Mohammed A. Haj-ahmed

The Influence of Inverter-Based DGs and Their Controllers on Distribution Network Protection

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers.

Protection Strategies for Medium-Voltage Direct-Current Microgrid at a Remote Area Mine Site

This paper presents protection strategies for a medium-voltage dc (MVDC) microgrid at a remote area mine site. The microgrid is operated to provide high power quality and reliability to sensitive loads and to improve the energy efficiency of the mining equipment. In the MVDC microgrid, various local distributed energy resources have been used, including photovoltaic arrays, wind turbines, a fuel-cell stack, an energy storage system, and mobile diesel generators. For the protection of transmission lines, a communication-based differential protection scheme with solid-state electronic relays is employed to isolate the faulted part of the MVDC microgrid. This is further reinforced by dc overcurrent protection as a backup. Earlier research work had neglected the backup protection for dc systems. In addition, communication-based dc directional overcurrent protective relays are used for both source protection and load protection to support a bidirectional power flow. MATLAB/Simulink modeling and simulation results are presented and discussed to illustrate the proposed systems dependability and security.

Comprehensive protection strategy for an islanded microgrid using intelligent relays

In this paper, a comprehensive protection strategy is proposed for insuring dependable and secure operation of an islanded microgrid system. This is implemented using microprocessor-based relays to prevent unnecessary loss of critical loads and distributed generators (DGs). Several improvements are proposed to clear the way for plug-and-play of DGs. Furthermore, recommendations are presented to tackle the elusive high-impedance fault problem, commonly encountered in distribution systems. An optimal directional overcurrent bus protection is also presented. Several case studies and analyses are carried out to demonstrate the proposed protection strategy. Results from simulation using MATLAB/Simulink are also shown.

An MVDC microgrid for a remote area mine site: Protection, operation and control

This paper investigates the design of a medium voltage direct current (MVDC) microgrid for a remote area mine site. The various aspects covered include its protection schemes as well as operation and control. This is intended to provide a voltage of high power quality and reliability at the sensitive load terminals, and also improve the energy efficiency of all the mining equipment. In the proposed MVDC microgrid, several local distributed energy resources (DERs) have been employed including PV arrays, wind turbines, a fuel cell stack, an energy storage system and mobile diesel generators. A comprehensive analysis is presented on the protection, operation and control of the MVDC microgrid system. A communication based differential protection scheme with solid state electronic relays is employed for isolating only the faulted portion of the MVDC microgrid. Previous research work had largely neglected the backup protection for DC systems. In this paper, the overcurrent protection device is utilized for backup protection. Furthermore, with an appropriate communication and cooperative framework among these DERs accompanied by dc bus signaling (DBS) control, the dc bus voltage can be maintained within an acceptable range. MATLAB/Simulink modeling and simulation results are presented and discussed to illustrate the systems reliability, security and power quality.

Investigation of protection schemes for flexible distribution of Energy and Storage resources in an industrial microgrid

It is well known that the control strategies of distributed energy resources (DERs) have a major influence on the protection schemes of both DERs and distribution systems. In view of that, the coordination between DER controls, DER relays, and distribution system relays is necessary to have a secure and reliable power delivery. The Flexible Distribution of EneRgy and Storage resources (FDERS) was a recently proposed framework that is extremely valuable for industrial power systems containing large and fluctuating loads as it offers several benefits, including enhanced controllability, improved system robustness, optimal energy resource deployment, and increased lifetime. It has been earlier demonstrated that FDERS can significantly extend the mean battery replacement time in industrial power systems. As FDERS makes use of adaptive DER controls, its application is found to also impact the distribution system protection schemes. In this paper, the protection of an industrial microgrid with FDERS is investigated. Several innovative relaying schemes are proposed to mitigate any adverse impact caused during the implementation of FDERS in a microgrid.

The influence of inverter-based DGs and their controllers on distribution network protection

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers.

Comprehensive Protection Strategy for an Islanded Microgrid Using Intelligent Relays

In this paper, a comprehensive protection strategy is proposed for insuring dependable and secure operation of an islanded microgrid system. This is implemented using microprocessor-based relays to prevent unnecessary loss of critical loads and distributed generators (DGs). Several improvements are proposed to clear the way for plug-and-play of DGs. Furthermore, recommendations are presented to tackle the elusive high-impedance fault problem, commonly encountered in distribution systems. An optimal directional overcurrent bus protection is also presented. Several case studies and analyses are carried out to demonstrate the proposed protection strategy. Results from simulation using MATLAB/Simulink are also shown.

Sliding mode control of power converters: DC/DC converters

ABSTRACT In recent years, a lot of research efforts have been devoted to the application of sliding mode control (SMC) techniques to power electronic equipment and electrical drives. Hundreds of technical papers have been published in this research field. The tendency stems from the nature of sliding mode with discontinuous control actions and due to its potential for circumventing parameter variation effects along with low implementation complexity. This paper presents a control design procedure for DC/DC power converters. It develops SMC algorithms for several types of DC/DC converters with different control objectives, complete and incomplete information about system states. A chattering reduction approach for power converters based on the idea of multi-phase converters is also proposed. A wide range of MATLAB/SIMULINK computer simulations along with experimental results are provided to demonstrate the effectiveness of the proposed control design.

Distributed energy resource planning for microgrids in the united states

New measures for increasing energy efficiency and reducing CO2 emissions are being introduced by several nations to tackle the growing concerns on climate change. This paper presents optimal distributed energy resource (DER) planning for establishing microgrids. Such microgrid systems are devised for industrial sites and campus communities in the United States after evaluating location specific DER options. These are designed to maximize fuel consumption savings, besides meeting the U.S. Department of Energy (DOE) requirements and state renewable energy mandates. A qualitative evaluation of various types of DERs is presented cogitating factors like cost, environment, fuel consumption, controllability, longevity and government policy. Furthermore, the method of Lagrange Multipliers is used to determine the optimal allocation of DERs for microgrids. Due consideration is given to various factors such as climatic conditions, prevailing energy resources, and environmental regulations. The planning strategy presented in this paper can be extended to other conditions with minimal adjustments.

Sliding-mode control of power converters: AC/DC converters & DC/AC inverters

ABSTRACT Sliding-Mode Control (SMC) has been widely utilised to control nonlinear systems with uncertain dynamics. This is due to its order reduction properties, low sensitivity to disturbances, great dynamic performance and ability to reduce the complexity of feedback control design by decoupling the system into independent lower dimensional subsystems. Therefore, significant research has been dedicated to the application of SMC techniques to power electronic equipment and electrical drives. This paper presents a comprehensive control design procedure for AC/DC converters and DC/AC inverters based on SMC. It develops SMC algorithms for several types of power electronic equipment with different control objectives, complete and incomplete information about system states. A wide range of MATLAB/SIMULINK computer simulations are provided to demonstrate the effectiveness of the proposed control design.