Study on dual-DSP-controlled three-phase series-parallel compensated line-interactive UPS system (delta-conversion UPS)

A three-phase series-parallel compensated line-interactive UPS system consisting of two voltage-source inverters controlled separately by two digital signal processors is studied in this paper. According to international IEEE standards, AC UPS system can be classified into three of a kind, i.e. passive-standby, line-interactive and double-conversion. Why this kind of UPS system is often called "delta-conversion", which is a member of the line-interactive UPS family in nature, may lie in a little power bandied by both inverters in standby mode and the quasi-feedback PWM technique it adopted. "Delta-inverter" can be controlled either as AC fundamental sinusoidal current source or as nonsinusoidal voltage source to compensate harmonic voltage at the utility, while "main-inverter" can be controlled either as AC constant-voltage constant-frequency fundamental sinusoidal voltage source or as nonsinusoidal current source to compensate reactive and harmonic currents deriving from inductive and nonlinear loads. Compared to double-conversion counterpart, "delta-inverter" is of a small kilo-volt-ampere rating in any modes, while a little reactive and harmonic currents flow through "main-inverter" in standby mode. Thus, the efficiency and reliability of this kind of UPS are both increased with reduced cost. Some simulation waveforms and partial experimental oscillograms are shown in detail to verify the theoretic analysis.