چكيده به لاتين
In recent years, due to the disadvantages of conventional fossil fuels such as air pollution and extinction of them, the concept of using Renewable Energy Sources (RESs) has attracted more attention. Microgrid (MG) and DG concepts have been emerged for better use of the RESs and enhancing efficiency, power quality and reliability of the conventional power systems. Since the output voltage of many of the RESs are unregulated DC or variable/high frequency AC, the integration of renewable energy to the utility grid or MG requires power electronic converters having an inverter as the last conversion stage in case of AC systems. Voltage Source Inverters (VSIs) are widely used as interfaces of Distributed Generation (DG) units in distributed systems and microgrids (MGs). They can be operated in Current/Voltage Control Modes (CCM/VCM) depending on the operation modes of MGs and the nature of DG resources.
In this thesis, power quality enhancement capability of VCM and CCM DG interfacing inverters is investigated and a flexible control method is proposed to compensate voltage and current unbalance and harmonics using the Distributed Generation (DG) interfacing inverters. This method is applicable to both grid-connected and islanded microgrids.
Two control methods including decentralized and secondary control based methods are proposed for power quality enhancement and reactive power sharing coordination of VCM and CCM units in islanded MG. This control scheme is based on local measurement without any communication links; hence, the reliability and simplicity of the system are enhanced in comparison to communication-based methods. In secondary based compensation method, more effective power quality enhancement is achieved, however, the complexity and cost of the system is increased.
A coordinated harmonic compensation and voltage support scheme is presented for distributed generations’ (DGs’) interface inverters in a resistive grid-connected MG. Voltage support is performed by reactive power compensation which can mitigate the over/under voltage problem; furthermore, the active power curtailment is proposed in order to mitigate the overvoltage problem when the reactive power compensation is not sufficient. Harmonic compensation is achieved by using virtual admittances in selected harmonic frequencies.
The control of hybrid photovoltaic and battery energy storage interfacing inverter for power quality enhancement and power management is proposed in single-phase and three-phase systems. A control approach for Battery State of Charge (SOC) and power management is proposed for improving the performance of BESS and load leveling purpose. Furthermore, in order to prevent the BESS from frequently charge and discharge during a day, the discharge of it can be can be controlled by operator or Microgrid central controller.
Simulation and experimental results which are implemented in different operational condition verify the effectiveness of the proposed method. The results show that not only the DG interfacing inverters can inject the active and reactive power and regulates the voltage amplitude and frequency but also they can contribute in power quality enhancement of MG.
