Grid-connected converter control during unbalanced grid conditions based on delay signal cancellation

Abstract

Summary Considering the recent trend in energy sector transformation towards high share of renewable energy sources, it has become very hard to imagine modern power system without the integration of power electronic devices. A grid‐connected converter will be on the forefront of future energy trading, while simultaneously striving to offer good dynamic behaviour and operation in full accordance with the relevant grid requirements. The control algorithm of the grid‐connected converter has to be capable of achieving the stable steady state operation even during the most severe faults in the system. More importantly, the power quality of the injected currents (and thus the power) needs to be kept at the maximum possible level. This paper presents the control strategy for the grid‐connected converter that offers the possibility of symmetrical grid current injection at the point of common coupling even during unbalanced grid conditions. Proposed control strategy uses delay signal cancellation in the negative sequence synchronous rotating reference frame for the mitigation of the respective current components. The negative influence of asymmetrical grid voltages, present at the point of common coupling as a result of unbalanced grid loads or faults, will be shown within the paper. The key features of the improved control method are outlined, with a special reference to basic theoretical background. The proposed method is experimentally verified using sophisticated research and development station for control of grid‐connected converter.

Voltage Support under Grid Faults with Inherent Current Limitation for Three-Phase Droop-Controlled Inverters

“…By substituting the proposed controller (14), (15), (21) and (22) into the system dynamics (4) and (5), the closed-loop system takes the form…”

“…The way current limitation is achieved under unbalanced grid conditions still represents a challenging task, especially when droop controlled inverters are considered, since their task is to regulate the grid voltage and frequency. The authors in [6,21] have implemented controllers that ensure a balanced current provision under voltage sags. As explained in [6], this enhances the fault-ride-through capability in terms of injecting only positive sequence powers/current that comply with the FRT requirement, while current limitation at the steady-state is achieved through the controller reference powers.…”

Three‐phase converter power control under grid imbalance with consideration of instantaneous power components limitation

“…Separation of positive and negative sequence current components was proposed as a solution of nonfixed control variables . In recent papers, improvement of this method was described, like delay signal cancellation in the negative sequence reference frame for the mitigation of negative sequence currents . Nevertheless, even if applied, sequence decomposition‐based methods generally assume symmetrical current target, which is not fully beneficial for the grid either in the inverter or the rectifier operation mode.…”

Power quality improvement in grid integrated solar water pumping system using Vienna converter

“…A delayed signal cancelation method has been introduced to improve the conventional PLL performance. However, the enhanced performance is achieved at the cost of increased complexity and computational burden . Generalized integrator (GI)–based method has been explored recently and found effective to deal with weak‐grid scenarios.…”

“…However, the enhanced performance is achieved at the cost of increased complexity and computational burden. 20 Generalized integrator (GI)-based method has been explored recently and found effective to deal with weak-grid scenarios. A second order GI is reported in another research 21 for distortion rejection; however, they have been found ineffective in dealing with dominant lower order harmonics and DC offset.…”