A High-Performance Online Uninterruptible Power Supply (UPS) System Based on Multitask Decomposition

High quality online uninterruptible power supplies (UPS) are widely used in applications, e.g., precision medical equipment with critical loads. This article proposes a low-cost and high-performance online UPS system. First, the performance improvement of a bidirectional switch-based bridgeless power factor converter, which is regulated by a hybrid control strategy with load current feedforward, is studied. Second, the proposed closed-loop controller integrates improved predictive current control with predictive voltage control and applies to the second-stage neutral-point-clamped three-level inverter for low output voltage harmonics. Moreover, a push-pull dc-dc converter interfaces and boosts voltage of a 24 V battery bank as the backup energy source. Considering complexity of the UPS system as well as cost reduction, we implement a multitask decomposition method for control on a monolithic low-cost digital signal processor embedded with control law accelerator. Finally, the experimental results from a 1 kVA prototype can effectively verify validity of the theoretical analysis and design.