Multi-Loop Transient Stability Control via Power Modulation From Energy Storage Devices

Abstract

This paper presents an optimal transient-stability control strategy that modulates the real power injected and absorbed by distributed energy-storage devices. These devices are located at the high-voltage bus of several generators in a synchronous power system. The system is broken into areas based upon groupings of generators. The control strategy consists of two parallel feedback loops. One loop focuses on preserving the synchronism of the generator to its own area. The second loop focuses on preserving the synchronism of a given area to the other areas. Each control loop strategy is based upon local and center-of-inertia frequency measurements. The strategy is derived from two perspectives. With the first, the goal is to remove as much kinetic energy gained during a disturbance as quickly as possible before it is converted to potential energy. With the second perspective, an optimal transient control costfunction is minimized. Both perspectives result in the same strategy. The performance of the control strategy is evaluated on a four-machine power system model and on a 34-generator reduced-order model of the western North-American grid. The results show that this control approach significantly improves the transient stability of power systems.

Real Power Modulation Strategies for Transient Stability Control

“…The emergence of utility-scale inverter-based resources (IBR) enables the implementation of feedback control systems that can modulate real power with sufficient bandwidth to provide synchronizing torque. Energy storage systems are particularly well suited for these applications because of their ability to both source and sink real power [36]. This paper focuses on real power modulation strategies because of their ability to produce synchronizing torque without altering the response of the system load to deviations in voltage [37].…”

“…In contrast, IBRs are capable of rapidly modulating their real power output to provide synchronizing torque over the first few swings of a disturbance. Doing so requires a different control approach than the standard droop relationship between real power and frequency [36].…”

“…An alternative approach is to modulate a component of P ei (t) that drives ω i (t) towards ω(t). Because ω(t) is easier to estimate in real-time, these strategies are more readily implemented; however, this control action is more correlated with damping torque than synchronizing [36], [53].…”

“…In [36], Ojetola et al formulate a problem for determining the optimal charging response of an energy storage device located near the terminals of a synchronous generator. The concept is similar to dynamic braking.…”

“…When the device charges, it absorbs excess energy, much like a braking resistor. For the jth device co-located with the ith synchronous generator, the optimization problem in [36] may be stated as minimize…”