Open Access
Active damping based on the capacitor voltage positive-feedback for grid-connected power converters with LCL filter
(IEEE, 2019) Samanes Pascual, Javier; Gubía Villabona, Eugenio; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
The capacitor voltage positive-feedback is a widely extended active damping strategy. It can effectively damp the LCL output filter resonant poles for low ratios of resonance to sampling frequencies. However, the existing delays in the control loop limit the applicability of the capacitor-voltage positive-feedback. For high ratios of resonance to sampling frequencies, it becomes ineffective and can even destabilize the system. This limitation is overcome in this paper by adjusting the delay in the feedback path. With the delay adjustment, a robust damping can be achieved if the delays are properly considered, including the filters, and the grid impedance variations are taken into account. Simulation results validate the proposed active damping strategy.
Open Access
On the limits of the capacitor-voltage active damping for grid-connected power converters with LCL filter
(IEEE, 2018) Samanes Pascual, Javier; Gubía Villabona, Eugenio; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Active damping strategies are widely extended to avoid stability issues at the LCL filter resonant poles in grid-connected voltage source converters. The capacitor voltage derivative active damping effectively damps the filter resonant poles without additional sensors, but it loses its effectiveness as the resonance frequency approaches the converter control Nyquist frequency, influenced by the existing delays in the control loop. To reduce this limitation, the delays can be reduced by performing a multisampled derivative, however, even though the stability limits might be extended, the oversampled approach might increase noise amplification problems. An appropriate filtering solution is required in the feedback path in order to reduce noise amplification and eliminate aliasing problems, without compromising the stability, as a result of a modification in the active damping feedback path. This work examines the limits of applicability of the capacitor voltage derivative strategy taking into account the filters used in the AD path, providing experimental results to validate the presented approach.
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
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
Common-mode and phase-to-ground voltage reduction in back-to-back power converters with discontinuous PWM
(IEEE, 2020) Samanes Pascual, Javier; Gubía Villabona, Eugenio; Juankorena Saldias, Xabier; Gironés Remírez, Carlos; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Discontinuous space vector pulsewidth modulation (DSVPWM) techniques are an interesting option for three-phase, two-level power converters when efficiency is a key factor. Such is the case of back-to-back (B2B) power converters used mainly in wind energy conversion systems and electrical drives. The application of DSVPWMs to B2B converters increases the common-mode (CM) and phase-to-ground (PG) voltages by 50%, compared to conventional space vector pulsewidth modulation (SVPWM7). Higher CM and PG voltages cause bearing currents and insulation stress, which reduce system reliability. In this article, this problem is addressed and two DSVPWM strategies are presented to reduce the CM and PG voltages in B2B power converters. In the first proposal, the CM and PG are both limited to the same values as the conventional SVPWM7 without introducing additional commutations. In the second proposal, a further modification is added to reduce the CM by 50%, compared to the SVPWM7, although this modulation strategy eventually requires two additional commutations in certain periods. Experimental and simulation results validate the performance of the proposed strategies.
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
Multisampled-capacitor-voltage active damping for parallel interleaved grid connected voltage source converters with LCL filter
(IEEE, 2017) Samanes Pascual, Javier; Gubía Villabona, Eugenio; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Parallel interleaved converters for high power renewable energy systems present stability issues at the LCL resonance frequency. A multisampled measurement and filtering strategy is proposed to stabilize the system based on the capacitor voltage derivative active damping, overcoming its limitations for low switching power converters. The effects of the delays on the stability of the active damping strategy would be analysed. The solution developed is robust against grid inductance variations, ensuring the fulfilment of the stringent harmonic grid codes.
Open Access
Robust multisampled capacitor voltage active damping for grid-connected power converters
(Elsevier, 2019) Samanes Pascual, Javier; Urtasun Erburu, Andoni; Gubía Villabona, Eugenio; Petri, Alberto; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The derivative feedback of the capacitor voltage is one of the most extended active damping strategies, used to eliminate stability problems in grid-connected power converters with an LCL filter. This strategy is equivalent to the implementation of a virtual impedance in parallel with the filter capacitor. This virtual impedance is strongly affected by the control loop delays and frequency, creating changes in the sign of the emulated virtual resistor, and raising instability regions where the active damping is ineffective. As a consequence, the LCL resonance frequency is restricted to vary, as the effective grid inductance changes, within the active damping stability region. This is an additional restriction imposed on the LCL filter design that can compromise the achievement of an optimised design. For this reason, in this work, a different strategy is presented; by adjusting the delay in the active damping feedback path, it becomes stable within the range where the LCL resonance frequency can be located for a given filter design, achieving a robust damping. Analytical expressions are provided to adjust this delay. To widen the stability region of the capacitor voltage derivative active damping, a multisampled derivative is implemented, overcoming its limitations close to the control Nyquist frequency. Experimental and simulation results validate the active damping strategy presented.
Open Access
Capacitor current feedback active damping with lagged compensator for DFIG wind turbines with LCL filter
(IEEE, 2020) Rosado Galparsoro, Leyre; Samanes Pascual, Javier; Gubía Villabona, Eugenio; López Taberna, Jesús; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
Several active damping strategies have been proposed in the literature for grid-connected converters with LCL filter but there are not specific strategies for DFIG wind turbines. In this system, there is an interaction between the two converters of the back-to-back conversion structure, which must be properly modeled in order to design effective damping strategies for the LCL filter resonant poles. This paper proposes a robust active damping strategy for DFIG wind turbines with LCL filter that considers the special features of this system. In this technique the filter capacitor current is fed back through a lag compensator that adjusts the delay of the feedback loop to emulate a virtual impedance that has dominant resistive behavior in the range of possible resonance frequencies. It is shown that a similar damping of the LCL filter resonance is achieved when the strategy isimplemented in either of the two converters.
Open Access
Control design and stability analysis of power converters: the MIMO generalized bode criterion
(IEEE, 2020) Samanes Pascual, Javier; Urtasun Erburu, Andoni; Barrios Rípodas, Ernesto; Lumbreras Magallón, David; López Taberna, Jesús; Gubía Villabona, Eugenio; Sanchis Gúrpide, Pablo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Three-phase dynamic systems and multiphase generators are frequently modeled and controlled in the synchronous reference frame. To properly model the cross-coupling terms in this reference frame, complex vector theory and transfer function matrices are commonly applied, obtaining multiple-input multiple-output (MIMO) dynamic models. The stability of MIMO systems can be assessed through the Nyquist generalized stability criterion. However, the use of the Nyquist diagram complicates the controller design. The Bode diagram is a more intuitive tool for the controller design; however, the Bode stability criterion is not applicable to MIMO systems. In this article, the MIMO generalized Bode criterion is proposed. Since this stability criterion is based on the Nyquist generalized stability criterion, it can be applied to any system. Furthermore, it is simple to use, as it only requires information contained in the open-loop transfer matrix and the Bode diagram. The proposed stability criterion thus offers an interesting tool for the controller design procedure in MIMO systems, as it is shown in this article for two common applications: the current control loop of a power converter, a 2 × 2 system, and the current control loop of two independent power converters in parallel, a 4 × 4 system.