A Novel Pulse-Width Modulation Method for Reactive Power Generation on a CoolMOS- and SiC-Diode-Based Transformerless Inverter

摘要

For efficiency considerations in the photovoltaic (PV) power generation, high-efficiency CoolMOS- and SiC-diode-based transformerless inverters have been proposed and studied in the previous literatures, but the reactive power generation capability to meet the upcoming standards has never been discussed. By reviewing the high efficiency converters with CoolMOS and SiC-diodes, this paper improves a previous transformerless inverter circuit and presents related operating modes for reactive power generation. A novel pulse-width modulation (PWM) method for this improved inverter topology is then proposed for reactive power generation. The ground-loop voltage of this inverter under the proposed PWM method is also derived with common mode (CM) and differential mode (DM) circuit analyses, which indicate that high-frequency voltage components can be minimized with symmetrical design of inductors. A 250-W inverter hardware prototype has been designed and fabricated. Steady-state and transient operating conditions are tested to demonstrate the validity of the improved inverter and proposed PWM method for reactive power generation, and the high-frequency-free ground loop voltage.