New Direct Power Control Strategies of Three-Phase VSIs for the Minimization of Common-Mode Emissions in Distributed Generation Systems

This paper presents two new direct power control (DPC) strategies of three-phase grid connected VSIs for distributed generation, devised for the minimization of common- mode emissions. These strategies have been called DPC-EMC 1 (electro magnetically compatible) and DPC-EMC 2. Both of them reduce the common-mode emissions of the VSI by using either even or odd voltage vectors in each of the six sectors in which the grid voltage lies, without using any null vector. DPC- EMC 2 outperforms DPC-EMC 1 in terms of harmonic content of the injected current and ripple of the active and reactive power waveforms, especially for low DC link voltage/grid voltage ratios. These approaches permit the common-mode emissions to be reduced in comparison with the classic DPC algorithm, at the expense of a slight increase of the harmonic content of the injected current waveform. An experimental comparison among the classic DPC, DPC-EMC 1 and DPC-EMC 2 is presented in terms of dynamic performance, harmonic content of the injected current and harmonic content of the common-mode voltage.