Chen Yuan

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.

Co-Optimization Scheme for Distributed Energy Resource Planning in Community Microgrids

Microgrids with distributed energy resources are being favored in various communities to lower the dependence on utility-supplied energy and cut the CO2 emissions from coal-based power plants. This paper presents a co-optimization strategy for distributed energy resource planning to minimize total annualized cost at the maximal fuel savings. Furthermore, the proposed scheme aids the community microgrids in satisfying the requirements of U.S. Department of Energy (DOE) and state renewable energy mandates. The method of Lagrange multipliers is employed to maximize fuel savings by satisfying Karush–Kuhn–Tucker conditions. With the Fourier transform and particle swarm optimization, the right mix of distributed energy resources is determined to decrease the annualized cost. A case study to test the proposed scheme for a community microgrid is presented. To validate its effectiveness, an economic justification of the solution and its comparison with HOMER Pro are also illustrated.

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.

Modified Viterbi Algorithm Based Distribution System Restoration Strategy for Grid Resiliency

This paper presents a novel modified Viterbi algorithm to identify the optimal distribution system restoration plan for improving the grid resiliency. In the proposed algorithm, the switching operations performed for system restoration are the states with the minimum bus voltage being seen as the cost metric for each state and the extent of load recovery as the observed event. When full load recovery is spotted, the dynamic programming algorithm stops, thereby giving the least number of switching pairs necessary for system restoration. Moreover, an improved flexible switching pair operation is employed to maintain the radial nature of distribution system. Several case studies are presented for verifying the performance of the proposed strategy. Multi-fault conditions are considered in testing the system restoration scheme on 33-bus and 69-bus distribution systems. Furthermore, the effects of integrating distributed energy resources and microgrid systems are analyzed.

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.

Nine-phase induction machine with electric pole change for emerging heavy-duty and off-road micro/mild hybrid vehicle applications

Multiphase induction machine offers many advantages over the conventional three-phase machine, like lower harmonics, reduced torque pulsation amplitude while increasing its frequency, decreased phase current, and cutting down power loss. It is particularly useful in the emerging heavy-duty and off-road vehicle applications. In this paper, a control strategy for multifunction nine-phase induction machine is proposed to increase the maximum speed without sacrificing the maximum torque. Another advantage of this machine drive system is lower voltage and current requirements. With electric pole change, the induction machine can reduce mutual inductance at high speeds. Due to lower mutual inductance, the back EMF is lower and a large dc-link voltage is not necessary at high speeds. This helps in lowering the dc-dc power conversion requirements. Moreover, the conduction loss is also reduced with the decrease in phase current, thereby cutting the costs of cooling. The proposed park inverse transformation is elaborated for multiphase condition. Simulation results from MATLAB/Simulink are displayed first to illustrate the effectiveness of control strategy. The proposed nine-phase induction machine was tested on a Caterpillar off road vehicle and the brief performance evaluation of the system-level benefits is also presented in this paper.

Multilayered Protection Strategy for Developing Community Microgrids in Village Distribution Systems

Village or community microgrids are being encouraged to improve resiliency against unexpected events. They also improve energy efficiency and reliability of power delivery to critical loads. However, many protection challenges exist in making the shift away from conventional distribution systems. In this paper, a multilayered protection strategy is presented for developing a community microgrid in a village within the 69-bus distribution system. The proposed strategy is verified by simulation studies in MATLAB/Simulink against various fault conditions. A comparison between the proposed strategy and existing distribution protection schemes is also provided.