Effective Inertia Constant: A Frequency-Strength Indicator For Converter-Dominated Power Grids

The system inertia constant is the predominant indicator for power system frequency strength, but fails to account for non-inertial contributions such as fast frequency response. In this paper, the effective inertia constant is proposed as a new indicator to account for the contribution from both synchronous generators and power-electronic interfaced sources. Time-domain simulations show that the effective inertia constant is a better indicator for frequency nadir than the conventional inertia constant

On Coordinated Control of OLTC and Reactive Power Compensation for Voltage Regulation in Distribution Systems With Wind Power

Active management strategies such as coordinated on load tap changer (OLTC) voltage control and reactive power compensation (RPC) are frequently suggested for voltage regulation in a distribution system with a high level of distributed generation (DG). This paper proposes a control and coordination algorithm for these two active management strategies. Voltage control through OLTC is achieved by using state estimation (SE) to determine the voltage in the network. To lower the implementation cost of the proposed control strategy, pseudo-measurements are used together with real-time measurement data in the SE. Moreover, the deadband of the automatic voltage control (AVC) relay is relaxed so that the AVC relay acts on the network's maximum or minimum voltage obtained through the SE. This is found to be simpler to realize than adjusting the set point of the AVC relay. Voltage control through RPC is actualized by using integral controllers implemented locally at the wind turbine site. Furthermore, RPC from the local wind turbine is also used to mitigate an overvoltage at a remote bus on the same feeder when the remote wind turbine reaches its regulation limit. The applicability of the proposed voltage regulation algorithm is successfully demonstrated using a case study syste

Inertia Support During Variable Wind Conditions

Wind variations are important to consider while designing inertia support strategies. A model has been evaluated but the findings should reflect issues with several control strategies utilizing a fixed inertia support pattern. Wind variability of 0.5 m/s from second to second is observed in real wind data. However, drastic changes in wind speed can occur within the duration of inertia support. An improved inertia control algorithm has been presented allowing a stable delivery of inertia support from variable speed wind turbines (VSWT) subjected to realistic wind conditions. The controller improves the previously presented inertia algorithm and smoothly transitions from a locked operation window to MPPT-operation. The impact of the utilized wind speed filter is described and its impact on the simulation found to be of great importance

Physics-informed machine learning of the correlation functions in bulk fluids

The Ornstein-Zernike (OZ) equation is the fundamental equation for pair correlation function computations in the modern integral equation theory for liquids. In this work, machine learning models, notably physics-informed neural networks and physics-informed neural operator networks, are explored to solve the OZ equation. The physics-informed machine learning models demonstrate great accuracy and high efficiency in solving the forward and inverse OZ problems of various bulk fluids. The results highlight the significant potential of physics-informed machine learning for applications in thermodynamic state theory.Comment: 8 figure

The Effect of Wind Power Integration on the Frequency of Tap Changes of a Substation Transformer

As the capacity of wind power installed in a radial distribution system (DS) increases, there is a concern that it may introduce more frequent tap change operations in substation transformers. The increase in the frequency of tap changes (FTC) can accelerate the wear and tear of the tap changers. As a result, the introduction of wind power to DSs may be hindered. Hence the aim of this paper is to investigate the effect of wind power integration on the FTC in a radial DS. A case study shows that the changes on the FTC in DSs connected to relatively strong external grid is negligible up to significant level of penetration. But in DSs connected to a relatively weak external grid, a significant increase in the FTC has been observed as wind power penetration increases. Hence a further investigation is carried out to limit the FTC by using reactive power from local wind turbines. The results have shown that the methodology is very effective

Evaluating Maximum Wind Energy Exploitation in Active Distribution Networks

The increased spreading of distributed and renewable generation requires moving towards active management of distribution networks. In order to evaluate maximum wind energy exploitation in active distribution networks, a method based on a multi-period optimal power flow analysis is proposed. Active network management schemes such as coordinated voltage control, energy curtailment and power factor control are integrated in the method in order to investigate their impacts on the maximisation of wind energy exploitation. Some case studies, using real data from a Danish distribution system, confirmed the effectiveness of the proposed method in evaluating the optimal applications of active management schemes to increase wind energy harvesting without costly network reinforcement for the connection of wind generation

Protection of converter dominated MV microgrid using changes in current\u27s phase angle

Converter interfaced distributed generations in a microgrid feed the modulated current of limited magnitude during fault conditions. The protection design and its operation are thus challenging due to limited fault current which is further reduced by Petersen coil grounding in medium-voltage (MV) level. This paper aims to address this challenge by developing a current-only directional relay algorithm for the protection of converter dominated MVmicrogrid with Petersen coil grounding. The relay’s operating principle is based on the sign of the change in phase angle of the fault current with respect to the prefault which indicates the direction of fault. The negative and positive changes in current’s phase angle determine the fault in forward and reverse direction, respectively. The tripping decision is derived by comparing the binary output of the relay at both ends of the line segment under protection. This requires a simple, flexible and low bandwidth communication channel. Both theoretical analyses and simulation studies have been performed on a typical distribution grid intended to be operated as microgrid. The proposed protection method is suitable for microgrid having the converters with and without reactive power support. Various operating conditions are evaluated, including bidirectional power flow, high resistance fault,different fault types, loading conditions and signals with noise