Harmonic Disturbance Suppression Based on Precise Shaping of Output Impedance at Selected Frequencies for Standalone Voltage Source Inverter

The output impedance of the voltage source inverter (VSI) would degrade the performance of the VSI when the load is connected. A load current feedforward control is usually used to act as a virtual impedance to reduce the output impedance of the VSI and achieve disturbance suppression. However, due to the variation of the frequency characteristics between the implemented feedforward controller and the theoretical feedforward controller, the output impedance of the VSI cannot be reduced to a lower level, especially the output impedance at harmonic frequencies. In this article, to improve the performance of harmonic disturbance suppression, the method of precise shaping of output impedance at selected frequencies is proposed for the VSI. By introducing multiple resonant controllers into the load current feedforward control with the consideration of the interaction among the resonant controllers, the variation of the frequency characteristics mentioned above can be compensated accurately at selected frequencies. Then the output impedance of the VSI is further reduced at selected frequencies (including harmonic frequencies), and the performance of the VSI under nonlinear load condition is further improved.