Modelling of the modified-LLCL-filter-based single-phase grid-tied Aalborg inverter

Owing to less conduction and switching power losses, the recently proposed Aalborg inverter has high efficiency within a wide range of input DC voltage for single-phase DC/AC power conversion. In theory, the conduction power losses can be further decreased, if an LLCL-filter is adopted instead of an LCL-filter for a voltage source inverter, mainly due to the reduced inductance. The Aalborg inverter shows the characteristic of a current source inverter, when working in the boost' state. Whether the LLCL-filter can meet the control requirement of this type inverter needs to be further explored. In this study, the small signal analysis for the modified-LLCL-filter-based Aalborg inverter is addressed. Through the modelling, it can be proven that compared with the LCL-filter, the modified-LLCL-filter causes no extra control challenge for the Aalborg inverter, and therefore more inductance in the power loop can be safely saved as well as a complete smaller filter size. A 220 V/50 Hz, 2000 W prototype is used to demonstrate the theoretical analysis.