A microgrid is a small-scale power system that includes distributed energy sources, energy storage devices, an‎d a variety of loads that can operate in both on-grid an‎d off-grid modes. DC microgrids have lower construction cost an‎d higher efficiency than AC microgrids due to their easier compatibility with renewable energy generation sources, battery storage systems, an‎d electronic loads. Among renewable energy sources, photovoltaic systems have become a popular energy source due to their low panel construction cost, high efficiency, an‎d long service life an‎d ability to track their maximum power point, so that their use in microgrids an‎d distribution systems is increasing every year. One of the most important challenges in islan‎ded microgrids is the imbalance between production an‎d consumption, which leads to instability in the main bus voltage of the microgrid. In recent years, extensive studies have been conducted on control methods for photovoltaic systems, which have led to the development of new control methods for achieving a flexible power point. The goal of these methods is to adjust the power of photovoltaic systems to a certain value that maintains the stability of the microgrid. The most important drawbacks of some methods for flexible power point tracking of photovoltaic systems are constant oscillation around the desired power point, severe disturbances caused by the denominator of zero in the calculations. In this thesis, a control system based on flexible power point tracking an‎d droop control for photovoltaic system in DC microgrid is presented. Then, the secondary microgrid control system is presented to adjust the power of the photovoltaic system an‎d the battery storage systems to stabilize the main bus voltage of the microgrid. In the improved flexible power point tracking control system, a discrete signal analysis method with a filter is used to calculate the derivative of power in terms of panel voltage along with anti-windup control, which significantly reduces the fluctuations of the panel output power. Also, this system has the ability to change the operating point between the maximum achievable power mode an‎d powers less than the maximum power continuously an‎d in the main loop of the droop control based on the derivative of power in terms of voltage. In order to properly share the power, the improved droop method is used at the primary control level of the microgrid units, which in the battery storage, the charge level parameter an‎d in the photovoltaic system, the slope of the solar panel P-V curve are entered in the control algorithm. Droop algorithm based on battery charge level is able to continuously change the state of the battery between charge an‎d discharge state. Finally, controller design an‎d system stability analysis have been done by extracting the small signal model. The efficiency of this scheme is first investigated by simulation in the Simulink environment an‎d then by designing an‎d building a DC microgrid including a photovoltaic system, a battery storage system an‎d a programmable fixed power load, the accuracy of the proposed control system is demonstrated practically an‎d in the form of different scenarios.

محمد سعيد مهدوي

حميدرضا كارشناس , فاطمه زارع