Investigations on Power Flow Control and Power Quality Improvement in Renewable Energy Sources Integrated Smart Grid

Abstract

Due to the growth of population along with suburban and urban industrials, the demand for power is growing day-by-day. As the power consumption rate is high, the supply from fossil fuels is not enough to meet consumer demand. Further, the depletion of fossil fuels and environmental concern forces the extraction of power from low carbon fuels causes generation problems due to its uncertainty and intermittent nature. So, low carbon fuels such as wind, solar, etc. can therefore, be incorporated into a more efficient hybrid system. This research work proposes a hybrid system configurations are the AC coupled micro-grid, DC coupled micro-grid, and the AC-DC coupled microgrid. However, a significant amount of non-linear power electronic loads in the system causes power quality problems. These issues have to be addressed adequately by developing an appropriate SAPF based bi-directional control methods. Firstly, the most implemented hybrid system around the globe is the AC coupled micro-grid. In this system, hybrid renewable energy sources or distributed generation are connected to the main-grid through individual DC-AC converters. This system is reliable because if any one of the DCAC converters fails, the other DC-AC converter can supply power to the loads. But, the control algorithm is very complex, and also there is a need for synchronization with the main-grid. Secondly, nowadays, more and more DC loads like LED lights are connected to the AC distribution system, which increases power quality problems and power conversion stages. These issues are taken into consideration by the DC coupled hybrid micro-grid system. This system is simpler because there is no reactive power control. Further, there is no need for synchronization to integrate renewable energy sources or distributed generations with the main-grid. However, this topology needs to restructure the current distribution system, and consequently, the cost increases drastically. Also, the DC protection system is more challenging than the AC protection system. iLastly, based on the benefits of the individual AC and DC coupled hybrid micro-grid systems, an AC-DC coupled hybrid micro-grid system is proposed in this research work. It consists of AC renewable energy sources, and the AC loads are connected to the AC bus, whereas the DC renewable energy sources and DC loads are connected to the DC bus, thereby reducing the power conversion stages. Further, the power conversion loss calculation is also discussed by compared with the AC-DC coupled hybrid micro-grid system over individual AC and DC coupled hybrid micro-grid systems. The shunt active power filter based 3φ 4-leg DC-AC bi-directional intermediate converter using d-q load current control without a phase-locked loop is proposed to achieve the inverter-based and rectifier-based power flow between the AC and DC bus with acceptable power quality as per IEEE 519 standards at a common connecting point. The hysteresis based current control is used to compare the actual current with a reference current to generate switching pulses to drive the bi-directional intermediate converter. The MATLAB simulation is carried out, and the performance of the proposed system is analyzed using the d-q load current control based fuzzy logic and PI controller. To validate the proposed control technique, different case studies are performed by considering balanced and unbalanced grid and load conditions with variation in renewable energy sources. The observed results demonstrate that the overall system performance improves with the d-q load current control based fuzzy logic controller.