DSP implementation of output voltage reconstruction in CSI-based converters

Current-source-inverter-based uninterruptible power supplies and V=f -controlled induction motor drives require sensing of two or more load voltages in addition to the dc voltage sensors used for protection purposes. This paper proposes a digital-signal-processor (DSP)-based load voltage control scheme that requires only information provided by the dc-bus voltage sensor. Load voltage estimation is based on ac line voltage reconstruction by means of a recursive least-square error algorithm that uses the information available on the dc bus and knowledge of the pulsewidth modulation gating pattern. Thus, the system minimizes the transducer count and, therefore, enhances reliability and ruggedness. Experimental results show that the load voltage can be reconstructed and its rms value controlled for a wide range of operating conditions with errors of at most 4%. Moreover, the use of the space-vector modulation technique ensures a reduced load voltage harmonic distortion, which remains within the 5% range at nominal voltage and for all load conditions. The paper presents the DSP algorithms required for the operation of the system and key experimental results obtained on a three-phase 208-V 60-Hz 2-kVA prototype unit.