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

Energy Storage System (ESS), with its fast ramping and bi-direction power flow capabilities, is playing a more vital role in the electric market. However, it still stands on the farther end of economic viability. As a result, a good estimate of battery service life, and therefore revenue, is necessary before the investment is made in any given application. In this paper, a set of improved degradation models are propose to estimate the useful life of an ESS when subjected to daily duty cycles (4-sec resolution). The models are validated and tuned for the target Li-Nickel Cobalt Aluminum Oxide (NCA) batteries. Time to End of Life (EOL) is estimated for batteries of different sizes to provide ancillary services and/or energy services in electric market, given different end-of-cycle state of charge. Finally, the strategies which can be used to size the battery for maximizing time to EOL are discussed.

A novel approach towards energy storage system sizing considering battery degradation

The More Electric Vehicles (MEV) concept emphasizes the utilization of electrical systems instead of mechanical, hydraulic, and pneumatic systems to optimize vehicle fuel economy, emissions, performance, and reliability. In addition, the need for improvement in comfort, convenience, entertainment, safety, security, and communications necessitates more electric automotive systems. As a result, an electric power distribution system with larger capacity and more complex configuration is required to facilitate increasing electrical loads. Due to the environmental concerns, there is also a definite development towards new propulsion systems for the future cars in the form of electric and hybrid electric vehicles (EV and HEV). Most of these new electrical systems in advanced cars utilize power electronic converters and motor drives. In this paper, a modeling tool, which has been developed to study automotive systems using PSIM software, is presented. Different heat engines, transmissions, differentials, mechanical systems, control strategies, batteries, solar cells, and fuel cells have been modeled to enable simulation of vehicular systems. Suitability of the software package in design of different automotive systems is explored as well.

A PSIM-based modeling tool for conventional, electric, and hybrid electric vehicles studies

This paper presents a low-inductance dc busbar for SiC-based electric vehicle traction inverters operating at high ambient temperatures. Unlike the laminated busbars, which use parallel copper sheets to establish low-inductance connection between the dc-link capacitor bank and all the switching devices, the proposed busbar uses capacitor sections which are vertically mounted on top of each power semiconductor module. This significantly reduces the busbar’s parasitic inductance and eliminates the unreliable snubber circuit which is typically used with laminated and PCB busbars to reduce the overvoltage spikes across the fast-switching semiconductor devices during the device turn-off transients.

A low-inductance Sectional Busbar for Snuberless Operation of SiC-based EV Traction Inverters

This paper presents a new topology appropriate for dynamic wireless charging of electric vehicles. We propose a source coil made from multiple lumped coils powered by a single inverter, with the receiver coil mounted on the vehicle. The proposed system uses the reflected reactance from the receiver to automatically limit the field strength in uncoupled portions of the source-receiver system, thus allowing the system to more easily meet the electromagnetic field emission standards without complex shielding circuits, switches, electronics and communication systems. The power transfer is at its peak when the source-receiver coils pair is strongly coupled resulting in improved system-level efficiency. The analysis is supported by simulation and experiments.

Field containment in dynamic wireless charging systems through source-reciever interaction

This paper presents a multi-agent system (MAS) approach for automated service restoration for futuristic distribution systems with distributed energy resources (with/without microgrid forming capabilities). The proposed algorithm provides an architecture for interchangeable agent roles which is more robust and reliable compared to other approaches with rigid agent roles. The restoration algorithm is greedy (loosely based on distributed Prim's algorithm) to form the largest possible online sections. This helps improving system stability and makes it less susceptible to changing load/demand in the system by aggregation. The performance is demonstrated for a 33–bus distribution system with and without DERs. It is seen that algorithm always results in maximum possible loads be connected.

Srdjan Lukic

Papers

A novel approach towards energy storage system sizing considering battery degradation

A PSIM-based modeling tool for conventional, electric, and hybrid electric vehicles studies

A low-inductance Sectional Busbar for Snuberless Operation of SiC-based EV Traction Inverters

Field containment in dynamic wireless charging systems through source-reciever interaction

Multi-Agent Distributed Service Restoration Scheme for Distribution Systems with Embedded Microgrids