Development and Performance Assessment of Low Power Converters Using Wide Band-Gap Devices

摘要

The emergence of wide band-gap (WBG) power devices including silicon carbide (SiC) and gallium nitride (GaN) has opened up new possibilities in various applications. Their distinctive advantages, compared to the silicon (Si) counterparts, can aid in achieving low cost, reliable and efficient power management of energy generation systems. In this thesis, the switching performance of different Si and SiC power semiconductors is evaluated and the measured power loss components is compared in a 1.2kW DC-DC converter. Thermal performance evaluation of power semiconductors is also compared using: (i) various switching frequencies up to 300kHz, in steps of 25kHz; (ii) case temperatures from 25 to 150°C; and (iii) natural convection heatsinks with temperature increase rate of 0.5°C/W. The results demonstrate an opportunity to design power electronic (PE) systems with enhanced reliability and less effort required for thermal management. Also, an ultra-fast SiC MOSFET gate driver, which uses eGaN technology to realise MHz range switching capability is proposed. Using this gate driver, the operational performance of a SiC MOSFET for a 600W non-isolated DC-DC boost converter at 2MHz is experimentally analysed, and the maximum achievable switching frequency with this gate driver is determined. The effects of switching speeds on electromagnetic interference (EMI) generation from all-SiC and SiC-Si device combinations are investigated in a two-stage cascaded boost converter. A common mode (CM) EMI model for the converter is derived to identify noise sources. It is revealed that CM EMI emissions are independent of the device switching time when operated in the low-frequency range, while there is some dependence in the high-frequency range.Lastly, the performance of the SiC MOSFET device in a five-level flying capacitor (FC) converter is explored. Loss analysis is performed based on a calculation model, which verifies the correspondence between measurement and simulation results. In particular, the volume of the FC converter, and the passive components in the filter, are significantly reduced. This reduction is achieved by elevating the operating frequency for each controllable power switch based on self-balancing properties of the FC converter with phase shifted-PWM control. All theoretical considerations are supported by analysis, simulation and laboratory experimental results taken from low-power hardware prototypes.