Apparatus for controlling grid-connected inverter

An apparatus for controlling a grid-connected inverter, the inverter including a DC link capacitor receiving a voltage from a DC power source, the apparatus comprising:

• a first determinator configured to determine active power and reactive power based on an output voltage and current of the inverter;
• a power controller configured to use an active power command, a reactive power command and the determined active power and reactive power to generate a current command;
• a current controller configured to generate a voltage based on the current command, the generated voltage synthesized by the inverter;
• a voltage generating unit configured to generate a voltage command based on the generated voltage, the generated voltage command applied to the inverter;
• and
• a controller configured to use the generated voltage command to generate a PWM (Pulse Width Modulation) signal to control a switching unit of the inverter,
• wherein the voltage generating unit includes a second determinator, a third determinator and an applying unit,
• wherein the second determinator is configured to determine a size of the generated voltage,
• wherein the third determinator is configured to use the determined active power and reactive power to determine apparent power, and
• wherein the applying unit is configured to generate the voltage command by applying an offset voltage to the generated voltage and using the determined size of the generated voltage, a voltage at the DC link capacitor and the determined apparent power.