Coordinated control among PSS, WTG and BESS for improving Small-Signal Stability

The goal towards attaining a sustainable future has led to the rapid increase in the integration of converter control based generators (CCBGs). The low inertia response characteristics of CCBGs and the weak tie lines in interconnected systems pose a huge threat to Small-Signal Stability (SSS). Adequate damping of low-frequency oscillations (LFO) is pivotal in ensuring the maximum power transfer through the critical transmission corridors. These operational issues become more serious with the significant reduction in system inertia as a result of the high penetration of CCBGs. Therefore, appropriate control techniques are an absolute requirement for preventing LFOs from limiting the penetration of CCBGs in interconnected networks. This may also eventually lead to revisions in grid codes mandating CCBGs to provide auxiliary damping control. But, the progressive addition of multiple damping controllers for specific target modes can lead to the drifting of eigenvalues (EVs) associated with other electromechanical modes (EMs) in the system. This is due to the adverse interactions between multiple damping controllers in the uncoordinated control approach and may result in deteriorating SSS. Therefore, this paper proposes a simultaneous coordinated control among Battery Energy Storage System (BESS), Wind Turbine Generators (WTG) and Power System Stabilizer (PSS) for enhancing SSS in networks with high wind penetration by considering both inter-area (IA) and local modes. The performance of the proposed coordinated control is corroborated using IEEE 68 bus system for multiple operating scenarios for which the critical modes in the system have the lowest damping index (DI). The effectiveness of modulating the active power, reactive power and simultaneous modulation of both active and reactive power injected by BESS along with a dual-channel Optimized WTG Damping Controller (DOWDC) and PSS is evaluated. The impact of the different coordinated control strategies on voltage dynamics is also investigated. The simulation results validate the better performance of the proposed coordinated control over uncoordinated control approaches.

Additional Damping Control of a Hybrid Multi-infeed DC System with a Wind Farm

Background: In a hybrid multi-infeed direct current (HMIDC) system, the interaction between the AC and DC systems will have an influence on the damping characteristics of the system, while a doubly-fed induction generator (DFIG) -based wind turbine connected to the grid complicates the coupling between AC and DC. Objective: Based on the basic principles of wind power generation and low-frequency oscillation (LFO), a DFIG -based wind turbine is respectively connected to the LCC-HVDC side and VSC-HVSC side of an HMIDC system to study the influence of the oscillation mode on a hybrid system with different wind power access locations, and two kinds of additional DC damping controllers are designed to suppress the LFO. Comparing the effects of different additional DC damping controllers on the suppression of the LFO in the system. Methods: First, the total least squares- estimation of signal parameters via rotational invariance techniques (TLS-ESPRIT) is used to obtain the system’s oscillation mode. Second, the transfer function is determined by the Butterworth bandpass filter. Third, the LCC-HVDC and VSC-HVDC additional damping controllers are designed based on the H2/H∞ hybrid control theory. Results: The designed additional DC damping controller has a good suppression effect on LFO in the HMIDC system and can meet the system damping deficit. The effect of the LCC-HVDC additional damping controller is better than that of VSC-HVDC. Conclusion: Through a simulation analysis on PSCAD/EMTDC simulation software, the effectiveness of the designed additional DC damping controller is verified.