Space vector modulation method for single phase on-line three-leg UPS

This paper presents a new modulation method for single phase on-line three-leg uninterruptible power supplies. The proposed modulation method brings the flexibility of the well-known space vector modulation for the single-phase UPS considered and it can be easily implemented in a digital controller. Three switching sequences are presented and evaluated in terms of total harmonic distortion and the location of the harmonics in the frequency spectrum of the input current and output voltage. Simulation and experimental results have been presented to demonstrate the feasibility of the proposed modulation method. A performance indicative is obtained by the comparison of distortion factors of the input current and output voltage and switching losses to each switching sequence. It is found out that first switching sequence would require simpler soft switching auxiliary circuit since one of the converter legs is commutated at low frequency. The second switching sequence is the best suited for hard switched implementation since it has the smallest switching losses. Finally, the third switching sequence has moderate switching losses while producing harmonics in well defined frequency for all operating conditions. Experimental results using the DSP controller TMS320F243 are presented to validate the proposed method.