Resilience-Oriented Dispatch of Microgrids Considering Grid Interruptions

By providing a reliable and economical supply of energy, microgrids (MGs) may play a pivotal role in the case of large grid disruptions. However, the resilience benefits of microgrids in terms of outage survivability that often lead to economic paybacks are not well investigated in the existing literature. To address this concern, this paper optimizes and simulates a grid-connected MG placed at a hospital consisting of a photovoltaic (PV) module and an energy storage unit that can adequately prevent a prolonged blackout. The impact of net energy metering (NEM) and diesel generator (DG) has further been examined for this hybrid system. Four different cases have been optimized and results show that the PV and battery work in tandem, both with and without considering the existing DG and NEM and meets all critical load demand during a grid outage. The findings also indicate that the proposed approach yields significant economic benefits for two cases relative to business as usual case

A Probabilistic Generative Model for Fault Analysis of a Transmission Line with SFCL

The fault analysis of a transmission line (TL) are the key factors for the rapid restoration of the power network. Due to the recent expansion of the power system as well as the increased generation capacity, the magnitude of the fault current increases beyond the interruption capability of the existing circuit breaker. In this turn, the superconducting fault current limiters (SFCLs) come in handy which limits the fault current and facilitates the tripping operation without upgrading the breaker rating. Besides, the SFCLs affect the three-phase signals which, in turn, negatively affect the transmission line protection scheme. This paper proposes an unsupervised framework for fault detection and classification of a transmission line with SFCLs. The proposed scheme receives 1/2 cycle post-fault three-phase signals and hierarchically extracts the fault information for fault analyzing purposes. The effectiveness of the proposed approach is justified in terms of overall and individual accuracy. Further assessment of the model\u27s performance against noise and measurement error is also carried out in order to confirm the high reliability of the proposed model

Transient Performance Augmentation of DFIG Based Wind Farms by Nonlinear Control of Flux-Coupling-Type Superconducting Fault Current Limiter

Any fault related to grid is a matter of great concern for doubly fed induction generator (DFIG) based power system as DFIG\u27s stator windings are connected to the grid directly. To augment the transient performance of the DFIGs, superconducting fault current limiter (SFCL) is a certified device. To boost the performance of a flux-coupling-type SFCL (FC-SFCL) by ensuing the adaptive use of fault current limiting impedance based on fault severity, rather involving the full impedance unnecessarily, a nonlinear controller (NC) for FC-SFCL (NC-FC-SFCL) is presented in this paper. Reason behind choosing a straightforward NC for this work is to have simple implementation capability with the full flavor of a nonlinear controller. Effectiveness of the NC-FC-SFCL is compared with conventionally controlled FC-SFCL for various fault scenarios. Simulation results suggest that, NC-FC-SFCL can improve the overall fault ride through (FRT) capability which is verified both graphically and numerically. Additionally, this effective use of the fault current limiting impedance guarantees better transient sub-synchronous resonance (SSR) performance, and exhibits better total harmonic distortion responses

The High Frequency Magnetic-Link with Distributed HTS YBCO Windings for Power Converter Applications

High frequency magnetic-link (HFML) is widely used in medium/high voltage power electronic converters for various applications. In this paper, a 440 V, 100 kHz compact HFML is designed with ANSYS/Maxwell software environment where the amorphous material is used as the magnetic core. The HFML is analyzed with solid toroidal cores with various winding configurations. A comparison of the HFML is performed for both the conventional copper winding and superconducting winding. Yttrium barium copper oxide material-based superconductor tape is applied to obtain the maximum power of the HFML. In addition, suitable winding configuration is selected to ensure possible maximum electrical power transfer while minimizing the magnetic saturation in the core. Simulation results show the electrical parameters of the HFML along with its magnetic flux density and power. The proposed HFML design with distributed winding is validated experimentally with a small-scale prototype where it is found that the maximum power transfer capability is increased more than 48% than that of the conventional one

An Advanced Control Scheme for Voltage Source Inverter Based Grid-Tied PV Systems

Nowadays, the use of superconductive magnetic energy storage (SMES) devices in grid integration are highly escalated with the technological amelioration of magnetic components. The power quality and energy conversion efficiency of the power conditioning system of the SMES and renewable energy systems depend on the control algorithms of the voltage source inverter (VSI). However, the traditional control schemes cause inferior response and conversion efficiency. In this paper, an advanced control technique named PI+LLC controller is proposed, which is based on the proportional integral (PI) controller and lead-lag compensator (LLC). The proposed control technique offers significant reduction in the total harmonic distortion (THD), superior dynamic response, smooth response against fault, excellent reference tracking capability of grid current and improved power quality performance at both inverter side and grid side for a 5-level neutral point clamped inverter based grid-tied photovoltaic system. It is expected that, the proposed control scheme can also be used to mitigate the excessive heat of the VSI based SMES system by improving the performance of the power conditioning system. The performance of the proposed control technique is evaluated in MATLAB/Simulink environment to validate the excellent features of the proposed control scheme

Enhanced profitability of photovoltaic plants by utilizing cryptocurrency-based mining load

The grid connected photovoltaic (PV) power plants (PVPPs) are booming nowadays. The main problem facing the PV power plants deployment is the intermittency which leads to instability of the grid. In order to stabilize the grid, either energy storage device - mainly batteries - or a power curtailment technique can be used. The additional cost on utilizing batteries make it not preferred solution, because it leads to a drop in the return on investment (ROI) of the project. A good alternative, is using a customized load (such as; cryptocurrency-based loads) which consumes the surplus energy. This paper investigating the usage of a customized load - cryptocurrency mining rig - to create an added value for the owner of the plant and increase the ROI of the project. These devices are widely used to perform the required calculations for validating the transactions on the network of the Blockchain. A comparison between the ROI of the mining rig and the battery have been conducted in this study. Based on this study the mining rig has superior ROI of 7.7% - in the case with the lowest ROI - compared to 4.5% for battery. Moreover, an improved controlling strategy is developed to combine both the battery and mining rig in the same system. The developed strategy is able to keep the profitability as high as possible during the fluctuation of the mining network

Model Predictive Control Based Advanced Switching Strategy for H-bridge Converter Used in SMES applications to Obtain Even Loss Sharing

The power converters are mostly prone to frequent failures. One of the major causes for their failures is the uneven distribution of power losses among the semiconductor devices. As a consequence, an improved switching strategy with even loss distribution is strongly recommended. The conventional equal loading bus clamping pulse width modulation scheme guarantees equal loss sharing among the devices when the converter operates at unity power factor (pf). However, when the converter operates at non-unity pf, some of the devices are heavily stressed due to high loss density, i.e., junction temperatures of some of the devices become higher than the others. This paper proposes an advanced switching strategy based on model predictive control for a grid-connected single-phase H-bridge converter used in various applications including superconducting magnetic energy storage system. The proposed strategy can achieve balanced loss sharing and almost uniform thermal stress among the devices of the converter under all pf. The novelty of the proposed technique is verified with a scaled-down laboratory test prototype

A soft-switching inverting high step-down converter with a pair of coupled inductors and self-driven synchronous rectifier

In this paper, a non-isolated coupled-inductor high step-down converter with extended duty cycle is proposed, which operates under discontinuous conduction mode. The soft-switching condition is provided for all the switches and diodes, which results in the reduction of the switching losses, and the losses related to diode reverse recovery problem. Also, a self-drive circuit is used to automatically generate the ON and OFF gate signals of the synchronous rectifier, which recovers the gate energy and reduces the complexity. In this topology, only a single coupled inductor is proposed which decreases the size and cost of the proposed converter. A 200 W laboratory prototype is implemented, and its results confirm the validity of theoretical analysis and advantages of the proposed converter over previous structures

An Advanced PWM Technique for MMC Inverter Based Grid-Connected Photovoltaic Systems

Recent developments in multilevel inverters have provided impetus for their applications in the medium voltage renewable energy generation processes. This paper proposes an advanced pulse width modulation technique for a modular multilevel cascaded (MMC) inverter based grid integrated solar photovoltaic (PV) system. It offers lower total harmonic distortion (THD) and power losses compared to the existing modulation techniques. This paper shows the design and performance evaluation of the proposed technique using a 3-phase 5-level MMC inverter-based grid connected PV system. The proposed PWM technique offers 12.49% (without filter) and 0.96% (with filter) output line voltage THDs. It also offers 4.64% output current THD, which complies with the IEEE-519 standard for grid integration. Besides THD reduction, it also reduces the switching and conduction power losses of the MMC inverter. Lower losses may help to keep device temperature low, which is essential for power converters used in superconducting magnetic energy storage (SMES) systems. The simulation is performed in MATLAB/Simulink and the proposed technique is experimentally validated with a laboratory test platform

A Modified reference saturated third harmonic injected equal loading pwm for vsc-based renewable energy systems

Mitigation of excessive heat due to high frequency switching of voltage source converter (VSC) is always an industrial concern for superconducting magnetic energy storage (SMES) or high temperature superconducting (HTS) material based power conditioning system with grid-tied renewable energy interface. The pulse width modulation (PWM) technique employed for the switching of the VSC has a significant impact on joules heating, switching and conduction power losses, total harmonic distortion (THD) profile of the VSC output, and conversion efficiency in the SMES/HTS based grid-tied power system. In this paper, a modified reference saturated third harmonic injected equal loading PWM technique is proposed for a VSC-based grid-tied photovoltaic (PV) system, which offers lower THD and reduced power conversion losses. The proposed PWM technique employed in the VSC can be used in a PV-based SMES/HTS integrated power system to improve the performance of the power conditioner. To prove the superiority of the proposed PWM technique, a simulation in MATLAB/Simulink was carried out and the simulation results were validated by laboratory tests