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
State-of-charge-based droop control for stand-alone AC supply systems with distributed energy storage
(Elsevier, 2015) Urtasun Erburu, Andoni; Sanchis Gúrpide, Pablo; Marroyo Palomo, Luis; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The droop method is an advantageous technique for stand-alone AC supply systems, allowing for power sharing among various inverters with no need for communication cables. However, in stand-alone systems with multiple distributed energy storage units, the conventional droop methods are unable to control the storage unit state-of-charge (SOC) in order to change simultaneously. Existing techniques endeavor to solve this problem by changing the slope of the P – f curve however this solution compromises the power response performance. As an alternative, this paper proposes a new SOC-based droop control, whereby the P – f curve is shifted either upwards or downwards according to the battery SOC. The proposed technique makes it possible to select the time constant for the battery SOC convergence and, at the same time, to optimize the power response performance. The paper also shows how the SOC changes when the ratios between the battery capacity and the inverter rated power are different and how the proposed technique can limit the SOC imbalance. Simulation and experimental results corroborate the theoretical analysis.
Open Access
Energy management strategy for a battery-diesel stand-alone system with distributed PV generation based on grid frequency modulation
(Elsevier, 2014) Urtasun Erburu, Andoni; Sanchis Gúrpide, Pablo; Barricarte Rivas, David; Marroyo Palomo, Luis; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
A hybrid PV-Battery-Diesel configuration is very attractive for stand-alone systems in terms of cost and reliability. In many applications, the battery and the diesel generator are centralized and generate the AC grid while the PV generators and loads are distributed and are connected to the grid. However, in these cases, long communication cables are required in order to reduce the PV power when the battery is fully charged. This paper proposes an energy management strategy which makes it possible to avoid the use of communication cables, rendering the system simpler, cheaper and more reliable. The strategy dictates that should a power reduction be required, the battery inverter increases the grid frequency. This is detected by the PV inverters, which continuously reduce their power in order to prevent the battery from overcharge or over-current. The strategy also optimizes the efficiency and operating life of the diesel generator. Simulation and experimental validation is carried out for a system with 10 kW PV generation, a 5 kVA battery inverter, a 5 kVA diesel generator and a 5 kVA load.
Open Access
Frequency-based energy management strategy for stand-alone systems with distributed battery storage
(IEEE, 2015) Urtasun Erburu, Andoni; Barrios Rípodas, Ernesto; Sanchis Gúrpide, Pablo; Marroyo Palomo, Luis; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Distributed generation is an attractive solution for stand-alone AC supply systems. In such systems, the installation of two or more energy-storage units is recommended for system redundancy and may also be required when there is a consumption increase following installation. However, energy management with multiple energy-storage units has been but vaguely analyzed in the literature and the few studies made are based on communication cables with a central supervisor. This paper proposes an energy management strategy for a multiple-battery system which makes it possible to avoid the use of communication cables, rendering the system more cost-effective and reliable. The strategy modifies the conventional droop method so that the power becomes unbalanced, allowing for the regulation of one or more battery voltages or currents, as required. Furthermore, whenever the frequency is high, the PV inverters reduce their power in order to prevent the battery from overcharge or high charging currents. On the other hand, whenever the frequency is low, then either the non-critical loads are regulated or the system stops in order to prevent the battery from over-discharge or high discharging currents. Simulation and experimental validation are performed for a system with two battery inverters, two PV inverters and a number of loads.

Marroyo Palomo, Luis

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