Vehicle-To-Grid Technology in a Micro-grid Using DC Fast Charging Architecture

 Abstract

Electric Vehicle (EV) batteries can be utilized as potential energy storage devices in micro-grids. They can help in micro-grid energy management by storing energy when there is surplus (Grid-To-Vehicle, G2V) and supplying energy back to the grid (Vehicle-To-Grid, V2G) when there is demand for it. Proper infrastructure and control systems have to be developed in order to realize this concept. Architecture for implementing a V2G-G2V system in a micro-grid using level-3 fast charging of EVs is presented in this paper. A micro-grid test system is modeled which has a dc fast charging station for interfacing the EVs. Simulation studies are carried out to demonstrate V2G-G2V power transfer. Test results show active power regulation in the micro-grid by EV batteries through G2V-V2G modes of operation. The charging station design ensures minimal harmonic distortion of grid injected current and the controller gives good dynamic performance in terms of dc bus voltage stability.

Keywords

DC fast charging, Electric vehicle, Grid connected inverter, Micro-grid, Off-board charger, Vehicle-to-grid

A Common Capacitor Based Three Level STATCOM and Design of DFIG Converter for a Zero-Voltage Fault Ride-Through Capability

 Abstract

The doubly-fed induction generator (DFIG) based wind power conversion system (WECS) is a viable option for meeting increased load power demand. External reactive power sources like STATCOM type FACTS devices can further improve power flow capability and system security margin. This paper proposes a lookup table-based control scheme for the outer control loops of the Rotor Side Converter (RSC) and the Grid Side Converter (GSC) of DFIG, with a three-level STATCOM coordinating the system. The aim is to enhance power flow transfer and dynamic as well as transient stability, mitigate voltage fluctuations, enable DFIG operation during symmetrical and asymmetrical faults, and limit surge currents. The performance of the DFIG system is evaluated by examining winding currents, torque, and rotor speed at varying loads and symmetrical voltage dips. Additionally, zero-voltage fault ride through is investigated for both super-synchronous and sub-synchronous rotor speeds under symmetrical and asymmetrical LG faults. Finally, the DFIG system's performance is analyzed under different phases to ground faults with and without a three-level STATCOM.

Keywords

Doubly-fed induction generator (DFIG), Field oriented control (FOC), Common-capacitor based STATCOM, Voltage compensation, Balanced and unbalanced faults, Zero-voltage fault ride through

A Lyapunov-Function Based Controller for 3-Phase Shunt Active Power Filter and Performance Assessment Considering Different System Scenarios

 Abstract

The Shunt Active Power Filter (SAPF) is a custom power device that compensates for harmonics, reactive power, and distribution power network imbalances caused by customer-side nonlinear loads in current control mode (CCM). SAPF performance as a harmonic compensator depends on the control technique used for accurate detection of the harmonic current components requiring compensation. This study proposes a 3-phase SAPF based on a Lyapunov function control approach to compensate for harmonics resulting from customer-side nonlinearity in feeder currents. The proposed strategy utilizes a control law that ensures the Lyapunov function's derivative remains consistently negative across a range of stable states. The proportional-integral (PI) controller regulates the DC-link capacitor voltage at a constant reference. This Lyapunov function-based SAPF significantly reduces the rating required compared to two conventional methods. The harmonic compensation efficacy of the proposed SAPF is compared to two conventional approaches in four system scenarios, including increasing the harmonic-constrained penetration level of renewable energy. MATLAB/Simulink simulations show that the Lyapunov function-based controller's performance improves total harmonic distortion (THD) of source current, dynamic and steady-state performance compared to the other two conventional methods. Additionally, the SAPF demonstrates robust compensation performance when dealing with high penetration of renewable energy.

Keywords

SAPF, Lyapunov function, Harmonic compensation, Hysteresis controller, Renewable energy

A Model Predictive Control Method for Hybrid Energy Storage Systems

 Abstract

This paper presents a model predictive control (MPC) strategy for controlling three-level bidirectional DC/DC converters to grid-connect a hybrid energy storage system (HESS) in a DC microgrid. The traditional PI controller has limitations, including difficult tuning of controller parameters and additional filters to handle power fluctuations. The proposed method establishes a mathematical model for the HESS with a battery and ultra-capacitor (UC), solves the neutral point voltage imbalance of a three-level converter, and uses an MPC approach for controlling the grid-connected converters.

The MPC method involves Similarity an outer layer for voltage regulation and a dynamic rolling optimization inner layer that uses predictive control for reducing system current ripple. The proposed cascaded topology has two independent controllers and eliminates the need for filters to allocate high and low-frequency power fluctuations. The strategy enables Contrast independent voltage regulation of two types of energy storage devices, thereby allowing the battery and UC to allocate power. Simulation studies conducted in PSCAD/EMTDC validate the effectiveness of the proposed HESS control strategy and show its superiority over traditional PI controllers. The strategy's robustness is also demonstrated through fault scenarios.

Keywords

Double layer control method, Hybrid energy storage system (HESS), Model predictive control (MPC), Three-level DC/DC converter

A Novel Unified Controller for Grid-Connected and Islanded Operation of PV-Fed Single-Stage Inverter

 Abstract

A Novel Unified Controller for Grid-Connected and Islanded Operation of PV-Fed Single-Stage Inverter In this paper, a novel robust current droop controller (RCDC) using a single droop loop is proposed. The controller supports dual modes of operation for micro-grids (MGs), including grid connected mode (GCM) and islanded mode (ISM), while ensuring seamless transition between the two modes with proportional power sharing maintained. An improved maximum power point tracking (MPPT) technique is also incorporated for the parallel operation of single-stage inverters fed by multi-string PV array topology. Additionally, an improved phase-locked-loop-less (PLL-less) method is presented for the self-synchronization strategy of the parallel operation of PV-inverters with the main grid while maintaining the full capabilities of the unified control architecture, obviating the usage of conventional PLLs. The performance of the proposed control scheme is validated through real-time simulations (RTS) using dSPACE MicroLabBox.

Keywords

Smart Grid, Distributed Generation,Unified Droop Controller,Self-Synchronization, MPPT

A Sub-Synchronous Oscillation Suppression Strategy for Doubly Fed Wind Power Generation System

 Abstract

IEEE Power Electronics Projects A Sub-Synchronous Oscillation Suppression Strategy for Doubly Fed Wind Power Generation System addresses the issue of sub-synchronous oscillation that can occur in the power transmission of doubly-fed induction generator (DFIG), particularly due to the series compensating capacitance and long-distance transmission.

IEEE Power Electronics Projects The paper establishes a mathematical model of the DFIG system and discusses the cause of sub-synchronous oscillation and its effect on the control strategy. An improved PLL is proposed to address the performance degradation of the conventional phase-locked loop (PLL) under sub-synchronous oscillation. In addition, quasi-resonant control is added to improve the performance of the PLL under sub-synchronous oscillation. Experimental results demonstrate the effectiveness of the proposed strategy.

Keywords

Doubly fed induction generator, Sub-synchronous oscillation, Rotor side converter, Stator side converter, Phase-locked loop, Quasi resonance controller

Active Fault Current Limitation for Low-Voltage Ride-Through of Networked Microgrids

 Abstract

With the continuously increasing penetration of networked microgrids (MGs) on the local utility grid (UG), MGs face the challenge to avoid increasing system fault currents during low-voltage ride-through (LVRT). To solve this challenge, an active fault current limitation (AFCL) method is proposed with three parts: 1) a novel phase angle adjustment (PAA) strategy is conducted to relieve the impact of MGs output fault current on system fault current; 2) the current injection (CI) strategy for LVRT is formulated to fit the function of PAA; 3) a novel converter current generation (CCG) strategy is developed to achieve a better voltage support ability by considering network impedance characteristics. The proposed AFCL method is applied to the back-to-back converter, as a connection interface between MGs and UG. Extensive tests and pertinent results have verified the improvements of proposed AFCL method with better LVRT performance, while the networked MGs output fault current does not increase the amplitude of system fault current.

Keywords

Networked microgrids, Back-to-back converter,Low-voltage ride-through,Fault current limitation

Hybrid Five-Level Inverter with Modified Quasi-Z-Source

Abstract

 Hybrid Five-Level Inverter with Modified Quasi-Z-Source proposes the combination of a novel modified quasi-Z-source (MqZS) inverter with a single-phase symmetrical hybrid three-level inverter in order to boost the inverter three-level output voltage. The proposed single-phase MqZS hybrid three-level inverter provides a higher boost ability and reduces the number of inductors in the source impedance, compared with both the single-phase three-level neural-point clamped (NPC) qZSI and the single-phase quasi-Z source cascaded multilevel inverter (CMI).

Hybrid Five-Level Inverter with Modified Quasi-Z-Source Additionally, it can be extended to obtain the nine-level output voltage by cascading two three-level PWM switching cells with a separate MqZS and dc source, which herein is called a single-phase MqZS cascaded hybrid five-level inverter (MqZS-CHI). A modified modulation technique based on an alternative phase opposition disposition (APOD) scheme is suggested to effectively control the shoot-through state for boosting the dc-link voltage and balancing the two series capacitor voltages of the MqZS. The performances of both the proposed MqZS-CHI and the modulation techniques are verified through simulation and experimental results.

Keywords

Cascaded inverter, hybrid five-level inverter, modulation technique, quasi-Z-source.

Designing Fault-Tolerant Control for Reliable Multilevel Inverters with Improved Power Quality

 Abstract

Design of Active Fault-Tolerant Modern renewable energy systems mostly utilize multilevel converter applications for improved power quality and grid synchronization purposes. A multilevel converter is an electrical device that may offer several amounts of voltage levels at the output in order to make the output more comparable to a pure sine wave. The integrity of the multilevel converter depends on the reliability of individual switches such that the converter will collapse in case of faults in these switches.

In this paper, a novel 7-level Fault-Tolerant Cascaded H-Bridge Multilevel Inverter (FT-CHB-MLI) has been proposed that offers high reliability with improved power quality.Adedicated Fault Detection and Isolation (FDI) unit has been built to diagnose the faulty switch and replace it with a standby redundant switch. Total Harmonic Distortion (THD) and the determination of a normalized output voltage factor are employed for fault diagnosis. The Phase Disposition Pulse Width Modulation (PD-PWM) technique has been utilized for switching due to its superior performance as compared to other conventional techniques.

This early fault detection method not only identified the issues but also performed preventative actions to keep the system healthy and stable. The proposed system was tested on the MATLAB / Simulink environment to verify its performance. The simulation results demonstrated that the THD has been reduced to almost 18% with a significant increase in reliability with advanced fault-tolerant architecture consisting of FDI units. The reliability analysis was carried out using Markov chains that also showed its increased reliability. A comparison of the proposed work with literature was also carried out to demonstrate its superior performance with increased reliability.

keywords

Fault-tolerant control, cascaded H-Bridge MLI, 7-level multilevel inverter, inverter fault diagnosis techniques.

A Step-up Multilevel Inverter Topology using Novel Switched Capacitor Converters with Reduced Components

 Abstract

A Step-up in Multilevel Inverters with Novel SCCs , basic cell (BC) of a novel switched capacitor converter (SCC) has been proposed first. After that, the generalized structure of proposed SCC is developed. The developed SCC requires reduced number of switches, drivers, diodes, capacitors and lower number of conducting switches in current flow paths and capacitor charging paths as compared to the other recently developed SCCs. A switched capacitor multilevel inverter (SCMLI) utilizing 2 number of generalized SCCs is developed next.

A Step-up Multilevel Inverters with Novel SCCs Further, cascaded extension of proposed SCMLI is realized and analyzed for symmetric and asymmetric dc source configurations. A detail analysis of optimum selection of capacitance for switched capacitors of 13 level SCMLI is presented. An extensive comparison study shows that the proposed SCMLI requires lower number of components as compared to other SCMLIs. Further, the proposed structure has minimum cost function per level per boosting factor as compared to the other SCMLIs. Extensive experimental results considering fundamental switching frequency scheme are presented to validate the merits and effectiveness of the proposed structure.

Keywords

Boosting factor, multilevel inverter, switched capacitor, reduced devices, voltage balance

Generation of Higher Number of Voltage Levels by Stacking Inverters of Lower Multilevel Structures with Low Voltage Devices for Drives

 Abstract

Generation of Higher Number of Voltage Levels by Stacking Inverters of Lower Multilevel Structures with Low Voltage Devices for Drives Low Voltage Inverters for High-Level Voltage Generation in Drives This paper proposes a new method of generating higher number of levels in the voltage waveform by stacking multilevel converters with lower voltage space vector structures. An important feature of this stacked structure is the use of low voltage devices while attaining higher number of levels. This will find extensive applications in electric vehicles since direct battery drive is possible.

Generation of Higher Number of Voltage Levels by Stacking Inverters of Lower Multilevel Structures with Low Voltage Devices for Drives The voltages of all the capacitors in the structure can be controlled within a switching cycle using the switching state redundancies (pole voltage redundancies). This helps in reducing the capacitor size. Also, the capacitor voltages can be balanced irrespective of modulation index and load power factor. To verify the concept experimentally, a 9-level inverter is developed by stacking two 5-level inverters and an induction motor is run using V/f control scheme. Both steady state and transient results are presented.

Keywords

Induction motor drive, PWM, Multilevel inverter, Topology, CHB, Flying capacitor, Low voltage devices.

A Symmetrical Cascaded Compact-Module Multilevel Inverter (CCM-MLI) with Pulse Width Modulation

 Abstract

A Symmetrical Cascaded Compact-Module Multilevel with PWM for Multilevel Inversion Cascaded H-bridge multilevel inverters have been widely used for power electronics systems. While high-voltage blocking across power switches is not a constraint for low voltage applications, research trend has been oriented to the design of more compact module topologies as an alternative for cascaded H-bridge. Despite the generation of more voltage levels with reduced switch count, the existing module topologies in recent literature take no account of the freewheeling current path during dead-time, and thus inducing multistep jumps in voltage levels and give rise to undesirable voltage spikes.

A Symmetrical Cascaded Compact-Module Multilevel with PWM for Multilevel Inversion Addressing this concern, this paper proposes two symmetrical compact-module topologies for cascaded multilevel inverter, where freewheeling current path during dead-time is provided for smooth transition between voltage levels to prevent voltage spikes. The proposed 7-level and 13-level compact-modules demonstrated low number of conducting switches for all voltage levels. Comprehensive analysis and comparison with the latest module topologies are conducted. To validate the operation of the proposed compact-module topologies, simulation and experimental results are presented.

keywords

Cascaded multilevel inverter, compact module, pulse width modulation, symmetrical module

Development of Cascaded Multilevel Inverter Based Active Power Filter With Reduced Transformers

 Abstract

Development of Cascaded Multilevel Inverter Based Active Power Filter With Reduced Transformers Active power filter is a power electronic converter used for improving the quality of supply by eliminating the effect of harmonics due to non-linear loads. This paper recommends a concept for shunt active power filter (SAPF) using a single power source fed to a cascaded multilevel inverter (CMI) with 3-φ transformers. Apart from traditional transformer based topolo-gies, the required number of transformers are substantially reduced, resulting in less space requirement, which leads to low cost and simple control system.

Development of Cascaded Multilevel Inverter Based Active Power Filter With Reduced Transformers The proposed CMI based SAPF has a capacity to compensate for contaminated load with high harmonic and a low power factor. The effective id − iq theory is used to calculate compensation currents. DC link voltage regulator analyzed through delay time and controller gain. The tasks of the controller in the SAPF can perform all necessary actions for correct operation in SAPF. A wide range of computer simulation results demonstrated and validated the results with the prototype experimental setup.

keywords

Cascaded multilevel inverter, id − iq theory, shunt active power filter, three-phase transformers.

Novel Symmetric Modular Hybrid Multilevel Inverter with Reduced Number of Semiconductors and Low Voltage Stress across Switches

 Abstract

Symmetric Hybrid MLI Novel Symmetric Modular In this paper, by using a modular hybrid structure, a new topology for symmetric multilevel inverters (MLI) with a small number of semiconductors and low voltage stress across switches is proposed. Despite many other topologies, this topology can inherently produce negative levels and zero levels without using the H-bridge. The voltage stress across a particular switch of the proposed MLI is inversely proportional to the number of the switching of that switch in a voltage period. The proposed structure is based on two types of module, that is, the f-module and the e-module. The e-module uses a capacitive voltage divider to double the number of non-zero levels.

Symmetric Hybrid MLI Novel Symmetric Modular The voltages of the capacitors are approximately balanced without complex control methods. The basic structure of the proposed topology is formed by connecting the f-module and the e-module in series with each other, and the cascaded topology is developed by cascading multiple f-modules with an e-module. To investigate the proposed topology and proving its practicability, simulation results with MATLAB/Simulink, investigation of the capacitor voltages, loss calculations and experimental results are presented. A comparative study is also performed to show the merit of the new multilevel inverter over other topologies.

Keywords

new modular hybrid multilevel inverter, low voltage stress, reduced number of semiconductor

Optimal Design of a New Cascaded Multilevel Inverter Topology With Reduced Switch Count

 Abstract

Optimal Design of Reduced-Switch Count Cascaded Inverter Multilevel inverters (MLIs) are a great development for industrial and renewable energy applications due to their dominance over conventional two-level inverter with respect to size, rating of switches, filter requirement, and efficiency. A new single-phase cascaded MLI topology is suggested in this paper. The proposed MLI topology is designed with the aim of reducing the number of switches and the number of dc voltage sources with modularity while having a higher number of levels at the output. For the determination of the magnitude of dc voltage sources and a number of levels in the cascade connection, three different algorithms are proposed. Optimal Design of Reduced-Switch Count Cascaded Inverter The optimization of the proposed topology is aimed at achieving a higher number of levels while minimizing other parameters.

A detailed comparison is made with other comparable MLI topologies to prove the superiority of the proposed structure. A selective harmonic elimination pulse width modulation technique is used to produce the pulses for the switches to achieve high-quality voltage at the output. Finally, the experimental results are provided for the basic unit with 11 levels and for cascading of two such units to achieve 71 levels at the output. cascaded multilevel inverters have gained popularity in the power electronics industry due to their ability to generate high-quality waveforms with reduced harmonic distortion. However, the main disadvantage of these topologies is the high number of switches required to achieve the desired output voltage levels, which can lead to increased complexity and cost.

keywords

Basic unit, cascaded inverter, multilevel inverter (MLI), selective harmonic elimination,
SHEPWM, optimization, reduce switch count.

Modeling, Implementation and Performance Analysis of a Grid-Connected Photovoltaic/Wind Hybrid Power System

Abstract

Modeling, Implementation and Performance Analysis of a Grid-Connected Photovoltaic/Wind Hybrid Power System Wind Hybrid System Grid-Connected PV Modeling & Analysis focuses on the dynamic modeling, design, and control strategy of a grid-connected photovoltaic (PV)/wind hybrid power system. By integrating PV stations and wind farms through a main AC-bus, the system's performance is improved. The Maximum Power Point Tracking (MPPT) technique is utilized for both PV and wind power sources to maximize the power extracted from the hybrid system, even in changing environmental conditions.

In this paragraph Using Matlab/Simulink software, the hybrid power system is modeled and simulated, and the effectiveness of the MPPT technique and control strategy is evaluated. Simulation results demonstrate the effectiveness of the MPPT technique in maximizing power extraction, and show that the hybrid power system operates at unity power factor and maintains constant grid voltage regardless of environmental conditions and injected power.

Keywords

PV; wind; hybrid system; wind turbine; DFIG; MPPT control.

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