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

Battery is one of the most important energy storage devices in high power energy storage applications. It is widely used in the plug-in hybrid electric vehicles (PHEVs) and energy storage systems for renewable power generation such as wind and PV. In conventional series-connected high capacity battery string, due to the imbalance of battery cells, there are a few issues such as the cell damage due to over charge or over discharge, reliability and safety concerns. Conventional approaches to address these issues include the battery monitor system (BMS) and cell equalizer circuits. With BMS battery pack performance is still limited by the weakest cell in the string. The cell equalizer is limited by the current rating of the circuit, the equalization speed and the additional cost and weight. In this paper, a new concept of distributed energy storage device (DESD) module is proposed. Instead of using one high power DC-DC converter which connects to the whole battery string, a few distributed high voltage gain, high frequency and high efficiency bi-directional DC-DC converters are integrated with small battery packs respectively to form DESD modules. The module outputs are connected in parallel to form a battery energy storage system. The advantages and challenges of the DESD module are presented in this paper. A 200kHz, 400V to 12.8V, 256W soft switched bi-directional DC-DC converter is demonstrated for DESD modularization.

High-frequency high-efficiency DC-DC converter for distributed energy storage modularization

This letter presents an overview of design mechanisms to abstract device access protocols in the resilient information architecture platform for smart grid, a middleware for developing distributed smart grid applications. These mechanisms are required to decouple the application functionality from the specifics of the device mechanisms built by the device vendors.

Device Access Abstractions for Resilient Information Architecture Platform for Smart Grid

In dynamic wireless charging applications, segmented transmitter coils transfer power to a moving receiver coil. This article proposes a method in which the field strength in coupled transmitter coils automatically adjusts based on the position of the receiver. Specifically, a saturable inductor is applied to provide a high uncompensated inductive reactance in the uncoupled condition. By exploiting the reflected reactance as the system approaches the maximum coupled condition, the inductor saturates and the field strength in the coupled transmitter coils automatically increases. The field strength is at its peak when the transmitting and receiving coils reach their maximum coupling and sharply decreases when the receiver is decoupled from the transmitter. Consequently, the difference between the coupled and uncoupled currents in the transmitter coil is maximized, resulting in a near six-fold improvement in field containment performance compared to previously reported findings. This allows for system-level efficient power transfer and compliance with electromagnetic emission standards without complex shielding circuits and auxiliary active position detection approaches. We present the analysis, design criteria of the compensation network, and experimental validation for the proposed method.

Dynamic Wireless Charging: Reflexive Field Containment Using Saturable Inductors

To maintain a stable, flexible and economic operation of a microgrid, hierarchical control architecture consisting of primary, secondary and tertiary control is proposed. However, the differences in dynamics of microgrid, bandwidths of control levels and speed of communication channels make it difficult to comprehensively validate the performance of the hierarchical control schemes. In this paper we propose a hardware-in-the-loop real-time testbed for microgrid hierarchical control. The proposed testbed can be used to validate control performance under different microgrid operating modes (grid-tied or islanded), different primary control schemes (current or voltage mode) and different secondary control approaches (centralized or distributed). The integration of industry-grade hardware that runs primary and secondary control into the testbed allows for complete emulation of microgrid operation, and facilitates the study of the effects of measurement noise, sampling and communication delays.

A Hardware-in-the-Loop Real-Time Testbed for Microgrid Hierarchical Control

Auto rickshaws are three-wheeled vehicles used extensively in many Asian countries as taxis of people and goods. Although the vehicle design is well-suited to the environment in which it operates, it is a crude, inefficient design. Due to poor vehicle maintenance and the use of inefficient 2 or 4 stroke engines with very little pollution control, auto rickshaws present a huge pollution problem in major Indian cities. Illinois Institute of Technology's (IIT) rickshaw project is aimed at developing an advanced solar-based electric auto rickshaw. This paper presents research on the conventional auto rickshaw, future conceptual infrastructure designs for electric rickshaws, and the recent design research and simulations of the next auto rickshaw. IIT's solar/battery electric three-wheeler is meant to match and exceed the conventional vehicle's performance, but with a more intelligent and efficient design. We introduce the next overall design of the rickshaw in this paper as the Auto Rickshaw 2.0, where the conventional vehicle is version 1.0. IIT's technical development aim for Auto Rickshaw 2.0 is to decrease the total electric power needed for propulsion with an optimized battery system and a more efficient motor. Four system drive train options are covered, and the selected configuration is simulated and analyzed in ADVISOR software. Additionally, conceptual infrastructure designs are modeled and optimized in HOMER software.

Srdjan Lukic

Papers

High-frequency high-efficiency DC-DC converter for distributed energy storage modularization

Device Access Abstractions for Resilient Information Architecture Platform for Smart Grid

Dynamic Wireless Charging: Reflexive Field Containment Using Saturable Inductors

A Hardware-in-the-Loop Real-Time Testbed for Microgrid Hierarchical Control

Solar/battery electric auto rickshaw three-wheeler