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
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
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
Modeling of a droop-controlled grid-connected DFIG wind turbine
(IEEE, 2022) Oraa Iribarren, Iker; Samanes Pascual, Javier; López Taberna, Jesús; Gubía Villabona, Eugenio; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Traditionally, to characterize the response of droop-controlled systems RMS models have been used. However, as it is demonstrated in this work, when droop control is applied to doubly-fed induction generators, RMS models do not allow to predict the system stability and dynamic response. Thus, in this article, a linearized small-signal model that overcomes the limitations of RMS models is presented. The proposed model is validated by simulation in MATLAB/Simulink demonstrating that it allows to accurately analyze the stability and dynamic response of the system under study. This model is an interesting tool that can be used in future works to design and adjust grid-forming controllers for doubly-fed induction generators.
Open Access
Single-loop droop control strategy for a grid-connected DFIG wind turbine
(IEEE, 2023) 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
When grid-forming droop control strategies are implemented in grid-connected power converters, two control strategies are widely used: the single-loop and multiloop droop controls. However, only multiloop droop control strategies with inner control loops have been implemented in doubly fed induction generator (DFIG)-based wind turbines so far. This article proposes the application of a single-loop droop control strategy to a DFIG wind turbine, which has not been previously explored or implemented. As shown in the article, the application of the conventional droop control without inner control loops to DFIG-based wind power systems does not ensure a stable response. After modeling the system dynamics and evaluating its stability, two causes of instability have been identified: a resonance at the rotor electrical frequency relevant at high slips and a phase margin reduction at low slips. To solve these instability issues two control solutions are proposed: the emulation of a virtual resistor and a phase rotation. The proposed control strategy allows stabilizing the system and achieving a fast and damped dynamic response. The effectiveness of the proposed control strategy is validated by experimental results.
Open Access
Selective harmonic mitigation: limitations of classical control strategies and benefits of model predictive control
(IEEE, 2023) Rosado Galparsoro, Leyre; Samanes Pascual, Javier; Gubía Villabona, Eugenio; López Taberna, Jesús; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Selective harmonic mitigation pulsewidth modulation (SHMPWM) combined with model predictive control (MPC) is a promising approach for grid-connected power converters. SHMPWM can guarantee grid code compliance in steady state, e.g. grid harmonic injection, with a reduced output converter filter, while MPC improves dynamic response and allows grid code compliance in the event of grid transients. This paper presents a survey of the MPC strategies already published in the literature developed for their use with SHMPWM. The existing strategies fall into two categories: direct model predictive control with an implicit selective harmonic mitigation modulator, and direct model predictive control based on finite control set (FCS-MPC). One representative control strategy of each group is compared to each other and to the performance of classical proportional- integral (PI) controllers combined with SHMPWM. The goal is to identify the potential benefits of MPC for grid-connected power converters, and determine the main advantages and limitations of the two selected state-of-the-art control strategies. Their performance is assessed through Hardware-in-the-Loop (HIL) experimental results in terms of real-time implementation, harmonic content grid code compliance, dynamic response and performance under grid transients.