System Strength and Inertia Constrained Optimal Generator Dispatch Under High Renewable Penetration

Abstract

System strength and inertia inherently provided by synchronous generators (SGs) empower a power system to ride through voltage and frequency disturbances. The requirements of system strength and inertia were not enforced in the National Electricity Market (NEM) of Australia since SGs dominated the generation fleet in the past. However, the increasing wind and solar generation continuously displaces SGs and consequently reduces system strength and inertia in the NEM. This paper proposes a formulation of system strength and inertia constrained generator dispatch to reassure NEM operational security in light of emerging high renewable penetration. A fault current iterative solver is developed to evaluate system strength, in which the current limitation and voltage control logics of inverter-based generators, and the fault current contribution from VAR compensators are properly modelled in the phasor domain. The system strength contribution factor of an SG is defined to linearize system strength constraint for unit commitment (UC). System and sub-network inertia constraints are also formulated for the UC to limit the rate of change of frequency (RoCoF) in the event of generator/interconnector trip. The proposed generator dispatch formulation can fully meet system strength and inertia requirements in the NEM.

Market design for system security in low carbon electricity grids

“…There are physical characteristics of synchronous generators (and other resources, such as synchronous condensers) that have traditionally supported system strength. By contrast, IBRs have characteristics that have limited their ability to contribute to system strength (Gu et al, 2019a(Gu et al, , 2019bShair et al, 2019). First, IBRs are limited in the amount of current they can inject during a fault.…”

Short‐circuit current constrained unit commitment and transmission switching model for improving renewable integration: An MILP formulation

“…However, the high investment cost limits its application in large‐scale power systems. In [8], the unit commitment (UC) considering the SCC constraints is proposed to assure operational security in light of emerging high renewable penetration. However, the contributions of SCC from the RERs are not included.…”

Short Circuit Current Constrained UC in High IBG-Penetrated Power Systems

“…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. In the operational timescale, [11] proposes a system strength and inertia constrained optimal generator dispatch model, where explicit constraints are developed to achieve the optimal system scheduling while satisfying the SCC requirement. However, since the nonlinear SCC constraint is linearized by neglecting the interaction between different generators, an iterative process is necessary to determine the optimal scale factor for SCC calibration and the contribution from IBGs is not considered.…”

“…The IEC 60909-0-2016 standard [13] models the IBGs as constant current source and approximates the SCC by adding the contribution from IBGs to the classic SCC expression yet neglecting the pre-fault operating condition, which may lead to overestimation of the SCC in the system. [11] proposes a fault current iterative solver, which properly models the current limitation and voltage control logic of IBGs. 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.…”