Journal
IEEE TRANSACTIONS ON SUSTAINABLE ENERGY
Volume 12, Issue 4, Pages 2074-2085Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TSTE.2021.3079305
Keywords
Phase locked loops; Power system stability; Stability criteria; Power system dynamics; Voltage-source converters; Steady-state; Small-signal stability; voltage source converter (VSC); weak grid; asymmetric faults; phase-locked loop (PLL); improved control strategy
Categories
Funding
- National Natural Science Foundation of China (NSFC) [51977019, U1966208]
- State Grid Corporation of China (SGCC) [U1966208]
- 111 Project of China [B18062]
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This paper investigates small-signal stability issues of voltage source converters (VSC) connected to weak networks during asymmetric faults, and proposes an improved control strategy to enhance the system's small-signal stability.
Small-signal stability issues of the voltage source converters (VSC) connected weak-network during asymmetric faults is currently rarely studied. This paper develops mathematic model of VSC system during weak-grid asymmetric faults, which reveals dynamic coupling between the phase-locked loop (PLL) and both positive-sequence (PS) control system and negative-sequence (NS) control system. Based on the deduced model, the generalized Nyquist criterion (GNC) method and modal analysis are adopted to study the small-signal stability of the VSC system during asymmetric fault steady-state. The analysis demonstrates that the small-signal stability of the system during asymmetric faults is dominated by the PLL mode, and the dynamic coupling between PLL and current control loops (CCLs) will produce negative damping, which will introduce the small-signal instability risk to the system. Moreover, an improved control strategy is designed for enhancing the small-signal stability of the VSC system during weak-grid asymmetric faults, by compensating the disturbance terms related to PLL dynamic to suppress the negative damping introduced by coupling between the PLL and both the PS and NS CCLs. Finally, this paper verifies the effectiveness of the proposed control strategy through simulation and experiment.
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