Control Strategy for Three-Phase Grid-Connected PV Inverters Enabling Current Limitation Under Unbalanced Faults

Abstract

Abstract-Power quality and voltage control are among the most important aspects of the grid-connected power converter operation under faults. Non-sinusoidal current may be injected during unbalanced voltage sag and active or/and reactive power may include double frequency content. This paper introduces a novel control strategy to mitigate the double grid frequency oscillations in the active power and dc-link voltage of the two-stage three-phase grid-connected Photovoltaic (PV) inverters during unbalanced faults. With the proposed control method, PV inverter injects sinusoidal currents under unbalanced grid faults. In addition, an efficient and easy-to-implement current limitation method is introduced, which can effectively limit the injected currents to the rated value during faults. In this case, the fault-ride-through operation is ensured and it will not trigger the overcurrent protection. A Non-MPPT operation mode is proposed for the dc-dc converter. The mode is enabled under severe faults, when the converter cannot handle the maximum PV power. Finally experimental validation is provided by implementing method in an experimental setup including a 2kW PV inverter.

Improved Control of Grid-connected DFIG-based Wind Turbine using Proportional-Resonant Regulators during Unbalanced Grid

“…where K p is the proportional constant, K i is the integral constant of the regulator, ω c is the cutoff frequency and ω e is the resonance frequency. The grid current references expressions in the stationary reference frame (i * gα and i * gβ ) are written according to the active and reactive current components (i * gα,P and i * gβ,P ) and (i * gα,Q and i * gβ,Q ), respectively [49]:…”

“…In addition, the grid code imposes the 227 necessity to inject some reactive power for specific levels in the depth of the voltage dips [51] and to 228 limit the current amplitude near its nominal value in order to avoid the generator disconnection 229 from the grid. Figure 8a presents the LVRT requirements according to IEC 61400-21 [41]; Figure 8b 230 presents the Spanish grid code requirements for the reactive power during grid faults [49]. for the reactive power [52].…”

“…N SCs, and the extracted positive sequence is used to detect the voltage sag by dividing it with the 236 nominal value of the line-to-line utility grid voltage as expressed in the following equation [49]: As it was motioned in the previous section, the measured grid voltage is used to calculate the P-N SCs, and the extracted positive sequence is used to detect the voltage sag by dividing it with the nominal value of the line-to-line utility grid voltage as expressed in the following equation [49]:…”

“…(a) LVRT requirements according to IEC 61400-21 and (b) Spanish grid code requirements for the reactive power[49].…”

Şebekeye bağlı yenilenebilir enerji kaynaklı eviriciler için yeni bir akım kontrol stratejisi

“…Şebekeye bağlı tek fazlı eviricinin kontrolü için oransal rezonans (PR) kontrol algoritması önerilmiş ve sistemin senkronizasyonu yeni tek faz kilitlemeli döngüler (PLL) ile sağlanmıştır [4]. Diğer bir çalışmada, ideal olmayan şebeke durumları için, akım sınırlamasını sağlayan üç fazlı şebekeye bağlı fotovoltaik eviricinin kontrolü ayarlanabilen referans akımı ile yapılarak aktif ve reaktif güç üzerindeki salınımlar (oscillations) ortadan kaldırılmıştır [5]. dq dönüşüm tabanlı oransal PI kontrolcü ve PR tabanlı kontrolcünün performansı şebekeye bağlı YEKE'nin kontrolü üzerinde denenmiştir [6].…”