Robust Fault Ride-Through of Converter-based Generation during Severe Faults with Phase Jumps

Abstract

As grid-connected converters are at risk of losing synchronism with the grid when exposed to extreme voltage sags, this might jeopardize the stability during a fault and a converter's ability to comply with fault ride-through requirements. This paper investigates the synchronization stability of grid-tied converters during severe symmetrical faults with phase jumps. To achieve zero-voltage ride-through capability, a frozen PLL structure can be employed to guarantee stability during faults. However, as the frozen PLL approach is unaware of frequency drifts and phase-angle jumps in the grid voltage, its performance during non-constant frequency and phase is unknown. Therefore, this paper investigates and provides new insight into how the frozen PLL performs during phase jumps and reveals whether phase compensation should be utilized to improve the converter response during a severe symmetrical fault. It is disclosed, that even though phase compensation can improve the injected currents during a fault situation including large phase jumps, a non-compensated frozen PLL can inherently ensure stability and allow for zero-voltage ride-through capability at an acceptable current injection. Furthermore, the robustness of the frozen PLL has been analyzed through a comprehensive simulation study where three test cases have been experimentally verified, which confirms the presented findings.

Grid-Synchronization Stability of Converter-Based Resources—An Overview

“…The simplest method is the PLL freezing method visualized in Fig. 16(a), which nullifies the PLL control error when a predefined severe fault is detected [66], [67]. This effectively makes the PLL-synchronized converter able to operate in a stand-alone mode based on its pre-fault frequency and phase estimations.…”

“…Stabilizing control through modifying the PLL synchronization dynamics during the fault. (a) PLL freezing method [66], [67]. (b) Increase PLL damping ratio [59], [68].…”

“…(d) Switch to a first-order PLL when maximum ROCOF is exceeded [22], [70]. Proposal [66], [67] Freeze the PLL during the fault [59], [68] Increase damping ratio of PLL [69] Gain schedules during fault [22], [70] Switch PLL to a first-order loop during fault decreased, respectively, to improve the system damping, which enhances the transient stability. This method is simple to implement, yet it only works when the converter has two equilibrium points during the fault and lacks parametertuning guidelines.…”

CPS Attacks Mitigation Approaches on Power Electronic Systems With Security Challenges for Smart Grid Applications: A Review

“…5 depicts an outline of the control functions of ACgrid-connected voltage source converters according to their timescales. As depicted, the control loops are illustrated next to each other for operating simultaneously (i.e., DC-link voltage control along with synchronization [29], fault-ride through (FRT) along with AC current control [30], or active damping as well as virtual impedance/admittance control [31]…”

Decentralized Fast Delayed Signal Cancelation Secondary Control for Low Voltage Ride-Through Application in Grid Supporting Grid Feeding Microgrid

“…Furthermore, for Grid Supporting Grid Feeding converters to comply with the grid-code requirement of fault ride-through and grid supports, an accurate estimation of the grid voltage's phase angle is essential. Under low-voltage or weakgrid grid conditions, the voltage's instantaneous value at the Point of Common Coupling (PCC) can be significantly distorted or counterproductive due to the PLL being destabilized, which causes instabilities in the current controller (Taul et al, 2020).…”