Research And Application Of The GaN Power Device For Photovoltaic Inverter System

With the development of new power grid integration technologies, the requirements for performance and reliability of power electronic devices are increasingly demanding. Traditional power electronic devices based on silicon material have been gradually approaching the theoretical limit determined by the physical properties of materials. As a typical representative of the3rd generation wide band-gap semiconductor materials, the gallium nitride (GaN) has many outstanding performance which silicon do not have. It is especially good for high frequency,high pressure, high temperature and high power applications, and it is applicable both in the industry and the military fields. With the advances in GaN technology, large-diameter silicon (Si)-based GaN epitaxial technology matures to the business direction. Since2010, several manufacturers have introduced the High-Electron Mobility Transistor (HEMT), and the application research of wide-band-gap GaN power device is achieving increasingly significant results. However, the research work for the characteristics and application of wide bandgap GaN devices is still in its initial stage, and the deep and systematic analysis of these devices are scarce.This work focuses on the characteristics and application optimization of the enhancement mode GaN HEMT, Cascode GaN HEMT in micro-inverter, and the main conclusion are as follows:Firstly, this work improves the third quadrant operating characteristic curve of GaN HEMT, and presents the full-range output voltage-current characteristic curves for different types GaN HEMT. Through the theoretical operation mode analysis of the enhancement mode GaN HEMT, Cascode GaN HEMT, we obtain the conditions for different operation mode of GaN HEMT, which provides a theoretical foundation for the application research later.This paper analyzes the impact factor of the GaN HEMT driver circuit in high frequency application, and we proved layout optimization method of the GaN HEMT driver circuit. Experiments demonstrate the effectiveness of this method. Through the dynamic characteristics analysis of enhancement mode GaN HEMT, we conclude that it is suitable for parallel applications. We propose the driven design essentials and parallelling applications impact factors for enhancemet mode GaN HEMT. On this basis, the PCB layout design method of paralleling enhancement mode GaN HEMT is presented. Enhancemet mode GaN HEMT parallelling experiment results demonstrate that the impact analysis of the parasitics is correct.For reliability of GaN device, this paper presents the GaN HEMT overcurrent protection circuit suitable for high frequency application. The circuit detects the overcurrent fault by measuring the drain-source voltage of GaN HEMT. The GaN HEMT overcurrent protection circuit has many advantages, such as short delay, simple circuit structure, strong anti-interference, etc.Enhancement mode GaN HEMT is one of the wide bandgap devices with the highest power density. This work present optimization method based on enhanced GaN HEMT flyback-forward DC/DC converter circuit. This paper by reducing the leakage inductance and optimizating the dead time settings will significantly reduce turn-on losses of the GaN HEMT, and it will realize the target of high efficiency, high step-up ratio and high power density. The soft switching characteristics of the flyback-forward DC/DC converter circuit of enhancement mode GaN can further reduce the voltage and current stress and switching losses of the device and improve the efficiency of the converter. We present the design of the flyback-forward DC/DC converter circuit, and make the detailed analysis of its loss.In addition, the characteristics analysis and experimental verification of GaN Schottky diode shows that GaN and SiC Schottky diodes works nearly without reverse recovery and have significant efficiency advantages compared to Si-based fast recovery diodes.Cascode GaN HEMT is typical device of wide bandgap devices for high voltage applications, making it suitable for micro-inverter’s DC/AC circuit. The peculiar structure of Cascode GaN HEMT result in more complex dynamic process than monomers devices such as Si MOSFET, therefore, the dynamic process analysis of Cascode GaN HEMT also requires the introduction of parasitic parameters for detailed analysis. This paper presents a dynamic process analysis and theoretical derivation method of high voltage Cascode GaN HEMT. GaN HEMT equivalent circuit considers the parasitic inductances and parasitic capacitances, which have an important influence on the switching process and switching losses. The impact of parasitic parameters on switching process of the device is discussed and analysised. Theory analysis and experiment results demonstrate the great effect of parasitic parameters for high-voltage GaN HEMT switching process.