The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

High-efficiency and compact single-phase inverters are desirable in many applications such as solar energy harvesting and electric vehicle chargers. This paper presents a 2-kW, 60-Hz, 450-V $ _{\text{DC}}$ -to-240-V $_{\text{AC}}$ power inverter, designed and tested subject to the specifications of the Google/IEEE Little Box Challenge. The inverter features a seven-level flying capacitor multilevel converter, with low-voltage GaN switches operating at 120 kHz. The inverter also includes an active buffer for twice-line-frequency power pulsation decoupling, which reduces the required capacitance by a factor of 8 compared to conventional passive decoupling capacitors, while maintaining an efficiency above 99%. The inverter prototype is a self-contained box that achieves a high power density of 216 W/in $^3$ and a peak overall efficiency of 97.6%, while meeting the constraints including input current ripple, load transient, thermal, and FCC Class B EMC specifications.

A 2-kW Single-Phase Seven-Level Flying Capacitor Multilevel Inverter With an Active Energy Buffer

Remaining useful lifetime prediction and extension of Si power devices have been studied extensively. Silicon carbide (SiC) power devices have been developed and commercialized. Specifically, SiC mosfet s have been utilized for the next generation high-voltage, high-power converters with smaller size and higher efficiency, covering various mainstream applications, including photovoltaic systems, electric vehicles, solid-state transformers, and more electric ships and airplanes. However, the SiC-based devices have different failure modes and mechanisms compared with Si counterparts. Therefore, a comprehensive review is critical to develop accurate lifetime prediction and extension strategies for SiC power converter systems. The SiC power device component-level failure modes and mechanisms are first investigated. Different accelerated lifetime tests and component-level lifetime models are then compared. Power converter system-level offline lifetime modeling techniques and software tools are further summarized. Besides, the SiC power converter condition monitoring strategies and health indicators are surveyed. The online measurement challenges are also studied. Furthermore, the system-level lifetime extension strategies are reviewed. By integrating device physics, statistical modeling, reliability engineering, and mechanical engineering with power electronics, this article is intended to provide a comprehensive overview, address existing challenges, and unfold new research opportunities regarding the SiC power converter real-time lifetime prediction and extension.

Overview of Real-Time Lifetime Prediction and Extension for SiC Power Converters

Driving solutions for power semiconductor devices are experiencing new challenges since the emerging wide bandgap power devices, such as silicon carbide (SiC), with superior performance become commercially available. Generally, high switching speed is desired due to the lower switching loss, yet high $dv/dt$ and $di/dt$ can result in elevated electromagnetic interference (EMI) emission, false-triggering, and other detrimental effects during switching transients. Active gate drivers (AGDs) have been proposed to balance the switching losses and the switching speed of each switching transient. The review of the in-existence AGD methodologies for SiC devices has not been reported yet. This review starts with the essence of the slew rate control and its significance. Then, a comprehensive review categorizing the state-of-the-art AGD methodologies is presented. It is followed by a summary of the AGDs control and timing strategies. In this work, using AGD to reduce the EMI noise of a 10-kV SiC MOSFET system is reported. This work also highlights other capabilities of AGDs, including reliability enhancement of power devices and rebalancing the mismatched electrical parameters of parallel- and series-connected devices. These application scenarios of AGDs are validated via simulation and experimental results.

A Review of Switching Slew Rate Control for Silicon Carbide Devices Using Active Gate Drivers

Power devices based on wide-bandgap material such as silicon carbide (SiC) can operate at higher switching speeds, higher voltages, and higher temperatures compared to those based on silicon material. This article highlights some opportunities brought by SiC devices in existing and emerging applications in terms of efficiency and power density improvement. While the opportunities are clear, there are also design challenges that must be met in order to realize their full potential. For example, the fast switching speeds and high dv/dt of SiC devices can cause increased electromagnetic interference, current overshoot, cross-talk effect, and have a negative impact on loads such as motors. This article presents several potential solutions to tackle the application challenges and to fully exploit the superior characteristics of SiC devices and converters while attenuating their negative side effects. This article provides an overview of recent SiC device research and development activities based on academic literature, work carried out by the authors and collaborators as well as input from industry. It aims to provide benchmark results and a timely and useful reference to accelerate the adoption and deployment of SiC devices and converters.

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Opportunities, Challenges, and Potential Solutions in the Application of Fast-Switching SiC Power Devices and Converters

The requirements for peripheral circuits of power converters are becoming more restrictive due to the enhancement of Si-based power devices and due to practical use of SiC device. In the design of modern high-speed switching converters, the stray inductances and capacitances both in the device package and in the gate drive circuit in addition to those in the main circuit of the power converter must be considered. In these situations, the gate driving technique represents the key technology for enhancement of high-speed switching ability of power devices, as there are design limitations to reduce the stray inductances and capacitances. So far, several active gate control methods have been proposed. Most conventional active gate drivers are configured using analog circuits such as transistors and diodes. Thus, it is difficult to reconfigure their control parameters to fit the stray inductances and capacitances after the implementation of power converter and gate circuits. As a solution to these problems, the authors have proposed a programmable gate driver IC, which is a digitally controlled circuit. This gate driver IC can control the gate current at 63 separate levels, operated by programmable fully digital 12-bit and clock signals. In this paper, an active gate current control based on the load current in a half-bridge inverter with two programmable gate driver ICs is demonstrated. This developed gate control is different to the general current feedback control followed the reference value. It is verified that the proposed active gate control can effectively improve the tradeoff relationship between the surge voltage and switching loss of the pulsewidth modulation half-bridge inverter circuit.

Active Gate Control in Half-Bridge Inverters Using Programmable Gate Driver ICs to Improve Both Surge Voltage and Converter Efficiency

In comparison with conventional two-level inverter, multilevel inverter provides more than two levels of voltage to achieve high power, smoother and less distorted alternating voltage by using several semiconductor switches and lower level DC voltages as input. Among the available types of multilevel inverter topologies, the H-bridge multilevel inverter requires less number of power switching components, has higher efficiency and has simpler circuit layout. However, it is still limited by switching and conduction losses which mainly occur in main switching devices, and using more than one DC source for more than three voltage levels. To demonstrate an alternative way to reduce the losses without disputing advantageous features of H-bridge inverter, this paper presents a five-level multilevel inverter with reduced switching count, discussing its design features which contribute to less switching losses and Total Harmonic Distortion for motor drives. A computer based model of five levels single phase multilevel inverter was constructed and phase shifted sinusoidal pulse width modulation has been adopted based on 6-kHz switching frequency. The PSIM software environment is used to simulate the results.

Design of 5-level reduced switches count Η-bridge multilevel inverter

To realize massive integration of distributed renewable energy resources in future power system, the development of efficient measures for their integration is required. Using DC grid is more efficient and more compatible for the integration of renewable energy resources and energy storage devices. In the next-generation DC power network, many kinds of nodes which consist of generators, loads, energy storage devices, and so on and links (distribution lines) are connected. Thus, the grid structure is complex, and flexible power flow controls are essential. In a DC distribution network, the only controllable parameter is voltage of nodes, thus it is difficult to control the power flow of each link independently. In this paper, we study a power flow control on the links named link voltage control based on a bidirectional buck-boost converter implemented on the link. In addition to the voltage difference between the nodes, the link voltage controller generates additional voltage difference on the link intentionally. Thus, it is possible to control power flow of a specific link independently without affecting power flow of other links. In this way, flexible controls of power flows in a multi-terminal DC power network become possible. The effectiveness of the power flow control is demonstrated by experiments. The high controllability of the link voltage controller will contribute to the realization of future DC power grid.

Flexible power flow control for next-generation multi-terminal DC power network

The emerging trend of internet of things (IoT) and artificial intelligence (AI) technologies will bring about a major change in power electronics and create a new generation of the power electronics (Power Electronics 2.0). To enable the IoT- and Al-assisted Power Electronics 2.0, the integration of the sensors, the programmable hardware, and VLSIs for the controller into the power devices/modules is very important. In this paper, a 6-bit programmable gate driver IC with automatic optimization of gate driving waveform for IGBT is presented as the first step toward Power Electronics 2.0. In the proposed gate driver, the 6-bit gate control signals with four 160-ns time steps are globally optimized using a simulated annealing algorithm, reducing the collector current overshoot by 37% and the switching loss by 47% at the double pulse test of 300V, 50A IGBT. The gate driver is also applied to a half-bridge inverter, where the gate driving waveform is changed depending on the load current.

Power electronics 2.0: IoT-connected and Al-controlled power electronics operating optimally for each user

Among the various multi-level topologies, flying capacitor converters are promising from the view point of the high power density because the size of the capacitors, which is a major concern, is expected to be reduced. Although the voltages of the capacitors theoretically can stay in the balanced condition, they tend to be unbalanced under some practical conditions. So far, it has been clarified quantitatively that the capacitor voltage becomes unbalance due to inequality in switching delay of power devices. In this paper, some countermeasures to reduce the unbalance in the capacitor voltages are investigated to realize simple multi-level converters. The effectiveness of the initial charging resistors of the capacitors on the voltage balance is clarified analytically. Based on the investigations, a prototype is constructed to demonstrate attainable power density of the converters with balanced capacitor voltages. Some experimental investigations confirm that high efficiency and high power density can be realized.

Hidemine Obara

Papers

Active Gate Control in Half-Bridge Inverters Using Programmable Gate Driver ICs to Improve Both Surge Voltage and Converter Efficiency

Design of 5-level reduced switches count Η-bridge multilevel inverter

Flexible power flow control for next-generation multi-terminal DC power network

Power electronics 2.0: IoT-connected and Al-controlled power electronics operating optimally for each user

Development of high power density flying capacitor multi-level converters with balanced capacitor voltage