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Liming Liu - IEEE Xplore Author Profile

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The 650 V and 1200 V SiC MOSFETs have gained significant market acceptance in the recent years, mainly, due to the promise of higher power conversion efficiency and power density. However, the lack of field-proven long-term reliability data of SiC MOSFETs is still a major concern, particularly in applications where the devices are exposed to harsh thermal and electrical cycles. This paper discusse...Show More
A unique three-step short-circuit protection method is proposed for the 650-V enhancement mode (E-mode) gallium nitride high-electron mobility transistor (GaN HEMT). This method can quickly detect the short-circuit event, reduce gate voltage to enhance the device short-circuit capability, and turn off the device under fault after confirmation. Experimental results prove that with this method, the ...Show More
In dc microgrids, load power sharing and bus voltage regulation are two common control objectives. In this article, a consensus-based algorithm is presented to achieve proportional power sharing and regulation of weighted geometric mean of bus voltages in dc microgrids with ZIP (constant impedance, constant current, and constant power) loads simultaneously. By using the virtue of the Laplacian mat...Show More
This paper presents a new short-circuit protection method developed for Gallium Nitride (GaN) gate injection transistors (GITs). The proposed protection method is based on ultra-fast detection of the voltage dip on the phase leg of the converter, active current clamping of the gate drive, and fault confirmation with a low pass filter based de-saturation fault detection. Thus, it achieves an ultra-...Show More
This paper proposes a high temperature design of an integrated three phase inverter using direct drive GaN HEMT devices and metal clad PCBs (MCPCB). The inverter features a modular design approach, utilizing a 600 V direct drive GaN device with integrated overcurrent and overtemperature protection. Aluminum based PCBs with high thermal conductivity are also used to achieve a natural cooling soluti...Show More
Capacitor voltage balancing circuits are required for applications using series capacitor to provide high dc-link voltage. This paper propose a new dc-link capacitor voltage balancer integrated into the LLC auxiliary power supply. Only small balancing inductors are added which are connected between the middle points of adjacent capacitors and half-bridge legs in the LLC auxiliary converter. Taking...Show More
The Enhancement-mode (E-mode) Gallium Nitride High-Electron Mobility Transistor (GaN HEMT) has several hundred nanosecond level short circuit withstand time, much shorter than that of the silicon (Si) devices. Reliable ultra-fast protection solutions for the GaN HEMTs are in great demand. In this paper, a three-step GaN HEMT short circuit protection solution is proposed, including ultra-fast detec...Show More
In this paper, a hybrid PWM modulation method is proposed to reduce the EMI filter size of GaN based inverters. Time-based PWM modulation and frequency-based modulation methods are combined to achieve a reduced EMI profile, which reduces the filter size required to meet EMI standards. An EMI test bed based on the CISPR EMI standard is built using a 10-kW GaN inverter and modeled using LTspice simu...Show More
Wide bandgap (WBG) device-based power electronics converters are more efficient and lightweight than silicon-based converters. WBG devices are an enabling technology for many motor drive applications and new classes of compact and efficient motors. This paper reviews the potential applications and advances enabled by WBG devices in ac motor drives. Industrial motor drive products using WBG devices...Show More
This paper presents the short-circuit behavior and degradation of 650-V/60-A enhancement-mode Gallium nitride (GaN) high electron mobility transistors (HEMTs) under various test conditions. First, this paper introduces the basic information of device, test method, and platform. Subsequently, single pulse, 10-μs short-circuit tests are performed from 50 to 400 V to extract the typical behavior of d...Show More
The Enhancement-mode (E-mode) Gallium Nitride High-Electron Mobility Transistor (GaN HEMT) has proven excellent electrical performance in various applications. Meantime, multiple comprehensive studies on the short circuit behavior show that GaN HEMTs has much shorter short circuit withstand time compared to conventional silicon (Si) devices. In this paper, the GaN HEMT short circuit capability is ...Show More
This paper presents a grid-interactive dual-paralleled buck/boost converter with four-quadrant power flow capability. The primary advantage of this topology compared to the traditional H-bridge inverter is its inherent robustness against shoot-through problems. Further, by combining the use of traditional Si devices with wide bandgap devices, one can get reduced power loss and higher power density...Show More
With increasing interest in smart grid and renewable energy, significant investments have been allocated to promote related studies. Since there is a wide spectrum of topics to study, it is necessary to have an advanced experimental platform that can accommodate both system- and component-level studies, both hardware and algorithm designs, and both teaching and research. Unfortunately, such experi...Show More
This paper presents a hybrid active power filter (APF) with DrGaNplus module for a 5kW single phase inverter. Considering the low voltage stress on the devices in hybrid APF, a module integrated with gate driver is selected to achieve high power density and high efficiency for the overall system. An effective control is proposed to keep the APF capacitor from depleting, while at the same time mana...Show More
With the rapid development of the wide bandgap (WBG) power transistor technology, the latest Silicon-Carbide and Gallium-Nitride (SiC and GaN) based power transistors can be used as the main switches in the medium power (≥10 kW) conversion systems. Electrical signal based efficiency measurement could be very challenging due to the high-frequency output signals and the high power to loss ratio. In ...Show More
This paper presents a hybrid multilevel inverter with DC bypass. Mixed modulation method is proposed to balance dc voltage, and enables Si devices & wide bandgap devices integration to reduce power loss and achieve high power density. Simulation results are firstly provided to verify the validity of the proposed approach.Show More
This paper introduces a general method to evaluate the power losses of active (power semiconductors) and magnetic (inductors) components in power electronic systems. The bidirectional current conduction of silicon-carbide MOSFETs is analyzed to more accurately estimate the conduction and switching losses. Compared to conventional methods, the core loss of the magnetic components is estimated in a ...Show More
The emerging 650 V large current rating, Enhancement-mode (E-mode) Gallium Nitride High-Electron-Mobility Transistor (GaN HEMT) is a promising device for low to medium power, high power density converters (e.g., motor drives, battery chargers), which require high robustness levels. Thus, a comprehensive study of the short circuit behavior of high power E-mode GaN HEMT is the subject of this paper....Show More
This paper presents a mixed three-level neutral point clamped (NPC) inverter with hybrid modulation method. It enables traditional Si devices and wide bandgap devices integration to reduce power loss and achieve high power density. Simulation results are firstly provided to verify the validity of the proposed approach.Show More
This paper investigates a dc collection grid architecture to process energy from offshore wind turbine generators (WTGs), which can be further interfaced with the shore via a high-voltage dc network. In the proposed approach, WTG output voltage is rectified and converted to medium frequency (MF). Then, a transformer isolation stage is used, followed by a boost rectification stage. The boost rectif...Show More
The medium power rating two-level three phase voltage source inverter is among the most popular power conversion systems. The typical switching frequency of the commercial medium power rating inverter, however, is limited to tens of kHz. By increasing the switching frequency and using emerging gallium-nitride devices, the size of the overall system can be greatly reduced. This paper begins by revi...Show More
Paralleling devices is an effective way to achieve higher power applications while still having the convenience brought by discrete devices. However, very few papers investigate the challenges of paralleling Gallium Nitride high electron mobility transistors (GaN HEMTs) in cascode configuration, especially the potential failure modes and its related mechanisms. In this paper, a comprehensive study...Show More
Paralleling devices is an effective way to achieve a higher power application while still having the convenience of using discrete devices. However, the mechanisms of potential failures and the circuit design considerations have not been thoroughly studied yet, when paralleling gallium nitride high-electron-mobility transistors (GaN HEMTs) in cascode configuration. This paper presents a comprehens...Show More
To isolate the negative impacts of pulsed power loads (PPL) in a shipboard power system (SPS), energy storage systems (ESS) are usually equipped for online ESS charging and offline ESS discharging for PPL deployment. In order to achieve fast and smooth ESS charging, the generation control and ESS charging control need to be well coordinated. In addition, control constraints, such as generation and...Show More
Quasi-Z-source based modular cascaded multilevel converter featuring both the advantages of multilevel converter like modularity, scalability, distributed maximum power point tracking (MPPT) capability and the advantages of quasi-Z-source network (qZSN) like high efficiency, no consideration for annoying switching dead-zone, wide dc voltage boosting range etc. is a promising option for high power ...Show More