Analysis of Local Anti-Islanding Detection Methods for Photovoltaic Generators in Distribution Systems

In the current decade, technology innovations and cost reduction of inverter-based Distributed Energy Resources (DERs) have led to higher integration of distributed energy storage and photovoltaic (PV) solar power systems. Increasing growth in PV penetration to the distribution system can raise operational and safety concerns especially in case of an unintended islanding. In general, standards require distributed generators (DGs) to detect islanding from the main grid and cease to energize the local system. Multiple methods have been introduced in the literature to detect these islands reliably and quickly. In order to connect an inverter to distribution system, inverter should pass certain certification tests such as UL 1741 certification test. The anti-islanding test in UL 1741 standard tests only one type of load over a limited range of loading conditions with a single inverter and lumped load and no impedances in between them. The overall goal of this thesis is to determine those parameters to which run-on times (ROTs) are relatively insensitive and thus do not need to be emphasized in certification testing or risk of islanding studies. This thesis presents a generic MATLAB Simulink inverter model and studies sensitivity of anti-islanding tests to parameters such as inverter location, inverter operating point, load location, load type and circuit impedance. Inverters in these studies are equipped with Group 2A and Group 2B anti-islanding methods. The key contributions in this thesis can be summarized as follows: A comprehensive review of anti-islanding techniques in the literature. An anti-islanding detection model was developed in MATLAB software with at least one method from different groups of anti-islanding methods; the model can be used further for industrial applications and research purposes. The result of analyses indicated that the level of phase-phase imbalance, constant-power load, harmonic-current load and irradiance level have a low or negligible impact on anti-islanding and can be omitted from these studies. These findings are expected to lower the cost and improve the speed of these studies, in large distribution systems. Adviser: Sohrab Asgarpoo

Optimum Renewable Generation Capacities in a Microgrid Using Generation Adequacy Study

Microgrids, as small power systems, may be comprised of different types of loads and distributed generation. As the integration of renewable power generation increases, the total available generation capacity of the system will be more derated due to the effect of equipment failures and the intermittent nature of these resources. Therefore, it is critical to determine optimum renewable generation capacities and provide enough reserve margin to meet the target reliability of the microgrid. In this paper, we first model a microgrid, including conventional and renewable distributed generation and the loads. Second, we determine the renewable generation capacity required to meet growth in demand at a certain level of grid reliability through a generation adequacy study. Adequacy of the microgrid is evaluated using parameters such as loss of load probability (LOLP) and expected energy not served (EENS). Third, the impact of different conditions, such as wind speed diversity (captured by correlating the wind power output), a combination of wind and solar power, and load diversity, on generation adequacy is studied through sensitivity analyses. Finally, the optimum renewable generation capacities are determined such that the total cost of generation and unserved power is minimized. The optimization process is based on the particle swarm optimization (PSO) method which uses Monte Carlo (MC) simulation for generation adequacy studies in each iteration

Optimum Renewable Generation Capacities in a Microgrid Using Generation Adequacy Study

Microgrids, as small power systems, may be comprised of different types of loads and distributed generation. As the integration of renewable power generation increases, the total available generation capacity of the system will be more derated due to the effect of equipment failures and the intermittent nature of these resources. Therefore, it is critical to determine optimum renewable generation capacities and provide enough reserve margin to meet the target reliability of the microgrid. In this paper, we first model a microgrid, including conventional and renewable distributed generation and the loads. Second, we determine the renewable generation capacity required to meet growth in demand at a certain level of grid reliability through a generation adequacy study. Adequacy of the microgrid is evaluated using parameters such as loss of load probability (LOLP) and expected energy not served (EENS). Third, the impact of different conditions, such as wind speed diversity (captured by correlating the wind power output), a combination of wind and solar power, and load diversity, on generation adequacy is studied through sensitivity analyses. Finally, the optimum renewable generation capacities are determined such that the total cost of generation and unserved power is minimized. The optimization process is based on the particle swarm optimization (PSO) method which uses Monte Carlo (MC) simulation for generation adequacy studies in each iteration

Analysis of Local Anti-Islanding Detection Methods for Photovoltaic Generators in Distribution Systems

In the current decade, technology innovations and cost reduction of inverter-based Distributed Energy Resources (DERs) have led to higher integration of distributed energy storage and photovoltaic (PV) solar power systems. Increasing growth in PV penetration to the distribution system can raise operational and safety concerns especially in case of an unintended islanding. In general, standards require distributed generators (DGs) to detect islanding from the main grid and cease to energize the local system. Multiple methods have been introduced in the literature to detect these islands reliably and quickly. In order to connect an inverter to distribution system, inverter should pass certain certification tests such as UL 1741 certification test. The anti-islanding test in UL 1741 standard tests only one type of load over a limited range of loading conditions with a single inverter and lumped load and no impedances in between them. The overall goal of this thesis is to determine those parameters to which run-on times (ROTs) are relatively insensitive and thus do not need to be emphasized in certification testing or risk of islanding studies. This thesis presents a generic MATLAB Simulink inverter model and studies sensitivity of anti-islanding tests to parameters such as inverter location, inverter operating point, load location, load type and circuit impedance. Inverters in these studies are equipped with Group 2A and Group 2B anti-islanding methods. The key contributions in this thesis can be summarized as follows: A comprehensive review of anti-islanding techniques in the literature. An anti-islanding detection model was developed in MATLAB software with at least one method from different groups of anti-islanding methods; the model can be used further for industrial applications and research purposes. The result of analyses indicated that the level of phase-phase imbalance, constant-power load, harmonic-current load and irradiance level have a low or negligible impact on anti-islanding and can be omitted from these studies. These findings are expected to lower the cost and improve the speed of these studies, in large distribution systems. Adviser: Sohrab Asgarpoo