Analysis of High Switching Frequency Quasi-Z-Source Photovoltaic Inverter Using Wide Bandgap Devices

摘要

Power inverters continue to play a key role in todays electrical system more than ever. Power inverters employ power semiconductors to converter direct current (DC) into alternating current (AC). The performance of the semiconductors is based on speed and efficiency. Until recently, Silicon (Si) semiconductors had been established as mature. However, the continuous optimization and improvements in the production process of Si to meet today technology requirements have pushed Si materials to their theoretical limits. In an effort to find a suitable replacement, wide bandgap devices mainly Gallium Nitride (GaN) and Silicon Carbide (SiC), have proved to be excellent candidates offering high operation temperature, high blocking voltage and high switching frequency; of which the latter makes GaN a better candidate in high switching low voltage in Distributed Generations (DG).;The single stage Quasi-Z-Source Inverter (qZSI) is also able to draw continuous and constant current from the source making ideal for PV applications in addition to allowing shoot-through states. The qZSI find best applications in medium level ranges where multiples qZS inverters can be cascaded (qZS-CMI) by combining the benefit of the qZSI, boost capabilities and continuous and constant input current, and those of the CMI, low output harmonic content and independent MPPT. When used with GaN devices operating at very high frequency, the qZS network impedance can be significantly reduced. However, the impedance network becomes asymmetric.;The asymmetric impedance network (AIN-qZSI) has several advantages such as increased power density, increases system lifetime, small size volume and size making it more attractive for module integrated converter (MIC) concepts. However, there are technical challenges. With asymmetric component, resonance is introduced in the system leading to more losses and audible noise. With small inductances, new operation states become available further increasing the system complexity. This report investigates the AIN-qZSI and present solutions to aforementioned issues.