Allowing Distributed Generation to Improve Power System Stability By Applying Virtual Synchronous Machine Approach

The installed power capacity of DG is increasing; many of distributed generators are connected to a grid by inverters. The DC/AC inverters are controlled by a Phase Locked Loop (PLL) so they can be synchronized with power system frequency. If this capacity becomes larger, the grid power system become unstable, because the inverter is controlled to follow the power grid frequency. Performance of a photovoltaic generation (PV) plant with an integrated battery energy storage system (BESS) is examined under different system conditions. Although the penetration of distributed renewable energy sources into the traditional grid has risen over the past decade, the potential negative impact of this integration can never be overemphasized. The proposed scheme is evaluated in system studies under fluctuating levels of solar irradiation related to the weather conditions. As the changes in irradiation and temperature occur, the dc link voltage changes due to the changes in power produced, the inverter ac power is controlled to regulate the dc voltage. This research models are energy management system which is based on a hysteresis control algorithm for the battery, which limits the abrupt charging/discharging of the battery, thus increasing battery lifespan which also compensating for change in PV output and power system conditions. The PV source does not have significant energy storage. However, it can supply small quantity of energy for the grid system because it has dc capacitor located in the dc link. Separate energy storage, such as a battery, can work with a PV source to supply energy for the frequency control. In addition, with increasing penetration of the inverter based power generation, there is decrease in inertia due to the fast frequency tracking of the PLL, which speed up dynamic behavior and stability problems on the power grid. To mitigate this problem, the integration of virtual synchronous generators (VSG) based on the photovoltaic (PV) generation plus energy storage is proposed. This research implemented the VSG control based on the swing equation model of a synchronous generator. The VSG can be designed to aid the integration of large-scale photovoltaic generation into the power grid. Through this concept, it is plausible for the DG to exhibit the characteristics and behavior of synchronous generators (SG) such as inertia behaviour, droop functions and damping. These factors make it possible for the PV to contribute to the control and stability of the power grid. The work also presents a proposed a simple method calculating approximate for approximating battery sizing with respect to power and energy by providing emulation inertia in order to meet the target system inertia and power/frequency characteristics. Three cases were simulated in order to calculate the amount of the battery energy sizing needed to support the power grid inertia which reduces the rate of change of frequency deviation. These models are designed and simulated in the electromagnetic alternate transients program (ATP) to simulate the power system. The power grid is testing with the ATP program and validated with powerworld simulator.doctoral, Ph.D., Electrical and Computer Engineering -- University of Idaho - College of Graduate Studies, 2020-0