Stabilising transient disturbances with utility‐scale inverter‐based resources

Abstract

This study presents a trajectory tracking control strategy that modulates the active power injected by geographically distributed inverter-based resources to support transient stability. Each resource is independently controlled, and its response drives the local bus voltage angle towards a trajectory that tracks the angle of the centre-of-inertia. The centre-of-inertia angle is estimated in real time from wide-area measurements. The main objectives are to stabilise transient disturbances and increase the amount of power that can be safely transferred over key transmission paths without loss of synchronism. Here the authors envision the actuators as utility-scale energy storage systems; however, equivalent examples could be developed for partiallycurtailed photovoltaic generation and/or Type 4 wind turbine generators. The strategy stems from a time-varying linearisation of the equations of motion for a synchronous machine. The control action produces synchronising torque in a special reference frame that accounts for the motion of the centre-of-inertia. This drives the system states toward the desired trajectory and promotes rotor angle stability. For testing, a reduced-order dynamic model of the North American Western Interconnection is employed. The results show that this approach improves system reliability and can increase capacity utilisation on stabilitylimited transmission corridors.

Real Power Modulation Strategies for Transient Stability Control

“…Because the large-signal dynamics of power systems are inherently nonlinear, different design and tuning procedures are required for transient stability control. Nevertheless, linear analysis can still provide valuable information about control performance in these cases [7].…”

“…These control strategies can improve system reliability and alleviate capacity constraints on stability-limited transmission corridors. They can also reduce the need for under-frequency load shedding, helping to maintain service for more customers following severe disturbances [7].…”

“…where T e (t) is the per-unit electromagnetic torque acting on the rotor (the air-gap torque), and T m (t) the per-unit mechanical torque supplied to the rotor by the prime mover. Suppose we linearize the dynamical system defined by ( 5) and (7) about some static equilibrium denoted {x s , u s }, i.e.,…”

“…For real power applications, this entails modulating a component of P ei (t) that is in phase with the error of δ i (t) from its post-disturbance equilibrium, or some trajectory that converges toward this point. This requires that the post-disturbance equilibrium or desired trajectory be estimated in real time, which is a non-trivial task [7]. An alternative approach is to modulate a component of P ei (t) that drives ω i (t) towards ω(t).…”

“…The primary objective of damping controllers is to maintain small-signal (oscillatory) stability [4], [5]. By contrast, the primary objective of synchronizing controllers is to maintain large-signal (transient) stability [6], [7].…”