Wide band-gap gallium nitride (GaN) device has the advantages of large band-gap, high electron mobility and low dielectric constant. Compared with traditional Si devices, these advantages make it suitable for fast-switching and high-power-density power electronics converters, thus reducing the overall weight, volume and power consumption of power electronic systems. As a review paper, this paper summarizes the characteristics and development of the state-of-art GaN power devices with different structures, analyzes the research status, and forecasts the application prospect of GaN devices. In addition, the problems and challenges of GaN devices were discussed. And thanks to the advantages of GaN devices, both the power density and efficiency of motor drive system are improved, which also have been presented in this paper.

This paper proposes an improved Thevenin model of the Lithium-ion battery taking into account temperature influence on the calculation accuracy of the open circuit voltage of a battery. The calculation accuracy of the terminal voltage of a battery is improved without increasing the order of the model. Firstly, the model was proposed based on Thevenin model and the relationship between the open-circuit voltage and the state of charge. Then, based on the experimental results of the open-circuit voltage test and hybrid power pulse characteristic test, the parameters of the battery model were identified by polynomial fitting and genetic algorithm, respectively. Furthermore, the temperature effects were considered in both the open-circuit voltage and hybrid power pulse characteristic tests. Finally, the proposed model was tested and verified by experiments under the Dynamic Stress Test condition and the Urban Dynamometer Driving Schedule at different temperatures. The accuracy of the proposed model is high and the parameter identification error is less than 1%.

This paper investigates the inverter nonlinearities in a drive system based on SiC-MOSFETs and compares its performance with that of an equivalent Si-IGBT system. Initially, a novel comprehensive analytical model of the inverter voltage distortion is developed. Not only voltage drops, dead time and output capacitance, but also switching delay times and voltage overshoot of the power devices are taken into account in the model. Such a model yields a more accurate prediction of the inverter's output voltage distortion, and is validated by experimentation. Due to inherent shortcomings of the commonly used double pulse test (DPT), the switching characteristics of both SiC-MOSFETs and Si-IGBTs in the PWM inverter are tested instead, such that the actual performances of the SiC and Si devices in the motor drive system are examined. Then, the switching performance is incorporated into the physical model to quantify the distorted voltages of both the SiC-based and Si-based systems. The results show that, despite its existing nonlinearities, the SiC-based drive has lower voltage distortion compared to the conventional Si-based drive as a result of its shorter switching times and smaller voltage drop, as well as a higher efficiency. Finally, theoverriding operational advantages of the SiC-based drive over its Si-based counterpart is fully demonstrated by comprehensive performance comparisons.

A novel non-dissipative two-stage equalization circuit topology based on the traditional Buck-Boost circuit is proposed to achieve balancing of series-connected lithium-ion battery packs with higher efficiency and less cost, considering the background on international energy issues and the development trend of battery balancing. The proposed topology achieves high efficient balancing of lithium-ion battery packs without adding additional devices. Detailed illustration of the presented topology, the operation principles and control approaches are described with visualized figures in this paper. Then, under the condition of accurate modeling of the lithium-ion battery, relying on the experimental data, the simulation block is built based on MATLAB. Furthermore, the prototype of the proposed topology was designed and manufactured. The effectiveness of the proposed topology is verified by both the simulation and experiment.

Abstract:The DC/DC converters and DC/AC inverters based on silicon carbide (SiC) devices as battery interfaces, motor drives, etc., in electric vehicles (EVs) benefit from their low resistances, fast switching speed, high temperature tolerance, etc. Such advantages could improve the power density and efficiency of the converter and inverter systems in EVs. Furthermore, the total powertrain system in EVs is also affected by the converter and inverter system based on SiC, especially the capacity of the battery and the overall system efficiency. Therefore, this paper investigates the impact of SiC on the powertrain systems in EVs. First, the characteristics of SiC are evaluated by a double pulse test (DPT). Then, the power losses of the DC/DC converter, DC/AC inverter, and motor are measured. The measured results are assigned into a powertrain model built in the Advanced Vehicle Simulator (ADVISOR) software in order to explore a direct correlation between the SiC and the performance of the powertrain system in EVs, which are then compared with the conventional powertrain system based on silicon (Si). The test and simulation results demonstrate that the efficiency of the overall powertrain is significantly improved and the capacity of the battery can be remarkably reduced if the Si is replaced by SiC in the powertrain system.