This paper presents an adaptive multi-loop control scheme for inverters interlinking dc voltage sources to single-phase, low-voltage ac grids. Control self-adaptation is particularly useful in the ...case of weak grids that, due to frequent physical modifications (e.g., network reconfigurations and disconnection of generators/loads) and intrinsic lack of inertia, present strongly time-variant characteristics. The solution presented in this paper is based on a high-performance converter controller with auto-tuning capabilities. It is shown that the applied auto-tuning method can significantly widen the stability region of the interlinking converter, covering a broad range of grid impedance values. In addition, within the stable region, the controller maintains the nominal performance. Experimental results are reported validating the proposed approach in realistic operating conditions, including grid voltage distortion and variations of amplitude and frequency.
Wind turbines (WTs) are prone to lose the synchronization during severe grid faults due to the absence of equilibrium point. To cope with the issue, this letter proposes a power compensation control ...for doubly fed induction generator based WT to enhance the transient synchronization stability from the new perspective of active power balance. In the method, the active power of WT is controlled to compensate the power loss on the network. Compared with the existing methods, the proposed method has more widely application scenarios because it avoids using the frequency error as control signal. Experimental tests are performed to validate proposed method.
The increasing adoption of renewable energy sources (RES), such as solar photovoltaics and wind turbines, is transforming electricity generation. However, integrating RES within DC microgrids (DCM) ...for applications such as fast DC charging in electric vehicles (EVs) presents challenges, including low inertia, power fluctuations, and voltage instability. This study addresses these challenges with novel control strategies and optimization algorithms. A hybrid Firefly Algorithm-Particle Swarm Optimization (FA-PSO) approach is used to tune Takagi-Sugeno Fuzzy Inference Systems (TSFIS), Adaptive Neuro-Fuzzy Inference Systems (ANFIS), and Fractional Order Proportional-Integral-Derivative (FO-PID) controllers. This strategy optimizes power management within the DCM, ensuring faster convergence, superior accuracy, and reduced topological constraints. In addition, a comprehensive Small Signal Stability Analysis (SSSA) evaluates the impact of the proposed hybrid optimization techniques on DC microgrid stability. Crucially, a hardware prototype validates these strategies under real-world uncertainties, such as varying wind speed and solar insolation, demonstrating their effectiveness and feasibility for practical DC microgrid applications with integrated EV charging.
Cyber-physical systems (CPSs) in the twenty-first century are paving new ways to have better connectivity among the power system devices, effective control, and improved reliability. Thus, ...manipulating this system by foreign interventions like false data injection (FDI) must be handled with utmost priority. Power system monitoring using micro phasor measurement units (μPMUs) gives more insight into the transient performance of the system. Using the optimal placement of PMUs, fewer μPMUs can ensure the complete observability of the power system. This comprehensive view of the system can be used to detect any event that occurs in the system. The measurements of μPMUs connected to the end points of each radial line can be used to detect the event location. However, any FDI-type attack on these devices can degrade the result of the event detection algorithm. In this paper, we work on the IEEE 33 bus system to find the effect of falsified μPMU data on the event detection algorithm. This work presents attack detection using a tolerance limits violation in the presence of an attack. Further, attack effect mitigation on the μPMU readings is inspected to find its detrimental effect on the detection algorithm. The manipulated μPMUs are detected, and their readings are avoided for the proper event location. Event location information is processed to find the control action needed to maintain the stability of the power system. Further, simultaneous event detection of multiple events using a transformer neural network (TNN) classifier is implemented to improve the resiliency of smartgrids.
Generation is shifting from a centralized power generating facility having large synchronous generators to distributed generation involving sources of smaller capacity. Most of these sources require ...inverters on the front end while being connected to the grid. Lower available kinetic energy, coupled with less short-circuit current ratio compared to large synchronous generators, compromises the transient stability of the microgrid when isolated from the main grid. Sources in the microgrid use droop control to share power according to their capacity without any form of communication. This paper proposes a novel controller for inverters to improve the frequency response of microgrid under disturbances involving large frequency deviations. It also discusses design of various parameters defined for the proposed control. The microgrid, which has two inverters and two synchronous generators, is simulated using Simulink/MATLAB software to test the proposed control strategy.
This paper analyzes the power transfer limitation of the photovoltaic (PV) power plant under the ultra-weak grid condition, i.e., when the short-circuit ratio (SCR) is close to 1. It explicitly ...identifies that a minimum SCR of 2 is required for the PV power plant to deliver the rated active power when operating with the unity power factor. Then, considering the reactive power compensation from PV inverters, the minimum SCR in respect to power factor (PF) is derived, and the optimized coordination of the active and reactive power is exploited. It is revealed that the power transfer capability of PV power plant under the ultra-weak grid is significantly improved with the low PF operation. An adaptive reactive power droop control is next proposed to effectively distribute the reactive power demands to the individual inverters, and meanwhile, maximize the power transfer capacity of the PV power plant. Simulation results of a 200-MW PV power plant demonstrate that the proposed method can ensure the rated power transfer of PV power plant with the SCR of 1.25, provided that the PV inverters are operated with the minimal PF=0.9.
In recent years, the cascaded LCC-MMC (line commutated converter- modular multilevel converter) inverter has been suggested as a viable option for High Voltage Direct Current (HVDC) transmission ...systems due to its capability to combine the advantages of LCC and MMC inverters, e.g., a reduced susceptibility to commutation failures and cost-effectiveness. However, ensuring the stability of this inverter when connected to a weak grid has become a significant area of focus, particularly with the growing integration of renewable energy sources into the power grid. This paper addresses this concern by developing a small-signal admittance model for the hybrid LCC-MMC inverter. Using this model and the general Nyquist criterion, the study investigates how the conditions on the AC side of the rectifier and the DC circuit affect the stability of the cascaded LCC-MMC inverter when connected to a weak grid. This aspect, which is often overlooked, is examined in detail. In order to enhance the stability, this paper proposed an improved control strategy for managing circulating currents. This strategy is intended to reshape the DC equivalent impedance, thereby minimizing the effects of conditions on the AC side of the rectifier and the DC circuit on the LCC-MMC inverter. To validate the model's accuracy and assess the effectiveness of the proposed control strategy, time domain simulations are conducted.
Synchronized control (SYNC) is widely adopted for doubly fed induction generator (DFIG)-based wind turbine generators (WTGs) in microgrids and weak grids, which applies P-f droop control to achieve ...grid synchronization instead of phase-locked loop. The DFIG-based WTG with SYNC will reach a new equilibrium of rotor speed under frequency deviation, resulting in the WTG's acceleration or deceleration. The acceleration/deceleration process can utilize the kinetic energy stored in the rotating mass of WTG to provide active power support for the power grid, but the WTG may lose synchronous stability simultaneously. This stability problem occurs when the equilibrium of rotor speed is lost and the rotor speed exceeds the admissible range during the frequency deviations, which will be particularly analyzed in this paper. It is demonstrated that the synchronous stability can be improved by increasing the P-f droop coefficient. However, increasing the P-f droop coefficient will deteriorate the system's small signal stability. To address this contradiction, a modified synchronized control strategy is proposed. Simulation results verify the effectiveness of the analysis and the proposed control strategy.
Grid-connected renewable energy conversion systems (RECSs) are usually required by grid codes to possess the low voltage ride through (LVRT) and reactive power support capabilities so as to cope with ...grid voltage sags. During LVRT, RECS's terminal voltage becomes sensitive and changeable with its output current, which brings a great challenge for the RECS to resynchronize with the grid by means of phase-locked loops (PLLs). This paper indicates that loss of synchronism (LOS) of PLLs is responsible for the transient instability of grid-connected RECSs during LVRT, and the LOS is essentially due to the transient interaction between the PLL and the weak terminal voltage. For achieving a quantitative analysis, an equivalent swing equation model is developed to describe the transient interaction. Based on the model, the transient instability mechanism of RECSs during LVRT is clarified. Furthermore, a transient stability enhancement method is proposed to avoid the possibility of transient instability. Simulations performed on the New England 39-bus test system verify the effectiveness of the method.
In this paper, the predefined-time consensus tracking problem of second-order multiagent systems (MASs) is investigated. A distributed observer is presented to estimate the tracking error for each ...follower within predefined time. A novel sliding surface is constructed to ensure predefined-time system convergence along the sliding surface and a terminal sliding mode consensus protocol is presented to overcome singularity problem and achieve leader-following consensus within predefined time. It is mathematically proved that the followers' states can track the leader's trajectory within predefined time. In particular, the settling time bound is directly related to tunable parameters, which facilitates the control protocol design to meet the desired convergence time requirement. Besides, the estimation bound for convergence time is less conservative than some existing fixed-time consensus protocols. The effectiveness of the proposed method is verified by the consensus tracking control for networked single-link robotic manipulators.
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