Input filter interaction in three phase AC-DC converters

It is well known that the addition of an input filter preceding a switched mode regulator poses a problem of performance degradation and potential instability due to its negative input impedance at low frequencies. Three phase converters are essentially multivariable systems. The objective of this paper is to analyze the problem of input filter interaction in three phase AC-DC converters from a multivariable perspective and to establish criteria that guarantee stability and satisfactory performance of the converter with an input filter. The dq average model of a three phase boost rectifier is used for the analysis. The minor loop, the stability of which has to be guaranteed is identified. A sufficient condition for stability, based on the singular values of the filter output impedance and converter input admittance matrices is derived. Simulation results are presented to illustrate the results