Parallel operation of digital controlled UPS system

A digital control algorithm for parallel connected three-phase inverters used in a UPS (uninterruptible power supply) is proposed. Each inverter module has an LC filter. The digital voltage controller, which has high-speed current control as a minor loop, provides low voltage distortion even for nonlinear loads. A parallel operation controller supplements the voltage controller in each inverter module. Voltage reference command of each inverter is controlled to balance the load current. It was confirmed by simulation and an experiment that low distortion characteristics of output voltage and good load sharing control characteristics were achieved by this control algorithm.<
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