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.

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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

Executing distributed cyber-physical software processes on edge devices that maintains the resiliency of the overall system while adhering to resource constraints is quite a challenging trade-off to consider for developers. Current approaches do not solve this problem of deploying software components to devices in a way that satisfies different resilience requirements that can be encoded by developers at design time. This paper introduces a resilient deployment framework that can achieve that by accepting user-defined constraints to optimize redundancy or cost for a given application deployment. Experiments with a microgrid energy management application developed using a decentralized software platform show that the deployment configuration can play an important role in enhancing the resilience capabilities of distributed applications as well as reducing the resource demands on individual nodes even without modifying the control logic.

An Automated Deployment and Testing Framework for Resilient Distributed Smart Grid Applications

The concept of track sectioning of roadway power system has been presented long time before. But the implementation of this concept is rarely found in literature. A solution based on the idea of dual-powered track sections is proposed in this paper. Current balancing issue along with this new topology is discussed and solutions are provided. Different control strategies are compared to find the optimal control for this topology.

Dual-powered track sections for roadway powered electric vehicles

The recently introduced power-electronics-based dynamic VAR compensator (DVC) offers an effective solution in mitigating the impacts that high penetration distributed energy resources (DERs) have on distribution systems. One of the concerns about adopting these devices is their impact on distribution system protection, especially islanding detection. This paper proposes a hardware-in-loop (HIL) test-bed based approach to investigate the performance of islanding detection schemes on a distribution feeder. This approach facilitates the assessment of protection system performance under more realistic conditions by emulating actual devices and a distribution system. The results are based on an actual case study that is outlined to show the effectiveness of existing passive anti-islanding schemes and assess the impact of a DVC on islanding detection.

Assessment of Anti-Islanding Schemes on a Distribution System with High DER Penetration and Dynamic VAR Compensators

This paper presents a new algorithm for electromagnetic torque and flux estimation in a sensorless drive when uncompensated dc offset of current and/or voltage sensors are present. The novel feature of the offset error correction algorithm is an attempt not to eliminate the consequence of problem but to identify its source. The algorithm uses the first harmonic of estimated torque and dc value of estimated stator flux to identify the source and value of the current and/or voltage offset error. Identified values can be used for offset cancelation which improves estimation process.

New method for current and voltage measuring offset correction in an induction motor sensorless drive

Voltage support is one of ancillary services that can be provided by grid-connected microgrids. This paper presents a new microgrid-level voltage controller to enable microgrids to contribute to distribution system voltage regulation. Like the Volt-Var droop control of the smart inverters, the proposed controller makes sure that the voltage and reactive power flow at microgrid point of common coupling (PCC) follows a proportional relationship. To increase flexibility and avoid centralized computation, a distributed controller design is developed using the distributed averaging algorithm in order to achieve reactive power sharing among multiple distributed energy resources (DERs) within the microgrid. A large signal analysis is performed to study the stability and dynamic characteristics of the closed-loop system. Simulation results show that the proposed controller is effective in providing voltage regulation for distribution systems with multi-microgrid architecture.

Srdjan Lukic

Papers

An Automated Deployment and Testing Framework for Resilient Distributed Smart Grid Applications

Dual-powered track sections for roadway powered electric vehicles

Assessment of Anti-Islanding Schemes on a Distribution System with High DER Penetration and Dynamic VAR Compensators

New method for current and voltage measuring offset correction in an induction motor sensorless drive

A New Distributed Voltage Controller for Enabling Volt-Var Support of Microgrids in Grid-Connected Operation