Single phase UPS inverter with variable output voltage and digital state feedback control

Uninterruptible power supplies (UPS) are needed to provide a source of electrical energy with high quality, stability and disposability in case the public mains cannot fulfil these demands. The technical requirements of low power UPS systems are, above all, a high power density, small size and weight, low noise level and a stable and harmonic free output voltage. This paper presents a concept of a transformerless single-phase inverter for a battery-supplied static online UPS, which is especially designed to generate two output voltages with different frequencies. The presented inverter topology has the same efficiency and device stresses, irrespective of the chosen output voltage at the same output power. A design procedure of a predictive digital state feedback control scheme to ensure a sufficient quality of output voltage under typical linear and nonlinear load conditions is shown. Additional necessary functions like overload and short circuit protection are implemented in the control strategy. Finally some simulation results of the proposed concept using SIMPLORER(R) are given.