Open Access
DC capacitance reduction in three-phase photovoltaic inverters by using virtual impedance emulation
(IEEE, 2019) Urtasun Erburu, Andoni; Sanchis Gúrpide, Pablo; Marroyo Palomo, Luis; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
DC voltage regulation in grid-connected three-phase PV inverters is a fundamental requirement. In order to reduce the influence of the PV non-linear behavior and ensure stability in the whole operating range, the input capacitance in high-power inverters is currently oversized, thus increasing the converter cost. This paper proposes a control method which emulates a virtual impedance in parallel with the PV generator, making it possible to reduce the capacitance by a factor of 5. Simulation results confirm that the proposed control is stable and fast enough in the whole operating range with such a small capacitor.
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
Single feedback regulation of the AC voltage for high-power inverters under stand-alone operation
(IEEE, 2019) Erdocia Zabala, Ioseba; Urtasun Erburu, Andoni; Marroyo Palomo, Luis; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Energy-storage inverters under stand-alone operation must control the output voltage. However, existing methods for instantaneous voltage regulation are not suitable for high-power inverters due to their limited sampling frequency. To avoid this problem, a single feedback voltage loop with feedforward compensation is proposed in this paper, making it possible to actively damp the LCL filter resonance and thus facilitating the controller design. Simulation results demonstrate the fast reference tracking and the high-quality voltage obtained with non-linear loads.
Open Access
The generalized bode criterion: application to the dc voltage control of a three-phase photovoltaic grid-tied inverter
(IEEE, 2019) Lumbreras Magallón, David; Barrios Rípodas, Ernesto; Urtasun Erburu, Andoni; Sanchis Gúrpide, Pablo; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
As renewable energies are becoming more important in the electrical generation system, power electronic converters are facing new design issues related not only to their components but also to their control loops. In this context, the Generalized Bode Criterion (GBC) appears as a good tool to correctly determine stability and to help the controller design. In order to show the potential of the GBC and how it can be applied, this paper studies a dc voltage regulation with compensation of the photovoltaic power in a three-phase photovoltaic grid-tied inverter.

Urtasun Erburu, Andoni

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