Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Multilevel inverters: a survey of topologies, controls, and applications

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

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

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

Cascaded multilevel inverters synthesize a medium-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltages and input currents and also outstanding availability due to their intrinsic component redundancy. Due to these features, the cascaded multilevel inverter has been recognized as an important alternative in the medium-voltage inverter market. This paper presents a survey of different topologies, control strategies and modulation techniques used by these inverters. Regenerative and advanced topologies are also discussed. Applications where the mentioned features play a key role are shown. Finally, future developments are addressed.

A Survey on Cascaded Multilevel Inverters

Synchronous generators are being gradually replaced by power electronics based renewable energy generations. However, this may reduce the power system stability and resiliency due to a reduced inertia support to the grid. A viable solution is to change the inverter from grid-following to grid-forming which provides grid inertia. An ideal grid forming PV inverter should operate at the maximum power point to maximize the energy production while providing the inertia and other grid forming functions. This paper presents the design of a 150kW/1500V silicon carbide grid-forming Photovoltaic Synchronous Generator (PVSG). The developed PVSG integrates a 150kW three-phase PV inverter, a 100kW DC-DC converter and a 2.4F supercapacitor energy storage for inertia support. An inverter peak efficiency of 99.1% and a DC-DC converter efficiency of 99.5% are predicted or tested.

Hardware Design of a 150kW/1500V All-SiC Grid-forming Photovoltaic Synchronous Generator (PVSG)

Voltage-balancing controller in cascaded multilevel converters has been discussed extensively in previous literatures where several effective methods have been proposed. The coupling effect between a voltage-balancing controller and the original system controller is however not addressed comprehensively. This paper proposes a new voltage-balancing controller for single-phase cascaded multilevel converters in a d-q coordinate. The theoretical finding shows that the proposed method can effectively eliminate the coupling between two controllers in both steady and dynamic state. Simulation and experimental results validate the proposed method.

A new voltage-balancing controller in cascaded multilevel converters

FREEDM-Pair is an innovative power semiconductor switch which reduces the loss and cost through the hybrid integration of a Si IGBT and a SiC MOSFET. During the turn-off of the FREEDM-Pair, the Si IGBT is turned off first under ZVS condition and after a carefully selected delay time, the SiC MOSFET is turn-off. In this way, the turn-off loss of the Si IGBT is significantly reduced due to the ZVS turn-off condition. During the delay time, the current will be carried by the SiC MOSFET only. During the turn-on, the SiC MOSFET and the IGBT can be turned on at the same time. Due to faster turn-on speed of the MOSFET, the IGBT is also turned on under the ZVS condition. FREEDM-Pair also has better conduction characteristics compared to the Si IGBT by the combined current conduction capability of the unipolar and bipolar devices. Therefore the FREEDM-Pair provides an ideal option to realize the tradeoff between the cost and performance, and can be applied to main stream applications which currently use IGBT. Previously, the 1200V/200A FREEDM-Pair with individual gate terminals for IGBT and MOSFET have been designed and published. In this paper, a three terminal 1200V/200A FREEDM-Pair is presented and analyzed for the first time. In the three terminal FREEDM-Pair, a passive delay circuit is designed and integrated into the power module, so only one gate driver signal is needed. The designed delay circuit will generate the desired delay gate signal for the MOSFET automatically. To verify the designed gate driver function and the FREEDM-Pair performance in continuous operation, a half-bridge (HB) power module consisting of two FREEDM-Pair switches is developed. The continuous operation of the 1200V/200A FREEDM-Pair in a buck converter topology is reported for the first time.

Gate driver design and continuous operation of an improved 1200V/200A FREEDM-pair half-bridge power module

Comprehensive numerical simulations were performed to investigate a novel double gate-injection enhanced gate transistor (DG-IEGT). The DG-IEGT structure eliminates the need for trading off the forward voltage with the switching loss. Because DG-IEGT is a four-quadrant switch, it is capable of conducting currents and blocking voltages in both directions. This capability enables DG-IEGT to be used in many applications to replace multiple switches and diodes. DG-IEGT, therefore, is close to an ideal power switch and should be developed as a next generation device to replace high power insulated gate bipolar transistor.

Comprehensive investigations of high voltage non-punch-through double gate-injection enhanced gate transistor

Stability is the key requirement in designing switching converter ASIC. Achieving this requires an accurate loop gain design. Since DC-DC switching converters are time-varying system, traditional small signal analysis in SPICE cannot be directly used to simulate the loop gain of this kind of system. A new method named periodic small signal analysis is proposed to analyze and simulate DC-DC switching converter inside a SPICE like simulator without the need for averaging. This general method is suitable for any switching regulators. The results are accurate comparing with average modeling and experiment results even beyond half switching frequency. A general procedure to design loop gain is demonstrated in a peak current control buck.

Alex Q. Huang

Papers

Hardware Design of a 150kW/1500V All-SiC Grid-forming Photovoltaic Synchronous Generator (PVSG)

A new voltage-balancing controller in cascaded multilevel converters

Gate driver design and continuous operation of an improved 1200V/200A FREEDM-pair half-bridge power module

Comprehensive investigations of high voltage non-punch-through double gate-injection enhanced gate transistor

Frequency response analysis for switching converters in SPICE without averaging