamic characterization of these elements and theirmaximum power point tracking (MPPT) algorithms under real operating conditions.In order to make these conditions repeatable at the laboratory, PV array simulatorsare used. However, actual simulators, including the commercial simulators, recreateonly a single or small set of PV array characteristic curves in which quite commonlytheoretical calculations are included in order to simulate irradiance and temperatureartificial variations. This is far from being a recreation of the real and long dynamicbehavior of a PVarray or generator. The testing and evaluation of the performance ofPV inverters and MPPT algorithms has to be carried out when the PV system movesdynamically according to real operating conditions, including processes such asrapidly changing atmospheric conditions, partial shadows, dawn, and nightfall. Thispaper tries to contribute to the analysis of this problem by means of an electronicsystem that both measures the real evolution of the characteristic curves of PVarraysat outdoor operation and then recreates them at the laboratory to test PV inverters.This way the equipment can highlight the different performances of PV inverters andMPPT techniques when they operate under real operating conditions. As an example,two commercial inverters are tested and analyzed under the recreated behavior of aPV generator during 2 singular days that include processes of partial shading and fastirradiance variations.
Open Access
Modeling a grid-forming DFIG wind turbine
(IEEE, 2023-08-31) Oraa Iribarren, Iker; Samanes Pascual, Javier; López Taberna, Jesús; Gubía Villabona, Eugenio; 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 presents a small-signal state-space model that allows analyzing the dynamics of doubly-fed induction generator (DFIG)-based wind turbines in which grid-forming control strategies are implemented. Specifically, in this paper, a droop-controlled DFIG wind turbine is modeled. The system is modeled in the dq-axis, synchronized with the grid voltage, which simplifies the modeling by not having to linearize the terms dependent on the rotational speed of the dq-axis. Independent models for each element of the system are obtained, which are then combined to model the complete system under study. This modeling methodology provides great flexibility, allowing for easy inclusion of the LC harmonic filter, and enabling future incorporation of the grid-side converter to analyze its interaction with the rotor-side converter. The developed model is validated through simulation, demonstrating that it accurately reproduces the dynamic response of the system under study.
Open Access
Deadbeat voltage control for a grid-forming power converter with LCL filter
(IEEE, 2023) Samanes Pascual, Javier; Rosado Galparsoro, Leyre; Gubía Villabona, Eugenio; López Taberna, Jesús; Pérez, Marcelo A.; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
Grid-forming power converters are controlled as voltage sources to regulate the grid voltage and frequency. These converters can increase power system strength if they impose a voltage waveform resilient to grid transients. For this reason, in this paper, we propose a deadbeat control strategy of the capacitor voltage for high power converters with LCL filter. To damp the LCL resonant poles, an active damping strategy is developed, based on a modification of the deadbeat control law. With this purpose, a notch filter is applied to the electrical variables allowing to emulate different damping resistances for the fundamental component and the harmonics. As a result, the active damping does not introduce tracking errors of the fundamental frequency component, while it provides damping to the filter resonance. The proposed strategy does not require knowledge of the grid impedance, an interesting feature in grid-connected power converters because the grid impedance is generally unknown. Experimental results validate the proposed strategy.
Open Access
Robust active damping strategy for DFIG wind turbines
(IEEE, 2021) Rosado Galparsoro, Leyre; Samanes Pascual, Javier; Gubía Villabona, Eugenio; López Taberna, Jesús; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Doubly fed induction generators (DFIGs) with an LCL filter are widely used for wind power generation. In these energy conversion systems, there is an interaction between the grid-side converter (GSC) and the rotor-side converter (RSC) control loops, the generator and the LCL filter that must be properly modeled. Such interaction between the GSC and the RSC proves to have a significant influence on the stability. Several active damping (AD) methods for grid-connected converters with an LCL filter have been proposed, nevertheless, the application of these techniques to a DFIG wind turbine is not straightforward, as revealed in this article. To achieve a robust damping irrespective of the grid inductance, this article proposes an AD strategy based on the capacitor current feedback and the adjustment of the control delays to emulate a virtual impedance, in parallel with the filter capacitor, with a dominant resistive component in the range of possible resonance frequencies. This work also proves that, by applying the AD strategy in both converters simultaneously, the damping of the system resonant poles is maximized when a specific value of the grid inductance is considered. Experimental results show the interaction between the GSC and the RSC and validate the proposed AD strategy. © 1986-2012 IEEE.
Open Access
Control strategy for a droop-controlled grid-connected DFIG wind turbine
(IEEE, 2022) Oraa Iribarren, Iker; Samanes Pascual, Javier; López Taberna, Jesús; Gubía Villabona, Eugenio; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The application of droop control techniques without inner current control loops to doubly-fed induction generator (DFIG) based wind turbines does not allow to provide a stable response at all operating points in terms of rotational speed and active and reactive power. After modeling the system dynamics and analyzing the causes of instability, this paper proposes a control strategy that allows to stabilize the system response at all possible operating points. Simulation results performed in MATLAB/Simulink validate the proposed control strategy proving its effectiveness.
Open Access
Dual-stage control strategy for a three-level neutral point clamped converter with selective harmonic mitigation PWM
(IEEE, 2023-11-01) Rosado Galparsoro, Leyre; Norambuena, Margarita; Samanes Pascual, Javier; Lezana, Pablo; Gubía Villabona, Eugenio; López Taberna, Jesús; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Grid-connected converters must meet the requirements imposed by grid codes, such as harmonic emission limits and grid voltage support during voltage dips. Selective harmonic mitigation pulsewidth modulation (SHMPWM) is a very interesting technique for high power converters to meet the maximum harmonic emission levels, while keeping a low switching frequency. However, the combination of this modulation with a proportional integral (PI) controller requires slow dynamics, which makes it difficult to comply with the dynamic response requirements of grid codes. As an alternative, model predictive control (MPC) offers a very fast dynamic response, but a wide spread harmonic spectrum in steady state. Thus, the combination of MPC with a PI controller with SHMPWM is advantageous. In this work, a dual-stage control strategy is implemented. During transients, finite control set MPC (FCS-MPC) is activated to rapidly drive the current to the desired reference, while in steady state, the PI controller with SHMPWM is used. Therefore, the dual-stage control strategy allows to comply with the two requirements of grid codes, becoming a suitable strategy for grid-connected converters.
Open Access
Inertial response and inertia emulation in DFIG and PMSG wind turbines: emulating inertia from a supercapacitor-based energy storage system
(IEEE, 2021) Sacristán Sillero, Javier; Goñi, Naiara; Berrueta Irigoyen, Alberto; López Taberna, Jesús; Rodríguez Rabadan, José Luis; Ursúa Rubio, Alfredo; Sanchis Gúrpide, Pablo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The increasing wind power penetration in electrical power systems results in a reduction of operative conventional power plants. These plants include synchronous generators directly connected to the grid. Facing a change in grid frequency, these generators inherently respond by varying their stored kinetic energy and their output power, which contributes to grid stability. Such a response is known as inertial response. Wind turbines (WTs) are mostly based on Doubly-Fed Induction Generator (DFIG) or Permanent Magnet Synchronous Generator (PMSG) machines. Their power electronics interface decouples the electromechanical behaviour of the generator from the power grid, making their inertial response null or insignificant. Therefore, in order not to weaken the frequency response of the power system, WTs must be able to react to frequency variations by changing their output power, i.e., emulating an inertial response. Common techniques for inertia emulation in WTs rely on pitch control and stored kinetic energy variation. This contribution proposes a strategy (applicable for both DFIG and PMSG) which uses the energy stored in a supercapacitor connected to the back-to-back converter DC link to emulate the inertial response. Its performance is compared by simulation with aforementioned common techniques, showing ability to remove certain limitations.
Open Access
Optimized DFIG electrical design under voltage sags
(IEEE, 2021) Urtasun Salinas, Ibai; Larrea León, Pablo; López Taberna, Jesús; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
This paper addresses the dual problem (electrical-mechanical) of DFIG-based wind turbines under voltage sags and proposes an optimized solution that, starting from a design aimed to mitigate the mechanical loads in the structural components of the wind turbine, provides the electrical capability to meet the most demanding grid codes.
Open Access
MIMO based decoupling strategy for grid connected power converters controlled in the synchronous reference frame
(IEEE, 2018) Samanes Pascual, Javier; Gubía Villabona, Eugenio; López Taberna, Jesús; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Power converters are frequently connected to the grid through a LCL filter, controlling its power transfer through a current control loop in the synchronous reference frame. In this reference frame, cross coupling terms appear between the current and voltages of the passive components, which, without a proper decoupling strategy, penalize the converter transient response and the current control adjustment. In this work, an intuitive decoupling strategy is presented to improve the dynamic behavior, based on Multiple-Input-Multiple-Output systems theory. The approach developed is particularly interesting in extremely weak grids, allowing an easier adjustment of the main controller.
Open Access
Modeling of small wind turbines based on PMSG with diode bridge for sensorless maximum power tracking
(Elsevier, 2013) Urtasun Erburu, Andoni; Sanchis Gúrpide, Pablo; San Martín Biurrun, Idoia; López Taberna, Jesús; Marroyo Palomo, Luis; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The Permanent Magnet Synchronous Generator (PMSG) with diode bridge is frequently used in small Wind Energy Conversion Systems (WECS). This configuration is robust and cheap, and therefore suitable for small WECS. In order to achieve Maximum Power Point Tracking (MPPT) with no mechanical sensors, it is possible to impose the relationship between the DC voltage and the DC current on the optimum operating points. However, this relationship is difficult to calculate theoretically since the whole system is involved. In fact, as there is no model of the whole system in the literature, the optimum curve IL*(Vdc) is obtained with experimental tests or simulations. This paper develops an accurate model of the whole WECS, thereby making it possible to relate the electrical variables to the mechanical ones. With this model, it is possible to calculate the optimum curve IL*(Vdc) from commonly-known system parameters and to control the system from the DC side. Experimental results validate the theoretical analysis and show that maximum power is extracted for actual wind speed profiles.