Weighted Dynamic Aggregation Approach for Modular Large-scale Power Systems Modeling and Analysis
Creators: Shabanikia, Navid
Publisher: name: University of Alberta Library
Year: 2023

<p>Regardless of the power level, many recent power systems are designed with modular and distributed units forming complex systems. Such large-scale systems normally consist of several units with similar hardware and control configurations, which can be connected to the rest of the system at a Point of Common Coupling (PCC). The higher number of units improves reliability, system efficiency, and energy harvesting, however, it makes the system response analysis and control system design challenging. Interactions between a large number of units and the rest of the system connected to the PCC can lead to unpredictable system behaviors such as oscillations, instability, and undesirable transient responses, which can limit the flexibility and scaling of the system. Therefore, power system studies such as power planning, steady-state, and stability analyses should be continuously conducted to ensure a desirable system performance, which requires an accurate and computationally efficient model for modular large-scale systems.<br>
This thesis proposes Weighted Dynamic aggregation (WD agg) approach to model large-scale modular systems with an equivalent unit that has a similar order and structure to an individual unit of the large-scale system. For example, the WD agg model of a PV farm becomes an equivalent single PV array, single inverter, and a controller with weighted average parameters, which hugely reduces the computational burden of the system studies. The parameter weights of each unit are obtained based on the contribution of that unit in the overall dynamic behavior of the system. The proposed approach is applied to find the WD agg model of n parallel DC-DC buck converter to facilitate the sensitivity analyses and control design of the system. Moreover, an equivalent inverter and a controller is found for n  grid-forming inverters in an islanded microgrid with droop control power sharing by the proposed WD agg method. Furthermore, the proposed approach is applied to find the WD agg model of n grid-following inverters in large-scale PV farms considering non-linearity of the PV sources. Additionally, the proposed WD agg approach is used to aggregate n induction machine-based Wind Turbine Generators (WTGs) in a large-scale wind farm considering the mechanical and electric machine dynamics. The performance of the proposed method is evaluated by simulations and experiments of small and large-scale DC microgrids, grid-forming inverter-based islanded microgrids, PV farms, and induction machine-based wind farms with equal or unequal parameters with various inputs and stability conditions under harsh power system events such as line-to-line faults and voltage sags for a comprehensive study.<br>
The simulation and experiment results show that compared with the existing full-order models, simplified models, equivalent circuits, and conventional full, semi, and cluster/zone agg models, the proposed WD agg model can provide an accurate and computationally efficient single equivalent unit for a large number of units with different operating points and parameters, which can be readily used in the steady-state, transient, and stability analyses with superior accuracy. It also can be used to design the large-scale system controller and unit parameters to ensure a desirable system performance.</p>