Passivity Improvement of the Grid Connected VSI using Active Damping and Investigation of Inaccuracy of the Direct Discrete Plant Model

It is proved in this work that even the most accurate direct discrete-time plant model fails to exactly represent the PWM-based Voltage Source Inverter (VSI) connected to the grid via L-filter for all grid conditions due to the incapability to sample the present average voltage at the Point of Common Coupling (PCC). Thus, a state observer derived from the direct discrete-time plant model can not accurately estimate future signals to compensate for the unavoidable digital delays for all frequency ranges. Therefore, this compensation method does not provide passivity to the PWM-based converter. Active damping is a simple and straightforward solution to improve the passivity of the converter by increasing the converter’s positive resistance. But the active damping in the discrete-time domain could deteriorate the passivity plot if not done correctly due to delays in the system. An accurate way to realize the active damping is proposed to improve the passivity of a PWM-based power converter.