Abstract
The paper deals with design and control of a fault tolerant and reconfigurable photovoltaic converter integrating a Battery Energy Storage System as a standby backup energy resource. When a failure occurs, an appropriate control method makes the energy conversion system capable of operating in open-delta configuration in parallel with the grid as well as in islanded mode. In case network voltage is lacking due to heavy anomalies or maintenance reasons, the proposed control system is able to quickly disconnect the inverter from the grid while ensuring the energy continuity to the local load and the emergency fixtures by means of the integrated battery packs. In particular, the paper proposes a fast islanding detection method essential for the correct operation of the control system. This specific technique is based on the Hilbert transform of the voltage of the point of common coupling, and it identifies the utility lack in a period of time equal to half a grid cycle in the best case (i.e., 10 ms), thus resulting in good speed performance fully meeting the standard requirements. A thorough numerical investigation is carried out with reference to a representative case study in order to demonstrate the feasibility and the effectiveness of the proposed control strategy.
Highlights
Over the last years, the electric energy generated from renewable energy sources (RES) has grown exponentially
With the aim of ensuring that the state of the system remains close to the sliding surface, a suitable operation is necessary for the switch, which links its state with the value of S(x)
As already discussed in the introduction, the proposed method is based on the pure observation of the envelope of the point of common coupling (PCC) voltage obtained by performing the absolute value of the Hilbert transform, it can be classified as a passive ID methods (IDMs)
Summary
The electric energy generated from renewable energy sources (RES) has grown exponentially. IDMs; [12] reports a feedback-based passive islanding detection technique for one-cycle-controlled (OCC) single-phase inverter used in photovoltaic system This method, as stated by the authors, is not generic and limited to OCC-based inverters while providing a detection time of about 200 ms (i.e., 10 grid cycles). In [16], a combination of rate of change of frequency (ROCOF), rate of change of phase angle difference (ROCPAD), rate of change of voltage (ROCOV), and over frequency/under frequency (OF/UF) methods is reported In such a case, the proposed algorithm represents the merge of different passive ID techniques, the detection time is always the minimum among the different used algorithms. The continuous power supply of the load is ensured due to to the addition, the proposed method can strategy be used independently the specificgrid-connected application. The PV source delivers the energy to the load and, if the load request is not met, the grid provides the residual while the is double-stage configuration of Figure
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