Research has been conducted to use an interconnection inverter for a stand-alone generator with an aim to provide a small gas engine cogeneration system with a backup function to serve as an emergency power generator in case of blackout. When a diode rectifier with a large capacitor (hereinafter referred to as a rectifier load) is connected to the interconnection inverter during backup operation, harmonic distortion of the output voltage becomes larger, and in some cases, resulting in miss operation of connected equipment.
In order to address this issue, types of connected loads were estimated by focusing on the crest factor of the inverter output current. The crest factor is the value in which the maximum current value is divided by the actual current value. When deterioration is identified in the output voltage harmonic distortion caused by rectifier loads, processes were conducted for dynamically varying the output current feedback relative to the normal set value and for approximating the output voltage to a sine wave by the output voltage feedback. By these methods, the total harmonic distortion of the output voltage at the rating during backup operation with a rectifier load was reduced by 4.7 points.
As a result, an inverter was realized which is capable of high-quality power supply even during backup operation without degrading the inverter performance in grid connection.
