Access to clean, affordable and reliable energy has been a cornerstone of the world's increasing prosperity and economic growth since the beginning of the industrial revolution. Our use of energy in the twenty–first century must also be sustainable. Solar and water–based energy generation, and engineering of microbes to produce biofuels are a few examples of the alternatives. This Perspective puts these opportunities into a larger context by relating them to a number of aspects in the transportation and electricity generation sectors. It also provides a snapshot of the current energy landscape and discusses several research and development opportunities and pathways that could lead to a prosperous, sustainable and secure energy future for the world.

Opportunities and challenges for a sustainable energy future

Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

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Recent Advances and Industrial Applications of Multilevel Converters

Overview of current development in electrical energy storage technologies and the application potential in power system operation

This paper reviews the current status and implementation of battery chargers, charging power levels, and infrastructure for plug-in electric vehicles and hybrids. Charger systems are categorized into off-board and on-board types with unidirectional or bidirectional power flow. Unidirectional charging limits hardware requirements and simplifies interconnection issues. Bidirectional charging supports battery energy injection back to the grid. Typical on-board chargers restrict power because of weight, space, and cost constraints. They can be integrated with the electric drive to avoid these problems. The availability of charging infrastructure reduces on-board energy storage requirements and costs. On-board charger systems can be conductive or inductive. An off-board charger can be designed for high charging rates and is less constrained by size and weight. Level 1 (convenience), Level 2 (primary), and Level 3 (fast) power levels are discussed. Future aspects such as roadbed charging are presented. Various power level chargers and infrastructure configurations are presented, compared, and evaluated based on amount of power, charging time and location, cost, equipment, and other factors.

/pdf/review-of-battery-charger-topologies-charging-power-levels-85yy2igx2w.pdf

Review of Battery Charger Topologies, Charging Power Levels, and Infrastructure for Plug-In Electric and Hybrid Vehicles

Wireless power transfer (WPT) using magnetic resonance is the technology which could set human free from the annoying wires. In fact, the WPT adopts the same basic theory which has already been developed for at least 30 years with the term inductive power transfer. WPT technology is developing rapidly in recent years. At kilowatts power level, the transfer distance increases from several millimeters to several hundred millimeters with a grid to load efficiency above 90%. The advances make the WPT very attractive to the electric vehicle (EV) charging applications in both stationary and dynamic charging scenarios. This paper reviewed the technologies in the WPT area applicable to EV wireless charging. By introducing WPT in EVs, the obstacles of charging time, range, and cost can be easily mitigated. Battery technology is no longer relevant in the mass market penetration of EVs. It is hoped that researchers could be encouraged by the state-of-the-art achievements, and push forward the further development of WPT as well as the expansion of EV.

Wireless Power Transfer for Electric Vehicle Applications

Dynamic microgrids (MG)have shown great potential in distribution system restoration as they could be frequently and actively reconfigured as per request from system operator. MGs usually have smaller inertia compared to conventional power systems thus require more delicate controller for operation safety. In addition, most distribution systems have unbalanced configurations which requires dedicated regulations on system operation states in both positive and negative sequence. This paper proposes a distributed secondary control strategy for unbalanced dynamic MGs operation. System frequency and voltage regulation are constantly enabled, along with voltage unbalance (VU)mitigation on critical load buses. The proposed control strategy provides automatic management of DGs within the same MG and seamless system transition as reconfiguration is requested. Detailed controller designs for both positive and negative sequence regulations are presented. Small-signal stability analysis of the proposed controller is derived and its dynamic performances are validated using MATLAB/Simulink.

Dynamic Microgrids with Voltage Unbalance Mitigation Using Distributed Secondary Control

In many industrial settings, momentary power disruptions commonly occur, resulting in tripping of large electric machines, which then have to be brought to zero speed before the machine can be restarted. This approach can result in frequent interruptions in an industrial process, which can have negative effects on productivity. A more practical control implementation would restart the machine back to the original speed as soon as power is restored, not having to wait for the machine to be at a standstill. This concept is known as flying restart. In this paper we propose an approach to implement the universal restart for SynRM (Synchronous Reluctance Machine) through a simple identification algorithm which determines the speed and position of the machine so that the correct voltage vector can be applied and thus minimize the inrush current during the restart. The novelty of the proposed method is that its implementation only requires nameplate machine parameters and needs no machine-specific tuning, making the approach suitable for implementation with both high-inertia vector and scalar-controlled SynRM.

Restart Strategy for Synchronous Reluctance Machine Driving a High Inertia Load

Momentary power disruptions commonly occur in many industrial settings, and can trip large electric machines, which must then be brought to zero speed before the machine can be restarted. The resulting frequent interruptions in industrial processes can have negative effects on productivity. A restart algorithm brings the machine back to the original speed as soon as power is restored, without waiting for the machine to reach zero speed. This paper proposes an approach for implementing a restart algorithm for synchronous reluctance machines (SynRMs) that use a simple identification algorithm to determine the speed and position of the machine so that the appropriate voltage vector can be applied, thus minimizing the inrush current during the restart. The proposed method only requires nameplate machine parameters and needs no machine-specific tuning, making the approach suitable for implementation with both high-inertia vector and scalar-controlled SynRM.

Restart Strategy for Scalar ( V/f ) Controlled Synchronous Reluctance Machine Driving a High-Inertia Load

This paper introduces a controller hardware-in-the-loop (HIL) microgrid testbed that is built to allow not only dynamic validation, but performance evaluation of community microgrid controllers. The performance metrics and evaluation methodology are developed related to efficiency, greenhouse gas (GHG) emission, economics and reliability. The real-time community microgrid model is developed to adapt to extended time-domain simulation that includes the voltage and frequency dynamics of the microgrid components. A hybrid testbed configuration is described to demonstrate the capability of controller integration, testing automation and post-processing analysis. Case studies based on an actual utility distribution system are presented to demonstrate the functionality of the microgrid testbed as well as the effectiveness of the evaluation methodology.

Community Microgrid Controller Evaluation using Hardware-in-the-Loop Testbed

This paper presents a destination prediction algorithm based on a markov model method to build a probability matrix of possible destination GPS coordinates. This matrix is then used in a real time algorithm to predict the distance remaining when the vehicle is running. Simulation based on real GPS data shows the precision of the algorithm and its possible implementation in the control strategy for a PHEV.

http://ieeexplore.ieee.org/iel7/6569392/6573455/06573504.pdf

Srdjan Lukic

Papers

Dynamic Microgrids with Voltage Unbalance Mitigation Using Distributed Secondary Control

Restart Strategy for Synchronous Reluctance Machine Driving a High Inertia Load

Restart Strategy for Scalar ( V/f ) Controlled Synchronous Reluctance Machine Driving a High-Inertia Load

Community Microgrid Controller Evaluation using Hardware-in-the-Loop Testbed

Distance estimation algorithm for plug-in hybrid electric vehicle control strategy