Resonant controllers with three-degree of freedom for AC power electronic converters

Grid-connected and stand-alone applications need inverters that accurately control the filter output voltages. Nowadays, resonant controllers represent a good tradeoff between implementation issues and control performances. However, the unknown nature and size of supplied loads affect the dynamic control behavior and may reduce the effectiveness of the control system. A new structure of resonant controller is introduced with the purpose to provide three-degree of freedom and allowing to select independently the controller's magnitude, width and phase. In order to fully take advantage of the proposed resonant controller form, the on-line tuning procedure based on the output filter analysis is also proposed. According to that, several resonant compensators can be placed in the loop to achieve better output voltage waveform, (i.e. lower total harmonic distortion).