Sajeeb Saha

The global power grid is undergoing a major transformation as a result of the growing utilization of renewable energy sources (RESs). The incorporation of these RESs is leading to a decline in the use of conventional synchronous generators and an increase in the use of inverter-based RESs. This shift is causing a decrease in the grid's inertia, presenting substantial difficulties for grid operators to maintain frequency stability. The purpose of this study is to examine the impact of declining inertia on the frequency behavior of the grid, as RESs become more prevalent. In order to measure the impact, this study utilizes eigenvalue analysis of power grids to assess the sensitivity of grid frequency and rate of change of frequency (RoCoF) characteristics, as well as the lowest frequency, to variations in grid inertia resulting from changes in RES penetration. Moreover, we have introduced indices that quantify the impact of RES penetration on the grid frequency behaviour in comparison to a grid without RES. To showcase the proposed approach, this research presents case studies using the modified IEEE 39 bus test system, which demonstrate the ability to assess the impact of a high RESs penetration on grid frequency characteristics.

The worldwide electricity network is undergoing a crucial transformation, shifting from traditional synchronous generators to inverter‐based renewable energy sources (IRESs). This shift is expected to reduce the grid's available fault level (AFL), potentially impacting grid functionality, particularly during the integration of IRESs into weak grids. This paper examines the challenges associated with weak grids, focusing on the steady‐state and dynamic stability of IRES when integrated into these systems. In the steady‐state analysis, the effects of AFL, injected power volume, and grid characteristics on the steady‐state voltage at the point of interconnection were explored. For dynamic stability, eigenvalue and H ₂ norm analyses are used for evaluation. Sensitivity analysis is conducted to assess the impact of these factors on the stability of IRESs connected to weak grids. A detailed case study using the IEEE 39 bus test power system is included to demonstrate our findings, where the steady‐state and dynamic stability of IRES connected to the test system are assessed using the proposed methods. The accuracy of these analyses is confirmed by extensive simulation studies on the OPAL‐RT real‐time digital simulator platform.

In this paper, a composite nonlinear controller is developed for stabilizing a constant power load (CPL) feeding DC-DC boost converter (DBC) for DC microgrid applications. If the boost converter is not properly controlled, the negative incremental impedance (NII) of CPLs can cause DC-bus voltage instability. As the original model is not adequate for designing the proposed controller, the nonlinear dynamical model of the DBC is transformed into Brunovsky’s canonical forms. Large load and input voltage changes hinder the controller’s performance. Therefore, the dynamical model has been updated to include constrained external uncertainty. Then, the proposed hybrid controller, which is a combination of the nonlinear backstepping controller and the sliding mode controller, is designed. The sliding mode controller has a double-integral-based sliding surface and a fast power-based reaching law to improve hybrid controller performance. The global stability of the proposed system is analyzed using the control Lyapunov function theory. Lastly, simulation studies in MATLAB/Simulink and experiments on an in-house hardware platform show that the proposed composite controller works well even when there are big changes.

This paper presents an adaptive rate of change of frequency (ROCOF) based passive Islanding detection technique (IDT) to overcome the non-detection zone (NDZ) issue and limitation of existing islanding detection techniques. The proposed ROCOF based passive IDT relies on the settings of the phase locked loop (PLL) closed loop control system for frequency, ROCOF and threshold ROCOF value for the PCC relay setting calculations. So, the PLL results in alternate frequency and ROCOF output value with respect to the PLL settings modification. The PLL settings can be different in different types of microgrid systems. Therefore, the proposed adaptive ROCOF based IDT provides a generic solution for islanding detection applications for the safe and reliable operation of different types of microgrid systems. The adaptive ROCOF based IDT is developed and implemented on two different types of the microgrid systems such as (I) generator based microgrid (ii) generator, PV and storage based hybrid microgrid in Matlab/Simpower System. Results showed that the proposed IDT successfully detected the islanding condition even with zero power mismatch and it is fully capable to distinguish between islanding (loss of mains and external fault) and non-islanding (internal fault, load switching, motor starting etc.) conditions with a diverse range of operating conditions.

In this paper a sensor fault resilient control approach for electronically interfaced distributed energy resources (DERs) in islanded microgrids is proposed. The proposed control strategy consists of a sliding mode observer (SMO) and a H infinity output feedback controller that ensures resiliency of the DER units in an islanded microgrid against erroneous measurements due to sensor malfunctioning. Any error in the measurements due to malfunctioning of the associated sensors are modelled as sensor faults in this paper. The SMO in the proposed approach estimates the sensor faults, and the estimated faults are used to devise fault tolerant control strategy so that the H infinity output feedback control remains unperturbed by the erroneous measurements. In order to demonstrate the efficacy of the proposed control strategy, rigorous simulation studies are carried out on a test islanded microgrid system with single DER and multiple DERs. The efficacy of the proposed approach has been further validated through an experimental study carried out on a prototype islanded microgrid system

In the design procedure of a PV‐based microgrid, optimal sizing of its components plays a significant role, as it ensures optimum utilization of the available solar energy and associated storage devices. This in turn ensures efficient and economic operation of the microgrid. Various approaches have been reported in the literature in order to approach the sizing problem in PV‐based microgrids. However, the existing approaches are subjective to the requirements of the microgrid and there is no unique framework for approaching the microgrid sizing problem. In this study, a comprehensive review of the existing approaches used for sizing of PV‐based microgrids with a summary of the commonly adopted design considerations has been presented. Also, the optimization problem, including the usually considered designed objectives and constraints, for PV‐based microgrid sizing have been thoroughly reviewed in this study. Furthermore, the adopted approaches for solving the optimization problem associated with the sizing of a PV‐based microgrid system available in the literature have been reviewed comprehensively. With a view to present a generic framework for the optimal sizing of a PV‐based microgrid, this study further presents a framework based on the comprehensive review of the existing literature. The developed framework will be useful for both the practising engineers and academics to understand and apply the usual practices for optimal sizing of PV‐based microgrids.

Grid integration of solar photovoltaic (PV) systems has been escalating in recent years, with two main motivations: reducing greenhouse gas (GHG) emission and minimizing energy cost. However, the intermittent nature of solar PV generated power can significantly affect the grid voltage stability. Therefore, intermittent solar PV power generation and uncertainties associated with load demand are required to be accounted for to gain a holistic understanding on power grid voltage stability with the high penetration of PV energy sources. This article presents a framework for power grid voltage stability analysis considering uncertainties associated with PV power generation and load demand using Monte Carlo simulation. Commonly used voltage stability indicators such as critical eigenvalue, line loss, reactive power margin have been considered in the proposed framework. The proposed methodology has been verified by analyzing the voltage stability of the IEEE 14 bus test system, with the high penetration of PV energy sources and considering uncertainties associated with load demand. The results provide a clear insight into the voltage stability of power grid with different penetration levels of PV energy sources into the power grid.