Capacity of a battery is a measure of the amount of charge, in Ampere hours (Ah), stored in the battery. With the battery ageing processes, the capacity of the battery reduces. Consequently, it is essential to have an accurate knowledge of battery capacity in order to perform crucial battery management tasks. For example, in the field of battery reuse, the estimated residual capacity of batteries will help in determining a suitable secondary application for the retired battery pack. Existing literature on offline capacity estimation are often based on low-discharge or 1C rate discharge of the battery. This means that a minimum of one hour wait is required before an estimate of capacity is made. In this paper, a novel approach is proposed for fast offline estimation of battery capacity using the knowledge of the open-circuit voltage (OCV) - state of charge (SOC) curve of the battery. The proposed approach consists of a novel method to estimate the battery OCV by applying a current profile that is optimized to reduce the uncertainty in OCV estimation. For capacity estimation, a constant current pulse is applied for a short duration. The capacity estimation accuracy is theoretically derived as a function of this current duration. The proposed fast capacity estimation approach is shown to be able to estimate the battery capacity within as short as 1 minute duration with an estimation error standard deviation of 0.02 Ah.
The impacts of high voltage (HV) insulators on equivalent circuit parameters of wireless power transfer (WPT) system is evaluated and analyzed in this study. Flat spiral coils are inserted under the HV insulators and convey power to charge monitoring devices' battery at the top of the power line towers. All the external metal objects over the magnetic flux path are identified, and their material type, relative permeability, and conductivity are explained. An equivalent circuit for the WPT system is specified, and its parameters are calculated with and without the presence of external metal objects. In this sense, 3-D finite element method (FEM) simulations are conducted in ANSYS Maxwell. The variation of the magnetic flux within the airgaps is displayed, the eddy current induction initiation over the external metal objects is shown, and changes in the equivalent circuit parameters of the WPT system are clearly discussed. The results of the simulation study are then validated through experimental studies by means of fabricated flat spiral coils.
Power grids are critical cyber-physical systems that employ advanced Information and Communication Technologies (ICTs), e.g., Wide Area Measurement Systems (WAMSs), to deliver the energy to end users reliably and efficiently. WAMSs are used to collect real-time data from Phasor Measurement Units (PMUs) to improve the operator's situational awareness, as well as to enhance real-time monitoring and control of power systems. The WAMS, however, is vulnerable to cyber-attacks due to the susceptibility of its components-such as PMUs and Phasor Data Concentrators (PDCs)-and the lack of embedded security mechanisms in its communication protocols. Some more-destructive cyber-attacks, such as malware injection, can propagate themselves into the components of a WAMS through the communication network. Thus, in such attacks, an attacker can compromise a larger number of components, resulting in more-severe consequences. Therefore, investigating the propagation of cyber-attacks in WAMSs and devising effective countermeasures for this problem are of paramount importance. On this basis, this paper initially develops a model to analyze cyber-attack propagation in WAMS. Then, the impacts of the attacker's capability and the network operator's defensive ability on attack propagation are investigated in detail. Such a study can elucidate the required security measures and defensive strategies to prevent the spread of cyber-attacks in WAMSs. Finally, a Learning-Based Framework (LBF) is developed to estimate the attacker's capability. The simulation results corroborate the effectiveness of the proposed LBF in estimating the attacker's capability.
The concept of virtual synchronous generators (VSGs) has been developed in the literature as an effective approach for controlling power-electronics-based wind power generation. Therein, the converters are controlled to emulate the classic synchronous generators with droop characteristics and to regulate their inertia and damping for better dynamic response. In this paper, a new droop controller is proposed for VSGs which has the capability to regulate the converter frequency after disturbances for maximum power harnessing. The performance of the proposed controller is evaluated through simulation studies carried out in MATLAB/Simulink. It is demonstrated that the new droop controller improves the capability of the VSGs for maximum power point extraction by enabling smooth transition between different operating modes after a frequency disturbance in the grid.
The advent of wide-area measurement systems (WAMSs) in modern power systems enables deployment of wide-area damping controllers (WADCs) to effectively deal with dominant oscillation modes. However, the reliance of WAMSs on information and communication technologies (ICTs) exposes WADCs to potential cyber attacks. To come up with effective countermeasures, extensive knowledge about the existing vulnerabilities and possible cyber attacks is required. On this basis, this paper presents an attack model against WADCs by exploiting the vulnerabilities in the time-alignment strategies utilized by phasor data concentrators (PDCs) to aggregate the stream of phasor measurements. In this attack, the adversary manipulates data timestamp of phasor measurement units (PMUs) to compromise PDCs functionality, causing dropout in the WADC's critical phasor measurements data. To obtain the targeted PMUs and manipulated timestamp, a stochastic mixed-integer linear (MIL) model is developed from adversary prospective considering uncertainty of communication delay. The time-domain dynamic study on two-area Kundur test system demonstrates that the developed attack can jeopardize the WADC performance and even cause system instability.
