Short Circuit Current Constrained UC in the High IBG-Penetrated Power Systems
Abstract : Inverter Based Generators (IBGs) have been increasing significantly in power systems. Due to the demanding thermal rating of Power Electronics (PE), their contribution to the system Short Circuit Current (SCC) is much less than that from the conventional Synchronous Generators (SGs) thus reducing the system strength and posing challenges to system protection and stability. This paper proposes a Unit Commitment (UC) model with SCC constraint in high IBG-penetrated systems to ensure minimum operation cost while maintaining the SCC level at each bus in the system. The SCC from synchronous generators as well as the IBGs are explicitly modeled in the formulation leading to an SCC constraint involving decisiondependent matrix inverse. This highly nonlinear constraint is further reformulated into linear form conservatively. The influence of the SCC constraint on the system operation and its interaction with the frequency regulation are demonstrated through simulations on IEEE 30- and 118-bus systems.
? In the existing studies, the simulation methods are mainly adopted to analyze fault current contribution from REG. As a result, the explanations on the fault current show diversity and cannot reach a recognized standard.
? The REGs’ mathematical model in relay-setting calculations is unknown. Thus, this paper theoretically analyses the fault current characteristics of inverter-interfaced REGs (IIREGs) with fault-ride-through (FRT) ability.
? In order to understand the fault current characteristics, the FRT control strategy for IIREGs is firstly studied. Then the characteristics of high-frequency and fundamental-frequency fault currents from IIREGs are theoretically analyzed after and during the faults.
? An optimal synchronous condenser allocation approach is presented in to maintain the system minimum SCC. However, the mixed-integer nonlinear based problem formulation and the considerable investment cost (up to 1M$ fixed cost plus 3M$ per 100MVar) may limit its large scale deployment.
? However, all these methods either require iterations or are too complex to obtain an analytical expression, thus unable to be directly incorporated into a UC problem.
? At each time step, a 24-hour horizon SUC problem is performed with only the decisions of the current node being applied and all the future decisions discarded.
• An iterative solver based on the augmented nodal network equation is proposed to calculate fault currents in a power system dominated by IBGs, which properly models the current limitation and voltage control logic of IBGs, and the fault current contribution from VAR compensators.
• The proposed solver is used to calculate the fault level of a fault level node.
• The proposed fault current iterative solver is shown in Fig.1. Passive components (e.g., loads and network impedances) and active components (e.g., SGs and IBGs) are the inputs.
? Due to this rolling planning method, different realizations of nodes in the scenario tree are consistently generated at every hourly timestep according to the forecast eror quantile based probability.
? Therefore, the out-of-sample scheduling performances can be well captured in the simulation process rather than through Monte-Carlo simulations afterwords.
? Before incorporating the SCC constraint into the SUC problem, the performance of the linearized SCC constraints proposed.
? Therefore, the out-of-sample scheduling performances can be well captured in the simulation process rather than through Monte-Carlo simulations afterwords
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