Analysis and Design of DC Bus Voltage Control Regarding Third Harmonic Reduction and Dynamic Improvement for Half-Bridge Microinverter

The half-bridge inverter is attractively employed to be a second stage dc-ac converter of microinverter since it is low component count, low cost and high efficiency. However, the microinverter is usually connected to the single-phase utility grid and its instantaneous power pulsates with double-line frequency. This frequency also appears on dc bus voltage and propagates into voltage loop control, which consequently causes third harmonic occurring on the output current injected into the grid. This paper investigates the detail of dc bus ripple voltage and analyzes the reference output grid current thoroughly. Particular design of a PI controller in order to reduce the third harmonic complying with the grid standard IEEE 1547 is presented. Thanks to the feed forward technique, the dynamic response of dc bus voltage is drastically improved to be fast and steadily even under input power suddenly changed. Theoretical analysis and proposed control strategy are verified by experimental results.