Resonant Controllers With Three Degrees 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 (RCs) 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 RC is introduced with the purpose of providing three degrees of freedom and allowing us to select independently the controller's magnitude, width, and phase. In order to fully take advantage of the proposed RC form, the online 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 a better output voltage waveform (i.e., lower total harmonic distortion).